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Rheology of high performance shotcrete Beaupré, Denis 1994

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RHEOLOGY OF HIGH PERFORMANCE SHOTCRETE by DENIS BEAUPRI B.Sc., Université Laval, 1986 M.Sc., Université Laval, 1987 A THESIS SUBMI flED iN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES (Department of Civil Engineering)  We accept this thesis as conforming  THE UNWERS1TY OF BRITISH COLUMBIA  February 1994 © Denis Beaupré, 1994  In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Ubrary shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. it is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission.  (Signature)  Department of  CIV)  The University of British Columbia Vancouver, Canada Date  DE-6 (2/88)  jg  II  ABSTRACT The main goal of this study was to develop high performance shotcrete and to provide a fundamental understanding of the shooting process. For this, a laboratory concrete pump, to pump and/or shoot a number of shotcrete mixes, and a rheometer, to measure the rheological properties on the fresh shotcrete, were designed and constructed. A model based on rheological behavior was finally developed to predict pumpability and shootability. The values of both flow resistance and torque viscosity were used to represent the rheological behavior of fresh shotcrete, which is similar to the Bingham model. Important fundamental relationships were obtained between rheological properties and pumping pressure, build-up thickness and compaction of shotcrete. With a new parameter, the fresh concrete aging rate, these relationships are used in a model which predicts pumpability and shootability. Production of high performance shotcrete can be carried out in two different ways: the “traditional method” consists of using superplasticizers while in the second method, the “concept of high initial air content” consists of using a very high air content to improve the workability. In both cases the requirements for good pumpability and shootability must be satisfied in order to be able to apply the shotcrete. These requirements are in conflict in terms of flow resistance: pumpability requires a low flow resistance while shootability requires a high flow resistance. The range of acceptable values for the flow resistance is reduced for mixes with high torque viscosity. The concept of a temporary high air content has some advantages over the traditional method: when compared to the use of superplasticizers only, the use of air, by reducing the torque viscosity, allows a wider range of acceptable values for the flow resistance to be maintained. Also, the compaction process allows a recovery of the flow resistance during shooting. Thus, this concept allows low water-cement ratio shotcrete having enhanced pumpability, shootability, strength, and durability to be produced. It could probably be an excellent way to avoid the use of accelerators which have adverse effects both on worker health and on concrete properties, especially the durability.  m  iv  TABLE OF CONTENTS Abstract  ii  Table of Contents  iv  List of Figures  ix  List of Tables  xii  Acknowledgments  xiii  Forward  xiv  INTRODUCTION  1  CHAPTER -1SHOTCRETE TECHNOLOGY 1.0 Introduction 1.1 Shotcrete production 1.1.1 Dry-mix process 1.1.2 Wet-mix process 1.1.3 Comparison of wet-mix and dry-mix processes 1.1.4 Other processes 1.2 General requirements of wet-mix shotcrete 1.2.1 Equipment 1.2.2 Wet-mix shotcrete composition 1.3 Fresh wet-mix shotcrete 1.3.1 Build-up thickness 1.3.2 Rebound 1.3.3 Compaction 1.4 Plain shotcrete 1.4.1 Cement and water-cement ratio (W/C) 1.4.2 Aggregates 1.4.3 Admixtures 1.4.4 Additives 1.5 Hardened shotcrete 1.5.1 Effect of compaction on hardened properties 1.5.2 Effects of accelerators on hardened properties 1.6 Silica fume wet-mix shotcrete 1.6.1 Effect on fresh shotcrete 1.6.2 Effect on hydration 1.6.3 Effect on hardened properties 1.7 Steel fiber reinforced shotcrete 1.7.1 Fiber content 1.7.2 Fiber orientation 1.7.3 Toughness 1.8 High performance shotcrete 1.9 References  3 3 3 4 5 5 5 7 8 8 10 10 12 13 16 16 17 17 18 19 20 20 21 21 22 23 23 24 24 25 26 26  V  CHAPTER -2PROPERTIES OF FRESH CONCRETE 2.0 Introduction 2.1 Importance of fresh properties 2.2 Workability 2.2.1 Definition of physical properties 2.2.2 Empirical measurement of physical properties 2.3 Pump ability 2.3.1 Mobility requirements 2.3.2 Stability requirements 2.3.3 Mix design 2.4 Compactibility 2.5 Shootability 2.6 Mobility related tests 2.6.1 Slump test 2.6.2 Flow test 2.6.3 VeBe test 2.7 Compactibility related tests 2.7.1 Compacting factor test 2.7.2 Compaction (Walz) test 2.7.3 Pressuremeter (air content) 2.8 Stability related tests 2.8.1 Aging (slump) 2.8.2 Pressure bleed test 2.9 References  .31 31 31 32 32 33 34 34 36 38 39 39 40 40 41 42 43 43 43 44 45 45 46 47  CHAPTER -3RhEOLOGY OF FRESH CONCRETE 3.0 Introduction 3.1 Rheology 3.1.1 Viscosity (Newtonian liquid) 3.1.2 Other behavior 3.2 Cement pastes 3.2.1 Structure of fresh cement paste 3.2.2 Time dependence 3.3 Bingham model for concrete 3.3.1 Rheometer 3.3.2 Practical implications 3.3.3 Conversion to fundamental units 3.4 Effects of mix composition on concrete rheology 3.4.1 Time (aging) 3.4.2 Water-cement ratio (W/C) 3.4.3 Admixtures 3.4.4 Water-reducers (WR) 3.4.5 Air-entraining agents (AEA) 3.4.6 Fibers 3.5 Rheology of high performance concrete 3.5.1 Low water-cement ratio 3.5.2 Silica fume (SF) 3.5.3 Superplasticizers (SP)  49 49 49 49 52 53 54 55 56 56 57 59 60 61 61 62 62 64 65 66 66 67 67  vi 3.6 Rheology of shotcrete 3.6.1 Pumping vs. rheology 3.6.2 Shooting vs. rheology  .68 69 70  3.7 References  71  CHAPTER -4RESEARCH PROGRAM 4.0 Introduction 4.1 High performance shotcrete (HPS) 4.1.1 Low water-cement ratio (W/C) 4.1.2 High initial air content 4.1.3 Mix identification code 4.2 Testing program 4.2.1 Fresh properties 4.2.2 Hardened properties 4.3 Pumpability study 4.3.1 Pumping pressure 4.3.2 Pressure bleed test 4.4 Shootability studies 4.5 Materials 4.5.1 Cement 4.5.2 Silica fume and fly ash 4.5.3 Aggregates 4.5.4 Fibers 4.5.5 Superplasticizers 4.5.6 Other products 4.6 Equipment 4.6.1 Concrete mixers 4.6.2 Shooting equipment 4.7 References  74 74 74 75 76 77 78 78 78 78 78 79 79 79 79 79 79 80 80 80 80 80 81 81  CHAPTER -5DEVELOPMENT OF THE UBC RHEOMETER 5.0 Introduction 5.1 The concrete rheometer: historical review 5.1.1 First generation rheometers 5.1.2 Second generation rheometers 5.1.3 Third generation rheometers 5.2 UBC rheometer 5.2.1 Design considerations 5.2.2 Physical description 5.2.3 UBC rheometer user documentation 5.3 Computer programs 5.3.1 Program: Calibrate 5.3.2 Program: Incremental test 5.3.3 Program: Duration test 5.4 Calibration of torque measuring device 5.4.1 Torque calibration procedure 5.4.2 Torque calibration results  82 82 82 83 84 86 88 88 88 90 91 91 91 92 93 93 94  vu 5.5 Rheometer testing program 5.5.1 Mix composition 5.5.2 Physical test results 5.5.3 Rheometer test results 5.5.4 Test parameters 5.6 Other test results 5.6.1 Theoretical analysis of impeller motion 5.6.2 New impeller test 5.6.3 Sensitivity tests 5.7 Proposed modification to the UBC rheometer 5.8 References  .96 96 97 97 105 105 105 109 111 113 114  CHAPTER -6PUMPABILITY 6.0 Introduction 6.1 Laboratory concrete pump 6.1.1 Design criteria 6.1.2 Pump description 6.2 Pressure bleed test 6.2.1 Design criteria and apparatus description 6.2.2 Test procedure 6.2.3 Pressure bleed test results 6.3 Pumpability 6.3.1 Slump and pressure bleed test vs. pumpability 6.3.2 Rheology vs. pumpability 6.4 Pumping of concrete with high air content 6.4.1 Pumping rate 6.4.2 Compressibility 6.4.3 Pumping sequence of the laboratory concrete pump 6.5 References  115 115 115 115 116 118 119 120 121 125 125 127 132 132 132 134 135  CHAPTER -7SHOOTABILITY 7.0 Introduction 7.1 Shootability 7.1.1 Definition of shootability 7.1.2 Pumpability vs. shootability 7.2 Build-up thickness 7.2.1 Measurement of build-up thickness 7.2.2 Relationships between shootability and rheological properties 7.2.3 Theoretical analysis 7.3 Rebound 7.3.1 Measurement of rebound 7.3.2 Relationship between rebound and rheological properties 7.4 Aging effect 7.4.1 Aging 7.4.2 Fresh concrete aging rate (FCAR) 7.5 Compaction 7.5.1 Definition  136 136 136 136 137 137 137 139 140 141 141 142 143 143 144 146 147  vifi 7.5.2 Possible effect of compaction on shootabiity 7.5.3 Measurement 7.5.4 Results 7.5.5 Summary on compaction 7.6 Model for predicting pumpability and shootability 7.6.1 Required relationships and properties 7.6.2 Prediction of pumpability 7.6.3 Prediction of shootabiity 7.7 Shootabiity of high air content shotcrete  147 149 150 157 158 158 159 161 163  CHAPTER -8EFFECT OF MIX COMPOSITION ON SHOTCRETE PROPERTIES 8.0 Introduction 8.1 Effect of mix composition on rheological properties 8.1.1 Relationships between g, h and FCAR 8.1.2 Relationship between initial flow resistance and slump 8.1.3 Effect of cement-superplasticizer combinations 8.1.4 Effect of high volume of air and fibers 8.2 Effect of mix composition on hardened properties 8.2.1 Compressive strength 8.2.2 Absorption test 8.2.3 Durability  165 165 165 167 169 170 171 173 173 174 175  SUMMARY AND CONCLUSIONS  178  Appendix A: Materials  182  Appendix B: UBC rheometer user documentation  188  Appendix C: Rheometer results (small testing program)  200  Appendix D: Pumping and shooting equipment  207  Appendix E: Mix composition  213  Appendix F: Pressure bleed test results  218  Appendix G: Rheometer results  223  Appendix H: Hardened shotcrete test results  248  ix  LIST OF FIGURES Figure Figure Figure Figure Figure Figure  1.1: Representation of dry-mix process 1.2: Representation of wet-mix process 1.3: Representation of a wet-to-dry-mix method (Top Shot) 1.4: Typical wet-mix nozzle 1.5: Thickness-to-sloughing test set-up 1.6: Effect of thickness on average rebound of dry-mix shotcrete (Parker, 1977) Figure 1.7: Stuart’s results on dry-mix shotcrete (Glassgold, 1989) Figure 1.8: Hypothetical relationship between speed of particles and degree of compaction Figure 1.9: Effect of non-caustic accelerator on some shotcrete properties (Schutz, 1982) Figure 2.1: Effect of “paste saturation” on pumpability Figure 2.2: Dewatering of concrete in a pipe line Figure 2.3: Relationship between slump, water emitted and pumpabiity (Browne and Bamforth, 1977) Figure 2.4: Slump cone apparatus Figure 2.5: Flow test apparatus Figure 2.6: VeBe test apparatus Figure 2.7: Compacting factor measuring apparatus Figure 2.8: Slump loss in mixtures containing superplasticizers compared with control (Whiting and Dziedzic, 1989) Figure 2.9: Pressure Bleed test apparatus (Browne and Bamforth, 1977) Figure 2.10: Typical results from the pressure bleed test (Browne and Bamforth 1977) Figure 3.1: Determination of coefficient of viscosity Figure 3.2: Representation of the coaxial cylinders viscometer Figure 3.3: Nonlinear flow curves and Bingham model (t = to + p. y) Figure 3.4: Flow curve and schematic model for structural breakdown (Tattersall and Banfill, 1983) Figure 3.5: illustration of thixotropic behavior Figure 3.6: Typical results from rheometer MKII (Tattersall, 1991) Figure 3.7: Relationship between slump and g (Scullion, 1975) Figure 3.8: Relationship between g and h and workability box (adapted from Tattersall 1991) Figure 3.9: Effects of addition of water and different admixtures (Gjørv, 1992) Figure 3.10: Effect of lignosuiphonate on g and h (Waddicor, 1980) Figure 3.11: Effect of air content on g and h (Tattersall and Banfihl, 1983) Figure 3.12: Effect of steel fibers (volume and length) on g and h (Tattersall, 1991) Figure 3.13: Effect of silica fume on yield strength and viscosity (Gjørv, 1992) Figure 3.14: Effect of superplasticizers (Banfill, 1980) Figure 3.15: Effect of SP dosage and time on yield and viscosity (Gjørv, 1992) Figure 3.16: Concrete in pipeline: plug flow (Browne and Bamforth, 1977)  .4 5 7 8 11 13 15 16 21 35 36 37 40 41 42 44 45 46 47 50 51 52 55 56 57 58 59 62 64 65 66 67 68 69 70  x Figure 4.1: Mix identification code  .77  Figure 5.1: Schematic representation of the MKII apparatus (Tattersall, 1991) Figure 5.2: Schematic representation of the impeller of the MKIII (Tattersall, 1991) Figure 5.3: Example of data from Wallevik and Gjørv (1990a) Figure 5.4: Slip ring set-up and trace from the recorder (Cabrera and Hopkins, 1984) Figure 5.5: General view of UBC rheometer Figure 5.6: Torque measuring device and slip ring of UBC rheometer Figure 5.7: Schematic representation of a rheometer test Figure 5.8: Set-up used to calibrate the torque measuring device Figure 5.9: Calibration of 4 mm beam Figure 5.10: Calibration of 7 mm beam Figure 5.11: Normal (a) and “deep” (b) position of the impeller Figure 5.12: Mix T10.43a (fast test) Figure 5.13: Mix T10.43a (“slow test) Figure 5.14: Mix T10.43a çslow” results with decreasing speed) Figure 5.15: Mix T10.43b Figure 5.16: Mix T10.43c Figure 5.17: Effect of air content (Mixes T10.43a, b and c) Figure 5.18: Effect of air content (Mixes SF.43a and b) Figure 5.19: Effect of cement type (W/C = 0.38) Figure 5.20: Effect of W/C and the use of superplasticizer Figure 5.21: Effect of shooting on g and h (mixes T10.40 and T10.40s) Figure 5.22: Effects of mix composition and shooting on g and h Figure 5.23: Schematic representation of observed deviation from Bingham behavior Figure 5.24: Position I and position T of the impeller Figure 5.25: Hypothetical impeller and relative tangential speed for I and T positions Figure 5.26: Four hypothetical fluid behaviors Figure 5.27: Expected torque requirement with respect to time Figure 5.28: Results from the impeller motion analysis Figure 5.29: New impeller geometry Figure 5.30: Oscillatory effect caused by the movement of the impeller Figure 5.31: Effect of impeller (number of fmgers) on the spread of torque Figure 5.32: Reometer test carried out on air (bowl empty) and on water  84  Figure 6.1: Schematic diagram of the pump Figure 6.2: Hydraulic system and proximity switches Figure 6.3: New pressure bleed apparatus Figure 6.4: Typical pressure bleed test results (mix: (8.1 1A)3OT1SF-D) Figure 6.5: Relationship between air content and calculated compaction during the pressure bleed test Figure 6.6: Relationships between slump, pressure bleed test and pumpability Figure 6.7: Pumpability box: all mixes Figure 6.8: Effect of artificial “aging” on pumping pressure Figure 6.9: Pumping pressure (a) and pumping rate (b) vs. rheological properties Figure 6.10: Effect of air content on pumping rate Figure 6.11: Hypothetical pressure distribution in pipes Figure 7.1: Build-up thickness test set-up  85 86 87 89 90 92 93 95 96 98 100 100 100 101 101 101 102 102 102 104 104 106 106 107 108 108 110 111 112 112 113 116 117 121 122 125 126 130 130 131 132 133 138  xi Figure 7.2: Relationship between the build-up thickness and the slump before pumping Figure 7.3: Relationship between the build-up thickness and the torque viscosity (h) Figure 7.4: Relationship between the build-up thickness and the in-place flow resistance (g and g’) Figure 7.5: Analysis of build-up test Figure 7.6: Rebound test set-up Figure 7.7: Rebound characteristics of mix (6.1S)35T3SF-AM Figure 7.8: Relationship between rebound and W/C Figure 7.9: Rheological test results on mix (6.1A)35T3SF-AM at different times Figure 7.10: Determination of fresh concrete aging rate on mix (6.1A)35T3SF-AM Figure 7.11: Determination of fresh concrete aging rate on mix (8.4A)3OT1SF-DNF Figure 7.12: Effect of air content (a) and compaction (b) on flow resistance Figure 7.13: Possible relationships between compaction and shootability Figure 7.14: Defmition of pumping compaction, shooting compaction and total compaction Figure 7.15: Effect of compaction on mix (8. 19APS)25T1SF-C (no AEA) Figure 7.16: Effect of compaction on mix (7.26APS)3OL1SF-CF (no AEA but with fibers) Figure 7.17: Effect of compaction on mix (6.1AS)35T3SF-AM (with AEA) Figure 7.18: Effect of compaction on mix (8.4APS)3OT1SF-DNF (with AEA and fibers) Figure 7.19: Relationship between compaction and stiffening Figure 7.20: Required relationships Figure 7.21: Characteristics of fresh concrete Figure 7.22: Determination of pumpabiity life Figure 7.23: Determination of maximum build-up thickness (high air content) Figure 7.24: Determination of maximum build-up thickness (a) and waiting period (b) (no compaction) Figure 7.25: Effect of time, pumping and shooting on rheological properties of mix (8.4APS)3OT1SF-DNF (with AEA) Figure 7.26: Effect of time, pumping and shooting on rheological properties of mix (7.12APS)3OL3SF-AF (without AEA) Figure 8.1: Relationship between g and h (all mixes) Figure 8.2: Relationship between FCAR and h (all mixes) Figure 8.3: Relationship between FCAR and g (all mixes) Figure 8.4: Relationships between the slump and g (a) or g’ (b) Figure 8.5: Effect of superplasticizer type and dosage on g, h and FCAR Figure 8.6: Effect of superplasticizer type and dosage on g, h and FCAR Figure 8.7: Effect of W/C and superplasticizers on g, h and FCAR Figure 8.8: Effect of AEA and fibers on g, h and FCAR Figure 8.9: Relationship between air content, W/C and compressive strength Figure 8.10: Effect of pumping and shooting on compressive strength Figure 8.11: Effect of water-cement ratio on scaling resistance (AEA mixes only)  139 139 140 141 142 142 144 145 145 146 147 148 150 153 153 154 154 157 159 159 160 161 162 163 164 168 168 169 169 170 171 172 172 173 174 177  XII  LIST OF TABLES Table 1.1: Comparison of operational features of dry-mix and wet-mix processes Table 1.2: Typical plain wet-mix composition Table 1.3: Effect of certain parameters on the amount of rebound (Morgan and Pigeon, 1992) Table 1.4: Effect of shooting process on air content of air-entrained wet-mix shotcrete Table 1.5: Gradings of fine and combined aggregate (ACT 506) Table 1.6: Rebound characteristics of wet-mix steel fiber reinforced shotcrete (Banthia et al. 1992)  25  Table 3.1: G and K values for MKII and MKIII (Tattersall and Bloomer, 1979) Table 3.2: Concrete admixtures (Tattersall and Banfill, 1983)  60 63  Table 5.1: Calibration data for the 7 mm beam Table 5.2: Mix composition Table 5.3: Physical test results  95 97 98  6 9 12 14 17  Table 6.1: Geometric characteristics of bleed test apparatus Table 6.2: Effect of surface area and water content on the bleeding rate of cement paste (Powers, 1968) Table 6.3: Pressure bleed and other test results Table 6.4: Rheological properties and pumpability (mixes without fibers) Table 6.5: Rheological properties and pumpability (mixes with fibers)  123 124 128 129  Table 7.1: Result of the build-up thickness Table 7.2: Average rebound measurement data Table 7.3: Effects of pumping and shooting on shotcrete properties  138 143 151  Table 8.1: Air content, slump, g, h, FCAR, and compressive strength Table 8.2: Absorption test results Table 8.3: Results of ASTM C-39, ASTM C-672 and ASTM C-457 on shotcrete  166 175  119  176  XIII  ACKNOWLEDGMENTS  First, I would like to sincerely thank my adviser, Dr. Sidney Mindess, for his unconditional support. I really appreciated the freedom he gave me in the choice of the subject and in the completion of the experimental work. I equally thank my co-adviser Dr. Michel Pigeon for the financial support but mostly for the trust he showed in me, both in the past and during this research project. This thesis would not exist without him. I also thank Dr. Rusty Morgan, who acted also as a co-adviser, for his constant interest in my work. He was always there to provide useful information when needed. Most of the experimental work was done with the help of Kevin Campbell. I would like to thank him and Catherine des-Rivières-Pigeon, who patiently entered into the computer most of the test results. It would be too long a list to name all of the members of the UBC Civil Engineering staff who assisted me, but I would like to thank them all, particularly Dick Postgate and John Wong for their work and advice in the building of the various frames required in this study. I also thank the University of British Columbia and the Canadian Network of Centers of Excellence on High Performance Concrete who fmanced the project. Finally, there are no appropriate words to express my deep gratitude to my wife Johanne, whom I love deeply, for her presence, support and the numerous sacrifices she has made during these four years.  xiv  A yolzanne  .1.  INTRODUCTION  This thesis on the Rheology of High Performance Shotcrete is divided into eight chapters: the first three chapters cover the literature survey, the fourth presents the research program and chapters five to eight present the results. Several appendices provide additional information. References have been placed at the end of each chapter. The main goal of this study is to apply the principles of rheology to shotcrete in order to try to predict its pumpability and shootability. Only the wet-mix shotcrete is considered in this work. In the first chapter, various aspects of shotcrete technology or the “art of shotcreting” are presented. There is an emphasis on wet-mix shotcrete, along with its general requirements in terms of mix composition and placing equipment. Next, the fresh and hardened properties of wet-mix shotcrete with respect to mix composition are discussed: the concept of using fresh concrete with a high initial air content to produce shotcrete is explained. Finally, the characteristics of silica fume shotcrete, steel fiber reinforced shotcrete and high performance shotcrete are also discussed. Chapter two describes the importance of the fresh concrete properties and their measurement, from subjective assessment of workability to the definitions of more standard test procedures. Pumpability, compactibility and shootability, which are very important in shotcrete technology, are defmed and their evaluation is discussed. Finally, mobility, compactibiity and stability tests for fresh concrete are described. In chapter three, the rheological properties of cement pastes and concretes are discussed. First, the fundamentals of rheology, including Newtonian fluid behavior as well as some measurement techniques for determining the coefficient of viscosity are presented. Next, Bingham behavior, applicable to cement pastes and concretes, is discussed with respect to the time dependence of a cementitious mixtures. Then, considerations regarding to the use of coaxial cylinder viscometers and rheometers are outlined. The effects of mix composition on rheological properties are also discussed with an emphasis on high performance concrete technology. Finally, the implications on shotcrete technology, especially those related to pumping and shooting, are discussed with respect to the Bingham behavior.  2 The testing program carried out on both the fresh and hardened concretes and shotcretes is outlined in the fourth chapter. The specific operations carried out to evaluate both the pumpability and the shootability are also described. Finally, the materials and the equipment built and used during this study are presented. Detailed information is presented in Chapters 5 to 8 or in the Appendices. In the fifth chapter, the development and use of a new rheometer referred to in this work as the UBC rheometer, is described. The UBC rheometer is conirolled by a computer and automatically evaluates the rheological properties of fresh concrete. The design considerations and the physical description of the new apparatus are given, as well as the results of a small testing program carried out to evaluate the performance of the rheometer. Chapter six describes the development of a laboratory concrete pump and a pressure bleed test. Rheological properties as well as the results of the slump and the pressure bleed tests are analyzed in order to predict pumpability. The paste volume concept is explained and the effect of air-entrainment on pumpability, especially the compaction during pumping is taken into account. In chapter seven, the relationship between the build-up thickness and the rheological properties, especially the flow resistance, are presented and analyzed. Results of a few rebound tests are also given, along with some considerations regarding the aging effect on rheological properties. To take into account the change in rheological properties with respect to time, a fresh concrete aging rate factor is defined. Finally, compaction during pumping and shooting are analyzed: a new model to predict pumpability and shootability in terms of maximum build-up thickness is presented. The effects of mix composition on fresh and hardened concrete properties are considered in the last chapter. The influence of mix composition on fresh rheological properties (initial values and fresh concrete aging rate) is analyzed. The effect of pumping and shooting, as well as the effects of variations in mix composition on some hardened properties such as compressive strength, absorption, air void spacing factor and deicer salt scaling resistance are explained. Finally, a discussion on the production of high performance shotcrete is given; the implications and effects of using superplasticizers in shotcrete as opposed to using the concept of high initial air content are pointed out. At the end of the thesis, several appendices present information on the materials used, different test results and the composition of most of the mixes cast in this study.  3  CHAPTER -1SHOTCRETE TECHNOLOGY  1.0 INTRODUCTION In this chapter, different aspects of shotcrete technology or the “art of shotcreting” are presented, with an emphasis on wet-mix process and its general requirements in terms of mix composition and equipment. Next, the fresh and hardened properties of wet-mix shotcrete with respect to mix composition are discussed. Finally, the characteristics of silica fume shotcrete, steel fiber reinforced shotcrete and high performance shotcrete are also discussed.  1.1 SHOTCRETE PRODUCTION Shotcrete should not be considered as a special material. Rather, it should be regarded as a special process used to place and compact cementitious materials. Over the years, several different processes have been developed, all of which use compressed air to shoot concrete or mortar at high velocity onto a receiving surface. The two most popular processes are the wet-mix process and the dry-mix process (Litvin and Shideler, 1966). Hybrid processes have also been developed. These processes have been used for many structural and architectural applications (Crom, 1981a). Traditionally used for applications such as swimming pools, canal and tunnel linings, rock and slope stabilization, corrosion protection, all kinds of concrete structural repairs, etc., they are now, more and more, used for construction. They play a large part in new construction techniques such as soil nailing (Taguchi et al., 1993). Their ease of use makes them very effective for the construction of curved and irregular structures. In Central Europe, principally in Germany and Austria, the dry-mix process is very popular compared to the wet-mix process. On the other hand, in Northern Europe, principally in Sweden and Norway, the wet-mix process is predominantly used. In America, the preference goes to the process which is most likely to yield the best results for the particular conditions of the project and to local practice. Both processes have  4 certain advantages and disadvantages, which make them more or less suitable for a particular application. The choice of one or the other process is not always easy and many factors must be taken into consideration (Egger, 1977).  1.1.1 Dry-mix process The dry-mix process was first used in 1907, to shoot a mixture of sand and Portland cement to shape an artificial dinosaur. Since then, this technique has been improved and a great deal of equipment has been developed, but the original idea remains almost unchanged. With this process, compressed air is used to carry, at high velocity, a mixture of cementitious material and aggregates to a nozzle where some water is added. The amount of water is controlled by the nozzleman to obtain a consistency appropriate for the application. At the nozzle, in addition to water, it is possible to add other materials such as latex, air-entraining agents and/or set accelerators. Figure 1.1 present a schematic representation of the dry-mix process. compressed  cement + aggregates  water  Figure 1.1: Representation of dry-mix process The quality of the final product is strongly affected by the experience of the nozzleman (Crom, 1981b). Bad workmanship may cause sand pockets and/or layering. Excessive layering indicates heterogeneity of the in-place material produced by frequent variations in the amount of water used during shooting or lack of uniform feed.  5  1.1.2 Wet-mix process This process was first used around 1950. With this technique, fresh concrete is pumped to the nozzle where compressed air is added to project the fresh mixture onto the receiving surface. Accelerators are sometimes added at the nozzle to increase the layer thickness applied in a single pass and also to the speed up strength development. Figure 1.2 presents a schematic representation of the wet-mix process.  fresh concrete concrete I  nozzle  compressed afr  Figure 1.2: Representation of wet-mix process 1.1.3 Comparison of wet-mix and dry-mix processes Table 1.1 from the report of ACT Committee 506 (1987) summarizes the advantages of both processes. These characteristics will affect the choice of which method to use according to field conditions and expected results. 1.1.4 Other processes With the development of new shotcreting equipment, other processes have emerged, though they are all more or less related to one or other of the two original processes (Zangerle, 1993). All of these processes, including the “pure” dry-mix and wet-mix processes, produce the same final result: a stream of air, water, cementitious material and aggregates (which may also include fibers, additives and/or admixtures). This stream is projected at high velocity onto a surface, where it is consolidated by the impacting process  6  and remains  in place to develop strength  and other properties  similar to those of concrete  with the same composition.  The wet-mix and dry-mix processes are differentiated by the point at which air and water are added to the mix to form the stream. Other processes can also be differentiated by the manner in which the components  are  introduced to form the spray. Most of these newer  hybrid processes address some of the disadvantages of either the “pure” or the “pure” wet-mix process. They have originated from both the  dry-mix process  dry-mix  process  and  the wet-mix process. Those originating from the dry-mix process will be referred to as dry-to-wet-mix processes. Those originating from the wet-mix process will be referred to as wet-to-dry-mix processes.  Table 1.1: Comparison of operational features of dry-mix and wet-mix processes  Dry-mix process  Wet-mix process  1. Instantaneous control over mixing water and consistency of mix at the nozzle to meet variable field conditions  1. Mixing water is controlled at the delivery equipment and can be accurately measured  2. Better suited for placing mixes containing lightweight aggregates, refractory materials and shotcrete requiring early strength  2. Better assurance that the mixing water is thoroughly mixed with other ingredients  properties 3. Capable of being transported longer  distance  3. Less dusting and cement loss accompanies the shooting operations  4. Start and stop placement characteristics are better with minimal waste and greater placement flexibility  4. Normally has lower rebound resulting in less material waste 5. Capable of greater production  In  the dry-to-wet-mix process, the  mixing time of the cement and the water is increased by  adding the water at an earlier stage of the process. (between  3  to  5%  of the weight of the concrete mix) be added before mixing the material  with the compressed air, in order to reduce dust place material.  It is recommended that some water  This  and to improve the homogeneity of the  procedure is known as pre-wetting.  At present,  in  the dry-mix process  without pre-wetting is not frequently used. Also, a special nozzle (with the water ring placed some distance from the nozzle end, and called “long nozzle”) can be used to produce a more homogenous material, with less dust and less rebound, by increasing the  7 mixing time of the cement and the water. This dry-to-wet-mix process maintains the advantage of having lighter hoses. In the wet-to-dry-mix process, the compressed air is added some distance from the end of the hose. This process maintains all of the advantages of the wet-mix process, plus the lighter weight of the hoses which is characteristic of the dry-mix process. For example, Figure 1.3 shows the Top-Shot method which can be classified as a wet-to-dry-mix process (Von Eckardstein, 1993). fresh concrete concrete air + water+ cement + aggregates+  admixture  accelerator  compressed air  turbo / injector nozzle  Figure 1.3: Representation of a wet-to-dry-mix method (Top Shot)  1.2 GENERAL REQUIREMENTS OF WET-MIX SHOTCRETE From the definition of the wet-mix process, it is obvious that two steps have to be carried out in order to produce wet-mix shotcrete: the fresh concrete must first be pumped, and then shot. It is often said that if concrete can be pumped, it can also be shot. Thus, the first step in making shotcrete is indeed to verify that it is pumpable. If this step is successful, then according to the first statement shooting should not be a problem. However, even if the concrete can be shot, there is no guarantee that it will remain in place after shooting. In fact, both pumping and shooting operations have special requirements in terms of mix composition and equipment.  8  1.2.1 Equipment A wet-mix shotcrete application requires the following equipment at a minimum: a concrete pump, an air compressor, some hoses and a nozzle. In addition, an experienced crew is essential. Depending on the application, accessory equipment (accelerator dispenser, robotic arm, shuttle belt, etc.) may also be used (Breitenbucher, 1993). Almost any concrete pump can be used for wet-mix shotcrete applications. However, to ease the application, a steady concrete flow is better than a discontinuous flow. If an accelerating additive is to be added at the nozzle, it is more economical to use a specially designed shotcrete pump which will constantly adjust the accelerator dosage with the concrete flow. The Top-Shot system described in Figure 1.3 is a good example of such specialized equipment. The compressor should have enough capacity with respect to the flow of concrete (Andersen and Dalseg, 1993). An insufficient compressed air capacity will result in poor compaction and high rebound. The nozzle should be designed to produce a homogenous stream of high velocity particles. A wet-mix process nozzle usually possesses three enthes: a central one for the concrete, one for the compressed air (which is made up of small holes) and one for the accelerator. Although accelerators are not always used, a good nozzle should have this feature. Figure 1.4 shows the details of a commercial nozzle. air air chamber  holes accelerator  r-  shotcrete  Figure 1.4: Typical wet-mix nozzle 1.2.2 Wet-mix shotcrete composition The composition of wet-mix shotcrete is very similar to that of normal (cast-in-place) concrete because it includes the same basic components: water, cement, sand and stone.  9 Adrnixtures such as water-reducers, superplasticizers, air-entraining agents, retarders, accelerators, etc. are used most of the time. Silica fume, fly ash and fibers (either steel or polypropylene) are also often used. As for normal concrete, the proportions of these components are adjusted in such a way that the shotcrete can meet the requirements of both the fresh and the hardened properties. From the point of view of fresh shotcrete, the mix composition should be adjusted to meet the pumpability and shootability requirements. The common dilemma of the conflicting requirements for pumpability versus shootability remains: when the pumpability is increased (by increasing the slump, for example) the shootability is generally reduced and vice versa. It is often considered that a slump of 50 to 80 mm is a good compromise between pumpabiity and shootability. Pumpability and shootability will be discussed in more detail in the later chapters (Chapters 2, 3 and 6). Generally, in order to enhance both pumpability and shootability, the cement and sand contents of the mix are increased, compared to conventional concrete, and the coarse aggregate content and maximum size are decreased. Silica fume is also used for the same reason. Table 1.2 shows a typical composition for plain wet-mix shotcrete. Table 1.2: Typical plain wet-mix composition  material  cement water sand coarse aggregate (12 mm) water-reducer air-eniraining admixture  amount (kg/rn ) 3  400 170 1100 600 1.2 1/rn 3 0.2 I/rn 3  From the point of view of the hardened shotcrete, the mix composition should be adjusted in such a way that the in-place hardened shotcrete will develop acceptable mechanical and physical properties. As a general rule, mix composition will affect hardened shotcrete properties in the same way as for normal concrete properties. However, effects associated with the shooting process, such as compaction and/or preferred fiber orientation may modify this general rule.  10 Depending on the application and the specified mechanical and physical properties, the mix compositions can vary widely. It is more convenient to identify classes or types of shotcrete, for example: plain shotcrete, silica fume shotcrete, steel fiber reinforced shotcrete, high strength shoterete, high performance shotcrete, or combinations of these (e.g. high volume polypropylene fly ash shoterete (Morgan, 1990a)). Some of these types of shotcrete will be treated separately in the sections which follow. 1.3 FRESH WET-MIX SHOTCRETE This section describes those properties of fresh wet-mix shotcrete which are directly related to the shooting process: build-up thickness, rebound and compaction. The fresh properties related to concrete technology, such as workability, pumpability, etc., will be discussed in the next chapter. At this point, let us assume that the concrete is pumpable and shootable. 1.3.1 Build-up thickness An important characteristic of fresh shotcrete is its build-up thickness. This is defined as the maximum thickness that can be built-up in a stable way. It is very important, from a practical and economical point of view, to minimize the number of layers required to achieve the required shotcrete thickness. A single application, without a long waiting period between passes, is of course, by far the most desired option. There is, unfortunately, no standard test to measure this important characteristic. The maximum build-up thickness is generally obtained by trial and error. Depending on the application (vertical wall, overhead ceiling, presence of reinforcement, etc.) this thickness may vary for the same mix. It is thus very difficult to provide a numerical (quantitative) value for this characteristic. To try to quantify the build-up thickness, Morgan (1991a) defined a thickness-to sloughing test measurement. He observed two failure mechanisms which may cause the freshly applied concrete to behave in an unstable manner: adhesion failure and cohesion failure. Adhesion can be defined as the ability of shotcrete to adhere to another surface, while cohesion can be defined as self-adhesion, or the ability of the shotcrete to adhere to itself. Adhesion failure occurs when, for a vertical application, the shotcrete starts sliding or sloughing under its own weight. Cohesive failure occurs when the fresh shotcrete ruptures within itself.  11 Figure 1.5 shows the set-up used by Morgan to measure the thickness-to-sloughing parameter. Depending on the shape of the applied shotcrete, the measured thickness can be very variable. In case (a) because of a bigger base and a better shape, the shotcrete would probably exhibit adhesion failure compared to case (b) which is more likely to exhibit cohesion failure. As stated by Morgan (1991a): This is a useful test for differentiating between the adhesive and cohesive characteristics of djfferent shotcrete mixtures; however, the test should not be viewed as providing an absolute statement of the full thickness to which shotcrete can be applied on vertical surfaces.  cohesion failure  adhesion failure  (a)  (b)  Figure 1.5: Thickness-to-sloughing test set-up From this kind of test, and from experience, some general observations can be made: •  the build-up thickness is generally increased when the slump of the concrete before pumping is reduced.  •  the use of silica fume generally increases this thickness; and  •  the use of accelerators increases this thickness, proportional to the accelerator addition rate.  The presence of fibers and the use of a high initial air content, because of greater compaction, can also increase the build-up thickness (Beaupré et al., 1991b).  12 1.3.2 Rebound During shooting, some particles (aggregates, cement grains, fibers ...) do not remain in place after the impact. These particles constitute the rebound. The amount of rebound and its composition have been studied by many researchers for the dry-mix process (Parker, 1977; Crom, 1981b; Morgan and Pigeon, 1992; Banthia et aL, 1992; Jardrijevic, 1993). For the wet-mix process, some information is also available (Morgan, 1991a; Beaupré et al., 1991b; Morgan and Pigeon, 1992; Banthia et aL, 1994). Many parameters influence the amount of rebound. They can be separated into two categories: parameters related to the shooting technique, and those related to the mix composition. The most important parameters related to the shooting technique are: the process (wet-mix or dry-mix), shooting position, angle, thickness and presence of reinforcement (bars or mesh). The most important parameters with respect to the mix composition are: aggregate characteristics and content, cement content, presence of silica fume, and fibers. Table 1.3 shows the effect of technique (process and shooting position) and mix composition (presence of silica fume). Additional results have also been presented by Morgan and Wolsiefer (1992). Table 1.3: Effect of certain parameters on the amount of rebound (Morgan and Pigeon. 1992  Technique  plain mix rebound (%)  silica fume mix  Wet: vertical Wet: overhead  4 15  3 13  Dry: vertical Dry: overhead  42 46  20 20  rebound (%)  No standard test exists to evaluate the amount of rebound, but most researchers have used closed chambers or large plastic sheets to collect the rebound. The mass of rebound is then compared to the mass of the in-place shotcrete to determine rebound as a percentage of either the in-place material, or the total shot material. It is important to maintain the same shooting parameters when performing a rebound test. Figure 1.6 shows the effect of thickness on average rebound. From these results, it may  13 be seen that it is important to shoot a sufficient amount of shotcrete to be in the lower, flat part of the curve, so that a small difference in thickness will not significantly change the overall result. Results from the analysis of rebound composition show that fibers and large aggregate particles rebound the most, while cement paste has the lowest rebound percentage. These results mean that there is segregation and a change in mix composition during shooting. When the rebound is low, and this is generally the case for the wet-mix process, these changes in mix composition would have very little effect on hardened shotcrete properties.  trend  I  more overhead shooting coarser material shooting drier higher air pressure  Total thickness (mm)  Figure 1.6: Effect of thickness on average rebound of dry-mix shotcrete (Parker, 1977) However, when fibers are present, it is important to know their rebound characteristics. Because of their high rebound rate, their cost and their small addition rate (usually around 0.8 % by volume), the determination of the in-place fiber content is very important. This issue is described and discussed in Section 1.7.1. 1.3.3 Compaction Compaction of shotcrete is due to the expulsion of air. To achieve a certain degree of compaction, a certain amount of work must be done. For cast-in-place concrete, this energy is usually provided by vibration. For shotcrete, the speed of the particles and their impact on the receiving surface produces the compaction. It is well known that pumping reduces the air content and thus produces compaction. During pumping, the loss of air can be very significant (Yingling et al., 1992; Hover, 1989) and is generally accompanied by a slump reduction. (Further discussion about pump related compaction is given in Chapter 2). It is also well known that additional air is removed during the shooting process. Table 1.4 shows the air content of the fresh  14 shotcrete, measured both before pumping and after shooting, and also the air content of the hardened shotcrete. The results show that a large amount of both the entrapped air and the entrained air can be removed during the pumping and shooting process. When air entraining agents are used, the final air content of the in-place shotcrete is around 3-6 percent, irrespective of the initial air content before pumping. Similar results can be compiled for non-air-entrained shotcrete: the final air content of the in-place shotcrete is then around 2-4 percent. The air content of the hardened shotcrete is generally slightly higher than if measured on fresh shotcrete shot directly into the air meter (see Table 1.4). The exact mechanism of air loss or compaction is not known. Table 1.4: Effect of shooting nrocess on air content of air-entrained wet-mix shotcrete  initial fresh air  fmal fresh air  content’ (%)  content 2 (%)  hardened air 3 content (%)  8.8  4.4  4.9  7.0  4.6  43* 6.2  4.1 4.3 3.2* 4.2  6.8  4.0  7.4  4.3  9.0 7.0  5.0 5.0 5.0 4.5 5.0  4.4  13.0  10.0 20.0 8.5 6.4  4.8 3.9  inference  Beaupréetal.