UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Rheology of high performance shotcrete Beaupré, Denis 1994

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata


831-ubc_1994-953098.pdf [ 4.61MB ]
JSON: 831-1.0050424.json
JSON-LD: 831-1.0050424-ld.json
RDF/XML (Pretty): 831-1.0050424-rdf.xml
RDF/JSON: 831-1.0050424-rdf.json
Turtle: 831-1.0050424-turtle.txt
N-Triples: 831-1.0050424-rdf-ntriples.txt
Original Record: 831-1.0050424-source.json
Full Text

Full Text

RHEOLOGY OF HIGH PERFORMANCE SHOTCRETEbyDENIS BEAUPRIB.Sc., Université Laval, 1986M.Sc., Université Laval, 1987A THESIS SUBMI flED iN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR THE DEGREE OFDOCTOR OF PHILOSOPHYinTHE FACULTY OF GRADUATE STUDIES(Department of Civil Engineering)We accept this thesis as conformingTHE UNWERS1TY OF BRITISH COLUMBIAFebruary 1994© Denis Beaupré, 1994In presenting this thesis in partial fulfilment of the requirements for an advanceddegree at the University of British Columbia, I agree that the Ubrary shall make itfreely available for reference and study. I further agree that permission for extensivecopying of this thesis for scholarly purposes may be granted by the head of mydepartment or by his or her representatives. it is understood that copying orpublication of this thesis for financial gain shall not be allowed without my writtenpermission.(Signature)___________________________Department of CIV)The University of British ColumbiaVancouver, CanadaDate jgDE-6 (2/88)IIABSTRACTThe main goal of this study was to develop high performance shotcrete and to provide afundamental 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 therheological properties on the fresh shotcrete, were designed and constructed. A modelbased on rheological behavior was finally developed to predict pumpability andshootability.The values of both flow resistance and torque viscosity were used to represent therheological behavior of fresh shotcrete, which is similar to the Bingham model. Importantfundamental relationships were obtained between rheological properties and pumpingpressure, build-up thickness and compaction of shotcrete. With a new parameter, the freshconcrete aging rate, these relationships are used in a model which predicts pumpability andshootability.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 theworkability. In both cases the requirements for good pumpability and shootability must besatisfied in order to be able to apply the shotcrete.These requirements are in conflict in terms of flow resistance: pumpability requires a lowflow resistance while shootability requires a high flow resistance. The range of acceptablevalues 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 traditionalmethod: when compared to the use of superplasticizers only, the use of air, by reducing thetorque viscosity, allows a wider range of acceptable values for the flow resistance to bemaintained. Also, the compaction process allows a recovery of the flow resistance duringshooting. Thus, this concept allows low water-cement ratio shotcrete having enhancedpumpability, shootability, strength, and durability to be produced. It could probably be anexcellent way to avoid the use of accelerators which have adverse effects both on workerhealth and on concrete properties, especially the durability.mivTABLE OF CONTENTSAbstract iiTable of Contents ivList of Figures ixList of Tables xiiAcknowledgments xiiiForward xivINTRODUCTION 1CHAPTER -1-SHOTCRETE TECHNOLOGY 31.0 Introduction 31.1 Shotcrete production 31.1.1 Dry-mix process 41.1.2 Wet-mix process 51.1.3 Comparison of wet-mix and dry-mix processes 51.1.4 Other processes 51.2 General requirements of wet-mix shotcrete 71.2.1 Equipment 81.2.2 Wet-mix shotcrete composition 81.3 Fresh wet-mix shotcrete 101.3.1 Build-up thickness 101.3.2 Rebound 121.3.3 Compaction 131.4 Plain shotcrete 161.4.1 Cement and water-cement ratio (W/C) 161.4.2 Aggregates 171.4.3 Admixtures 171.4.4 Additives 181.5 Hardened shotcrete 191.5.1 Effect of compaction on hardened properties 201.5.2 Effects of accelerators on hardened properties 201.6 Silica fume wet-mix shotcrete 211.6.1 Effect on fresh shotcrete 211.6.2 Effect on hydration 221.6.3 Effect on hardened properties 231.7 Steel fiber reinforced shotcrete 231.7.1 Fiber content 241.7.2 Fiber orientation 241.7.3 Toughness 251.8 High performance shotcrete 261.9 References 26VCHAPTER -2-PROPERTIES OF FRESH CONCRETE .312.0 Introduction 312.1 Importance of fresh properties 312.2 Workability 322.2.1 Definition of physical properties 322.2.2 Empirical measurement of physical properties 332.3 Pumpability 342.3.1 Mobility requirements 342.3.2 Stability requirements 362.3.3 Mix design 382.4 Compactibility 392.5 Shootability 392.6 Mobility related tests 402.6.1 Slump test 402.6.2 Flow test 412.6.3 VeBe test 422.7 Compactibility related tests 432.7.1 Compacting factor test 432.7.2 Compaction (Walz) test 432.7.3 Pressuremeter (air content) 442.8 Stability related tests 452.8.1 Aging (slump) 452.8.2 Pressure bleed test 462.9 References 47CHAPTER -3-RhEOLOGY OF FRESH CONCRETE 493.0 Introduction 493.1 Rheology 493.1.1 Viscosity (Newtonian liquid) 493.1.2 Other behavior 523.2 Cement pastes 533.2.1 Structure of fresh cement paste 543.2.2 Time dependence 553.3 Bingham model for concrete 563.3.1 Rheometer 563.3.2 Practical implications 573.3.3 Conversion to fundamental units 593.4 Effects of mix composition on concrete rheology 603.4.1 Time (aging) 613.4.2 Water-cement ratio (W/C) 613.4.3 Admixtures 623.4.4 Water-reducers (WR) 623.4.5 Air-entraining agents (AEA) 643.4.6 Fibers 653.5 Rheology of high performance concrete 663.5.1 Low water-cement ratio 663.5.2 Silica fume (SF) 673.5.3 Superplasticizers (SP) 67vi3.6 Rheology of shotcrete .683.6.1 Pumping vs. rheology 693.6.2 Shooting vs. rheology 703.7 References 71CHAPTER -4-RESEARCH PROGRAM 744.0 Introduction 744.1 High performance shotcrete (HPS) 744.1.1 Low water-cement ratio (W/C) 754.1.2 High initial air content 764.1.3 Mix identification code 774.2 Testing program 784.2.1 Fresh properties 784.2.2 Hardened properties 784.3 Pumpability study 784.3.1 Pumping pressure 784.3.2 Pressure bleed test 794.4 Shootability studies 794.5 Materials 794.5.1 Cement 794.5.2 Silica fume and fly ash 794.5.3 Aggregates 794.5.4 Fibers 804.5.5 Superplasticizers 804.5.6 Other products 804.6 Equipment 804.6.1 Concrete mixers 804.6.2 Shooting equipment 814.7 References 81CHAPTER -5-DEVELOPMENT OF THE UBC RHEOMETER 825.0 Introduction 825.1 The concrete rheometer: historical review 825.1.1 First generation rheometers 835.1.2 Second generation rheometers 845.1.3 Third generation rheometers 865.2 UBC rheometer 885.2.1 Design considerations 885.2.2 Physical description 885.2.3 UBC rheometer user documentation 905.3 Computer programs 915.3.1 Program: Calibrate 915.3.2 Program: Incremental test 915.3.3 Program: Duration test 925.4 Calibration of torque measuring device 935.4.1 Torque calibration procedure 935.4.2 Torque calibration results 94vu5.5 Rheometer testing program .965.5.1 Mix composition 965.5.2 Physical test results 975.5.3 Rheometer test results 975.5.4 Test parameters 1055.6 Other test results 1055.6.1 Theoretical analysis of impeller motion 1055.6.2 New impeller test 1095.6.3 Sensitivity tests 1115.7 Proposed modification to the UBC rheometer 1135.8 References 114CHAPTER -6-PUMPABILITY 1156.0 Introduction 1156.1 Laboratory concrete pump 1156.1.1 Design criteria 1156.1.2 Pump description 1166.2 Pressure bleed test 1186.2.1 Design criteria and apparatus description 1196.2.2 Test procedure 1206.2.3 Pressure bleed test results 1216.3 Pumpability 1256.3.1 Slump and pressure bleed test vs. pumpability 1256.3.2 Rheology vs. pumpability 1276.4 Pumping of concrete with high air content 1326.4.1 Pumping rate 1326.4.2 Compressibility 1326.4.3 Pumping sequence of the laboratory concrete pump 1346.5 References 135CHAPTER -7-SHOOTABILITY 1367.0 Introduction 1367.1 Shootability 1367.1.1 Definition of shootability 1367.1.2 Pumpability vs. shootability 1377.2 Build-up thickness 1377.2.1 Measurement of build-up thickness 1377.2.2 Relationships between shootability and rheologicalproperties 1397.2.3 Theoretical analysis 1407.3 Rebound 1417.3.1 Measurement of rebound 1417.3.2 Relationship between rebound and rheological properties 1427.4 Aging effect 1437.4.1 Aging 1437.4.2 Fresh concrete aging rate (FCAR) 1447.5 Compaction 1467.5.1 Definition 147vifi7.5.2 Possible effect of compaction on shootabiity 1477.5.3 Measurement 1497.5.4 Results 1507.5.5 Summary on compaction 1577.6 Model for predicting pumpability and shootability 1587.6.1 Required relationships and properties 1587.6.2 Prediction of pumpability 1597.6.3 Prediction of shootabiity 1617.7 Shootabiity of high air content shotcrete 163CHAPTER -8-EFFECT OF MIX COMPOSITION ON SHOTCRETE PROPERTIES 1658.0 Introduction 1658.1 Effect of mix composition on rheological properties 1658.1.1 Relationships between g, h and FCAR 1678.1.2 Relationship between initial flow resistance and slump 1698.1.3 Effect of cement-superplasticizer combinations 1708.1.4 Effect of high volume of air and fibers 1718.2 Effect of mix composition on hardened properties 1738.2.1 Compressive strength 1738.2.2 Absorption test 1748.2.3 Durability 175SUMMARY AND CONCLUSIONS 178Appendix A: Materials 182Appendix B: UBC rheometer user documentation 188Appendix C: Rheometer results (small testing program) 200Appendix D: Pumping and shooting equipment 207Appendix E: Mix composition 213Appendix F: Pressure bleed test results 218Appendix G: Rheometer results 223Appendix H: Hardened shotcrete test results 248ixLIST OF FIGURESFigure 1.1: Representation of dry-mix process .4Figure 1.2: Representation of wet-mix process 5Figure 1.3: Representation of a wet-to-dry-mix method (Top Shot) 7Figure 1.4: Typical wet-mix nozzle 8Figure 1.5: Thickness-to-sloughing test set-up 11Figure 1.6: Effect of thickness on average rebound of dry-mix shotcrete(Parker, 1977) 13Figure 1.7: Stuart’s results on dry-mix shotcrete (Glassgold, 1989) 15Figure 1.8: Hypothetical relationship between speed of particles anddegree of compaction 16Figure 1.9: Effect of non-caustic accelerator on some shotcrete properties(Schutz, 1982) 21Figure 2.1: Effect of “paste saturation” on pumpability 35Figure 2.2: Dewatering of concrete in a pipe line 36Figure 2.3: Relationship between slump, water emitted and pumpabiity(Browne and Bamforth, 1977) 37Figure 2.4: Slump cone apparatus 40Figure 2.5: Flow test apparatus 41Figure 2.6: VeBe test apparatus 42Figure 2.7: Compacting factor measuring apparatus 44Figure 2.8: Slump loss in mixtures containing superplasticizerscompared with control (Whiting and Dziedzic, 1989) 45Figure 2.9: Pressure Bleed test apparatus (Browne and Bamforth, 1977) 46Figure 2.10: Typical results from the pressure bleed test (Browne andBamforth 1977) 47Figure 3.1: Determination of coefficient of viscosity 50Figure 3.2: Representation of the coaxial cylinders viscometer 51Figure 3.3: Nonlinear flow curves and Bingham model (t = to + p. y) 52Figure 3.4: Flow curve and schematic model for structural breakdown(Tattersall and Banfill, 1983) 55Figure 3.5: illustration of thixotropic behavior 56Figure 3.6: Typical results from rheometer MKII (Tattersall, 1991) 57Figure 3.7: Relationship between slump and g (Scullion, 1975) 58Figure 3.8: Relationship between g and h and workability box (adaptedfrom Tattersall 1991) 59Figure 3.9: Effects of addition of water and different admixtures (Gjørv, 1992) 62Figure 3.10: Effect of lignosuiphonate on g and h (Waddicor, 1980) 64Figure 3.11: Effect of air content on g and h (Tattersall and Banfihl, 1983) 65Figure 3.12: Effect of steel fibers (volume and length) on g and h (Tattersall,1991) 66Figure 3.13: Effect of silica fume on yield strength and viscosity (Gjørv, 1992) 67Figure 3.14: Effect of superplasticizers (Banfill, 1980) 68Figure 3.15: Effect of SP dosage and time on yield and viscosity (Gjørv, 1992) 69Figure 3.16: Concrete in pipeline: plug flow (Browne and Bamforth, 1977) 70xFigure 4.1: Mix identification code .77Figure 5.1: Schematic representation of the MKII apparatus (Tattersall, 1991) 84Figure 5.2: Schematic representation of the impeller of the MKIII (Tattersall,1991) 85Figure 5.3: Example of data from Wallevik and Gjørv (1990a) 86Figure 5.4: Slip ring set-up and trace from the recorder (Cabrera andHopkins, 1984) 87Figure 5.5: General view of UBC rheometer 89Figure 5.6: Torque measuring device and slip ring of UBC rheometer 90Figure 5.7: Schematic representation of a rheometer test 92Figure 5.8: Set-up used to calibrate the torque measuring device 93Figure 5.9: Calibration of 4 mm beam 95Figure 5.10: Calibration of 7 mm beam 96Figure 5.11: Normal (a) and “deep” (b) position of the impeller 98Figure 5.12: Mix T10.43a (fast test) 100Figure 5.13: Mix T10.43a (“slow test) 100Figure 5.14: Mix T10.43a çslow” results with decreasing speed) 100Figure 5.15: Mix T10.43b 101Figure 5.16: Mix T10.43c 101Figure 5.17: Effect of air content (Mixes T10.43a, b and c) 101Figure 5.18: Effect of air content (Mixes SF.43a and b) 102Figure 5.19: Effect of cement type (W/C = 0.38) 102Figure 5.20: Effect of W/C and the use of superplasticizer 102Figure 5.21: Effect of shooting on g and h (mixes T10.40 and T10.40s) 104Figure 5.22: Effects of mix composition and shooting on g and h 104Figure 5.23: Schematic representation of observed deviation fromBingham behavior 106Figure 5.24: Position I and position T of the impeller 106Figure 5.25: Hypothetical impeller and relative tangential speed for Iand T positions 107Figure 5.26: Four hypothetical fluid behaviors 108Figure 5.27: Expected torque requirement with respect to time 108Figure 5.28: Results from the impeller motion analysis 110Figure 5.29: New impeller geometry 111Figure 5.30: Oscillatory effect caused by the movement of the impeller 112Figure 5.31: Effect of impeller (number of fmgers) on the spread of torque 112Figure 5.32: Reometer test carried out on air (bowl empty) and on water 113Figure 6.1: Schematic diagram of the pump 116Figure 6.2: Hydraulic system and proximity switches 117Figure 6.3: New pressure bleed apparatus 121Figure 6.4: Typical pressure bleed test results (mix: (8.1 1A)3OT1SF-D) 122Figure 6.5: Relationship between air content and calculated compactionduring the pressure bleed test 125Figure 6.6: Relationships between slump, pressure bleed test and pumpability 126Figure 6.7: Pumpability box: all mixes 130Figure 6.8: Effect of artificial “aging” on pumping pressure 130Figure 6.9: Pumping pressure (a) and pumping rate (b) vs. rheologicalproperties 131Figure 6.10: Effect of air content on pumping rate 132Figure 6.11: Hypothetical pressure distribution in pipes 133Figure 7.1: Build-up thickness test set-up 138xiFigure 7.2: Relationship between the build-up thickness and the slumpbefore pumping 139Figure 7.3: Relationship between the build-up thickness and the torqueviscosity (h) 139Figure 7.4: Relationship between the build-up thickness and the in-place flowresistance (g and g’) 140Figure 7.5: Analysis of build-up test 141Figure 7.6: Rebound test set-up 142Figure 7.7: Rebound characteristics of mix (6.1S)35T3SF-AM 142Figure 7.8: Relationship between rebound and W/C 144Figure 7.9: Rheological test results on mix (6.1A)35T3SF-AM atdifferent times 145Figure 7.10: Determination of fresh concrete aging rate on mix(6.1A)35T3SF-AM 145Figure 7.11: Determination of fresh concrete aging rate on mix(8.4A)3OT1SF-DNF 146Figure 7.12: Effect of air content (a) and compaction (b) on flow resistance 147Figure 7.13: Possible relationships between compaction and shootability 148Figure 7.14: Defmition of pumping compaction, shooting compaction andtotal compaction 150Figure 7.15: Effect of compaction on mix (8. 19APS)25T1SF-C (no AEA) 153Figure 7.16: Effect of compaction on mix (7.26APS)3OL1SF-CF (no AEAbut with fibers) 153Figure 7.17: Effect of compaction on mix (6.1AS)35T3SF-AM (with AEA) 154Figure 7.18: Effect of compaction on mix (8.4APS)3OT1SF-DNF (with AEAand fibers) 154Figure 7.19: Relationship between compaction and stiffening 157Figure 7.20: Required relationships 159Figure 7.21: Characteristics of fresh concrete 159Figure 7.22: Determination of pumpabiity life 160Figure 7.23: Determination of maximum build-up thickness (high air content) 161Figure 7.24: Determination of maximum build-up thickness (a) and waitingperiod (b) (no compaction) 162Figure 7.25: Effect of time, pumping and shooting on rheologicalproperties of mix (8.4APS)3OT1SF-DNF (with AEA) 163Figure 7.26: Effect of time, pumping and shooting on rheologicalproperties of mix (7.12APS)3OL3SF-AF (without AEA) 164Figure 8.1: Relationship between g and h (all mixes) 168Figure 8.2: Relationship between FCAR and h (all mixes) 168Figure 8.3: Relationship between FCAR and g (all mixes) 169Figure 8.4: Relationships between the slump and g (a) or g’ (b) 169Figure 8.5: Effect of superplasticizer type and dosage on g, h and FCAR 170Figure 8.6: Effect of superplasticizer type and dosage on g, h and FCAR 171Figure 8.7: Effect of W/C and superplasticizers on g, h and FCAR 172Figure 8.8: Effect of AEA and fibers on g, h and FCAR 172Figure 8.9: Relationship between air content, W/C and compressive strength 173Figure 8.10: Effect of pumping and shooting on compressive strength 174Figure 8.11: Effect of water-cement ratio on scaling resistance(AEA mixes only) 177XIILIST OF TABLESTable 1.1: Comparison of operational features of dry-mix and wet-mix processes 6Table 1.2: Typical plain wet-mix composition 9Table 1.3: Effect of certain parameters on the amount of rebound(Morgan and Pigeon, 1992) 12Table 1.4: Effect of shooting process on air content of air-entrained wet-mixshotcrete 14Table 1.5: Gradings of fine and combined aggregate (ACT 506) 17Table 1.6: Rebound characteristics of wet-mix steel fiber reinforced shotcrete(Banthia et al. 1992) 25Table 3.1: G and K values for MKII and MKIII (Tattersall and Bloomer, 1979) 60Table 3.2: Concrete admixtures (Tattersall and Banfill, 1983) 63Table 5.1: Calibration data for the 7 mm beam 95Table 5.2: Mix composition 97Table 5.3: Physical test results 98Table 6.1: Geometric characteristics of bleed test apparatus 119Table 6.2: Effect of surface area and water content on the bleeding rateof cement paste (Powers, 1968) 123Table 6.3: Pressure bleed and other test results 124Table 6.4: Rheological properties and pumpability (mixes without fibers) 128Table 6.5: Rheological properties and pumpability (mixes with fibers) 129Table 7.1: Result of the build-up thickness 138Table 7.2: Average rebound measurement data 143Table 7.3: Effects of pumping and shooting on shotcrete properties 151Table 8.1: Air content, slump, g, h, FCAR, and compressive strength 166Table 8.2: Absorption test results 175Table 8.3: Results of ASTM C-39, ASTM C-672 and ASTM C-457 onshotcrete 176XIIIACKNOWLEDGMENTSFirst, I would like to sincerely thank my adviser, Dr. Sidney Mindess, for hisunconditional support. I really appreciated the freedom he gave me in the choice of thesubject and in the completion of the experimental work.I equally thank my co-adviser Dr. Michel Pigeon for the financial support but mostly forthe trust he showed in me, both in the past and during this research project. This thesiswould not exist without him.I also thank Dr. Rusty Morgan, who acted also as a co-adviser, for his constant interest inmy 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 tothank him and Catherine des-Rivières-Pigeon, who patiently entered into the computermost of the test results.It would be too long a list to name all of the members of the UBC Civil Engineering staffwho assisted me, but I would like to thank them all, particularly Dick Postgate and JohnWong for their work and advice in the building of the various frames required in thisstudy.I also thank the University of British Columbia and the Canadian Network of Centers ofExcellence 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 madeduring these four years.xivA yolzanne.1.INTRODUCTIONThis 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 programand chapters five to eight present the results. Several appendices provide additionalinformation. 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 totry to predict its pumpability and shootability. Only the wet-mix shotcrete is considered inthis work.In the first chapter, various aspects of shotcrete technology or the “art of shotcreting” arepresented. There is an emphasis on wet-mix shotcrete, along with its general requirementsin terms of mix composition and placing equipment. Next, the fresh and hardenedproperties of wet-mix shotcrete with respect to mix composition are discussed: the conceptof 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 andhigh performance shotcrete are also discussed.Chapter two describes the importance of the fresh concrete properties and theirmeasurement, from subjective assessment of workability to the definitions of morestandard test procedures. Pumpability, compactibility and shootability, which are veryimportant 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 somemeasurement techniques for determining the coefficient of viscosity are presented. Next,Bingham behavior, applicable to cement pastes and concretes, is discussed with respect tothe time dependence of a cementitious mixtures. Then, considerations regarding to the useof coaxial cylinder viscometers and rheometers are outlined. The effects of mixcomposition on rheological properties are also discussed with an emphasis on highperformance concrete technology. Finally, the implications on shotcrete technology,especially those related to pumping and shooting, are discussed with respect to theBingham behavior.2The testing program carried out on both the fresh and hardened concretes and shotcretes isoutlined in the fourth chapter. The specific operations carried out to evaluate both thepumpability and the shootability are also described. Finally, the materials and theequipment built and used during this study are presented. Detailed information ispresented 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 workas the UBC rheometer, is described. The UBC rheometer is conirolled by a computer andautomatically evaluates the rheological properties of fresh concrete. The designconsiderations and the physical description of the new apparatus are given, as well as theresults 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 bleedtest. Rheological properties as well as the results of the slump and the pressure bleed testsare analyzed in order to predict pumpability. The paste volume concept is explained andthe effect of air-entrainment on pumpability, especially the compaction during pumping istaken into account.In chapter seven, the relationship between the build-up thickness and the rheologicalproperties, especially the flow resistance, are presented and analyzed. Results of a fewrebound tests are also given, along with some considerations regarding the aging effect onrheological properties. To take into account the change in rheological properties withrespect to time, a fresh concrete aging rate factor is defined. Finally, compaction duringpumping and shooting are analyzed: a new model to predict pumpability and shootabilityin terms of maximum build-up thickness is presented.The effects of mix composition on fresh and hardened concrete properties are consideredin 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 andshooting, as well as the effects of variations in mix composition on some hardenedproperties such as compressive strength, absorption, air void spacing factor and deicer saltscaling resistance are explained. Finally, a discussion on the production of highperformance shotcrete is given; the implications and effects of using superplasticizers inshotcrete 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.3CHAPTER -1-SHOTCRETE TECHNOLOGY1.0 INTRODUCTIONIn this chapter, different aspects of shotcrete technology or the “art of shotcreting” arepresented, with an emphasis on wet-mix process and its general requirements in terms ofmix composition and equipment. Next, the fresh and hardened properties of wet-mixshotcrete with respect to mix composition are discussed. Finally, the characteristics ofsilica fume shotcrete, steel fiber reinforced shotcrete and high performance shotcrete arealso discussed.1.1 SHOTCRETE PRODUCTIONShotcrete should not be considered as a special material. Rather, it should be regarded as aspecial process used to place and compact cementitious materials. Over the years, severaldifferent processes have been developed, all of which use compressed air to shootconcrete or mortar at high velocity onto a receiving surface. The two most popularprocesses 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 tunnellinings, rock and slope stabilization, corrosion protection, all kinds of concrete structuralrepairs, etc., they are now, more and more, used for construction. They play a large partin new construction techniques such as soil nailing (Taguchi et al., 1993). Their ease ofuse 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 verypopular 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. InAmerica, the preference goes to the process which is most likely to yield the best resultsfor the particular conditions of the project and to local practice. Both processes have4certain advantages and disadvantages, which make them more or less suitable for aparticular application. The choice of one or the other process is not always easy and manyfactors must be taken into consideration (Egger, 1977).1.1.1 Dry-mix processThe dry-mix process was first used in 1907, to shoot a mixture of sand and Portlandcement to shape an artificial dinosaur. Since then, this technique has been improved and agreat deal of equipment has been developed, but the original idea remains almostunchanged.With this process, compressed air is used to carry, at high velocity, a mixture ofcementitious material and aggregates to a nozzle where some water is added. The amountof water is controlled by the nozzleman to obtain a consistency appropriate for theapplication. At the nozzle, in addition to water, it is possible to add other materials such aslatex, air-entraining agents and/or set accelerators. Figure 1.1 present a schematicrepresentation of the dry-mix process.Figure 1.1: Representation of dry-mix processThe 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. Excessivelayering indicates heterogeneity of the in-place material produced by frequent variations inthe amount of water used during shooting or lack of uniform feed.compressedcement +aggregates water51.1.2 Wet-mix processThis process was first used around 1950. With this technique, fresh concrete is pumped tothe nozzle where compressed air is added to project the fresh mixture onto the receivingsurface. Accelerators are sometimes added at the nozzle to increase the layer thicknessapplied in a single pass and also to the speed up strength development. Figure 1.2presents a schematic representation of the wet-mix process.fresh concreteFigure 1.2: Representation of wet-mix process1.1.3 Comparison of wet-mix and dry-mix processesTable 1.1 from the report of ACT Committee 506 (1987) summarizes the advantages ofboth processes. These characteristics will affect the choice of which method to useaccording to field conditions and expected results.1.1.4 Other processesWith 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-mixprocesses, produce the same final result: a stream of air, water, cementitious material andaggregates (which may also include fibers, additives and/or admixtures). This stream isprojected at high velocity onto a surface, where it is consolidated by the impacting processIconcretenozzlecompressed afr6and remains in place to develop strength and other properties similar to those of concretewith the same composition.The wet-mix and dry-mix processes are differentiated by the point at which air and waterare added to the mix to form the stream. Other processes can also be differentiated by themanner in which the components are introduced to form the spray. Most of these newerhybrid processes address some of the disadvantages of either the “pure” dry-mix processor the “pure” wet-mix process. They have originated from both the dry-mix process andthe wet-mix process. Those originating from the dry-mix process will be referred to asdry-to-wet-mix processes. Those originating from the wet-mix process will be referred toas wet-to-dry-mix processes.Table 1.1: Comparison of operational features of dry-mix and wet-mix processesDry-mix process Wet-mix process1. Instantaneous control over mixing water 1. Mixing water is controlled at the deliveryand consistency of mix at the nozzle to meet equipment and can be accurately measuredvariable field conditions2. Better suited for placing mixes containing 2. Better assurance that the mixing water islightweight aggregates, refractory materials thoroughly mixed with other ingredientsand shotcrete requiring early strengthproperties3. Capable of being transported longer 3. Less dusting and cement loss accompaniesdistance the shooting operations4. Start and stop placement characteristics are 4. Normally has lower rebound resulting inbetter with minimal waste and greater less material wasteplacement flexibility5. Capable of greater productionIn the dry-to-wet-mix process, the mixing time of the cement and the water is increased byadding the water at an earlier stage of the process. It