(1991a)  5.8 4.0* 5.1  5.2 5.6  7.0  Beaupré et al. (1991b)  7.3  5.6 8.7 7.2 5.0 3.3  Morgan and Pigeon (1992)  1 before pumping (using ASTM C-23 1) 2- as shot into pressuremeter base (modified ASTM C-231) 3 as measured on hardened shotcrete (ASTM C-457) * no air-entraining admixture. -  -  -  In properly executed shotcrete, as for cast-in-place fresh concrete, no honeycombing should be present. In fresh shotcrete, voids are sometime developed around reinforcement, if proper shooting technique is not used and/or if care is not taken to remove trapped rebound. Proper shooting techniques should lead to sound and dense shotcrete: i.e. no honeycombing.  15 The speed of the particles, which depends on the amount of compressed air used at the nozzle, and their impact on the receiving surface produces the compaction. As mentioned by Glassgold (1989) in describing Stuart’s results on dry-mix shotcrete which are presented in Figure 1.7: it appears that on a comparative basis, shotcrete strength increases to an optimum level. .there is a definite correlation between exit velocity and compressive strength.” “...  ..  42  35  I:  100  20 and 25 mm nozzles  ,,iozzl  150 Velocity (m/sec)  200  Figure 1.7: Stuart’s results on dry-mix shotcrete (Glassgold, 1989) Even though the information in Figure 1.7 was obtained with the dry-mix process, it can be postulated that the strength variations were caused by differences in the fmal degree of compaction or in air content, although the air contents were not measured. It is a fact that compaction increases the compressive strength and generally improves all mechanical properties. Physical properties such as permeability are also improved by compaction. There is considerable uncertainty as to the absolute values of the measured velocities in Figure 1.7. However, the improvement in the degree of compaction when the speed (and thus the energy) of the particles increases is certainly true. From the results in Figure 1.7 and in Table 1.2, it is possible to draw a hypothetical relationship between the degree of compaction and the speed of the particles for both air entrained and non-air-entrained shotcrete (Figure 1.8). From previous results (Beaupré et al., 1991 a and b), one can say that the in-place air content of shotcrete should be in the order of 2-4 percent for non-air-entrained shotcrete and 3-6 percent for air-entrained shotcrete. If this degree of compaction can be achieved with a specific shotcrete  16 composition and equipment, the shooting application may be considered to have been done properly.  insufficient 12  compaction  shooting application done properly  10  U  .4 2 I’  Shotcrete nozzle velocity Figure 1.8: Hypothetical relationship between speed of particles and degree of compaction  1.4 PLAIN SHOTCRETE Plain shotcrete is, by definition, shotcrete which is made from water, portland cement, sand and sometimes coarse aggregates. Plain shotcrete may also include admixtures (water-reducers, superplasticizers, air-entraining agents, etc.). Accelerators may be added at the nozzle to enhance build-up thickness or to promote strength development. Compaction during pumping and shooting modifies the air content and the air void system of the in-place shotcrete. 1.4.1 Cement and water-cement ratio (W/C) Many types of cement (portland, high alumina, refractory, etc.) may be used to produce wet-mix shotcrete. In North America, portland cement type 10 (ASTM type 1) is the most commonly used. The cement content for most applications is around 400-450 kg/rn . 3 Leaner mixes are more difficult to pump and have higher rebound, while richer mixes can produce shrinkage cracking problems. The W/C differs from application to application, but generally varies between 0.5 and 0.35. The use of a lower W/C may lead to the production of high performance shotcrete (Section 1.8).  17  1.4.2 Aggregates Normal concrete sand and aggregate can be used to produce shotcrete. When coarse  aggregates are not used, the material is referred to as sprayed mortar. For sprayed concrete or shotcrete, the sand content is generally around 1000 kg/rn , and the coarse aggregate 3 content up to 600 kg/rn . 3 ACI Committee 506 on shotcrete has recommended gradings for fine (sand only for mortar) and combined fine-coarse aggregates in order to minimize both the drying shrinkage and the  amount of rebound.  Table 1.5 presents these recommended gradings.  Table 1.5: Gradings of fine and combined aggregate (ACT 506)  Sieve size U.S. (metric)  Percent passing individual sieves  grading no.1  3/4 in. (20 mm) 1/2 in. (12 mm) 3/8 in. (8 mm) No. 4 (5 mm) No. 8 (2.5 mm) No. 16 (1.25 mm) No. 30 (630 jim) No. 50 (315 jim) No. 100 (160 jim)  -  -  100 95-100 80-100  grading no. 2 -  100 90-100 70-85  50-85  50-70 35-55  25-60 10-30 2-10  20-35 8-20 2-10  grading no. 3  100 80-95  70-90 50-70 35-55  20-40 10-30 5-17  2-10  1.4.3 Admixtures Admixtures are chemical products generally used to enhance the performance of the  shotcrete. Three admixtures are most commonly used in wet-mix shotcrete technology: water-reducers, air-entraining agents and superplasticizers. Other products, such as retarders, hydration controlling admixtures, etc. may also be used. It is current practice to use water-reducers in almost all shotcrete mixtures, as is the case in normal concrete technology. These admixtures (often lignosulphonates) help in permitting a reduction in the cement content and/or the W/C ratio. This practice has economic reasons and also provides some benefits from a technological point of view. The reduction in the W/C ratio reduces shrinkage and increases strength and durability.  18 It is well known that the use of air-entraining admixtures improves the freeze-thaw durability of normal concrete. They are also used to improve the freeze-thaw durability of shotcrete (Schrader and Kaden, 1987; Morgan et al., 1988; Morgan, 1987; Glassgold, 1989; Beaupré et aL, 1991a). These chemical products (neutralized vinsol resin, salts of sulphonated hydrocarbons and salts of fatty acids) stabilize the small air bubbles created during mixing. As mentioned earlier, some of these bubbles will be lost during pumping  and shooting. Thus, according to Morgan (1989), it is important to start with a high air content (as much as 12 %) to compensate for these losses. Superplasticizers act in the same way as water-reducers, but with higher efficiency. By electrically charging the cement particles, superplasticizers (melamine, naphthalene) increase the workability of the mix. They can be used to replace normal water-reducers or to produce high performance concrete or shotcrete (AItcin, 1990). Superplasticizers have a short effective “life”: they lose their effect after a relatively short period of time (see Section 2.8.1). This side effect can be controlled by the use of a retarder. Retarders increase the length of the dormant period, that is they increase the time between batching and initial set. These products coat the cement particles and allow the concrete to remain workable for a longer period of time. They have no particular side effects except for retardation of strength development. Retarders which contain chlorides or alkalis, however, may have adverse effects on steel corrosion or on the development of alkaliaggregate reactions. One of the most recent developments in admixtures for shotcrete involves hydration control (Melbye, 1993). With this technology, a stabilizing admixture is used to suspend the hydration of the fresh concrete (the concept is to give to the wet-mix process the flexibility of the dry-mix process) for as long as desired. The hydration is restarted by the use of an activator which is added at the nozzle, like a normal accelerator. 1.4.4 Additives Additives are admixtures which are not part of the initial mix, but which are added at the nozzle during shooting. The most widely used additives in wet-mix shotcrete are set accelerators. Accelerators are used for different purposes: increasing the build-up thickness and/or accelerating the early strength development. Many different chemical products can be used as accelerators. One of the most popular is sodium silicate, also known as waterglass. Many of these products, especially those  19 which are aluminate based, can have very deleterious effects on both crew health and on the concrete properties. The durability is generally affected, possibly because of a more heterogeneous hydrate distribution. During the last symposium on sprayed concrete held in Norway in 1993, many concerns were raised concerning the use of accelerators in both wet-mix and dry-mix shotcrete (Bangzho, 1993; Haave and Bracher, 1993; Hirose and Yamazaki, 1993; Lukas and Kusterle, 1993). During his presentation, Kusterle showed a picture of the eye of a worker who is now blind because of an accident during the handling of a set accelerator. The caustic nature of the set accelerator made the attempt to restore his vision by surgery unsuccessful. These concerns have long been known but the use of accelerators can sometime not be avoided (Burge, 1982). Non-caustic accelerators have been around for many years (Shutz, 1982). Their higher price and less effectiveness, even though health hazard effects are almost non-existent, makes many contractors reluctant to use them. (Haave and Bracher, 1993). Their mode of action and effect on hardened properties is not well known. The mode of action of an accelerator could be to accelerate the hydration of the 3 C or to create a gel that modifies A the rheological behavior. Nearly all accelerators are known to reduce the long term strength of shotcrete. Special equipment is necessary to deliver the correct dosage of accelerator. Activators are also additives that can be added at the nozzle during shooting. They are used to restart and/or to accelerate the hydration process which was previously delayed by the used of a hydration control admixture. The long-term performance of these new products is not yet available (see also Section 1.4.3).  1.5 HARDENED SHOTCRETE There are no mechanical or physical properties which apply specifically to hardened shotcrete. All tests carried out on hardened concrete can also be carried out on hardened shotcrete. As with ordinary concrete, the mechanical and physical properties of shotcrete vary with mix composition and curing conditions. Because rebound, compaction and the use of accelerators modify the in-place mix composition, these factors also affect the hardened properties. The sampling of shotcrete by coring and sawing, as opposed to mold filling for cast in-place concrete, may also affect the measurement of these properties (Gebler and Schutz, 1990).  20 The influence of curing conditions is not included in this study but it is always good to remember that, as for normal cast in-place concrete, shotcrete needs proper curing. More hydration always improves the mechanical and physical performance of shotcrete. Rebound may affect both mechanical and physical properties if the amount is significant. With the wet-mix process, the amount of rebound is usually low (as opposed to the drymix process), so no major changes in mechanical properties should be expected. When steel fibers are used, there is a preferred orientation of fibers in a plane perpendicular to the shooting direction (Ramakrishnan et al., 1981). This preferred orientation will improve flexural properties, especially the shotcrete toughness characteristics. In this case, comparison with cast concrete could be inappropriate. This phenomenon is discussed in Section 1.7.1. 1.5.1 Effect of compaction on hardened properties Compaction, as for cast-in-place concrete, will improve the mechanical properties of shotcrete. However, excessive compaction may have an adverse effect on frost durability, by disrupting the air void system. The quality of the air void system can be characterized by the value of the spacing factor (ASTM C-457). Low spacing factors are needed to resist rapid thawing and freezing cycles. Gendreau (1989) has shown that the concept of a critical spacing factor for frost durability can also be applied to wet-mix shotcrete. However, a particular shotcrete may be frost resistant as measured by ASTM C-666, but not resistant to deicer salt scaling as measured by ASTM C-672 (Vézina, 1985; Beaupré et al., 1991a). The effects of pumping on the air volume variations of concrete have been studied by Yingling et al. (1992). The effects of the shooting process on the air void system have not yet been studied. It is however most probable that pumping and shooting produce an increase in the spacing factor, accordingly reducing the deicer salt scaling resistance of the shotcrete. 1.5.2 Effects of accelerators on hardened properties When the use of accelerators cannot be avoided, it is important to know what their effects are on hardened shotcrete properties. Figure 1.9 shows the typical improvement in early strength, which is generally accompanied by a reduction in the final compressive strength, for a non-caustic accelerator relative to a non-accelerated shotcrete. The usual  21 improvements in the initial set of shotcrete are also visible on this figure. These effects are usually proportional to the accelerator dosage (Schutz, 1982). Different accelerators at different dosages will react differently with different cements. It is the author’s hope that caustic accelerators will eventually no longer be used, because of their health hazards.  1% non-caustic  40  •I  non-caustic accierator  2%  30 20 10 0  8 hours  Age (days)  Figure 1.9: Effect of non-caustic accelerator on some shotcrete properties (Schutz, 1982)  1.6 SILICA FUME WET-MIX SHOTCRETE Since about 1970, silica fume has been used in Norway in wet-mix shotcrete. It was first used in Canada in shotcrete around 1980 almost simultaneously with steel fibers. A by product waste some years ago, the cost of silica fume is now about four times the cost of cement in Canada. Its pozzolanic reactivity and especially its fineness enhance the performance of concrete by modifying the spatial distribution of both cement grains and hydrates. Silica fume in wet-mix shotcrete improves the properties of both the fresh and the hardened shotcrete. In Canada, it is common to replace from 7.5 to 12 % by mass of the cement with silica fume. 1.6.1 Effect on fresh shotcrete Silica fume, when replacing a part of the cement, reduces the workability of fresh concrete and, for this reason, is often used with a superplasticizer. This increase in water demand is caused by its very high specific surface (Mehta, 1983). By changing the cohesion of the mix, silica fume reduces bleeding and segregation. This will improve pumpability by reducing the risk of pump blocking (see Chapter 2). However, reduced bleeding increases susceptibility to early plastic shrinkage cracking if the curing is not appropriate.  22 Because silica fume increases the cohesiveness of the shotcrete, it reduces rebound and increases the build-up thickness (Wolsiefer and Morgan, 1993). The addition of silica fume in dry-mix shotcrete allows an increase in overhead thickness by a factor of two, and in some cases, by a factor of three. This effect should be less for wet-mix shotcrete. The effects of silica fume on these two properties have a great deal to do with the popularity of silica fume in shotcrete technology. 1.6.2 Effect on hydration The normal hydration process of portland cement is now well known. It can be simplified as follows: the chemical reaction between cement and water produces calcium silicate hydrates (CSH), calcium hydroxide (CH) and aluminate phases which progressively surround the cement particles and link the aggregates and cement particles together. Because full hydration of the cement grain is never achieved and also because water in excess of that needed for hydration is used for workability purposes, some voids will remain around the cement grains. The porosity of the hardened concrete will then depend on the initial W/C ratio and the degree of hydration. The presence of silica fume affects the distribution and the composition of the hydrates (Mehta, 1983). Because of their size, silica fume particles (and they are very numerous) will act as sites for the deposition of the newly formed hydrates. This will not change the total porosity but will lead to smaller voids. This explains the large reduction in permeability observed when silica fume is used. The better distribution of hydrates also improves the bond between the paste and the aggregates: i.e. there is less of a transition zone effect with silica fume. This helps to explain the improvement in mechanical properties. Calcium hydroxide (CH) can be considered the weak part of the paste (because it concentrates in the transition zone) as opposed to the calcium silicate hydrates (CSH) which are the strong components of the paste. Silica fume, if cured long enough, reacts with CH to produce more CSH. This pozzolanic reaction usually starts after about three days of moist curing (Regourd, 1987). Because of this, it is the improvement in spatial distribution of hydrates, rather than the pozzolanic reaction, which is primarily responsible for the improvement in physical and mechanical properties.  23  1.6.3 Effect on hardened properties As mentioned in the last section, because it gives a better distribution of the porosity, silica fume reduces permeability and improves the bond between the cement paste and the aggregates. Properties which are affected either by permeability or by bond should thus also be affected similarly. The durability of silica fume shotcrete has been studied by many researchers over the last fifteen years (Morgan et al. 1988, Beaupré et al., 1991a). Durability to deicer salt scaling resistance is generally improved and chloride ion permeability is greatly reduced by the use of silica fume. Because rapid freezing and thawing durability is not related only to permeability, the use of silica fume dose not always improve freezing and thawing resistance. Mechanical properties are also improved by the use of silica fume. The reduction in the thickness and porosity of the transition zone at the paste/aggregate interface is probably the main factor in the improvement of mechanical properties.  1.7 STEEL FIBER REINFORCED SHOTCRETE Fiber orientation is modified by the shooting process: from random orientation before shooting to a preferred orientation after shooting. Different types of fibers (steel, polypropylene, asbestos etc.) have been used in shotcrete (Morgan 1981; Ramakrishnan et al., 1981; Morgan and Mowat, 1984; Beaupré et al. 1991b). However, only steel fiber reinforced shotcrete will be discussed in this section, since steel fibers are currently the most popular fibers in shotcrete technology especially for mining and tunneling applications (ACT 506.1). For example, in Norway, 70 000 m 3 of steel fiber reinforced shotcrete is used for rock support every year (Bakken and Holtermann, 1993). In Canada, steel fibers are also widely used for tunneling (Morgan, 1990b; Morgan, 1991b). In mining and tunneling, the criterion for load capacity is replaced by a deformation control criterion. The underground lining must restrict the movement of the surrounding ground but it must also be able to adapt to some extent to some non-preventable ground movement. The toughness characteristics of the shotcrete are then as important as its ultimate strength. Traditionally, the ductility of underground shotcrete linings has been obtained by the use of steel mesh. Now, mesh is more and more commonly replaced by steel fibers all around  24 the world. The performance of steel fiber reinforced shotcrete compared to traditional mesh reinforced shotcrete has been studied by many researchers (Ramakrishnan et al., 1981; Morgan and Mowat, 1984; Morgan et aL 1989; Vandewalle, 1992; Alemo et al. 1990). The load bearing capacity and the post-cracking behavior of steel fiber reinforced shotcretes are comparable to those of mesh reinforced shoteretes. Because of rebound, the fiber content of the in-place shotcrete is usually lower than the fiber content of the original shotcrete. Also, the shooting process gives a preferential orientation of steel fibers: most fibers are oriented perpendicular to the shooting direction i.e., parallel to the receiving surface. The main effect of the fiber reinforcement is to give some load bearing capacity at large deformations after cracking, to control restrained shrinkage deformation and to improve impact resistance (Morgan, 1981). This postcracking behavior can be evaluated by a flexural toughness test. 1.7.1 Fiber content Before pumping and shooting, the fiber content of most wet-mix shotcretes is usually around 45 to 60 kg/m 3 (Henager, 1981). During shooting, because of rebound, the inplace fiber content is usually reduced. To minimize fiber rebound and to avoid pumping blockages, short fibers (25-35 mm) are normally used in shotcrete technology. The fiber content of the in-place shotcrete can be measured by a wash-out test on the fresh concrete or by a crushing test on the hardened concrete. In both methods, the fibers are separated from the concrete using a magnet. Table 1.6 shows the rebound characteristics obtained from wash-out tests on five different silica fume steel fiber reinforced shotcrete mixes with the same initial fiber content. From these results, it is obvious that different fibers will behave differently: shape and length will affect the results. The in-place fiber content is always lower than the original fiber content and the fiber rebound is higher than the shotcrete rebound: i.e., the fibers have a higher tendency to rebound than the rest of the mix. 1.7.2 Fiber orientation In cast-in-place concrete, fibers have a random three-dimensional orientation. In shotcrete technology, the fibers possess a preferential orientation. Ramakrishnan et al. (1981) have shown X-rays of sliced shotcrete in which the preferred orientation in a plane perpendicular to the shooting direction is clearly noticeable.  25  An orientation index has been developed to quantify the degree of orientation. This index is obtained by counting the number of visible fibers on the faces of a rectangular prism. To help in counting the visible intercepted fibers, the specimens are stored in water to promote fiber surface corrosion. The preferred orientation of fibers is positive for thin linings: the fibers are oriented in a direction in which they are more likely to be effective after cracking. Table 1.6: Rebound characteristics of wet-mix steel fiber reinforced shotcrete (Banthia et  al. 1992  mix  MF1 MF2 MF3 MF4 MF5  Original fiber  In-place fiber  Shotcrete  Fiber  volume fraction  volume fraction  ibound  iebound  (%)  (%)  (%)  (%)  0.77 0.77 0.77 0.77 0.77  0.63 0.68 0.67 0.64 0.68  8.8 9.0  18.3 11.5  12.5 14.8 11.3  12.5 17.0 11.8  1.7.3 Toughness The toughness of steel fiber shotcrete is generally obtained by a flexure test. In North America, ASTM C-1018 describes the standard procedure for steel fiber reinforced concrete. Other testing procedures for determining post cracking performance (Austin and Robins, 1993; Skjolsvold and Hammer, 1993), have also been developed in other countries. The ASTM C-1018 test has been criticized because its indices are based on the determination of the first crack which is almost impossible to determine exactly. The energy absorption, or the area under the load-deflection curve, has also been used to determine the post-cracking behavior of shotcrete. New testing methods (different specimen sizes, loading characteristics) place the emphasis on the residual strength after cracking measured at specific deformations (Holtmon et al., 1993).  26  1.8 HIGH PERFORMANCE SHOTCRETE As is the case for high performance concretes, high performance shotcretes are made by reducing the water-cement ratio (WIC), using superplasticizers and by adding silica fume. Kompen and Opsahi (1986) were successful in producing a high performance steel fiber reinforced shotcrete with a low W/C mix containing silica fume and superplasticizer. The effects of W/C reduction on strength and durability of concrete are well known. Because superplasticizers may behave differently with different cements, it is important to choose the right cement-superplasticizer combination (Aitcin, 1990). This point will be discussed in detail in Chapter 3. The majority of high performance concretes and/or shotcrete (HPC or HPS) are used not for their high strength but for their improved durability. Gebler (1993) used a HPS with a water-cement ratio of 0.22 to successfully repair abrasion damage in sewer pipes. The durability of high performance shotcretes has not been studied but it is expected that it could be a good way to improve the deicer salt resistance of shotcrete, which is a major problem with wet-mix shotcrete in Quebec.  1.9 REFERENCES ACI Committee 506.1, (1987), “Recommended Practice for Shotcreting”, in ACT Manual of Concrete Practice (part 5), Detroit, 1987, iSp. ACI Committee 506.3, (1987), “State-of-the-Art Report on Fiber Reinforced Shotcrete”, in ACI Manual of Concrete Practice (part 5), Detroit, 1987, 13 p. AItcin P.-C., (1990), “Les fluidifiants dans les B.H.P.” Les Bëtons a Hautes Performances du Matériau a l’ouvrage, Presses de l’Ecole des ponts et chaussées, 1990, pp. 31-59. Alemo J., Holmgren J. and Skarendahi A., (1990), “Steel Fiber Concrete Testing and Evaluation”, Engineering Foundation Conference, Shotcrete for Underground Support V, Uppsala, Sweden, June 3-7, 1990, pp. 521-553. Andersen P.G. and Dalseg A., (1993), “High Capacity Shotcreting Equipment”, Proceedings of the International Symposium on Sprayed Concrete, October 17-2 1, 1993, Fagernes, Norway, pp. 153-166. Austin S.A. and Robins P.J. (1993), “Test Methods for Strength and Toughness of Sprayed Fiber Concrete”, Proceedings of the International Symposium on Sprayed Concrete, October 17-21, 1993, Fagernes, Norway, pp. 7-19.  27 Bakken A. and Holtermann E., (1993), “Wet Steel Fibre Reinforced Sprayed Concrete as Temporary and Final Rock Support in the Tunnels”, Proceedings of the International Symposium on Sprayed Concrete, October 17-2 1, 1993, Fagernes, Norway, pp. 339-345. Bangzho L., (1993), “The Causticity of Accelerator for Shotcrete and its Impairement on Strength of Shotcrete”, Engineering Foundation Conference, Shotcrete for Underground Support VI, Niagara-on-the-Lake, Canada, May 2-6, 1993, pp. 17-24. Banthia N., Trottier 3.-F., Beaupré D. and Wood D., (1994), “Influence of Fiber Geometry in Steel Fiber Reinforced Wet-Mix Shotcrete”, Concrete International, Vol. 16, No. 6, June, 1994, pp. 27-32. Banthia N., Trottier J.-F., Wood D. and Beaupré D, (1992), “Steel Fiber Reinforced Dry-Mix Shotcrete: Influence of fiber Geometry”, Concrete International, Vol. 14, No. 5, May, 1992, pp. 24-28. Beaupré D., Pigeon M., Talbot C. and Gendreau M., (1991a), ‘Résistance a Pécaillage du béton soumis au gel en presence de sd déglacants”, Proceedings of the Second Canadian Symposium on Cement and Concrete, University of British Columbia, Vancouver, July 24-26, 1991, . 196 182 pp. Beaupré D., Pigeon M., Morgan D.R. and McAskill N., (1991b), “Le béton projeté renforcé de fibres d’amiante”, Proceedings of the First Canadian University Industry Workshop on Fibre Reinforced Concrete, Université Laval, Quebec city, 28-29 October, 1991, pp. 197-211. Breitenbucher R., (1993), “Shotcrete and Environment New Developments”, Proceedings of the International Symposium on Sprayed Concrete, October 17-2 1, 1993, Fagernes, Norway, pp. 182-190. -  Burge T.A., (1982), “Fiber Reinforced, High Strength Shotcrete”, Engineering Foundation Conference, Shotcrete for Underground Support IV, Paipa, Boyaca., Colombia, September 5-10, 1982, pp. 11-20. Burge T.A., (1986), “Fiber Reinforced High Strength Shotcrete with Condensed Silica Fume (SP-91-57)”, In ACT SP-91: Second International Conference on Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, Vol. 2, Madrid, Spain, pp. 1153-1170. Crom T.R., (1981a), “Introduction: Application and Use of Shotcrete”, Concrete International, Vol. 3, No. 1, January, 1981, pp. 23-26. Crom T.R., (1981b), “Dry-Mix Shotcrete Nozzling”, Concrete International, Vol. 3, No. 1, January, 1981, pp. 80-93. Egger H.R., (1977), “Wet or Dry Process”, in ACSE and ACT SP-54, Shotcrete for Ground Support, Detroit, pp. 241-249. Gebler 5., (1993), Presentation made at the Spring convention of the ACT, Vancouver, 1993.  28 Gebler S. and Schutz R., (1990), “Is O.85f’c Valid for shotcrete?”, Concrete International, Vol. 12, No. 9, September, 1990, pp. 67-69. Glassgold I.L., (1989), “Shotcrete Durability: An Evaluation’, Concrete International, Vol. 11, No. 8, August, 1989, pp. 78-85. Haave T. and Bracher G., (1993), “Non-Toxic Admixture for Sprayed Concrete”, Proceedings of the International Symposium on Sprayed Concrete, October 17-2 1, 1993, Fagernes, Norway, pp. 209- 220. Henager C., (1981), “Steel Fibrous Shotcrete: A summary of the State-of-theArt”, Concrete International, Vol. 3, No. 1, January, 1981, pp. 5 1-57. Hirose H. and Yamazaki Y., (1993), “Hydration Properties of Shotcrete with an Accelerator based on Calcium Aluminate”, Engineering Foundation Conference, Shotcrete for Underground Support VI, Niagara-on-the-Lake, Canada, May 2-6, 1993, pp.25-32. Hoitmon J.P., Lilleas T. and Opsahi O.A., (1993), “Norwegian Wet-Mix Sprayed Concrete: State-of-the-Art and Future Development”, Proceedings of the International Symposium on Sprayed Concrete, October 17-2 1, 1993, Fagernes, Norway, pp. 78-91. Hover K.C., (1989), “Some Recent Problems with Air-entrained Concrete”, Cement Concrete and Aggregates, Vol. 11, No. 1, Summer, 1989, pp. 67-72. Jardrijevic A., (1993), “Decomposition of Shotcrete Mixes” ,Proceedings of the International Symposium on Sprayed Concrete, October 17-2 1, 1993, Fagernes, Norway, pp. 92-101. Khalil S.M., Ward M.A. and Morgan D.R., (1978), “Freeze-Thaw Durability of Non-air-Entrained High Strength Concrete Containing Superplasticizers”, ASTM STP 691, Durability of Building Materials and Components, 1978, pp. 509-519. Kompen R. and Opsahi O.A., (1986) “Wet-Process Shotcrete with Steel Fibre and Silica Fume State of the Art in Norway”, personnel comunication, 1986. -  Kusterle W., (1993), “Regulating the Strength Development of Shotcrete”, Proceedings of the International Symposium on Sprayed Concrete, October 17-21, 1993, Fagernes, Norway, pp. 22 1-232. Litvin A. and Shideler J.J., (1966). “Laboratory study of shotcrete”, In ACI SP 14: Shotcreting, Detroit, 1966, pp. 165-184. Lukas W. and Kusterle W., (1993), “The Influence of Water Glass on The Technological Parameters of Shotcrete”, Engineering Foundation Conference, Shotcrete for Underground Support V, Uppsala, Sweden, June 3-7, 1993, pp. 197-212. Mehta K.P., (1983), “Pozzolanic and Cimentitious By-products as Mineral Admixtures for Concrete A Critical Review (SP-79-1)”, in ACI SP-79: Proceedings of the CANMET/ACI First Conference on the Use of Fly Ash, Silica Fume, Slag and Other Mineral By-products in Concrete, Detroit, 1983, pp. 1-46. -  29 Melbye T.A. (1993), “DEVELO®CRETE Hydration Shotcrete Mixes for Underground and Repair Projects”, Proceedings of the International Symposium on Sprayed Concrete, October 17-21, 1993, Fagernes, Norway, pp. 233-249. Morgan D.R., (1981), “Steel Fiber Reinforced Shotcrete, A Laboratory Study”, Concrete International, Vol. 3, No. 1, January, 1981, pp. 50-54. Morgan D.R., (1989), “Freeze-Thaw Durability of Shotcrete”, Concrete International, Vol. 11, No. 8, August, 1989, pp. 86-93. Morgan D.R., (1990a), “ Evaluation of Polypropylene Fiber Reinforced High Volume Fly Ash Shotcrete”, CANMET International Workshop on Fly Ash in Concrete, Calgary, Alberta, Canada, October, 1990. Morgan D.R., (1990b), “Advance in Shotcrete Technology for Support of Underground Opening in Canada”, Engineering Foundation Conference, Shotcrete for Underground Support V, Uppsala, Sweden, June, 4-7, 1990, pp. 358-382. Morgan D. R., (1991a), “High Early Strength Blended-Cement Wet-Mix Shotcrete”, Concrete International, Vol. 13, No. 5, May 1991, pp. 35-39. Morgan D.R., (1991b), “Steel Fibre Reinforced Shotcrete for Support of Underground Opening in Canada”, Concrete International, Vol. 13, No. 11, November, 1991, pp. 56-64. Morgan D.R. and McAskill N., (1984), “Rocky Mountain Tunnel Lined with Steel Fiber Reinforced Shotcrete”, Concrete International, Vol. 6, No. 12, December, 1984, pp. 33-38. Morgan D.R. and Mowat D.N., (1984) “A Comparative Evaluation of Plain, Mesh and Steel Fibre Reinforced Shotcrete”, American Concrete Institute, International Symposium on Fibre Reinforced Concrete, ACT SP 8 1-15, 1984, pp. 307324. Morgan D.R. and Pigeon M., (1992), “Proceedings from the Half-day Presentation of the 4th Semiannual Meeting of the Network of Centers of Excellence on High-performance Concrete”, Toronto, Ontario, Canada, October 6, 1992, pp. 31-56. Morgan D.R. and Wolsiefer J.Sr., (1992), “Wet-Mix Silica Fume Shotcrete: Effect of Silica Fume Form”, CANMET/ACI International Conference on Fly Ash, Slag and Natural Pozzolans in Concrete, Istanbul, Turkey, May 3-8, 1992, Vol. 2, pp. 1251- 1271. Morgan D.R., Kirkness A.J., McAskill N. and Duke N., (1988), “Freeze-Thaw Durability of Wet-Mix and Dry-Mix Shotcrete with Silica Fume and Steel Fibre”, Cement, Concrete and Aggregates, Vol. 10, No. 2, Winter 1988, pp. 96-102. Morgan D.R., McAskill N., Richardson E.W. and Zeller R.C., (1989), “A Comparative Evaluation of Plain, Polypropylene Fibre, Steel Fiber and Wire Mesh Reinforced Shotcrete”, Transportation Research Record 1226, Washington, D.C., 1989, pp. 78-87.  30 Parker H.W., (1977), “A Practical New Approach to Rebound Losses”, in ACSE and ACI SP-54, Shotcrete for Ground Support, Detroit, pp. 149-187. Ramakrishnan V., Coyle W.V., Dahi L.F. and Schrader E.K., (1981), “A Comparative Evaluation of Fiber Shotcrete”, Concrete International, Vol. 3, No. 1, January, 1981, PP. 59-69. Regourd M., (1987), “Microstructure of Cement Based Materials Containing Silica fume; its Relationship with some Properties”, Proceedings of International Workshop on Condensed Silica Fume in Concrete, Montréal, 1987, 8 p. Schrader E. and Kaden, (1987), “Durability of Shotcrete (SP 100-57)”, in ACT SP-100: Concrete Durability, Vol. 2, pp. 1070-1102. Schutz R., (1982), “Effects of Accelerators on Shotcrete Properties”, Engineering Foundation Conference, Shotcrete for Underground Support IV, Papia Boyaca, Colombia, September 5-10, 1982. Skjolsvold 0. and Hammer T.A., (1993), “Toughness Testing of Fibre Reinforced Shotcrete”, Proceedings of the International Symposium on Sprayed Concrete, October 17-21, 1993, Fagernes, Norway, pp. 67-77. Stewart E.P., (1993), “New Test Data Aid Quality Control of Gunite”, Engineering News-Record, No. 9, 1933, 4 p. Taguchi Y., Mitsutaka M., Kagawa K. and Hara. T, (1993), “Soil Nailing Technique in Tunnel Support”, Engineering Foundation Conference, Shotcrete for Underground Support VI, Niagara-on-the-Lake, Canada, May 2-6, 1993, pp. 158-165. Vandewalle, M., (1992), “Tunnelling the World”, Second Edition, Bekaert, Belgium, 1992, 229 p. Vézina D., (1985), “Étude du béton projeté”, Ministère des Transports du Québec, Rapport no. 884160, Janvier, 1984, 19 p. Von Eckardstein K.E., (1993), “Technology of the Top-Shot Wet-Mix Shotcrete System”, Proceedings of the International Symposium on Sprayed Concrete, October 17-21, 1993, Fagernes, Norway, pp. 3 10-321. Wolsiefer J. Sr. and Morgan D.R., (1993), ‘Silica Fume in Shotcrete”, Concrete International, Vol. 12, No. 4, April, 1993, Pp. 34-39. Yingling J., Mullings G.M. and Gaynor R.D., (1992), “Loss of Air Content in Pumped Concrete”, Concrete International, Vol. 11, No. 10, October, 1992, pp. 5761. Zangerle D., (1993), “ALIVA the Three Techniques of Sprayed Concrete Conveyance”, Proceedings of the International Symposium on Sprayed Concrete, October 17-21, 1993, Fagernes, Norway, pp. 322-335.  31  CHAPTER -2PROPERTIES OF FRESH CONCRETE 2.0 INTRODUCTION In this chapter, the importance of the properties of fresh concrete are described. A discussion of the principles of fresh property measurement, from subjective assessment of workability to the definition of more standard test procedures, is presented. Pumpability, compactibility and shootability are also defmed and their evaluation and measurement are discussed. Finally, mobility, compatibility and stability tests for fresh concrete are described.  2.1 IMPORTANCE OF FRESH PROPERTIES For most engineers, the important properties of concrete are those in the hardened state. Most of the time, concrete or shotcrete are used because they develop certain properties, such as strength, impermeability or durability. In fact, every time one uses concrete, it is expected that the freshly mixed material will set and develop some strength. The properties of fresh concrete are then only important with respect to the expected hardened properties. However, even though the fresh properties are required for only a short period of time, they are no less important than the hardened ones. In fact, if the concrete cannot be placed, compacted and/or fmished properly, the entire structure can be rejected. Because each application is different (floor finishing, cast concrete, roller compacted concrete, pumped concrete, shotcrete, etc.), each kind of concrete has its own requirements for “workability”, transportation, fluidity, compaction and finishing. It is necessarily assumed that the concrete is mixable and that it will maintain its workability during these operations. Mixes should be designed in such a way that small changes in mix proportions will not cause excessive changes in either the fresh properties or the hardened ones. The concept of stability is thus very important: the fresh properties should be maintained for a long enough time to ensure that all operations such as placing, finishing, etc. can be carried out properly.  32 2.2 WORKABILITY When a particular mixture fulfills all of the requirements for a specific application, and if it is stable, it is usually called a workable mix or a mix with good workability. If one of the requirements is not fulfilled, the mix might not be considered workable. Workability has traditionally been used as an overall estimation of the qualities of fresh concrete mentioned above. However, good workability has different meanings for a floor finisher, or a pump operator (for pumping), or for a nozzleman (for shotcreting). Properties such as finishability, pumpability and shootability are traditionally subjective estimations. To be useful, better estimations of these properties are necessary. 2.2.1 Definition of physical properties According to Tattersall and Banfill (1983), the process of defining a physical property proceeds through three stages: stage I: the property is described only in comparative terms, based either on purely subjective assessment or on a simple empirical test. Stage II: a numerical scale based on an empirical test or tests is established. This scale may or may not be found to be satisfactory but will inevitably have a restricted application. Stage III: the property is rigorously defined, possibly through the consideration of an ideal model in terms of physical constants derivedfrom thefundamental quantities mass, length and time, ...“  It is obvious that workability, because of its non-precise definition and its subjective assessment, is a stage I property. It is an overall estimation based implicitly on parameters which may be more precisely defined such as: viscosity, yield stress, cohesion, internal friction, mobility, pumpability, stability, segregation, bleeding, compactibility, finishability, shootabiity, etc. Some of these characteristics, such as viscosity and yield value are well defined scientific (stage ifi) parameters. These fundamental rheological parameters will be discussed in Chapter 3. Other characteristics can be estimated through stage II properties. For example, mobility is defined as the capability of the fresh concrete to flow. Some standard mobility related tests, such as slump, VeBe and flow (see Section 2.6), can be used to give a numerical scale to this property.  33 Pumpability is, with compactibility and shootability, one of the most important characteristics in wet-mix shotcrete technology. It is defined as the mobility and stability under pressure within an enclosed pipe. Obviously, more than a single stage II property or test would be required to give a quantitative estimation of pumpabiity. Compactibility is also a stage I property. It is related to the amount of energy or to the compacting effort needed to adequately compact a fresh concrete mix. It can also be considered as the ability to achieve a certain degree of compaction when a fixed amount of energy is used. There is no standard definition for shootability; it could probably be estimated through some stage II properties, such as build-up thickness or rebound measurements as described in Chapter 1. 2.2.2 Empirical measurement of physical properties In order to estimate and measure these various aspects of fresh concrete behavior, many empirical quantitative (stage II) tests have been developed. The “ideal” test (for any application), should have the following characteristics:  •  It should be suitable for either laboratory or field testing.  •  The results should be quantitative.  •  The results should lead to a meaningful and useful estimate of the parameter in question.  •  The test should be sensitive and reproducible.  •  The apparatus should be simple, robust and portable, and should not require frequent calibration.  •  The apparatus should give a reading without the necessity of further calibration or analysis  Because it is difficult to fulfill all of these requirements, it is easy to understand why only a few of the proposed laboratory tests have been standardized and have achieved wide use. Also, no test among those which have been standardized provides an estimate from a  34 single result of any fundamental properties related to rheology. Nevertheless, some tests have been standardized and used for both quality control and for research: slump, flow table and VeBe are all used to estimate mobility. These tests provide only empirical values obtained in a very specific manner. Attempts have been made to use these tests to estimate properties such as pumpability, but these have generally not been very successful. Most of these tests have been developed for very specific purposes. Some have been standardized and a few of these will be briefly described. Emphasis is placed on their scope and on the interpretation of their results. It is important to remember that all of these tests have only limited applicability. When these tests are used for purposes other than the one for which they were originally designed, problems can be expected.  2.3 PUMPABILITY As mentioned earlier, pumpability may be defined as the concrete mobility and stability under pressure within an enclosed pipe. Another definition for pumpability is “pressure workability” (Gary, 1962). This would mean that pumpability is the mobility under pressure. It is relatively easy to estimate workability or mobility by different standardized tests (slump, for example). It is not so easy to measure stability, which can be defined as the capacity of the concrete to maintain its initial homogeneity during transport, handling and placing. Pumpability has often been estimated by measuring the power requirement (Dawson, 1949) or the actual pressure (Ede, 1957; Gary, 1962 and; Browne and Bamforth, 1977; Idom, 1982) needed to effectively pump a certain concrete mixture. Some people have thed to estimate the pumping rate graphically by considering the pump pressure, slump, pumping distance and line diameter (Littlejohn, 1980; Eckardstein, 1983). 2.3.1 Mobility requirements Ad Committee 304 (1982) gives recommendations regarding the slump limits for pumping. They recommend that concrete should possess a slump between 50 mm and 150 mm, although properly proportioned flowing concrete with a slump higher than 180 mm can also be pumped.  35 Results of pumpability tests carried out by Gary (1962) on the influence of aggregate shape and grading have shown that for the same slump (around 100 mm) concrete can be either pumpable or not. His test amounted to a “go or no go” test because the pumping pressures measured were either low or very high, but with no intermediate values. From these results, Gary concluded that:  f concrete is pumpable, it would have adequate workability, while on the other hand, it may be workable but not pumpable. The additional requirements for stability may explain the above statement: mobility is a required parameter but it is not in itself sufficient. Because of the stability requirement, an attempt to predict pumpability only from mobility test measurements will not always be successful. Ede (1957) has described the effects of water content on the pump pressure requirement (improperly called flow resistance in Figure 2.1). A concrete with sufficient water to fill all voids between the aggregates, referred to as “saturated”, is much easier to pump than an “unsaturated” one Figure 2.1 shows the change in axial pressure with respect to the W/C (related to the total water content). .  E  I 0.40  0.50  Water-cement ratio Figure 2.1: Effect of “paste saturation” on pumpabiity  36  2.3.2 Stability requirements An intensive study on concrete pumpability was carried out by Browne and Bamforth (1977). They showed, in relation to the results obtained by Ede (1957), that it is possible during pumping, to change locally from the saturated state to the unsaturated state and thus cause blockage. Figure 2.2 illustrates the dewatering effect caused by the local expulsion of paste from the aggregates. To avoid such occurrences, they stated: particle —i interlocking \  j—  /  migration of mix water  A  .9  *— .4— frictional resistance Figure 2.2: Dewatering of concrete in a pipe line it is essential that the concrete has low permeability to the flow of its own mix water, and also that this property is maintained. The fresh water permeability in concrete can be evaluated from a pressure bleed test, which can be viewed as a measure of stability under pressure. In conjunction with the slump test, it can be used to predict pumpability (Figure 2.3). See Section 2.8.1 for more details on the pressure bleed test. Segregation and aging (change in mobility with time) are also important parameters in determining stability. Bartos (1992) has provided a list of factors which usually increase stability by reducing segregation: •  Continuous grading of aggregates, and a smaller maximum size.  •  Air-entrainment.  •  Increased proportion of fines, including cement and cement substitutes.  37 •  Optimum water-cement ratio and paste content  •  Admixtures causing thickening of the liquid phase of the mix.  All of these factors will reduce the pressure bleeding and thus increase stability.  10  I E  Water emitted (cm ) 3 Figure 2.3: Relationship between slump, water emitted and pumpability (Browne and Bamforth, 1977)  The use of a small amount of entrained air has been known to increase pumpability; ACT Committee 304 on Concrete Pumping states: Air-entrained concrete is considerably more plastic and workable than nonair-entrained concrete. It can be pumped with less coarse aggregate segregation and there is less tendencyfor the concrete to bleed.  38 The use of silica fume and a reduction in the W/C reduce bleeding considerably, but also generally reduce mobility. Low W/C and/or silica fume concretes generally need superplasticizers to bring the mobility back to an acceptable level. 2.3.3 Mix design In order to satisfy the mobility and the stability requirements, adequate mix design is required. The proportions and types of constituents are known to affect both the fresh and the hardened properties of concrete: aggregate type, maximum size, grading and variability; cement type; presence of other cementitious materials; use of admixtures; and their relative proportions. Concrete can be considered as a mixture of aggregates surrounded by cement paste. Cement paste in turn can also be seen as a suspension of small solid particles in water. If there is either a paste deficiency or a water deficiency, the concrete will not be workable. Mobility requirements tend to increase both the paste and water content requirements. On the other hand, the properties of the hardened concrete and the considerations of economy require one to minimize both the paste content (e.g. to reduce shrinkage, creep) and the water content (e.g. to increase strength, durability). To minimize the paste and water content requirements, many researchers have tried to evaluate and then to minimize the void content of the dry aggregates. Some researchers have simply directly measured the void content of the combined aggregates (e.g. Brown and Bamforth 1977). Others have tried an analytical approach, by using the coarseness factor, mortar factor, aggregate particle disthbution, or some similar factor, to optimize mix proportions (e.g. Shilstone, 1990). An extensive discussion regarding the void content of dry aggregate mixtures has been provided by Powers (1968). He also discussed a dry mixture of cement and combined aggregates: In terms ofpresent-day concrete technology, or of its probable form in the future, there is no practical reason to study dry mixtures of cement and aggregate. However, the relationships found in such mixtures are of interestfrom an analytical point of view; they are related on the one hand to the mixture of aggregates... and on the other to the mixture of cement, aggregate and water... It seems that the only way to optimize the mix composition effectively is to make fresh concrete and measure its properties. This is especially true for shotcrete mixtures, where  39 in addition to the pumpability requirement, the aggregate grading will also depend on the requirements for shootabiity, at least in order to minimize the rebound. The objectives of minimizing the paste and water contents are still valid in terms of mobility. However, to satisfy the stability requirement, a paste that is stable with respect to the aggregate grading must be used. The use of a low WIC ratio mixtures and silica fume is certainly a good place to start.  2.4 COMPACTIBILITY Compactibility, for cast-in-place technology, refers to the facility with which the concrete can be fully compacted. For cast concrete, the energy required is generally obtained through vibration. It can be seen as an overall estimation of the efficiency of a placing method with respect to the concrete mobility. For shotcrete, the speed of the particles, which depends on the amount of compressed air used at the nozzle, and their impact on the receiving surface produce the compaction effect. Compactibility should thus be seen as the efficiency of the method and/or the equipment used to properly produce dense shotcrete with respect to the workability of the fresh shotcrete. If the method and equipment used are capable of properly placing a dense material, one can say that the compactibility is satisfactory.  2.5 SHOOTABILITY Shootability, like finishability, has no precise definition; it can only be considered qualitatively as the ability of concrete to be shot. Parameters such as rebound and build-up thickness (see Chapter 1) can be used to estimate shootability: less rebound and a greater build-up thickness imply increased shootability. The efficiency of the whole process can also be used to estimate shootabiity.  40  2.6 MOBILITY RELATED TESTS Mobility is the ability of a fresh mix to flow and fill the formwork or other space. It is a very important characteristic not only for cast-in-place concrete but also for shotcrete, because mobility is one of the characteristics that defme pumpability. Many tests (stage II) have been designed to evaluate mobility. The best known is the slump test. Other tests such as the VeBe and the flow table are now used in many countries as standard tests. Only these three are described here. For more details about the few tests described in this and the next sections, it would be appropriate to refer to the corresponding standards. Quicker and more interesting surveys are given by Tattersall (1991) and by Bartos (1992). Bartos (1992) also looks at the effect of mix composition on fresh concrete properties. 2.6.1 Slump test Slump measurement is the most commonly used test in North America and also one of the oldest. It was developed by Abrams at the beginning of the century. The slump test (ASTM C-143 or CAN3-A23.2-5A) consists of filling a cone with concrete in a standard way; the cone is then lifted and the slump measured after the concrete has reached an equilibrium position (Figure 2.4). The higher the slump, the higher the mobility. 100 mm 4 i  slump  Figure 2.4: Slump cone apparatus Originally, the slump test was developed to measure the effect of water content on the workability of fresh concrete. The limits of its proper application correspond to slumps between 40 mm and 180 mm. In other words, this method is not good for very stiff or very fluid concrete.  41 Other factors beside the variation in water content may cause variations in slump measurements: operator and other influences have been studied by Mittelacher (1992). Almost any change in mix composition or in the material characteristics will affect the slump. The time history is also important when measuring slump, since concrete is known to lose slump with time. This phenomenon can be very important when superplasticizers are being used (Whiting and Dziedzic, 1989). Stability could then be estimated by the rate of slump loss (see section 2.8.1). 2.6.2 Flow test This test has been developed in Germany and is very popular in Europe (DIN-1048 or BS-1881-105; formerly ASTM C-124). It is much like a miniature slump test but it measures the spread in mm after the concrete has been jolted 15 times with a fixed amount of energy: the 40 mm drop height shown in Figure 2.5. I_  7W) -  flow table  [1  (mm)  2OO1  U Figure 2.5: Flow test apparatus  It is a very simple test, but not suited for use with very high workability concretes. The applied shocks during the test encourage segregation: the cement paste tends to move away from the center of the flow table, leaving the coarse material behind. This test has a dynamic component, compared to the slump test which is quasi-static. When vibration is being used to help in placing the concrete, this test might be more appropriate. There is an empirical relationship between the slump test and the flow test, but this relationship is variable (Bossi, 1973).  42  2.6.3 VeBe test The VeBe test is a molding test which consists of measuring the ease with which the mortar or concrete can fill a mold under vibration (BS-1881-104, ACI-21 1). It can be used to assess the mobility of low workability concrete and also, to some extent, its compactibiity. The VeBe apparatus is shown in Figure 2.6. It consists of a vibrating table with a cylindrical container in which a slump cone is placed and filled with concrete. The “slump” is measured and a plastic transparent disk is put in contact with the upper part of the concrete cone. The time taken for the concrete to be completely remolded into the cylindrical container under vibration is then measured. The VeBe time is calculated using the measured time and the change in unit weight or density due to the vibrations. cone holder  container (mm)  vibrating table  Figure 2.6: VeBe test apparatus This test is sensitive to the mix water content, and to the experience of the operator in estimating when the remolding is completed. This method is adequate for low workability concretes with slumps below 50 mm. If the workability is too high, the remolding time is too short to be measured accurately.  43  2.7 COMPACTIBILITY RELATED TESTS Compactibiity is related to the energy required to adequately compact (remove entrapped air) a fresh concrete mix (ex.: Waltz test). But, since it is difficult to measure the work required to achieve a given amount of compaction, tests that measure the amount of compaction produced by a given amount of energy have been designed (ex.: Compacting factor test). The air content measurement test is also presented. Although it is not a compaction test, it can be used to determine the degree of compaction achieved for a standard placement method because it measures the amount of air. In the case of shotcrete, by shooting directly into the air meter base, the in-place degree of compaction can be assessed. 2.7.1 Compacting factor test This test measures the change in unit weight after two successive drops of the concrete (BS-1881-103). Figure 2.7 shows the apparatus and the test set-up. It consists of two inverted cones with bottom trap doors and a receiving container. The upper cone is first filled with concrete. The concrete falls under its own weight successively into the intermediate cone, and then, into the bottom container. The mass of the concrete in the container is compared to the mass of the same volume filled with concrete with maximum compaction (i.e. compacted by vibration). There is a relationship between the results of this test and compactibility. In practice, compaction is achieved by vibration and not by dropping the concrete from a certain height. Then, this test is far from representative of the “real world”. Also, more or less energy is lost in friction along the cone surfaces. This energy loss can be important, but it is difficult to evaluate, and varies with the workability of the concrete. For this last reason, this test is not recommended for low workability concrete. 2.7.2 Compaction (WaIz) test This test was developed by Walz in the 1960’s, and is now a German standard (DIN 1048). This test is applicable for low to high workability concretes. It measures the volume of a concrete sample in a standard container before and after full compaction. The compaction is generally achieved by vibration. It is often referred to as the Compaction Index test.  44 The apparatus essentially consists of a metallic box of dimensions 200 mm x 200 mm x 400 mm. It is recommended that a vibrating table be used to ensure total compaction, although rod tamping by hand is accepted. This test is more relevant and much simpler than the compacting factor test. It is also less expensive, though it requires a large sample. Few results are available for this test, so, it is difficult to discuss its precision.  00  (mm) compaction factor apparatus  Figure 2.7: Compacting factor measuring apparatus 2.7.3 Pressuremeter (air content) This test measures the amount of air in the fresh concrete (ASTM C-231). The method is very well known, and so no further explanation is given here. Other methods of determining the fresh air content also exist: gravimetric and volumetric. However, these methods are not used in the field because, while they are more complex, they are not necessarily more accurate.  45  2.8 STABILITY RELATED TESTS Stability in concrete technology can refer to bleeding, segregation or aging. For pumpability purposes, aging (loss in mobility with time or due to pressure) and pressure bleeding should be considered. 2.8.1 Aging (slump) Aging or the reduction in mobility can be estimated by measuring mobility at different times. For example, Whiting and Dziedzic (1989) have measured the loss in slump for different concretes containing different superplasticizers or high-range water-reducers (Figure 2.8). They also noted that bleeding (which also is a measure of stability) was significant for flowing superplasticized concrete. Other factors such as high temperatures, use of high-early strength cements, etc. may cause fast aging.  U  control  • SP-N SP-M A SP-B sP.x  4  1 0 0  20  40  100 60 80 Elapsed time (mm)  120  Figure 2.8: Slump loss in mixtures containing superplasticizers compared with control (Whiting and Dziedzic, 1989)  46  2.8.2 Pressure bleed test This non-standardized test was developed by Browne and Bamforth (1977). It measures the amount of water emitted from concrete under pressure. Figure 2.9 shows the test set up. The apparatus is described as follows: It consists essentially of a 12.5 cm diameter cylinder with a detachable top cap and base. The top cap houses a piston which runs on two rubber “0” rings and is attached to the plunger of a double acting hydraulic jack. The jack is screwed into the top of the piston housing and hence aforce can be applied to the piston through the top cap. The jack is operatedfrom a hand pump with a four-way valve, allowing the piston to be moved in two directions. The travel of the piston enables the rapid removal of the compressed concrete plug after the test. The base plate has a bleed hole drilled into the side and a tap has been inserted. The inside of the bleed hole is covered by a 50 mesh wire gauge to prevent blockages in the tap (Browne and Bamforth, 1977).  —  calibrated  double action hydraulic cylinder  0” rings 125 mm  diameter cylinder 0” ring ‘bleed tap gauge retainig plate  mesh wire gauge measuring cylinder  Figure 2.9: Pressure Bleed test apparatus (Browne and Baniforth, 1977)  47 The test procedure is to fill the cylinder with fresh concrete, to apply a pressure of 3.5 MPa (500 psi) on the concrete and to collect the water emitted from the concrete. The volume of water is recorded with respect to time. Typical results are presented in Figure 2.10. The volume of water at 10 seconds is subtracted from the volume at 140 seconds to calculate the V14o-Vlo value (in ml or %). According to the inventors of the test, for a given slump, when V14o-Vlo is small, the concrete is not pumpable and when it is high, the concrete is pumpable (see Figure 2.3).  120 100 80  I:: 20 0  0  20  40  60  80  100  120  140  Time (s) Figure 2.10: Typical results from the pressure bleed test (Browne and Bamforth 1977)  2.9 REFERENCES ACI Committee 304, (1982), “Placing Concrete by Pumping Methods”, in ACI Manual of Concrete Practice, part 3, revised in 1982. Bartos P., (1992), “Fresh Concrete Properties and Tests”, Elsevier, 1992, 292 p. Bossi J.A., (1973), “Concrete Workability Measurement, Fresh Concrete: Important Properties and their Measurement”, Proceedings RILEM Seminar, Leeds, March 2-4, 1973, pp. 1-10. Browne R.D. and Bamforth P.B., (1977), “Test to Establish Concrete Pumpability”, Journal of American Concrete Institute, May 1977, pp. 193-207.  48 Dawson 0., (1949) “Pumping Concrete Friction between Concrete and Pipe line”, Magazine of Concrete Research, Vol.1, No. 3, December, 1949, . 140 135 pp. -  Eckardstein K.E., (1983), “Pumping Concrete and Concrete Pumps”, SCHWINGS publications, 1983, 133 p. Ede A.N., (1957), “The Resistance of Concrete Pumped through Pipelines”, Magazine of Concrete Research, Vol. 9, No. 27, 1957, pp. 129-140. Gary J.E., (1962), “Laboratory Procedure for Comparing Pumpability of Concrete Mixtures”, Proceedings, ASTM Vol. 62, 1962, pp. 964-971. Idorn G.M., (1982), “Rheology in Fresh Concrete”, Proceedings, Symposium M, Material Research Society, Annual meeting, Boston, Massachusetts, November 1-4, 1982, pp. 230-233. Littlejohn G.S, (1980) “Wet Process Shotcrete”, Proceedings of the Symposium on Sprayed Concrete, C180, The Construction Press, April 15, 1980, pp. 18-35. Mittelacher M., (1992) “Re-Evaluating the Slump Test”, Concrete International, Vol. 14, No. 10, October, 1992, pp. 53-56. Powers T.C., (1968) “Properties of Fresh Concrete”, Wiley & Son, 1968, 664 p. Shilstone J.M. (1990) “Concrete Mixture Optimization”, Concrete International, Vol. 12, No. 6, June 1990, pp. 33-40. Tattersall G. H., (1991), “Workability and Quality Control of Concrete”, Chapman & Hall, 1991, 262 p. Tattersall G. H. and Banfill P.F.G. (1983) “The Rheology of Fresh Concrete”, Pitman, London, 1983, 365 p. Whiting D. and Dziedzic W., (1989), “Behavior of Cement-Reduced and ‘Flowing’ Fresh Concrete Containing Conventional Water-Reducing and ‘Second-Generation’ High Range Water-Reducing Admixtures”, Cement, Concrete, and Aggregates, CCGDG, Vol. 11, No. 1, Summer 1989, pp. 30-39.  49  CHAPTER -3RHEOLOGY OF FRESH CONCRETE  3.0 INTRODUCTION In this chapter, the rheological properties of cement pastes and concretes are discussed. First, the fundamentals of rheology and Newtonian fluid behavior, as well as some measurement techniques for the coefficient of viscosity are presented. Next, Bingham behavior, applicable to cement pastes and concretes, is discussed with respect to the time dependence of cementitious mixtures. Then, considerations regarding the use of coaxial cylinder viscometers and rheometers are given. The effects of mix composition on rheological properties are also discussed with an emphasis on high performance concrete technology. Finally, the possible implications for shotcrete technology, especially those related to pumping and shooting, are discussed with respect to Bingham behavior.  3.1 RHEOLOGY Rheology is defined as the science of deformation and flow of matter. It covers relationships between stress, strain and time. In terms of fresh concrete, the field of rheology is related to the flow properties of concrete or with its mobility before setting takes place. In Chapter 2, it was mentioned that physical properties can be defined in terms of physical constants derived from fundamental properties. These properties do not depend on the circumstances under which the material is tested. For example, viscosity is the fundamental property that describes the flow or the behavior of a Newtonian fluid. 3.1.1 Viscosity (Newtonian liquid) When a shear stress is applied to a liquid, the liquid deforms and keeps deforming until the stress is relieved. There is no stress-strain relationship as for solid matter, but rather a stress-strain rate relationship. When the strain rate (under shear) is proportional to the applied stress (shear stress), the liquid is called Newtonian. One may consider a liquid confined between two parallel plates: one fixed and one mobile (Figure 3.1 a). If a constant force is applied to the top plate, this plate will start moving,  50 and reach and maintain a constant speed until the force is removed. Under these conditions, it is possible to calculate a shear stress: (t) = force (F) divided by the plate area (A). The rate of shear strain (or velocity gradient dv/dx) can be calculated by using the speed profile shown in Figure 3.lb: (dv/dx = y) = velocity (V) divided by the distance (H) between the two plates.  1/TI  Shear stress (a)  (b)  (t)  (c)  Figure 3.1: Determination of coefficient of viscosity For a Newtonian fluid, the reciprocal slope of the linear relationship shown in Figure 3. ic is the coefficient of viscosity (ri). The following relationship is only valid for laminar flow of a Newtonian fluid: t=ry  (3.1)  The experimental determination of the coefficient of viscosity requires the measurement of shear stress under known conditions of shear rate or vice-versa. The above experiment satisfies this requirement, though it is not practical for physical reasons to conduct such an experiment. In most practical cases, the shear rate varies within the liquid but, by integration (because the viscosity coefficient is independent of the applied shear rate), it is possible to obtain an equation for the coefficient of viscosity. Some practical methods have been developed to determine this coefficient. The coaxial cylinders viscometer has been used very often to study cement paste rheology. The apparatus is shown in Figure 3.2a. It consists of two cylinders coaxially mounted; one is fixed and the other rotates at various speeds. When the liquid fills the space between the cylinders (the t gap’) and when the rotating cylinder is in motion, a torque is  51 induced on the fixed cylinder through the sheared liquid. A relationship similar to Figure 3.2b can be obtained for a Newtonian fluid.  TI  Torque (Nm) c T (a)  (b)  Figure 3.2: Representation of the coaxial cylinders viscometer For this apparatus, the shear stress  (t)  equals the torque (T) divided by the surface area of  the cylinder (2itrh) and its radius (r). The relationship between the shear rate (or velocity gradient rdoldr) is: T/(2iurhr)=rj rdw/dr,  (3.2)  where fl is the coefficient of viscosity. By integrating Equation 3.2 between Rb and Rc for r and between 0 and 2 for o and by isolating r (assuming ri is independent of shear rate), the following relationship is obtained: [(1/Rb ’ ) (1/Rc2)I. 1 =T 2 24ith -  (3.3)  In Equation 3.3, the ratio 2/T is the slope of the line in Figure 3.2b. From a constant factor G =[(1/Rb ) (1/Re 2 )] / (4ith), the slope of the plot of Q vs. T is equal to Gil for a 2 -  coaxial cylinders viscometer with physical characteristics similar to those of Figure 3.2a.  52  3.1.2 Other behavior Newtonian behavior is the simplest possible behavior for a fluid, but many fluids do not behave in this way. For more complicated behavior, where the observed rate of shear is not linearly proportional to the applied shear stress, different relationships may be observed. In these cases, the behavior cannot be expressed by a single coefficient. Different equations have been developed for different liquid materials. The graphical representation by a flow curve, as shown in Figure 3.3, is also a very useful way of presenting the flow behavior.  Shear thickening  Shear thinning  Bingham behavior  Shear stress (t)  Shear stress (t)  Shear stress (t)  (a)  (b)  (c)  Figure 3.3: Nonlinear flow curves and Bingham model (‘r  =  to + .t  y)  In Figure 3.3 three hypothetical, non-Newtonian flow curves have been plotted. Curve (a) is a shear thickening liquid in which the viscosity increases when the shear rate is high: the liquid flows less as the flow rate increases. Curve (b) is a shear thinning liquid in which the viscosity decreases when the shear rate increases (more flow at high shear rates). Liquids (b and c) also have a yield value: a minimum shear stress that must be applied before the liquid starts to flow (the curves do not pass through the origin). For flow curve (c), when the yield (to) value is overcome, there is a linear relationship between the applied shear stress and the shear rate. This last behavior is referred to as the Bingham model and can be expressed by the following relation: (3.4) where t is the plastic viscosity and ‘y is the shear rate. In this case, only two parameters are needed to fully describe the fluid behavior: the yield value and the plastic viscosity.  53 Cement paste flow curves can be expressed by different models. Banfihl (1973) reported five different ones: •  Bingham:  •  Hersschel-Bulldey:  •  Robertson-Stiff:  •  Eyring:  •  Ostwald-deWaele:  (3.5)  t=to+I.Ly,  a ‘y”,  (3.6)  =  a (y+e)b,  (3.7)  t  =  a y + b sinh  t  =  to +  to +  b sinh  (b/)1, (bI)1)  (3.8) (39)  Banfihl (1990) also noted that cement pastes do possess a yield value. Most authors have used the Bingham model (Tattersall and Banfill, 1983) for cement paste. This can be explained, by the good correlation (correlation coefficients “r” presented by Tattersall are usually in the range of 0.99 or 0.98) with the Bingham model. It seems that, with respect to the precision of the apparatus, there is no reason to use more a complex model. 3.2 CEMENT PASTES Concrete can be viewed as a suspension of large particles in cement paste. Cement paste can in turn be modeled as a suspension of solid, reactive particles in water (Haritori and Izumi, 1982). To study fresh concrete rheology, it seems appropriate to start with a study of fresh cement paste rheology. Even though is has been shown that cement paste possesses a more complex rheological behavior than concrete and cannot be used to predict the behavior of concrete, some useful information can be obtained which helps one to understand some phenomena that may occur in concrete (Tattersall and Banfill, 1983). Studies of cement paste can be separated into three distinct groups: •  studies which are mostly related to the development of measuring methods applicable to cement paste,  •  studies of cement paste related to the composition of the paste, and  •  studies of the time dependence of the rheological properties of cement paste.  None of these topics is related to the scope of this study on high performance shotcrete. However, the study of the structure of the cement paste and its time dependence on  54 rheology is of interest to illustrate the phenomenon of structural breakdown and thixotropy. 3.2.1 Structure of fresh cement paste Cement paste is made by mixing cement and water. The rheological behavior of cement paste is very different from the behavior of a suspension of inert solid particles of similar grading. Because of the electric charges on the surfaces of dry cement particles, they do not disperse easily in pure water, but tend to form floes (Pallière and Briquet, 1980). After, and even during mixing, several physical and chemical reactions occur. Rapid reactions take place during the first minutes after the initial contact between the water and the cement: some of the lime and sulfates dissolve, and a surface skin of hydrated minerals begins to form around other components. This period is followed by a dormant period (25 hours) during which the reactions are slow and the paste remains workable until setting takes place. After the initial contact between cement and water, the cement grain surface slowly becomes covered by a membrane of gelatinous calcium silicate-suiphoaluminate hydrates. These membranes form around the floes, and are responsible for the physical phenomenon known as structural breakdown illustrated in Figure 3.4a. The plot of the curve of increasing shear rate (arrow pointing up) is different from the curve of decreasing shear rate (arrow pointing down) of a cement paste undergoing structural breakdown. The “up-curve” is typical of a thinning material, in which the apparent viscosity (reciprocal of the slope at any point on the curve) decreases when the shear rate increases. The destruction of the membrane surrounding the cement floe under increased shear explains the observed reduction in apparent viscosity. After the maximum shear is reached, the membranes around smaller floes or individual cement particles reform and the apparent viscosity remains almost constant (plastic viscosity) during the “down-curve”. Figure 3.4b shows the steps at different points on the curves (from Tattersall and Banfill, 1983). This phenomenon is strongly dependent on the mixing method used to make the cement paste. A hand mixed cement paste will exhibit more structural breakdown than one made using a more vigorous mixing method. In fact, the amount of shear used during the mixing of the paste will affect its rheological behavior. For concrete, because of the presence of aggregates, the shear action is so intense that the mixing method usually has no significant influence on the rheological properties. Similar behavior could be caused by  55 a thixotropic material. This effect is also time dependent and will be discussed in the next section. membrane envelopes  2- after mixing  Cl)  Shear stress (t)  3- during shear  (a)  4- during shear  (b)  Figure 3.4: Flow curve and schematic model for structural breakdown (Tattersall and Banfill, 1983) 3.2.2 Time dependence The elapsed time after initial mixing (i.e. the age of the cement paste) is an important factor to consider when determining the rheological properties. Because hydration proceeds even during the dormant period, the amount of water and the concentrations of the various ions change, and so does the viscosity and the yield of the paste. Depending on the nature of the cement, it is possible that the structural breakdown described in the previous section might be reversible. If it is reversible, the material is thixotropic. A material which exhibits a decrease in apparent viscosity, but does not show an increase at rest, is not a thixotropic material. Two successive tests are needed to determine whether a material that exhibits structural breakdown is thixotropic. Figure 3.5a shows a first test carried out on a material that shows a decrease in apparent viscosity. Figures 3.5b and 3.5c are the possible results of a second test carried out after a short period of time on the same material. In case (b), the second up-curve and down-curve are identical to the first down-curve; the material is not thixotropic. In case (c), the second up-curve is close to or identical to the first up-curve; the structural breakdown is reversible, and so the material is thixotropic.  56  second test: non-thixotropic  first test  second test: thixotropic  ‘I  L.a Cl)  Shear stress  (t)  (a)  Shear stress (b)  (t)  Shear stress  (t)  (c)  Figure 3.5: Illustration of thixotropic behavior The amount of time needed to reverse the effect of structural breakdown may vary from one thixotropic material to another. The exact shape of the hysteresis loop will depend on the material and its time history.  3.3 BINGHAM MODEL FOR CONCRETE 3.3.1 Rheometer For concrete, it is more appropriate, for practical reasons (principally the size of the aggregates) to use a rheometer instead of a coaxial cylinders viscometer to measure the rheological properties. A rheometer consists of an impeller and a sampling bowl. During testing, the impeller is driven, at different speeds, through the bowl previously filled with concrete, and the required torque and the impeller speed are measured. More details on rheometers are given in Chapter 5. Typical results obtained with the MKII rheometer (Tattersall, 1991) on different concretes are shown in Figure 3.6. In this figure, the flow curves strongly suggest a Bingham behavior for concrete. The rheological behavior can be expressed in term of two constants by the following equation: T=g+hN  (3.10)  57  where T is the torque to drive an impeller (Nm), g is the flow resistance (Nm), h is the torque viscosity (Nm.s) and N is the impeller angular speed (rev/s). Equation 3.10 is very similar to Equation 3.4, which suggests that the flow resistance is related to the yield and that the torque viscosity is related to the plastic viscosity. W/C  4  =  0.75  0.65  0.70  0.60  0.55  I  I I II I, II I,  E  _o.  I--  0  1  I I I I I  F I—I  2 Torque (Nm)  3  4  Figure 3.6: Typical results from rheometer MKII (Tattersall, 1991)  Unfortunately, these constants (g and h) are not in the fundamental units of yield (to = Pa) or plastic viscosity (ii = Pa.s). The g and h values are affected by the geometry of the apparatus with which they are measured. However, it is possible, by proper calibration, to convert them into the fundamental units for j.t and to. Even if not in fundamental units, the rheological parameters g and h can be used to evaluate the concrete mobility or other related properties. 3.3.2 Practical implications One implication of the existence of the Bingham behavior is that the values of g and h can be obtained with only two measurements of torque at two different speeds. This principle has been used by Tattersall to defme the two-point workability test. Another implication is that any test method which uses only one shear rate during testing is not appropriate to describe concrete workability in teinis of rheological properties. In the case of the slump test, the only measurement is made in a quasi-static way. This characteristic of the slump test explains why the slump is related to the flow resistance (g) which governs the “static” flow behavior of concrete. The relationship between slump test results and the flow resistance is shown in Figure 3.7 (Scullion, 1975). The relation proposed by Scullion is:  58 11 S =Ag  (3.11)  where S is the slump in mm, n is -0.47 and A = 0.007. This is approximately an inverse square-root relationship. This kind of experimental relationship has been confirmed by a theoretical simulation assuming a Bingham behavior: the effect on slump on a change in yield value is much greater than that of a comparable change in plastic viscosity (Tanigawa, Mon and Watanabe, 1990). Except for certain cases (e.g. change in W/C ratio only), there is no relationship between g and h. As shown in Figure 3.8 (adapted from Tattersall, 1991), it is possible to obtain any combination of g and h. It has been shown by Tattersall (1982) that for different concrete placing methods (for example: filling a pipe with flowing concrete), it is possible to identify a region, a workability box, which would enclose all combinations of g and h suitable for a particular application. In Figure 3.8, all concretes represented by a black dots would be suitable for this particular workability box; concretes represented by white dots would not.  70 60 0  5o .4O  0  I  E 30  iO  ‘—‘  Cl)  E  20  Cl)  1  23  4  Flow resistance g (arbitrary units) Figure 3.7: Relationship between slump and g (Scullion, 1975)  59  8  0 0  0  correlation coefficient = 0.19 0  7 6  0  0  o  0  0 00  0  A  5 4 3 0  2  0  0 0  00  1 0  I  0  1  I  I  I  4 2 3 h (arbitrary units)  l_  5  6  Figure 3.8: Relationship between g and h and workability box (adapted from Tattersall 1991) Also in Figure 3.8, concretes A and B, which have the same g, would behave differently, even if, according to Scullion, they should have the same slump (A is suitable, but not B). In this case, the slump test would not be sufficient to assess the workability. For some applications, where the viscosity is an important factor as well, the measurement of both g and h is certainly the best way to avoid such problems. Possible implications for pumping and shooting are discussed later. 3.3.3 Conversion to fundamental units It is possible to calibrate an apparatus with liquids of known viscosity to relate these intermediate values g and h to the fundamental properties t and to. As summarized by Tattersall and Banfill (1983): The rate of shear in a mixer variesfrom point to point and it is not possible to carry out a full analysis. However, some progress may be made if it is assumed that there is an average effective shear rate that is proportional to the speed of the impeller so that y = KN and by suitable calibration it is possible to determine the value of K. A knowledge of this constant and of another calibration constant G permits  60 the expressing ofyield value and plastic viscosity in fundamental units by the use of the equations: (KIG) g  (3.12)  u=(1/G)h.  (3.13)  ‘to  =  This means that the values of g and h are, respectively, proportional to and p. but the constants ofproportionality are djfferent.  to  Readers who are interested in the mathematical development should read Tattersall and Bloomer (1979) or Tattersall and Banfill (1983). By using different oils at different temperatures, Tattersall and Bloomer (1979) have been able to obtain numerical values G and K for the MKTI and MKJII (H impeller) apparatus (see Table 3.1). To obtain the yield value to in Pascal, the g value must be multiplied by 136 for the MXIII apparatus with planetary motion. Similarly, to obtain the viscosity t in Pascal-second, the h value must be multiplied by 15.2. Table 3.1: G and K values for MXII and MKJII (Tattersall and Bloomer, 1979)  constant  MKII  MKIII (H impeller)  G K K/G  0.045 6.09 135 22.2  0.066 8.94 136 15.2  hG  3.4 EFFECTS OF MIX COMPOSITION ON CONCRETE RHEOLOGY Almost any change in mix composition may affect the rheological behavior of concrete including the following: •  age of the mix (time elapsed after initial mixing)  •  content, shape, gradation, porosity, and texture of aggregates  61 •  content and type of cement  •  presence of other cemenhitious materials (fly ash, silica fume...)  •  use of admixtures (superplasticizers, air-entraining agents, accelerators, retarders...)  •  presence of fibers (type and quantity)  •  proportions of all constituents (e.g. WIC)  Interactions between constituents complicate the situation because they are not independent of each other in their effects. Only the effects of certain parameters, related specifically to this study, are presented here. For example, the effect of aggregate gradation is not discussed because it is not a variable in this study and it would take too long to review all of the papers published on this subject. The effects of silica fume and the use of superplasticizers are discussed in Section 3.5.  3.4.1 Time (aging) During mixing, there is an initial period of very rapid hydration followed by the dormant period during which very little reaction takes place. This period is responsible for the usual 2-3 hour grace period during which the placing usually takes place. Once setting has occurred, the properties of concrete are measured in terms of strength. During the dormant period, the properties of concrete change slowly: the flow resistance increases, but the plastic viscosity is usually not affected. Factors such as high temperature, low W/C, the presence of superplasticizers, high cement content, or rapid hardening cement may modify the usually observed slow “loss of slump”. As shown by Banfill (1980), the increase in g value can be sufficient to shorten the period during which concrete can be considered to be “fresh” when superplasticizers are used. 3.4.2 Water-cement ratio (W/C) The water-cement ratio (W/C) is certainly the most important parameter with respect to the properties of hardened concrete; for fresh concrete properties, it is no less important. It has been shown (Figure 3.5) that an increase in W/C produces a reduction in both the plastic viscosity and the flow resistance. This reduction is so great that for low W/C, a water-reducer or a superplasticizer must be used to produce workable concretes.  62 The type of cement, especially the C A content, the content of other components which 3 react rapidly and the sulfate content will affect the initial rheology; more detail is given in Section 3.5. 3.4.3 Admixtures Table 3.2 lists the most common types of admixtures and indicates their effect on rheology. For more details on admixtures in general, the reader should consult Tattersall (1991) or Tattersall and Banfill (1983). Because there is only a limited amount of experimental data on the subject, and because of possible interactions between the cement, mineral admixtures or other admixtures it is very difficult to predict the specific effect of any particular mix without preliminary testing. Experimentation is still the best way to obtain the information. Figure 3.9 shows the usual effect of the addition of water or different admixtures. When more than one admixture is added, the overall effect cannot be predicted, except for the general trend. Admixture AEA: air entraining SP: superplasticizer WR: water-reducer reference ++  +  sp  Viscosity (Pa.s)  —  Figure 3.9: Effects of addition of water and different admixtures (Gjørv, 1992) 3.4.4 Water-reducers (WR) Although water-reducers and superplasticizers produce generally similar effects (large reduction of flow resistance (g) and small reduction of plastic viscosity (h)), they are treated differently because the effects of superplasticizers are much greater and also because they are usually used for low W/C concretes.  63  Table 3.2: Concrete admixtures (Tattersall and Banfihl. 1983’)  admixture  Accelerators  Retarders  typical material  sodium aluminate sodium silicate lime  facilitates shooting  potassium hydroxide calcium chloride calcium formate sodium nitrite  development  hydroxycarboxylic acids  maintain workability at high temperatures reduce rate of heat development extend placing time  sugar  Water-reduceis  advantage I uses  calcium and sodium lignosuiphonates  effect on rheology  increased rate of change with time  more rapid early strength  initially may be significant reduced rate of change with time  a) higher workability with strength unchanged b) higher strength with unchanged workability c)less cement for same strength and workability  very significant effect in all three uses low reduction in h high reduction in g  Superplasticizers suiphonated melamineformaldehyde resin suiphonated naphthaleneformaldehyde resin mixture of saccharates and acid amides  as for water-reducer with greater efficiency  very significant in all three uses low reduction in h high reduction in g may modify the rate of change of g with time  Retarding water-reducer  mixture of sugars or hydroxylcarboxylic acids and lignosuiphonate  as for water-reducer, with slower loss of workability  very significant initial effect decreased rate of change with time  Air-entraining agents  wood resin (vinsol resin) salts of fatty acids lignosuiphonates  increase frost durability without increasing cement content and heat evolution  significant increase in workability reduce both g and h  Pumping aids  polyethylene oxide cellulose ether alginates alkylsuiphonate  widen the range of mixtures suitable for pumping  significant  64 Figure 3.10 presents the result of Waddicor (1980) as reported by Tattersall (1991). Up to a certain dosage (0.15% of cement weight) the addition of lignosuiphonate produces a large reduction in flow resistance (g) and a significant reduction in plastic viscosity (h). At higher addition rates, there is no further reduction of g, but a proportional reduction in h. The W/C used in this experiment was 0.65.  .  7 6 5  .  14 1 0  0.075 0.15 0.225 0.30 Lignosuiphonate (% wlw)  Figure 3.10: Effect of lignosulphonate on g and h (Tattersall and Banfill, 1983) 3.4.5 Air-entraining agents (AEA) The effect of air content on concrete mixes with three different W/C ratios is presented in Figure 3.11. From this figure it is obvious that an increase in the air content produces a rapid decrease in both g and h. For air contents higher than 5 %, there is no significant reduction in h, but the flow resistance (g) reduces for values of air content up to 10 percent. These dramatic reductions in g and h explain why air-entrained concretes are more workable even if, for the same strength level, their W/C ratios are lower in order to compensate for the strength reduction caused by the presence of entrained air. The reduction in W/C would otherwise result in less workable concrete. The improvement of  65 workability (especially the reduction of g) is often explained by the “ball-bearing” effect of air voids.  