is recommended that some water(between 3 to 5 % of the weight of the concrete mix) be added before mixing the materialwith the compressed air, in order to reduce dust and to improve the homogeneity of the inplace material. This procedure is known as pre-wetting. At present, the dry-mix processwithout pre-wetting is not frequently used. Also, a special nozzle (with the water ringplaced some distance from the nozzle end, and called “long nozzle”) can be used toproduce a more homogenous material, with less dust and less rebound, by increasing the7mixing time of the cement and the water. This dry-to-wet-mix process maintains theadvantage of having lighter hoses.In the wet-to-dry-mix process, the compressed air is added some distance from the end ofthe hose. This process maintains all of the advantages of the wet-mix process, plus thelighter 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-mixprocess (Von Eckardstein, 1993).turboinjectornozzleFigure 1.3: Representation of a wet-to-dry-mix method (Top Shot)1.2 GENERAL REQUIREMENTS OF WET-MIX SHOTCRETEFrom the definition of the wet-mix process, it is obvious that two steps have to be carriedout in order to produce wet-mix shotcrete: the fresh concrete must first be pumped, andthen shot. It is often said that if concrete can be pumped, it can also be shot. Thus, thefirst step in making shotcrete is indeed to verify that it is pumpable. If this step issuccessful, 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 placeafter shooting. In fact, both pumping and shooting operations have special requirements interms of mix composition and equipment.fresh concreteconcreteacceleratorair + water+cement +aggregates+admixturecompressed air /81.2.1 EquipmentA wet-mix shotcrete application requires the following equipment at a minimum: aconcrete pump, an air compressor, some hoses and a nozzle. In addition, an experiencedcrew is essential. Depending on the application, accessory equipment (acceleratordispenser, robotic arm, shuttle belt, etc.) may also be used (Breitenbucher, 1993).Almost any concrete pump can be used for wet-mix shotcrete applications. However, toease the application, a steady concrete flow is better than a discontinuous flow. If anaccelerating additive is to be added at the nozzle, it is more economical to use a speciallydesigned shotcrete pump which will constantly adjust the accelerator dosage with theconcrete flow. The Top-Shot system described in Figure 1.3 is a good example of suchspecialized 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 poorcompaction and high rebound. The nozzle should be designed to produce a homogenousstream of high velocity particles. A wet-mix process nozzle usually possesses threeenthes: a central one for the concrete, one for the compressed air (which is made up ofsmall holes) and one for the accelerator. Although accelerators are not always used, agood nozzle should have this feature. Figure 1.4 shows the details of a commercialnozzle.Figure 1.4: Typical wet-mix nozzle1.2.2 Wet-mix shotcrete compositionThe 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.airair chamberaccelerator r-holesshotcrete9Adrnixtures 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 orpolypropylene) are also often used. As for normal concrete, the proportions of thesecomponents are adjusted in such a way that the shotcrete can meet the requirements ofboth the fresh and the hardened properties.From the point of view of fresh shotcrete, the mix composition should be adjusted to meetthe pumpability and shootability requirements. The common dilemma of the conflictingrequirements for pumpability versus shootability remains: when the pumpability isincreased (by increasing the slump, for example) the shootability is generally reduced andvice versa. It is often considered that a slump of 50 to 80 mm is a good compromisebetween 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 usedfor the same reason. Table 1.2 shows a typical composition for plain wet-mix shotcrete.Table 1.2: Typical plain wet-mix compositionmaterial amount(kg/rn3)cement 400water 170sand 1100coarse aggregate (12 mm) 600water-reducer 1.2 1/rn3air-eniraining admixture 0.2 I/rn3From the point of view of the hardened shotcrete, the mix composition should be adjustedin such a way that the in-place hardened shotcrete will develop acceptable mechanical andphysical properties. As a general rule, mix composition will affect hardened shotcreteproperties in the same way as for normal concrete properties. However, effects associatedwith the shooting process, such as compaction and/or preferred fiber orientation maymodify this general rule.10Depending on the application and the specified mechanical and physical properties, themix compositions can vary widely. It is more convenient to identify classes or types ofshotcrete, for example: plain shotcrete, silica fume shotcrete, steel fiber reinforcedshotcrete, high strength shoterete, high performance shotcrete, or combinations of these(e.g. high volume polypropylene fly ash shoterete (Morgan, 1990a)). Some of these typesof shotcrete will be treated separately in the sections which follow.1.3 FRESH WET-MIX SHOTCRETEThis section describes those properties of fresh wet-mix shotcrete which are directlyrelated to the shooting process: build-up thickness, rebound and compaction. The freshproperties related to concrete technology, such as workability, pumpability, etc., will bediscussed in the next chapter. At this point, let us assume that the concrete is pumpableand shootable.1.3.1 Build-up thicknessAn important characteristic of fresh shotcrete is its build-up thickness. This is defined asthe maximum thickness that can be built-up in a stable way. It is very important, from apractical and economical point of view, to minimize the number of layers required toachieve the required shotcrete thickness. A single application, without a long waitingperiod between passes, is of course, by far the most desired option.There is, unfortunately, no standard test to measure this important characteristic. Themaximum build-up thickness is generally obtained by trial and error. Depending on theapplication (vertical wall, overhead ceiling, presence of reinforcement, etc.) this thicknessmay 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-tosloughing test measurement. He observed two failure mechanisms which may cause thefreshly applied concrete to behave in an unstable manner: adhesion failure and cohesionfailure. 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 toitself. Adhesion failure occurs when, for a vertical application, the shotcrete starts slidingor sloughing under its own weight. Cohesive failure occurs when the fresh shotcreteruptures within itself.11Figure 1.5 shows the set-up used by Morgan to measure the thickness-to-sloughingparameter. Depending on the shape of the applied shotcrete, the measured thickness can bevery variable. In case (a) because of a bigger base and a better shape, the shotcrete wouldprobably exhibit adhesion failure compared to case (b) which is more likely to exhibitcohesion failure. As stated by Morgan (1991a):This is a useful testfor differentiating between the adhesive and cohesivecharacteristics of djfferent shotcrete mixtures; however, the test should notbe viewed as providing an absolute statement of thefull thickness to whichshotcrete can be applied on vertical surfaces.Figure 1.5: Thickness-to-sloughing test set-upcohesionfailureFrom this kind of test, and from experience, some general observations can be made:• the build-up thickness is generally increased when the slump of theconcrete before pumping is reduced.• the use of silica fume generally increases this thickness; and• the use of accelerators increases this thickness, proportional to theaccelerator addition rate.The presence of fibers and the use of a high initial air content, because of greatercompaction, can also increase the build-up thickness (Beaupré et al., 1991b).adhesionfailure(a) (b)121.3.2 ReboundDuring shooting, some particles (aggregates, cement grains, fibers...) do not remain inplace after the impact. These particles constitute the rebound. The amount of rebound andits 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 etal., 1991b; Morgan and Pigeon, 1992; Banthia et aL, 1994).Many parameters influence the amount of rebound. They can be separated into twocategories: parameters related to the shooting technique, and those related to the mixcomposition. The most important parameters related to the shooting technique are: theprocess (wet-mix or dry-mix), shooting position, angle, thickness and presence ofreinforcement (bars or mesh). The most important parameters with respect to the mixcomposition are: aggregate characteristics and content, cement content, presence of silicafume, 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 beenpresented by Morgan and Wolsiefer (1992).Table 1.3: Effect of certain parameters on the amount of rebound (Morgan and Pigeon.1992Technique plain mix silica fume mixrebound (%) rebound (%)Wet: vertical 4 3Wet: overhead 15 13Dry: vertical 42 20Dry: overhead 46 20No standard test exists to evaluate the amount of rebound, but most researchers have usedclosed chambers or large plastic sheets to collect the rebound. The mass of rebound is thencompared to the mass of the in-place shotcrete to determine rebound as a percentage ofeither 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 may13be seen that it is important to shoot a sufficient amount of shotcrete to be in the lower, flatpart of the curve, so that a small difference in thickness will not significantly change theoverall result.Results from the analysis of rebound composition show that fibers and large aggregateparticles rebound the most, while cement paste has the lowest rebound percentage. Theseresults 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, thesechanges in mix composition would have very little effect on hardened shotcrete properties.IFigure 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 around0.8 % by volume), the determination of the in-place fiber content is very important. Thisissue is described and discussed in Section CompactionCompaction of shotcrete is due to the expulsion of air. To achieve a certain degree ofcompaction, a certain amount of work must be done. For cast-in-place concrete, thisenergy is usually provided by vibration. For shotcrete, the speed of the particles and theirimpact 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 aboutpump related compaction is given in Chapter 2). It is also well known that additional air isremoved during the shooting process. Table 1.4 shows the air content of the freshtrendmore overhead shootingcoarser materialshooting drierhigher air pressureTotal thickness (mm)14shotcrete, measured both before pumping and after shooting, and also the air content ofthe hardened shotcrete. The results show that a large amount of both the entrapped air andthe entrained air can be removed during the pumping and shooting process. When airentraining agents are used, the final air content of the in-place shotcrete is around 3-6percent, irrespective of the initial air content before pumping. Similar results can becompiled for non-air-entrained shotcrete: the final air content of the in-place shotcrete isthen around 2-4 percent. The air content of the hardened shotcrete is generally slightlyhigher 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 shotcreteinitial fresh air fmal fresh air hardened air inferencecontent’ content2 content3(%) (%) (%)8.8 4.4 4.9 Beaupréetal.(1991a)7.0 4.1 4.64.4 4.3 5.843* 3.2* 4.0*6.2 4.2 5.16.8 4.0 5.27.4 4.3 5.69.0 5.0 7.0 Beaupré et al. (1991b)7.0 5.0 7.313.0 5.0 5.610.0 4.5 8.720.0 5.0 7.28.5 4.8 5.0 Morgan and Pigeon (1992)6.4 3.9 3.31- 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 honeycombingshould be present. In fresh shotcrete, voids are sometime developed aroundreinforcement, if proper shooting technique is not used and/or if care is not taken toremove trapped rebound. Proper shooting techniques should lead to sound and denseshotcrete: i.e. no honeycombing.15The speed of the particles, which depends on the amount of compressed air used at thenozzle, and their impact on the receiving surface produces the compaction. As mentionedby Glassgold (1989) in describing Stuart’s results on dry-mix shotcrete which arepresented in Figure 1.7:“... it appears that on a comparative basis, shotcrete strength increases toan optimum level. .. .there is a definite correlation between exit velocity andcompressive strength.”42 20 and 25 mm nozzles35I:,,iozzl100 150 200Velocity (m/sec)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 canbe postulated that the strength variations were caused by differences in the fmal degree ofcompaction or in air content, although the air contents were not measured. It is a fact thatcompaction increases the compressive strength and generally improves all mechanicalproperties. Physical properties such as permeability are also improved by compaction.There is considerable uncertainty as to the absolute values of the measured velocities inFigure 1.7. However, the improvement in the degree of compaction when the speed (andthus 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 hypotheticalrelationship between the degree of compaction and the speed of the particles for both airentrained and non-air-entrained shotcrete (Figure 1.8). From previous results (Beaupré etal., 1991 a and b), one can say that the in-place air content of shotcrete should be in theorder of 2-4 percent for non-air-entrained shotcrete and 3-6 percent for air-entrainedshotcrete. If this degree of compaction can be achieved with a specific shotcrete16composition and equipment, the shooting application may be considered to have beendone properly.1210U.42I’Figure 1.8: Hypothetical relationship between speed of particles and degree of compaction1.4 PLAIN SHOTCRETEPlain 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 addedat 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 systemof 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 producewet-mix shotcrete. In North America, portland cement type 10 (ASTM type 1) is the mostcommonly used. The cement content for most applications is around 400-450 kg/rn3.Leaner mixes are more difficult to pump and have higher rebound, while richer mixes canproduce 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 theproduction of high performance shotcrete (Section 1.8).insufficientcompactionshootingapplicationdoneproperlyShotcrete nozzle velocity171.4.2 AggregatesNormal concrete sand and aggregate can be used to produce shotcrete. When coarseaggregates are not used, the material is referred to as sprayed mortar. For sprayed concreteor shotcrete, the sand content is generally around 1000 kg/rn3,and the coarse aggregatecontent up to 600 kg/rn3.ACI Committee 506 on shotcrete has recommended gradings for fine (sand only formortar) and combined fine-coarse aggregates in order to minimize both the dryingshrinkage 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 PercentU.S. (metric) passing individual sievesgrading no.1 grading no. 2 grading no. 33/4 in. (20 mm) -- 1001/2 in. (12 mm) - 100 80-953/8 in. (8 mm) 100 90-100 70-90No. 4 (5 mm) 95-100 70-85 50-70No. 8 (2.5 mm) 80-100 50-70 35-55No. 16 (1.25 mm) 50-85 35-55 20-40No. 30 (630 jim) 25-60 20-35 10-30No. 50 (315 jim) 10-30 8-20 5-17No. 100 (160 jim) 2-10 2-10 2-101.4.3 AdmixturesAdmixtures are chemical products generally used to enhance the performance of theshotcrete. Three admixtures are most commonly used in wet-mix shotcrete technology:water-reducers, air-entraining agents and superplasticizers. Other products, such asretarders, 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 innormal concrete technology. These admixtures (often lignosulphonates) help in permittinga reduction in the cement content and/or the W/C ratio. This practice has economic reasonsand also provides some benefits from a technological point of view. The reduction in theW/C ratio reduces shrinkage and increases strength and durability.18It is well known that the use of air-entraining admixtures improves the freeze-thawdurability of normal concrete. They are also used to improve the freeze-thaw durability ofshotcrete (Schrader and Kaden, 1987; Morgan et al., 1988; Morgan, 1987; Glassgold,1989; Beaupré et aL, 1991a). These chemical products (neutralized vinsol resin, salts ofsulphonated hydrocarbons and salts of fatty acids) stabilize the small air bubbles createdduring mixing. As mentioned earlier, some of these bubbles will be lost during pumpingand shooting. Thus, according to Morgan (1989), it is important to start with a high aircontent (as much as 12 %) to compensate for these losses.Superplasticizers act in the same way as water-reducers, but with higher efficiency. Byelectrically charging the cement particles, superplasticizers (melamine, naphthalene)increase the workability of the mix. They can be used to replace normal water-reducers orto produce high performance concrete or shotcrete (AItcin, 1990). Superplasticizers have ashort effective “life”: they lose their effect after a relatively short period of time (seeSection 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 betweenbatching and initial set. These products coat the cement particles and allow the concrete toremain workable for a longer period of time. They have no particular side effects exceptfor retardation of strength development. Retarders which contain chlorides or alkalis,however, may have adverse effects on steel corrosion or on the development of alkali-aggregate reactions.One of the most recent developments in admixtures for shotcrete involves hydrationcontrol (Melbye, 1993). With this technology, a stabilizing admixture is used to suspendthe hydration of the fresh concrete (the concept is to give to the wet-mix process theflexibility of the dry-mix process) for as long as desired. The hydration is restarted by theuse of an activator which is added at the nozzle, like a normal accelerator.1.4.4 AdditivesAdditives are admixtures which are not part of the initial mix, but which are added at thenozzle during shooting. The most widely used additives in wet-mix shotcrete are setaccelerators. Accelerators are used for different purposes: increasing the build-upthickness and/or accelerating the early strength development.Many different chemical products can be used as accelerators. One of the most popular issodium silicate, also known as waterglass. Many of these products, especially those19which are aluminate based, can have very deleterious effects on both crew health and onthe concrete properties. The durability is generally affected, possibly because of a moreheterogeneous hydrate distribution. During the last symposium on sprayed concrete heldin Norway in 1993, many concerns were raised concerning the use of accelerators in bothwet-mix and dry-mix shotcrete (Bangzho, 1993; Haave and Bracher, 1993; Hirose andYamazaki, 1993; Lukas and Kusterle, 1993). During his presentation, Kusterle showed apicture of the eye of a worker who is now blind because of an accident during thehandling of a set accelerator. The caustic nature of the set accelerator made the attempt torestore his vision by surgery unsuccessful. These concerns have long been known but theuse of accelerators can sometime not be avoided (Burge, 1982).Non-caustic accelerators have been around for many years (Shutz, 1982). Their higherprice 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 ofaction and effect on hardened properties is not well known. The mode of action of anaccelerator could be to accelerate the hydration of the C3A or to create a gel that modifiesthe rheological behavior.Nearly all accelerators are known to reduce the long term strength of shotcrete. Specialequipment is necessary to deliver the correct dosage of accelerator.Activators are also additives that can be added at the nozzle during shooting. They areused to restart and/or to accelerate the hydration process which was previously delayed bythe used of a hydration control admixture. The long-term performance of these newproducts is not yet available (see also Section 1.4.3).1.5 HARDENED SHOTCRETEThere are no mechanical or physical properties which apply specifically to hardenedshotcrete. All tests carried out on hardened concrete can also be carried out on hardenedshotcrete. As with ordinary concrete, the mechanical and physical properties of shotcretevary with mix composition and curing conditions. Because rebound, compaction and theuse of accelerators modify the in-place mix composition, these factors also affect thehardened properties. The sampling of shotcrete by coring and sawing, as opposed to moldfilling for cast in-place concrete, may also affect the measurement of these properties(Gebler and Schutz, 1990).20The influence of curing conditions is not included in this study but it is always good toremember that, as for normal cast in-place concrete, shotcrete needs proper curing. Morehydration 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 dry-mix 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 planeperpendicular to the shooting direction (Ramakrishnan et al., 1981). This preferredorientation will improve flexural properties, especially the shotcrete toughnesscharacteristics. In this case, comparison with cast concrete could be inappropriate. Thisphenomenon is discussed in Section Effect of compaction on hardened propertiesCompaction, as for cast-in-place concrete, will improve the mechanical properties ofshotcrete. 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 characterizedby the value of the spacing factor (ASTM C-457). Low spacing factors are needed toresist rapid thawing and freezing cycles. Gendreau (1989) has shown that the concept of acritical 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, butnot resistant to deicer salt scaling as measured by ASTM C-672 (Vézina, 1985; Beaupré etal., 1991a).The effects of pumping on the air volume variations of concrete have been studied byYingling et al. (1992). The effects of the shooting process on the air void system have notyet been studied. It is however most probable that pumping and shooting produce anincrease in the spacing factor, accordingly reducing the deicer salt scaling resistance of theshotcrete.1.5.2 Effects of accelerators on hardened propertiesWhen the use of accelerators cannot be avoided, it is important to know what their effectsare on hardened shotcrete properties. Figure 1.9 shows the typical improvement in earlystrength, which is generally accompanied by a reduction in the final compressive strength,for a non-caustic accelerator relative to a non-accelerated shotcrete. The usual21improvements in the initial set of shotcrete are also visible on this figure. These effects areusually proportional to the accelerator dosage (Schutz, 1982). Different accelerators atdifferent dosages will react differently with different cements. It is the author’s hope thatcaustic accelerators will eventually no longer be used, because of their health hazards.•IAge (days)Figure 1.9: Effect of non-caustic accelerator on some shotcrete properties (Schutz, 1982)1.6 SILICA FUME WET-MIX SHOTCRETESince about 1970, silica fume has been used in Norway in wet-mix shotcrete. It was firstused in Canada in shotcrete around 1980 almost simultaneously with steel fibers. A byproduct waste some years ago, the cost of silica fume is now about four times the cost ofcement in Canada. Its pozzolanic reactivity and especially its fineness enhance theperformance of concrete by modifying the spatial distribution of both cement grains andhydrates. Silica fume in wet-mix shotcrete improves the properties of both the fresh andthe hardened shotcrete. In Canada, it is common to replace from 7.5 to 12 % by mass ofthe cement with silica fume.1.6.1 Effect on fresh shotcreteSilica fume, when replacing a part of the cement, reduces the workability of fresh concreteand, for this reason, is often used with a superplasticizer. This increase in water demandis caused by its very high specific surface (Mehta, 1983). By changing the cohesion of themix, silica fume reduces bleeding and segregation. This will improve pumpability byreducing the risk of pump blocking (see Chapter 2). However, reduced bleeding increasessusceptibility to early plastic shrinkage cracking if the curing is not appropriate.1% non-caustic4030201008 hours2% non-causticaccierator22Because silica fume increases the cohesiveness of the shotcrete, it reduces rebound andincreases the build-up thickness (Wolsiefer and Morgan, 1993). The addition of silicafume in dry-mix shotcrete allows an increase in overhead thickness by a factor of two, andin some cases, by a factor of three. This effect should be less for wet-mix shotcrete. Theeffects of silica fume on these two properties have a great deal to do with the popularity ofsilica fume in shotcrete technology.1.6.2 Effect on hydrationThe normal hydration process of portland cement is now well known. It can be simplifiedas follows: the chemical reaction between cement and water produces calcium silicatehydrates (CSH), calcium hydroxide (CH) and aluminate phases which progressivelysurround 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 inexcess of that needed for hydration is used for workability purposes, some voids willremain around the cement grains. The porosity of the hardened concrete will then dependon 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 thetotal porosity but will lead to smaller voids. This explains the large reduction inpermeability observed when silica fume is used. The better distribution of hydrates alsoimproves the bond between the paste and the aggregates: i.e. there is less of a transitionzone effect with silica fume. This helps to explain the improvement in mechanicalproperties.Calcium hydroxide (CH) can be considered the weak part of the paste (because itconcentrates 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, reactswith CH to produce more CSH. This pozzolanic reaction usually starts after about threedays of moist curing (Regourd, 1987). Because of this, it is the improvement in spatialdistribution of hydrates, rather than the pozzolanic reaction, which is primarily responsiblefor the improvement in physical and mechanical properties.231.6.3 Effect on hardened propertiesAs mentioned in the last section, because it gives a better distribution of the porosity, silicafume reduces permeability and improves the bond between the cement paste and theaggregates. Properties which are affected either by permeability or by bond should thusalso be affected similarly. The durability of silica fume shotcrete has been studied by manyresearchers over the last fifteen years (Morgan et al. 1988, Beaupré et al., 1991a).Durability to deicer salt scaling resistance is generally improved and chloride ionpermeability is greatly reduced by the use of silica fume. Because rapid freezing andthawing durability is not related only to permeability, the use of silica fume dose notalways improve freezing and thawing resistance.Mechanical properties are also improved by the use of silica fume. The reduction in thethickness and porosity of the transition zone at the paste/aggregate interface is probably themain factor in the improvement of mechanical properties.1.7 STEEL FIBER REINFORCED SHOTCRETEFiber orientation is modified by the shooting process: from random orientation beforeshooting to a preferred orientation after shooting. Different types of fibers (steel,polypropylene, asbestos etc.) have been used in shotcrete (Morgan 1981; Ramakrishnan etal., 1981; Morgan and Mowat, 1984; Beaupré et al. 1991b). However, only steel fiberreinforced shotcrete will be discussed in this section, since steel fibers are currently themost popular fibers in shotcrete technology especially for mining and tunnelingapplications (ACT 506.1). For example, in Norway, 70 000 m3 of steel fiber reinforcedshotcrete 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 deformationcontrol criterion. The underground lining must restrict the movement of the surroundingground but it must also be able to adapt to some extent to some non-preventable groundmovement. The toughness characteristics of the shotcrete are then as important as itsultimate strength.Traditionally, the ductility of underground shotcrete linings has been obtained by the useof steel mesh. Now, mesh is more and more commonly replaced by steel fibers all around24the world. The performance of steel fiber reinforced shotcrete compared to traditionalmesh 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 reinforcedshotcretes are comparable to those of mesh reinforced shoteretes.Because of rebound, the fiber content of the in-place shotcrete is usually lower than thefiber content of the original shotcrete. Also, the shooting process gives a preferentialorientation of steel fibers: most fibers are oriented perpendicular to the shooting directioni.e., parallel to the receiving surface. The main effect of the fiber reinforcement is to givesome load bearing capacity at large deformations after cracking, to control restrainedshrinkage deformation and to improve impact resistance (Morgan, 1981). This post-cracking behavior can be evaluated by a flexural toughness test.1.7.1 Fiber contentBefore pumping and shooting, the fiber content of most wet-mix shotcretes is usuallyaround 45 to 60 kg/m3 (Henager, 1981). During shooting, because of rebound, the in-place fiber content is usually reduced. To minimize fiber rebound and to avoid pumpingblockages, 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 freshconcrete or by a crushing test on the hardened concrete. In both methods, the fibers areseparated from the concrete using a magnet.Table 1.6 shows the rebound characteristics obtained from wash-out tests on five differentsilica fume steel fiber reinforced shotcrete mixes with the same initial fiber content. Fromthese results, it is obvious that different fibers will behave differently: shape and lengthwill affect the results. The in-place fiber content is always lower than the original fibercontent and the fiber rebound is higher than the shotcrete rebound: i.e., the fibers have ahigher tendency to rebound than the rest of the mix.1.7.2 Fiber orientationIn cast-in-place concrete, fibers have a random three-dimensional orientation. In shotcretetechnology, the fibers possess a preferential orientation. Ramakrishnan et al. (1981) haveshown X-rays of sliced shotcrete in which the preferred orientation in a planeperpendicular to the shooting direction is clearly noticeable.25An orientation index has been developed to quantify the degree of orientation. This indexis 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 topromote fiber surface corrosion. The preferred orientation of fibers is positive for thinlinings: the fibers are oriented in a direction in which they are more likely to be effectiveafter cracking.Table 1.6: Rebound characteristics of wet-mix steel fiber reinforced shotcrete (Banthia etal. 1992Original fiber In-place fiber Shotcrete Fibermix volume fraction volume fraction ibound iebound(%) (%) (%) (%)MF1 0.77 0.63 8.8 18.3MF2 0.77 0.68 9.0 11.5MF3 0.77 0.67 12.5 12.5MF4 0.77 0.64 14.8 17.0MF5 0.77 0.68 11.3 ToughnessThe toughness of steel fiber shotcrete is generally obtained by a flexure test. In NorthAmerica, ASTM C-1018 describes the standard procedure for steel fiber reinforcedconcrete. Other testing procedures for determining post cracking performance (Austin andRobins, 1993; Skjolsvold and Hammer, 1993), have also been developed in othercountries.The ASTM C-1018 test has been criticized because its indices are based on thedetermination of the first crack which is almost impossible to determine exactly. Theenergy absorption, or the area under the load-deflection curve, has also been used todetermine the post-cracking behavior of shotcrete. New testing methods (differentspecimen sizes, loading characteristics) place the emphasis on the residual strength aftercracking measured at specific deformations (Holtmon et al., 1993).261.8 HIGH PERFORMANCE SHOTCRETEAs is the case for high performance concretes, high performance shotcretes are made byreducing the water-cement ratio (WIC), using superplasticizers and by adding silica fume.Kompen and Opsahi (1986) were successful in producing a high performance steel fiberreinforced 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 tochoose the right cement-superplasticizer combination (Aitcin, 1990). This point will bediscussed in detail in Chapter 3.The majority of high performance concretes and/or shotcrete (HPC or HPS) are used notfor their high strength but for their improved durability. Gebler (1993) used a HPS with awater-cement ratio of 0.22 to successfully repair abrasion damage in sewer pipes. Thedurability of high performance shotcretes has not been studied but it is expected that itcould be a good way to improve the deicer salt resistance of shotcrete, which is a majorproblem with wet-mix shotcrete in Quebec.1.9 REFERENCESACI Committee 506.1, (1987), “Recommended Practice for Shotcreting”, in ACTManual of Concrete Practice (part 5), Detroit, 1987, iSp.ACI Committee 506.3, (1987), “State-of-the-Art Report on Fiber ReinforcedShotcrete”, 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 HautesPerformances 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 Testingand Evaluation”, Engineering Foundation Conference, Shotcrete for UndergroundSupport 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 Toughnessof Sprayed Fiber Concrete”, Proceedings of the International Symposium onSprayed Concrete, October 17-21, 1993, Fagernes, Norway, pp. 7-19.27Bakken A. and Holtermann E., (1993), “Wet Steel Fibre Reinforced SprayedConcrete as Temporary and Final Rock Support in the Tunnels”, Proceedingsof 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 itsImpairement 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 FiberGeometry in Steel Fiber Reinforced Wet-Mix Shotcrete”, ConcreteInternational, Vol. 16, No. 6, June, 1994, pp. 27-32.Banthia N., Trottier J.-F., Wood D. and Beaupré D, (1992), “Steel Fiber ReinforcedDry-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 aPécaillage du béton soumis au gel en presence de sd déglacants”,Proceedings of the Second Canadian Symposium on Cement and Concrete, University ofBritish Columbia, Vancouver, July 24-26, 1991, pp.182-96.Beaupré D., Pigeon M., Morgan D.R. and McAskill N., (1991b), “Le béton projetérenforcé de fibres d’amiante”, Proceedings of the First Canadian UniversityIndustry Workshop on Fibre Reinforced Concrete, Université Laval, Quebec city, 28-29October, 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”, EngineeringFoundation 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 withCondensed Silica Fume (SP-91-57)”, In ACT SP-91: Second InternationalConference 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 forGround Support, Detroit, pp. 241-249.Gebler 5., (1993), Presentation made at the Spring convention of the ACT, Vancouver,1993.28Gebler S. and Schutz R., (1990), “Is O.85f’c Valid for shotcrete?”, ConcreteInternational, Vol. 12, No. 9, September, 1990, pp. 67-69.Glassgold I.L., (1989), “Shotcrete Durability: An Evaluation’, ConcreteInternational, Vol. 11, No. 8, August, 1989, pp. 78-85.Haave T. and Bracher G., (1993), “Non-Toxic Admixture for SprayedConcrete”, Proceedings of the International Symposium on Sprayed Concrete, October17-2 1, 1993, Fagernes, Norway, pp. 209- 220.Henager C., (1981), “Steel Fibrous Shotcrete: A summary of the State-of-the-Art”, Concrete International, Vol. 3, No. 1, January, 1981, pp. 5 1-57.Hirose H. and Yamazaki Y., (1993), “Hydration Properties of Shotcrete with anAccelerator 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 SprayedConcrete: State-of-the-Art and Future Development”, Proceedings of theInternational 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 theInternational 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 ofNon-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 Fibreand 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 SP14: Shotcreting, Detroit, 1966, pp. 165-184.Lukas W. and Kusterle W., (1993), “The Influence of Water Glass on TheTechnological 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 MineralAdmixtures 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. 1-46.29Melbye T.A. (1993), “DEVELO®CRETE Hydration Shotcrete Mixes forUnderground and Repair Projects”, Proceedings of the International Symposium onSprayed Concrete, October 17-21, 1993, Fagernes, Norway, pp. 233-249.Morgan D.R., (1981), “Steel Fiber Reinforced Shotcrete, A LaboratoryStudy”, Concrete International, Vol. 3, No. 1, January, 1981, pp. 50-54.Morgan D.R., (1989), “Freeze-Thaw Durability of Shotcrete”, ConcreteInternational, Vol. 11, No. 8, August, 1989, pp. 86-93.Morgan D.R., (1990a), “ Evaluation of Polypropylene Fiber Reinforced HighVolume Fly Ash Shotcrete”, CANMET International Workshop on Fly Ash inConcrete, Calgary, Alberta, Canada, October, 1990.Morgan D.R., (1990b), “Advance in Shotcrete Technology for Support ofUnderground Opening in Canada”, Engineering Foundation Conference, Shotcretefor Underground Support V, Uppsala, Sweden, June, 4-7, 1990, pp. 358-382.Morgan D. R., (1991a), “High Early Strength Blended-Cement Wet-MixShotcrete”, Concrete International, Vol. 13, No. 5, May 1991, pp. 35-39.Morgan D.R., (1991b), “Steel Fibre Reinforced Shotcrete for Support ofUnderground 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 withSteel 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. 307-324.Morgan D.R. and Pigeon M., (1992), “Proceedings from the Half-dayPresentation of the 4th Semiannual Meeting of the Network of Centers ofExcellence on High-performance Concrete”, Toronto, Ontario, Canada, October6, 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-ThawDurability of Wet-Mix and Dry-Mix Shotcrete with Silica Fume and SteelFibre”, 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), “AComparative Evaluation of Plain, Polypropylene Fibre, Steel Fiber andWire Mesh Reinforced Shotcrete”, Transportation Research Record 1226,Washington, D.C., 1989, pp. 78-87.30Parker H.W., (1977), “A Practical New Approach to Rebound Losses”, inACSE 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), “AComparative Evaluation of Fiber Shotcrete”, Concrete International, Vol. 3, No.1, January, 1981, PP. 59-69.Regourd M., (1987), “Microstructure of Cement Based Materials ContainingSilica fume; its Relationship with some Properties”, Proceedings ofInternational Workshop on Condensed Silica Fume in Concrete, Montréal, 1987, 8 p.Schrader E. and Kaden, (1987), “Durability of Shotcrete (SP 100-57)”, in ACTSP-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, PapiaBoyaca, Colombia, September 5-10, 1982.Skjolsvold 0. and Hammer T.A., (1993), “Toughness Testing of FibreReinforced Shotcrete”, Proceedings of the International Symposium on SprayedConcrete, 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 NailingTechnique in Tunnel Support”, Engineering Foundation Conference, Shotcrete forUnderground 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 ShotcreteSystem”, Proceedings of the International Symposium on Sprayed Concrete, October17-21, 1993, Fagernes, Norway, pp. 3 10-321.Wolsiefer J. Sr. and Morgan D.R., (1993), ‘Silica Fume in Shotcrete”, ConcreteInternational, Vol. 12, No. 4, April, 1993, Pp. 34-39.Yingling J., Mullings G.M. and Gaynor R.D., (1992), “Loss of Air Content inPumped Concrete”, Concrete International, Vol. 11, No. 10, October, 1992, pp. 57-61.Zangerle D., (1993), “ALIVA the Three Techniques of Sprayed ConcreteConveyance”, Proceedings of the International Symposium on Sprayed Concrete,October 17-21, 1993, Fagernes, Norway, pp. 322-335.31CHAPTER -2-PROPERTIES OF FRESH CONCRETE2.0 INTRODUCTIONIn this chapter, the importance of the properties of fresh concrete are described. Adiscussion of the principles of fresh property measurement, from subjective assessment ofworkability to the definition of more standard test procedures, is presented. Pumpability,compactibility and shootability are also defmed and their evaluation and measurement arediscussed. Finally, mobility, compatibility and stability tests for fresh concrete aredescribed.2.1 IMPORTANCE OF FRESH PROPERTIESFor 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 isexpected that the freshly mixed material will set and develop some strength. The propertiesof 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 compactedconcrete, pumped concrete, shotcrete, etc.), each kind of concrete has its ownrequirements for “workability”, transportation, fluidity, compaction and finishing. It isnecessarily assumed that the concrete is mixable and that it will maintain its workabilityduring these operations. Mixes should be designed in such a way that small changes inmix proportions will not cause excessive changes in either the fresh properties or thehardened ones. The concept of stability is thus very important: the fresh properties shouldbe maintained for a long enough time to ensure that all operations such as placing,finishing, etc. can be carried out properly.322.2 WORKABILITYWhen a particular mixture fulfills all of the requirements for a specific application, and if itis stable, it is usually called a workable mix or a mix with good workability. If one of therequirements is not fulfilled, the mix might not be considered workable. Workability hastraditionally been used as an overall estimation of the qualities of fresh concrete mentionedabove. However, good workability has different meanings for a floor finisher, or a pumpoperator (for pumping), or for a nozzleman (for shotcreting). Properties such asfinishability, pumpability and shootability are traditionally subjective estimations. To beuseful, better estimations of these properties are necessary.2.2.1 Definition of physical propertiesAccording to Tattersall and Banfill (1983), the process of defining a physical propertyproceeds through three stages:stage I: the property is described only in comparative terms, based eitheron purely subjective assessment or on a simple empirical test.Stage II: a numerical scale based on an empirical test or tests isestablished. This scale may or may not befound to be satisfactorybut will inevitably have a restricted application.Stage III: the property is rigorously defined, possibly through theconsideration of an ideal model in terms of physical constantsderivedfrom thefundamental quantities mass, length and time, ...“It is obvious that workability, because of its non-precise definition and its subjectiveassessment, is a stage I property. It is an overall estimation based implicitly on parameterswhich may be more precisely defined such as: viscosity, yield stress, cohesion, internalfriction, 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 inChapter 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 mobilityrelated tests, such as slump, VeBe and flow (see Section 2.6), can be used to give anumerical scale to this property.33Pumpability is, with compactibility and shootability, one of the most importantcharacteristics in wet-mix shotcrete technology. It is defined as the mobility and stabilityunder pressure within an enclosed pipe. Obviously, more than a single stage II property ortest 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 thecompacting effort needed to adequately compact a fresh concrete mix. It can also beconsidered as the ability to achieve a certain degree of compaction when a fixed amount ofenergy is used.There is no standard definition for shootability; it could probably be estimated throughsome stage II properties, such as build-up thickness or rebound measurements asdescribed in Chapter Empirical measurement of physical propertiesIn order to estimate and measure these various aspects of fresh concrete behavior, manyempirical quantitative (stage II) tests have been developed. The “ideal” test (for anyapplication), 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 theparameter in question.• The test should be sensitive and reproducible.• The apparatus should be simple, robust and portable, and should notrequire frequent calibration.• The apparatus should give a reading without the necessity of furthercalibration or analysisBecause it is difficult to fulfill all of these requirements, it is easy to understand why onlya few of the proposed laboratory tests have been standardized and have achieved wideuse. Also, no test among those which have been standardized provides an estimate from a34single result of any fundamental properties related to rheology. Nevertheless, some testshave been standardized and used for both quality control and for research: slump, flowtable and VeBe are all used to estimate mobility.These tests provide only empirical values obtained in a very specific manner. Attemptshave been made to use these tests to estimate properties such as pumpability, but thesehave generally not been very successful. Most of these tests have been developed for veryspecific purposes. Some have been standardized and a few of these will be brieflydescribed. Emphasis is placed on their scope and on the interpretation of their results. It isimportant to remember that all of these tests have only limited applicability. When thesetests are used for purposes other than the one for which they were originally designed,problems can be expected.2.3 PUMPABILITYAs mentioned earlier, pumpability may be defined as the concrete mobility and stabilityunder pressure within an enclosed pipe. Another definition for pumpability is “pressureworkability” (Gary, 1962). This would mean that pumpability is the mobility underpressure.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 thecapacity of the concrete to maintain its initial homogeneity during transport, handling andplacing.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 havethed 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 requirementsAd Committee 304 (1982) gives recommendations regarding the slump limits forpumping. They recommend that concrete should possess a slump between 50 mm and 150mm, although properly proportioned flowing concrete with a slump higher than 180 mmcan also be pumped.35Results of pumpability tests carried out by Gary (1962) on the influence of aggregateshape and grading have shown that for the same slump (around 100 mm) concrete can beeither pumpable or not. His test amounted to a “go or no go” test because the pumpingpressures measured were either low or very high, but with no intermediate values. Fromthese results, Gary concluded that:f concrete is pumpable, it would have adequate workability, while onthe other hand, it may be workable but not pumpable.The additional requirements for stability may explain the above statement: mobility is arequired parameter but it is not in itself sufficient. Because of the stability requirement, anattempt to predict pumpability only from mobility test measurements will not always besuccessful.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 fillall voids between the aggregates, referred to as “saturated”, is much easier to pump thanan “unsaturated” one . Figure 2.1 shows the change in axial pressure with respect to theW/C (related to the total water content).EI0.40 0.50Water-cement ratioFigure 2.1: Effect of “paste saturation” on pumpabiity362.3.2 Stability requirementsAn 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 possibleduring pumping, to change locally from the saturated state to the unsaturated state and thuscause blockage. Figure 2.2 illustrates the dewatering effect caused by the local expulsionof paste from the aggregates. To avoid such occurrences, they stated:particle—i j— migration ofinterlocking \ / mix water.9 A*— .4—frictional resistanceFigure 2.2: Dewatering of concrete in a pipe lineit is essential that the concrete has low permeability to the flow of itsown 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 theslump test, it can be used to predict pumpability (Figure 2.3). See Section 2.8.1 for moredetails on the pressure bleed test.Segregation and aging (change in mobility with time) are also important parameters indetermining stability. Bartos (1992) has provided a list of factors which usually increasestability by reducing segregation:• Continuous grading ofaggregates, and a smaller maximum size.• Air-entrainment.• Increased proportion of fines, including cement and cementsubstitutes.37• Optimum water-cement ratio andpaste content• Admixtures causing thickening of the liquidphase of the mix.All of these factors will reduce the pressure bleeding and thus increase stability.IEWater emitted (cm3)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; ACTCommittee 304 on Concrete Pumping states:Air-entrained concrete is considerably more plastic and workable than non-air-entrained concrete. It can be pumped with less coarse aggregatesegregation and there is less tendencyfor the concrete to bleed.1038The use of silica fume and a reduction in the W/C reduce bleeding considerably, but alsogenerally reduce mobility. Low W/C and/or silica fume concretes generally needsuperplasticizers to bring the mobility back to an acceptable level.2.3.3 Mix designIn order to satisfy the mobility and the stability requirements, adequate mix design isrequired. The proportions and types of constituents are known to affect both the fresh andthe hardened properties of concrete: aggregate type, maximum size, grading andvariability; cement type; presence of other cementitious materials; use of admixtures; andtheir 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. Ifthere 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. Onthe other hand, the properties of the hardened concrete and the considerations of economyrequire one to minimize both the paste content (e.g. to reduce shrinkage, creep) and thewater content (e.g. to increase strength, durability).To minimize the paste and water content requirements, many researchers have tried toevaluate and then to minimize the void content of the dry aggregates. Some researchershave simply directly measured the void content of the combined aggregates (e.g. Brownand Bamforth 1977). Others have tried an analytical approach, by using the coarsenessfactor, mortar factor, aggregate particle disthbution, or some similar factor, to optimizemix proportions (e.g. Shilstone, 1990). An extensive discussion regarding the voidcontent of dry aggregate mixtures has been provided by Powers (1968). He alsodiscussed a dry mixture of cement and combined aggregates:In terms ofpresent-day concrete technology, or of its probable form in thefuture, there is no practical reason to study dry mixtures of cement andaggregate. However, the relationships found in such mixtures are ofinterestfrom an analytical point ofview; they are related on the one hand tothe 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 freshconcrete and measure its properties. This is especially true for shotcrete mixtures, where39in addition to the pumpability requirement, the aggregate grading will also depend on therequirements for shootabiity, at least in order to minimize the rebound.The objectives of minimizing the paste and water contents are still valid in terms ofmobility. However, to satisfy the stability requirement, a paste that is stable with respectto the aggregate grading must be used. The use of a low WIC ratio mixtures and silicafume is certainly a good place to start.2.4 COMPACTIBILITYCompactibility, for cast-in-place technology, refers to the facility with which the concretecan be fully compacted. For cast concrete, the energy required is generally obtainedthrough vibration. It can be seen as an overall estimation of the efficiency of a placingmethod with respect to the concrete mobility.For shotcrete, the speed of the particles, which depends on the amount of compressed airused at the nozzle, and their impact on the receiving surface produce the compactioneffect. Compactibility should thus be seen as the efficiency of the method and/or theequipment used to properly produce dense shotcrete with respect to the workability of thefresh shotcrete. If the method and equipment used are capable of properly placing a densematerial, one can say that the compactibility is satisfactory.2.5 SHOOTABILITYShootability, like finishability, has no precise definition; it can only be consideredqualitatively as the ability of concrete to be shot. Parameters such as rebound and build-upthickness (see Chapter 1) can be used to estimate shootability: less rebound and a greaterbuild-up thickness imply increased shootability. The efficiency of the whole process canalso be used to estimate shootabiity.402.6 MOBILITY RELATED TESTSMobility is the ability of a fresh mix to flow and fill the formwork or other space. It is avery 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 theslump test. Other tests such as the VeBe and the flow table are now used in manycountries 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 beappropriate to refer to the corresponding standards. Quicker and more interesting surveysare given by Tattersall (1991) and by Bartos (1992). Bartos (1992) also looks at the effectof mix composition on fresh concrete properties.2.6.1 Slump testSlump measurement is the most commonly used test in North America and also one of theoldest. 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 standardway; the cone is then lifted and the slump measured after the concrete has reached anequilibrium position (Figure 2.4). The higher the slump, the higher the mobility.Figure 2.4: Slump cone apparatusOriginally, the slump test was developed to measure the effect of water content on theworkability of fresh concrete. The limits of its proper application correspond to slumpsbetween 40 mm and 180 mm. In other words, this method is not good for very stiff orvery fluid concrete.100 mmi4slump41Other factors beside the variation in water content may cause variations in slumpmeasurements: operator and other influences have been studied by Mittelacher (1992).Almost any change in mix composition or in the material characteristics will affect theslump. The time history is also important when measuring slump, since concrete is knownto lose slump with time. This phenomenon can be very important when superplasticizersare being used (Whiting and Dziedzic, 1989). Stability could then be estimated by the rateof slump loss (see section 2.8.1).2.6.2 Flow testThis test has been developed in Germany and is very popular in Europe (DIN-1048 orBS-1881-105; formerly ASTM C-124). It is much like a miniature slump test but itmeasures the spread in mm after the concrete has been jolted 15 times with a fixed amountof energy: the 40 mm drop height shown in Figure 2.5.7W)I_ -1[2OO1U(mm)Figure 2.5: Flow test apparatusIt is a very simple test, but not suited for use with very high workability concretes. Theapplied shocks during the test encourage segregation: the cement paste tends to moveaway 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 moreappropriate. There is an empirical relationship between the slump test and the flow test,but this relationship is variable (Bossi, 1973).flowtable422.6.3 VeBe testThe VeBe test is a molding test which consists of measuring the ease with which themortar or concrete can fill a mold under vibration (BS-1881-104, ACI-21 1). It can beused to assess the mobility of low workability concrete and also, to some extent, itscompactibiity.The VeBe apparatus is shown in Figure 2.6. It consists of a vibrating table with acylindrical 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 ofthe concrete cone. The time taken for the concrete to be completely remolded into thecylindrical container under vibration is then measured. The VeBe time is calculated usingthe measured time and the change in unit weight or density due to the vibrations.Figure 2.6: VeBe test apparatusThis test is sensitive to the mix water content, and to the experience of the operator inestimating when the remolding is completed. This method is adequate for low workabilityconcretes with slumps below 50 mm. If the workability is too high, the remolding time istoo short to be measured accurately.(mm)containercone holdervibratingtable432.7 COMPACTIBILITY RELATED TESTSCompactibiity is related to the energy required to adequately compact (remove entrappedair) a fresh concrete mix (ex.: Waltz test). But, since it is difficult to measure the workrequired to achieve a given amount of compaction, tests that measure the amount ofcompaction produced by a given amount of energy have been designed (ex.: Compactingfactor test).The air content measurement test is also presented. Although it is not a compaction test, itcan be used to determine the degree of compaction achieved for a standard placementmethod because it measures the amount of air. In the case of shotcrete, by shootingdirectly into the air meter base, the in-place degree of compaction can be assessed.2.7.1 Compacting factor testThis 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 twoinverted cones with bottom trap doors and a receiving container. The upper cone is firstfilled with concrete. The concrete falls under its own weight successively into theintermediate cone, and then, into the bottom container. The mass of the concrete in thecontainer is compared to the mass of the same volume filled with concrete with maximumcompaction (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 certainheight. Then, this test is far from representative of the “real world”. Also, more or lessenergy is lost in friction along the cone surfaces. This energy loss can be important, but itis 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) testThis test was developed by Walz in the 1960’s, and is now a German standard (DIN1048). This test is applicable for low to high workability concretes. It measures thevolume of a concrete sample in a standard container before and after full compaction. Thecompaction is generally achieved by vibration. It is often referred to as the CompactionIndex test.44The apparatus essentially consists of a metallic box of dimensions 200 mm x 200 mm x400 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 simplerthan 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.