10  —  oWIC=O.55 o wIC=O.60 WIC = 0.65  Air content (%) Figure 3.11: Effect of air content on g and h (Tattersall and Banfill, 1983) 3.4.6 Fibers The effect of steel fiber additions has been studied by Tattersall (1991) using the MKIII rheometer with planetary motion. He mentioned that fresh fiber reinforced concrete conforms to the Bingham model; however, he presents no flow curve. The results on five mixes presented in Figure 3.12 show that when the fiber content increases, both g and h increase but when the fiber length is increased, only the flow resistance (g value) is increased. These results were obtained on concretes with W/C ratios ranging from 0.5 to  0.65. Similar results have been obtained by Llewellyn (1990) [as reported by Tattersall (1991)] with the same apparatus by using three concentrations of up to 0.1 % by volume of polypropylene fibers. The increases in the flow resistance were greater than the increase in the plastic viscosity. The W/C ratios were between 0.47 and 0.67. These observations are in broad agreement with the decrease in workability usually observed by using single-point workability tests such as the Vebe, inverted slump cone or slump tests.  66  10  . 0.5%2Omm 00.5% 25mm o 0.5% 60 mm 1.0%2Omm O%2Smm  1  20  C 0.5  0.6 0.55 wIC  0.65  Figure 3.12: Effect of steel fibers (volume and length) on g and h (Tattersall, 1991)  3.5 RHEOLOGY OF HIGH PERFORMANCE CONCRETE High performance concretes (HPC) usually possess high degrees of workability because of the high dosages of superplasticizers (SP) used to produce them. Other common characteristics of HPC are the low W/C (0.22-0.35) and the use of silica fume (around 10% by weight of cement). The combined effects of low W/C ratio, the presence of silica fume and the high dosage of superplasticizers, give a special rheology. Smeplass (1993) and Osterberg (1993) have shown that high performance flowing concrete can also be represented by the Bingham model. 3.5.1 Low water-cement ratio According to the trends shown in figure 3.5, low W/C ratio concretes made without superplasticizers (if they could be made) would possess very high flow resistance and a very high torque viscosity. As the W/C is reduced, the SP content is increased to maintain the required flow properties.  67  3.5.2 Silica fume (SF) As mentioned in Chapter 1, silica fume is very often used in shotcreting operations because it is known to reduce rebound and increase build-up. The effects of silica fume additions on rheology of concrete have been studied by Wallevik and Gjørv (1990) and reported by Gjørv (1992). Figure 3.13 shows that the flow resistance is nearly constant until a threshold value in silica fume content is reached (around 7%). Over that threshold value, the yield increases rapidly. Also, when the cement content is high (or when the W/C is low), the increase in yield value is less pronounced.  I Plastic viscosity (Pa.s) Figure 3.13: Effect of silica fume on yield strength and viscosity (Gjørv, 1992) For high performance concrete or shotcrete, the high cement content and the use of 10 % silica fume or even 15% for some shotcrete applications should produce a reduction in plastic viscosity (which is good for pumping), but also an increase in yield value (which is good for shootability), as opposed to a mix without silica fume (see Chapters 6 and 7). 3.5.3 Superplasticizers (SP) Banfihl (1980) has carried out an intensive study on the effect of superplasticizers by using two-point tests for workability. Because the W/C ratios used in his study were in the range of 0.65 to 0.73, which is far from the W/C usually used in HPC, one should be cautious in the application of these findings to HPC. He found that at low dosages up to 0.7 % by weight of cement, the addition of superplasticizer reduces the flow resistance (g) but produces an increase in the torque viscosity (h) (Figure 3. 14a). At higher concentrations, the addition of superplasticizer produces unstable mixes prone to segregation. He also found that the melamine-based SP produces more rapid hardening  68 (faster increase in g with time but little change in h) than the naphthalene-based ones (Figure 3.14b).  M = melamine N = naphthalene 0 = no SP  5 .,.... . . .  ftp  %M  I  1.5% N  >2.5  15%N  4  E  2  1  0  0. 0 SP concentration (% w/w)  (a)  120 180 60 Time (mm) (b)  Figure 3.14: Effect of superplasticizers (Banfill, 1980) Recently, some rheological results on HPC from Norway have been published (Wallevic and Gjørv, 1990; Osterburg, 1993; Smeplass, 1993). They were obtained on low W/C  (0.5 to 0.27) flowing concretes. Results from Gjørv (1992) and Osterburg (1993) show that the flow resistance is much more affected by aging than is the plastic viscosity. In Figure 3.15, it is clear that the yield increases with time as opposed to the viscosity, which remains almost constant.  3.6 RHEOLOGY OF SHOTCRETE As mentioned in Chapter 1, the wet-mix process includes two major steps: pumping and shooting. Since the rheological behavior is now accepted to be fundamental to the behavior of concrete, it might be possible to relate or define the requirements of these operations in terms of yield and plastic viscosity. Unfortunately, there is no study known to the author in which an attempt was made to relate the pumping and shooting operations  69 to the fundamental behavior of fresh concrete. The following discussion is thus theoretical. 4  10 mm 2.4 % (SPdosage)  Plastic viscosity (Pa.s) Figure 3.15: Effect of SP dosage and time on yield and viscosity (Gjørv, 1992) 3.6.1 Pumping vs. rheology So far, it has been mentioned that the behavior of concrete can be measured with a rheometer and the results expressed in terms of two constants h and g (Nm.s and Nm, respectively) or j.t and to (Pa.s and Pa). These parameters have meaning only if they can be used to specify certain limits within which the concrete will meet the specific job requirements for workability. At present, the workability is mostly specified in terms of slump, or occasionally in terms of other standard tests. In Chapter 2, the pumpability requirements were described in terms of slump and water emitted during a pressure bleed test. There is no existing “workability box” (see Section 3.3.2) to relate the pumping requirements in terms of yield and plastic viscosity. However, the most casual observation of pumped concrete is sufficient to realize that concrete moves into the pipeline as a solid plug as shown in Figure 3.16. In this figure, the central part, the plug, is surrounded by a lubricating layer within which most of the shearing action takes place.  70  Morinaga (1973) has been unsuccessful in correlating the radius of the plug with the yield value of the concrete. The main explanation for this is the presence of a lubricating layer which has different properties than the bulk of the concrete. In considering Bingham behavior for the bulk concrete, lubricated by another Bingham material, Tattersall and Banfill (1983) have carried out a theoretical treatment of the earlier observations of other researchers (Aleekseev, 1953; Ede, 1957; Gary, 1962; Weber, 1963). Their assumption of a lubricating layer is in conformity with the normal practice of establishing a lubricating layer by pumping a grout before the concrete is pumped. Their analysis is valid only for straight pipes with constant cross sections. When singularities such as reducers or elbows are present, the behavior is certainly different and is affected by the properties of the bulk concrete, not only by those of the lubricating layer. lubricating  pipe  _-I  plug  Figure 3.16: Concrete in pipeline: plug flow (Browne and Bamforth, 1977) An understanding of the influence of the mobility (flow properties) is probably not sufficient by itself to establish pumpability. The stability requirement, as mentioned in Chapter 2, should also be considered, as well as the characteristics of the lubricating layer. 3.6.2 Shooting vs. rheology Up to the present, there have been no studies on rheology of shotcrete reported in the literature. Beaupré et al. (1993) have proposed an explanation as to why shotcrete is shootable and why it stays in place after shooting. They stated:  71  The existence of a yield value seems to provide a good explanation as to why shotcrete is shootable. Intuitively, the higher the yield stress, the better the shootabilily (i.e. the greater the thickness that can be built up without sloughing). In fact, a material with no yield value (such as water) could not remain in place after shooting. Similarly, aflowing concrete with low yield value would not be suitable for shotcreting; it would simply slough off the receiving surface unless special agents (such as sodium silicate) were added at the nozzle. On the other hand, mixtures with high yield value (low workability) could be unsuitablefor shotcreting, because ofpumping and consolidation difficulties. According to this statement, there should be a relationship between the flow resistance and the build-up thickness described in Chapter 1. The flow resistance might then be an indicator of the shootability.  3.7 REFERENCES Aleekseev A.N., (1952), “On the Calculation of Resistance in Pipe of Concrete Pumps”, Building Research Station Library Communication, No. 450, 1952. Banfill P.F.G., (1990), “The Rheology of Cement Paste: Progress since 1973”, Proceedings of RILEM Colloquium on Properties of Fresh Concrete, University of Hannover, October 3-5, 1990, Chapman & Hall, London, pp. 3-9. Banfill P.F.G., (1980), “Workability of Flowing Concrete”, Magazine of Concrete Research, Vol. 32, No. 110, March, 1980, pp. 17-27. Beaupré D., Mindess S. and Morgan D.R., (1993), “Development of High Performance Shotcrete (theoretical considerations)”, Engineering Foundation Conference, Shotcrete for Underground Support VI, Niagara-on-the-Lake, Canada, May 2-6, 1993, pp. 1-8. Browne R.D. and Bamforth P.B., (1977), “Test to Establish Concrete Pumpability”, Journal of American Concrete Institute, May 1977, pp. 193-207. Ede A.N., (1957), “The Resistance of Concrete Pumped through Pipelines”, Magazine of Concrete Research, Vol. 9, No. 27, 1957, pp. 129-140. Gary J.E., (1962), “Laboratory Procedure for Comparing Pumpability of Concrete Mixtures”, Proceedings, ASTM Vol. 62, 1962, pp. 964-97 1.  72 Gjørv O.E., (1992), “High Strength Concrete”, Advances in Concrete Technology, Energy Mines and Resources, Otawa, Canada, MSL 92-6 (R), 1992, pp. 21-77. Haritori K. and Izumi K., (1982), “New Rheological Theory of Concentrated Suspension”, in Effect of Surface and Colloid Phenomena on Properties of Fresh Concrete, Proceedings, Symposium M, Material Research Society, November 1-4, 1982, pp. 14-28. Liewellyn D.H., (1990), “The Effect of Polypropylene Fibers on the Properties of Concrete and Mortar”, B. Eng. Project Sheffield City Polytechnic. 95 p. Morinaga S., (1973), “Pumpability of Concrete and Pumping Pressure in Pipeline”, in Fresh Concrete: Important Properties and Their Measurement, Proceedings of RILEM Seminar, March 22-24, Leeds, Vol.: 3, Leeds, The University, pp. 7.3-1 7.3-39. -  Osterburg T., (1993), “Measurement on Properties of High Performance Concrete in Fresh State”, Proceedings International RILEM Workshop on Special Concrete: Workability and Mixing, University of Paisley, March 2-3, 1993. Pallière A.M. and Briquet P., (1980), “Influence of Fluidifying Sinthetic Resin on the Rheology and Deformation of Cement Pastes Before and During Setting”, in Proceedings of 7th International Congress on Chemistry of Cements, Vol. Ill, Paris, Edition Septima, 1980, pp. VI-186 to VI-191.  Scullion T., (1975), “The Measurement of the Workability of Fresh Concrete”, Masters Thesis, University of Sheffield, 1975. Smeplass S., (1993), “Applicability of the Bingham Moodel to High Strength Concrete”, Proceedings International RILEM Workshop on Special Concrete: Workability and Mixing, University of Paisley, March 2-3, 1993. Tanigawa Y., Mon H. and Watanabe K., (1990), “Computer Simulation of Consistency and Rheology Tests of Fresh Concrete by Viscoplastic Finite Element Method”, Proceedings of RILEM Colloquium on Properties of Fresh Concrete, University of Hannover, October 3-5, 1990, Chapman & Hall, London, pp. 301-308. Tattersall G. H., (1982), “Measurement of Rheological Properties of Fresh Concrete and Possible Application to Production Control”, in Effect of Surface and Colloid Phenomena on Properties of Fresh Concrete, Proceedings, Symposium M, Material Research Society, November 1-4, 1982, pp. 79-97. Tattersall G. H., (1991), “Workability and Quality Control of Concrete”, Chapman & Hall, London, 1991, 262 p. Tattersall G. H. and Banfill P.F.G. (1983) “The Rheology of Fresh Concrete”, Pitman, London, 1983, 365 p. Tattersall G.H. and Bloomer S.J., (1979), “Further Development of the TwoPoint Test for Workability and Extension of its Range”, Magazine of Concrete Research, Vol. 31, No. 109, December, 1979, pp. 202-210.  73 Wallevic O.H. and GjØrv O.E., (1990), “Practical Description of the Rheology of Fresh Concrete”, Report BML9O.602, Division of Building Material, The Norwegian Institute of Technology, NTH, Trondheim, 1990, 13 pp. Weber R., (1963), “The Transportation of Concrete by Pipeline”, Cement and Concrete Association Translation No. 129, 1963.  74  CHAPTER -4RESEARCH PROGRAM  4.0 INTRODUCTION In this chapter, the goals of this study (Rheology of High Performance Shotcrete) and its primary objectives are first described. Then, the testing programs on both the fresh and hardened concretes and wet-mix shotcretes are outlined. The specific operations carried out to evaluate both the pumpability and the shootability are also described. Finally, the material and equipment built and used during this study are presented. 4.1 HIGH PERFORMANCE SHOTCRETE (HPS) What is high performance shotcrete? It is a specially designed cementitious material, applied pneumatically, with superior mechanical and/or physical fresh or hardened properties. The most cited properties are strength and durability, but it may also include workability or, for shotcrete, improved shootability. In this study, HPS can be any of these. The main goal of this study was to develop a high performance shotcrete (if possible, to improve strength, durability and shootability) and also to provide fundamental information on the pumping and shooting process. The required properties for the high performance shotcrete are good pumpability and shootability, and also improved mechanical and physical properties. To develop HPS, the use of low water-cement ratio mixture (W/C) and superplasticizers (SP) is the most logical alternative. Another option is to replace some of the SP with a high amount of entrained air to temporarily enhance the workability for pumping purposes. The study of the fundamentals of pumpability and shootability presented below is based on the measurement of rheological properties.  75  4.1.1 Low water-cement ratio (W/C) It is well known that a reduction in W/C increases the durability of concrete; this should also be true for shotcrete. The use of SP, compensates for the reduction in WIC by producing a large reduction in the yield value of fresh concrete. However, it appears that the yield value is the fundamental property which governs the shootability, by controlling the build-up thickness. The use of SP may also change the length of the dormant period, reducing the life span of the fresh concrete. For these two reasons, the production of HPS by reducing the W/C is not, at first, straight forward. In this study, many mixes with low W/C have been produced and shot inside a specially equipped laboratory. To avoid the contamination problems (such as by fibers in pervious mixes) usually encountered when doing shotcrete studies because of the small amount of shotcrete carried in a concrete truck mixer, the shotcrete was cast in the laboratory. However, some mixes were also ordered from a nearby concrete producer to validate the pumping and shooting methods used in this study. By using an iterative process, the mix compositions of subsequent batches were modified based on previous test results. It is thus not possible to present a chart showing a predetermined testing program. However, testing started with conventional shotcrete mixes, and the W/C was reduced gradually. Because different superplasticizers produce different effects with different cements, several superplasticizers have been studied in this project to test their compatibility. The goal was to find a combination which permitted the production of the best rheology at the lowest dosage, without either fast aging (loss of workability with time) or excessive set retardation. It was decided at the beginning of the project that most shotcrete mixes would contain silica fume, since its effects had been proven to be beneficial in both shooting technology,  and for the production of high performance concrete. Some shotcrete mixes also contained a fixed amount (around 50 kg/m )of steel fibers. 3 The same sand and coarse aggregate were used for the entire study, except for the mixes ordered from the commercial concrete producer.  76  4.1.2 High initial air content Concrete and shotcrete can be considered as mixtures of aggregates and cement paste. The paste is itself composed of cementitious material, water, admixtures and air. Depending on the aggregate specific surface area and grading, any specific mixture requires a certain amount of paste to coat all of the aggregate surfaces (and, if used, fiber surfaces) and to fill all voids between particles. Extra paste provides lubrication for workability. Depending on the rheological properties of the paste (yield stress and viscosity) the amount of extra paste needed may differ from one mix to another in order to achieve a certain concrete workability. To increase the workability of a given mix, it is possible either to increase the paste content or to reduce the paste yield stress and/or paste viscosity. The adverse effects of increasing the water content and cement content (to increase paste content) or of increasing the W/C (to reduce paste yield and viscosity) on hardened shotcrete (shrinkage, strength reduction, etc.) are well known. The usual way of reducing the yield of the paste and the W/C by using a SP has already been discussed in the previous section. The last option is then to increase the paste content by increasing the air content; it is shown in Chapter 3 that air-entraining agents will also reduce yield and paste viscosity. In Chapter 1, it was mentioned that shotcretes with initial air contents as high as 20 % have been pumped and shot with very little rebound. It was also mentioned that the loss of air for this mix during pumping and shooting was very high, about 15% (i.e. leaving about 5 % air content in the hardened shotcrete). This new method improves the pumpability and shootability by increasing the build-up thickness (by increasing the flow resistance because of air loss) and by reducing the rebound. This new way of looking at shotcrete technology was used in this study to make HPS. The improvement in paste volume and the reduction in yield and viscosity were used to overcome the expected reduction in workability usually associated with a reduction of W/C. It was also expected that the residual air content of the in-place shotcrete would help to improve the deicing salt resistance of shotcrete. The air void spacing factor was measured and related to the deicing salt scaling resistance. The strength reduction was expected not to be large if the in-place air content was of the order of 5 %.  77 It is expected that the information on the rheological properties will be useful in predicting the pumpability and the shootability of a mix. As previously published (Beaupré et aL, 1993), a strong relationship between the in-place flow resistance and the maximum build up thickness is expected. 4.1.3 Mix identification code Because of the large number of mixes cast during this study, a mix identification code has been used. This code, shown in Figure 4.1, is composed of numbers and letters, and consists of three parts: •  the first part gives the date (month and day) and the type of mixer used (see section 4.6.1),  •  the second part starts with the WIC (x 100) followed by cement type (e.g.: Li, see section 4.5.1) and by the letter SF or FA to indicate the presence of silica fume or fly ash.  •  the last part is used to indicate the presence of admixtures: SP (superplasticizers) A to E; AEA (air-entraining agents) N or M; WR (waterreducers) W used as well as the presence of fibers (F). first  second  third  (6-2A) 33L1SF-AMF  TTT date silica W/C fume mixer cement  si  fibers  AEA  Figure 4.1: Mix identification code This code was used to identify all mixes except those of the small testing program carried out to select the appropriate test parameters for the rheometer. These mixes possess their own identification code and are presented in Chapter 5.  78  4.2 TESTING PROGRAM 4.2.1 Fresh properties Different standard tests were carried out during this project. The slump (ASTM C-143), the air content and the unit weight (ASTM C-231) were measured before and after pumping to evaluate the effects of pumping on compaction. The air content was also measured after shooting, especially when the concept of a temporarily high initial air content was used, in order to check the compaction achieved during shooting. Some non-standard tests have also been used. The rheological properties were measured at different times to estimate the effect of aging on workability. They were also measured before and after the pumping and shooting. To determine those properties, a new rheometer was built; the rheometer is described in detail in Chapter 5. Other non-standard tests specifically related to pumpabiity and shootability were also performed (see Chapters 6 and 7). 4.2.2 Hardened properties Different standard tests were carried out on hardened concrete and shotcrete: compressive strength (ASTM C-39), absorption test (ASTM C-236), deicer salt scaling resistance (ASTM C-672), and air void spacing factor (ASTM C-457). Because this study was primarily directed at the rheology of high performance shotcrete, these tests were only performed on a limited number of mixes. However, compressive strengths were measured on most mixes.  4.3 PUMPABILITY STUDIES 4.3.1 Pumping pressure In order to pump the concrete, a laboratory concrete pump was built. The pump is equipped with a pressure gauge, so it was possible to determine the required pressure to pump a certain concrete mixture. The pump is fully described in Chapter 6.  79 4.3.2 Pressure bleed test During the project, it was decided to build a pressure bleed test apparatus. This equipment and the test procedure are fully described in Chapter 6.  4.4 SHOOTABILITY STUDIES The shooting operations were carried out near the civil engineering materials laboratory at University of British Columbia. For this purpose, a rebound chamber was built. Inside this chamber, several tests were performed to evaluate the shootabiity including the build up thickness test and rebound test. These tests are presented in Chapter 7.  4.5 MATERIALS 4.5.1 Cement Several cements were used in order to find a good cement-superplasticizer combination. The chemical composition and the physical properties of the cements used in this study are given in Appendix A. In the mix identification code, the letters L or T have been used to identify the cement brand and the numbers 1, 3 and 5 to indicate CSA cement Types 10, 30 and 50, respectively. 4.5.2 Silica fume and fly ash Only one condensed silica fume was used in this project. For one mix, a fly ash of type F was used. The chemical compositions and the physical properties of the silica fume and the fly ash used in this study are given in Appendix A. 4.5.3 Aggregates To maintain a constant supply of sand and coarse aggregates, it was decided to stockpile a large amount of sand (10 000 kg) and coarse aggregates (5000 kg) at the beginning of the project. The physical characteristics, including the grading of the sand and the 10 mm aggregate are given in Appendix A. The sand had an absorption of 1.5 % and corresponded to the ACI 506 gradation number 1 (see Chapter 1). The coarse aggregate had a maximum size of 10 mm and an absorption of 1.1%.  80 4.5.4 Fibers Only one type of steel fiber was used in this project. It had a length of 30 mm, a diameter of 0.5 mm, and deformed ends. This fiber is known commercially as Dramix 30/50 (produced by Bekaert Corporation, Belgium). Both the loose and collated forms of this fiber were used. 4.5.5 Superplasticizers Five different superplasticizers were used. They are referred to by the letters A to E. Results of chemical analysis and physical tests on these SP’s are given in Appendix A. 4.5.6 Other products Water-reducers and air-entraining agents were also used in this project. The air-entraining agents were both vinsol resins, but from different suppliers (M and N in the mix identification code). A water-reducer (W in the mix identification code) was used for a few mixes. The manufacturer product information is available in Appendix A.  4.6 EQUIPMENT Many pieces of equipment were used in this project. Some of them were built, others were bought or rented (air compressor). Equipment used to perform standard tests such as the slump test is not described nor mentioned in this section. The rheometer (Chapter 5), the concrete pump (chapter 6) and the pressure bleed test apparatus (chapter 6) were designed and built at UBC. 4.6.1 Concrete mixers Two concrete mixers were used in this project: a pan mixer and an inclined drum mixer. The pan mixer is a standard laboratory concrete mixer with a planetary motion, and was used for small trial batches (approx. 0.03 m ). Mixes done with this mixer have in the 3 first part of their ID the letters E, F, G or H. The inclined drum mixer was used for larger batches (up to 0.1 m ). This mixer was 3 mounted on a stage in order to allow it to discharge directly into the pump hopper. Mixes done with the drum mixer have the letter A, B or C in the first part of their mix identification code.  81 Mixes batched at the concrete plant were mixed with a pre-mix drum. They were transported in a truck mixer in 1 m 3 batches. Mixes batched at the concrete plant have the letter T in the first part of their mix identification code. 4.6.2 Shooting equipment Five different nozzles were used in this study. However, most of the mixes were shot with a 50 mm Putzmeister nozzle (nozzle b), which geometry similar to that shown in Figure 1.4. The rebound chamber is a cubical box open on one side (dimensions 2.3 m x 2.3 mx2.3m).  4.7 REFERENCES Beaupré D., Mindess S. and Morgan D.R. (1993), “Development of High Performance Shotcrete (theoretical considerations)”, Engineering Foundation Conference, Shotcrete for Underground Support VI, Niagara-on-the-Lake, Canada, May 2-6, 1993, pp. 1-8.  82  CHAPTER -5DEVELOPMENT OF THE UBC RHEOMETER  5.0 INTRODUCTION In this chapter, the development and use of a new rheometer, referred to hereafter as the ‘UBC rheometer” will be described. First, an overview of the historical development of other types of rheometers, starting with the first Tattersall MKI is given; three categories of rheometers, based on the torque measurement technique, are described. Next, the considerations involved in the design of the UBC rheometer are presented. A physical description of the new apparatus is given, and modifications made to the torque measuring device in the early stages of the rheometer development are explained. The three computer programs which were developed to operate the rheometer are also described. Results from a small testing program carried out to evaluate the performance of the rheometer are presented, and the operations of the rheometer are described. Finally, the results of other tests carried out to evaluate the information obtained from this apparatus are presented. Suggested modifications to improve the apparatus are also indicated.  5.1 THE CONCRETE RHEOMETER: HISTORICAL REVIEW Much of the information presented in this section can be found in Tattersall and Banfill (1983) or in Tattersall (1991). Information from these two references is not further specifically identified. The rheology of cement pastes and mortars has been studied with various coaxial cylinder viscometers for many decades. However, the first attempts by Tattersall to use a similar type of apparatus on concrete were not successful. Indeed, Bloomer (1979) (as quoted by Tattersall (1990)) has stated that: No coaxial cylinder viscometer yet used in concrete research has satisfied the general requirements, particularly as regards the size ofgap between the two cylinders.  83 Only those types of apparatus which can be used with concrete are discussed here; viscometers for cement paste and mortar are not included. Many researchers have used mixer type rheometers to evaluate workability or to determine rheological parameters. These apparatus should be considered as “first generation”; they are all based on the measurement of the electric mixing power requirements. However, the lack of precision in determining the applied torque by electric measurements led to the development of a second generation of concrete rheometers. This second generation of rheometers uses a hydraulic transmission in order to eliminate the imprecision in evaluating the torque requirement with electhc power. Two separate apparatus, the MKII and the MKIII were developed by Tattersall. Modifications to these apparatus have been made by many researchers, as will be discussed later. These first and second generation rheometers were hand operated. The third generation of rheometers uses strain gauge technology to measure the applied torque. Most of them use plotters or computers to record the torque measurement and speed; some are fully automatic. 5.1.1 First generation rheometers Tattersall first used a Hobart food mixer to plot flow curves based on the power requirements to drive an impeller in fresh concrete. An important result was obtained with this apparatus (now known as the MKI): Bingham behavior was observed in concrete. These results have already been presented in Chapter 3. As stated above, the first generation of rheometers used the electric power requirement to evaluate the torque of an impeller turning in fresh concrete: the power used to drive the impeller in an empty bowl was subtracted from the reading obtained when the impeller was driven in the concrete in order to determine the power requirement. Power measurements were carried out using a wattmeter. This type of torque measurement is not precise. Problems such as the regularity of the input voltage, a long warm-up period, the necessity of frequent calibrations, and the small differences in power requirement between an empty bowl and a full bowl with respect to the absolute value of the reading, rendered this type of apparatus unsuitable for serious rheology measurements. Thus, a second generation of rheometers was developed.  84  5.1.2 Second generation rheometers The lack of precision in measuring the torque was corrected by using a hydraulic transmission. The Tattersall MKJI and MKJII apparatus, and modified versions of these made by other researchers made up the second generation. The MKII was developed for medium to high workability concretes and the MKIII was developed for medium to low workability concretes. The original MKII used the coaxial impeller shown schematically in Figure 5.1. This apparatus was hand operated at five different speed levels. The torque was measured by a pressure gauge reading. The results obtained with this rheometer were much better than those obtained with the first generation rheometers.  Figure 5.1: Schematic representation of the MKII apparatus (Tattersall, 1991) The MKII was slightly modified to become the MKIII apparatus, which was suitable for handling medium to low workability concretes. While keeping the same general set-up, the impeller was changed and a planetary motion was introduced by the addition of two  85 gears. Planetary motion was chosen in order to insure that the new impeller would not move only through the same region of the concrete sample. For this, a gear ratio of 2.25 was chosen (not a whole number). A new gear box was used to obtain the correct impeller speed, and the diameter of the sampling bucket was enlarged to accommodate the new impeller motion (from 254 mm to 356 mm). Figure 5.2 shows the new impeller with the gears which give the planetary motion. Wimpenny and Ellis (1987) have used a tachometer, a pressure transducer and a chart recorder with the MKII to eliminate the operator influence when reading the pressure gauge. Their analysis showed that, by recording the signals from a pressure transducer, they were able to reduce the time required at each speed to obtain a reliable reading. In this way, the risks of segregation and bleeding were also reduced by the shorter testing time. As stated by Tattersall (1990), the improvement in the precision of the readings, allows to only one apparatus to cover a wide range of workabilities: the MKIII can also be used for high workability.  I  Tooth gear 16DP 45 fixed to bearing  Tooth gear 16DP 20 fixed to impeller shaft  housing Main shaft H impeller shaft (12 mm Lleter)  mm End shaft — (10 mm dia.) I—  —I  130 mm  Figure 5.2: Schematic representation of the impeller of the MKIII (Tattersall, 1991) A similar modification of the MKII apparatus was used by Wallevik and Gjørv (1990a) to remove the operator influence in estimating the pressure. They made these modifications to reduce the testing time, in order to minimize the chance of segregation. They concluded, by using a segregation factor, that a decrease in the testing time reduces segregation. This  86 segregation factor is based on the measurement of the aggregate contents of the upper and lower part of the rheometer sampling bowl. After segregation caused by a long testing procedure, the concrete from the upper part of the bowl shows a reduced aggregate content while the concrete from the bottom part of the bowl possesses a higher aggregate content. Wallevik and Gjørv (1990a) were able to obtain plots similar to that shown in Figure 5.3 by using a chart recorder. They were able to record the flow curves which give a better estimation of the flow resistance, after analysis, than does the operating procedure originally developed by Tattersall.  1.0  I Torque (Nm)  8  Figure 5.3: Example of data from Wallevik and GjØrv (1990a) 5.1.3 Third generation rheometers The third generation of rheometers uses modern electronic equipment to measure the applied torque and also to measure and record the speed. With the development of computers and data acquisition facilities, fully automatic rheometers are under development; some are now commercially available. Some rheometers still use the original design of the MKJI or the MKIII. Others have developed modern versions of coaxial-cylinder viscometers (see Chapter 3) or plane/plane rheometers (the concrete is sheared between two rotating coaxial plates in relative motion). Cabrera and Hopkins (1984) used strain gauges and a slip ring to measure and record the torque on a MKII frame. They also used a chart recorder to obtain the torque vs. speed plots. Figure 5.4 presents a schematic representation of the set-up for the slip ring and  87  shows a typical trace from the chart recorder. It is obvious that the data in Figure 5.4 are more scattered than the plot in Figure 5.3.  80 ‘—  e1  ?  40  ;j  30 20 —E I  16  I  I  I  I  4 12 8 Torque (Nm)  I  0  Figure 5.4: Slip ring set-up and trace from the recorder (Cabrera and Hopkins, 1984) Wallevik and Gjørv (1990a) have criticized these results, and concluded that electric noise, mechanical vibrations and poor contact between the brushes and the slip ring explain the observed spread in the data. The same authors have described a coaxial-cylinder viscometer, now commercially available as the BML-Viscometer (Wallevik and Gjørv, 1990b). This apparatus is driven by a computer. A fixed load cell is used to measure the torque. Because there is no planetary motion, the torque can be measured on the fixed cylinder, and the speed on the rotating one. They presented a very good correlation between the results obtained from the MKII and those obtained from their BML Viscometer. However, coaxial-cylinders viscometers cannot be used with medium-low to low workability concretes (slump limit about 90 mm) because the impeller creates a hole in the middle of the sampling bowl. DeLarrard has recently described a plane/plane rheometer (DeLarrard et al., 1993). This rheometer is still under development and should be available soon. It was designed for use with high to medium workability concretes and can be used to study the effect of vibration on rheological behavior.  88  5.2 UBC RHEOMETER 5.2.1 Design considerations In the research project described in Chapter 4, one of the objectives was to measure the rheological properties of concrete before and after pumping, and also after shooting (if possible). The in-place shotcrete can be considered as a low to very low workability material. Therefore, a modified version of the MKIII apparatus was chosen for this study. The dimensions of the impeller, the sampling bowl and the gears used to provide the planetary motion are those originally chosen and used by Tattersall (Figure 5.2). This makes it possible to use the calibration constants, K and G (see Chapter 3) to obtain the rheological properties in fundamental units if desired, as calculated by Tattersall for his IVIKIII apparatus. In the experimental procedure used here, many operations had to be carried out in a short period of time with limited human resources: concrete casting, slump test, air test, actual shooting, rebound test, build-up test, washout test, etc. Therefore, the apparatus had to be easy to use and fully automatic, so that an operator was needed only to do the concrete sampling and start the test. The option of using a computer to control the test execution was thus chosen. To increase the accuracy in determining the impeller speed, a commercially available magnetic tachometer was located between the motor and the reducer, where the speed is at a maximum, since it is difficult to measure low angular speed with accuracy. Because of the planetary motion, it was not possible to use the set-up of a fixed load cell and a turning basket, as with the BML-Viscometer. The slip ring/strain gauges option was thus chosen. To minimize the electrical noise and interference in the slip ring, the signal from the strain gauges was amplified before going through the slip ring. 5.2.2 Physical description The major features of the UBC Rheometer are shown in Figure 5.5: computer, motor, tachometer, reducer, slip ring, torque meter, impeller and sampling bowl.  89 tachometer  DC motor 1/2 HP  IH  I  control panel  reducer POWER  A slip ring  F AUTO  MANUAL  transfer gear SPEED CONTROL  amplifier strain gauges  computer IBM AT 286 with PCL-812PG card  S  // “crete level impeller lOOmmil 130 mn,j bowl: 0 :356 mm, h: 250 mm  Figure 5.5: General view of UBC rheometer The computer is used to control the test procedure. It contains an acquisition board (PCLAB 8 12PG) which drives the motor and takes readings from the torque and speed measurement devices. The motor (1/2 HP DC), the reduction gear box (60 to 1 ratio) and the planetary motion gears provide the required impeller speed range, from 0 to 1.2 revolutions per second. The torque measuring device, which is the critical component, has been designed and built as shown in Figure 5.6. This device consists principally of a small beam working in flexure and instrumented with four strain gauges. When the torque is applied, two gauges are compressed and the two others are extended, for maximum sensivity.  90  shaft from reducer  side view  plan view  Figure 5.6: Torque measuring device and slip ring of UBC rheometer The original cross sectional dimensions of the beam were 4 mm x 20 mm, in order to carry the maximum required torque with sufficient deformation (for accuracy). This maximum torque was estimated to be 20 Nm according to the results presented by Tattersall and Banfill (1983, p. 21 1). The thickness was subsequently increased to 7 mm, because the shotcrete workabiities were much lower than expected (torque requirement of about 30 Nm on the main shaft = 13.3 Nm on the impeller shaft). The signal from the strain gauge bridge is amplified 470 times before passing through the slip ring (a device used to carry the signal out from the turning shaft). In this way, the electric noise problem observed by Cabrera and Hopkins (1984) is largely avoided. 5.2.3 UBC Rheometer user documentation The computer programs used to run the UBC rheometer were developed in collaboration with a group of undergraduate students who were working on a civil engineering materials project: Kevin Campbell, Stefano Donadonibus, Jeff Friesen, Einar Halbig and Kevin  91 Wong. They also prepared a user manual for the rheometer. This manual is given in Appendix B. They also assisted in completing the computer programs, calibrating the torque measuring device, and testing the apparatus with some concrete mixes. The user documentation explains in detail how to use the rheometer. It describes the hardware components, the use of parameter files, the program operation, the calibration procedure (before each test session), how to input test data and how to recover the output files. Finally, the manual explains how to conduct an incremental test (described below) which is used to measure the rheological properties.  5.3 COMPUTER PROGRAMS Three programs were developed: Calibrate; Incremental test; and Duration test.. 5.3.1 Program: Calibrate This program constantly takes readings from the torque measuring device and displays the results on the computer screen (speed set to zero). It is used primarily to adjust the offset of the strain gauge bridge, which should read zero when no load is applied. This operation is carried out only at the beginning of a test session, and is not generally required after each test. This procedure is described in detail in Appendix B. This program is also used to calibrate the torque measuring device as described in Section 5.4. 5.3.2 Program: Incremental test This program allows one to measure the rheological properties of a concrete mix. The Incremental test is explained in detail in the user documentation under the heading “run test”. Different test parameters, such as the maximum speed setting, the speed increment, the speed decrement, the time for the motor to stabilize at a given speed, the sampling interval for the speed and the torque readings and finally the number of readings at each speed can be changed as desired. Default values or parameter files can also be used. Figure 5.7 describes the way in which a test is run. After taking a number (8 for this example) of readings of speed and torque, the program increases the voltage of the motor  92  drive by an increment (here 300 in internal units). After a stabilization time (30 internal units, which corresponds to 1.7 sec), the computer executes another series of readings (speed and torque). Each reading is separated by a sampling interval (here 5 internal units or 0.3 sec). When the maximum speed chosen is reached, the speed is reduced step by step (here a decrement of 600) until zero speed is reached and the fmal value of torque is measured. example of test (Max, incr, decr, stab, hit, N) (1000, 300, 600, 30, 5, 8)  N (8) reading of speed and torque at sampling interval of(5 = 0.3 seq) .  900  .—  speed decrement (600)  .—  end of test  300  1 Time (seconds)  Figure 5.7: Schematic representation of a rheometer test To prevent damage to the rheometer, the test is automatically halted if a particular maximum torque is reached. A data file is created for each run, containing the motor voltage input, the impeller speed and the torque as well as the test parameters and a brief description of the mix. 5.3.3 Program: Duration test This program is used to measure the torque required to drive the impeller at a desired speed. The torque can be averaged over a number of sampling intervals. Duration test is not explained in the user documentation because it was written after the production of the manual; details are given in Section 5.6.  93  5.4 CALIBRATION OF TORQUE MEASURING DEVICE The torque calibration procedure is different from the zeroing procedure described in the User Manual though both procedures use the same program: Calibrate. The torque calibration is carried out only once to establish the relationship between the applied torque on the main shaft with the voltage output from the slip ring. Two calibrations were carried out: one for the 4 mm thick beam which was originally used, and one for the 7 mm thick beam. The smaller beam was used during the small testing program presented in Section 5.5. The thicker beam was used for the rest of the research project, to test all of the mixes described in Appendix E. 5.4.1 Torque calibration procedure The procedure requires the use of two pulley wheels, and numerous weights of different mass. The first pulley is fixed to the main shaft (as shown in Figure 5.8), and the second is used to convert a horizontal force to a vertical force. 