(mm)compactionfactorapparatusFigure 2.7: Compacting factor measuring apparatus2.7.3 Pressuremeter (air content)This test measures the amount of air in the fresh concrete (ASTM C-231). The method isvery well known, and so no further explanation is given here. Other methods ofdetermining the fresh air content also exist: gravimetric and volumetric. However, thesemethods are not used in the field because, while they are more complex, they are notnecessarily more accurate.00452.8 STABILITY RELATED TESTSStability in concrete technology can refer to bleeding, segregation or aging. Forpumpability purposes, aging (loss in mobility with time or due to pressure) and pressurebleeding should be considered.2.8.1 Aging (slump)Aging or the reduction in mobility can be estimated by measuring mobility at differenttimes. For example, Whiting and Dziedzic (1989) have measured the loss in slump fordifferent concretes containing different superplasticizers or high-range water-reducers(Figure 2.8). They also noted that bleeding (which also is a measure of stability) wassignificant for flowing superplasticized concrete. Other factors such as high temperatures,use of high-early strength cements, etc. may cause fast aging.Figure 2.8: Slump loss in mixtures containing superplasticizers compared with control(Whiting and Dziedzic, 1989)4U control• SP-NSP-MA SP-BsP.x100 20 40 60 80 100 120Elapsed time (mm)462.8.2 Pressure bleed testThis non-standardized test was developed by Browne and Bamforth (1977). It measuresthe amount of water emitted from concrete under pressure. Figure 2.9 shows the test setup. The apparatus is described as follows:It consists essentially ofa 12.5 cm diameter cylinder with a detachable topcap 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. Thejack is screwed into the top of the piston housing and hence aforce can beapplied to the piston through the top cap. The jack is operatedfrom a handpump with a four-way valve, allowing the piston to be moved in twodirections. The travel of the piston enables the rapid removal of thecompressed concrete plug after the test. The base plate has a bleed holedrilled into the side and a tap has been inserted. The inside of the bleedhole is covered by a 50 mesh wire gauge to prevent blockages in the tap(Browne and Bamforth, 1977).125 mmdiametercylinder0” ringgauge retainigplatecalibrated— double actionhydraulic cylinder0” rings‘bleedtapmesh wire gaugemeasuring cylinderFigure 2.9: Pressure Bleed test apparatus (Browne and Baniforth, 1977)47The test procedure is to fill the cylinder with fresh concrete, to apply a pressure of 3.5MPa (500 psi) on the concrete and to collect the water emitted from the concrete. Thevolume of water is recorded with respect to time. Typical results are presented in Figure2.10.The volume of water at 10 seconds is subtracted from the volume at 140 seconds tocalculate the V14o-Vlo value (in ml or %). According to the inventors of the test, for agiven slump, when V14o-Vlo is small, the concrete is not pumpable and when it is high,the concrete is pumpable (see Figure 2.3).12010080I::2000 20 40 60 80 100 120 140Time (s)Figure 2.10: Typical results from the pressure bleed test (Browne and Bamforth 1977)2.9 REFERENCESACI Committee 304, (1982), “Placing Concrete by Pumping Methods”, in ACIManual 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 ConcretePumpability”, Journal of American Concrete Institute, May 1977, pp. 193-207.48Dawson 0., (1949) “Pumping Concrete - Friction between Concrete and Pipeline”, Magazine of Concrete Research, Vol.1, No. 3, December, 1949, pp.135-40.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 ofConcrete 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 onSprayed 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. 30-39.49CHAPTER -3-RHEOLOGY OF FRESH CONCRETE3.0 INTRODUCTIONIn this chapter, the rheological properties of cement pastes and concretes are discussed.First, the fundamentals of rheology and Newtonian fluid behavior, as well as somemeasurement techniques for the coefficient of viscosity are presented. Next, Binghambehavior, applicable to cement pastes and concretes, is discussed with respect to the timedependence of cementitious mixtures. Then, considerations regarding the use of coaxialcylinder viscometers and rheometers are given. The effects of mix composition onrheological properties are also discussed with an emphasis on high performance concretetechnology. Finally, the possible implications for shotcrete technology, especially thoserelated to pumping and shooting, are discussed with respect to Bingham behavior.3.1 RHEOLOGYRheology is defined as the science of deformation and flow of matter. It coversrelationships between stress, strain and time. In terms of fresh concrete, the field ofrheology is related to the flow properties of concrete or with its mobility before settingtakes place. In Chapter 2, it was mentioned that physical properties can be defined interms of physical constants derived from fundamental properties. These properties do notdepend on the circumstances under which the material is tested. For example, viscosity isthe 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 untilthe stress is relieved. There is no stress-strain relationship as for solid matter, but rather astress-strain rate relationship. When the strain rate (under shear) is proportional to theapplied 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,50and reach and maintain a constant speed until the force is removed. Under theseconditions, 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 thespeed profile shown in Figure 3.lb: (dv/dx=y) = velocity (V) divided by the distance (H)between the two plates.(c)Figure 3.1: Determination of coefficient of viscosityFor a Newtonian fluid, the reciprocal slope of the linear relationship shown in Figure 3. icis the coefficient of viscosity (ri). The following relationship is only valid for laminar flowof a Newtonian fluid:t=ry (3.1)The experimental determination of the coefficient of viscosity requires the measurement ofshear stress under known conditions of shear rate or vice-versa. The above experimentsatisfies this requirement, though it is not practical for physical reasons to conduct such anexperiment. In most practical cases, the shear rate varies within the liquid but, byintegration (because the viscosity coefficient is independent of the applied shear rate), it ispossible to obtain an equation for the coefficient of viscosity. Some practical methodshave 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 spacebetween the cylinders (thetgap’) and when the rotating cylinder is in motion, a torque is1/TI(a) (b)Shear stress (t)51induced on the fixed cylinder through the sheared liquid. A relationship similar to Figure3.2b can be obtained for a Newtonian fluid.(b)Figure 3.2: Representation of the coaxial cylinders viscometerFor this apparatus, the shear stress (t) equals the torque (T) divided by the surface area ofthe cylinder (2itrh) and its radius (r). The relationship between the shear rate (or velocitygradient 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 forr and between 0 and 2 for o and by isolating r (assuming ri is independent of shear rate),the following relationship is obtained:1 =T [(1/Rb2’) - (1/Rc2)I.24ith(3.3)In Equation 3.3, the ratio 2/T is the slope of the line in Figure 3.2b. From a constantfactor G =[(1/Rb2)- (1/Re2)]/ (4ith), the slope of the plot of Q vs. T is equal to Gil for acoaxial cylinders viscometer with physical characteristics similar to those of Figure 3.2a.TIc T(a)Torque (Nm)523.1.2 Other behaviorNewtonian behavior is the simplest possible behavior for a fluid, but many fluids do notbehave in this way. For more complicated behavior, where the observed rate of shear isnot linearly proportional to the applied shear stress, different relationships may beobserved. In these cases, the behavior cannot be expressed by a single coefficient.Different equations have been developed for different liquid materials. The graphicalrepresentation by a flow curve, as shown in Figure 3.3, is also a very useful way ofpresenting the flow behavior.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: theliquid flows less as the flow rate increases. Curve (b) is a shear thinning liquid in whichthe 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 appliedbefore 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 theapplied shear stress and the shear rate. This last behavior is referred to as the Binghammodel 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 parametersare needed to fully describe the fluid behavior: the yield value and the plastic viscosity.Shear thickening Shear thinning Bingham behaviorShear stress (t) Shear stress (t) Shear stress (t)(a) (b) (c)53Cement paste flow curves can be expressed by different models. Banfihl (1973) reportedfive different ones:• Bingham: t=to+I.Ly, (3.5)• Hersschel-Bulldey: to + a ‘y”, (3.6)• Robertson-Stiff: = a (y+e)b, (3.7)• Eyring: t = a y + b sinh (b/)1, (3.8)• Ostwald-deWaele: t = to + b sinh (bI)1) (39)Banfihl (1990) also noted that cement pastes do possess a yield value. Most authors haveused the Bingham model (Tattersall and Banfill, 1983) for cement paste. This can beexplained, by the good correlation (correlation coefficients “r” presented by Tattersall areusually in the range of 0.99 or 0.98) with the Bingham model. It seems that, with respectto the precision of the apparatus, there is no reason to use more a complex model.3.2 CEMENT PASTESConcrete can be viewed as a suspension of large particles in cement paste. Cement pastecan in turn be modeled as a suspension of solid, reactive particles in water (Haritori andIzumi, 1982). To study fresh concrete rheology, it seems appropriate to start with a studyof fresh cement paste rheology. Even though is has been shown that cement pastepossesses a more complex rheological behavior than concrete and cannot be used topredict the behavior of concrete, some useful information can be obtained which helps oneto 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 methodsapplicable 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 on54rheology is of interest to illustrate the phenomenon of structural breakdown andthixotropy.3.2.1 Structure of fresh cement pasteCement paste is made by mixing cement and water. The rheological behavior of cementpaste is very different from the behavior of a suspension of inert solid particles of similargrading. Because of the electric charges on the surfaces of dry cement particles, they donot 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. Rapidreactions take place during the first minutes after the initial contact between the water andthe cement: some of the lime and sulfates dissolve, and a surface skin of hydrated mineralsbegins to form around other components. This period is followed by a dormant period (2-5 hours) during which the reactions are slow and the paste remains workable until settingtakes place.After the initial contact between cement and water, the cement grain surface slowlybecomes covered by a membrane of gelatinous calcium silicate-suiphoaluminate hydrates.These membranes form around the floes, and are responsible for the physicalphenomenon known as structural breakdown illustrated in Figure 3.4a. The plot of thecurve of increasing shear rate (arrow pointing up) is different from the curve of decreasingshear 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 ofthe slope at any point on the curve) decreases when the shear rate increases. Thedestruction of the membrane surrounding the cement floe under increased shear explainsthe observed reduction in apparent viscosity. After the maximum shear is reached, themembranes around smaller floes or individual cement particles reform and the apparentviscosity remains almost constant (plastic viscosity) during the “down-curve”. Figure3.4b 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 cementpaste. A hand mixed cement paste will exhibit more structural breakdown than one madeusing a more vigorous mixing method. In fact, the amount of shear used during themixing of the paste will affect its rheological behavior. For concrete, because of thepresence of aggregates, the shear action is so intense that the mixing method usually hasno significant influence on the rheological properties. Similar behavior could be caused by55a thixotropic material. This effect is also time dependent and will be discussed in the nextsection.membraneenvelopesCl)(a) (b)Figure 3.4: Flow curve and schematic model for structural breakdown (Tattersall andBanfill, 1983)3.2.2 Time dependenceThe elapsed time after initial mixing (i.e. the age of the cement paste) is an important factorto consider when determining the rheological properties. Because hydration proceeds evenduring the dormant period, the amount of water and the concentrations of the various ionschange, and so does the viscosity and the yield of the paste.Depending on the nature of the cement, it is possible that the structural breakdowndescribed in the previous section might be reversible. If it is reversible, the material isthixotropic. A material which exhibits a decrease in apparent viscosity, but does not showan increase at rest, is not a thixotropic material.Two successive tests are needed to determine whether a material that exhibits structuralbreakdown is thixotropic. Figure 3.5a shows a first test carried out on a material thatshows a decrease in apparent viscosity. Figures 3.5b and 3.5c are the possible results of asecond test carried out after a short period of time on the same material. In case (b), thesecond up-curve and down-curve are identical to the first down-curve; the material is notthixotropic. 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.2- after mixingShear stress (t) 3- during shear 4- during shear56‘IL.aCl)(a) (b)Figure 3.5: Illustration of thixotropic behaviorThe amount of time needed to reverse the effect of structural breakdown may vary fromone thixotropic material to another. The exact shape of the hysteresis loop will depend onthe material and its time history.3.3 BINGHAM MODEL FOR CONCRETE3.3.1 RheometerFor concrete, it is more appropriate, for practical reasons (principally the size of theaggregates) to use a rheometer instead of a coaxial cylinders viscometer to measure therheological properties. A rheometer consists of an impeller and a sampling bowl. Duringtesting, the impeller is driven, at different speeds, through the bowl previously filled withconcrete, and the required torque and the impeller speed are measured. More details onrheometers are given in Chapter 5.Typical results obtained with the MKII rheometer (Tattersall, 1991) on different concretesare shown in Figure 3.6. In this figure, the flow curves strongly suggest a Binghambehavior for concrete. The rheological behavior can be expressed in term of two constantsby the following equation:first test second test:non-thixotropicsecond test:thixotropicShear stress (t) Shear stress (t) Shear stress (t)(c)T=g+hN (3.10)57where T is the torque to drive an impeller (Nm), g is the flow resistance (Nm), h is thetorque viscosity (Nm.s) and N is the impeller angular speed (rev/s). Equation 3.10 is verysimilar to Equation 3.4, which suggests that the flow resistance is related to the yield andthat the torque viscosity is related to the plastic viscosity.4 W/C = 0.75 0.70 0.65 0.60 0.55IE_o. I-- I—I0 1 4Torque (Nm)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 theapparatus with which they are measured. However, it is possible, by proper calibration, toconvert them into the fundamental units for j.t and to. Even if not in fundamental units, therheological parameters g and h can be used to evaluate the concrete mobility or otherrelated properties.3.3.2 Practical implicationsOne implication of the existence of the Bingham behavior is that the values of g and h canbe obtained with only two measurements of torque at two different speeds. This principlehas been used by Tattersall to defme the two-point workability test. Another implication isthat any test method which uses only one shear rate during testing is not appropriate todescribe concrete workability in teinis of rheological properties.In the case of the slump test, the only measurement is made in a quasi-static way. Thischaracteristic 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 testresults and the flow resistance is shown in Figure 3.7 (Scullion, 1975). The relationproposed by Scullion is:I I III II, III I FI, I2 358S11=Ag (3.11)where S is the slump in mm, n is -0.47 and A = 0.007. This is approximately an inversesquare-root relationship. This kind of experimental relationship has been confirmed by atheoretical simulation assuming a Bingham behavior: the effect on slump on a change inyield 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 gand h. As shown in Figure 3.8 (adapted from Tattersall, 1991), it is possible to obtain anycombination of g and h.It has been shown by Tattersall (1982) that for different concrete placing methods (forexample: filling a pipe with flowing concrete), it is possible to identify a region, aworkability box, which would enclose all combinations of g and h suitable for a particularapplication. In Figure 3.8, all concretes represented by a black dots would be suitable forthis particular workability box; concretes represented by white dots would not.070605o.4OIE‘—‘ 30Cl)E20Cl)0iO41 23Flow resistance g (arbitrary units)Figure 3.7: Relationship between slump and g (Scullion, 1975)598765432100Figure 3.8: Relationship between g and h and workability box (adapted from Tattersall1991)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 someapplications, where the viscosity is an important factor as well, the measurement of both gand h is certainly the best way to avoid such problems. Possible implications for pumpingand shooting are discussed later.3.3.3 Conversion to fundamental unitsIt is possible to calibrate an apparatus with liquids of known viscosity to relate theseintermediate values g and h to the fundamental properties t and to.As summarized by Tattersall and Banfill (1983):The rate ofshear in a mixer variesfrom point to point and it is not possibleto carry out a full analysis. However, some progress may be made if it isassumed that there is an average effective shear rate that is proportional tothe speed of the impeller so thaty = KNand by suitable calibration it is possible to determine the value of K. Aknowledge of this constant and of another calibration constant G permits00correlation coefficient = 0.1900 0o 0A0 000 0000000I I I I l_1 2 3 4h (arbitrary units)5 660the expressing ofyield value and plastic viscosity in fundamental units bythe use of the equations:‘to = (KIG) gu=(1/G)h.(3.12)(3.13)This means that the values of g and h are, respectively, proportional to toand p. but the constants ofproportionality are djfferent.Readers who are interested in the mathematical development should read Tattersall andBloomer (1979) or Tattersall and Banfill (1983).By using different oils at different temperatures, Tattersall and Bloomer (1979) have beenable 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 by136 for the MXIII apparatus with planetary motion. Similarly, to obtain the viscosity t inPascal-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 0.045 0.066K 6.09 8.94K/G 135 136hG 22.2 15.23.4 EFFECTS OF MIX COMPOSITION ON CONCRETE RHEOLOGYAlmost any change in mix composition may affect the rheological behavior of concreteincluding the following:• age of the mix (time elapsed after initial mixing)• content, shape, gradation, porosity, and texture of aggregates61• 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 independentof each other in their effects. Only the effects of certain parameters, related specifically tothis study, are presented here. For example, the effect of aggregate gradation is notdiscussed because it is not a variable in this study and it would take too long to review allof the papers published on this subject. The effects of silica fume and the use ofsuperplasticizers are discussed in Section Time (aging)During mixing, there is an initial period of very rapid hydration followed by the dormantperiod during which very little reaction takes place. This period is responsible for theusual 2-3 hour grace period during which the placing usually takes place. Once setting hasoccurred, the properties of concrete are measured in terms of strength.During the dormant period, the properties of concrete change slowly: the flow resistanceincreases, but the plastic viscosity is usually not affected. Factors such as hightemperature, low W/C, the presence of superplasticizers, high cement content, or rapidhardening cement may modify the usually observed slow “loss of slump”. As shown byBanfill (1980), the increase in g value can be sufficient to shorten the period during whichconcrete 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 theproperties of hardened concrete; for fresh concrete properties, it is no less important. Ithas been shown (Figure 3.5) that an increase in W/C produces a reduction in both theplastic viscosity and the flow resistance. This reduction is so great that for low W/C, awater-reducer or a superplasticizer must be used to produce workable concretes.62The type of cement, especially the C3A content, the content of other components whichreact rapidly and the sulfate content will affect the initial rheology; more detail is given inSection AdmixturesTable 3.2 lists the most common types of admixtures and indicates their effect onrheology. 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 ofpossible interactions between the cement, mineral admixtures or other admixtures it is verydifficult 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 usualeffect of the addition of water or different admixtures. When more than one admixture isadded, the overall effect cannot be predicted, except for the general trend.AdmixtureAEA: air entrainingSP: superplasticizerWR: water-reducer++reference+ spViscosity (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 (largereduction of flow resistance (g) and small reduction of plastic viscosity (h)), they aretreated differently because the effects of superplasticizers are much greater and alsobecause they are usually used for low W/C concretes.63Table 3.2: Concrete admixtures (Tattersall and Banfihl. 1983’)admixture typical material advantage I uses effect on rheologyAccelerators sodium aluminate facilitates shooting increased rate of changesodium silicate with timelime more rapid early strengthpotassium hydroxide developmentcalcium chloridecalcium formatesodium nitriteRetarders hydroxycarboxylic acids maintain workability at high initially may betemperatures significantsugar reduce rate of heatdevelopment reduced rate of changeextend placing time with timeWater-reduceis calcium and sodium a) higher workability with very significant effect inlignosuiphonates strength unchanged all three usesb) higher strength with low reduction in hunchanged workability high reduction in gc)less cement for samestrength and workabilitySuperplasticizers suiphonated melamine- as for water-reducer with very significant in allformaldehyde resin greater efficiency three usessuiphonated naphthalene- low reduction in hformaldehyde resin high reduction in gmixture of saccharates may modify the rate ofand acid amides change of g with timeRetarding mixture of sugars or as for water-reducer, with very significant initialwater-reducer hydroxylcarboxylic acids slower loss of workability effectand lignosuiphonate decreased rate of changewith timeAir-entraining wood resin (vinsol resin) increase frost durability significant increase inagents salts of fatty acids without increasing cement workabilitylignosuiphonates content and heat evolution reduce both g and hPumping aids polyethylene oxide widen the range of mixtures significantcellulose ether suitable for pumpingalginatesalkylsuiphonate64Figure 3.10 presents the result of Waddicor (1980) as reported by Tattersall (1991). Up toa certain dosage (0.15% of cement weight) the addition of lignosuiphonate produces alarge reduction in flow resistance (g) and a significant reduction in plastic viscosity (h). Athigher 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..7651410Figure 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 inFigure 3.11. From this figure it is obvious that an increase in the air content produces arapid decrease in both g and h. For air contents higher than 5 %, there is no significantreduction in h, but the flow resistance (g) reduces for values of air content up to 10percent. These dramatic reductions in g and h explain why air-entrained concretes aremore workable even if, for the same strength level, their W/C ratios are lower in order tocompensate for the strength reduction caused by the presence of entrained air. Thereduction in W/C would otherwise result in less workable concrete. The improvement of.0.075 0.15 0.225 0.30Lignosuiphonate (% wlw)65workability (especially the reduction of g) is often explained by the “ball-bearing” effect ofair voids.oWIC=O.5510 — o wIC=O.60WIC = 0.65Air content (%)Figure 3.11: Effect of air content on g and h (Tattersall and Banfill, 1983)3.4.6 FibersThe effect of steel fiber additions has been studied by Tattersall (1991) using the MKIIIrheometer with planetary motion. He mentioned that fresh fiber reinforced concreteconforms to the Bingham model; however, he presents no flow curve. The results on fivemixes presented in Figure 3.12 show that when the fiber content increases, both g and hincrease but when the fiber length is increased, only the flow resistance (g value) isincreased. These results were obtained on concretes with W/C ratios ranging from 0.5 to0.65.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 ofpolypropylene fibers. The increases in the flow resistance were greater than the increase inthe plastic viscosity. The W/C ratios were between 0.47 and 0.67.These observations are in broad agreement with the decrease in workability usuallyobserved by using single-point workability tests such as the Vebe, inverted slump cone orslump tests.6610. 