4 strain gauges  main shaft pulley #2 weight R=95.9mm  Figure 5.8: Set-up used to calibrate the torque measuring device  The steps needed to calibrate the rheometer are: •  Remove the impeller arm from the main shaft and attach pulley #1 firmly to the main shaft.  94 •  Select the calibrate option on the main menu (See UBC rheometer user documentation in Appendix B).  •  Use a screwdriver to get “0” reading from the torque measuring device (section: Calibration procedure in user manual).  •  Set pulley # 2 on a table top in such a fashion that the weights may be loaded onto the cable and so induce a torque on the rheometer.  •  Apply the weights to the cable in different load combinations. Record the total mass and the torque reading each time.  •  Analyze results as described in next section.  5.4.2 Torque calibration results Figure 5.9 shows the plot of applied torque vs. the readings from the torque meter (in internal units) for the 4 mm thick beam. The linearity stops at around 26 Nm. This was due to the near yielding of the thin beam which was designed for 20 Nm. Table 5.1 presents the results of the second calibration, carried out with the 7 mm thick beam. The first and second columns are the weight combination and the corresponding mass in kilograms, respectively. The third column is the torque calculated using the torque arm of pulley #1: 95.9 mm. The last column is the reading from the torque measuring device. Results from Table 5.1 are plotted in Figure 5.10. The correlation coefficient is 0.99988, which indicates a very good linearity between the applied torque and the reading from the torque measuring device. The slopes of Figures 5.9 and 5.10 were used in the programs Incremental test and duration test to transform the readings to actual torque values. These values were also divided by 2.25 (gear ratio for planetary motion) to obtain the net impeller torque.  95 1750  1500 1250  1000 750 500  250 0  0  5  20 10 15 Torque applied on main shaft (Nm)  25  Figure 5.9: Calibration of 4 mm beam Table 5.1: Calibration data for the 7 mm beam  Weight combination  Mass (kg)  1 2 3 4 1+2 1+3 1+2+3 1+2÷3+4 3÷5 3+4+5 2+3+4+5 1+2+3+4+5  Torque (Nm)  Readings (internal units)  7.4417  7  2.3316 7.7427  2 7  132 42 137  5.7976 9.7733 15.1844 17.5160 23.3136  5 9 14 16 22  105 172 268 310 414  18.9309  18  339  24.7285 27.0601 34.5018  23 25 32  441 478 609  30  96 700 600 500 .  400 300 200 100 0 0  5  10  15  20  25  30  35  Torque applied on main shaft (Nm) Figure 5.10: Calibration of 7 mm beam  5.5 RHEOMETER TESTING PROGRAM Eleven concrete mixes were cast over four days to verify the performance of the apparatus and to determine the best test parameters (maximum speed, number of readings etc.). The emphasis was on the determination of the flow resistance. This first step was intended to verify whether the extrapolations (at zero speed) made by Tattersall were a valid means of determining the flow resistance. The mix compositions and the results of some physical tests are presented first. Results from the rheometer tests are then presented and discussed. 5.5.1 Mix composition The mix selection included ordinary plain shotcrete mixes and silica fume shotcrete mixes with different air contents. Effects of cement type and the use of small dosages of superplasticizer were also determined. The compositions of the various mixes are presented in Table 5.2. The mix identification, which uses a different code than that used in the main study, gives the cement type (Type 10 (Tb), Type 50 (T50) and Type 10 with replacement of 10% silica fume (SF)). This is followed by the W/C and a letter which indicates the different dosage of airentraining agents (ex.: mix T10.43a compared to mix T10.43b).  97  Table 5.2: Mix comnosition  Mix  T10.43a T10.43b T10.43c SF.43a SF.43b T10.38 T50.38 SF.38 T10.40 T10.35 T10.48  Cement (lcg/m ) 3  Silica fume ) 3 (kg/rn  Water (kg/rn ) 3  Aggregates )* 3 (kg/m  WR (1/ms)  ABA (IJm)  SP (I/ms)  412 390 380 429  0 0 0 48 40 0 0 46 0 0 0  176 167 162 184 154 177 174 170 140 158 189  1772 1679 1632 1590 1330 1723 1731 1703 1487** 1671 1702  0.91 0.86 0.83 1.15 0.96 0.00 0.00 0.00 1.25 1.30 0.86  0.00 0.20 0.58 0.80  0.00 0.00 0.00 0.00 0.00 1.35 1.35 1.98 0.00 4.68 0.00  359 463 464 411 351 448 396  4.50 0.00 0.00 0.00 2.30 0.00 0.20  50% sand and 50% 10 mm max. size stone 60% sand and 40% 10 mm max. size stone WR = water reducer, ABA = air-entraining agent, SP = superplasticizer *  **  Mixes T10.35, T50.38, T10.38 and SF.38 were cast on the first day. Three rheometer tests were carried out on each mix. These tests employed different values for the speed increment and decrement. Various rheological tests were carried out on the other mixes on the following days. Mix T10.40 was shot and tested similarly on the last day.  5.5.2 Physical test results  The results of some standard tests (slump, air content, unit weight, and 7d and some 28d compressive strengths measured on three 100 x 200 mm cylinders) are given in Table 5.3.  5.5.3 Rheometer test results All available rheometer test results (for the above mixes) are given in Appendix C. Most of these tests were carried out with 150 mm of concrete in the rheometer bowl (normal position for this test series). Tests carried out with 200 mm of concrete in the bowl will be referred to as “deep” tests. Figure 5.11 shows the position of the impeller with respect to the concrete level for the normal (a) and the “deep” (b) positions.  98  Table 5.3: Physical test results  Mix identification  Tl0.43a Tl0.43b T10.43c  SF.43a SF.43b T10.38 T50.38 SF.38 T10.40 T10.40s* T10.35 T10.48  Slump  Air content  Unit weight  (mm)  (%)  95 240 250  3.5 8.0 9.0  60  5.0  195 85 230 80 50  15.0 3.0 3.5 5.0 15.0 3.5 3.0 4.5  -  280 230  ) 3 (kg/rn  Compressive strength (7d) (MPa)  Compressive strength (28d) (MPa)  2364 2256 2202 2281  49.3 28.1 29.8 39.7  67.3 41.1 39.7  2023  18.0 48.4  2395 2392 2364 2114 2378 2395 2307  46.0 47.2 19.5 30.7 -  34.5  -  -  -  -  67.3 -  -  -  45.2  *after being shot  (a) normal position  (b) “deep” position  Figure 5.11: Normal (a) and “deep” (b) position of the impeller Because the first concrete tested was very viscous, it was not possible to run the test in the deep position (test halted: maximum torque reached during the test in “deep” position). The normal position was then adopted for most tests in this small testing program. Even in this position, the 20 Nm initial torque limit on the main shaft was reached (20/2.25 = 8.8 Nm on the impeller shaft). The 4 mm beam was used for the rest of this small test  99 program (tests described in this chapter), but was then replaced with the 7 mm thick beam. The deep position was used for all test results presented in Appendix E. The most important results obtained on the first shotcrete mixes (none of these mixes were actually pumped or shot except for mix T1O.40 in Figure 5.21) are presented in Figures 5.12 to 5.21. On these figures, each dot represents the average of all of the torque measurements made at a fixed speed (except in Figure 5.14, where each dot represents one measurement of torque at one speed). For each test, the test parameters described in the user documentation are given: maximum speed, speed increment, speed decrement, stabilization time, sampling interval and number of readings (ex.: 3000, 300, 300, 30, 5, 10). All numbers are in internal units. See also Figure 5.7 for details. Figure 5.12 shows the results of a plain shotcrete mix. The torque measurements obtained when the speed is increasing (arrow pointing up) are different from those obtained when the speed is decreasing. This behavior is similar to that obtained by Wallevik and Gjørv (1990) and presented in Figure 5.3. This result suggests some structural breakdown or thixotropic behavior, as explained in Chapter 3. The straight solid line in Figure 5.12 is representative of the Tattersall two-point experimental method analysis (the zero speed measurement has been disregarded). Using the solid line extrapolation, the flow resistance (g) of this concrete would be 3.5 Nm and its torque viscosity (h) would be 1.9 Nm.s. But, by considering the zero speed measurement and using the dotted line, these values would be 2.6 Nm fOr g and 2.8 Nm.s for h. Figure 5.13 presents the results of a “slow test (about 5.5 mm.) carried Out by using smaller speed increments and decrements as well as a greater number of readings at each speed on the same mix as in Figure 5.12, which is considered a “fast” test (about 1.1 mm.). From Figure 5.13, h is 1.6 Nm and g is about 2.6 Nm.s. These results (and those available in Appendix C) show that the use of small speed increments and decrements gives the best results with respect to linearity. However, this increases the testing time and, as mentioned in Chapter 3, the risk of segregation. It is thus important to find optimum values for the test parameters.  0  C  CD  o  CD  C  ao  -J  —  • .1  —  • .-i  iji  •  ;:11:. ,jI•  —  U  •  ‘-  —. i• 4 I. •ii ..,...I .—,——J  — -Il  iIl I I.’ —— UI— •J U  •:‘  iL,;..  i !—ii.i  —  Impeller speed (revls)  cf  C  C  00  —  —  Impeller speed (revls) •L  C  C  U’  —  Impeller speed (rev/s)  C  C  0  -.  —I  I—  if  I 00  Impeller speed (rev/s) —  0  I  I  C  .  —  —  —I.  —.*  %%  —  . —  00 —  ——————  ——————  ——————  ——————  ——  —  L’  Impeller speed (revls)  n  p p  p  —  rM -  —  I  r1  —1  C.’  I:  o  ej  — .  .  9  —  .  .  —  .  .  .  .  —  .  h  .  —  C  C —  00  —————  —————  —————  — — — — —  —  .  .  —  C  Impeller speed (revls)  -J  ©  ‘e  t,.  ._  —  —  102 1.2  4: I  a  I  • test (2500,300,50,10,1,19)  A’_______  A test (2500,50,50,5,1,20)  0  5  7  6  8  Torque (Nm) Figure 5.18: Effect of air content (Mixes SF.43a and b) 1.2 test (3000,100,100,50,5,5) V.—  T .rlt II I  —  .  ,  0  - type 10 jOtypelO • type 50  F.S.  +  : ([ 71 /  0.4 a E 0.2  —  -—  J/1,iI  1  0  6  2  4 3 Torque (Nm) Figure 5.19: Effect of cement type (WIC = 0.38)  7  8  1.2  ‘‘‘‘42  • test (3000,100,100,50,5,5) test (3000,200,200,70,5,5) A test (2500,500,250,10,3,5)  ‘—Si  ..  I:: I 0.4 i0.  • 0.43W.R. - 0.38 W.R. A  LLI’  4  —  ri-  44 %  % ZS/7I4  1  44 -  —  4 3 5 Torque (Nm) Figure 5.20: Effect of W/C and the use of superplasticizer 0  2  I  6  .  —  7  8  103 In order to visualize the spread of the data, all of the data from the descending part of the test shown in Figure 5.13 are plotted in Figure 5.14. These results are similar to those obtained by Cabrera and Hopkins (1984) reproduced in Figure 5.4. An interesting point is that the degree of spread is reduced at lower speeds, which is good for the determination of the flow resistance. Figures 5.15 and 5.16 show the results of tests on the same plain shotcrete mix but cast with some air-entraining agent. On both curves, the extrapolation made without taking measurements at speeds lower than 0.2 rev/s overestimates the g value (flow resistance) and consequently, underestimates the h value (torque viscosity). In Figure 5.17, the effect of increasing the air content on the flow resistance is clearly shown. Tests with smaller speed increments and decrements were used (compared to Figure 5.15 and 5.16) for mixes T10.43 b and c. Again, the “slow” tests (smaller speed increments and decrements) give more linear behavior. Figure 5.18 also shows the effect of air content on flow resistance for silica fume shotcrete mixes. In Figures 5.17 and 5.18, the main effect of air-entrainment is a large reduction of the flow resistance with little reduction of the torque viscosity. Figure 5.19 shows the effect of cement type and silica fume replacement. The use of Type 50 cement increases the workability by reducing the flow resistance. As expected, the replacement of cement by silica fume (10 % in this case) produces an increase in the flow resistance, and a small reduction in torque viscosity if the W/C is reduced (see Figure 3.13). Figure 5.20 shows the effect of W/C and the effect of using a superplasticizer. The dotted line represents the expected results for a mix with a W/C of 0.35 without a superplasticizer. The use of a superplasticizer reduces the flow resistance considerably and increases the torque viscosity accordingly. Figure 5.21 shows the effect of air loss (compaction) which occurs during shooting; this is primarily an increase in flow resistance without a significant change in viscosity when the air content drops from 15.0% to 3.5%. This reduction in air content is accompanied by an improvement in 7-days compressive strength, from 19.5 MPa to 30.7 MPa. The effect of shooting will be discussed further in Chapter 7. The results shown in Figure 5.21 indicate that rheological properties can be measured on shotcrete by shooting directly into the rheometer sampling bowl.  104 1.2 test (2400,200,50,20,1,50) 0.8 0.6 0.4  L. —  —  0.2  E  1  0  2  3 4 5 Torque (Nm)  6  7  8  Figure 5.21: Effect of shooting on g and h (mixes T10.40 and T10.40s) Values of g and h obtained from Figures 5.12 to 5.21 have been plotted in Figure 5.22. These results are similar to those of Figure 3.13. This representation is an efficient way of illustrating the effects of many variables on the rheological properties g and h. However, it must be kept in mind that, with respect to concrete mix composition, it is difficult to vary only one parameter (e.g.: a reduction in water content affects the proportion of other components as well as the W/C)  9  o reference (T10.43a) o 0.43 + air • 0.43 + SF • 0.43 + SF + air  +SP  0.40 + air 0.40 + air + shot 0.38 ‘ 0.38 + SF 0.38 (type 50) 0.35? (not tested) • 0.35 + SP  5 -  4  water?  A.  •  •  13 z  K  +sF  -water/  sho.Ing  type 50 +aW  0  1 0  •  0  I  I  1  2  I  -  I  3 45 h (Nm.s)  Figure 5.22: Effects of mix composition and shooting on g and h  105  5.5.4 Test parameters From the results presented in section 5.5.3, the test parameters chosen for the rest of this study were (3000, 300, 100, 20, 1, 50) for a test duration of 2.8 minutes. During each test, a maximum impeller speed of about 1.08 rev/s (3000 speed internal units) was reached in 10 speed increments. The speed was then gradually reduced to zero in 30 decrements. At each speed setting, 50 measurements of speed and torque at an interval of approximately 0.06 sec (1 time internal unit) were executed after an initial waiting period of about 1.2 seconds (20 time internal units). These test parameters were chosen as a compromise between precision and duration of the test. For the determination of the flow resistance, the zero value have been neglected except when specified. When the real intercept has been used, it is noted by g’ instead of g. As usual, only the descending branch of the curve has been used.  5.6 OTHER TEST RESULTS Additional tests were carried out during the rest of the project. A new impeller was built to check the theoretical results obtained from the impeller motion analysis. Finally, some modifications to the rheometer are proposed. 5.6.1 Theoretical analysis of impeller motion This analysis was carried out in order to explain some intriguing results obtained at low impeller speeds, as well as the spread in the results observed in Figures 5.5 and 5.14. Tn Figure 5.23, three possible results are presented. Case (a) is a linear speed-torque relationship, representative of a Bingham behavior. Cases (b) and (c) are non-linear at low impeller speeds. One explanation for the spread of the data and the non-linearity at low impeller speeds is the possible influence of the impeller position on the torque requirement. Figure 5.24 shows two positions of the impeller during the planetary motion. Case (a) is referred to as the I position, and case (b) is referred to as the T position. If the torque requirement is different depending on the position, spread as observed in Figures 5.5 and 5.14 should be expected. Also, because the average torque is measured  106 with very little displacement at low speeds, behavior as in cases (b) or (c) of Figure 5.22 should be expected depending on the final position of the impeller.  I  Torque (Nm)  Figure 5.23: Schematic representation of observed deviation from Bingham behavior  Top view 0—  ]  —  Side view main shaft  impeller shaft  fingers (a): I position  (b): T position  Figure 5.24: Position I and position T of the impeller To simplify the analysis, the geometry of the hypothetical impeller shown in Figure 5.25a was used. A gear ratio of 2 was chosen: the impeller angular speed is twice the angular speed of the main shaft. The relative tangential speeds are given for the I and T positions in Figure 5.25b and 5.25c, respectively.  107 R -I  I  Gear ratio: (2 1)  1,1 111111111111N111! III iriI_li_li  2or  .. -—  r shaft  2or 2wr  2o  Main shaft  r 2wr  Concrete level  ‘  R=2r  U  2or  .4  r  1  (a) hypotetical impeller: side view  (b): I position  (c): T position  Figure 5.25: Hypothetical impeller and relative tangential speed for I and T positions Two calculation examples are presented below, which were done for a fluid behavior similar to that shown in Figure 5.26 (fluid C). Assume an angular velocity of the main shaft o=O.5 rad/s, and r 5 cm. A radius of 5 for this geometry gives a similar rate of shear to the UBC rheometer with a radius of 6.5 cm: position I: for o=0.5 rad/s, the tangential speed of the upper finger is 4or = 10 cm/s (Figure 5.25b). The force (F) required to move the finger at that speed in fluid (C) is F 6 N according to Figure 5.26. The speed of the lower finger is zero. The torque is then: 3Fr = 3 x 6 x 5 = 90 Ncm or 0.9 Nm. position T: for w=0.5 rad/s, the tangential speed of both fingers is 2J2Q)r 7.07 cm/s (Figure 5.24c). The force (F) required to move one finger at that speed in fluid (C) is F = 5.41 N (Figure 5.26). The torque is then: 2 x (F x 2r} = 2 x 5.41 x 2.07 x 5 = 1120 Ncm or 1.12 Nm. 1 (3/2)’  108 20  I  I  Fluid(B)  I  / / 20  4 Force (N)  4 Force (N)  Figure 5.26: Four hypothetical fluid behaviors In this example, the torque requirements are different for different impeller positions. If a chart recorder were used to trace the torque requirement with respect to time, the torque requirement of a test carried out with the parameters of this example would show a fluctuation from 0.9 Nm in the I position to 1.12 Nm in the T position, as shown in Figure 5.27.  I C  T position  :z: 0 1,12  (1/co = 2s)  0  I position  2  6 Time (s)  Figure 5.27: Expected torque requirement with respect to time  109 The torque requirements of the hypothetical impeller have been calculated at three different speeds in both positions for the four hypothetical fluids shown in Figure 5.26. These calculations were also made for the UBC Rheometer geometry (gear ratio of 2.25 and R= 0.77 r with r= 6.5 cm) but considering only the two fingers (without the transverse bar). Both impellers will reach almost the same maximum finger tangential speed (20 and 19.6 cm/s) at maximum angular velocity (in this case 1 radls on the main shaft). Results of these calculations are plotted in Figure 5.28 for both impellers and for the four hypothetical fluids of Figures 5.26. The spread of the results is clearly indicated. Because the model impeller motion diameter is 300 mm, while the UBC impeller motion diameter is only 230 nmi, the torque requirements are higher for the model impeller (Figure 5.28). From these results, it is clear that the fluid behavior influences the amount of spread (because of the planetary motion). The impeller geometry (gear ratio and RIr) is also an important factor. The amount of spread is not dependent of the angular velocity. This analysis shows that some spread in the torque measurements should be expected. By running a test similar to the one in Figure 5.27, it should be possible to observe the spread. At this point, it is important to remember that fresh concrete is a non-homogenous material, and this too could contribute to the spread. The maximum aggregate size certainly has some influence, as well as the presence of other components, such as steel fibers. 5.6.2 New impeller test Tests were carried out in order to try to observe the theoretical behavior shown in Figure 5.27. For this, a new impeller was built and used with the program Duration test. Figure 5.29. shows the new impeller which possesses four removable fingers. The program Duration test allows one to constantly read the torque while the impeller is turning at a constant speed. The torque can be averaged over a certain number of measurements if desired.  110  1.0  8 0.0 1.0  o.s 0.0 1.0  0.5 $ 0.0 1.0  10.5 8 0.0 Torque (Nm)  Torque (Nm)  A) Hypothetical Impeller  B) UBC impeller  Figure 5.28: Results from the impeller motion analysis  111  New impeller shaft (12 mm diameter)  Steel plate 3 mm thick  145 mm 4 removable fingers 9 mm diameter  Figure 5.29: New impeller geometry Figure 5.30 shows the results of tests carried out with two fingers. Each bar chart represents one torque reading. On this graph, one can observe the oscillatory effect caused by the change in position of fingers. The fluctuations amongst the individual readings, probably due to the heterogeneity of the concrete (typical shotcrete mix, 10 mm maximum size) are also noticeable. The heterogeneity effect is less marked than the position effect. Similar tests were carried out with one, two, and four fingers while using the new impeller and also with the H-impeller (which was used for the entire study). The results of these tests are presented in Figure 5.31. In this figure, each measurement represents the average of five readings. The results show that the amount of spread decreases with the number of fingers (less effect of position), while the average torque requirement increases with the number of fingers. Thus, a four finger impeller of this type would give less spread than the H impeller. However, by the time that these measurement were done, most of the research project was completed. It was therefore decided to keep the H impeller for the remainder of the project.  5.6.3 Sensitivity tests A test without any concrete in the bowl was conducted to evaluate the possible effect of inertia forces and/or friction during the test. A test was also carried out with the sampling bowl filled with water. These results are shown in Figure 5.32.  112  140 120 100 80 !60  if  40  100  0  200  300 400 500 600 Number of readings  700  800  900  Figure 5.30: Oscillatory effect caused by the movement of the impeller 400 350  ••  4• 4<44t4+  4<&•+(4+•4  • •  tl)  . • 4• •  •t%.  <44’•<•  44(((•••tt<_  300  E  150 100 50 0  10  20  30  40  50 60 70 80 Number of readings  90  100  Figure 5.31: Effect of impeller (number of fingers) on the spread of torque  110  120  113 The test on air indicate that the inertia effect or friction are negligible. The offset of 0.0 15 Nm, which is very small on the scale used to present the results on concrete (usually 0-5 Nm) is caused by the zeroing procedure described in Section 5.3.1. 1.2 1  0.4 0.2 0  0.01  0.02  0.03  0.04  0.05  Torque (Nm) Figure 5.32: Rheometer test carried out on air (bowl empty) and on water The test on water confirms that the 0.015 Nm mentioned above is really a zeroing offset, because the flow curve of the water (Newtonian fluid) crosses the abscissa at this same value (no flow resistance expected). Because the viscosity of water is very small (0.001 Pa.s), the flow inside the sampling bowl becomes turbulent early in the test. For this reason, in this case, the calibration constants (K and G) as described in Section 3.3.3, cannot be used (See Chapter 8 of Tattersall and Banfihl, 1983). However, this test indicates that the apparatus is very sensitive.  5.7 PROPOSED MODIFICATION TO THE UBC RHEOMETER If a second version of the apparatus becomes necessary, the following modifications should be made: •  Replace the manual crank and the counterweight with an electric device to raise the bucket platform.  •  Modify the program to remove the calibration procedure before each testing session.  114 •  Modify the screen output to have the flow curve on the screen when the test is finished.  •  Make provisions to be able to transform the rheometer to a coaxial-cylinders viscometer: -  -  •  increase the motor power to 1-1/2 HP, and change the reducer ratio to 30:1.  Design an impeller and a smaller bowl for mortar. A coaxial-cylinders viscometer for mortar would be a plus.  5.8 REFERENCES Cabrera J.G. and Hopkins C.G., (1984), “A Modification of the Tattersall TwoPoint Test Apparatus for Measuring Concrete Workability”, Magazine of Concrete Research, Vol. 36, No. 129, December, 1984, pp. 237-240. DeLarrard F., Szitkar J.C., Hu C. and July M., (1993), “Design of a Rheometer for Fluid Concrete”, International RILEM Workshop on Special Concrete: Workability and Mixing, Paisley, March 2-3, 1993, pp. 125-134. Tattersall G.H. and Banfill P.F.G., (1983), “The Rheology of Fresh Concrete”, Pitman, London, 1983, 356 p. Tattersall G.H., (1990) “Progress in Measurement of Workability by the TwoPoint Test”, Proceedings of RILEM Colloquium on Properties of Fresh Concrete held University of Hannover, October 3-5, 1990, Chapman & Hall, London, pp. 203-312. Tattersall G.H., (1991), “Workability and Quality Control of Concrete”, Chapman & Hall, London, 1991, 262 p. Wallevik O.H. and Gjørv O.E., (1990a), “Modification of the Two-Point Workability Apparatus”, Magazine of Concrete Research, Vol. 42, No. 152, September, 1990, pp. 135-142. Wallevik O.H. and Gjørv O.E., (1990b), “Development of a Coaxial-Cylinders Viscometer for Fresh Concrete”, Proceedings of RILEM Colloquium on Properties of Fresh Concrete held University of Hannover, October 3-5, 1990, Chapman & Hall, London, pp. 213-243. Wimpenny D.E. and Ellis C., (1987), “Oil-Pressure Measurement in the Two Point Workability apparatus”, Magazine of Concrete Research, Vol. 39, No. 140, September, 1987, pp. 169-174.  115  CHAPTER -6PUMPABILITY  6.0 INTRODUCTION In this chapter, the development of a laboratory concrete pump and a pressure bleed test are presented. The results from both tests are analyzed in order to predict pumpabiity. The paste volume concept is explained and the effect of air entrainment on pumpabiity is taken into account.  6.1 LABORATORY CONCRETE PUMP The usual experimental set-up for wet-mix shotcrete studies requires a specialized crew, the use of a commercial concrete pump, a truck mixer, and large amounts of concrete: at least 1 m 3 for each mix tested. These requirements make shotcrete studies very expensive. Also, because the concrete is then made at the batching plant rather than at the shooting site, it is difficult to achieve the degree of control generally achieved when all operations are performed in the laboratory. In addition, when using a truck mixer, it is difficult to avoid contamination of the mix by any concrete or water left in the mixer drum. Finally, in most shotcrete studies, because of logistics all shooting operations are concentrated into one or two days. It is then very difficult to recast one mix, or to use previous results to plan the next step or experiment. So, in order to perform the present laboratory shotcrete study at a reasonable cost, and to enable the use of previous results to plan the next experiment or mix design, a small laboratory size concrete pump was designed and built. This pump was used to pump and shoot high performance shotcrete (lIPS). It is essentially a research tool and was not designed for large volume operations. 6.1.1 Design criteria In order to shoot concrete in the laboratory, it is important to reduce the amount of concrete needed to fill the pump. Moreover, the pump must be able to pump every  116 kilogram of concrete placed into the hopper. For inside use, it must be small in size and powered by electricity. The pumping characteristics, especially the speed of the concrete at the end of the hose must be representative of a real concrete pump: i.e. while pumping, the pump must be able to achieve sufficient output with respect to the nozzle size. To shoot the shotcrete, compressed air is added at the nozzle (see Chapter 7 for shotcrete test results). A design similar to the one used by Dawson (1949) was chosen: one pumping piston and gates to control the flow of concrete. This set-up gives a longer waiting period before each surge in comparison to the usual two piston pump where the waiting period is very short. This would be bad economically in a real shooting operation, but for the laboratory this is of no importance. The size of the pump has been greatly reduced with respect to Dawson’s pump, so that it can handle small amounts of concrete. 6.1.2 Pump description Figure 6.1 shows a schematic diagram of the pump which possesses a single rubber pumping piston (125 mm diameter) with a stroke of 300 mm. The pump is capable of 10 strokes per minute. A pumping rate of 3 m Ih can be achieved. An electric motor (10 Hp) 3 powers the three hydraulic pistons (two gates and one pumping piston) which control the flow of the concrete. A remote control can be used to activate the proper pumping sequence which is controlled by six proximity switches and three solenoid valves. The hopper has a capacity of 0.1 m . 3  outlet hydraulic gates  exit 100 mm rubber piston  Figure 6.1: Schematic diagram of the pump  0: 125 mm  remote control  117 The majority of the pump components were purchased from various manufacturers. The electric control box and the final assembly were completed in the civil engineering laboratories at UEC. Six proximity switches are used to control the movement of all of the pistons. The hydraulic system (Figure 6.2) is composed of a hydraulic pump, a pressure gauge, safety valves, three electric valves, a pumping piston, two gate pistons, a filter, an oil tank and safety devices for oil level and oil temperature. ps4 psi ps6 outlet gate cylinder  filter  level and temperature safety  Figure 6.2: Hydraulic system and proximity switches The power is provided by a 10 HP electric motor (208 V/ 3 ph /60 Hz). The flow and the pressure of the hydraulic pump (Continental PVA6-6B30-R-0-1R) can be adjusted if required. The user should refer to the pump operating instructions. The flow was set to a maximum (about 30 1/mm.) and remained at this setting throughout this study. The pump was first set to produce a pressure of 1.67 MPa on the fresh concrete. This pressure was increased up to 2.50 MPa to permit the pumping of stiffer mixes. A “Bourdon” pressure gauge was used to read the actual pumping pressure (from 10.5 1VIPa to 15.8 MPa). Detailed plans of the major components of the pump are available in Appendix D.  118 A safety valve, which was set at 17.5 MPa was used to prevent accidents. This safety feature is located before the first solenoid valve (solenoid A) that is used to enable or disable the pumping sequence. The pumping sequence can be started and stopped manually, or a remote control can be used for this purpose. When the pumping sequence is started, a control box alternately activates the four other solenoids, which control the two others valves. In Figure 6.2, the position of the pistons indicates that the pump is ready to start pumping (solenoids B and D are ON). When the  pumping piston is fully extended, the signal from proximity switch 2 (ps2) switches the power from solenoid D to solenoid E. The inlet and outlet gate cylinders move simultaneously (inlet opens and outlet closes) until both ps3 and ps6 have been triggered. At this point, the pump is ready to suck concrete from the hopper. A combined signal from ps3 and ps6 switches the power from solenoid B to solenoid C and initiates the sucking of concrete from the hopper. When the pump piston is fully retracted, psi switches power from solenoid E to solenoid D and both gates move simultaneously again (inlet closes and outlet opens). When both gates are fully open or closed, a signal from ps4 and ps5 switches the power from solenoid C to solenoid B and the pumping starts again. This sequence continues until the power to solenoid A is turned OFF. Some problems were encountered during the research project. One of them is the poor design of the hydraulic gates: aggregates have occasionally been trapped, thus preventing the gate from closing completely, and preventing proximity switches 4 or 6 from being triggered, resulting in a breach in the pumping sequence. This problem has been resolved by grinding the end of the gate to prevent the aggregates from being trapped. The outlet gate and its cylinder have been slightly twisted and damaged accidently by the froklift. The resulting misalignment between the cylinder and the gate resulted in frequent blockage of the gate. A new blade and a protective device for the gate were built and put in place to prevent further damage.  6.2 PRESSURE BLEED TEST When most of the problems with the pump were solved, the few results available were not promising enough to suggest that the measurement of rheological properties alone would  119 be sufficient to predict the pumpability of a concrete mix. Therefore, it was decided to build a modified pressure bleed test apparatus, similar to the one used by Browne and Bamforth (1977) as described in Chapter 2. 6.2.1 Design criteria and apparatus description For all practical considerations, the piston used for the pressure bleed apparatus is identical to the concrete pump piston. Compressed air and an air bag were used to apply and maintain the load on the piston, instead of the hydraulic piston used by Browne and Bamforth (1977). Table 6.1 summarizes the principal geometric characteristics of their apparatus and those of the new pressure bleed apparatus, as well as those of the laboratory concrete pump. One can see that the pressure applied on the concrete with the new apparatus is lower than that used by Browne and Bamforth, but is more representative of the actual pressure applied on the concrete during pumping. The size of the sample on which the amount of bleeding water is measured has been increased.  Table 6.1: Geometric characteristics of bleed test atmaratus  Item piston diameter cylinder length sample volume pressure on concrete loading system  Browne and Bamforth 12.5 cm 13.9 cm 3 1700 cm 3.5 MPa hydraulic manual  concrete pump  new apparatus 12.5 cm 21.5 cm  2640 cm 3 2.1 MPa compressed air automatic  12.5 cm 30 cm 3 3670 cm 1.7 2.5 MPa hydraulic automatic -  Figure 6.3a shows the front view of the pressure bleed test apparatus used in this project. A rubber piston and an air balloon are used to apply a pressure of 2.1 MPa (300 psi) on the concrete. A regulator is used to adjust and maintain a pressure of 630 kPa (90 psi) inside the air balloon. The piston has a maximum travel distance of 60 mm (figure 6.3b). At the top of the cylinder, a 50 gauge mesh is used to prevent blocking of the tap hole. A porous polypropylene disc is used to hold the mesh in place and allows the water or paste  120 to drain into the tap hole. Figure 6.3b shows the side view of the apparatus at the beginning of a test. 6.2.2 Test procedure Other equipment required to perform a pressure bleed test include: clock or stop watch, graduated cylinder of 250 ml capacity, 0.7 MPa air supply, trowel, tamping rod and wrench. The test is carried out by executing the following steps: •  Check that the piston is fully retracted by using the articulated arm (not shown in Figure 6.3).  •  Fill the cylinder with concrete as if it were a standard cylinder (three layers, rodded 25 times each, close voids between layers by tamping with the rod).  •  Remove excess concrete with a trowel to obtain a flat surface, clean the top of the cylinder and place the mesh over the concrete.  •  Place the porous polypropylene disk into the top cap. The disk must be soaked in water before being placed in the cap.  •  Put the top cap in place and use the bolts to seal the cap. Be sure that the “0” ring is clean.  •  Place the graduated cylinder under the bleed hole.  •  Start the stop watch and open the air valve simultaneously.  •  Take readings of the amount of water inside the graduated cylinder regularly, until the level of water is stable (no change for 2 minutes).  •  Remove the top cap and the concrete, and clean the apparatus. Record the final length of the concrete specimen.  121  porous polypropylene disk measuring cylinder  topcap  —“  “O”rings  concrete sample  rubber piston  maximum travel = 60 mm  Li  I )  (a)  (b)  Figure 6.3: New pressure bleed apparatus 6.2.3 Pressure bleed test results Because the pressure bleed test apparatus was not built at the beginning of the project, only a few test results are available. Figure 6.4 shows a typical curve obtained during a bleed test: the amount of water emitted during the test is plotted with respect to time. The compositions of all of the mixes used during this study (except those used to test the rheometer and presented in Chapter 5) are available in Appendix E. All curves from the pressure bleed tests are available in Appendix F.  122  120  •  100 ii  2  80  /  6O  /  40/  20  r0  20  40  60  80  100  120  140  Time (mm) Figure 6.4: Typical pressure bleed test results (mix: (8.1 1A)30T1 SF-D) The results in Figure 6.4 are similar in shape but very different in time scale compared to the typical results obtained by Browne and Bamforth (see Figure 2.10). In their test, most of the water was emitted after two minutes; with the new apparatus, for the pressure used and this particular mix composition, it took over two hours to emit most of the water. Obviously, the value V14O-V1Osec proposed by Browne and Bamforth, as described in Chapter 2 (Section 2.8) as a measure of stability under pressure, is not applicable to these results. Differences in mix composition and/or the lower pressure used during the present tests might explain these results. According to Powers (1968), bleeding (not pressure bleeding) can be expressed by two principal determinants: the initial bleeding rate and the total amount of water expelled. For pressure bleeding, these might be represented by the initial slope of the curve in Figures 6.4 or 2.10, and by the final amount of water emitted. The rate of bleeding (03 should be controlled by Darcy’s law: Q=KpgAh/L  (6.1)  where K is the coefficient of permeability, p is the density of the liquid, g is the gravitational constant and Ah/L is the hydraulic gradient. In normal bleeding, the hydraulic gradient depends on the unbuoyed weight of the solid material which is a function of the solid content of the mixture. K is a function of the specific surface area and of the solid content of the mixture. For pressure bleeding, it is logical to assume that the hydraulic  123 gradient is proportional to the applied pressure, because the unbuoyed weight is small compared to the applied pressure. The initial bleeding rate in Figure 6.4 is about 2.6 x10 /min., if expressed as a fraction of 3 the sample, while for Browne and Bamforth (Figure 2.10) it is about 211 3 x10 / min, which is about 100 times faster. According to Darcy’s law, a concrete tested in the Browne and Bamforth apparatus would exhibit a bleeding rate faster by a factor equal to the ratio of the applied pressures: 3.5 MPa/2.1 MPa = 1.7. This means that most concretes tested in this study exhibit a bleeding rate about 100/1.7 = 60 time slower than those of Browne and Bamforth. The only logical explanation is that the low water-cement ratio (W/C) used in this study is responsible, in part, for this difference; the use of silica fume (SF), which is known to reduce bleeding, is probably responsible for the remainder. According to Table 6.2 from Powers (1968), a reduction in W/C can change the bleeding rate of cement paste by a factor of more than 20. Since Browne and Bamforth (1977) did not give any mix compositions, one cannot be certain but, according to these results, it is highly probable that their mix compositions were very different (high W/C, no SF) compared to the mixes used in this study because superplasticizers and silica fume were not often used in 1977. Table 6.2: Effect of surface area and water content on the bleeding rate of cement paste (Powers. 1968) Bleeding rate of cement paste 6 cm/see) (x10  wic  specific surface area of cement /g) 2 (cm  0.26 0.32 0.39 0.48 0.59 0.74  1085  1540  2045  2550  103 210  39 80 150 270  17 38 73 133  9 20 40 75 128 213  -  -  -  -  -  -  223 -  The results of all of the pressure bleed tests carried out in this study are presented in Table 6.3. The first column is the mix identification as described in Section 4.1.3. The second  124 column is the amount of water emitted after 240 minutes, expressed as a volume percentage of the sample (2.64 liters of concrete). The third column is the final length of the fresh concrete cylinder after being pressurized for 240 mm. The fourth and fifth columns are the results of slump and air content tests, respectively. The sixth column is the air content, calculated as described in the next paragraph, and the last column gives some indications regarding the pumpability of these mixes: a mixture is considered not pumpable if it causes the pump to block. Table 6.3: Pressure bleed and other test results Mix identification  Final bleed water  (%) (7.20A)3OL1SF-AF (7.23E)33L1SF-AF (7.26A) 3OL1SF-CF (7.27A)3OT1SF-AM (7.29A)3OT1SF-AM (8.3A)3OT1SF-DN (8.5A)3OT1SF-D (8.11A)3OT1SF-D (8.16A)25T15F-CF (8.19A)25T15F-CF (8.23A)25T1SF-CNF (8.24T)41L1SF-AWF (8.25T)??L1SF-E (8.30A)48L1FA-W  3.4 3.7 3.3  4.5 5.5 4.4 4.1 4.5 1.2 4.4 4.0 5.3 9.1 5.6  Final length (mm)  -  -  195 172 168 152 181 188 -  189 164 195 193 200  Slump  Air content  Calculated compaction  (mm)  (%)  (%)  35  3.7 7.8 6.8 13.9 16.1 25 14 11.1 9.2 8.1 21.4 3.4 3.2 4.8  230 110 60 115 160 270 170 225 250 175 120 115 60  -  -  6.0 15.5 16.3 24.9 11.7 8.1 9.2 7.7 19.7 4.0 1.2 1.4  notes  not pumpable no pump test borderline borderline  pumpable pumpable pumpable pumpable not pumpable pumpable pumpable pumpable pumpable not pumpable  By measuring the final length of the concrete specimen after the test, it is possible to calculate the initial air content if one assumes that the total volume of the air bubbles becomes negligible during the test because of the 2.1 MPa applied pressure. For example, the final length of the mix shown in Figure 6.4 is 188 mm and the initial length is 215 (for all tests), which gives an air content + water emitted of (215-188) / 215 x 100 = 12.6 %. The amount of water emitted at 240 mm. is 119 ml = 119 I 2640 x 100 = 4.5 %. Figure 4.5 shows the relationship between the air content before pumping and the calculated compaction during the pressure bleed test. The straight line represents the ideal relationship; the results are in reasonable agreement.  125  25 ‘—‘  20  0 I  0 0  5 10 15 20 Pressure bleed compaction (%)  25  Figure 6.5: Relationship between air content and calculated compaction during the pressure bleed test  6.3 PUMPABILITY As mentioned in Chapter 2, pumpability can be defined as the mobility and stability under pressure within a pipe. It seems appropriate to try to relate the slump or the rheological properties, which measure mobility, to pumpabiity. The pressure bleed test was related to slump and to pumpability by Browne and Bamforth (1977). However, no one has yet attempted to relate the rheological properties of concrete directly to pumpability, although some theoretical studies have been oriented in this direction. Also, while working with very high air contents, stability problems other than bleeding may arise (possible blockage of high air content mixes because of an increase in g caused by compaction). 6.3.1 Slump and pressure bleed test vs. pumpability Since the factor Vl4OsecVlOsec proposed by Browne and Bamforth (1977) is not applicable to this apparatus and/or these mixes, two new factors Vl4omjn and Vl4OmjnViOmin have been used to try to predict pumpability (because of the longer testing time with low WIC mixes). Vl4Omjn is simply the final amount of water emitted at the end of the pressure bleed test. The Vl4omjnVlomjn is similar to the Vl4OsecVlOsec proposed by Browne and Bamforth (to take into account the shape of the curve), but with a different  126 time scale. Figure 6.6 shows the relationships between slump and these factors (Figure 6.6a: Vl4omjn; Figure 6.6b: Vl4Omjn-VlOmjn) with respect to the pumpability.  300 / •  / \  >  250  liii  jIIIIIIIIIIIIIIIII•IIIIIIIIIIIIIIIIIII •  200 E 1 Q.  E  150 .4::. A•  ...  A  100  •  v.  1.11• .....  •::.  ....  • pumpable  50  I  I A  0  •  0  2  4  I  I  6 10 8 (a) Water emitted:V140 (%)  0  1  I 2  borderline not pumpable  I 3  (b) Water emitted:V140-V1O  4  (%)  Figure 6.6: Relationships between slump, pressure bleed test and pumpability Unfortunately, the limited amount of data for the borderline and not pumpable categories does not allow one to reach any firm conclusions regarding the implication of the pressure bleed test. However, these results give credits to the possible relationship between the saturated/unsaturated state and the stability requirement which defines pumpability. Blockage of very workable concrete can most probably be related to a stability problem, i.e. a change from a saturated to an unsaturated state (see Figure 2.1). The stability could possibly be explained in teniis of the amount of water emitted under pressure and by the bleeding rate (which is most probably related to the viscosity of the paste). A minimum limit in the amount of water emitted could be seen as a requirement for extra paste to stay in the saturated state under pressure (with respect to the amount of paste needed to fill the voids between the aggregates). This limit regarding the minimum amount of water emitted, is probably function of the bleeding rate: for a low bleeding rate (Low W/C and silica fume mixes...), the concrete needs only a small increase in the percentage (3% in our case) of extra paste to be maintained in the saturated state, and for a  127 high bleeding rate, this minimum requirement in extra paste is probably higher. These percentages may also be affected by the period of time under which the concrete is maintained under pressure.  6.3.2 Rheology vs. pumpability Theoretical models have been proposed to analyze the pumping process with respect to the rheological properties. Models of a Bingham material lubricated by a Bingham lubricating layer have been mentioned in Chapter 3. One may suppose that the properties of the lubricating layer (the cement paste) control the steady flow of concrete in a straight pipe of constant diameter: i.e. where the concrete moves as a solid plug (the properties of the lubricating layer may also control the bleeding rate under pressure). The properties of the concrete will be important when the concrete has to deform around singularities. Sakuta et al. (1979) explain the presence of a lubricating layer by a concentration of cement paste at the walls of the pipes. This phenomenon would be more important for small pipes. However, none of these models are satisfactory at the moment. For now, a more practical approach is called for. A practical approach, such as the workability box proposed by Tattersall (1991), might be a good way to assess pumpability. Tables 6.4 and 6.5 present some information on rheological properties and pumpability for mixes without and with steel fibers, respectively. The first column gives the mix identification. The second column gives the air content before pumping, after pumping or when the pump blocked when the first letter of the mix identification is A (and T), P or Q, respectively. Columns three, four, five and six give the slump, the flow resistance (g), the torque viscosity (h) and the paste fraction of the mix, respectively. The last column gives information on the pumpability: whether it is pumpable or not, the required pumping pressure (applied on the concrete) and/or the pumping rate. These results and some others are presented in Figure 6.7. All mixes included within the box are pumpable (except for two non-reinforced mixes). A different pumping set-up or mixes with high W/C ratios may have a different pumpability box. Many factors such as pump type, pumping speed, length and diameter of pipes, presence of singularities, etc. may change the limits of the box. Also, it is possible, that for high WIC ratios mixes or for mixes susceptible to segregation (with a bad grading of aggregates for example) that there might be a lower limit in g or h under which the concrete will not be pumpable. Anyhow, for low W/C mixes containing silica fume, no lower limit was found.  128  Table 6.4: Rheological properties and pump ability (mixes without fibers  Mix identification  Air content  (%)  Slump (mm)  (3.24A)4OT5SF-AMW (3.24P)4OT5SF-AMW (3.26A)40T1-WM (5.20A)35T1SF-AM (5.25A)33L1CF-AM (5.27A)3OL1SF-AM (6.1A)35T35F-AM (7.27A)3OT1SF-AM (7.27P)3OT1SF-AM (8.3A)3OT1SF-DN (8.5A)3OT1SF-D (8.5P)3OT1SF-D (8.11A)3OT1SF-D (8.11P)3OT1SF-D (8.11Q)3OT1SF-D (8.18T41L1SF-AW (8.18P)41L1SF-AW (8.19A)25T1SF-C (8.19P)25T1SF-C (8.25T)??L1SF-E (8.25P)??L1SF-E (8.30A)48L1FA-W (8.30B)54L1FA-W (8.30P)54L1FA-W  9.9 6.5 15.0 6.7 14.3 12.9 11.1 13.9 8.1 25.0 14.0 7.5 11.1 5.4  40 50 30 15 100 170 60 15 160 270 250 170 90  *  -  2.5 2.5 8.1 7.0 3.2 2.9 4.6 4.8 3.9  -  -  70 50 250 -  115 120 30 60 40  g* (Nm)  h paste fraction (Nm.s) (%)  -  -  -  -  2.1 4.0 3.4 1.6 0.5 2.4 2.2 0.8 0.3 0.3 1.3 1.3 3.1(3.9) 1.5 1.5 .5 .5 1.1 0.9 2.3(3.0) 1.4(1.8) 1.4(1.8)  0.5 0.2 0.4 0.4 1.5 0.1 0.3 0.3 0.4 0.7 0.6 0.6 0.3 0.2 0.2 0.9 1.1 0.1 0.1 0.1 0.1 0.1  40.1 37.6 41.1 35.0 41.1 42.1 42.2 43.3 39.0 50.4 43.6 39.1 41.7 37.9 -  34.0 34.0 39.9 39.2 7? 7? 37.6 37.6 36.5  Notes  pumpable pumpable pumpable borderline borderline pumpable pumpable pumpable 3.90 kg/stroke 2.74 kg/stroke pumpable pumpable pumpable (1.18 MPa) pumpable (1.18 MPa) block (2.25 MPa) pumpable (0.86 MPa) pumpable (0.86 MPa) pumpable (0.86 MPa) pumpable (0.86 MPa) 6.63 kg/stroke 6.63 kg/stroke not pumpable pumpable (0.64 MPa) 7.40 kg/stroke  number in ()represent the real flow resistance, i.e. the real intercept with the abscissa.  A test was also carried out by pumping the same concrete over and over in a closed loop (i.e. by pumping the concrete into the pump hopper). This process caused some sort of accelerated artificial “aging”. At various times, the pumping pressure was recorded and the pump stopped to permit a sample to be taken of the pumped concrete for the determination of rheological properties. Figure 6.8 shows the results of this pumping test done on mix:  (8.1 1P)30T1 SF-D. As the “aging” takes place with time (mostly an increase in g), the required pumping pressure increases.  129  Table 6.5: Rheological properties and pumpabilitv (mixes with fibers)  Mix identification  Air content  (6.15A)3OT1SF-AMF (7.6A)25L3SF-AF (7.8A)25L3SF-AF (7.12A)3OL3SF-AF (7.12P)3OL3SF-AF (7.19A)3OL3SF-AF (7.19P)3OL3SF-AF (7.20A)3OL1SF-AF (7.26A)3OL1SF-CF (7.26P)3OL1SF-CF (7.29A)3OT1SF-AM (8.4A)3OT1SF-DNF (8.4P)3OT1SF-DNF (8.4Q)3OT1SF-DNF (8.9A)3OT1SF-DF (8.9P)3OT1SF-DF (8.9Q)3OT1SF-DF (8.16A)25T1SF-CF (8.16B)25T1SF-CF (8.16C)25T1SF-CN (8.23A)25T1SF-CNF (8.23P)25T1SF-CNF (8.24T)41L1SF-AWF (8.24P)41L1SF-AWF  14.0 5.5 12.1 4.0 4.0 3.7 4.1 3.7 6.8 5.0 16.1 25.5 14.4 8.4 12.1 4.6 2.3 9.2 9.2 22.9 21.4 18.8 3.4 2.8  *  (%)  Slump (mm)  g (Nm)  210 200 260 140 25 140 60 35 110 100 115 162 85 5 210 70  4.5 4.3 1.0 3.5 3.8 3.1 3.8 5.1 1.9 2.3 1.5 1.5 2.6 4.7(5.5) 1.0 1.9 5.4 1.2 .5 .4 1.1 1.2 2.4 2.4  -  225 255 260 175 160 120 120  h paste fraction (Nm.s) (%) 0.4 1.7 3.1 1.0 1.3 1.9 1.2 0.1 1.5 1.8 0.1 0.5 0.4 0.1 0.9 1.2 0.2 3.2 3.0 1.0 0.7 0.6 0.6 0.6  43.3 37.1 41.8 35.2 36.0 35.2 35.1 35.2 36.9 35.6 45.7 51.0 43.7 39.5 42.7 36.8 35.5 38.3 38.7 49.0 49.0 47.4 36.9 35.3  Notes not pumpable borderline borderline 6.38 kg/stroke 6.38 kg/stroke 6.73 kg/stroke 6.73 kg/stroke notpumpable 5.93 kg/stroke 5.93 kg/stroke pumpable pumpable pumpable block (2.41 MPa) pumpable pumpable block (2.41 MPa) not pumpable block (2.41 MPa) pumpable (0.32 MPa) pumpable (0.86 MPa) pumpable (0.86 MPa 6.51 kg/stroke 6.51 kg/stroke  number in ()represent the real flow resistance, i.e. the real intercept with the abscissa.  Results from Tables 6.4 and 6.5 plus the results from Figure 6.8 have been plotted in  Figure 6.9 to try to find some relationships between the required pumping pressure (Figure 6.9a) or the pumping rate (Figure 6.9b) and the rheological properties. From this Figure, it is obvious that the rheological properties affect the required pumping pressure,  but do not affect the pumping rate when the concrete is pumpable (the hydraulic unit of the pump works at constant volume but variable pressure). Pumping rates (Figure 6.9b) are discussed in Section 6.4.1.  130  5 4  3  2  1  0 0  1  2 3 h (Nm.s)  4  5  Figure 6.7: Pumpability box: all mixes 1.2 1  I  —  0.8  —  0.6 —  0.4  Pumping pressure (MPa) • 1.18 El 1.50 • 1.72 0 1.93 A 2.26  •  I  • • II  —  I  •  -0El El El  • I  I  0 1  El El El El El El 0 ‘2 LI El El  El  II  0.2  0  0 0  •  2  .0  A  .> • A A  •O • • .-  (  •0 •0 •0  A A A A A A A  .0 •  I]  •  3 Torque (Nm)  A A A  4  5  Figure 6.8: Effect of artificial ‘gaging” on pumping pressure The representation of pumpability (in Figure 6.9a) requires only one measurement of rheological properties as opposed to Figure 6.6 which requires the results of two tests (the slump test and the pressure bleed test) to assess pumpability. The use of rheological  131 properties to predict pumpability also gives better and more meaningful results by giving an estimation of the required pumping pressure (for a pump with a constant flow): as shown in Figure 6.9a, an increase in the value of g or h produces an increase in the required pumping pressure. Also, the rheological properties (flow resistance and torque viscosity) are easier to obtain (faster and without operator influence) and more precise than the slump and the pressure bleed tests.  6.73  I.  6.38  0 7.51  390 a  05.93  r  fl  pumping rate (kg/stroke) no fiber  6.63 0 2.74  —  0 with fibers I  0 h (Nm.s) (a)  1  2 h (Nm.s)  I  3  E  4  (b)  Figure 6.9: Pumping pressure (a) and pumping rate (b) vs. rheological properties More studies on the relationship between rheological properties and pumpability are needed: for mixes that could have stability problems (segregation, pressure bleeding, etc.), other parameters (pressure bleed, amount of extra paste, paste viscosity, etc.) must be studied to address the stability issue. Aging effects on the prediction of pumpability are discussed in Section 7.6.  132  6.4 PUMPING OF CONCRETE WITH HIGH AIR CONTENT 6.4.1 Pumping rate This study has involved pumping concrete mixes which contain high amounts of entrained air (up to 25 %). Some problems were encountered while pumping these concretes. The relationship between the pumping rate and the initial air content is shown in Figure 6.10. One can see that the pumping rate decreases with the amount of air: the pumping rates of the two mixes with high air contents are 3.9 kg/stroke and 2.7 kg/stroke for air contents of 14.1% and 25 %, respectively. Because these two mixes have lower g and h values than some other mixes, they should have been easier to pump (lower pressure).  8  0  6  ‘4  2 0 0  5  10 15 20 Air content (%)  25  Figure 6.10: Effect of air content on pumping rate 6.4.2 Compressibility When dealing with high air content, one has to deal with a highly compressible material, as opposed to concretes in which the air content is low. This compressibility causes a delay between the movement of the pumping piston and the movement of the concrete at the end of the hose. Figure 6.11 shows an idealized representation of the pressure distribution for three hypothetical cases: (a) non-compressible concrete with a good flow control sequence,  133 •  (b) compressible concrete with a good flow control sequence, and  •  (c) compressible concrete with a poor flow control sequence. (a) piston position  (b) non compressible good flow control  (c) compressible good flow control  inlet  (d) compressible poor flow control 0  (1) StOp  outlet  outlet  en  Ltend  —  ]  ‘MI ‘MI -  end  0  Dl  (2)4  outlet  l_  0  (3)  4Th  0.  I________  0.  —  I  -  I________  Stop  0. .4—  —  0  FL1  0.1  a..  a..  I________  0.  -  inlet  0  ‘MI  a.. (6)__  (a)  (b)  0.  (c)  (d)  Figure 6.11: Hypothetical pressure distribution in pipes In Figure 6.11, the flow control refers to the movement sequence of the inlet and outlet gates (see Figure 6.1). A good sequence is obtained when these two gates are never open simultaneously: they move in the proper sequence (case (b) and (c) in Figure 6.11). When both gates become open at the same time (because of the poor flow control sequence), the pressure built-up during pumping (for a compressible material) is lost when the concrete moves back to the hopper (case d). Case (b) is the case of a non-compressible material. When the pumping piston is fully retracted (Column a in Figure 6.11 gives the position of the piston) the pressure in the pipe line is shown by the graph lb (Line 1, Column b). The residual pressure due to the  134 residual friction which exists because of the flow resistance. When the piston starts moving (2a), the concrete starts to move immediately at the end of the hose (small arrows in graph 2b) and the pressure in the pipe line varies linearly. When the piston stops moving (4a), the pressure goes down abruptly (4b) and the concrete does not move anymore. For a compressible material (Figure 6.11, Column c), when the piston starts moving (2a), the concrete at the end of the pipeline does not move at the same speed because of the air being compressed (2c). The delay between the piston movement and the movement of the concrete at the end of the hose is caused by a progressive pressure build-up in the pipe line (graph 2c to 3c, Figure 6.11). This progressive pressure build-up is accompanied by a progressive increase in the concrete output. When the piston comes to a stop, with a proper flow control sequence the pressure can be maintained. While the piston is retracting  (5a and 6a), the stored pressure keeps the concrete moving. This is accompanied by a fast decrease in the output rate (5c) until the pressure equals the friction which causes the concrete to stop moving (6c). Case (d) is similar to case (c) until the piston comes to a stop (4a). Because both the inlet and the outlet gate are open simultaneously for a short period of time (with a poor pumping sequence), the concrete is pushed back into the hopper by the existing pressure in the pipeline (4d). Depending on the time lapse during which the two gates are simultaneously open, there might be enough pressure left to keep the concrete moving out of the pipe after a redistribution of the pressure (5d) until the friction pressure is reached (6d). 6.4.3 Pumping sequence of the laboratory concrete pump Some problems have been encountered during the pumping of high air content mixes. These problems have two principal causes: the poor flow control of the inlet and outlet gates (because of a bad design), and the malfunctioning of the outlet gate (because of an accident, one of the gates was torn). In this study much work has been done with concrete containing high amounts of entrained air. Because of the actual pumping sequence (the two gates move at the same time), behavior similar to that in Figure 6.11 (Column d) has been observed: for a fraction of a second, both gates were open simultaneously, and this was sufficient to lose the confinement in the pipe line. The concrete moved back into the hopper, reducing the pumping rate by about 60 %. This problem can be corrected by adding another solenoid  135 valve in the hydraulic system and by adjusting the pumping sequence. It is important to note that even if the pumping rates were reduced, it was possible to pump and shoot most of the mixes with high air contents. The outlet gate has suffered some blockage because it was not built strongly enough. The outlet gate was initially designed to withstand a pressure of 150 psi and the inlet gate for a pressure of 300. An outlet gate able to withstand a pressure of 300 psi would be subject to less blockage. 6.5 REFERENCES Browne R.D. and Bamforth P.B., (1977), “Test to Establish Concrete Pumpability”, ACI Journal, Vol. 74, No. 5, May, 1977, pp. 193-203. Dawson 0., (1949) “Pumping Concrete Friction between Concrete and Pipe line”, Magazine of Concrete Research, Vol. 1 No. 3, December, 1949, pp. 135-140. -  Powers T.C., (1968), “Properties of Fresh Concrete”, Wiley & Son, London, 1968, 664 p. Sakuta M., Yamane S., Kasami H. and Sakamoto A., (1979), “Pumpability and Rheological Properties of Fresh Concrete”, in Proceedings of Conference on Quality Control of Concrete Structures, Vol. 2, Swedish Cement and Concrete Research Institute, Stockholm, 17-19 June, 1979, pp. 125-132. Tattersall G.H., (1991), “Workability and Quality Control of Concrete”, Chapman & Hall, London, 1991, 262 p.  136  CHAPTER -7SHOOTABILITY  7.0 INTRODUCTION In this chapter, a new test set-up to measure the build-up thickness, which is used to assess shootability, is presented. The relationship between the build-up thickness and the rheological properties, especially the flow resistance are then analyzed. The results of a few rebound tests are also given, along with some considerations regarding aging effects on rheological properties. Finally, compaction during pumping and shooting is analyzed, and a new model to predict shootability in terms of maximum build-up thickness is presented.  7.1 SHOOTABILITY It is often said that if concrete can be pumped, it can be shot. The first step in maldng shotcrete is indeed to verify that it is pumpable. This process was described in Chapter 6. Accordingly, all concretes that were found to be pumpable in Chapter 6 should be shootable, but to what level? In Chapter 3, it was mentioned that the existence of the flow resistance provides a good explanation as to why shotcrete is shootable. It allows one to explain why the shotcrete remains in place after shooting. Then the first step in studying shootability is thus to define this characteristic. 7.1.1 Definition of shootability Shootability is a property which incorporates parameters such as adhesion (the ability of plastic shotcrete to adhere to a surface), cohesion (the ability of plastic shotcrete to stick to itself and to be built-up in thick sections) and rebound (the material which ricochets off the impacted surface). The efficiency with which concrete can be applied is also dependent on the equipment used, but this is not considered here.  137 In this study, shootability is considered in terms of the efficiency with which a mix sticks to the receiving surface and to itself. Thus, the build-up thickness is used to assess shootability. A mix that can be built-up to a great thickness in a single pass without sloughing will be referred to as possessing good shootability. 7.1.2 Pumpability vs. shootability From past experience, one knows how to apply thick coats of material efficiently. By pumping a stiff mix and by adding an accelerator, it is possible to build-up a substantial thickness of shotcrete in a single pass. In most cases, however, it is possible, and usually better (see Chapter 1), to avoid the use of accelerators. There is a permanent conflict between pumpabiity and shootability: when the pumpability increases (by increasing the slump for example), the shootability decreases (smaller build up thickness); when the pumpability decreases, the shootability increases. It is always a challenge to find the best compromise between pumpability and shootability. However, when this optimum is reached, one may avoid the use of accelerators or, for more difficult applications, it may at least allow a reduction in their addition rate.  7.2 BUILD-UP THICKNESS 7.2.1 Measurement of build-up thickness To measure the build-up thickness, a frame as shown in Figure 7.1 was used. It was decided to remove the effect of the shooting technique itself by having the nozzle immobile during the test. For this, a fixed base of 200 mm x 230 mm was mounted 100 mm from the wall. During the test, the shotcrete was projected horizontally onto the receiving surface without moving the nozzle until the in-place shotcrete fell under its own weight. The rheological properties of the shotcrete were then measured on concrete shot directly into the rheometer sampling bowl. A video camcorder was used to record the tests; then, the build-up thickness could be determined by reviewing the experiment on video. The results of the build-up tests and of the rheological properties of the in-place shotcrete, as well as the slump and the air content of the mixes as measured before pumping, are given in Table 7.1. The mix identification code was described in Chapter 4 and the corresponding mix compositions are given in  138 Appendix E. The small letter (a, b, c or d) added at the end of the mix identification indicates which nozzle was used during shooting (see Appendix D for details on nozzles).  300  200  [mm]  Figure 7.1: Build-up thickness test set-up Table 7.1 Result of the build-up thickness  Mix identification  (7.6S)26L3SFAFb** (7.8S)26L3SF-AF-b (7.19S)3OL3SF-AF-b (7.295)30T1SF-AM-a (7.295)3OT1SF-AM-b (7.29S)3OT1SF-AM-c (7.29S)3OT1SF-AM-d (8.4S)3OT1SF-DNF-b (8.11S)3OT1SF-D-b (8-16S)25T1SF-CF-d (8.18S)41L1SF-AW-b (8.23S)25T1SF-CNF-b (8.23S)25T1SFCNFb*** (8.24S)41L1SF-AWF-b (8.255)??L1SF-E-b (8.30S)54L1FA-W-b *  real intercept with the abscissa  **  nozzle type see Appendix D second test  ***  (%)  Air  Slump (mm)  g Nm)  (Nm)  5.5 12.0 4.0 16.1 16.1 16.1 16.1 25.5 8.1 9.2 3.0 21.4 21.4 3.4 3.2 4.6  200 260 140 115 115 115 115 160 170 255 70 175 175 120 115 60  8.0 0.4 6.3 2.2 2.4 2.6 2.9 3.9 1.4 0.6 3.7 2.6 4.1 4.0 1.0 1.7  8.0 0.4 6.0 2.4 2.6 2.8 3.2 4.1 1.4 0.3 4.5 2.8 3.2 4.0 1.1 2.2  h (Nm.s)  Build-up (mm)  0.5 4.5 0.3 0.2 0.2 0.2 0.2 0.1 1.2 3.2  350 10 300 110 190 180 190 215 90 10 190 200 225 200 50 55  0.8 0.8 0.7 0.4 0.1 0.2  139  7.2.2 RelationshiPS between shootability and rheological properties Figure 7.2 presents the relationship between the build-up thickness and the slump. From these results, it is not possible to predict the shootability or the maximum build-up of a mix just by measuring the slump before pumping. However, it is possible that some relationship might be observed for mixes of the same composition and approximately the same initial air content.  350 300 250 200 150 100  5o 0  100  50  150  200  250  300  Slump (mm) Figure 7.2: Relationship between the build-up thickness and the slump before pumping Figures 7.3 shows the relationship between torque viscosity (h) and the build-up thickness. One can see that there is no clear relationship between the h value and the maximum build-up thickness (no relationship was expected). 350 300  250 . 200 150 100 50 0 0  1  2  3  4  5  h (Nm.s) Figure 7.3: Relationship between the build-up thickness and the torque viscosity (h)  140 Figure 7.4. shows a good relationship between g (flow resistance) and the maximum build-up thickness. In this Figure, the black squares refer to the flow resistance (g) obtained by considering a true Bingham behavior, while the white squares represent the reading of the flow resistance (g’) on the abscissa (e.g., in Figure 5.12, g would be 3.5 while g’ would be 2.6). It is not possible to determine which of g or g’ gives the best relationship, since they are generally close and very often the same. 350 300 250 200 150 100 50 0 01234567  8  g (Nm) Figure 7.4: Relationship between the build-up thickness and the in-place flow resistance (gandg’) 7.2.3 Theoretical analysis The relationship shown in Figure 7.4 can be analyzed by considering the equilibrium of a sample of fresh concrete on the verge of falling from a wall. For this demonstration, only the shear stress (bending effect ignored) between the wall and the fresh concrete and the weight of the concrete are considered. Equation 7.1 (in Figure 7.5) represents the equilibrium between the shear force Vr and the gravity force pa (a is used for gravitational acceleration because g is used for flow resistance). By considering the linear relation between to and g, (Equation 7.2) one can obtain a direct relationship between the build-up thickness.(t) and the yield stress (to) as shown in ,  Equation 7.3. According to Equation 7.1, the relationship between the build-up thickness and the yield should be linear and independent of the size of the sample (b x h) when only the shear stress is considered. The curvature observed in Figure 7.4 might be the effect of the cantilever flexural stress when t increases with respect to h.  141  Vr=P to b h = pa b h t  h.  ‘to = pa t I = (1/pa) to to = (KIG) g t= (1/pa) (K/G)g t = (KIGpa) g  (7.1) (7.2) (7.3)  Figure 7.5: Analysis of build-up test In Chapter 6, it was shown that the pumpability is reduced (increase in the required pumping pressure) when either the flow resistance or the viscosity increase (see Figures 6.8 and 6.9a). It is now obvious that shootability is increased when the flow resistance of the in-place shotcrete is high. Pumpability and shootability thus have special requirements in terms of rheological properties (especially the flow resistance) which are in opposition to each other.  7.3 REBOUND Rebound was defined in Chapter 1. It was stated that the instantaneous rebound rate is dependent on the thickness of previously applied fresh shotcrete. When impacting a hard surface, the rebound is at a maximum and decreases to a constant rate after a certain thickness has been applied (see Figure 1.6). The rheological properties of the previously applied shotcrete modify the condition of the surface (hardness, stickiness) and then influence the amount of rebound and its composition. Modifications in rebound composition have not been studied here. 7.3.1 Measurement of rebound To minimize external influences in measuring the rebound, it was decided to use the set-up shown in Figure 7.6. The receiving panel is mounted directly on a weigh-scale, so that the rebound can be determined at different thicknesses without having to disturb the previously shot material. The rebound was collected at different build-up thicknesses, and the weight of the shotcrete in the mold was recorded.  142 Figure 7.7 shows the results of four rebound tests carried out on mix (6.1S’35T3SF-AM. The hollow squares represent the cumulative rebound. The relationship between the cumulative rebound and the thickness is similar to the one shown in Figure 1.6. The interval rebound is the average rebound between two measurements of cumulative rebound. This interval rebound was quite constant after an initial thickness, as thin as 8 mm, was shot. This parameter appears to be independent of the thickness of shotcrete beyond the first layer. The cumulative rebound is close to the constant average rebound (in this case, the average of the interval rebound over the last three intervals) for thicknesses over 60 mm. scale  shote]  Figure 7.6: Rebound test set-up 60  III  so \ —  —  10  0  10  20 30 40 Thickness (mm)  50  60  Figure 7.7: Rebound characteristics of mix (6.1S)35T3SF-AM 7.3.2 Relationship between rebound and rheological properties Table 7.2 presents the constant average rebound of the shotcrete, the rheological properties measured on the in-place shotcrete, the air content before pumping, and the  143 paste volume (PV) which is the paste content as a percentage of the in-place shotcrete (calculated from the mix design and the in-place air content). The PV in brackets represents the paste volume of the shotcrete before pumping. The change in PV during pumping and shooting depends on the initial air content and on the compaction during pumping and shooting. Table 7.2: Average rebound measurement data  Mix identification  (6.1S)35T3SF-AM (7.19S)30L3SF-AF (7.29S)30T1SF-AM (8.18S)41L1SF-AW (8.19S)25T1SF-C (8.23S)25T1SF-CNF (8.24S)41L1SF-AWF (8.25S)??L1SF-E (8.30S)54L1FA-W  Rebound  g (Nm)  h (Nm.s)  Air  PV  (%)  (%)  (%)  13.6 18.0 21.8 1.8 15.2 44.1 2.7 1.3 4.9  8.0 6.3 2.2 3.7 0.5 4.1 4.0 1.0 1.7  0.5 0.3 0.2 0.8 2.5 0.7 0.4 0.1 0.2  13.5 4.0 16.1 3.0 8.0 21.4 3.4 3.2 4.8  36.3 34.3 35.4 36.1 36.0 38.4 36.7  (42.2) (35.2) (45.7) (36.2) (39.9) (48.1) (37.6)  35.8 (37.6)  In Table 7.2, it seems that no relationship can be found between the rebound and the rheological properties (g or h), the air content, or the paste volume before or after the shooting. One would expect that shotcrete with high in-place flow resistance would have higher rebound: shooting on a hard surface increases rebound. There is, however, some relationship with W/C as shown in Figure 7.8: the amount of rebound seems to decrease as the W/C increases. It is not possible to give any explanation on this observation but, because these results were obtained on only a limited number of mixes, there are some limitations with regard to this observation.  7.4 AGING EFFECT 7.4.1 Aging Aging, which causes stiffening of fresh concrete or shotcrete, is due to the slow hydration of the cement during the dormant period and to a progressive reduction in the efficiency of superplasticizers (if they are present). The aging caused by superplasticizers is difficult to predict and can be very rapid. Aging has been observed through slump reduction (as in  144 Figure 2.8), increases in yield (as in Figure 3.14) or flow resistance (as in Figure 7.9); viscosity is not much affected.  50  .30 20  10 0 0.20  0.25  0.40 0.45 0.50 0.30 0.35 Water-cement ratio (W/C)  0.55  Figure 7.8: Relationship between rebound and W/C 7.4.2 Fresh concrete aging rate (FCAR) To evaluate aging, one may define a fresh concrete aging rate (FCAR) which is the rate of change in flow resistance. Mixtures which are aging slowly will have a slow increase of flow resistance with time, i.e., a small FCAR. They will remain workable for a long period without significant changes in workability. Figure 7.9 shows the behavior of such a stable mix: there is only a very small increase in flow resistance and no change in viscosity over a two hour period (Cast 15 mm refers to the properties of the concrete before pumping but 15 minutes after casting). The flow resistance of mix (6.1A)35T3SF-AM has been plotted with respect to time in Figure 7.10 where the slope of the line represents the fresh concrete aging rate (FCAR) which is 0.2 Nm/h for this mix. Very low FCARs (in set retarded concrete) are not desirable in shotcrete application because they might overextend the waiting period between two successive applications. They are however useful for research purposes because the aging effect can be neglected.  145 1.2 1  ,  0.8  0.6 I.  0.4 0.2 0 0  1  2  4  3 Torque (Nm)  5  Figure 7.9: Rheological test results on mix (6. 1M35T3SF-AM at different times 11.0 —.------  ‘  0.5  -  1 hour  —  JO 0  30  60 Time (mm)  90  120  Figure 7.10: Determination of fresh concrete aging rate on mix (6. 1A)35T3SF-AM In some mixes, the flow resistance rapidly increases with time, due to a rapid stiffening of the mix. Figure 7.11 shows that the fresh concrete aging rate for mix (8.4A)3OT1SF-.DNF is 1.2 Nm/h.  146  C) -..  1.o  0  30  60 Time (mm)  90  120  Figure 7.11: Determination of fresh concrete aging rate on mix (8.4A)30T1 SF-DNF This kind of mix is good for field shotcreting applications because the waiting time between successive applications (e.g., for thick overhead applications) is reduced. Of course, if the fresh concrete aging rate is too high, pump blockage may occur. Because the value of the fresh concrete aging rate affects the shotcrete application, it has to be taken into account in a model which predicts shootability. The importance of the FCAR is discussed in Section 7.7. Because the rheological properties of the fresh concrete change at different rates in different mixtures, it is important to measure them with respect to time. Changes in flow resistance with time depend mainly on cement type, admixtures used and temperature. Some of these influences are discussed in Chapter 8.  7.5 COMPACTION Compaction is a very important phenomenon in shotcrete technology because it modifies the composition of the in-place shotcrete (compaction reduces air content). Some of the effects of compaction on hardened shotcrete properties are known: compaction increases the compressive strength and reduces the air content which may cause an increase in the value of the air void spacing factor and then migth reduce durability. Its effects on fresh shotcrete properties have never been studied (as far as can be ascertained from a review of the literature).  147  7.5.1 Definition Compaction is simply the expulsion of entrapped or entrained air. In cast-in-place concrete it is usually caused by internal vibration. Compaction may also be caused by the pumping process (pumping compaction) or by the shooting process (shooting compaction). The combined compaction (or total compaction) is the loss of air due to both pumping and shooting processes. The effect of increasing air content on the rheological properties of concrete is well known; it produces mainly a reduction in flow resistance (Figure 7. 12a). Similar behavior has been reported in Chapter 5 (Figures 5.17 and 5.18). Compaction should produce the reverse effect, i.e. an increase in flow resistance as shown in Figure 7. 12b. This behavior was also observed in Figure 5.21. 7.5.2 Possible effect of compaction on shootability Because compaction caused by the shooting process may affect flow resistance, it may also affect the build-up thickness and hence the shootability. From the behavior shown in 7.12b, one can predict four possible types of behavior with respect to compaction and shootability. Figure 7.13 illustrates these four hypothetical cases. Each case is shown by a graph with two lines. The dotted lines refer to the behavior of the concrete before pumping, while the solid lines refer to the rheological behavior of the shotcrete after shooting.  Torque (Nm) (a)  I.  Torque (Nm) (b)  Figure 7.12: Effect of air content (a) and compaction (b) on flow resistance  148  -  a. a.  :  -  —  Before shooting After shooting  no entrained air (no compaction) Torque (Nm)  (a) poor shootability  I  e  entrained air (no compaction)  Torque (Nm)  case (b): good shootability  with entrained air (compaction) compacton  a. a.  entrained air (compaction)  (c) good shootability  (d) excellent shootability  Figure 7.13: Possible relationships between compaction and shootability Figure 7.13a represents a very workable, easy to pump shotcrete mix with a low flow resistance and no entrained air. Because this concrete possesses no entrained air, there will be little compaction (there is always some entrapped air that can be lost) and the rheological behavior should be about the same before and after shooting. Also, because the in-place shotcrete has a low flow resistance, the build-up thickness should be small resulting in a poor shootability. Figure 7. 13b represents a workable, pumpable shotcrete mix with an acceptable (for pumping purposes) flow resistance and no entrained air. Because of little compaction the flow resistance should be approximately the same before and after shooting. Also, because the in-place shotcrete has an acceptable flow resistance, the build-up thickness should be sufficient to ensure good shootability. Many conventional shotcrete mixes are probably well represented by this case. Figure 7. 13c also represents a very workable, easy to pump shotcrete mix with a low flow resistance and with a reasonable amount of entrained air. Because this concrete possesses entrained air, there will be compaction, resulting in a higher flow resistance after shooting.  149 The in-place shotcrete, because of a high flow resistance, should have a high build-up thickness resulting in a good shootability. Figure 7. 13d represents a workable, pumpable shotcrete mix with an acceptable flow resistance and with a reasonable or high amount of entrained air. Because this concrete possesses entrained air, there will be compaction resulting in a higher flow resistance after shooting. The in-place shotcrete, because of a very high flow resistance, should have a very high build-up thickness resulting in excellent shootabiity. 7.5.3 Measurement It would appear that to verify the effect of compaction caused by the shooting process one would only have to measure the rheological properties before pumping and after shooting. It is, in fact, more complicated than this because one must take into account two other effects: the effects of aging and of the compaction caused by the pumping process. To deal with the time dependence of rheological properties which is referred to as the aging effect, one must measure the rheological properties of the concrete before pumping and after shooting at essentially the same time. In practice, this is important for mixes with a high FCAR but of less importance when the FCAR is low. Since only one rheometer was available, these properties were measured one after the other, within a three minute time interval (which may be considered simultaneous). It is well known that pumping may cause a reduction in the air content and also a decrease in slump (Chapter 1). In the previous analysis, no distinction was made between pumping compaction (caused by the pumping process) and shooting compaction (caused by the shooting process). However, a part of the combined compaction (total loss of air during pumping and shooting) is certainly caused by the pumping and should be measured. In order to isolate the net effect of the compaction caused by the shooting process, the best experimental procedure is to measure the air content and the rheological properties just after casting the concrete but before pumping (referred to as Cast), after pumping but before shooting (referred to as Pump), and after shooting (referred to as Shot). The expected results from this procedure are shown in Figure 7.14. Each compaction causes some stiffening (i.e., the increase in flow resistance caused by the compaction). Three types of stiffening can be defined: the pumping stiffening caused by the pumping compaction, the shooting stiffening caused by the shooting compaction, and the combined  150 stiffening caused by the total compaction (loss of air caused by both pumping and shooting).  total compaction Cast  Pump  I,  Shot  I  i pumping j shooting compactio’ compactio  f  Torque (Nm) Figure 7.14: Definition of pumping compaction, shooting compaction and total compaction 7.5.4 Results Table 7.3 gives the results of tests carried out on fresh and hardened shotcrete. Column 1 is the usual mix identification. Columns 2, 3 and 4 give the air contents of the fresh concrete or fresh shotcrete: Cast (before pumping(2)), Pump (after being pumped(3)) and Shot (after being shot directly into the air meter (4)). The fifth column is the slump measured before pumping. Columns 6, 7 and 8 give the flow resistance of the fresh concrete or fresh shotcrete. Columns 9 to 11 give the compressive strength. Cylinders (200 x 100 mm) were cast before and after pumping and cores (168 x 84 mm) were taken from shotcrete panels. The strength was measured at 28 days on three samples. In Table 7.3, the mixes have been separated into four groups, depending on the presence of air-entraining agents or fibers. The first two groups were cast without air-entraining agents while the third and fourth groups were cast with air-entraining agents (M or N in the code). The second and the fourth groups were cast with about 50 kg/m 3 of steel fibers (F in the code). The W/C decreases within each group and different admixtures were used.  151  Table 7.3: Effects of pumping and shooting on shotcrete properties  Mix identification  Column 1  Air (%) Cast 2  Slump (mm)  Pump Shot 4 3  Flow resistance (Nm)  28 d strength (MPa) Pump 10  Shot 11  Cast 5  Cast 6  Pump 7  Shot Cast 8 9  (8.30S)54L1FA-W (8.25S)??L1SF-E (8.11S)3OT1SF-D (8.195)25T15F-C  4.6 3.2 8.1 8.0  3.9 2.9 5.7 7.0  2.0 2.8 2.9 2.5  60 115 170 250  1.8 1.0 1.2 0.3  1.8 1.1 1.3 0.3  2.2 1.5 1.4 0.5  24* 61 85 97  24* 62 86 95  26* 55 94 113  (7.19S)30L35F-AF (7.12S)30L35F-AF (7.26S)3OL1SF-CF  4.0 4.9 6.8  4.0 4.0 5.0  2.8 2.2 2.5  140 100 110  3.1 3.4 1.9  3.8-5.4 3.7-4.3 2.1-2.2  6.3 4.6 2.3  81 83 77  80 84 85  90  (3.26S)40T1-AWM (6.1S)35T3SF-AM (7.27S)3OT1SF-AM (7.295)3OT1SF-AM  14.2 13.5 13.9 16.1  3.0 2.4 3.4 2.4  50 170 60 115  2.1 0.6 2.1 1.4  3.2 1.4 3.2 2.2  20* 30 48 33  (8.4S)3OT1SF-DNF (8.23S)25T1SF-CNF  25.5 21.4  3.2 4.8  160 175  1.6 1.2  3.9 2.7  40  -  -  8.1 -  14.4 18.8  -  -  2.3-2.7 -  2.6-?? 1.3  -  -  -  66 -  60 46  -  -  31* 57 78 79 90 105  *7 dinstead of 28 Some additional explanation is necessary concerning the determination of the flow resistance presented in Table 7.3 (columns 6-8). Flow curves (see Section 3.3.3) were used to determine the flow resistance before pumping (Cast: column 6), after pumping (Pump: column 7) and after being shot into the bowl (Shot: column 8). When only one measurement of flow resistance is given for Pump, this indicates that the measurements for Cast, Pump and Shot were made within a very short period and are considered simultaneous. When column 7 includes two numbers, this indicates that two sets of two simultaneous measurements have been obtained. The first measurement set is composed of column 6 and the left hand side of column 7, which correspond respectively to the flow resistance of the concrete before pumping and after pumping, measured simultaneously. The second measurement set is composed of the right hand side of column 7 and of column 8, which correspond respectively to the flow resistance of the concrete before shooting and after shooting, measured simultaneously but at a different time than the first measurement set.  152 From the tests carried out, it is possible to give a practical example of each hypothetical case shown in Figure 7.13: cases (a), (b), (c) and (d) in Figure 7.13 are represented by Figures 7.15, 7.16, 7.17 and 7.18, respectively. Figure 7.15 shows a case in which the concrete was cast without an air-entraining admixture and had a low initial flow resistance. It shows the rheometer test results for mix (8.19APS)25T1SF-C before and after pumping (Cast (mix A) and Pump (mix P)) and for the in-place shotcrete (Shot (mix 5)) at different times. Since the measurements were carried out simultaneously, no aging effect has to be taken into account. The values reported in Table 7.3 from those curves are: Cast  =  0.3 Nm, Pump  =  0.3 Nm and Shot  =  0.5 Nm. In the case of mix (8.19S)25T1SF-C, the torque viscosity has changed after shooting. In order to produce a mix with very low flow resistance, one must use a very high dosage of superplasticizer. Since it is difficult to find the optimum dosage, the mix is sometimes over superplasticized: the amount of superplasticizer, in excess of that used to reduce the flow resistance to zero (the SP reduces the attraction between cement particles and then reduces flow resistance), acts to reduce the viscosity (when there is no more attraction, the extra amount of SP increase the amount of paste). After shooting, because of some compaction, the viscosity is reduced first, and then the flow resistance is reduced if the compaction is high enough. This has been observed only in very flowing concrete (in our case, over superplasticized mixes).  153 1.2 1  0.2 0 0  1  2 3 Torque (Nm)  4  5  Figure 7.15: Effect of compaction on mix (8. 19APS)25T1 SF-C (no AEA) 1.2 1 j0.8 0.6 0.4 0.2 0 0  1  2 3 Torque (Nm)  4  5  Figure 7.16: Effect of compaction on mix (7.26APS)3OL1SF-CF (no AEA but with fibers)  154  1.2 1 0.8 0.6 0.4  0 0  1  2 3 Torque (Nm)  4  5  Figure 7.17: Effect of compaction on mix (6. 1AS)35T3SF-AM (with AEA) 1.2  10.8 0.6 0.4  E 0.2  5 Torque (Nm) Figure 7.18: Effect of compaction on mix (8.4APS)3OT1SF-DNF (with AEA and fibers)  155 During pumping (still Figure 7.15), there was no change in flow resistance: i.e. zero pumping stiffening (Pump-Cast = 0.3 Nm -0.3 Nm = 0 Nm). During shooting, the change in flow resistance (shooting stiffening) was very small (Shot Pump = 0.5 Nm -  -0.3 Nm  =  0.2 Nm). The combined stiffening caused by pumping and shooting is an  increase in flow resistance of only 0.2 Nm for this mix. During pumping, the compaction or the loss of air was only 1.0% (from 8.0% to 7.0%). During shooting, the compaction was 4.5% (from 7.0% to 2.5%). Then, the total compaction during pumping and shooting was 5.5% for this mix. Even though this mix was very easy to pump, it was not suitable for shotcreting and exhibited very bad shootability. Because of the very low flow resistance, it sloughed off the receiving surface and had a very low build-up thickness (estimated to be under 20 mm). The only way to get a test panel (to measure the strength) was to shoot downward into the mold. Figure 7.16 shows a case in which the concrete was cast without an air-entraining agent, though the concrete possessed enough flow resistance to be shot. It shows the rheometer test results for mix (7.26APS30L1SF-CF. Since the rheometer tests for Cast, Pump and Shot were not taken all at the same time, the aging effect has to be taken into account. The values reported in Table 2 for this mix are: Cast = 1.9 Nm, Pump = 2.1-2.2 Nm and Shot 2.3 Nm. As mentioned above, this indicates that the value for Cast (1.9) and the left hand value for Pump (2.1) were taken simultaneously (at 30 mm.). The right hand value for Pump (2.2) and the value for Shot (2.3) were taken simultaneously (at 45 mm.) but 15 =  minutes after the first set of data. The pumping stiffening was very small (Pump-Cast so was the shooting stiffening (Shot  -  Pump  =  =  2.1 Nm -1.9 Nm  2.3 Nm  -  2.2 Nm  =  0.2 Nm), and 0.1 Nm). The  combined stiffening (caused by pumping and shooting) is an increase in flow resistance of 0.3 Nm for this mix (not 0.4 Nm, which does not account for aging between the two measurement sets). During pumping, the compaction or the loss of air was only 1.8% (from 6.8% to 5.0%). During shooting, the compaction was 2.5% (from 5.0% to 2.5%). Then, the total compaction during pumping and shooting was 4.3% for this mix. This might seem important for a non-air-entrained mix but the high dosage of superplasticizer often entrains 5 to 8 % of air. In any case, compaction under 5% has little effect on g or h. This mix was pumpable at the beginning of the test but blocked after 60 minutes (probably due to aging). However it demonstrated good shootability before blocking (the build-up thickness was not measured).  