0.5%2Omm1 00.5% 25mm20 o 0.5% 60 mm1.0%2OmmC O%2Smm0.5 0.55 0.6 0.65wICFigure 3.12: Effect of steel fibers (volume and length) on g and h (Tattersall, 1991)3.5 RHEOLOGY OF HIGH PERFORMANCE CONCRETEHigh performance concretes (HPC) usually possess high degrees of workability becauseof the high dosages of superplasticizers (SP) used to produce them. Other commoncharacteristics of HPC are the low W/C (0.22-0.35) and the use of silica fume (around10% by weight of cement). The combined effects of low W/C ratio, the presence of silicafume and the high dosage of superplasticizers, give a special rheology. Smeplass (1993)and Osterberg (1993) have shown that high performance flowing concrete can also berepresented by the Bingham model.3.5.1 Low water-cement ratioAccording to the trends shown in figure 3.5, low W/C ratio concretes made withoutsuperplasticizers (if they could be made) would possess very high flow resistance and avery high torque viscosity. As the W/C is reduced, the SP content is increased to maintainthe required flow properties.673.5.2 Silica fume (SF)As mentioned in Chapter 1, silica fume is very often used in shotcreting operationsbecause it is known to reduce rebound and increase build-up. The effects of silica fumeadditions on rheology of concrete have been studied by Wallevik and Gjørv (1990) andreported by Gjørv (1992). Figure 3.13 shows that the flow resistance is nearly constantuntil a threshold value in silica fume content is reached (around 7%). Over that thresholdvalue, the yield increases rapidly. Also, when the cement content is high (or when theW/C is low), the increase in yield value is less pronounced.I_________________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 inplastic viscosity (which is good for pumping), but also an increase in yield value (which isgood 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 usingtwo-point tests for workability. Because the W/C ratios used in his study were in therange of 0.65 to 0.73, which is far from the W/C usually used in HPC, one should becautious in the application of these findings to HPC. He found that at low dosages up to0.7 % 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 higherconcentrations, the addition of superplasticizer produces unstable mixes prone tosegregation. He also found that the melamine-based SP produces more rapid hardeningPlastic viscosity (Pa.s)68(faster increase in g with time but little change in h) than the naphthalene-based ones(Figure 3.14b).M = melamineN = naphthalene0 = no SP>2.5% M1.5% N60 120 180Time (mm)Recently, some rheological results on HPC from Norway have been published (Wallevicand 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) showthat the flow resistance is much more affected by aging than is the plastic viscosity. InFigure 3.15, it is clear that the yield increases with time as opposed to the viscosity, whichremains almost constant.3.6 RHEOLOGY OF SHOTCRETEAs mentioned in Chapter 1, the wet-mix process includes two major steps: pumping andshooting. Since the rheological behavior is now accepted to be fundamental to thebehavior of concrete, it might be possible to relate or define the requirements of theseoperations in terms of yield and plastic viscosity. Unfortunately, there is no study knownto the author in which an attempt was made to relate the pumping and shooting operations5.,.......ftpEI410.02015%NSP concentration (% w/w)(a) (b)Figure 3.14: Effect of superplasticizers (Banfill, 1980)69to the fundamentaltheoretical.behavior of fresh concrete. The following discussion is thus10 mm2.4 % (SPdosage)Figure 3.15: Effect of SP dosage and time on yield and viscosity (Gjørv, 1992)3.6.1 Pumping vs. rheologySo far, it has been mentioned that the behavior of concrete can be measured with arheometer 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 canbe used to specify certain limits within which the concrete will meet the specific jobrequirements for workability. At present, the workability is mostly specified in terms ofslump, or occasionally in terms of other standard tests.In Chapter 2, the pumpability requirements were described in terms of slump and wateremitted during a pressure bleed test. There is no existing “workability box” (see Section3.3.2) to relate the pumping requirements in terms of yield and plastic viscosity.However, the most casual observation of pumped concrete is sufficient to realize thatconcrete 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 theshearing action takes place.4Plastic viscosity (Pa.s)70Morinaga (1973) has been unsuccessful in correlating the radius of the plug with the yieldvalue of the concrete. The main explanation for this is the presence of a lubricating layerwhich has different properties than the bulk of the concrete.In considering Bingham behavior for the bulk concrete, lubricated by another Binghammaterial, Tattersall and Banfill (1983) have carried out a theoretical treatment of the earlierobservations of other researchers (Aleekseev, 1953; Ede, 1957; Gary, 1962; Weber,1963). Their assumption of a lubricating layer is in conformity with the normal practice ofestablishing a lubricating layer by pumping a grout before the concrete is pumped. Theiranalysis is valid only for straight pipes with constant cross sections. When singularitiessuch as reducers or elbows are present, the behavior is certainly different and is affectedby the properties of the bulk concrete, not only by those of the lubricating layer.lubricatingplugFigure 3.16: Concrete in pipeline: plug flow (Browne and Bamforth, 1977)An understanding of the influence of the mobility (flow properties) is probably notsufficient by itself to establish pumpability. The stability requirement, as mentioned inChapter 2, should also be considered, as well as the characteristics of the lubricating layer.3.6.2 Shooting vs. rheologyUp to the present, there have been no studies on rheology of shotcrete reported in theliterature. Beaupré et al. (1993) have proposed an explanation as to why shotcrete isshootable and why it stays in place after shooting. They stated:pipe _-I71The existence of a yield value seems to provide a good explanation as towhy shotcrete is shootable. Intuitively, the higher the yield stress, thebetter the shootabilily (i.e. the greater the thickness that can be built upwithout sloughing). In fact, a material with no yield value (such as water)could not remain in place after shooting. Similarly, aflowing concrete withlow yield value would not be suitable for shotcreting; it would simplyslough off the receiving surface unless special agents (such as sodiumsilicate) were added at the nozzle. On the other hand, mixtures with highyield value (low workability) could be unsuitablefor shotcreting, becauseofpumping and consolidation difficulties.According to this statement, there should be a relationship between the flow resistance andthe build-up thickness described in Chapter 1. The flow resistance might then be anindicator of the shootability.3.7 REFERENCESAleekseev A.N., (1952), “On the Calculation of Resistance in Pipe of ConcretePumps”, Building Research Station Library Communication, No. 450, 1952.Banfill P.F.G., (1990), “The Rheology of Cement Paste: Progress since1973”, Proceedings of RILEM Colloquium on Properties of Fresh Concrete, Universityof Hannover, October 3-5, 1990, Chapman & Hall, London, pp. 3-9.Banfill P.F.G., (1980), “Workability of Flowing Concrete”, Magazine of ConcreteResearch, Vol. 32, No. 110, March, 1980, pp. 17-27.Beaupré D., Mindess S. and Morgan D.R., (1993), “Development of HighPerformance Shotcrete (theoretical considerations)”, Engineering FoundationConference, Shotcrete for Underground Support VI, Niagara-on-the-Lake, Canada, May2-6, 1993, pp. 1-8.Browne R.D. and Bamforth P.B., (1977), “Test to Establish ConcretePumpability”, 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 ofConcrete Mixtures”, Proceedings, ASTM Vol. 62, 1962, pp. 964-97 1.72Gjørv 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 ConcentratedSuspension”, in Effect of Surface and Colloid Phenomena on Properties of FreshConcrete, Proceedings, Symposium M, Material Research Society, November 1-4, 1982,pp. 14-28.Liewellyn D.H., (1990), “The Effect of Polypropylene Fibers on theProperties of Concrete and Mortar”, B. Eng. Project Sheffield City Polytechnic. 95p.Morinaga S., (1973), “Pumpability of Concrete and Pumping Pressure inPipeline”, in Fresh Concrete: Important Properties and Their Measurement, Proceedingsof 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 PerformanceConcrete in Fresh State”, Proceedings International RILEM Workshop on SpecialConcrete: Workability and Mixing, University of Paisley, March 2-3, 1993.Pallière A.M. and Briquet P., (1980), “Influence of Fluidifying Sinthetic Resinon the Rheology and Deformation of Cement Pastes Before and DuringSetting”, 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 FreshConcrete”, Masters Thesis, University of Sheffield, 1975.Smeplass S., (1993), “Applicability of the Bingham Moodel to High StrengthConcrete”, 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 ofConsistency and Rheology Tests of Fresh Concrete by Viscoplastic FiniteElement Method”, Proceedings of RILEM Colloquium on Properties of FreshConcrete, University of Hannover, October 3-5, 1990, Chapman & Hall, London, pp.301-308.Tattersall G. H., (1982), “Measurement of Rheological Properties of FreshConcrete and Possible Application to Production Control”, in Effect ofSurface 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 Two-Point Test for Workability and Extension of its Range”, Magazine of ConcreteResearch, Vol. 31, No. 109, December, 1979, pp. 202-210.Wallevic O.H. and GjØrv O.E., (1990), “Practical Description of the Rheology ofFresh Concrete”, Report BML9O.602, Division of Building Material, The NorwegianInstitute of Technology, NTH, Trondheim, 1990, 13 pp.Weber R., (1963), “The Transportation of Concrete by Pipeline”, Cement andConcrete Association Translation No. 129, 1963.7374CHAPTER -4-RESEARCH PROGRAM4.0 INTRODUCTIONIn this chapter, the goals of this study (Rheology of High Performance Shotcrete) and itsprimary objectives are first described. Then, the testing programs on both the fresh andhardened concretes and wet-mix shotcretes are outlined. The specific operations carriedout to evaluate both the pumpability and the shootability are also described. Finally, thematerial 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 hardenedproperties. The most cited properties are strength and durability, but it may also includeworkability or, for shotcrete, improved shootability. In this study, HPS can be any ofthese.The main goal of this study was to develop a high performance shotcrete (if possible, toimprove strength, durability and shootability) and also to provide fundamental informationon the pumping and shooting process. The required properties for the high performanceshotcrete are good pumpability and shootability, and also improved mechanical andphysical 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 ahigh amount of entrained air to temporarily enhance the workability for pumpingpurposes.The study of the fundamentals of pumpability and shootability presented below is basedon the measurement of rheological properties.754.1.1 Low water-cement ratio (W/C)It is well known that a reduction in W/C increases the durability of concrete; this shouldalso be true for shotcrete. The use of SP, compensates for the reduction in WIC byproducing a large reduction in the yield value of fresh concrete. However, it appears thatthe yield value is the fundamental property which governs the shootability, by controllingthe 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 HPSby 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 speciallyequipped laboratory. To avoid the contamination problems (such as by fibers in perviousmixes) usually encountered when doing shotcrete studies because of the small amount ofshotcrete 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 thepumping and shooting methods used in this study.By using an iterative process, the mix compositions of subsequent batches were modifiedbased on previous test results. It is thus not possible to present a chart showing apredetermined testing program. However, testing started with conventional shotcretemixes, 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. Thegoal was to find a combination which permitted the production of the best rheology at thelowest dosage, without either fast aging (loss of workability with time) or excessive setretardation.It was decided at the beginning of the project that most shotcrete mixes would containsilica 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 containeda fixed amount (around 50 kg/m3)of steel fibers.The same sand and coarse aggregate were used for the entire study, except for the mixesordered from the commercial concrete producer.764.1.2 High initial air contentConcrete and shotcrete can be considered as mixtures of aggregates and cement paste. Thepaste is itself composed of cementitious material, water, admixtures and air. Depending onthe aggregate specific surface area and grading, any specific mixture requires a certainamount of paste to coat all of the aggregate surfaces (and, if used, fiber surfaces) and tofill all voids between particles. Extra paste provides lubrication for workability.Depending on the rheological properties of the paste (yield stress and viscosity) theamount of extra paste needed may differ from one mix to another in order to achieve acertain concrete workability. To increase the workability of a given mix, it is possibleeither to increase the paste content or to reduce the paste yield stress and/or pasteviscosity.The adverse effects of increasing the water content and cement content (to increase pastecontent) or of increasing the W/C (to reduce paste yield and viscosity) on hardenedshotcrete (shrinkage, strength reduction, etc.) are well known. The usual way of reducingthe yield of the paste and the W/C by using a SP has already been discussed in theprevious section. The last option is then to increase the paste content by increasing the aircontent; it is shown in Chapter 3 that air-entraining agents will also reduce yield and pasteviscosity.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 ofair for this mix during pumping and shooting was very high, about 15% (i.e. leavingabout 5 % air content in the hardened shotcrete). This new method improves thepumpability and shootability by increasing the build-up thickness (by increasing the flowresistance 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 toovercome the expected reduction in workability usually associated with a reduction ofW/C. It was also expected that the residual air content of the in-place shotcrete would helpto improve the deicing salt resistance of shotcrete. The air void spacing factor wasmeasured and related to the deicing salt scaling resistance. The strength reduction wasexpected not to be large if the in-place air content was of the order of 5 %.77It is expected that the information on the rheological properties will be useful in predictingthe 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 buildup thickness is expected.4.1.3 Mix identification codeBecause of the large number of mixes cast during this study, a mix identification code hasbeen used. This code, shown in Figure 4.1, is composed of numbers and letters, andconsists of three parts:• the first part gives the date (month and day) and the type of mixer used (seesection 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 ofsilica 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 (water-reducers) W used as well as the presence of fibers (F).first second third(6-2A) 33L1SF-AMFTTTdate W/C silica si fibersfume AEAmixercementFigure 4.1: Mix identification codeThis code was used to identify all mixes except those of the small testing program carriedout to select the appropriate test parameters for the rheometer. These mixes possess theirown identification code and are presented in Chapter 5.784.2 TESTING PROGRAM4.2.1 Fresh propertiesDifferent 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 afterpumping to evaluate the effects of pumping on compaction. The air content was alsomeasured after shooting, especially when the concept of a temporarily high initial aircontent was used, in order to check the compaction achieved during shooting.Some non-standard tests have also been used. The rheological properties were measuredat different times to estimate the effect of aging on workability. They were also measuredbefore and after the pumping and shooting. To determine those properties, a newrheometer was built; the rheometer is described in detail in Chapter 5. Other non-standardtests specifically related to pumpabiity and shootability were also performed (see Chapters6 and 7).4.2.2 Hardened propertiesDifferent standard tests were carried out on hardened concrete and shotcrete: compressivestrength (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 wasprimarily directed at the rheology of high performance shotcrete, these tests were onlyperformed on a limited number of mixes. However, compressive strengths were measuredon most mixes.4.3 PUMPABILITY STUDIES4.3.1 Pumping pressureIn order to pump the concrete, a laboratory concrete pump was built. The pump isequipped with a pressure gauge, so it was possible to determine the required pressure topump a certain concrete mixture. The pump is fully described in Chapter 6.794.3.2 Pressure bleed testDuring the project, it was decided to build a pressure bleed test apparatus. This equipmentand the test procedure are fully described in Chapter 6.4.4 SHOOTABILITY STUDIESThe shooting operations were carried out near the civil engineering materials laboratory atUniversity of British Columbia. For this purpose, a rebound chamber was built. Insidethis chamber, several tests were performed to evaluate the shootabiity including the buildup thickness test and rebound test. These tests are presented in Chapter 7.4.5 MATERIALS4.5.1 CementSeveral 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 aregiven in Appendix A. In the mix identification code, the letters L or T have been used toidentify 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 ashOnly one condensed silica fume was used in this project. For one mix, a fly ash of type Fwas used. The chemical compositions and the physical properties of the silica fume andthe fly ash used in this study are given in Appendix A.4.5.3 AggregatesTo maintain a constant supply of sand and coarse aggregates, it was decided to stockpile alarge amount of sand (10 000 kg) and coarse aggregates (5000 kg) at the beginning of theproject. The physical characteristics, including the grading of the sand and the 10 mmaggregate are given in Appendix A. The sand had an absorption of 1.5 % andcorresponded to the ACI 506 gradation number 1 (see Chapter 1). The coarse aggregatehad a maximum size of 10 mm and an absorption of 1.1%.804.5.4 FibersOnly one type of steel fiber was used in this project. It had a length of 30 mm, a diameterof 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 thisfiber were used.4.5.5 SuperplasticizersFive 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 productsWater-reducers and air-entraining agents were also used in this project. The air-entrainingagents were both vinsol resins, but from different suppliers (M and N in the mixidentification code). A water-reducer (W in the mix identification code) was used for a fewmixes. The manufacturer product information is available in Appendix A.4.6 EQUIPMENTMany pieces of equipment were used in this project. Some of them were built, others werebought or rented (air compressor). Equipment used to perform standard tests such as theslump test is not described nor mentioned in this section. The rheometer (Chapter 5), theconcrete pump (chapter 6) and the pressure bleed test apparatus (chapter 6) were designedand built at UBC.4.6.1 Concrete mixersTwo 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 wasused for small trial batches (approx. 0.03 m3). Mixes done with this mixer have in thefirst part of their ID the letters E, F, G or H.The inclined drum mixer was used for larger batches (up to 0.1 m3). This mixer wasmounted on a stage in order to allow it to discharge directly into the pump hopper. Mixesdone with the drum mixer have the letter A, B or C in the first part of their mixidentification code.81Mixes batched at the concrete plant were mixed with a pre-mix drum. They weretransported in a truck mixer in 1 m3 batches. Mixes batched at the concrete plant have theletter T in the first part of their mix identification code.4.6.2 Shooting equipmentFive different nozzles were used in this study. However, most of the mixes were shotwith a 50 mm Putzmeister nozzle (nozzle b), which geometry similar to that shown inFigure 1.4. The rebound chamber is a cubical box open on one side (dimensions 2.3 m x2.3 mx2.3m).4.7 REFERENCESBeaupré D., Mindess S. and Morgan D.R. (1993), “Development of HighPerformance Shotcrete (theoretical considerations)”, Engineering FoundationConference, Shotcrete for Underground Support VI, Niagara-on-the-Lake, Canada, May2-6, 1993, pp. 1-8.82CHAPTER -5-DEVELOPMENT OF THE UBC RHEOMETER5.0 INTRODUCTIONIn 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 ofother types of rheometers, starting with the first Tattersall MKI is given; three categoriesof rheometers, based on the torque measurement technique, are described. Next, theconsiderations involved in the design of the UBC rheometer are presented. A physicaldescription of the new apparatus is given, and modifications made to the torque measuringdevice in the early stages of the rheometer development are explained. The three computerprograms which were developed to operate the rheometer are also described. Results froma small testing program carried out to evaluate the performance of the rheometer arepresented, and the operations of the rheometer are described. Finally, the results of othertests 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 REVIEWMuch 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 furtherspecifically identified.The rheology of cement pastes and mortars has been studied with various coaxial cylinderviscometers for many decades. However, the first attempts by Tattersall to use a similartype of apparatus on concrete were not successful. Indeed, Bloomer (1979) (as quoted byTattersall (1990)) has stated that:No coaxial cylinder viscometer yet used in concrete research has satisfiedthe general requirements, particularly as regards the size ofgap between thetwo cylinders.83Only 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 determinerheological parameters. These apparatus should be considered as “first generation”; theyare all based on the measurement of the electric mixing power requirements. However, thelack of precision in determining the applied torque by electric measurements led to thedevelopment of a second generation of concrete rheometers.This second generation of rheometers uses a hydraulic transmission in order to eliminatethe imprecision in evaluating the torque requirement with electhc power. Two separateapparatus, the MKII and the MKIII were developed by Tattersall. Modifications to theseapparatus have been made by many researchers, as will be discussed later. These first andsecond generation rheometers were hand operated.The third generation of rheometers uses strain gauge technology to measure the appliedtorque. Most of them use plotters or computers to record the torque measurement andspeed; some are fully automatic.5.1.1 First generation rheometersTattersall first used a Hobart food mixer to plot flow curves based on the powerrequirements to drive an impeller in fresh concrete. An important result was obtained withthis 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 toevaluate the torque of an impeller turning in fresh concrete: the power used to drive theimpeller in an empty bowl was subtracted from the reading obtained when the impeller wasdriven in the concrete in order to determine the power requirement. Power measurementswere carried out using a wattmeter.This type of torque measurement is not precise. Problems such as the regularity of theinput voltage, a long warm-up period, the necessity of frequent calibrations, and the smalldifferences in power requirement between an empty bowl and a full bowl with respect tothe absolute value of the reading, rendered this type of apparatus unsuitable for seriousrheology measurements. Thus, a second generation of rheometers was developed.845.1.2 Second generation rheometersThe lack of precision in measuring the torque was corrected by using a hydraulictransmission. The Tattersall MKJI and MKJII apparatus, and modified versions of thesemade by other researchers made up the second generation. The MKII was developed formedium to high workability concretes and the MKIII was developed for medium to lowworkability concretes.The original MKII used the coaxial impeller shown schematically in Figure 5.1. Thisapparatus was hand operated at five different speed levels. The torque was measured by apressure gauge reading. The results obtained with this rheometer were much better thanthose obtained with the first generation rheometers.The MKII was slightly modified to become the MKIII apparatus, which was suitable forhandling 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 twoFigure 5.1: Schematic representation of the MKII apparatus (Tattersall, 1991)85gears. Planetary motion was chosen in order to insure that the new impeller would notmove only through the same region of the concrete sample. For this, a gear ratio of 2.25was chosen (not a whole number). A new gear box was used to obtain the correct impellerspeed, and the diameter of the sampling bucket was enlarged to accommodate the newimpeller motion (from 254 mm to 356 mm). Figure 5.2 shows the new impeller with thegears which give the planetary motion.Wimpenny and Ellis (1987) have used a tachometer, a pressure transducer and a chartrecorder with the MKII to eliminate the operator influence when reading the pressuregauge. 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 thisway, 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 toonly one apparatus to cover a wide range of workabilities: the MKIII can also be used forhigh workability.Tooth gear 16DP 45fixed to bearinghousingMain shaftmmFigure 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) toremove the operator influence in estimating the pressure. They made these modificationsto 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. ThisI Tooth gear 16DP 20fixed to impeller shaftH impeller shaft(12 mm Lleter)End shaft —(10 mm dia.)I—130 mm—I86segregation factor is based on the measurement of the aggregate contents of the upper andlower part of the rheometer sampling bowl. After segregation caused by a long testingprocedure, the concrete from the upper part of the bowl shows a reduced aggregatecontent while the concrete from the bottom part of the bowl possesses a higher aggregatecontent.Wallevik and Gjørv (1990a) were able to obtain plots similar to that shown in Figure 5.3by using a chart recorder. They were able to record the flow curves which give a betterestimation of the flow resistance, after analysis, than does the operating procedureoriginally developed by Tattersall.1.0IFigure 5.3: Example of data from Wallevik and GjØrv (1990a)5.1.3 Third generation rheometersThe third generation of rheometers uses modern electronic equipment to measure theapplied torque and also to measure and record the speed. With the development ofcomputers and data acquisition facilities, fully automatic rheometers are underdevelopment; some are now commercially available.Some rheometers still use the original design of the MKJI or the MKIII. Others havedeveloped modern versions of coaxial-cylinder viscometers (see Chapter 3) or plane/planerheometers (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 thetorque on a MKII frame. They also used a chart recorder to obtain the torque vs. speedplots. Figure 5.4 presents a schematic representation of the set-up for the slip ring andTorque (Nm) 887shows a typical trace from the chart recorder. It is obvious that the data in Figure 5.4 aremore scattered than the plot in Figure 5.3.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 theobserved spread in the data.The same authors have described a coaxial-cylinder viscometer, now commerciallyavailable as the BML-Viscometer (Wallevik and Gjørv, 1990b). This apparatus is drivenby a computer. A fixed load cell is used to measure the torque. Because there is noplanetary motion, the torque can be measured on the fixed cylinder, and the speed on therotating one. They presented a very good correlation between the results obtained from theMKII and those obtained from their BML Viscometer. However, coaxial-cylindersviscometers cannot be used with medium-low to low workability concretes (slump limitabout 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). Thisrheometer is still under development and should be available soon. It was designed for usewith high to medium workability concretes and can be used to study the effect of vibrationon rheological behavior.80‘—e1 ?40 ;jj30__ ____E20 —I I I I I I16 12 8 4 0Torque (Nm)885.2 UBC RHEOMETER5.2.1 Design considerationsIn the research project described in Chapter 4, one of the objectives was to measure therheological properties of concrete before and after pumping, and also after shooting (ifpossible). The in-place shotcrete can be considered as a low to very low workabilitymaterial. 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 theplanetary motion are those originally chosen and used by Tattersall (Figure 5.2). Thismakes it possible to use the calibration constants, K and G (see Chapter 3) to obtain therheological properties in fundamental units if desired, as calculated by Tattersall for hisIVIKIII apparatus.In the experimental procedure used here, many operations had to be carried out in a shortperiod of time with limited human resources: concrete casting, slump test, air test, actualshooting, rebound test, build-up test, washout test, etc. Therefore, the apparatus had to beeasy to use and fully automatic, so that an operator was needed only to do the concretesampling and start the test. The option of using a computer to control the test executionwas thus chosen.To increase the accuracy in determining the impeller speed, a commercially availablemagnetic tachometer was located between the motor and the reducer, where the speed is ata 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 celland a turning basket, as with the BML-Viscometer. The slip ring/strain gauges option wasthus chosen. To minimize the electrical noise and interference in the slip ring, the signalfrom the strain gauges was amplified before going through the slip ring.5.2.2 Physical descriptionThe major features of the UBC Rheometer are shown in Figure 5.5: computer, motor,tachometer, reducer, slip ring, torque meter, impeller and sampling bowl.89reducerslip ringtransfer gearamplifierstrain gauges S“crete level__________impellerlOOmmil130 mn,jcomputerIBM AT 286 withPCL-812PG cardbowl: 0 :356 mm, h: 250 mmFigure 5.5: General view of UBC rheometerThe 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 speedmeasurement devices. The motor (1/2 HP DC), the reduction gear box (60 to 1 ratio) andthe planetary motion gears provide the required impeller speed range, from 0 to 1.2revolutions per second.The torque measuring device, which is the critical component, has been designed and builtas shown in Figure 5.6. This device consists principally of a small beam working inflexure and instrumented with four strain gauges. When the torque is applied, two gaugesare compressed and the two others are extended, for maximum sensivity.tachometer IH DC motor 1/2 HPI control panelPOWERAFMANUAL AUTOSPEED CONTROL//90Figure 5.6: Torque measuring device and slip ring of UBC rheometerThe original cross sectional dimensions of the beam were 4 mm x 20 mm, in order tocarry the maximum required torque with sufficient deformation (for accuracy). Thismaximum torque was estimated to be 20 Nm according to the results presented byTattersall 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 ofabout 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 theslip ring (a device used to carry the signal out from the turning shaft). In this way, theelectric noise problem observed by Cabrera and Hopkins (1984) is largely avoided.5.2.3 UBC Rheometer user documentationThe computer programs used to run the UBC rheometer were developed in collaborationwith a group of undergraduate students who were working on a civil engineering materialsproject: Kevin Campbell, Stefano Donadonibus, Jeff Friesen, Einar Halbig and Kevin_____shaft fromreducerside view plan view91Wong. They also prepared a user manual for the rheometer. This manual is given inAppendix B. They also assisted in completing the computer programs, calibrating thetorque measuring device, and testing the apparatus with some concrete mixes.The user documentation explains in detail how to use the rheometer. It describes thehardware components, the use of parameter files, the program operation, the calibrationprocedure (before each test session), how to input test data and how to recover the outputfiles. Finally, the manual explains how to conduct an incremental test (described below)which is used to measure the rheological properties.5.3 COMPUTER PROGRAMSThree programs were developed: Calibrate; Incremental test; and Duration test..5.3.1 Program: CalibrateThis program constantly takes readings from the torque measuring device and displays theresults on the computer screen (speed set to zero). It is used primarily to adjust the offsetof the strain gauge bridge, which should read zero when no load is applied. This operationis carried out only at the beginning of a test session, and is not generally required aftereach test. This procedure is described in detail in Appendix B.This program is also used to calibrate the torque measuring device as described in Section5. Program: Incremental testThis program allows one to measure the rheological properties of a concrete mix. TheIncremental test is explained in detail in the user documentation under the heading “runtest”.Different test parameters, such as the maximum speed setting, the speed increment, thespeed decrement, the time for the motor to stabilize at a given speed, the sampling intervalfor the speed and the torque readings and finally the number of readings at each speed canbe 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 thisexample) of readings of speed and torque, the program increases the voltage of the motor92drive by an increment (here 300 in internal units). After a stabilization time (30 internalunits, 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 unitsor 0.3 sec). When the maximum speed chosen is reached, the speed is reduced step bystep (here a decrement of 600) until zero speed is reached and the fmal value of torque ismeasured.example of test (Max, incr, decr, stab, hit, N)(1000, 300, 600, 30, 5, 8). 900.—.—300Figure 5.7: Schematic representation of a rheometer testTo prevent damage to the rheometer, the test is automatically halted if a particularmaximum torque is reached. A data file is created for each run, containing the motorvoltage input, the impeller speed and the torque as well as the test parameters and a briefdescription of the mix.5.3.3 Program: Duration testThis program is used to measure the torque required to drive the impeller at a desiredspeed. The torque can be averaged over a number of sampling intervals. Duration test isnot explained in the user documentation because it was written after the production of themanual; details are given in Section 5.6.N (8) reading of speedand torque at samplinginterval of(5 = 0.3 seq)speeddecrement (600)end of test1Time (seconds)935.4 CALIBRATION OF TORQUE MEASURING DEVICEThe torque calibration procedure is different from the zeroing procedure described in theUser Manual though both procedures use the same program: Calibrate. The torquecalibration is carried out only once to establish the relationship between the applied torqueon 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 originallyused, and one for the 7 mm thick beam. The smaller beam was used during the smalltesting program presented in Section 5.5. The thicker beam was used for the rest of theresearch project, to test all of the mixes described in Appendix E.5.4.1 Torque calibration procedureThe procedure requires the use of two pulley wheels, and numerous weights of differentmass. The first pulley is fixed to the main shaft (as shown in Figure 5.8), and the secondis used to convert a horizontal force to a vertical force.pulley #2weightFigure 5.8: Set-up used to calibrate the torque measuring deviceThe steps needed to calibrate the rheometer are:• Remove the impeller arm from the main shaft and attach pulley #1 firmly tothe main shaft.4 strain gaugesmain shaftR=95.9mm94• Select the calibrate option on the main menu (See UBC rheometer userdocumentation 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 beloaded onto the cable and so induce a torque on the rheometer.• Apply the weights to the cable in different load combinations. Record thetotal mass and the torque reading each time.• Analyze results as described in next section.5.4.2 Torque calibration resultsFigure 5.9 shows the plot of applied torque vs. the readings from the torque meter (ininternal units) for the 4 mm thick beam. The linearity stops at around 26 Nm. This wasdue 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 thickbeam. The first and second columns are the weight combination and the correspondingmass in kilograms, respectively. The third column is the torque calculated using the torquearm of pulley #1: 95.9 mm. The last column is the reading from the torque measuringdevice.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 thetorque measuring device. The slopes of Figures 5.9 and 5.10 were used in the programsIncremental test and duration test to transform the readings to actual torque values. Thesevalues were also divided by 2.25 (gear ratio for planetary motion) to obtain the netimpeller torque.9517501500125010007505002500Figure 5.9: Calibration of 4 mm beamTorque applied on main shaft (Nm)Table 5.1: Calibration data for the 7 mm beamWeight combination Mass Torque Readings(kg) (Nm) (internal units)1 7.4417 7 1322 2.3316 2 423 7.7427 7 1374 5.7976 5 1051+2 9.7733 9 1721+3 15.1844 14 2681+2+3 17.5160 16 3101+2÷3+4 23.3136 22 4143÷5 18.9309 18 3393+4+5 24.7285 23 4412+3+4+5 27.0601 25 4781+2+3+4+5 34.5018 32 6090 5 10 15 20 25 3096700600500.4003002001000Figure 5.10: Calibration of 7 mm beam5.5 RHEOMETER TESTING PROGRAMEleven concrete mixes were cast over four days to verify the performance of the apparatusand to determine the best test parameters (maximum speed, number of readings etc.). Theemphasis was on the determination of the flow resistance. This first step was intended toverify whether the extrapolations (at zero speed) made by Tattersall were a valid means ofdetermining the flow resistance. The mix compositions and the results of some physicaltests are presented first. Results from the rheometer tests are then presented anddiscussed.5.5.1 Mix compositionThe mix selection included ordinary plain shotcrete mixes and silica fume shotcrete mixeswith different air contents. Effects of cement type and the use of small dosages ofsuperplasticizer were also determined. The compositions of the various mixes arepresented in Table 5.2. The mix identification, which uses a different code than that usedin the main study, gives the cement type (Type 10 (Tb), Type 50 (T50) and Type 10 withreplacement of 10% silica fume (SF)). This is followed by the W/C and a letter whichindicates the different dosage of airentraining agents (ex.: mix T10.43a compared to mixT10.43b).0 5 10 15 20 25 30 35Torque applied on main shaft (Nm)97Table 5.2: Mix comnositionMix Cement Silica fume Water Aggregates WR ABA SP(lcg/m3) (kg/rn3) (kg/rn3) (kg/m3)* (1/ms) (IJm) (I/ms)T10.43a 412 0 176 1772 0.91 0.00 0.00T10.43b 390 0 167 1679 0.86 0.20 0.00T10.43c 380 0 162 1632 0.83 0.58 0.00SF.43a 429 48 184 1590 1.15 0.80 0.00SF.43b 359 40 154 1330 0.96 4.50 0.00T10.38 463 0 177 1723 0.00 0.00 1.35T50.38 464 0 174 1731 0.00 0.00 1.35SF.38 411 46 170 1703 0.00 0.00 1.98T10.40 351 0 140 1487** 1.25 2.30 0.00T10.35 448 0 158 1671 1.30 0.00 4.68T10.48 396 0 189 1702 0.86 0.20 0.00* 50% sand and 50% 10 mm max. size stone** 60% sand and 40% 10 mm max. size stoneWR = water reducer, ABA = air-entraining agent, SP = superplasticizerMixes T10.35, T50.38, T10.38 and SF.38 were cast on the first day. Three rheometertests were carried out on each mix. These tests employed different values for the speedincrement and decrement. Various rheological tests were carried out on the other mixes onthe following days. Mix T10.40 was shot and tested similarly on the last day.5.5.2 Physical test resultsThe results of some standard tests (slump, air content, unit weight, and 7d and some 28dcompressive strengths measured on three 100 x 200 mm cylinders) are given in Table Rheometer test resultsAll available rheometer test results (for the above mixes) are given in Appendix C. Most ofthese tests were carried out with 150 mm of concrete in the rheometer bowl (normalposition for this test series). Tests carried out with 200 mm of concrete in the bowl will bereferred to as “deep” tests. Figure 5.11 shows the position of the impeller with respect tothe concrete level for the normal (a) and the “deep” (b) positions.98Table 5.3: Physical test resultsMix Slump Air content Unit weight Compressive Compressiveidentification strength (7d) strength (28d)(mm) (%) (kg/rn3) (MPa) (MPa)Tl0.43a 95 3.5 2364 49.3 67.3Tl0.43b 240 8.0 2256 28.1 41.1T10.43c 250 9.0 2202 29.8 39.7SF.43a 60 5.0 2281 39.7 -SF.43b 195 15.0 2023 18.0 -T10.38 85 3.0 2395 48.4 -T50.38 230 3.5 2392 46.0 -SF.38 80 5.0 2364 47.2 67.3T10.40 50 15.0 2114 19.5 -T10.40s*- 3.5 2378 30.7 -T10.35 280 3.0 2395 - -T10.48 230 4.5 2307 34.5 45.2*after being shotFigure 5.11: Normal (a) and “deep” (b) position of the impellerBecause the first concrete tested was very viscous, it was not possible to run the test in thedeep 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 inthis position, the 20 Nm initial torque limit on the main shaft was reached (20/2.25 = 8.8Nm on the impeller shaft). The 4 mm beam was used for the rest of this small test(a) normal position (b) “deep” position99program (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 wereactually pumped or shot except for mix T1O.40 in Figure 5.21) are presented in Figures5.12 to 5.21. On these figures, each dot represents the average of all of the torquemeasurements made at a fixed speed (except in Figure 5.14, where each dot representsone measurement of torque at one speed).For each test, the test parameters described in the user documentation are given: maximumspeed, speed increment, speed decrement, stabilization time, sampling interval andnumber 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 obtainedwhen the speed is increasing (arrow pointing up) are different from those obtained whenthe 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 orthixotropic behavior, as explained in Chapter 3.The straight solid line in Figure 5.12 is representative of the Tattersall two-pointexperimental method analysis (the zero speed measurement has been disregarded). Usingthe solid line extrapolation, the flow resistance (g) of this concrete would be 3.5 Nm andits torque viscosity (h) would be 1.9 Nm.s. But, by considering the zero speedmeasurement and using the dotted line, these values would be 2.6 Nm fOr g and 2.8 Nm.sfor h.Figure 5.13 presents the results of a “slow test (about 5.5 mm.) carried Out by usingsmaller speed increments and decrements as well as a greater number of readings at eachspeed on the same mix as in Figure 5.12, which is considered a “fast” test (about 1.1mm.). From Figure 5.13, h is 1.6 Nm and g is about 2.6 Nm.s. These results (and thoseavailable in Appendix C) show that the use of small speed increments and decrementsgives the best results with respect to linearity. However, this increases the testing timeand, as mentioned in Chapter 3, the risk of segregation. It is thus important to findoptimum values for the test parameters.CCImpeller speed(revls) —Impeller speed(revls) —•LC cf—Impeller speed(rev/s)•.1C 0 CD o CD-J aoiIlII.’• ;:.•:11,jIiji•.-i—-Il—.I.•ii4i•.—,——J..,...IU‘-•—i!—ii.iiL,;..•:‘C—————UI—•JUCU’00C CI if I— -. 0IImpeller speed(rev/s)—000r1 IImpeller speed(revls)L’.00———————Impeller speed(revls)CC—C00C.I—I%%———I.—.*——————rM-——————— p——————p n p———————oej I: C.’ —1.——————. .9.........——._h—————t,.—————‘e—————© -J—————A’_______0Torque (Nm)Figure 5.18: Effect of air content (Mixes SF.43a and b)1.2‘—SiI::0.4i0..rlttest (3000,100,100,50,5,5)I — TV.— II: / 7- type 10 + F.S.([. — jOtypelO1 • type 50,-—1021.24:aI I• test (2500,300,50,10,1,19)A test (2500,50,50,5,1,20)5 6 7 81.20.4aE 0.20 J/1,iI0 1 2 3 4Torque (Nm)Figure 5.19: Effect of cement type (WIC = 0.38)6 7 8• test (3000,100,100,50,5,5)‘‘‘‘42.. test (3000,200,200,70,5,5)A test (2500,500,250,10,3,5)• 0.43W.R. 4 —I- 0.38 W.R. LLI’ ri- 44%AZS/7I4%I 44.- — —0 1 2 3 4 5 6 7 8Torque (Nm)Figure 5.20: Effect of W/C and the use of superplasticizer103In order to visualize the spread of the data, all of the data from the descending part of thetest shown in Figure 5.13 are plotted in Figure 5.14. These results are similar to thoseobtained by Cabrera and Hopkins (1984) reproduced in Figure 5.4. An interesting point isthat the degree of spread is reduced at lower speeds, which is good for the determinationof the flow resistance.Figures 5.15 and 5.16 show the results of tests on the same plain shotcrete mix but castwith some air-entraining agent. On both curves, the extrapolation made without takingmeasurements 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 clearlyshown. Tests with smaller speed increments and decrements were used (compared toFigure 5.15 and 5.16) for mixes T10.43 b and c. Again, the “slow” tests (smaller speedincrements and decrements) give more linear behavior. Figure 5.18 also shows the effectof air content on flow resistance for silica fume shotcrete mixes. In Figures 5.17 and5.18, the main effect of air-entrainment is a large reduction of the flow resistance withlittle reduction of the torque viscosity.Figure 5.19 shows the effect of cement type and silica fume replacement. The use of Type50 cement increases the workability by reducing the flow resistance. As expected, thereplacement of cement by silica fume (10 % in this case) produces an increase in the flowresistance, and a small reduction in torque viscosity if the W/C is reduced (see Figure3.13).Figure 5.20 shows the effect of W/C and the effect of using a superplasticizer. The dottedline represents the expected results for a mix with a W/C of 0.35 without asuperplasticizer. The use of a superplasticizer reduces the flow resistance considerably andincreases the torque viscosity accordingly.Figure 5.21 shows the effect of air loss (compaction) which occurs during shooting; thisis primarily an increase in flow resistance without a significant change in viscosity whenthe air content drops from 15.0% to 3.5%. This reduction in air content is accompanied byan improvement in 7-days compressive strength, from 19.5 MPa to 30.7 MPa. The effectof shooting will be discussed further in Chapter 7. The results shown in Figure 5.21indicate that rheological properties can be measured on shotcrete by shooting directly intothe rheometer sampling bowl.1040.8__0.6____ ____ ___L. 0.4—0.2EFigure 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 ofillustrating the effects of many variables on the rheological properties g and h. However, itmust be kept in mind that, with respect to concrete mix composition, it is difficult to varyonly one parameter (e.g.: a reduction in water content affects the proportion of othercomponents as well as the W/C)9- water?• A.•+SPK +sF -water/sho.Ing type 50+aW01.2test (2400,200,50,20,1,50)—0 1 2 3 4 5 6 7 8Torque (Nm)5413z10o reference (T10.43a)o 0.43 + air• 0.43 + SF• 0.43 + SF + air0.40 + air0.40 + air + shot0.38‘ 0.38 + SF0.38 (type 50)• 0.35? (not tested)• 0.35 + SPI I I- I0 1 2 3 45h (Nm.s)Figure 5.22: Effects of mix composition and shooting on g and h1055.5.4 Test parametersFrom the results presented in section 5.5.3, the test parameters chosen for the rest of thisstudy were (3000, 300, 100, 20, 1, 50) for a test duration of 2.8 minutes. During eachtest, a maximum impeller speed of about 1.08 rev/s (3000 speed internal units) wasreached in 10 speed increments. The speed was then gradually reduced to zero in 30decrements. At each speed setting, 50 measurements of speed and torque at an interval ofapproximately 0.06 sec (1 time internal unit) were executed after an initial waiting periodof about 1.2 seconds (20 time internal units). These test parameters were chosen as acompromise between precision and duration of the test.For the determination of the flow resistance, the zero value have been neglected exceptwhen specified. When the real intercept has been used, it is noted by g’ instead of g. Asusual, only the descending branch of the curve has been used.5.6 OTHER TEST RESULTSAdditional tests were carried out during the rest of the project. A new impeller was built tocheck the theoretical results obtained from the impeller motion analysis. Finally, somemodifications to the rheometer are proposed.5.6.1 Theoretical analysis of impeller motionThis analysis was carried out in order to explain some intriguing results obtained at lowimpeller speeds, as well as the spread in the results observed in Figures 5.5 and 5.14. TnFigure 5.23, three possible results are presented. Case (a) is a linear speed-torquerelationship, representative of a Bingham behavior. Cases (b) and (c) are non-linear at lowimpeller speeds.One explanation for the spread of the data and the non-linearity at low impeller speeds isthe possible influence of the impeller position on the torque requirement. Figure 5.24shows two positions of the impeller during the planetary motion. Case (a) is referred to asthe 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 inFigures 5.5 and 5.14 should be expected. Also, because the average torque is measuredwith very little displacement at low speeds, behavior as in cases (b) or (c) of Figure 5.22should be expected depending on the final position of the impeller.IFigure 5.23: Schematic representation of observed deviation from Bingham behavior1060— ] —Top viewSide viewmain shaftimpeller shaftfingers(a): I positionFigure 5.24: Position I and position T of the impeller(b): T positionTo simplify the analysis, the geometry of the hypothetical impeller shown in Figure 5.25awas used. A gear ratio of 2 was chosen: the impeller angular speed is twice the angularspeed of the main shaft. The relative tangential speeds are given for the I and T positionsin Figure 5.25b and 5.25c, respectively.Torque (Nm)‘R=2r 1(a) hypotetical impeller: side view (b): I position (c): T positionFigure 5.25: Hypothetical impeller and relative tangential speed for I and T positionsTwo calculation examples are presented below, which were done for a fluid behaviorsimilar to that shown in Figure 5.26 (fluid C). Assume an angular velocity of the mainshaft o=O.5 rad/s, and r 5 cm. A radius of 5 for this geometry gives a similar rate ofshear 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 thatspeed in fluid (C) is F 6 N according to Figure 5.26. The speed of thelower finger is zero. The torque is then: 3Fr = 3 x 6 x 5 = 90 Ncm or 0.9Nm.position T: for w=0.5 rad/s, the tangential speed of both fingers is 2J2Q)r7.07 cm/s (Figure 5.24c). The force (F) required to move one finger at thatspeed in fluid (C) is F = 5.41 N (Figure 5.26). The torque is then: 2 x (F x(3/2)’12r} = 2 x 5.41 x 2.07 x 5 = 1120 Ncm or 1.12 Nm.R-I I1, Gear ratio:111111111111N111! III iriI_li_li (2 1)1072or ..-—________________shaft 2oMain shaftConcrete levelr 2orr2orr2wr2wrU .4Figure 5.26: Four hypothetical fluid behaviorsIn this example, the torque requirements are different for different impeller positions. If achart recorder were used to trace the torque requirement with respect to time, the torquerequirement of a test carried out with the parameters of this example would show afluctuation from 0.9 Nm in the I position to 1.12 Nm in the T position, as shown inFigure 5.27.20I108I Fluid(B) I//204 4Force (N) Force (N)ICT position1,120:z:(1/co = 2s) I position0 2 6Time (s)Figure 5.27: Expected torque requirement with respect to time109The torque requirements of the hypothetical impeller have been calculated at three differentspeeds in both positions for the four hypothetical fluids shown in Figure 5.26. Thesecalculations 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 19.6cm/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 fourhypothetical fluids of Figures 5.26. The spread of the results is clearly indicated. Becausethe model impeller motion diameter is 300 mm, while the UBC impeller motion diameteris 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 animportant factor. The amount of spread is not dependent of the angular velocity. Thisanalysis shows that some spread in the torque measurements should be expected. Byrunning a test similar to the one in Figure 5.27, it should be possible to observe thespread.At this point, it is important to remember that fresh concrete is a non-homogenousmaterial, and this too could contribute to the spread. The maximum aggregate sizecertainly has some influence, as well as the presence of other components, such as steelfibers.5.6.2 New impeller testTests were carried out in order to try to observe the theoretical behavior shown in Figure5.27. For this, a new impeller was built and used with the program Duration test. Figure5.29. shows the new impeller which possesses four removable fingers.The program Duration test allows one to constantly read the torque while the impeller isturning at a constant speed. The torque can be averaged over a certain number ofmeasurements if desired.11080.01.0o.s0.01.00.5$ (Nm)A) Hypothetical ImpellerTorque (Nm)B) UBC impeller1.0Figure 5.28: Results from the impeller motion analysis111New impeller shaft(12 mm diameter)145 mmFigure 5.29: New impeller geometryFigure 5.30 shows the results of tests carried out with two fingers. Each bar chartrepresents one torque reading. On this graph, one can observe the oscillatory effect causedby 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 maximumsize) 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 newimpeller and also with the H-impeller (which was used for the entire study). The results ofthese tests are presented in Figure 5.31. In this figure, each measurement represents theaverage of five readings. The results show that the amount of spread decreases with thenumber of fingers (less effect of position), while the average torque requirement increaseswith the number of fingers. Thus, a four finger impeller of this type would give lessspread 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 Himpeller for the remainder of the project.5.6.3 Sensitivity testsA test without any concrete in the bowl was conducted to evaluate the possible effect ofinertia forces and/or friction during the test. A test was also carried out with the samplingbowl filled with water. These results are shown in Figure 5.32.Steel plate 3 mm thick4 removable fingers9 mm diameter11214012010080!60if 400 100 200 300 400 500 600 700 800 900Number of readingsFigure 5.30: Oscillatory effect caused by the movement of the impeller400350tl)300E 150100500 10 20 30 40 50 60 70 80 90 100 110 120Number of readings•• .4• • 4• •t%. <44’•4<44t4+ 4<&•+(4+•4 • <• 44(((•••tt<_••Figure 5.31: Effect of impeller (number of fingers) on the spread of torque113The test on air indicate that the inertia effect or friction are negligible. The offset of 0.0 15Nm, which is very small on the scale used to present the results on concrete (usually 0-5Nm) is caused by the zeroing procedure described in Section 5.32: Rheometer test carried out on air (bowl empty) and on water0.05The 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 samevalue (no flow resistance expected). Because the viscosity of water is very small (0.001Pa.s), the flow inside the sampling bowl becomes turbulent early in the test. For thisreason, 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 testindicates that the apparatus is very sensitive.5.7 PROPOSED MODIFICATION TO THE UBC RHEOMETERIf a second version of the apparatus becomes necessary, the following modificationsshould be made:• Replace the manual crank and the counterweight with an electric device toraise the bucket platform.• Modify the program to remove the calibration procedure before each testingsession.0 0.01 0.02 0.03 0.04Torque (Nm)114• Modify the screen output to have the flow curve on the screen when the testis finished.• Make provisions to be able to transform the rheometer to a coaxial-cylindersviscometer:- 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-cylindersviscometer for mortar would be a plus.5.8 REFERENCESCabrera J.G. and Hopkins C.G., (1984), “A Modification of the Tattersall Two-Point Test Apparatus for Measuring Concrete Workability”, Magazine ofConcrete 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 forFluid Concrete”, International RILEM Workshop on Special Concrete: Workability andMixing, 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 Two-Point Test”, Proceedings of RILEM Colloquium on Properties of Fresh Concrete heldUniversity 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-PointWorkability 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-CylindersViscometer for Fresh Concrete”, Proceedings of RILEM Colloquium on Propertiesof 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 TwoPoint Workability apparatus”, Magazine of Concrete Research, Vol. 39, No. 140,September, 1987, pp. 169-174.115CHAPTER -6-PUMPABILITY6.0 INTRODUCTIONIn this chapter, the development of a laboratory concrete pump and a pressure bleed testare presented. The results from both tests are analyzed in order to predict pumpabiity. Thepaste volume concept is explained and the effect of air entrainment on pumpabiity is takeninto account.6.1 LABORATORY CONCRETE PUMPThe 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: atleast 1 m3 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 shootingsite, it is difficult to achieve the degree of control generally achieved when all operationsare performed in the laboratory.In addition, when using a truck mixer, it is difficult to avoid contamination of the mix byany concrete or water left in the mixer drum. Finally, in most shotcrete studies, because oflogistics all shooting operations are concentrated into one or two days. It is then verydifficult 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 toenable the use of previous results to plan the next experiment or mix design, a smalllaboratory size concrete pump was designed and built. This pump was used to pump andshoot high performance shotcrete (lIPS). It is essentially a research tool and was notdesigned for large volume operations.6.1.1 Design criteriaIn order to shoot concrete in the laboratory, it is important to reduce the amount ofconcrete needed to fill the pump. Moreover, the pump must be able to pump every116kilogram of concrete placed into the hopper. For inside use, it must be small in size andpowered by electricity. The pumping characteristics, especially the speed of the concrete atthe end of the hose must be representative of a real concrete pump: i.e. while pumping, thepump must be able to achieve sufficient output with respect to the nozzle size. To shootthe shotcrete, compressed air is added at the nozzle (see Chapter 7 for shotcrete testresults).A design similar to the one used by Dawson (1949) was chosen: one pumping piston andgates to control the flow of concrete. This set-up gives a longer waiting period before eachsurge 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 isof no importance. The size of the pump has been greatly reduced with respect toDawson’s pump, so that it can handle small amounts of concrete.6.1.2 Pump descriptionFigure 6.1 shows a schematic diagram of the pump which possesses a single rubberpumping piston (125 mm diameter) with a stroke of 300 mm. The pump is capable of 10strokes per minute. A pumping rate of 3 m3Ih can be achieved. An electric motor (10 Hp)powers the three hydraulic pistons (two gates and one pumping piston) which control theflow of the concrete. A remote control can be used to activate the proper pumpingsequence which is controlled by six proximity switches and three solenoid valves. Thehopper has a capacity of 0.1 m3.exit100 mmoutlethydraulicgatesrubber piston 0: 125 mm remote controlFigure 6.1: Schematic diagram of the pump117The majority of the pump components were purchased from various manufacturers. Theelectric control box and the final assembly were completed in the civil engineeringlaboratories at UEC.Six proximity switches are used to control the movement of all of the pistons. Thehydraulic system (Figure 6.2) is composed of a hydraulic pump, a pressure gauge, safetyvalves, three electric valves, a pumping piston, two gate pistons, a filter, an oil tank andsafety devices for oil level and oil temperature.Figure 6.2: Hydraulic system and proximity switchesThe power is provided by a 10 HP electric motor (208 V/ 3 ph /60 Hz). The flow and thepressure of the hydraulic pump (Continental PVA6-6B30-R-0-1R) can be adjusted ifrequired. The user should refer to the pump operating instructions. The flow was set to amaximum (about 30 1/mm.) and remained at this setting throughout this study. The pumpwas first set to produce a pressure of 1.67 MPa on the fresh concrete. This pressure wasincreased up to 2.50 MPa to permit the pumping of stiffer mixes. A “Bourdon” pressuregauge 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.psips4ps6outlet gatecylinderfilterlevel andtemperaturesafety118A safety valve, which was set at 17.5 MPa was used to prevent accidents. This safetyfeature is located before the first solenoid valve (solenoid A) that is used to enable ordisable the pumping sequence. The pumping sequence can be started and stoppedmanually, or a remote control can be used for this purpose.When the pumping sequence is started, a control box alternately activates the four othersolenoids, which control the two others valves. In Figure 6.2, the position of the pistonsindicates that the pump is ready to start pumping (solenoids B and D are ON). When thepumping piston is fully extended, the signal from proximity switch 2 (ps2) switches thepower from solenoid D to solenoid E. The inlet and outlet gate cylinders movesimultaneously (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 Cand initiates the sucking of concrete from the hopper. When the pump piston is fullyretracted, psi switches power from solenoid E to solenoid D and both gates movesimultaneously again (inlet closes and outlet opens). When both gates are fully open orclosed, a signal from ps4 and ps5 switches the power from solenoid C to solenoid B andthe pumping starts again. This sequence continues until the power to solenoid A is turnedOFF.Some problems were encountered during the research project. One of them is the poordesign of the hydraulic gates: aggregates have occasionally been trapped, thus preventingthe gate from closing completely, and preventing proximity switches 4 or 6 from beingtriggered, resulting in a breach in the pumping sequence. This problem has been resolvedby 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 thefroklift. The resulting misalignment between the cylinder and the gate resulted in frequentblockage of the gate. A new blade and a protective device for the gate were built and put inplace to prevent further damage.6.2 PRESSURE BLEED TESTWhen most of the problems with the pump were solved, the few results available were notpromising enough to suggest that the measurement of rheological properties alone would119be sufficient to predict the pumpability of a concrete mix. Therefore, it was decided tobuild a modified pressure bleed test apparatus, similar to the one used by Browne andBamforth (1977) as described in Chapter Design criteria and apparatus descriptionFor all practical considerations, the piston used for the pressure bleed apparatus isidentical to the concrete pump piston. Compressed air and an air bag were used to applyand maintain the load on the piston, instead of the hydraulic piston used by Browne andBamforth (1977). Table 6.1 summarizes the principal geometric characteristics of theirapparatus and those of the new pressure bleed apparatus, as well as those of the laboratoryconcrete pump. One can see that the pressure applied on the concrete with the newapparatus is lower than that used by Browne and Bamforth, but is more representative ofthe actual pressure applied on the concrete during pumping. The size of the sample onwhich the amount of bleeding water is measured has been increased.Table 6.1: Geometric characteristics of bleed test atmaratusItem Browne and Bamforth new apparatus concrete pumppiston diameter 12.5 cm 12.5 cm 12.5 cmcylinder length 13.9 cm 21.5 cm 30 cmsample volume 1700 cm3 2640 cm3 3670 cm3pressure on concrete 3.5 MPa 2.1 MPa 1.7 - 2.5 MPaloading system hydraulic manual compressed air automatic hydraulic automaticFigure 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) onthe 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. Aporous polypropylene disc is used to hold the mesh in place and allows the water or paste120to drain into the tap hole. Figure 6.3b shows the side view of the apparatus at thebeginning of a test.6.2.2 Test procedureOther 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 andwrench. The test is carried out by executing the following steps:• Check that the piston is fully retracted by using the articulated arm (notshown 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 therod).