156 Figure 7.17 represents a concrete cast with an air-entraining agent and possessing a low initial flow resistance. It shows the rheometer test results for mix (6. lAS ‘)35T3SF-AM. Since there are no test results available after pumping (Pump), only the combined stiffening for this mix can be determined: Shot-Cast = 1.4 Nm-0.6 Nm =0.8 Nm for a total compaction of 13.5% 2.4% -  =  11.1%.  The compaction provided sufficient build-up to shoot a test panel. The total compaction produced an increase in 28-day strength from 30 MPa to 57 MPa. Without compaction, this mix would have displayed a similar rheological behavior to the mix in Figure 7.15. For the reasons explained above, the viscosity was only slightly affected. Figure 7.18 shows the case for a concrete cast with an air-entraining agent and possessing some flow resistance. It shows the rheometer test results for mix (8.4APS)3OT1SF-DNF. Since there are no test results available after pumping at 60 mm, the analysis could not take into account the aging effect. Nevertheless, it is possible to appreciate the pump induced compaction (from 25.5% to 14.4%= 11.1%) which produced a pumping stiffening of 2.5-1.5  1.0 Nm. The shooting stiffening is 1.5 Nm for a reduction in air content from 14.4% to 3.2% (which includes some aging effect and thus should be taken =  as a maximum). The total compaction (22.3% air reduction) produced a stiffening of 2.5 Nm (which includes some aging effect). The large increase in flow resistance produced excellent shootability. It was possible to shoot 300 mm (build-up thickness) of shotcrete on a vertical surface in a single pass without sloughing. It is interesting to note that the final strength of another mix: (8.23S)25T1SF-CNF, which had an initial strength of 40 MPa (air content of 21.4%) was 105.4 MPa (in-place air content of 4.8%). The relationships between the W/C and the air content are discussed further in Chapter 8. Figure 7.19 shows the relationship between compaction and the resulting stiffening (increase in flow resistance). Pumping stiffening, shooting stiffening as well as combined stiffening are presented. Data from Figures 7.15 to 7.18 are specifically identified (first part of the mix identification code only). Since the results from case 7.18 have to be treated as a maximum (because some aging effects are included in the stiffening), an arrow pointing down was added.  157 2.5 2.0  1.0 0.5 0 0  10  5  15  20  25  Compaction: loss of air (%) Figure 7.19: Relationship between compaction and stiffening 7.5.5 Summary on compaction From the results in Section 7.4.5, it is obvious that compaction caused by the shooting process produces an increase in flow resistance which results in a stiffer mix. Pumpinduced compaction produces similar effects. The stiffening effects are proportional to the amount of compaction. However, for compaction under 5%, it is difficult to predict the stiffening (Figure 7.19): small air losses (even a compaction of 1%) may cause a stiffening of O.5Nm, probably because of some evaporation during shooting which may affect low W/C mixes. It is not possible at the moment to determine whether small or large air bubbles are lost during pump-induced compaction or during the compaction caused by the shooting process. The mechanisms of air loss are also unknown. One may suppose that during pumping some air is lost by dissolution into the paste because of the applied pressure. It would be logical to assume (by considering the equilibrium between the internal pressure of an air void and the surface tension of the paste) that the small bubbles are more easily lost than the big ones. This could only be verified by looking at the distribution in the size of the air voids before and after pumping. This work is a whole research area. Compaction during shooting could occur inside the nozzle if one assumes that most particles are separated when the compressed air is mixed with the concrete inside the  158 nozzle to form the shotcrete. Another explanation for the compaction that occurs during shooting is that the air bubbles explode when the concrete hits the receiving surface. A more precise explanation must be found concerning these hypotheses.  7.6 MODEL FOR PREDICTING PUMPABILITY AND SHOOTABILITY With the relationships that have been developed in Chapters 6 and 7, it is possible to elaborate a model to predict pumpability and shootability if one measures certain properties of fresh concrete. It is also possible to talce into account the effects of aging and compaction. In practical applications, it should be possible to predict the effect of a waiting period in the case of more than one layer of application. 7.6.1 Required relationships and properties In order to use this model to predict pumpability and shootability in terms of maximum build-up thickness, a knowledge of several relationships and properties is needed. Assuming the relationships illustrated in Figure 7.20, one may predict pumpability and shootability: •  Figure 7.20a: relationship between rheological properties and pumpability (pressure requirement similar to Figure 6.9a, assuming no stability problem).  •  Figure 7.20b: relationship between shootability and rheological properties (build up thickness vs. in-place flow resistance similar to Figure 7.4).  •  Figure 7.20c: relationship between rheological properties and compaction (stiffening vs. compaction similar to Figure 7.19; not needed for concrete with low air content).  If the first two of the following properties are known, one may then draw Figure 7.21. •  The initial flow resistance: (IFR  •  The fresh concrete aging rate (FCAR = 0.5 N ni/h)  •  The initial torque viscosity: (ITV  •  The initial air content (IAC = 15%)  =  1.5 Nm)  0.5 Nm.s)  159  E  200  .4,  ii In-place flow resistance (Nm) (b)  h (Nm.s) (a)  (c)  Figure 7.20: Required relationships  4  ITV  =  0.5 Nm.s  3  I Z2  1 0  O234 Time (hours)  Figure 7.21: Characteristics of fresh concrete 7.6.2 Prediction of pumpability With the relationships and properties presented in the previous section, one may then check to see whether a mix is pumpable and for how long, if it is assumed that viscosity does not change with time (which is usually true). Figure 7.22 summarizes the determination of the pumpabiity life. The first step is to determine whether the concrete is pumpable. For this, one must plot the initial value of g and h in Figure 7.22a: if the dot is in the pumpability zone, the concrete is pumpable. For low W/C ratio concrete containing silica fume, since no stability problem caused by segregation are to be expected, blockage would occur only because of an increase in flow resistance. To be more realistic in the determination of the pumpability life, it has been assumed that the concrete was transported for 30 minutes before pumping. To determine for how long  160 the concrete can be pumped, a vertical arrow is first drawn (Figure 7.22 a) to determine the blocking value of the flow resistance. This value is then transferred to Figure 7.22b. In this figure the initial aging line (dotted) must be adjusted for stiffening caused by pumping compaction. If one assumes that the pumping compaction is 5% (for an initial air content of 15%) the resulting stiffening (from Figure 5.20c) is 0.5 Nm. A parallel solid line, starting at 45 mm can be drawn, 0.5 Nm from the original one. The intersection of this new line with the maximum allowed flow resistance gives the blocking time or a pumpability life of 2 hours and 30 minutes.  h (Nm.s) (a)  Time (hours) (b)  Figure 7.22: Determination of pumpabiity life In any event, after 2 1/2 hours, initial set would probably start to take place and the flow resistance would increase more rapidly after that time. However, a similar concrete (JAC = 15%, ITV = 0.5 Nm.s and IFR = 1.5 Nm) with an FCAR of 1.0 Nm/h (instead of 0.5 Nm/h), would have its pumpability life reduced to about 1 hour 20 minutes. Also, the last concrete (ITV = 0.5 Nm.s, IFR = 1.5 Nm and FCAR = 0.5 Nm/h) with an initial air content of only 3% instead of 15%, would not undergo compaction. Then, the pumpability life would be 2 1/2 hours, limited by the onset of initial set at that time. In this example, the compaction has been assumed because there is not enough data available from which to determine the real relationship between initial air content and pumping compaction. However, it is highly probable that the relationship is a function of the rheological properties: the amount of compaction as a ratio of the initial air content is probably influenced by the required pumping pressure and by the rheological properties g and h. In the preceding analysis, this would imply that the solid line (in Figure 7.22b) possesses a slightly steeper slope, and thus, an earlier blockage potential.  161  7.6.3 Prediction of shootability One may predict the shootability in terms of maximum build-up thickness or the waiting period required between two successive applications. For the next two examples, two concretes with the characteristics shown in Figure 7.21 but different air contents, 15% and 3% are assumed. In both cases, the contractor is required to apply a shotcrete thickness of 150mm. The first mix has an initial air content of 15%. As determined in the previous section, this concrete will be pumpable for 2 1/2 hours. After pumping and shooting, the in-place air content has been reduced to 3% because of a total compaction of 12%. Figure 7.23 summarizes the required steps in determining the maximum build-up thickness. The first step is to determine the stiffening associated with a compaction of 12 %. Figure 7.23 (a) shows that the corresponding stiffening is 1.2 Nm. 2  I .E 1  Is 0  0 Compaction (a)  (%)  Time (hours) (b)  In place g (Nm) (c)  Figure 7.23: Determination of maximum build-up thickness (high air content)  The shooting starts at 30 minutes. The compaction increases the flow resistance of the inplace shotcrete from 1.75 Nm to 2.95 Nm (Figure 7.23b). This implies that at the age of 30 minutes one may apply almost 150 mm (Figure 7.23c) of shotcrete in a single pass, compared to 200 mm after 2 1/2 hours (for g = 4 Nm). With the high initial air content, the contractor can apply the shotcrete in one lift. The second mix has an initial air content of 3%. No compaction is caused by pumping and shooting, and the initial set is assumed to impair pumping after three hours. Figure 7.24 summarizes the required steps in determining the maximum build-up thickness. At 30  162 minutes, just after starting shooting, the in-place flow resistance is 1.75 Nm (Figure 7.24a). The corresponding maximum build-up thickness is then about 88 mm as shown in Figure 7.24b. Obviously, because the contractor cannot benefit from the stiffening caused by compaction, the work has to be done in more than one layer. 200  1150 100  50 12 Time (hours) (a)  00  12 34 In place g (Nm) (b)  Figure 7.24: Determination of maximum build-up thickness (a) and waiting period (b) (no compaction) After a first layer of 80 mm has been applied, the contractor wishes to know how long to wait before applying the second 70 mm layer. After the second layer has been applied, the first layer must carry the stress caused by the total build-up thickness of 150 mm. From Figure 7.24b, one can determine that the required flow resistance is 3.0 Nm. In Figure 7.24a, one can determine that the flow resistance of the shotcrete will reach that value at 3 hours. Unfortunately, at this time the first concrete load will no longer be pumpable and a second truck must be ordered by the contractor. In determining the waiting period, it was assumed that the FCAR is the same after shooting and pumping as before pumping. Figures 7.25 and 7.26 show examples of fresh concrete aging rates (slope of lines) before and after pumping and also after shooting, for concretes cast with and without air-entraining agents, respectively. In these figures, one can see that the FCARs are similar for all concretes; the steps between the three lines are caused by pumping or shooting compaction. One can also see on these two figures that the torque viscosity (h) does not change significantly with time or because of the pumping or shooting operations.  163 3 —  E  —  —  -=  D Cast OPump AShot LI  6 5  2  1 0 0  15  45 30 60 Time (mm)  75  90  Figure 7.25: Effect of time, pumping and shooting on rheological properties of mix (8.4APS’)3OT1SF-DNF (with AEA)  7.7 SHOOTABILITY OF HIGH AIR CONTENT SHOTCRETE The hypothetical examples of Sections 7.6.2 show some of the advantages of using the concept of a temporary high initial air content. This concept is a good way to enhance the Ipumpabilityu. The “shootability” is also enhanced by the compaction. The common dilemma of the conflicting requirements for pumpability vs. shootability no longer exists with this concept. It has been shown that the concept of a temporary high air content (initial air content up to 25%) can be efficiently used to produce high performance shotcrete (Table 7.3: mixes (8.4S)3OT1SF-DNF and (8.23S’25T1SF-CNF). It would probably be an excellent way to avoid the use of accelerators for achieving build-up, since accelerators can have very harmful effects both on crew health and on the concrete properties, especially durability.  164 3  4  E  ICast  0 Pump A Shot  6 5  z 2 1 0 0  15  30 45 60 Time (mm)  75  90  Figure 7.26: Effect of time, pumping and shooting on rheological properties of mix (7.12APS)3OL3SF-AF (without AEA) As explained in Chapter 6, special care should be taken by those who wish to adopt this concept because in working with high air content mixtures, one has to deal with compressible materials, as opposed to non-air-entrained concretes which have little compressibility. Some types of pumping equipment would not be able to handle high air content mixtures, or would have significantly reduced pumping rates even if the flow resistance of the concrete is low (or if the slump is high). Thus special care should be exercised in selecting the appropriate pumping equipment for high air content mixtures.  165  CHAPTER -8EFFECT OF MIX COMPOSITION ON SHOTCRETE PROPERTIES  8.0 INTRODUCTION In the previous chapters, it was shown that the initial value of the flow resistance, the torque viscosity, the value of the fresh concrete aging rate (FCAR) and the relationship between stiffening and compaction can be used to predict some important parameters related to pumpability and shootability. Up to now, however, the effect of mix composition on these properties has not been considered. This issue, as well as the effect of mix composition on hardened shotcrete properties is considered in this chapter. First, the influence of mix composition on the rheological properties of fresh shotcrete is analyzed. Then, the influence of pumping and shooting on compressive strength with respect to compaction is examined. Also, the durability is discussed, in terms of the deicer salt scaling resistance. Finally, the production of high performance shotcrete by using superplasticizers or by using the concept of a high initial air content is considered.  8.1 EFFECT OF MIX COMPOSITION ON RHEOLOGICAL PROPERTIES Mix composition affects the values of the initial rheological properties (flow resistance and torque viscosity at 15 minutes of age), and also the values of the fresh concrete aging rates. The variables considered in this analysis include: the cement type, the type and addition rate of superplasticizers (SP), the water-cement ratio (W/C), the use of air entraining agents (AEA), and the presence of steel fibers. Table 8.1 presents the results of different tests carried out on 58 concrete mixes. These test results include the air content, the slump measured at the age of 15 minutes, the initial values of g and h (at 15 minutes), the fresh concrete aging rate (FCAR calculated from 15 to 90 minutes) and the compressive strengths at 7 and 28 days (average of 3 cylinders of 100 nm-i x 200 mm). The exact compositions of these mixes are available in Appendix E. Rheometer test results are available in Appendix G.  166  Table 8.1: Air content, slump.  Mix identification  (3.26A)40T1-AWM (5.18A)38T1SF-BMF (5.19A)38T1SF-AMF (5.20A)35T15F-AM (5.25A)33L1SF-AM (5.27A)30L1SF-AM (5.31A)33L1SF-AM (5.31E)35T3SF-AM (6.1A)35T3SF-AM (6.1E)35T3SF-AM (6.2E)33L1SF-AM (6.2F)33L1SF-B (6.7E)33L1SF-A (6.7F)33L15F-C (6.8E)33L1SF-D (6.15A)3OT1SF-AMF (6.16A)27T1SF-AM (6.21E)25L5SF-A (6.21F)25L1SF-A (6.21G)25L3SF-A (6.21H)25JMSF-A (6.23A)25L5SF-A (6.24A)2SL5SF-C (6.24B)25L1SF-C (6.24C)25L3SF-C (6.30A)25L3SF-AF (7.6A)26L3SF-AF (7.8A)26L3SF-AF (7.12A)3OL3SF-AF (7.19A)3OL1SF-AF (7.20A)3OL1SF-AP (7.23E)33L1SF-AF (7.26A)3OL1SF-CF (7.27A)3OT1SF-AM (7.29A)3OT1SF-AM (8.3A)3OT1SF-DN (8.4A)3OT1SF-DNF (8.5A)3OT1SF-D (8.9A3OT1SF-DF *  estimated slump  .  h. FCAR. and compressive sirength  Air  Slump  (%)  (mm)  g (Nm)  14.2 8.4 20.5 7.0 14.2 12.5 5.0 14.8 13.5 12.7 5.3 5.0 4.5 8.0 14.6 14.0 16.0 6.7 5.0 7.4 6.7 7.8 12.0 7.5 9.0 10.5 5.5 12.0 4.9 4.0 3.8 8.5 6.8 13.9 16.1 25.0 25.5 14.0 10.0  50 10 200* 30* 15 100 5 210 170 230 150 155 80 165 280 210 70 90 95 230 105 180 240 160 270 230* 200 260 100 140 50 260 110 60 115 160 160 270 210  2.1 3.1 0.5 4.1 3.2 1.3 2.9 0.8 0.5 0.5 0.9 0.8 1.6 0.7 0.0 4.2 1.3 1.7 2.8 0.5 2.4 1.0 0.1 1.0 0.1 1.0 3.1 0.7 1.6 2.3 5.1 0.5 1.7 1.6 1.1 0.7 1.1 0.3 0.6  h FCAR 7d (Nm.s) (Nm/h) (MPa)  0.5 0.5 0.3 0.4 0.6 0.3 0.9 0.3 0.4 0.7 1.0 1.0 0.9 1.0 1.0 0.7 0.5 0.9 0.7 2.0 1.4 1.3 1.1 1.0 1.0 2.5 1.2 2.8 1.3 1.9 0.1 1.3 1.6 0.2 0.2 0.3 0.3 0.6 0.8  -  19.5 35.0 17.9  28d (MPa)  -  49.9 24.2  3.0 .07 1.0 0.8 1.4 1.0 0.6 0.1 0.6 0.4 0.6 1.0 0.7 0.0 2.2 0.9 1.9 1.0 0.7 1.5 0.9 0.1 0.6 0.1  40.3 62.7 66.0 72.0 58.7 62.3 54.0 67.1 54.0  -  -  -  -  -  0.1 2.3 3.8 1.1 0.1 0.8 0.6 1.5 0.1 1.6 0.0 1.7  47.4 64.6 65.1 51.7 41.0 51.2 42.7 23.2  63.5 83.3 80.7 79.4 76.5 48.3 32.6  -  -  -  -  42.3 23.9 50.3 35.2 20.6 35.8 46.1 53.9 65.7 64.3 38.8  46.6 33.8 56.7 46.6 29.8 49.7 75.9 68.1 79.7 75.4 56.6 31.7 52.1 84.3 90.7 87.8 81.3 80.4 66.0 83.5 64.3  -  -  -  -  -  57.6 67.9  76.5 92.3  (continued on next page)  167  Table 8.1 (continued): Air content slumn  Mix identification  Air  (%) (8.11A)3OT1SF-D (8.16A)25T1SF-CF (8.16B)25T1SF-CF (8.16C)25T1SF-CNF (8.16E)41L1SF-CF (8.18T41L1SF-AW (8.19A)25T1SF-C (8.21E)33T1SF-E (8.21F)33L1SF-E (8.23A)25T1SF-CNF (8.23B)25T1SF-CNF (8.23E)3OT1SF-E (8.23F)3OL1SF-E (8.24T)41L1SF-AWF (8.251y??L1SF-E (8.27E)52L1FA**W (8.30A)48L1FA**W (8.30B)54L1FA**W *  8.1 9.2 9.2 22.8 9.0 3.0 8.0 3.0 2.9 21.4 19.2 3.8 4.2 3.4 3.2 3.4 4.8 4.6  Slump (mm)  g (Nm)  170 225 255  0.5 1.0 0.5 0.3 0.6 1.5 0.5 1.2 0.5 0.9 1.3 1.0 1.3 2.3 0.7 1.2 2.3 1.3  260  240 70 250 130 210 175 175 135 110 120 115 115 30 60  h FflAR nd comnressive strength  h FCAR Str.7d Str.28d (Nm.s) (Nm/h) (MPa) (MPa) 0.6 3.1 1.5 0.6 2.2 0.2 0.8 0.9 0.9 0.5 1.0 1.1 1.0 0.2 0.2 0.4 0.3 0.2  0.8 -  0.1 0.1 0.1 0.8 0.2 1.4 0.5 0.3 2.2 0.8 1.0 2.2 0.1 0.1 0.2 0.3  72.1 73.0  85.0 93.4  -  -  23.2 71.3 45.0 78.0  31.0  -  -  36.1  -  61.7 97.4 87.3 88.8 40.2  -  -  75.5 58.5 34.2 38.7 22.7 28.3 23.8  96.0 85.8 50.7 61.1 34.1 39.6 33.2  estimated slump fly ash instead of silica fume  **  8.1.1 Relationships between g, h and FCAR The mixes in Table 8.1 can be divided in four different groups: Plain (no fibers and no  AEA used), Fiber (with steel fibers but no AEA), Air (with AEA but no fibers) and AirFiber (with steel fibers and AEA). Figure 8.1 shows that there is no clear relationship between the g and h values for these four groups. One can see, however, that when high dosages of air-entraining agents are used, the viscosity is always below 1 Nm.s, which is good from a pumpability point of view. These strong reductions in viscosity caused by the use of air could probably be explained by a phenomenon similar to “dilution” (air can be seen as a fluid of very low viscosity): the resulting viscosity would then depend on the respective proportions of the two fluids.  168 6 5 4  13 1 0 0  1  2  3  4  h (Nm.s) Figure 8.1: Relationship between g and h (all mixes) Figures 8.2 and 8.3 show the relationships between the FCAR and the h and g values, respectively. There is no relationship between FCAR and h (Figure 8.2). However, one can see (Figure 8.3) that the FCAR is generally higher for high values of g, although the results aie quite scattered. A more detailed analysis based on mix composition with respect to g, h and FCAR is needed and is presented in Sections 8.1.3 and 8.1.4.  4  Iz 1 0 0  1  2 h (Nm.s)  3  Figure 8.2: Relationship between FCAR and h (all mixes)  4  169 4  Iz  ‘—‘2  0 0  1  2  4  3  5  6  g (Nm) Figure 8.3: Relationship between FCAR and g (all mixes) 8.1.2 Relationship between initial flow resistance and slump Figure 8.4a shows that there is a good relationship between the slump and the flow resistance (g). For low workability (low slump), the flow resistance seems to be higher for mixes with fibers. This may explain why the workability of fiber reinforced concrete in not properly estimated by a slump test for stiff mixes. The spread of the results is reduced when one compares the slump to the real intercept on the abscissa (g’ on Figure 8.4b) compared to g, especially for mixes with fibers. The increase in real g’ at low angular speed for fiber mixes might be caused by some sort of fiber pull-out on fresh concrete. 6  6  0 Slump (mm) (a)  Slump (mm) (b)  Figure 8.4: Relationships between the slump and g (a) or g’ (b)  170  8.1.3 Effect of cement-superplasticizer combinations The compatibility between cements and superplasticizers was not the main objective of this study. However, some results were obtained on this topic during the preliminary study on mix composition. This analysis shows some trends which might be important for further studies on the use of superplasticizers in high performance concrete or shotcrete. Figure 8.5 presents the g and h values, and the FCAR of five different mixes. The first part of the mix identification [e.g.: (6.7F)] is written below the bar charts. These mixes are in the “Plain” category (no fiber and no AEA). At the top of the bar charts, the letters represent the type of superplasticizer, with the corresponding addition rate (in 1/rn ) just 3 under the letters. All mixes shown in this figure were cast with the same cement (Li: Lafarge, Type 10). One can see that the viscosity (gray bars) is not affected by the type of superplasticizer for this particular cement and WIC ration (0.33); however, the flow resistance and the FCAR are affected. From these results, superplasticizer D is the best option because it produces a more workable and stable mix (with respect to aging) than superplasticizers A and E, which are the two worst in combination with this cement at this  wic. 2  A (12.9)  Eki  (6.7F)  B (16.3)  (6.2E)  C (12.5)  D (12.8)  (6.7F)  II[I (6.2E)  E (13.5)  W/C =(O.33) Cement = Li  8flrnJhj  (8.2iF)  Figure 8.5: Effect of superplasticizer type and dosage on g, h and FCAR The effect of cement type has been studied with two different superplasticizers: SP A and SP C. Figure 8.6 is similar to Figure 8.5 except that the top letters and numbers represent the cement-superplasticizer combination. These mixes are also in the Plain category. From the results of Figure 8.6, it is obvious that SP C works better with all cements than does SP A. It is possible to produce more workable concretes with cements L5 or Ti, with lower addition rates of superplasticizer C, than with cements Li or L3. 3M refers to a special cement usually used to inject cracks. It has a very high specific surface which explains the high amount of SP used. This cement was not used beyond this test.  171  Li-A (16.2)  L3-A (17.5)  L5-A (8.9)  L5-A (10.5)  JM-A (21.1)  W/C=(025)  01 (6.21F)  (6.2iG)  (6.2iE) (6.23A) (6.2iH)  Li-C (17.5)  L3-C (i7.2)  (6.24B)  (6.24C) (6.24A)  L5-C (13.9)  Ti-C (16.1)  (8.i9A)  w,c = (025) SPC  FCAR (Nm/h)  Figure 8.6: Effect of superplasticizer type and dosage on g, h and FCAR These few results show the importance of the cement-superplasticizer combination on the values of the initial rheological properties and on the FCAR. Superplasticizers C and D produce the best results: i.e. they give better initial workability with smaller addition rates and they are also more stable with respect to aging. They were used to cast the low WIC shotcrete mixes (W/C  =  0.30: D, DF, DN and DNF; W/C  =  0.25: C, CF, CN and CNF).  8.1.4 Effect of high volume of air and fibers Figure 8.7 is similar to the two previous figures, except that the dosage of air-entraining agent is shown under the dosage of superplasticizer (if applicable). Also, the air content measured on the fresh concrete is shown under the mix identification. The use of a high volume of air allows one to reduce the superplasticizer dosage and still produce workable concrete (mixes D and DF, compared to mixes DN and DNF in Figure 8.7). The use of air also considerably reduces the viscosity; this is more pronounced at low W/C. The presence of fibers seems to affect g and the FCAR, but has little effect on h (Figures 8.7 and 8.8). This means that use of fibers affects slump measurement (it causes a reduction in slump) but not the dynamic behavior of fresh concrete. Even if this section is very short, it shows the importance of choosing a compatible cement-superplasticizers combination. It also shows the importance of the FCAR and not only the rheological properties initial values. Since this study was not performed to study specifically these variables, no general conclusion can be made.  172 D (13.8)  D (13.1)  DF (14.0)  2  DN (8.0) (2.8)  DNF (13.1) (3.2)  •  I 0  v1c=  o  Ce=T1 (8.5A) (8.11A) (8.9A) (8.3A) (8.4A) (14.0) (8.1) (10.0) (25.0) (25.5) CF (15.9)  3  g(Nm) h (Nm.s) FCAR (Nm/h)  CF (17.0)  CF (17.1)  CNF (14.4) (2.9)  CNF (9.5) (3.3)  CNF (9.8) (1.5)  2  i11&j  1 0  WIC = 0.25 Cement = Ti SP = C  (8.16A) (8.16B) (8.16E) (8.16C) (8.23A) (8.23A) (9.2) (9.2) (22.8) (21.4) (19.2) (9.0) Figure  8.7: Effect of W/C and superplasticizers on g, h and FCAR C (12.5)  AM (8.5) (3.2)  D (13.1)  DN (8.0) (2.8)  D C •  g(Nm) h (Nm.s) FCAR (Nm/h)  No fiber (6.7F) (8.0) 4 3  CF (16.3)  (7.27A) (13.9)  n  AMF (10.5) (3.1)  (8.I1A) (8.1)  (8.3A) (25.0)  DF (14.0)  DNF (13.1) (3.2)  With fibers  (7.23E) (8.5) Figure  (6.15A) (14.0)  (8.9A) (10.0)  (8.4A) (25.5)  8.8: Effect of AEA and fibers on g, h and FCAR  173  8.2 EFFECT OF MIX COMPOSITION ON HARDENED PROPERTIES As mentioned earlier, the term high performance shotcrete could refer to any shotcrete with exceptional properties: high strength, high durability or even high shootability. This last property was discussed in Chapter 7. The issues of strength and durability are now considered. Detailed results of tests carried out on hardened shotcrete are available in Appendix H. 8.2.1 Compressive strength Table 8.1 shows the compressive strengths (at 7 and 28 days after casting) of all mixes before pumping and shooting. These results are in agreement with the usual relationship between compressive strength, air content and W/C. Figure 8.9 presents these results graphically: the compressive strength increases when the air content and the W/C are reduced. Three categories of concrete with different W/C are represented by the shaded lines. 120  60 40 20 0 0  4  8  12  16  20  24  Air content (%) Figure 8.9: Relationship between air content, W/C and compressive strength The compressive strengths of shotcrete mixes from Table 7.3 are plotted in Figure 8.10; the shaded lines from Figure 8.9 have also been reproduced in this figure. The compressive strengths before pumping (Cast), after pumping (Pump), and after shooting (Shot) are plotted. The values of strength for each mix in Table 7.3 are connected by a thin  174 line. One can see that the compressive strength after shooting is independent of the initial air content before pumping, and depends exclusively on the WIC. This last statement implies that the concept of high initial air content is appropriate to produce high strength shotcrete. The strength is detemtined only by the WIC used. A strength of 105 MPa was obtained after shooting on a mix with an initial air content of 21.4%, with a corresponding strength before pumping of 40 MPa. In this case total compaction increased the compressive strength by more than 160%. 8.2.2 Absorption test This test is routinely carried out on shotcrete and should give an indication on the overall durability of the shotcrete, especially for the dry-mix process. In this case, the skill of the nozzleman who constantly adjusts the amount of water in the mix may affect the absorption of the in-place shotcrete. For the wet-mix process, this relationship is not so clear. 120  I wic = 0.25  *  i:o  Ipump  O  LShot  i 11  0.30 0.35 0 A 0 • A  •  60 40 A W/C=038 035  C)  20  9  OW/C =033-030  Q WIC  0  0  =  4  0.27-0.25  8  12  16  20  24  Air content (%) Figure 8.10: Effect of pumping and shooting on compressive strength Table 8.2 presents the results of absorption tests carried out on the hardened shotcrete. Each result is the average of two specimens. One can observe that the absorption depends mostly on the W/C, and to a lesser degree on the presence of AEA. Results from the absorption tests, as for the results from the compressive strength test, can be compared to those of the cast-in place concrete of the same composition as mentioned in Section 1.5.  175  8.2.3 Durability The durability of wet-mix shotcrete was discussed in Chapter 1. It is more difficult to protect wet-mix shotcrete against deicer salt scaling than against internal freezing and thawing. That is, if the concrete or shotcrete is resistant to deicer salt scaling (ASTM C672), it will be resistant to internal freezing and thawing (ASTM C-666); the opposite is not necessarily true. It is well known that the frost resistance and the scaling resistance of concrete depend principally on the W/C, the adequacy of the curing, and the use of an air-entraining agent. It is not the volume of air, but the spacing between the air bubbles, evaluated by the air void spacing factor (ASTM C-457), which is important for frost resistance. For scaling resistance, a low spacing factor (L) is a necessary but not sufficient condition: the concrete must also possess a low W/C (usually below 0.45) and must have been cured properly. Table 8.2: Absorption test results  Mix identification  Boiled absorption  Density  (7.19S)30L3SF-AF (7.27S)3OT1SF-AM (7.29S)3OT1SF-AM (8.4S)3OT1SF-DNF (8.5S)3OT1SF-D (8.9S)3OT1SF-DF (8.11S)3OT1SF-D (8.18S)41L1SF-AW (8.19S)25T1SF-C (8.23S)25T1SF-CNF (8.24S)41L1SF-AWF (8.25S)??L1SF-E (8.30S)54L1FA-W  4.57 3.76 4.73 4.61 4.26 3.60 3.68 5.19 2.23 3.35 6.40 6.32 6.63  Permeable voids  (%)  (%) 2.43 2.23 2.34 2.40 2.40 2.41 2.39 2.41 2.38 2.40 2.37 2.37 2.29  10.57 8.05 10.49 10.60 9.87 8.38 8.46 11.88 5.18 7.77 14.25 14.11 14.25  A few shotcrete mixes were tested for deicer salt scaling resistance according to ASTM C 666. The weight of scaled-off particles (kg/rn ) and the visual estimation of the 2 deterioration (rating 0 = no deterioration, rating 5 = very severe deterioration) are presented in Table 8.3. The air void parameters of these concretes were also determined according to ASTM C-457. The most important characteristics of the air void system [the  176 hardened air content, the specific surface (c and cx*) and the spacing factor (L and L*)1 are presented in Table 8.3. The fresh air content (ASTM C-39) is also presented. Table 8.3: Results of ASTM C-39, ASTM C-672 and ASTM C-457 on shotcrete  ASTM C-39 Mix identification Initial fresh air (%) With AEA (5.20S)35T1SF-AM (5.25S)33L1SF-AM (5.27S)3OL1SF-AM (6.1S)35T3SF-AM (8.23S)25T1SF-CNF Without AEA (8.18S)41L1SF-AW (8.24S)41L1SF-AWF (8.25S)??L1SF-E (8.30S)54L1FA-W *  ASTM C-672  ASTM C-457  L* a* Final Air L a (pm) fresh air (%) 1 (jim) mm) 1 (mm) (%)  Loss of Visual weight rating (kglm2)  7.0 14.2 12.5 13.5 21.4  4.5 2.0 2.6 2.4 4.8  4.2 5.0 3.7 3.2 3.7  11.8 13.4 12.9 14.5 19.4  450 366 465 433 306  16.8 14.5 15.6 15.3 24.5  385 353 425 422 272  3.46 2.72 0.23 1.29 0.02  3 3 1 2 0  3.0 3.4 3.2 4.8  3.0 1.2 1.2 2.0  4.8 3.8 2.8 4.9  9.1 9.0 5.8 8.2  610 588 776 621  9.1 11.9 11.1 8.8  610 512 573  3.52 5.69 8.96 32.0**  3.5 3.5 5 5  606  without large air voids (see Appendix H for details) after 15 cycles  **  The mixes cast without air-entraining admixtures have very poor scaling resistance; their spacing factors are around 600 urn and they also have higher W/C ratios. For mixes cast with AEA, there is a direct relationship between the characteristics of the air void system and the initial air content before pumping and shooting. The scaling resistance is improved with the use of AEA as well as by a decrease in W/C. Even for air contents as high as 21%, it is difficult to produce spacing factors in the range of 230 .trn as required in the Canadian standard (CAN/CSA A23. 1-M90) for concrete. Figure 8.11 shows the effect of W/C on scaling resistance for the concretes cast with air  entraining adrnixtures. The scaling resistance is strongly affected by the W/C. A loss of weight of 1 kg/rn 2 is often used as a maximum limit for good scaling resistance. Only the shotcrete with W/C less than 0.30 satisfies this limit. However, the use of cement type 30 and a W/C of 0.35 is probably acceptable (1.29 kg/rn 2 weight loss). Thus, wet-mix shotcrete can be durable to deicer salt scaling if it possesses a low water-cement ratio. From past experience and from these results, it seems that, because of air stability problems (high spacing factor even when starting with a very high air content probably  177 because of the loss of small bubbles during pumping), a high initial air content is not in itself sufficient to protect the wet-mix shotcrete against scaling.  4  0  0.45  0.25 0.40 0.30 0.35 Water-cement ration (W/C)  Figure 8.11: Effect of water-cement ratio on scaling resistance (AEA mixes only) Unfortunately, no specimen from a mix with a W/C of 0.25 cast without AEA was available for testing (it is in any event difficult to shoot such mixes without AEA). Because of the excellent durability of the mix cast with AEA (mass of scaled off particules ), it might be possible that at a W/C of 0.25, air is not required for durability as 2 0.08 kg/rn is the case for some cast-in-place concretes of the same W/C.  178  SUMMARY AND CONCLUSIONS  During this study on the rheology of high performance shotcrete, a new apparatus (UBC rheometer) was developed to measure the rheological properties of the fresh shotcrete. The traditional method of using superplasticizers to produce workable low water-cement ratio mixes, and a new method consisting of using a high amount of air-entraining agent were used to cast several low water-cement ratio shotcrete mixes. A laboratory concrete pump was also developed to pump and/or shoot several of these mixes. A model based on rheological behavior was then developed to predict pumpabiity and shootabiity. The UBC rheometer is a new automatic apparatus which measures the rheological properties of fresh concrete or shotcrete. It measures the flow resistance and the torque viscosity, which describe the fundamental behavior of fresh concrete or shotcrete. This behavior is similar to the Bingham model. The rheological properties can be determined either by sampling the freshly mixed material or on the-in-place shotcrete by shooting directly into the rheometer sampling bowl. This apparatus was found to be precise and reliable. The values of the flow resistance and the torque viscosity are affected by the mix composition. It was observed that these properties, especially the flow resistance, change with time. To quantify this aging effect, a new parameter, the fresh concrete aging rate, was defined as the rate of change of flow resistance with time. This newly defined property is also affected by the mix composition, especially the cement type, and the type and dosage of superplasticizers. The laboratory concrete pump was used to analyze some aspects of pumping technology. The pressure bleed test, as described in Chapter 6, and the slump test cannot be used directly to predict the pumpability of high performance concrete mixes. However, is has been possible to verify that the pumpability and the pumping pressure of these mixes can be predicted by measuring the values of the flow resistance and the torque viscosity. The fresh concrete aging rate also affects the period of time during which a particular mix will remain pumpable. Stability problems related to bleeding and/or segregation were not observed on low water-cement ratio mixes containing sffica fume.  179 Important fundamental relationships were obtained between the rheological properties and the shootability which was defined and estimated in terms of the maximum build-up thickness. It was found that the build-up thickness is directly proportional to the value of the flow resistance of the in-place shotcrete. Compaction caused by the shooting process increases the in-place flow resistance proportionally. By knowing this last relationship (air loss during pumping and shooting), it is thus possible to predict the maximum build-up thickness by measuring the properties of the shotcrete before pumping. By measuring these properties at different times and by determining the value of the fresh concrete aging rate, it is also possible to estimate the minimum required waiting period between two successive applications. High performance shotcrete can be produced by reducing the water-cement ratio. This causes a reduction of workability which can be overcome in different ways. The most  common way, referred to as the “traditional method”, consists of using superplasticizers to bring the workability back to an acceptable level. The other way, referred to as the “concept of high initial air content”, consists of using a very high air content to improve the workability. In both cases the requirements of pumpability and shootability must be satisfied in order to allow one to apply the shotcrete. It was found that the above requirements can be expressed in terms of rheological properties. For pumpability, the flow resistance must not exceed a certain limit which decreases when the value of the viscosity increases. There is also a limit for torque viscosity below which not even a mix with no flow resistance can be pumped. For shootability, the higher the in-place flow resistance, the better the shootabiity. Mixes with no flow resistance do not remain in place after shooting. Practically, there is a minimum value of flow resistance below which the shooting operation is not efficient. The torque viscosity does not influence the build-up thickness. These requirements are in conflict in terms of flow resistance: pumpability requires a low flow resistance while shootability requires a high flow resistance. One can define a window for the values of the flow resistance within which the pumping and shooting operations can be carried out properly. The width of this window is affected by the torque viscosity: for high viscosity, the maximum allowed flow resistance is reduced (pumpability requirement). For this reason, the conflicting requirements of pumpability and shootabiity are more severe for mixes with high torque viscosity.  180 It was shown in this study, that low water-cement ratio mixes made according to the traditional method (use of superplasticizers only) are very viscous when fresh. These mixes must have less flow resistance (higher slump) in order to be pumped. Because of their high superplasticizer content, it is difficult to adjust their flow resistance: in the fluid state, small changes in the superplasticizer content produce major changes in flow resistance. The fresh concrete aging rate is reduced when high dosages of superplasticizers are used. Lowering the water-cement under 0.30 is not easy with this method unless special shooting methods are used, such as downward shooting or by using accelerators, although this last technique was not tested in this study. The optimum value for the fresh concrete aging rate was not determined. From the few results on practical mixes used on real jobsites, it seems that a high fresh concrete aging rate gives better results than a low one. More research is needed in this area. The concept of a temporary high initial air content is a good way to temporarily enhance the pumpability by reducing both the flow resistance and the torque viscosity. The shootability is also enhanced by the compaction during pumping and shooting which brings the flow resistance back to a level corresponding to the same concrete made without air. The common dilemma of the conflicting requirements for pumpabiity vs. shootability no longer exists with this concept, for two reasons: •  First, by reducing the torque viscosity, the use of air allows one to maintain a wider window for the acceptable values of the flow resistance, as opposed to the use of superplasticizers only.  •  Second, the compaction allows a recovery of the flow resistance after shooting. This particular effect also allows one to apply a thicker layer of shotcrete: after shooting, it is possible to obtain an in-place flow resistance which would have prevented pumping.  Special care must be taken by those who want to try this concept because in working with high air contents they will have to deal with a highly compressible material, as opposed to a non-air-entrained concrete with little compressibility. Some problems might be encountered when using this concept of temporary high air content. During this study, because of an inadequate gate control sequence, some pumping rate reductions were observed. Some types of pumping equipment will not be able to handle high air content mixtures or would have significantly reduced pumping rates even if the flow resistance of  181 the concrete were low (or if the slump were high). Thus special attention should be paid in selecting an appropriate type of pumping equipment for high air content mixtures. The concept of temporary high air content can be effectively used to produce high performance shotcrete: this allows one to produce a low water-cement ratio shotcrete with enhanced pumpability, strength, and durability. It would probably be an excellent way to avoid the use of accelerators, which have adverse effects both on crew health and on the concrete properties, especially durability. Many aspect of wet-mix shotcrete technology were studied and analyzed in this study. However, further studies should be carried out to understand more precisely some aspects of this technology. With respect to pumpability, it would be interesting to use different types of pumping equipment in order to develop a more comprehensive understanding of this process. The effect of rheological properties on pumping pressure, pumping rate, the compactionstiffening relationship, modification in the structure of the air void system, etc. should be looked at. Regarding shootability, because it is mostly related to the value of the flow resistance, it would be appropriate to develop some means of indirectly evaluating the flow resistance. It is reasonable to assume that there should be some relationship between a penetration test or similar in-situ static test and the flow resistance. With this tool, it would be easier to study other effects such as the use of accelerators on build-up thickness. Even if in general the hardened properties of wet-mix shotcrete are very similar to those of cast-in-place concrete of similar composition, it would be appropriate to study further those properties which are closely related to the air content or to the quality of the air void spacing factor, since only a few such results were presented in this thesis. In conclusion, the author hopes that this contribution will help to define the “science” of shotcrete as opposed to the traditional “art” of shotcrete.  182  Appendix A: Materials  This Appendix contains information on the material used to cast the concrete and the shotcrete mixes used in this study. The results of physical and chemical analysis carried out on five cements, as well as those carried out on the silica fume and the fly ash, are presented. Some information on the sand and the coarse aggregates used in the study is given, including the absorption, unit weight and aggregate gradings. Some information on the admixtures used in the study are also presented. Finally, the physical and chemical analysis on superplasticizers, carried out at the Université de Sherbrooke (Sherbrooke, Québec), are given.  