• Remove excess concrete with a trowel to obtain a flat surface, clean the topof the cylinder and place the mesh over the concrete.• Place the porous polypropylene disk into the top cap. The disk must besoaked 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, untilthe level of water is stable (no change for 2 minutes).• Remove the top cap and the concrete, and clean the apparatus. Record the finallength of the concrete specimen.121concrete samplemaximumtravel = 60 mmLi I(a) (b)Figure 6.3: New pressure bleed apparatus6.2.3 Pressure bleed test resultsBecause 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 ableed test: the amount of water emitted during the test is plotted with respect to time. Thecompositions of all of the mixes used during this study (except those used to test therheometer and presented in Chapter 5) are available in Appendix E. All curves from thepressure bleed tests are available in Appendix F.measuringcylinderporous polypropylene disktopcap —““O”ringsrubber piston)122120•1002 ii80/6O /40/20 r0 20 40 60 80 100 120 140Time (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 tothe typical results obtained by Browne and Bamforth (see Figure 2.10). In their test, mostof the water was emitted after two minutes; with the new apparatus, for the pressure usedand 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 inChapter 2 (Section 2.8) as a measure of stability under pressure, is not applicable to theseresults.Differences in mix composition and/or the lower pressure used during the present testsmight explain these results. According to Powers (1968), bleeding (not pressure bleeding)can be expressed by two principal determinants: the initial bleeding rate and the totalamount of water expelled. For pressure bleeding, these might be represented by the initialslope of the curve in Figures 6.4 or 2.10, and by the final amount of water emitted. Therate 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 thegravitational constant and Ah/L is the hydraulic gradient. In normal bleeding, the hydraulicgradient depends on the unbuoyed weight of the solid material which is a function of thesolid content of the mixture. K is a function of the specific surface area and of the solidcontent of the mixture. For pressure bleeding, it is logical to assume that the hydraulic123gradient is proportional to the applied pressure, because the unbuoyed weight is smallcompared to the applied pressure.The initial bleeding rate in Figure 6.4 is about 2.6 x103/min., if expressed as a fraction ofthe sample, while for Browne and Bamforth (Figure 2.10) it is about 211 x103/min,which is about 100 times faster. According to Darcy’s law, a concrete tested in theBrowne and Bamforth apparatus would exhibit a bleeding rate faster by a factor equal tothe ratio of the applied pressures: 3.5 MPa/2.1 MPa = 1.7. This means that most concretestested in this study exhibit a bleeding rate about 100/1.7 = 60 time slower than those ofBrowne and Bamforth.The only logical explanation is that the low water-cement ratio (W/C) used in this study isresponsible, in part, for this difference; the use of silica fume (SF), which is known toreduce bleeding, is probably responsible for the remainder. According to Table 6.2 fromPowers (1968), a reduction in W/C can change the bleeding rate of cement paste by afactor of more than 20. Since Browne and Bamforth (1977) did not give any mixcompositions, one cannot be certain but, according to these results, it is highly probablethat their mix compositions were very different (high W/C, no SF) compared to the mixesused 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(x106cm/see)wicspecific surface area of cement(cm2/g)1085 1540 2045 25500.26 103 39 17 90.32 210 80 38 200.39 - 150 73 400.48- 270 133 750.59 -- 223 1280.74 - -- 213The results of all of the pressure bleed tests carried out in this study are presented in Table6.3. The first column is the mix identification as described in Section 4.1.3. The second124column is the amount of water emitted after 240 minutes, expressed as a volumepercentage of the sample (2.64 liters of concrete). The third column is the final length ofthe fresh concrete cylinder after being pressurized for 240 mm. The fourth and fifthcolumns are the results of slump and air content tests, respectively. The sixth column isthe air content, calculated as described in the next paragraph, and the last column givessome indications regarding the pumpability of these mixes: a mixture is considered notpumpable if it causes the pump to block.Table 6.3: Pressure bleed and other test resultsMix Final bleed Final Slump Air Calculated notesidentification water length content compaction(%) (mm) (mm) (%) (%)(7.20A)3OL1SF-AF 3.4- 35 3.7 - not pumpable(7.23E)33L1SF-AF 3.7 - 230 7.8 - no pump test(7.26A) 3OL1SF-CF 3.3 195 110 6.8 6.0 borderline(7.27A)3OT1SF-AM 4.5 172 60 13.9 15.5 borderline(7.29A)3OT1SF-AM 5.5 168 115 16.1 16.3 pumpable(8.3A)3OT1SF-DN 4.4 152 160 25 24.9 pumpable(8.5A)3OT1SF-D 4.1 181 270 14 11.7 pumpable(8.11A)3OT1SF-D 4.5 188 170 11.1 8.1 pumpable(8.16A)25T15F-CF 1.2 - 225 9.2 9.2 not pumpable(8.19A)25T15F-CF 4.4 189 250 8.1 7.7 pumpable(8.23A)25T1SF-CNF 4.0 164 175 21.4 19.7 pumpable(8.24T)41L1SF-AWF 5.3 195 120 3.4 4.0 pumpable(8.25T)??L1SF-E 9.1 193 115 3.2 1.2 pumpable(8.30A)48L1FA-W 5.6 200 60 4.8 1.4 not pumpableBy measuring the final length of the concrete specimen after the test, it is possible tocalculate the initial air content if one assumes that the total volume of the air bubblesbecomes 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 (forall 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 %. Figure4.5 shows the relationship between the air content before pumping and the calculatedcompaction during the pressure bleed test. The straight line represents the idealrelationship; the results are in reasonable agreement.12525‘—‘ 200I025Figure 6.5: Relationship between air content and calculated compaction during thepressure bleed test6.3 PUMPABILITYAs mentioned in Chapter 2, pumpability can be defined as the mobility and stability underpressure within a pipe. It seems appropriate to try to relate the slump or the rheologicalproperties, which measure mobility, to pumpabiity. The pressure bleed test was related toslump and to pumpability by Browne and Bamforth (1977). However, no one has yetattempted to relate the rheological properties of concrete directly to pumpability, althoughsome theoretical studies have been oriented in this direction. Also, while working withvery high air contents, stability problems other than bleeding may arise (possible blockageof high air content mixes because of an increase in g caused by compaction).6.3.1 Slump and pressure bleed test vs. pumpabilitySince the factor Vl4OsecVlOsec proposed by Browne and Bamforth (1977) is notapplicable to this apparatus and/or these mixes, two new factors Vl4omjn and Vl4Omjn-ViOmin have been used to try to predict pumpability (because of the longer testing timewith low WIC mixes). Vl4Omjn is simply the final amount of water emitted at the end ofthe pressure bleed test. The Vl4omjnVlomjn is similar to the Vl4OsecVlOsec proposed byBrowne and Bamforth (to take into account the shape of the curve), but with a different0 5 10 15 20Pressure bleed compaction (%)126time scale. Figure 6.6 shows the relationships between slump and these factors (Figure6.6a: Vl4omjn; Figure 6.6b: Vl4Omjn-VlOmjn) with respect to the pumpability.10(%)Figure 6.6: Relationships between slump, pressure bleed test and pumpabilityUnfortunately, the limited amount of data for the borderline and not pumpable categoriesdoes not allow one to reach any firm conclusions regarding the implication of the pressurebleed test. However, these results give credits to the possible relationship between thesaturated/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 underpressure and by the bleeding rate (which is most probably related to the viscosity of thepaste). A minimum limit in the amount of water emitted could be seen as a requirementfor extra paste to stay in the saturated state under pressure (with respect to the amount ofpaste needed to fill the voids between the aggregates). This limit regarding the minimumamount 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 thepercentage (3% in our case) of extra paste to be maintained in the saturated state, and for a300250200EQ.1 150E100500_-j/• />\liii jIIIIIIIIIIIIIIIII•IIIIIIIIIIIIIIIIIII•.4::.... A••v.A1.11•.....•::.....• pumpableA borderlinenot pumpableI I0 1 2 3 4(b) Water emitted:V140-V1O (%)I I• I I0 2 4 6 8(a) Water emitted:V140127high bleeding rate, this minimum requirement in extra paste is probably higher. Thesepercentages may also be affected by the period of time under which the concrete ismaintained under pressure.6.3.2 Rheology vs. pumpabilityTheoretical models have been proposed to analyze the pumping process with respect to therheological properties. Models of a Bingham material lubricated by a Bingham lubricatinglayer have been mentioned in Chapter 3. One may suppose that the properties of thelubricating layer (the cement paste) control the steady flow of concrete in a straight pipe ofconstant diameter: i.e. where the concrete moves as a solid plug (the properties of thelubricating layer may also control the bleeding rate under pressure). The properties of theconcrete will be important when the concrete has to deform around singularities. Sakuta etal. (1979) explain the presence of a lubricating layer by a concentration of cement paste atthe 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 practicalapproach is called for. A practical approach, such as the workability box proposed byTattersall (1991), might be a good way to assess pumpability.Tables 6.4 and 6.5 present some information on rheological properties and pumpabilityfor mixes without and with steel fibers, respectively. The first column gives the mixidentification. The second column gives the air content before pumping, after pumping orwhen 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), thetorque viscosity (h) and the paste fraction of the mix, respectively. The last column givesinformation on the pumpability: whether it is pumpable or not, the required pumpingpressure (applied on the concrete) and/or the pumping rate.These results and some others are presented in Figure 6.7. All mixes included within thebox are pumpable (except for two non-reinforced mixes). A different pumping set-up ormixes with high W/C ratios may have a different pumpability box. Many factors such aspump 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 orfor mixes susceptible to segregation (with a bad grading of aggregates for example) thatthere 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.Table 6.4: Rheological properties and pumpability (mixes without fibersMix Air content Slump g* h paste fraction Notesidentification (%) (mm) (Nm) (Nm.s) (%)(3.24A)4OT5SF-AMW 9.9 - - - 40.1 pumpable(3.24P)4OT5SF-AMW 6.5 40 - - 37.6 pumpable(3.26A)40T1-WM 15.0 50 2.1 0.5 41.1 pumpable(5.20A)35T1SF-AM 6.7 30 4.0 0.2 35.0 borderline(5.25A)33L1CF-AM 14.3 15 3.4 0.4 41.1 borderline(5.27A)3OL1SF-AM 12.9 100 1.6 0.4 42.1 pumpable(6.1A)35T35F-AM 11.1 170 0.5 1.5 42.2 pumpable(7.27A)3OT1SF-AM 13.9 60 2.4 0.1 43.3 pumpable(7.27P)3OT1SF-AM 8.1 15 2.2 0.3 39.0 3.90 kg/stroke(8.3A)3OT1SF-DN 25.0 160 0.8 0.3 50.4 2.74 kg/stroke(8.5A)3OT1SF-D 14.0 270 0.3 0.4 43.6 pumpable(8.5P)3OT1SF-D 7.5 250 0.3 0.7 39.1 pumpable(8.11A)3OT1SF-D 11.1 170 1.3 0.6 41.7 pumpable (1.18 MPa)(8.11P)3OT1SF-D 5.4 90 1.3 0.6 37.9 pumpable (1.18 MPa)(8.11Q)3OT1SF-D-- 3.1(3.9) 0.3 - block (2.25 MPa)(8.18T41L1SF-AW 2.5 70 1.5 0.2 34.0 pumpable (0.86 MPa)(8.18P)41L1SF-AW 2.5 50 1.5 0.2 34.0 pumpable (0.86 MPa)(8.19A)25T1SF-C 8.1 250 .5 0.9 39.9 pumpable (0.86 MPa)(8.19P)25T1SF-C 7.0- .5 1.1 39.2 pumpable (0.86 MPa)(8.25T)??L1SF-E 3.2 115 1.1 0.1 7? 6.63 kg/stroke(8.25P)??L1SF-E 2.9 120 0.9 0.1 7? 6.63 kg/stroke(8.30A)48L1FA-W 4.6 30 2.3(3.0) 0.1 37.6 not pumpable(8.30B)54L1FA-W 4.8 60 1.4(1.8) 0.1 37.6 pumpable (0.64 MPa)(8.30P)54L1FA-W 3.9 40 1.4(1.8) 0.1 36.5 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 ofaccelerated artificial “aging”. At various times, the pumping pressure was recorded and thepump stopped to permit a sample to be taken of the pumped concrete for the determinationof 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), therequired pumping pressure increases.128Table 6.5: Rheological properties and pumpabilitv (mixes with fibers)Mix Air content Slump g h paste fractionidentification (%) (mm) (Nm) (Nm.s) (%) Notes(6.15A)3OT1SF-AMF 14.0 210 4.5 0.4 43.3 not pumpable(7.6A)25L3SF-AF 5.5 200 4.3 1.7 37.1 borderline(7.8A)25L3SF-AF 12.1 260 1.0 3.1 41.8 borderline(7.12A)3OL3SF-AF 4.0 140 3.5 1.0 35.2 6.38 kg/stroke(7.12P)3OL3SF-AF 4.0 25 3.8 1.3 36.0 6.38 kg/stroke(7.19A)3OL3SF-AF 3.7 140 3.1 1.9 35.2 6.73 kg/stroke(7.19P)3OL3SF-AF 4.1 60 3.8 1.2 35.1 6.73 kg/stroke(7.20A)3OL1SF-AF 3.7 35 5.1 0.1 35.2 notpumpable(7.26A)3OL1SF-CF 6.8 110 1.9 1.5 36.9 5.93 kg/stroke(7.26P)3OL1SF-CF 5.0 100 2.3 1.8 35.6 5.93 kg/stroke(7.29A)3OT1SF-AM 16.1 115 1.5 0.1 45.7 pumpable(8.4A)3OT1SF-DNF 25.5 162 1.5 0.5 51.0 pumpable(8.4P)3OT1SF-DNF 14.4 85 2.6 0.4 43.7 pumpable(8.4Q)3OT1SF-DNF 8.4 5 4.7(5.5) 0.1 39.5 block (2.41 MPa)(8.9A)3OT1SF-DF 12.1 210 1.0 0.9 42.7 pumpable(8.9P)3OT1SF-DF 4.6 70 1.9 1.2 36.8 pumpable(8.9Q)3OT1SF-DF 2.3 - 5.4 0.2 35.5 block (2.41 MPa)(8.16A)25T1SF-CF 9.2 225 1.2 3.2 38.3 not pumpable(8.16B)25T1SF-CF 9.2 255 .5 3.0 38.7 block (2.41 MPa)(8.16C)25T1SF-CN 22.9 260 .4 1.0 49.0 pumpable (0.32 MPa)(8.23A)25T1SF-CNF 21.4 175 1.1 0.7 49.0 pumpable (0.86 MPa)(8.23P)25T1SF-CNF 18.8 160 1.2 0.6 47.4 pumpable (0.86 MPa(8.24T)41L1SF-AWF 3.4 120 2.4 0.6 36.9 6.51 kg/stroke(8.24P)41L1SF-AWF 2.8 120 2.4 0.6 35.3 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 inFigure 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 thisFigure, 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 thepump works at constant volume but variable pressure). Pumping rates (Figure 6.9b) arediscussed in Section 6.7: Pumpability box: all mixesTorque (Nm)130Figure 6.8: Effect of artificial ‘gaging” on pumping pressureThe representation of pumpability (in Figure 6.9a) requires only one measurement ofrheological properties as opposed to Figure 6.6 which requires the results of two tests (theslump test and the pressure bleed test) to assess pumpability. The use of rheological5432100 1 2 3 4 5h (Nm.s)0.0 A• 0•El .>El • AEl AII1.21— Pumpingpressure(MPa)0.8 —• 1.18El 1.50• 1.720.6— 0 1.93A 2.260.4 —0.20• El• El •O AEl • AII 0 • A‘2I•II.- (•0•0•0LIElElEl-0-ElElElAAAA•II.0 A• AI]•A0 1 2 3 4 5131properties to predict pumpability also gives better and more meaningful results by givingan estimation of the required pumping pressure (for a pump with a constant flow): asshown in Figure 6.9a, an increase in the value of g or h produces an increase in therequired pumping pressure. Also, the rheological properties (flow resistance and torqueviscosity) are easier to obtain (faster and without operator influence) and more precise thanthe slump and the pressure bleed tests.6.73 6.380 7.51a39005.93fl r pumping rate6.63 —(kg/stroke) Eno fiber0 2.74 0 with fibersI IFigure 6.9: Pumping pressure (a) and pumping rate (b) vs. rheological propertiesMore studies on the relationship between rheological properties and pumpability areneeded: 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 ofpumpability are discussed in Section 7.6.I.h (Nm.s)0 1 2 3 4h (Nm.s)(a) (b)1326.4 PUMPING OF CONCRETE WITH HIGH AIR CONTENT6.4.1 Pumping rateThis study has involved pumping concrete mixes which contain high amounts of entrainedair (up to 25 %). Some problems were encountered while pumping these concretes. Therelationship 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 ofthe two mixes with high air contents are 3.9 kg/stroke and 2.7 kg/stroke for air contents of14.1% and 25 %, respectively. Because these two mixes have lower g and h values thansome other mixes, they should have been easier to pump (lower pressure).860‘420Figure 6.10: Effect of air content on pumping rate6.4.2 CompressibilityWhen 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 adelay between the movement of the pumping piston and the movement of the concrete atthe end of the hose. Figure 6.11 shows an idealized representation of the pressuredistribution for three hypothetical cases:0 5 10 15 20 25Air content (%)(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 (c) compressible (d) compressiblegood flow control good flow control poor flow controlinlet 0(1)____LtendStOp outlet outlet en outlet endDl 0__ __ _‘MI‘MI(2)4 ]____ _- l_—0(3) 4Th 0._ _ _0.____ __I_______________—I -0.I________Stop.4— —0FL1__a.. a.._ __0.1 0.I________-inlet 0‘MI(6)__a.._ __ _______ ______0.(a) (b) (c) (d)Figure 6.11: Hypothetical pressure distribution in pipesIn Figure 6.11, the flow control refers to the movement sequence of the inlet and outletgates (see Figure 6.1). A good sequence is obtained when these two gates are never opensimultaneously: they move in the proper sequence (case (b) and (c) in Figure 6.11). Whenboth gates become open at the same time (because of the poor flow control sequence), thepressure built-up during pumping (for a compressible material) is lost when the concretemoves back to the hopper (case d).Case (b) is the case of a non-compressible material. When the pumping piston is fullyretracted (Column a in Figure 6.11 gives the position of the piston) the pressure in thepipe line is shown by the graph lb (Line 1, Column b). The residual pressure due to the134residual friction which exists because of the flow resistance. When the piston startsmoving (2a), the concrete starts to move immediately at the end of the hose (small arrowsin graph 2b) and the pressure in the pipe line varies linearly. When the piston stopsmoving (4a), the pressure goes down abruptly (4b) and the concrete does not moveanymore.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 airbeing compressed (2c). The delay between the piston movement and the movement of theconcrete 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 aprogressive increase in the concrete output. When the piston comes to a stop, with aproper 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 fastdecrease in the output rate (5c) until the pressure equals the friction which causes theconcrete to stop moving (6c).Case (d) is similar to case (c) until the piston comes to a stop (4a). Because both the inletand the outlet gate are open simultaneously for a short period of time (with a poorpumping sequence), the concrete is pushed back into the hopper by the existing pressurein the pipeline (4d). Depending on the time lapse during which the two gates aresimultaneously open, there might be enough pressure left to keep the concrete moving outof 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 pumpSome 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 outletgates (because of a bad design), and the malfunctioning of the outlet gate (because of anaccident, one of the gates was torn).In this study much work has been done with concrete containing high amounts ofentrained air. Because of the actual pumping sequence (the two gates move at the sametime), behavior similar to that in Figure 6.11 (Column d) has been observed: for a fractionof a second, both gates were open simultaneously, and this was sufficient to lose theconfinement in the pipe line. The concrete moved back into the hopper, reducing thepumping rate by about 60 %. This problem can be corrected by adding another solenoid135valve in the hydraulic system and by adjusting the pumping sequence. It is important tonote that even if the pumping rates were reduced, it was possible to pump and shoot mostof the mixes with high air contents.The outlet gate has suffered some blockage because it was not built strongly enough. Theoutlet gate was initially designed to withstand a pressure of 150 psi and the inlet gate for apressure of 300. An outlet gate able to withstand a pressure of 300 psi would be subject toless blockage.6.5 REFERENCESBrowne R.D. and Bamforth P.B., (1977), “Test to Establish ConcretePumpability”, ACI Journal, Vol. 74, No. 5, May, 1977, pp. 193-203.Dawson 0., (1949) “Pumping Concrete - Friction between Concrete and Pipeline”, 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 andRheological Properties of Fresh Concrete”, in Proceedings of Conference onQuality Control of Concrete Structures, Vol. 2, Swedish Cement and Concrete ResearchInstitute, Stockholm, 17-19 June, 1979, pp. 125-132.Tattersall G.H., (1991), “Workability and Quality Control of Concrete”,Chapman & Hall, London, 1991, 262 p.136CHAPTER -7-SHOOTABILITY7.0 INTRODUCTIONIn this chapter, a new test set-up to measure the build-up thickness, which is used toassess shootability, is presented. The relationship between the build-up thickness and therheological properties, especially the flow resistance are then analyzed. The results of afew rebound tests are also given, along with some considerations regarding aging effectson rheological properties. Finally, compaction during pumping and shooting is analyzed,and a new model to predict shootability in terms of maximum build-up thickness ispresented.7.1 SHOOTABILITYIt is often said that if concrete can be pumped, it can be shot. The first step in maldngshotcrete 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 beshootable, but to what level?In Chapter 3, it was mentioned that the existence of the flow resistance provides a goodexplanation as to why shotcrete is shootable. It allows one to explain why the shotcreteremains in place after shooting. Then the first step in studying shootability is thus todefine this characteristic.7.1.1 Definition of shootabilityShootability is a property which incorporates parameters such as adhesion (the ability ofplastic shotcrete to adhere to a surface), cohesion (the ability of plastic shotcrete to stick toitself and to be built-up in thick sections) and rebound (the material which ricochets off theimpacted surface). The efficiency with which concrete can be applied is also dependent onthe equipment used, but this is not considered here.137In this study, shootability is considered in terms of the efficiency with which a mix sticksto the receiving surface and to itself. Thus, the build-up thickness is used to assessshootability. A mix that can be built-up to a great thickness in a single pass withoutsloughing will be referred to as possessing good shootability.7.1.2 Pumpability vs. shootabilityFrom past experience, one knows how to apply thick coats of material efficiently. Bypumping a stiff mix and by adding an accelerator, it is possible to build-up a substantialthickness of shotcrete in a single pass. In most cases, however, it is possible, and usuallybetter (see Chapter 1), to avoid the use of accelerators.There is a permanent conflict between pumpabiity and shootability: when the pumpabilityincreases (by increasing the slump for example), the shootability decreases (smaller buildup thickness); when the pumpability decreases, the shootability increases. It is always achallenge 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 difficultapplications, it may at least allow a reduction in their addition rate.7.2 BUILD-UP THICKNESS7.2.1 Measurement of build-up thicknessTo measure the build-up thickness, a frame as shown in Figure 7.1 was used. It wasdecided to remove the effect of the shooting technique itself by having the nozzle immobileduring the test. For this, a fixed base of 200 mm x 230 mm was mounted 100 mm fromthe wall. During the test, the shotcrete was projected horizontally onto the receivingsurface 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 directlyinto the rheometer sampling bowl.A video camcorder was used to record the tests; then, the build-up thickness could bedetermined by reviewing the experiment on video. The results of the build-up tests and ofthe rheological properties of the in-place shotcrete, as well as the slump and the air contentof the mixes as measured before pumping, are given in Table 7.1. The mix identificationcode was described in Chapter 4 and the corresponding mix compositions are given inAppendix E. The small letter (a, b, c or d) added at the end of the mix identificationindicates which nozzle was used during shooting (see Appendix D for details on nozzles).300[mm]Figure 7.1: Build-up thickness test set-upTable 7.1 Result of the build-up thickness138Mix identification Air Slump g h Build-up(%) (mm) Nm) (Nm) (Nm.s) (mm)(7.6S)26L3SFAFb** 5.5 200 8.0 8.0 0.5 350(7.8S)26L3SF-AF-b 12.0 260 0.4 0.4 4.5 10(7.19S)3OL3SF-AF-b 4.0 140 6.3 6.0 0.3 300(7.295)30T1SF-AM-a 16.1 115 2.2 2.4 0.2 110(7.295)3OT1SF-AM-b 16.1 115 2.4 2.6 0.2 190(7.29S)3OT1SF-AM-c 16.1 115 2.6 2.8 0.2 180(7.29S)3OT1SF-AM-d 16.1 115 2.9 3.2 0.2 190(8.4S)3OT1SF-DNF-b 25.5 160 3.9 4.1 0.1 215(8.11S)3OT1SF-D-b 8.1 170 1.4 1.4 1.2 90(8-16S)25T1SF-CF-d 9.2 255 0.6 0.3 3.2 10(8.18S)41L1SF-AW-b 3.0 70 3.7 4.5 0.8 190(8.23S)25T1SF-CNF-b 21.4 175 2.6 2.8 0.8 200(8.23S)25T1SFCNFb*** 21.4 175 4.1 3.2 0.7 225(8.24S)41L1SF-AWF-b 3.4 120 4.0 4.0 0.4 200(8.255)??L1SF-E-b 3.2 115 1.0 1.1 0.1 50(8.30S)54L1FA-W-b 4.6 60 1.7 2.2 0.2 55* real intercept with the abscissa** nozzle type see Appendix D*** second test2001397.2.2 RelationshiPS between shootability and rheological propertiesFigure 7.2 presents the relationship between the build-up thickness and the slump. Fromthese results, it is not possible to predict the shootability or the maximum build-up of amix just by measuring the slump before pumping. However, it is possible that somerelationship might be observed for mixes of the same composition and approximately thesame initial air content.3503002502001501005o0 50 100 150 200Slump (mm)Figure 7.2: Relationship between the build-up thickness and the slump before pumpingFigures 7.3 shows the relationship between torque viscosity (h) and the build-upthickness. One can see that there is no clear relationship between the h value and themaximum build-up thickness (no relationship was expected).350300250. 