183  Physical and Chemical analysis of Cements PHYSICAL TESTS Cement:  Li  L3  L5  Setting time (vicat: mm), initial:  i 13  90  i23  219  193  203  Fineness (Blame: m /kg): 2  422  532  4i8  Passing 45 p.m (%):  97.3  97.0  93.9  Autoclave expansion (%):  0.05  0.20  0.07  3 days:  25.2  31.0  26.6  7 days:  34.6  28 days:  43.2  final:  Strength (MPa) at  Ti  i58  -  448  509  -  -  32.2  -  -  -  43.0  48.3  6i  -  33.6  -  T3  44.8  -  CHEMICAL TESTS Cement:  Li  L3  L5  Ti  T3  Tricalcium silicate (C3S: %):  49  62  53  63  56  Dicalcium silicate (C2S: %):  23  ii  21  13  18  Tricalcium aluminate (C3A: %):  6  8  2  6  7  Tetracalcium silicate (C4AF: %):  9  7  13  ii  ii  CalciumOxide(CaO%):  63.4  63.9  6i.76  65.4  94.9  Silicon oxide (Si0 2 ):  21.1 5.2  20.3 21.5 4.54 3.27  21.1  21.0  Aluminiumoxide(Al302%): Iron oxide (Fe203 ): Magnesium oxide (MgO: %):  4.44  5.0  4.14  2.46  4.17  3.68  3.7  1.0  2.2  3.9  0.9  1.2  Sulphur trioxide (SO : %): 3  2.7  3.4  2.4  2.7  3.2  Loss on ignition (%):  1.23  2.13  1.79  1.61  0.7  0.49  0.48  0.55  0.38  0.48  Alkalies (Na20  +  0: %): 2 0.658 K  184  Physical and Chemical Analysis of Silica Fume (SF) and Fly Ash (FA) PHYSICAL TESTS (grading) Sieve (.tm)  Silica fume (% passing)  Fly ash (% passing)  100 100 99 98 96 93 92 90 88 83 78  97 93 87 74 60 34 26 17 8 1 0  100 70 50 30 20 10 8 6 4 2 1  CHEMICAL TESTS Silica fume Silicon oxide (Si0 2 %): Aluminium oxide (A1 2 %): 0 3 Titanium oxide (Ti0 2 %): Phosphorus oxide (P 5 %): 0 2 Iron oxide (Fe203 %): Calcium oxide (CaO %): Chromium oxide (Cr0 %): Magnesium oxide (MgO %): Sodium oxide (Na20 %): Potasium oxide (K 0 %): 2 Sulphur trioxide (SO 3 %): Loss on ignition (%):  91.7 0.07 0.01 0.04 0.05 0.09 0.05 0.23 0.12 0.60 0.28 6.55  Fly ash 49.7 23.8 3.36 0.93 5.30 8.51 0.43 2.07 4.33 0.51 0.57 0.58  185  Absorption, unit weigth and gradings of coarse and fine aggregates ABSORPTION sand:  1.1%  10 mm stone:  1.5 %  UNIT WEIGHT (S SD) sand:  2642 kg/rn 3  10 mm stone:  2697 kg/rn 3  GRADINGS  Passing (%) Sieve size U.S. (metric)  1/2 in. (12 mm) 3/8 in. (8 mm) No.4 (5 mm) No. 8 (2.5 mm) No.16(1.25mm) No. 30 (630 jim) No. 50 (315 jim) No. 100 (160 jim) No. 200 (74 jim)  Sand  10 mm stone  100 100 100 92 79 53 16 5 1  100 98 4 0 0 0 0 0 0  186  Admixtures information (from manufacturer) SUPERPLASTICIZER A Commercial name: Usual dosage: Chemical family: SUPERPLASTICIZER B  Rheobuild 1000 (Master builders) 650 to 1600 ml per 100 kg of cement cement dispersing agent  Commercial name: Usual dosage: Chemical family:  Pozzolith 440-N (Master builders) 650 to 1600 ml per 100 kg of cement cement dispersing agent  SUPERPLASTICIZER C Commercial name: Usual dosage: Chemical family:  Daracem 100 (W.R. Grace) 350 to 1250 ml per 100 kg of cement blend of sodium/potasium naphthalene sulphonate salts, lignosulphonate and hydroxycarboxylic acid salts concrete admixture  SUPERPLASTICIZER D Commercial name: Usual dosage: Chemical family:  WRDA-19 (W.R. Grace) 600 to 1250 ml per 100 kg of cement naphthalene sulphonate formaldehyde copolymer concrete admixture  SUPERPLASTICIZER E Commercial name: Usual dosage: Chemical family:  SPN (Master Builders) —400-1000 ml per 100 kg of cement concrete admixture  AIR-ENTRAINING AGENT M Commercial name: Usual dosage: Chemical family:  MBVR (Master Builders) 16 to 260 ml per 100 kg of cement vinsol resin  AIR-ENTRPJNING AGENT N Commercial name: Usual dosage: Chemical family:  DaRaVaiR (W.R. Grace) 47 to 188 ml per 100 kg of cement vinsol resin  WATER-REDUCER W Commercial name: Usual dosage: Chemical family:  Pozzolith 100-N (Master Builders) 200 to 325 ml per 100 kg of cement cement dispersing agent  187  Test results on admixture SUPERPLASTICIZER A Commercial name: % of solid: Density: Calcium oxide (CaO): Sodium oxide (Na20): Chemical family:  Rheobuild 1000 (Master builders) 44 % 1.19 5.0 0.0 naphthalene sulphonate  SUPERPLASTICIZER B Commercial name: %ofsolid: Density: Calcium oxide (CaO): Sodium oxide (Na20): Chemical family: SUPERPLASTICIZER C  Pozzolith 440-N (Master builders) 31% 1.15 0.0 % 4.6 % blend of naphthalene sulphonate and lignosuiphonate  Commercial name: % of solid: Density: Calcium oxide (CaO): Sodium oxide (Na20): Chemical family:  Daracem 100 (W.R. Grace) 40 % 1.2 0.0 % 5.4 % blend of naphthalene suiphonate and lignosuiphonate  SUPERPLASTICIZER D Commercial name: % of solid: Density: Calcium oxide (CaO): Sodium oxide (Na20): Chemical family:  WRDA-19 (W.R. Grace) 40 % 1.21 0.0 % 6.3 % naphthalene suiphonate  SUPERPLASTICIZER E Commercial name: % of solid: Density: Calcium oxide (CaO): Sodium oxide (Na20): Chemical family:  SPN (Master Builders) 43 % 1.2 0.0 % 5.0 % blend of naphthalene sulphonate and lignosulphonate  188  Appendix B: UBC Rheometer User Documentation  This Appendix presents the UBC Rheometer User Documentation. It has been prepared by: Kevin Campbell, Stefano Dondonibus, Jeff Freisen, Einar Halbig and Kevin Wong. I thank them for their work. The documentation does not contain the listings of the programs because their use has been licenced.  189  UBC Rheometer User Documentation  Developed by: Kevin Campbell Stefano Donadonibus Jeff Friesen Einar Halbig Kevin Wong  190  — Introduction! Pu mose  The rheometer is a computer-controlled device that tests the rheologi cal properties of concrete (specifically shotcrete). This machine’s design is based on a modified Mark III’ rheoineter. This manual describes the hardware components, calibration proce dure, and operation and set-up of the computer program that controls the rheometer. Theory and specifics of the actual control and feed-back electronics are not included in this manual, nor is a discussion of rheology or such properties of concrete. The intended audience of this documentation is the user of the rheometer.  Conventions  Computer-displayed material (screens, pmmpts, etc.) are displayed intheCourier typeface (what you are reading now). Responses that you are to type are shown in Bold Courier. The following keyboard conventions are observed:  Symbol <Eec> <Enter> <Space> cCntrl> <Break>  Assumptions  Hardware ‘.J’.J II IIJJI Ii II  MeaninfKev Escape key Enter or Return key Space bar Control key (pressed in conjunction with another key) Break key  The reader is assumed to be familiar with fundamental DOS com mands and concepts (directories, simple batch files, etc.).  A schematic of the rheometer is presented in Figure 2.1. An IBM PC computer with a PCL-812PG A/D and D/A (analogue-to-digital and digital-to-analogue) converter card controls motor (impeller) speed and data acquisition in the rheometer. Average speeds, torques, and other relevant data are stored in a data file which can be imported into a spreadsheet program. (please see Test Data Output). Motor control circuitry is contained in a grey box above the computer cabinet. • Be sure that the powerswitch is off whenever a test is not being run. • Ensure thai the auto/manual switch is in not in the centre position, as this will cause the motor to run at full speed.  191  The auto/manual switch should be at auto, and the speed dial should remain at the zero position during a test (the dial may be used for rotating the torque beam for calibration procedures with the auto/manual switch set to manual). Please refer to Calibration Procedure on page 5. The Motor and Speed Sensing The impeller is driven by a ooe half horsepower DC motor to which a tachometer is attached so that accurate motor speeds may be read into thecomputer. ThereisaóO:lreduceratthispointsoastoprovide smoother and more efficient motor use and speed change. This provides an excellent method of measuring speeds ranging from zero to inputted maximum speed and back to zero.  ‘‘-“ometeil c mot{ HP  11/2  [  Control penn  I  p SlIp r....,  p  computer 1511 PC AT 286 WI PCI-B 12P5 cerd Sm efl beem  G.er 16 D  6OP  Impeller  Figure 2.1  -  Schematic diagram of the rheometer  //  192  Drive Gearing and Torque Measurement At this point the shalt travels down to the torque/beam device. There is a 1:1 gear ratio that drives the impeller by way of the torque/beam. The beam then actually turns the impeller shaft and its deflection, caused by forcing the impeller through the concrete, is measured by 4 strain gauges. The signal from the gauges is amplified 470 times prior to being transferred to the computer via a slip ring situated at the top of the shaft. The Impeller As the previous MKIII rheometer this new rheometer uses an H shaped impeller that moves in planetary motion thereby assuring a different path through the concrete on every rotation. The gears leading to the impeller are a 16DP20 gear at the impeller shaft and a 16DP45 gear at the driving shaft. The Bucket The 19.2 L bucket is placed on a platform that can be raised by crank into the desired testing position. The platform is counter weighted and the safety pin should be placed in the stop hole while the bucket is off the platform and also while the test is being performed. The impeller should be removed whenever loading or unloading the bucket, and for cleaning, so as to avoid damaging the sensing equipment.  Program Operation  .  .  The Selection Menu screen suiular to Figure 3.1 will appear when the computer is turned on. You may: 1. 2. 3. 4.  Press 1 to run the calibration program, Press2torunarheologytest, Press <EBC> to leave the menu and return to the DOS operating system, Choose any other listed option in a similar manner.  The Selection Menu can also be invoked from the DOS prompt by typing the following (from any directory): RHEOLOGY <Enter>  Note thai when option 2 (test program) is selected, a DOS batchfile will set the current directory to CARHEOM..PARAM, and then run the program. This has the effect of telling the program to expect to find any specified parameter files (explained below) in the C:\RHEOM\PARAM directory. The program will expect to fmd parameter files in whatever directory it is run from  193  Selection Menu  Please press the number of your choice  1 2 3 4  -  -  -  -  EeC  Calibrate Run Test Directory Map (Change Directory) Copy/Move/Delete Files -  Exit menu to DOS  Figure 3.1 Opening menu screen, displayed on start-up of computer, or after running from DOS. -  Parameter files may be used as “templates” for tests. A parameter file is a plain text file created by the user (in any text editor) that contains al the test information required from the user by the computer for a single test. The information, or parameters, are read in by the computer, and displayed as “defaults,” or initial values. Repeated (identical or similar) tests on different shotcrete mixes can be run more easily by creating one simple parameter file that is used for all mixes. Figure 2 shows the contents of a typical parameter file (parameter meanings are explained later). Please observe the following rules when creating parameter files: • • •  A parameter file must end with a .REO extension The files must be located in the directory from which the program is run (typically C:\RHEOM\PARAM) The file must begin with a mix description: one line of text  only, no commas! • •  The values are all positive integers, and must each be entered on a separate line with no commas Parameters must be entered in the following order: Maximum Speed Speed Increment Speed Decrement Interval Between Increments/Decrements Number of Samples at Each Increment/Decrement  For information on how to use a parameter file, please refer to the Test Program Operation on page 6.  Parameter Files  194  To run the test program. choose 1 (Run Test) from the Selection Menu. Figure 3.4 shows the opening test program screen.  Test Program Operation  If you have created a parameter file for this test; type the filename at prompt 1 shown in Figure 3.4. Do not include the .REO extension in the name. A parameter file named TEST1.REO was specified in this example.  RHEOLOGY  -  1. Parameter filename (<Enter> for defaults)  Figure 3.4  -  V2.l  Rheometer Test Program  Opening screen of Test Program  If you do nothave a parameter file for this test, press <Enter> to use the program default parameter values.  Default Values Each prompt is presented in sequence as responses are provided, until the screen appears as in Figure 3.5. Each prompt requests a single value, and each prompt displays the default value in angle brackets ( c..>). To use the specified default, just press <Enter> at the prompt. To use a value different from the default, type a new value, and press <Enter> Parameter Prompts Once parameters have been entered, they cannot be corrected, in stead, the user must press <Cntrl> C and restart the test program. A test may be halted at any time by pressing <Fl>. Prompt 2: Mix Identification Code This U) code is mandatory there is no default value. This code will be used as the output file name and must therefore conform to DOS filename requirements. Do not add a file extension. The extension .DAT will be added to the filename automatically. Output files are written into the directory C:RIJEOM by defaulL To change this default directory to another, the program must be edited and re-compiled. -  :  TEST1  195  Type 10 cement with plasticizer 2500 500 25 S 70  Figure 2 Contents of a typical parameter file. -  Calibration Procedure  The Calibration Program allows for calibration (zeroing) of the torque-reading system. Calibration may only be required at the begin ning of the test session, and is generally not required after each test. The need for manual calibration may be eliminated in future updates of the Test Program. To Calibrate the system: 1. Run the Calibrate Program (Selection Menu option 1) 2. Enter 0 for the speed 3. Enter a maximum value of torque above O(say 300) 4. Slightly rotate the very small brass screw on the white ceramic component on the underside of the shroud covering the sensing electronics (near the metal beam with strain gauges attached). Watch the torque reading on the computer screen rotate the screw in the direction that gets the reading as close to zero as possible. One direction will make the reading more negative; the other will make it more positive. Refer to Figure 3.3 for location ofthe calibration screw. 5.. Once a value of zero (or very close to it) has been set, press <Space> to return to the Selection Menu. -  Figure 3.3 Location of calibration screw (barely visible on white ceramic block). A small jewelers screwdriver is required for the calibration.  196  RHEOLOGY  -  Rheometer Test Program  2. Enter mix identification code  V2.1  (for output filename) :MZX4B  Current mix description :Test la use on low air-content shotcrete 3. New description or <Enter> 4. Enter maximum speed (max. 4096) < 2200 > 5. Enter speed increment < 175 > :150 6. Enter speed decrement < 50 > 7. Enter increment interval < 15 > 8. Enter number of samples at each speed interval (Max. < 50 100 ) -  Figure 3.5  -  >  :75  Final screen showing all prompts, and some modified default values. The defaults were taken from a parameter file named TEST1 .REO  Prompt 3: Mix Description In this example (Figure 3.5), a mix description was provided in the parameter file TEST 1 .REO. The user is given the option of changing the description, or of leaving it as is (default) by pressing <Enter>. It is important that no commas be used in the mix description. Prompt 4: MaxImum Speed Enter this value as a positive integer. This value is the maximum speed value that may be sent to the drive motor controller. This number is in “internal units”, and is not the same as the speed read from the speed sensors. The maximum speed value actually sent to the motor controller may be less than this number. If increments are 300 speed units each, and the maximum speed is set to 1000, the maximum speed value sent will be 900 (3 x 300 = 900), and not 1000. Prompt 5: Speed Increment This positive integer represents the number ofinternal units the motor speed is to be increased by at each interval. Prompt 6: Speed Decrement Analogous to Speed Increment above.  197  Prompt 7: Increment Interval A positive integer representing the amount of time (1 unit = 1/l8ths ofa second) after the speed has been increased but before the samples are taken. This time period allows the rotating parts to overcome inertial resistances that would affect the sample data. Prompt 8: Number of Saipples The number of samples taken (and averaged) at each speed setting are set by this positive integer. Individual samples are separated by a fixed (very short) time period.  Test data axe displayed as the test progresses (Figure 3.6). Feed represents the internal speed value sent to the motor controller. Speed represents the speed value read from the rheometer’s speed sensor, and Torque is the instantaneous (not averaged) torque value read from the strain gauges and amplifier circuit. The value in parentheses to the right of the Torque reading is the maximum torque value read thus far in the test.  Test Data  The rheometer has a built-in over-torquing safeguard: the system will shut down ifthetorqueapproachesa value that would causepkzs& deformation of the sensing beam.  RHEOLOGY  -  V2.l  Rheometer Test Program  Test Mix Identification  : Test la  Name of output data file Maximum speed Speed increment Speed decrement Increment interval Samples per interval  : : : : : :  -  use on low air-content shotcrete  MIX4B.DAT 2200 150 50 15 75  : 150 Feed Speed : 76 Torque: 127  Figure 3.6  -  ( 235  The screen as it appears during a typical test run. Entered or default parameters are displayed in the top half of the screen, while current test data are displayed in the lower hail.  198  Test Data Output  Test data are written into a tab-delimited (e.g. data values are separated by tab characters) data file in the directoxy C:\RHEOM. The file name is the Mix Identification Code (see prompt 2 information) with a DAT extension appended to it. Figure 3.7 shows a typical output data file. The data are written in the order ofFeed, Torque, Speed. These data may be easily imported into a spreadsheet for analysis. Each data file is also time- and date-stamped.  Timestamp : 03-21-1993 15:38:52 Mix Identification : Test la Maximum Speed: 2200 Speed Increment : 175 Speed Decrement : 50 Increment Interval : 15 Number of Samples : 50 0 0 0 175 .125 12 350 .138 20 525 .150 47 700 60 .250 875 73 .299 1050 .356 85 1225 .385 94  250 200 150 100 50 0  .120 .116 .108 .095 .099 .045  Figure 3.7  Performing A Test  .  17 15 10 7 3 0  A typical output (.DAT) data file contents. The data files are easily imported into a spreadsheet for analysis. Data are written in the oiler Feed, Torque, Speed.  This section assumes the reader is familiar with the Test Program operation (see Program Operat.ion, Section 3). To perform a rheology test: 1.  Turn on the computer and ensure power switch for the motor and controls is tamed off and the auto/manual switch is on auto.  2.  Ensure the rheometer is calibrated (see Calibration Proce dure in Section 3).  199  Important: the motor power switch should be off whenever the rheometer is not being calibrated ora test is not being run. 3.  With the motor power turned off, remove the impeller (this is important to prevent damaging the sensing beam while installing or removing the testing bucket).  4.  Ensure the bucket elevator pin is installed to prevent the bucket elevatioh platform from rising when the bucket is removed.  5.  Remove the test bucket, and fill with shotcrete to approxi mately 8 inches (203 mm), thus ensuring that the impeller is fully submerged.  6.  Place the test bucket on the elevation platform.  7.  Re-install the impeller, making sure it “clicks” into place (the large key on the end of the impeller shaft should take the torque, not the small holding screw on the shaft sleeve).  8.  Remove the elevator pin, raise the platform and bucket using the hand crank, and re-install the elevator pin. The impeller should be submerged just below the surface of the shotcrete.  9.  Turn the motor power on.  10. Run the Test Program (see Test Program Operation on page 6). Important: do not run too many tests on a single bucket of shotcrete the impeller does not agitate the mix all the way to the bottom of the bucket, and mix hardening results. —  11. Once the test has completed, shut off the power to the motor. 12. Remove the elevator pin, lower the elevator platform and bucket, and replace the pin. 13. Remove the impeller, the bucket, and wash everything down.  200  Appendix C: Rheometer results (small testing program) This appendix presents the results obtained during the development of the UBC rheometer. These tests were carried out with the first torque measuring beam (4 mm thick) and with the impeller in the normal position (see Figure 5.1 la). The compositions of all mixes tested in this small program are given in Table 5.2. T50.38  (2500,200,200,70,5,5)  1,2 1 0,8 0,6 0,4 0,2 0 5  I  Torque (Nm)  T50.38 1,2 1 0,8 0,6 0,4 0,2 0  (3000,100,100,50,5,5)  L___ -i.——-i II’  ‘.d  _. _._  0  2  3  Torque (Nm)  4  5  9  £  V  nboi  (uIN)  Z  1  0 0 z’0 V’0 9’0  —.—.  .  . —.—..  ..  — .  I z’T  i•  rD  (‘‘o9’ooc’oog’ooo) .si (Uif4J)  9  1 ,nbio  V  Z  1  0 0  .—  .II.  B  T1 II• h”  V’0 9’0 x’0  -.——-  .  .  .. r.i  •..  . I. I —I.  I  ‘‘  •.;.  z’I  (‘s’os’ooI’oo1’ooo) xsi  9  £  I’  nbioi  (wN)  Z  1  0  —I I  I  0 z’o I”O 9’0 8’o I z’T  —I—  —.—  . —I— .  —•—  .  -._  I  . —.—  •.  ;‘  (‘‘oL’ooz’ooz’oosz)  B ‘  .  —  .si  •1 0z  202  FS.38  11  (3000,500,500,60,5,5)  1,2 1  I.  .  10  (I ‘J,—  ..  1L ,-  0, 4 -  A,,  .  .  -  0 0  1  2  3  4  5  6  Torque (Nm)  T10.43a  (2500,50,50,5,5,10)  1,  110, 0,  Torque (Nm)  T10.43a (2500,50,50,5,5,10) all dots 1, 0, 0, 0, 0, 0  1  2  3  4  Torque (Nm)  5  6  203  T10.43a  (4000,300,300,30,5,3)  1,2 U  U  0,8  —  —  —  —  -.—  •U  —  —.—  U .  —  —  U  —i—  —  —  U  U  —n  —  —  U I—  0  •—  U-.—  —  2  1  3  —  4  5  6  —  7  8  Torque (Nm)  T10.48  (2500,200,20,70,5,5)  1,2 U U.  .  0,8 0,6 v’.-.- 0,4 0,2 E — 0  II  U. U—.  .  U U U— —U U U —U——. U U  .  .  -I. I  .  !  0  U  U-  1  2  3  4  5  Torque (Nm)  T10.48  (3000,100,100,50,5,5)  1,2 I .-  0,8  i[•  I. L!  _______ 41 .__i ii .  T  .  0  —IU.UU  1  2  3  Torque (Nm)  4  5  204  T10.48 1,2 1 0,8 0,6 0,4 0,2 0  (300,500,500,60,5,5)  . .  ..  -I.  I. —I.____________  0  1  2  3  4  5  Torque (Nm)  T10.43b  1 0,8 0,6 0,4 0,2 0  (2500,200,200,70,5,5)  •.  -  jIL  .  .  ..  —.—.—  ,  .  .  —. .  ,  0  .  -.._____________  1  2  3  4  5  Torque (Nm)  T10.43b 1,2 1 0,8 • 0,6 0,4 0,2 E 0  (3000,100,100,50,5,5)  i!’ .— .!. —iu.--  :-i .  iI !  —  •. •re  iI  0  1  2  3  Torque (Nm)  4  5  205  T1O.43b  1’  1,2 1 0,8 0,6 0,4 0,2 0  (3000,500,500,560,5,5)  . I I I.  I U •1—U—  0  1  2  3  4  5  Torque (Nm)  T10.43c 70 60 50 40 30 20 10 0. 0  (2500,200,200,70,5,5)  ‘Ii U. —U— —. I I  .  .  U  .  II  -.  III.  •  I  i  I  II  2  3  4  5  Torque (Nm)  T10.43c  1’  0  1  (3000,100,100,50,5,5)  2  3  Torque (Nm)  4  5  (uIN)  nboi  S  1  0 0 z’o v’o 9’0 8’O I  I•  .—  .—  I Lj  L!  B —  nbioi Z  1  0  U—  •U  LU  —  qrsi  (oz’i’s’os’os’oosz)  (uiK)  I’ U  0 z’o 1’ ‘0 ‘0  —  -  !T  .;  —  B —  :ia .i  ——-U— .._J I.  I z’I  (D  (6T’T’oI’os’oo’ooSz)  901  207  Appendix D: Pumping and shooting equipment This appendix presents some drawings of the laboratory concrete pump. Other details were given in section 6.1. The pump was designed by Conseption GSR (near Quebec City).  00  1  313N3 1108 £L _9/1O S310H 9  0 S  (no  Lt 0  C  III  Yx 1  6 H0(S 111/16’ CN 6’ BOlT CIQ.E  1.1W  w 6\f  Y 1 i  x  2 H1ES l/4—20NC X 1/2  SEC11ON A —A 207/16’  S  \  I /  FOR ORING 2—258  4 A  -  AFTER 3.DINC AND ACHDINc RE—COVER ThE USI Cf 1NE TUBE 1H 0.010’ TIIO(JIESS OF HAR]) CHROUE.  091/2’  /  —  6 HOLES 011/16’ 8’ BOLT CIRCLE  I  /  06.250’  0.18  /o.in’  /  /  1  --  —  _LLri  __  3/8’V  SEC11OMA—A  W= 19 7/8’ M= 19.750  -._-——_-——_---—__.g.—---_____——___—.——_— .•1 __T  --  TWOOPENINGS 1’wD1Nx7o\  -.  -..  \  \  2  ____  1 1/2’  —__  —  __  212  :3.  ri?.  R3/8’ TVP. 1/32’ X 45 rrP.  II II II -  I I II I I  04  0361’ •— O363.  10• Ti?.  3/V  13/4’ 3 3/8’ 4.  213  Appendix E: Mix composition This appendix presents the mix compositions and the results of some usual tests (Slump at 15 mm, fresh air content and the compressive strength). The compressive strengths were measured on three cylinders or cores for the shotcrete. The results of other tests carried out on these mixes are presented in Chapters 6, 7 and 8 (including Figure 5.21).  214  Ci  C) ‘.0  00  I  I  I  I  I -  c  in  N  ‘.0 00  ‘.6 ‘.0 ‘.0  ‘  oq  q  r’0  ‘0 ‘.0 ‘.0 in  -  -  00  t-  r-  a  —  C  in  r  N  ‘.0 N N  CflC  N  C)  •  00 C C  C) C  “  ‘—  0 in  ‘0 N  —  ‘ ‘n  cn  000-00 ‘.6 c Ifl 00  N C) in C) in in fl C’ in  ‘  in ‘.0 ‘.0  C1)  in  CCC) C’1  rC)n%CC) -4  —‘  E E  C)  in in  -4  ,in  C)  ‘  -  in in C)C) ‘ N r  00  ‘.0 in in  C’  < S  Cr) -4  •  -4  Cr) Cr) C) -4 -4  C) -4  -4  -4  -4  -4  ©OininC)©C) 0 Cr) in in ‘-‘ ‘.000 -4  c’.  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N N C cI  1— 0 C CInInInnNrt-’ —  I  ci  —  —  C9  —  “  —  —  —  —  —  00 C 0%  —  s  N—  —  .  ) .-  cP1  -  E  —  —  ‘  —  —  ;-,_ ini-  0%  —  t—  —  —  —  —  N00C% C j- in in r in 1- In  ir’  ‘  -  C1) -  C — in  ij-  -  t t  i  ,  —  —  —  —  —  —  —  —  N ‘.o ci  o  —  —  —  —  —  —  —  —  r’.i  InIn0%00’.0- 0%c C0%000% N N00c%O%—’ N - C C — cl 00 C C ‘t ‘j- ‘o C ‘,c N in In C’ C’ C C’ C’ N N N CI fl l% ‘.D \ ‘— -  in —  —  —  —  —  —  —  —  —  —  —  —  —  —  —  —  c  .—  —  —  —  —  —  —  —  —  —  —  —  —  —  —  —  —  —  —  —  —  —  NCnN0000000%CC00c’It in1InInIn-InInI-’It’It InInInIn’It  ‘t’It1 In’1-InIn  ‘.0 00 ‘.0 N  ‘It c% ‘It  Q  in ‘n  —  in  I  —  In ‘n  —  Cc%C .-  00 C’ In  00 00 00 % In C1% — ‘It — in N ‘.0 ‘.0 C 0% ‘It C% N 0% C 00 C — C00InN0%0 00%1_cn000%0%00In In00 — C C C C—’  IJ ,  N Cfl in  %C D ‘C In In C4 cl CI in ‘J- C \CI ‘.0 00 CS — j- in in 0% In ‘.0 00 C CP 00 ‘.0 in 00 C 00 CI C, In N 0% ‘.0 N C% In In In — N N ‘j ‘.0 In In ‘.0 ‘.0 — 00N\0—N00’.0NN’%’.00000\0In00O00%f%NNN000%0% f% 1j ‘Ij (% ‘lj ‘j C% ‘1 ‘t ‘i  ‘  P1  flInIn  c  in — In c’1 0% N N C C c a ‘It N c% 0% C’ C’ ‘It  It  c%  N -  ‘j-  0%  ‘.6  ‘It  It  .—  —  —  In  —  c’%  C N 0% 00  C In — N N C In 0% 00 0% C —  c%  -  -  ‘It  ‘It  ‘:1‘It ‘It  ZZ i  I  :  II  I  I  C C  <  .  ‘6’’P’<  0%<—’.C’.C\0’.0\00000000%0%0%n% N000000000000000000000000000000000000000000 00000000000000000000 -, - ‘— ‘— s__ ‘.- , - - ‘— ‘-, ‘ - s__ ‘,  ,e  %  %  %.‘  %‘  217  000 ‘D Q 00  00  N  ,  N 0 fl  -  ‘n  -  .-  ir  .-  -i  C  “C fl C) C C  -  ,-  ‘D  N  r  N  ó  Voqo %-  .  C  00Q00000N00CflC 00NN  ‘Z’  —‘  ()  c  V000 l•) N 0  kn0 N  —  —  —  —  —  -  ag-  —  —  —  —  ‘-  —  Cl)  c  -  j-  j-  fl I  I  —  —  n  Cr1  cq.1  0  0  -  0  N N “C “C N N N N  —  —  0  —  N  —  —  ‘-‘  E  Cil  in —  0  -  ‘.C%CC  lfl  )  E  Cl)  0 00 N in  ef  ‘j  “CJ  0’  ‘  in ‘Cj  ‘  ‘  Cr)  in  Cr)  Cr)  Cr)  -  ‘  ‘  Cl)  E ‘J ,  ON00inin”CC f)000N 00 N N 00 0 C 0 N N ‘Ct “C 00 —  —  —  —  —  —  —  —  —  C-  N N C N N Cr)  C  —  0  0  —  .-i  .-  ‘  N  —  C-  —  —  .  — —  —  — .  Cr)  —  in in 00 00 00  —  — —  N  —  C’ Cr) N  —  C N C C’ 0 —i ‘ . .— N  ‘  ‘  ‘  in  ccodo 00 Cr) Cr) If) in in in Cr) Cr) ‘Ct ‘Ct ‘Ct in  -  —  00 C)  .— N - 00 N 0 N ‘-i 0 00 00 0 “C ) Cr) in N N in j- 00 C) C) in in Cr) N ‘1 ‘Ct ‘Ct c’ n  1)  —  “C N N  N Cr) “C in 00 ‘Ct - —‘ N  s  00 ‘I  C  .  —  —  —  —  —  Cfl N ,%  (i’)  ‘Ct  ‘  ‘I’ Cr) ‘Ct e—• C-. c-. Cr) ,—. ‘—S  —  : <  .-  ‘‘  S  ‘—‘  ‘—‘  —  —  —  —  —  —  —  —  C,)  Cl)  -‘  inCr)N0000 NNNNNNNNNNCr I  00  I  00 ‘  I  00  I  00 ‘  I  00  I  00  I  00  I  00  I  00 ‘  I  00  I  00 \  I  00  I  00  I  00  *  218  Appendix F: Pressure bleed test results This appendix presents the results of the pressure bleed tests carried on some mixes. The description of the apparatus and the test procedures are presented in Chapter 6. The analysis of these results is also presented in Chapter 6.  Pressure bleed test (7.20A)3OL1SF-AF  100. Qa. II  -.  E E  “U.  40. 20. 0. 0  20  40  60  80  100  120  140  Time (mm)  Pressure bleed test (7.23E)33L1SF-CF  -  .  E  60  80  Time (mm)  UO  120  140  219  Pressure bleed test (7.26A)3OL1SF-CF 100  I  I  60  80  60 .  E  -.  f-I 0  20  40  100 120  140  Time (mm)  Pressure bleed test (7.27A)3OT1SF-AM  I  0  20  40  60  80  100 120  140  Time (mm)  Pressure bleed test (7.29A)3OT1SF-AM  150 120  E E  90 60 30  -.  0 0  20  40  60  80  Time (mm)  100 120  140  220  Pressure bleed test (8.3A)3OT1SF-DN ‘‘  15 120  E E  90 60 3 20  40  60 Time (mm)  Pressure bleed test (8.5A)3OT1SF-D 150  LGD° 7  120  E E  90 60 30 0 0  20  40  60  80  100  120  140  Time (mm)  Pressure bleed test (8.11A)3OT1SF-D 150 120 E  E  90 60 30  -.  0 0  20  40  60  80  Time (mm)  100  120  140  221  Pressure bleed test (8.16A)25T1SF-CF ‘  n.  .  E  20  0  40  60  80  100  120  140  Time (mm)  Pressure bleed test (8.19A)25T1SF- C  E E  20  0  40  60  80  100  120  140  Time (mm)  Pressure bleed test (8.23A)25T1SFCNF 150 120 90 60 30 0 0  20  40  60  80  Time (mm)  100 120 140  222  Pressure bleed test (8.24T)41L1SFAWF  -.  15 120 90 60 30 0 20  0  40  60  80  100 120 140  Time (mm)  Pressure bleed test (8.25T)??L1SF-E ‘  ,n  E ‘  -D-  2’ I  150 100  1  0  20  40  60  80  Time (mm)  100  120  140  223  Appendix G: Rheometer results This appendix presents the results of the rheometer tests carried out on the mixes presented in Appendix E. The description of the apparatus and the test procedure are presented in Chapter 5. These tests were carried out with the second torque measuring beam (7 mm thick) with the impeller in the deep position (see Figure 5.11 a). Results in grey were obtained on pumped concrete while the results in black were obtained on the shotcrete (projected directly into the rheometer sampling bowl). These test results are discussed throughout Chapters 6, 7 and 8. (5.18A)38T1SF-BMF  L. C.  E  1.2 1 0.8 0.6 0.4 0.2 0  El 11 mm  o  26 mm  A 44 mm  o 62 mm 0  I  I  1  2  I  —  3  4  5  —  6  7  Torque (Nm)  (5.19A)38T1SF-AMF 1.2 1  p  El 20 mm O 36 mm  ‘ft  A 50 mm  10 U.L‘  0.6 0.” 0.2 0  o 65 mm  V  —  :  0  1  2  3  Torque (Nm)  4  112 miii  5  224  (5.20A)35T1SF-AMF 1.2 1 0.8 0.6 0.4 0.2 0 0  1  2  3  4  5  4  5  Torque (Nm)  (5.25A)33L1SF-AM 1.2 1 0.8 — —  C?  E  —  0.6 0.4 0.2 0 0  1  2  3  Torque (Nm)  (5.27A)3OL1SF-AM  C? C?  — —  C?  1.2 1 0.8  17 mm  O 32 mm ..  A 46 mm  0.6 0.4  r  0.2 0  o 68 mm —  0  1  2  3  Torque (Nm)  4  92 mm  5  225  (5.31A)33T3SF-AM  ii  1.2 1 0.8 0.6 0.4 0.2 0 0  1  2  3  4  5  Torque (Nm)  (5.3 1E)35T3SF-AM 1.2  rj — — ?  E  rM  1 0.8  H 10 mm  0.6  0 new 15 mm  0.4 0.2  H3Omin  0 0  1  2  3  4  5  Torque (Nm)  (6.1A)35T3SF-AM 15 mm  1.2 1 0.8  0  I:’ 1  0 27 mm ‘  49 mm  o 70 mm -  2  3  Torque (Nm)  100 mm  X 120 mm  226  (6.1S)35T3SF-AM • 49 mm  1.2  .  • 70 mm  —  0.8 0.6 0.4  -•&& .j1.:A  100 mm  A  • 115 mm  —  0  1  2  3  4  5  Torque (Nm) (6.1E)35T3SF-AM  ;‘  —  1.2 1 0.8 0.6 0.4  I] 35 mm O 45 mm  I  0  56 mm  -  0  1  2  3  4  5  Torque (Nm)  (6.2E)33L1SF-D  0 27 mm  1.2 1 0.8  o  38 mm 50 mm  0.6 0.4  o 60 mm  0.2 0  —  75 mm  —D  0  1  2  3  Torque (Nm)  4  X 90 mm  227  (6.2F)33L1SF-B 1 30 mm  1.2  o  jII  0.‘ 0.6  A 50 mm  o 60 mm  A  v’— n.’.  E  —  40 mm  0.2 0  75 mm  -  0  12  3  4  X 90 mm  Torque (Nm)  (6.7E)33L1SF-A  El 20 mm  1,2  O 30 mm  0,8  A40  mm  I,  o 60 mm —  1434  75 mm  X 90 mm  Torque (Nm)  D 20 mm  (6.7F)33L1SF-C  o  1,2 1  H E  —  30 mm  A 40 mm  0,8 0,6 0,4 0,2 0  o -  mm 60 mm  X 75 mm  0  1  2 Torque (Nm)  4 + 90 mm  228  (6.8E)27T30SF-D D 30 mm  1.2 1  o 40 mm  A  E  A 50 mm  o 60 mm 75 mm  —  —  0xc  0  1  2  3  4  X 90 mm  Torque (Nm)  (6.15A)33T1SF-AMF 1.2  -  1. rj  c  :__________  0 30 mm  0.8 0.6  —  a 20 mm —  A 40 mm  0.4  -__-__  0.2 00  o 50 mm 2  1  4  3  -0-  )A  J-!.Q0  A__  5  6  7  Torque (Nm)  (6. 16A)27T3SF-AM  a 20 mm  1.2  O 30 mm  1  I,.  LL.  0.8  ii  A 40 mm  o 50 mm  0.6 0.4  I —5--— ‘• -I  0.2  -  0  W  — -  f%_  I  X 75 mm  —_‘-I-  0  1  60 mm  LAP.’4  2  3  Torque (Nm)  4  + 90 mm  229  (6.21E)25L5SF-A 0 15  1.2 1  O 30  0.8 0.6  45  o 60  0.4 0.2  -  75  mm  mm  mm  L  c  %)C  mm  mm  o_  0  X 90  0  2  mm  3  4  5  Torque (Nm)  (6.21F)25L1SF-A 1.2 1 0.8 —  0.6 0.4 0.2 0 0  0 15  mm  O 30  mm  45  mm  -  f  -  -  -  o 60  1 —g  mm  I  -  -  -  75  — ,,  mm  —X  -  X90  i  2  miii  3  4  5  Torque (Nm)  (6.21G)25L3SF-A 1.2 1 0.8 — —  E —  4!_ ___  0.6 0.4 0.2 0  D 15  miii  0 30  mm  A 45  mm  o 60  mm  75  mm  X 90  mm  LI 1 r-  x-x 0  1  ) 2  3  Torque (Nm)  4  —  230  (6.21H)25JMSF-A 1.2 1  El 15 mm  0.8 0.6  0 30 mm A 45 mm  0.4 o 60 mm  0.2 0  -  0  1  2  3  4  75 mm  5  Torque (Nm)  (6.23A)25L5SF-A 1.2  El i5 mm 0 30 mm  1  L 0.8  A 45 mm  0.6  o  mm  -  60 mm  0.4  New  0.2 X 75 mm  0 0  1  2  3  + 90 mm  Torque (Nm)  (6.24A)25L1SF-C 1.2 1 0.8 — —  E  i:i i mm  0.6 0.4 0.2 0 0  J___ 1  2  3  Torque (Nm)  4  0 30 mm A 45 mm  o 60 mm -  90 mm  231  (6.24B)25L1SF-C  1:  1.2. 1 0.8 0.6  15 mm 0 30 mm A 45 mm  o 60 mm  0.4  -  0.2  0 —ci-jO 0 1  2  3  4  75 mm  X 90 mm  Torque (Nm)  (6.24C)25L3SF-C 1.2  15 mm  1  0 30 mm  x  0.8 0.6  A 45 mm  j’  .-ri’-’ o 60 mm  0.4 0.2  —  0 0  1  2  3  4  75 mm  X 90 mm  Torque (Nm)  (6.30)25L3SF-AF 1.2 1 0.8 0.6 0.4 0.2 0 0  1  2  3  Torque (Nm)  4  5  232  (7.6AS)25L3SF-AF 1.2 1 0.8 0.6 0.4 0.2 0 0  1  2  3  4  5  6  7  8  9  10  Torque (Nm)  (7.8A)2513SF-AF 1.2 1 0.8 0.6 0.4 0.2 0 Torque (Nm)  (7-8S)25L3SF-AF • 35 mm  1.2 • 48 mm  1 0.8 0.6  A  65 mm  0.4  • 80 mm  0.2  • 95 mm  0 0  1  2  3  Torque (Nm)  4  5  -  110 mm  233  (7.12APS)30L3S-AF castl5  1.2  mm  O cast 30 mm  1 0.8  • pump 30 mm  0.6 A pump 45 mm  0.4 0.2 0  shot 45 mill  o  i  2  3  4  5  6  7  8  • shot 60 mm  Torque (Nm)  (7.19APS)3OL3CF-AF  D Cast 15  1.2 1  I’  mill  0 Cast 30 mm  A Pump 45 mill  0.8 0.6 0.4 0.2  0 Pump 75  mm  Pump 80 mm  0  • Shot 90 mm  0  1  2  3  4  5  6  7  8  Torque (Nm)  (7.20A)3OL1SF-AF 1.2 1  IM  cast 20 mill  0.8  0 Cast  0.6 0.4  30 mm  A Cast 45 mm  0.2 0 0  1  2  3  Torque (Nm)  4  5  6  234  (7.23E)33L1SF-C 1.2 1 0.8 0.6 0.4 0.2 0 0  2  1  4  3  5  Torque (Nm)  (7.26APS)3OT1SF-AM D Cast 15 mm  1.2  o  1 0.8 0.6  Cast 30 mm  • Pump 30 mm  0.4  o Pump 45 mm  0.2  • Shot 45  0 0  1  2  3  4  5  • Shot 60 mill  Torque (Nm)  (7.29A)3OT1SF-AM Cast 15 mm  1.2 1 0.8 0.6 0.4 0.2  .fI_  o  Cast 30 mm  A Cast 45 mm  o Cast 60 mm -  Cast 75 mm  0 .—O——-—-—-  0  1  2  3  Torque (Nm)  X Cast 90 mm  235  (7.29S)3OT1SF-AM 1.2  • Shot 30 mm  1 • Shot 45 mm  0.8 0.6  -  A  0.4  Shot 60 mm  • Shot 75 mm  0.2 0 0  1  2  3  Shot 90 mm  Torque (Nm)  (8.3A)3OT1SF-DN Cast 15 mm  1.2 1  1’  _ L ______ I”,_______________  o  Ii’, %—I I’,_______  0.8 0.6 0.4 0.2  ‘j  A Cast 45 mm  ‘, W% .‘-, :..i  L  o Cast 60 mm  .%.# !‘  0 0  -  Cast 30 mm  2  3  Cast 75  mm  X Cast 90 mm  Torque (Nm)  (8.3P)3OT1SF-DN Cast 30 mm  1.2 • Pump 35 mm  ii 0.8.  A Pump 60 mm  0.6.1 0.4.1 0.2. 0 0  o Pump* 80 mm Pump* 95 mm  1i  1  2  3  Torque (Nm)  Pump**  105mm  236  (8.4A)3OT1SF-DNF D Cast 15 mm  1.2 1  2  O Cast 30 mm  0.8 0.6 0.4 0.2 0  Cast 45 mm  o Cast 60 mm -  0  1  2  Cast 75 mm  X Cast 90 mm  3  Torque (Nm)  (8-4APS)3OT1SF-DNF  _  1.2  Cast 30 mm  Al  0.8 0.6  Pump 30 mm A  J’I__  0.4  A  _J—2’i  A At A  0.2  ‘I A  0 0  1  2  4  3  0 Pump** 90 mm  —A— —4--  5  Shot 60 mm  6  Torque (Nm)  (8.5A)3OT1SF-D D Cast 15 mm  1.2  z  o  1 0.8  Cast 30 mm Cast 45 mm  0.6 0.4 0.2  o Cast 60 mm -  0 0  1  2  3  Torque (Nm)  Cast 75 mm  X Cast 90 mm  237  (8.5AP)3OT1SF-D 1.2 Cast 30 mm  1 rj  0.8 0.6  • Pump 40 mm  0.4  A Shot 30 mm  0.2  0 Pump** 135 mm  0  —  0  1  2  3  4  5  Torque (Nm)  (8.9A)30T 1SF-DF 0 Cast 15 mm  1.2 1  O Cast 30 mm  0.8 0.6  A Cast 45 mm  o Cast 60 mm  0.4 0.2  -  0 0  1  2  3  Cast 75 mm  X Cast 90 mm  Torque (Nm)  (8.9APS)3OT1SF-DF 1.2 1  Cast 60 mm  z____I_  0.8 — —  Pump 55 mm  1EiE •r.  0.6 0.4 0.2  • Shot 70 mm • Shot 90 mm A Block 145 mm  0 0  1  2  3  4  5  Torque (Nm)  6  7  8  0 Block 150 mm  238  (8.11A)3OT1SF-D 1.2 1 0.8 0.6 0.4 0.2 0  Cast 15 mm  O Cast 28 mm Cast 45 mm  LA’  0  1  2  o Cast 65 mm —  Cast 90 mm  3  Torque (Nm)  (8.11P)3OT1SF-D 1.2 1 0.8 0.6 —  E  —  0.4 0.2  1100 PSI  ___JiAq  • 1400 PSI 1600 PSI 0 1850 PSI  0  -  0  1  2  3  2100 PSI  4  Torque (Nm)  (8.16A)25T1SF-CF 1.2 1 0.8 0.6 0.4 0.2 0 0  1  2  3  Torque (Nm)  4  5  239  (8.16B)25T1CF-CF 1.2  Cast 30 mm  1 O Cast 45 mm  0.8 0.6  A Cast 60 mm  0.4 o Cast 75 mill  0.2 0  —  0  1  2  3  Cast 90 mm  Torque (Nm)  (8.16C)25T1SF-CNF 1.2  Cast 30 mm  1 0.8  o  0.6  A Cast 60 mm  Cast 45 mm  0.4 o Cast 75 mm  0.2 0  -  0  1  2  Cast 90 mm  3  Torque (Nm)  (8.16E)25T1SF-CF D Cast 15 mm  1.2 1  O Cast 30 mm  0.8 0.6  A Cast 45 mm  o Cast 60 mm  0.4 0.2  -  Cast 75 mm  0 0  1  2  3  Torque (Nm)  X Cast 90 mill  240  (8.11APS)3OT1SF-D  Cast 45 mm  1.2  G Cast 65 mill  1 0.8 0.6 0.4 0.2  8  Pump 43 mm  M  • Pump 58 mm J  r4d  .‘i  A  Shot 36 mm  ._  0  • Shot 50 mm  AI  0  1  2  3 +  Torque (Nm)  Shot 61 mm  (8.l6Pabc)25T1SF-CF (N) 1.2 1  A2250 Psi  0.8 0.6  • B1300 Psi  0.4 0.2  A C 300 Psi O B*2250 Psi  0 0  1  2  3  4  5  Torque (Nm)  (8.18T)41L1SF-AW Truck 0 mm  1.2  O Truck 15 mm  1 0.8  A Truck 30 mm  0.6  o Truck 45 mm  0.4 0.2  —  Truck 60 mm  0 0  1  2  3  Torque (Nm)  X Truck 75 mm  241  (8.18P)41L1SF-AW Pump 15 mm  1.2 1.  • Pump 30 mm  0.8. 0.  E  —  A Pump 45 mm  o Pump 60 mm  02.  Pump 75 mm  0., 0  i  i  I  Torque (Nm)  Pump 90 mm  (8.18TPS)41LT1SF-AW 1.2 1 Pump 60 mm  0.8 0.6  Truck 60 mm  p0.4 Shot 65 mm  0.2 0 0  1  2  3  4  5  Torque (Nm)  (8.19A)25T1SF-C Cast 15 mm  1.2  o  1 0.8  Cast 30 mm  A Cast 45 mm  0.6 o Cast 60 mm  0.4 0.2  -  Cast 75 mm  0 0  1  2  3  Torque (Nm)  X Cast 90 mm  242  (8.19APS)25T1SF-C Cast 30 mm  a?  1.2 1  o  Cast 45 mm  0.8 0.6  Pump 30 mm • Pump 45 mm  0.4 0.2  • Shot 30 mm  0 0  1  2  3  • Shot 45 mm  Torque (Nm)  (8.21E)33L1SF-E Castl5 mm  1.2 O Cast 30 mm  1 0.8  A Cast 45 mm  0.6 .—  G  —  o Cast 60 mm  0.4 0.2  -  Cast 75 mm  0 0  1  2  3  X Cast 90 mm  Torque (Nm)  (8.21F)33T1SF-E D Cast 15 mm  1.2 a?  ii  1  0.8 0.6 0.4 0.2  A,  0 0  1  2  3  Torque (Nm)  O Cast 30 mm A Cast 45 mm  o Cast 60 mm —  Cast 75 mm  X Cast 90 mm  243  (8.23A)25T1SF-CNF 1.2 1 0.8 0.6 0.4 0.2 0  Cast 30 mm  o  j_  0  2  1  Cast 45 mm Cast 60 mm  o Cast 75 mm -  Cast 90 mm  3  Torque (Nm)  (8.23APS)25T1SF-CNF Cast 60 mm  1.2 1  O Cast 75 mm  —..  ••  0.8  .  0.6 0.4  . .4  Pump 60 mm  .  .4 .  0.2  4  4  • Pump 75 mm  —.. 4  4-  -  .  0 0  1  2  3  Shot 60 mm  • Shot 75 mm  Torque (Nm)  (8.23B)25T1SF-CNF Cast 15 mm  1.2 1 0.8  O Cast 30 mm  0.6 0.4  o Cast 60 mm  A Cast 45 mm  0.2 0  -  0  1  2  3  Torque (Nm)  4  5  Cast 75 mm  X Cast 90 mm  244  (8.23E)3OT1SF-E Cast 15 mm  1.2 O Cast 30 mm  1 0.8  Cast 45 mm  0.6 o Cast 60 mm  0.4 0.2  -  Cast 75 mm  0 0  1  2  X Cast 90 mm  3  Torque (Nm)  (8.23F)3OL1SF-E 1.2 1  Cast 15 mm  o  0.8 0.6  Cast 30 mm Cast 45 mm  0.4 0.2  o Cast 60 mm  0 0  1  -  2  3  Cast 75 mm  Torque (Nm)  (8.24T)421L1SF-AWF D Truck 0 mm  1.2  O Truck 15 mm  1 0.8  A Truck 30 mm  0.6  o Truck 45 mm  0.4 0.2  -  Truck 60 mm  0 0  1  2  3  Torque (Nm)  4  5  X Truck 90 mm  245  (8.24P)41L1SF-AWF 1.2. 0.8. 0.6. 0.4. 0.2.  Pump 15 mm • Pump 30 mm A Pump 45 mm  o Pump 60 mm  Jø --F—-  0  1  .c i  2  3  4  5  Torque (Nm)  (8.24TPS)41L1SF-AWF D Truck 30 mm  1.2 1 0.8 0.6 0.4  Truck 45 mm Pump 30 mm • Pump 45 mm  0.2 0  • Shot 35 mm  0  1  2  3  4  5  Shot 45 mm  Torque (Nm)  (8.25T)? ?L1SF-E  Truck 30 mm  o  1.2  Truck 45 mm  A Truck 60 mm  0.8 0.6 0.4  o Truck 75 mm —  0.2 0  Truck  90 mm  X Truck 105 mm 0  1  2  3  Torque (Nm)  + Truck 120 mm  246  (8.25P)??L1SF-E 1.2 1  Pump 45 mm • Pump 60 mm  0.8 0.6  A Pump 75 mm  0.4 0.2  o Pump 90 mm  0  Pump 105 mm  0  1  2  3  Torque (Nm)  (8.25TPS)??L1SF-E Truck  1.2  90 mm  O Truck 105 mm  1 0.8  Pump 90 mm  0.6  • Pump 105 mm  0.4 0.2  Shot 90 mm  0 0  1  2  3  • Shot 105 mm  Torque (Nm)  (8.30A)54L1FA-W 1.2 1.  0.8. 0.6. 0.4. 0.2. 0. 0  O Cast 15 mm  O Cast 30 mm A Cast 45 mm  t_____ •_  1  2  3  Torque (Nm)  4  5  247  (8.30B)54L1FA-W 1 Seriesi  C? C?  1.2 1 0.8  o  Cast 30 mm Cast 45 mm  0.6 0.4  o Cast 60 mm  0.2 0  cast 75 mm  —  0  1  2  3  X Cast 90 mm  Torque (Nm)  (8.3OBPS)54L1FA-W cast 75 mm  1.2 C? C?  o  1  Cast 90 mm  0.8 0.6  Pump 75 mm  0.4  • Pump 90 mm  0.2  • Shot 75 mm  0 0  1  2  3  Torque (Nm)  Shot 90 mm  248  Appendix H: Hardened shotcrete test results This appendix presents the results of several tests carried out on hardened shotcrete. It contains the results of absorption tests, scaling tests, and the results of the determination of the air voids characteristics. Results of compressive strength are available in Appendix E. Absorption test results (ASTM C-236) The absorption tests were carried out on some shotcrete mixes according to ASTM C-642. Two specimens were used instead of three. Sample  (7.19S)3OL3SF-AF-a (7.19S)3OL3SF-AF-b (7.27S)3OT1SF-AM-a (7.27S)3OT1SF-AM-b (7.29S)30T1SF-AM-a (7.29S)3OT1SF-AM-b (8.45)3OT1SF-DNF-a (8.4S)3OT1SF-DNF-b (8.5S)3OT1SF-D-a (8.5S)3OT1SF-D-b (8.9S)3OT1SF-D-a (8.9S)3OT1SF-D-b (8.11S)3OT1SF-D-a (8.11S)3OT1SF-D-b (8.18S)41L1SF-AW-a (8.18S)41L1SF-AW-b (8.19S)41L1SF-AW-a (8.19S)41L1SF-AW-b (8.23S)25T1SF-CNF-a (8.23S)25T1SF-CNF (8.24S)41L1SF-AWF-a (8.24S)41L1SF-AWF-b (8.25S)??L1SFEa* (8.25S)??L1SFEb* (8.305)54L1FA-W-a (8.30S)54L1FA-W-b  Diy masse (g)  Saturated masse (g)  Masse in water (g)  Boiled absorption  1102.0 931.8 937.3 993.7 988.0 1035.8 1103.4 952.0 884.1 801.6 1061.0 1160.9 1394.5 828.4 856.6 1125.1 1679.9 1673.8 1127.4 1252.0 991.1 1026.7 922.4 977.8 951.4 905.0  1154.8 972.4 971.2 1032.5 1039.4 1077.7 1147.9 1001.4 917.7 839.4 1099.4 1202.5 1445.7 858.9 903.8 1179.8 1712.6 1715.9 1167.6 1291.2 1058.3 1088.6 979.6 1040.8 1013.7 965.7  673.1 573.2  4.79 4.36 3.62 3.90 5.20 4.05 4.03 5.19 3.80 4.72 3.62 3.58 3.67 3.68 5.51 4.86 1.95 2.52 3.57 3.13 6.78 6.03 6.20 6.44 6.55 6.71  506.1 593.0 596.9 615.2 669.9 585.6 538.2 492.1 638.3 708.6 839.2 499.4 530.3 687.8 993.0 993.1 679.3 754.1 611.4 628.9 564.8 604.2 571.6 544.3  Bulk density  Apparent density  Permeable voids  (%)  (%) 2.40 2.44 2.36 2.09 2.35 2.33 2.40 2.41 2.42 2.42 2.38 2.43 2.38 2.39 2.42 2.40 2.38 2.37 2.39 2.40 2.37 2.37 2.36 2.38 2.29 2.29  2.57 2.60 2.48 2.19 2.53 2.46 2.55 2.60 2.56 2.59 2.51 2.57 2.51 2.52 2.63 2.57 2.45 2.46 2.52 2.51 2.61 2.58 2.58 2.62 2.51 2.51  10.69 10.17 8.25 7.86 11.62 9.06 9.31 11.88 8.85 10.88 8.33 8.42 8.44 8.48 12.64 11.12 4.54 5.82 8.23 7.30 15.04 13.47 13.79 14.43 14.09 14.40  249  Scaling test results (ASTM C-672) The scaling tests were carried out according to ASTM C-672: 50 cycles of freezing and thawing with the concrete surface covered with water containing 2.5 % sodium chloride. Regularly, (about every 5 cycles) the specimens were visually rated and the weight of scaled off particles was recorded. Only the results every 10 cycles are presented except for mix (8.30S)54L1SF-W where the test was stopped at 15 cycles.  Sample  (5.20S)35T1SF-AM-a (5.20S)35T1SF-AM-b (5.25S)33L1SF-AM-a (5.25S)33L1SF-AM.-b (5.27S)3OL1SF-AM-a (5.27S)3OL1SF-AM-b (6.1S)35T3SF-AM-a (6.1S)35T3SF-AM-b (8.18S)41L1SF-AW-a (8.18S)41L1SF-AW-b (8.23S)25T1SF-CNF-a (8.23S)25T1SF-CNF-b (8.24S)41L1SF-AWF-a (8.24S)41L1SF-AWF-b (8.25S)??L1SF-E-a (8.25S)flL1SF-E-b (8.30S)54L1FA-W-a (8.30S)54L1FA-W-b  Loss of weight at 12 cycles ) 2 (kg/rn  Loss of weight at 22 cycles ) 2 (kg/rn  Loss of weight at 31 cycles ) 2 (kg/rn  Loss of weight at 41 cycles ) 2 (kg/rn  Loss of weight at 50 cycles ) 2 (kg/rn  Visual rating at 50 cycles  0.19 0.10 0.44 0.66 0.02 0.04 0.02 0.26 0.16 1.23 0.01 0.01 2.79 1.18 2.18 0.97 32.96 31.20  0.49 0.43 1.35 1.49 0.06 0.15 0.08 0.72 0.78 2.12 0.01 0.01 3.87 2.01 3.42 2.38  0.82 0.72 1.93 1.95 0.08 0.24 0.21 1.07 1.48 2.76 0.01 0.01 4.88 3.01 4.88 4.06  1.78 1.60 2.49 2.45 0.17 0.42 0.53 1.54 2.31 3.64 0.02 0.02 5.81 40.1 7.25 5.58  3.59 3.33 2.74 2.70 0.22 0.54 0.76 1.82 2.88 4.16 0.02 0.02 6.34 5.03 9.54 7.96  -  -  -  -  -  -  -  -  3.5 2.5 3 3 0.5 1 2 2 3 4 0 0 4 3 5 4.5 5 5  250 Air void characteristics  (ASTM C-457)  The detemilnation of the air void characteristics was carried out according to ASTM C-457: The results include the usual ones for the modified point count method, but also a second calculation of the air void parameters without considering the voids larger than 300 lIm. This second calculation slightly corrects the hypothesis of the method of equal size of air voids. This new calculation usually reduces the spacing factor for air-entrained concrete but does not affect significantly the spacing factor for non-air-entrained concrete.  Sample  St  N  Sv  Sp  Ngb Svgb  A  a  Lban  (%) (mm-i) (pm) (5.20S)35T1SF-AM-a (5.20S)35T15F-AM-b (5.25S)33L15F-AM-a (5.25S)33L15F-AM-b (5.27S)3OL1SF-AM-a (5.275)3OL1SF-AM-b (6.1S)35T3SF-AM-a (6.1S)35T3SF-AM-b (8.18S)41L1SF-AW-a (8.185)41L1SF-AW-b (8.23S)25T1SF-CNF-a (8.23S)25T1SF-CNF-b (8.24S)41L1SF-AWF-a (8.24S)41L1SF-AWF-b (8.25S)??L1SF-E-a (8.25S)??L1SF-E-b (8.305)54L1FA-W-a (8.30S)54L1FA-W-b  1600 1600 1500 1500 1600 1600 1600 1600 1600 1600 1600 1700 1600 1600 1600 1600 1600 1600  123 173 175 201 141 128 169 105 130 128 192 222 105 100 132 95 120 120  52  82 78 72 62 49 63 38 75 77 57 57 46 76 139 70 85 71  496 403 404 442 500 481 449 536 531 588 530 454 407 403 488 490 466 496  S t:  total number of stops (reading points)  N:  number of voids intercepted  Sv:  number of stops on void  Sp:  number of stops on paste  Ngb:  number of large voids (>300jim) intercepted  Svgb:  number of stops on large voids  A:  air content (%)  a:  ) 1 specific surface (mm  Lbarre: spacing factor (pm) A*:  air content without large voids (%)  a*:  specific surface (mm ) without large voids 1  L*:  spacing factor (jim) without large voids  18 7 5 1 8 1 2 0 0 0 4 6 3 4 17 8 5 2  32 16 12 2 20 2 6 0 0 0 11 15 9 24 93 19 11 4  3.3 5.1 5.2 4.8 3.9 3.1 3.9 2.4 4.7 4.8 3.6 3.4 2.9 4.8 8.7 4.4 5.3 4.4  12.6 11.3 12.0 14.9 12.1 13.9 14.3 14.7 9.2 8.9 18.0 20.8 12.2 7.0 5.1 7.2 7.5 9.0  492 408 393 342 475 451 381 501 587 634 342 276 493 678 693 746 624 599  a* A* (%) (mm-’)  (pm)  1.3 4.2 4.4 4.7 2.7 2.9 3.6 2.4 4.7 4.8 2.9 2.5 2.3 3.3 3.1 3.2 4.7 4.2  336 378 370 338 406 445 365 501 587 634 310 239 450 574 488 685 621 590  28.0 13.4 13.7 15.2 16.9 14.4 15.6 14.7 9.2 8.9 21.8 27.4 14.7 9.8 13.3 9.1 8.3 9.4  L*  

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