200150100500250 3000 1 2 3 4 5h (Nm.s)Figure 7.3: Relationship between the build-up thickness and the torque viscosity (h)140Figure 7.4. shows a good relationship between g (flow resistance) and the maximumbuild-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 thereading of the flow resistance (g’) on the abscissa (e.g., in Figure 5.12, g would be 3.5while g’ would be 2.6). It is not possible to determine which of g or g’ gives the bestrelationship, since they are generally close and very often the same.350300250200150100500g (Nm)Figure 7.4: Relationship between the build-up thickness and the in-place flow resistance(gandg’)7.2.3 Theoretical analysisThe relationship shown in Figure 7.4 can be analyzed by considering the equilibrium of asample of fresh concrete on the verge of falling from a wall. For this demonstration, onlythe shear stress (bending effect ignored) between the wall and the fresh concrete and theweight of the concrete are considered. Equation 7.1 (in Figure 7.5) represents theequilibrium between the shear force Vr and the gravity force pa (a is used for gravitationalacceleration because g is used for flow resistance).By considering the linear relation between to and g, (Equation 7.2) one can obtain a directrelationship between the build-up thickness.(t) and the yield stress (to) , as shown inEquation 7.3. According to Equation 7.1, the relationship between the build-up thicknessand the yield should be linear and independent of the size of the sample (b x h) when onlythe shear stress is considered. The curvature observed in Figure 7.4 might be the effect ofthe cantilever flexural stress when t increases with respect to h.01234567 8141Vr=Pto b h = pa b h t‘to = pa tI = (1/pa) to (7.1)to = (KIG) g (7.2)t= (1/pa) (K/G)gh.t = (KIGpa) g (7.3)Figure 7.5: Analysis of build-up testIn Chapter 6, it was shown that the pumpability is reduced (increase in the requiredpumping pressure) when either the flow resistance or the viscosity increase (see Figures6.8 and 6.9a). It is now obvious that shootability is increased when the flow resistance ofthe in-place shotcrete is high. Pumpability and shootability thus have special requirementsin terms of rheological properties (especially the flow resistance) which are in oppositionto each other.7.3 REBOUNDRebound was defined in Chapter 1. It was stated that the instantaneous rebound rate isdependent on the thickness of previously applied fresh shotcrete. When impacting a hardsurface, the rebound is at a maximum and decreases to a constant rate after a certainthickness has been applied (see Figure 1.6). The rheological properties of the previouslyapplied shotcrete modify the condition of the surface (hardness, stickiness) and theninfluence the amount of rebound and its composition. Modifications in reboundcomposition have not been studied here.7.3.1 Measurement of reboundTo minimize external influences in measuring the rebound, it was decided to use the set-upshown in Figure 7.6. The receiving panel is mounted directly on a weigh-scale, so that therebound can be determined at different thicknesses without having to disturb thepreviously shot material. The rebound was collected at different build-up thicknesses, andthe weight of the shotcrete in the mold was recorded.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 thecumulative rebound and the thickness is similar to the one shown in Figure 1.6. Theinterval rebound is the average rebound between two measurements of cumulativerebound. This interval rebound was quite constant after an initial thickness, as thin as 8mm, was shot. This parameter appears to be independent of the thickness of shotcretebeyond the first layer. The cumulative rebound is close to the constant average rebound (inthis case, the average of the interval rebound over the last three intervals) for thicknessesover 60 mm.Figure 7.6: Rebound test set-upscaleshote]14260so10III\——0 10 20 30 40 50 60Thickness (mm)Figure 7.7: Rebound characteristics of mix (6.1S)35T3SF-AM7.3.2 Relationship between rebound and rheological propertiesTable 7.2 presents the constant average rebound of the shotcrete, the rheologicalproperties measured on the in-place shotcrete, the air content before pumping, and the143paste 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 bracketsrepresents the paste volume of the shotcrete before pumping. The change in PV duringpumping and shooting depends on the initial air content and on the compaction duringpumping and shooting.Table 7.2: Average rebound measurement dataMix identification Rebound g h Air PV(%) (Nm) (Nm.s) (%) (%)(6.1S)35T3SF-AM 13.6 8.0 0.5 13.5 36.3 (42.2)(7.19S)30L3SF-AF 18.0 6.3 0.3 4.0 34.3 (35.2)(7.29S)30T1SF-AM 21.8 2.2 0.2 16.1 35.4 (45.7)(8.18S)41L1SF-AW 1.8 3.7 0.8 3.0 36.1 (36.2)(8.19S)25T1SF-C 15.2 0.5 2.5 8.0 36.0 (39.9)(8.23S)25T1SF-CNF 44.1 4.1 0.7 21.4 38.4 (48.1)(8.24S)41L1SF-AWF 2.7 4.0 0.4 3.4 36.7 (37.6)(8.25S)??L1SF-E 1.3 1.0 0.1 3.2(8.30S)54L1FA-W 4.9 1.7 0.2 4.8 35.8 (37.6)In Table 7.2, it seems that no relationship can be found between the rebound and therheological properties (g or h), the air content, or the paste volume before or after theshooting. One would expect that shotcrete with high in-place flow resistance would havehigher rebound: shooting on a hard surface increases rebound. There is, however, somerelationship with W/C as shown in Figure 7.8: the amount of rebound seems to decreaseas 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 somelimitations with regard to this observation.7.4 AGING EFFECT7.4.1 AgingAging, which causes stiffening of fresh concrete or shotcrete, is due to the slow hydrationof the cement during the dormant period and to a progressive reduction in the efficiency ofsuperplasticizers (if they are present). The aging caused by superplasticizers is difficult topredict and can be very rapid. Aging has been observed through slump reduction (as in144Figure 2.8), increases in yield (as in Figure 3.14) or flow resistance (as in Figure 7.9);viscosity is not much affected.50.30201000.20Figure 7.8: Relationship between rebound and W/C7.4.2 Fresh concrete aging rate (FCAR)To evaluate aging, one may define a fresh concrete aging rate (FCAR) which is the rate ofchange in flow resistance. Mixtures which are aging slowly will have a slow increase offlow resistance with time, i.e., a small FCAR. They will remain workable for a longperiod without significant changes in workability. Figure 7.9 shows the behavior of sucha stable mix: there is only a very small increase in flow resistance and no change inviscosity over a two hour period (Cast 15 mm refers to the properties of the concretebefore pumping but 15 minutes after casting).The flow resistance of mix (6.1A)35T3SF-AM has been plotted with respect to time inFigure 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 notdesirable in shotcrete application because they might overextend the waiting periodbetween two successive applications. They are however useful for research purposesbecause the aging effect can be neglected.0.25 0.30 0.35 0.40 0.45 0.50 0.55Water-cement ratio (W/C)1451.21, 0.80.6I.0.40.20Torque (Nm)Figure 7.9: Rheological test results on mix (6. 1M35T3SF-AM at different timesTime (mm)Figure 7.10: Determination of fresh concrete aging rate on mix (6. 1A)35T3SF-AMIn some mixes, the flow resistance rapidly increases with time, due to a rapid stiffening ofthe mix. Figure 7.11 shows that the fresh concrete aging rate for mix (8.4A)3OT1SF-.DNF0 1 2 3 4 511.0‘ 0.5JO—.------- 1 hour —0 30 60 90 120is 1.2 Nm/h.146C)-..1.oFigure 7.11: Determination of fresh concrete aging rate on mix (8.4A)30T1 SF-DNFThis kind of mix is good for field shotcreting applications because the waiting timebetween successive applications (e.g., for thick overhead applications) is reduced. Ofcourse, if the fresh concrete aging rate is too high, pump blockage may occur. Because thevalue of the fresh concrete aging rate affects the shotcrete application, it has to be takeninto account in a model which predicts shootability. The importance of the FCAR isdiscussed in Section 7.7.Because the rheological properties of the fresh concrete change at different rates indifferent mixtures, it is important to measure them with respect to time. Changes in flowresistance with time depend mainly on cement type, admixtures used and temperature.Some of these influences are discussed in Chapter 8.7.5 COMPACTIONCompaction is a very important phenomenon in shotcrete technology because it modifiesthe composition of the in-place shotcrete (compaction reduces air content). Some of theeffects of compaction on hardened shotcrete properties are known: compaction increasesthe compressive strength and reduces the air content which may cause an increase in thevalue of the air void spacing factor and then migth reduce durability. Its effects on freshshotcrete properties have never been studied (as far as can be ascertained from a review ofthe literature).0 30 60 90 120Time (mm)1477.5.1 DefinitionCompaction is simply the expulsion of entrapped or entrained air. In cast-in-place concreteit is usually caused by internal vibration. Compaction may also be caused by the pumpingprocess (pumping compaction) or by the shooting process (shooting compaction). Thecombined compaction (or total compaction) is the loss of air due to both pumping andshooting processes.The effect of increasing air content on the rheological properties of concrete is wellknown; it produces mainly a reduction in flow resistance (Figure 7. 12a). Similar behaviorhas been reported in Chapter 5 (Figures 5.17 and 5.18). Compaction should produce thereverse effect, i.e. an increase in flow resistance as shown in Figure 7. 12b. This behaviorwas also observed in Figure Possible effect of compaction on shootabilityBecause compaction caused by the shooting process may affect flow resistance, it mayalso affect the build-up thickness and hence the shootability. From the behavior shown in7.12b, one can predict four possible types of behavior with respect to compaction andshootability. Figure 7.13 illustrates these four hypothetical cases. Each case is shown by agraph with two lines. The dotted lines refer to the behavior of the concrete beforepumping, while the solid lines refer to the rheological behavior of the shotcrete aftershooting.I.Torque (Nm) Torque (Nm)(a) (b)Figure 7.12: Effect of air content (a) and compaction (b) on flow resistance148a.a.Figure 7.13: Possible relationships between compaction and shootabilityFigure 7.13a represents a very workable, easy to pump shotcrete mix with a low flowresistance and no entrained air. Because this concrete possesses no entrained air, there willbe little compaction (there is always some entrapped air that can be lost) and therheological behavior should be about the same before and after shooting. Also, becausethe in-place shotcrete has a low flow resistance, the build-up thickness should be smallresulting in a poor shootability. Figure 7. 13b represents a workable, pumpable shotcretemix with an acceptable (for pumping purposes) flow resistance and no entrained air.Because of little compaction the flow resistance should be approximately the same beforeand after shooting. Also, because the in-place shotcrete has an acceptable flow resistance,the build-up thickness should be sufficient to ensure good shootability. Manyconventional 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 flowresistance and with a reasonable amount of entrained air. Because this concrete possessesentrained air, there will be compaction, resulting in a higher flow resistance after shooting.-- Before shooting: — After shootingno entrained air(no compaction)Torque (Nm)(a) poor shootabilityI entrained aire (no compaction)Torque (Nm)case (b): good shootabilitya.a.with entrained air(compaction)compactonentrained air(compaction)(c) good shootability (d) excellent shootability149The in-place shotcrete, because of a high flow resistance, should have a high build-upthickness resulting in a good shootability.Figure 7. 13d represents a workable, pumpable shotcrete mix with an acceptable flowresistance and with a reasonable or high amount of entrained air. Because this concretepossesses entrained air, there will be compaction resulting in a higher flow resistance aftershooting. The in-place shotcrete, because of a very high flow resistance, should have avery high build-up thickness resulting in excellent shootabiity.7.5.3 MeasurementIt would appear that to verify the effect of compaction caused by the shooting process onewould 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 othereffects: 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 theaging effect, one must measure the rheological properties of the concrete before pumpingand after shooting at essentially the same time. In practice, this is important for mixes witha high FCAR but of less importance when the FCAR is low. Since only one rheometerwas available, these properties were measured one after the other, within a three minutetime interval (which may be considered simultaneous).It is well known that pumping may cause a reduction in the air content and also a decreasein slump (Chapter 1). In the previous analysis, no distinction was made between pumpingcompaction (caused by the pumping process) and shooting compaction (caused by theshooting process). However, a part of the combined compaction (total loss of air duringpumping 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 bestexperimental procedure is to measure the air content and the rheological properties justafter casting the concrete but before pumping (referred to as Cast), after pumping butbefore shooting (referred to as Pump), and after shooting (referred to as Shot). Theexpected results from this procedure are shown in Figure 7.14. Each compaction causessome stiffening (i.e., the increase in flow resistance caused by the compaction). Threetypes of stiffening can be defined: the pumping stiffening caused by the pumpingcompaction, the shooting stiffening caused by the shooting compaction, and the combined150stiffening caused by the total compaction (loss of air caused by both pumping andshooting).totalcompactionI,Cast Pump ShotIi pumping j shootingf compactio’ compactioTorque (Nm)Figure 7.14: Definition of pumping compaction, shooting compaction and totalcompaction7.5.4 ResultsTable 7.3 gives the results of tests carried out on fresh and hardened shotcrete. Column 1is the usual mix identification. Columns 2, 3 and 4 give the air contents of the freshconcrete or fresh shotcrete: Cast (before pumping(2)), Pump (after being pumped(3)) andShot (after being shot directly into the air meter (4)). The fifth column is the slumpmeasured before pumping. Columns 6, 7 and 8 give the flow resistance of the freshconcrete 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 takenfrom 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 presenceof air-entraining agents or fibers. The first two groups were cast without air-entrainingagents while the third and fourth groups were cast with air-entraining agents (M or N inthe code). The second and the fourth groups were cast with about 50 kg/m3 of steel fibers(F in the code). The W/C decreases within each group and different admixtures wereused.151Table 7.3: Effects of pumping and shooting on shotcrete propertiesMix identification Air Slump Flow resistance 28 d strength(%) (mm) (Nm) (MPa)Column Cast Pump Shot Cast Cast Pump Shot Cast Pump Shot1 2 3 4 5 6 7 8 9 10 11(8.30S)54L1FA-W 4.6 3.9 2.0 60 1.8 1.8 2.2 24* 24* 26*(8.25S)??L1SF-E 3.2 2.9 2.8 115 1.0 1.1 1.5 61 62 55(8.11S)3OT1SF-D 8.1 5.7 2.9 170 1.2 1.3 1.4 85 86 94(8.195)25T15F-C 8.0 7.0 2.5 250 0.3 0.3 0.5 97 95 113(7.19S)30L35F-AF 4.0 4.0 2.8 140 3.1 3.8-5.4 6.3 81 80 90(7.12S)30L35F-AF 4.9 4.0 2.2 100 3.4 3.7-4.3 4.6 83 84 -(7.26S)3OL1SF-CF 6.8 5.0 2.5 110 1.9 2.1-2.2 2.3 77 85 -(3.26S)40T1-AWM 14.2- 3.0 50 2.1 - 3.2 20* - 31*(6.1S)35T3SF-AM 13.5 - 2.4 170 0.6 - 1.4 30 - 57(7.27S)3OT1SF-AM 13.9 8.1 3.4 60 2.1 2.3-2.7 3.2 48 66 78(7.295)3OT1SF-AM 16.1- 2.4 115 1.4 - 2.2 33 - 79(8.4S)3OT1SF-DNF 25.5 14.4 3.2 160 1.6 2.6-?? 3.9 - 60 90(8.23S)25T1SF-CNF 21.4 18.8 4.8 175 1.2 1.3 2.7 40 46 105*7 dinstead of 28Some additional explanation is necessary concerning the determination of the flowresistance presented in Table 7.3 (columns 6-8). Flow curves (see Section 3.3.3) wereused 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 onemeasurement of flow resistance is given for Pump, this indicates that the measurementsfor Cast, Pump and Shot were made within a very short period and are consideredsimultaneous. When column 7 includes two numbers, this indicates that two sets of twosimultaneous measurements have been obtained. The first measurement set is composedof column 6 and the left hand side of column 7, which correspond respectively to the flowresistance 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 ofcolumn 8, which correspond respectively to the flow resistance of the concrete beforeshooting and after shooting, measured simultaneously but at a different time than the firstmeasurement set.152From the tests carried out, it is possible to give a practical example of each hypotheticalcase shown in Figure 7.13: cases (a), (b), (c) and (d) in Figure 7.13 are represented byFigures 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-entrainingadmixture 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 forthe in-place shotcrete (Shot (mix 5)) at different times. Since the measurements werecarried out simultaneously, no aging effect has to be taken into account. The valuesreported 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. Inorder to produce a mix with very low flow resistance, one must use a very high dosage ofsuperplasticizer. Since it is difficult to find the optimum dosage, the mix is sometimesover superplasticized: the amount of superplasticizer, in excess of that used to reduce theflow resistance to zero (the SP reduces the attraction between cement particles and thenreduces flow resistance), acts to reduce the viscosity (when there is no more attraction, theextra amount of SP increase the amount of paste). After shooting, because of somecompaction, the viscosity is reduced first, and then the flow resistance is reduced if thecompaction is high enough. This has been observed only in very flowing concrete (in ourcase, over superplasticized mixes).1531.210.20Figure 7.15: Effect of compaction on mix (8. 19APS)25T1 SF-C (no AEA)1.21j0. (Nm)Figure 7.16: Effect of compaction onfibers)mix (7.26APS)3OL1SF-CF (no AEA but with0 1 2 3 4 5Torque (Nm)1 2 3 4 (Nm)Figure 7.17: Effect of compaction on mix (6. 1AS)35T3SF-AM (with AEA) 1 2 3 4 51.2Torque (Nm)Figure 7.18: Effect of compaction on mix (8.4APS)3OT1SF-DNF (with AEA and fibers)155During pumping (still Figure 7.15), there was no change in flow resistance: i.e. zeropumping stiffening (Pump-Cast = 0.3 Nm -0.3 Nm = 0 Nm). During shooting, thechange 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 anincrease in flow resistance of only 0.2 Nm for this mix. During pumping, the compactionor the loss of air was only 1.0% (from 8.0% to 7.0%). During shooting, the compactionwas 4.5% (from 7.0% to 2.5%). Then, the total compaction during pumping and shootingwas 5.5% for this mix. Even though this mix was very easy to pump, it was not suitablefor shotcreting and exhibited very bad shootability. Because of the very low flowresistance, 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 rheometertest results for mix (7.26APS30L1SF-CF. Since the rheometer tests for Cast, Pump andShot were not taken all at the same time, the aging effect has to be taken into account. Thevalues 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 lefthand value for Pump (2.1) were taken simultaneously (at 30 mm.). The right hand valuefor Pump (2.2) and the value for Shot (2.3) were taken simultaneously (at 45 mm.) but 15minutes after the first set of data.The pumping stiffening was very small (Pump-Cast = 2.1 Nm -1.9 Nm 0.2 Nm), andso was the shooting stiffening (Shot - Pump = 2.3 Nm - 2.2 Nm = 0.1 Nm). Thecombined stiffening (caused by pumping and shooting) is an increase in flow resistance of0.3 Nm for this mix (not 0.4 Nm, which does not account for aging between the twomeasurement 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. Thismight seem important for a non-air-entrained mix but the high dosage of superplasticizeroften 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 (probablydue to aging). However it demonstrated good shootability before blocking (the build-upthickness was not measured).156Figure 7.17 represents a concrete cast with an air-entraining agent and possessing a lowinitial 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 combinedstiffening for this mix can be determined: Shot-Cast = 1.4 Nm-0.6 Nm =0.8 Nm for atotal compaction of 13.5% - 2.4% = 11.1%.The compaction provided sufficient build-up to shoot a test panel. The total compactionproduced 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 possessingsome 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 nottake into account the aging effect. Nevertheless, it is possible to appreciate the pumpinduced compaction (from 25.5% to 14.4%= 11.1%) which produced a pumpingstiffening of 2.5-1.5 = 1.0 Nm. The shooting stiffening is 1.5 Nm for a reduction in aircontent from 14.4% to 3.2% (which includes some aging effect and thus should be takenas a maximum).The total compaction (22.3% air reduction) produced a stiffening of 2.5 Nm (whichincludes some aging effect). The large increase in flow resistance produced excellentshootability. It was possible to shoot 300 mm (build-up thickness) of shotcrete on avertical surface in a single pass without sloughing.It is interesting to note that the final strength of another mix: (8.23S)25T1SF-CNF, whichhad an initial strength of 40 MPa (air content of 21.4%) was 105.4 MPa (in-place aircontent of 4.8%). The relationships between the W/C and the air content are discussedfurther 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 combinedstiffening are presented. Data from Figures 7.15 to 7.18 are specifically identified (firstpart of the mix identification code only). Since the results from case 7.18 have to betreated as a maximum (because some aging effects are included in the stiffening), an arrowpointing down was added.1572. loss of air (%)Figure 7.19: Relationship between compaction and stiffening7.5.5 Summary on compactionFrom the results in Section 7.4.5, it is obvious that compaction caused by the shootingprocess produces an increase in flow resistance which results in a stiffer mix. Pump-induced compaction produces similar effects. The stiffening effects are proportional to theamount of compaction. However, for compaction under 5%, it is difficult to predict thestiffening (Figure 7.19): small air losses (even a compaction of 1%) may cause astiffening of O.5Nm, probably because of some evaporation during shooting which mayaffect low W/C mixes.It is not possible at the moment to determine whether small or large air bubbles are lostduring pump-induced compaction or during the compaction caused by the shootingprocess. The mechanisms of air loss are also unknown. One may suppose that duringpumping some air is lost by dissolution into the paste because of the applied pressure. Itwould be logical to assume (by considering the equilibrium between the internal pressureof an air void and the surface tension of the paste) that the small bubbles are more easilylost than the big ones. This could only be verified by looking at the distribution in the sizeof 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 mostparticles are separated when the compressed air is mixed with the concrete inside the0 5 10 15 20 25158nozzle to form the shotcrete. Another explanation for the compaction that occurs duringshooting is that the air bubbles explode when the concrete hits the receiving surface. Amore precise explanation must be found concerning these hypotheses.7.6 MODEL FOR PREDICTING PUMPABILITY AND SHOOTABILITYWith the relationships that have been developed in Chapters 6 and 7, it is possible toelaborate a model to predict pumpability and shootability if one measures certain propertiesof fresh concrete. It is also possible to talce into account the effects of aging andcompaction. In practical applications, it should be possible to predict the effect of awaiting period in the case of more than one layer of application.7.6.1 Required relationships and propertiesIn order to use this model to predict pumpability and shootability in terms of maximumbuild-up thickness, a knowledge of several relationships and properties is needed.Assuming the relationships illustrated in Figure 7.20, one may predict pumpability andshootability:• 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 (buildup 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 lowair content).If the first two of the following properties are known, one may then draw Figure 7.21.• The initial flow resistance: (IFR = 1.5 Nm)• The fresh concrete aging rate (FCAR = 0.5 N ni/h)• The initial torque viscosity: (ITV 0.5 Nm.s)• The initial air content (IAC = 15%)159EiiFigure 7.21: Characteristics of fresh concrete7.6.2 Prediction of pumpabilityWith the relationships and properties presented in the previous section, one may thencheck to see whether a mix is pumpable and for how long, if it is assumed that viscositydoes not change with time (which is usually true). Figure 7.22 summarizes thedetermination of the pumpabiity life.The first step is to determine whether the concrete is pumpable. For this, one must plot theinitial value of g and h in Figure 7.22a: if the dot is in the pumpability zone, the concrete ispumpable. For low W/C ratio concrete containing silica fume, since no stability problemcaused by segregation are to be expected, blockage would occur only because of anincrease in flow resistance.To be more realistic in the determination of the pumpability life, it has been assumed thatthe concrete was transported for 30 minutes before pumping. To determine for how long.4,200h (Nm.s)(a)Figure 7.20: Required relationships(c)In-place flowresistance (Nm)(b)ITV = 0.5 Nm.sO234Time (hours)43IZ210160the concrete can be pumped, a vertical arrow is first drawn (Figure 7.22 a) to determinethe 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 bypumping compaction. If one assumes that the pumping compaction is 5% (for an initial aircontent of 15%) the resulting stiffening (from Figure 5.20c) is 0.5 Nm. A parallel solidline, starting at 45 mm can be drawn, 0.5 Nm from the original one. The intersection ofthis new line with the maximum allowed flow resistance gives the blocking time or apumpability life of 2 hours and 30 minutes.h (Nm.s)(a)Figure 7.22: Determination of pumpabiity lifeIn any event, after 2 1/2 hours, initial set would probably start to take place and the flowresistance 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 0.5Nm/h), would have its pumpability life reduced to about 1 hour 20 minutes. Also, the lastconcrete (ITV = 0.5 Nm.s, IFR = 1.5 Nm and FCAR = 0.5 Nm/h) with an initial aircontent of only 3% instead of 15%, would not undergo compaction. Then, thepumpability 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 dataavailable from which to determine the real relationship between initial air content andpumping compaction. However, it is highly probable that the relationship is a function ofthe rheological properties: the amount of compaction as a ratio of the initial air content isprobably influenced by the required pumping pressure and by the rheological properties gand 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.Time (hours)(b)1617.6.3 Prediction of shootabilityOne may predict the shootability in terms of maximum build-up thickness or the waitingperiod required between two successive applications. For the next two examples, twoconcretes with the characteristics shown in Figure 7.21 but different air contents, 15% and3% are assumed. In both cases, the contractor is required to apply a shotcrete thickness of150mm.The first mix has an initial air content of 15%. As determined in the previous section, thisconcrete will be pumpable for 2 1/2 hours. After pumping and shooting, the in-place aircontent has been reduced to 3% because of a total compaction of 12%.Figure 7.23 summarizes the required steps in determining the maximum build-upthickness. 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.2Figure 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 in-place shotcrete from 1.75 Nm to 2.95 Nm (Figure 7.23b). This implies that at the age of30 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 andshooting, and the initial set is assumed to impair pumping after three hours. Figure 7.24summarizes the required steps in determining the maximum build-up thickness. At 30I.E 1Is00Compaction (%)(a)Time (hours) In place g (Nm)(b) (c)162minutes, just after starting shooting, the in-place flow resistance is 1.75 Nm (Figure7.24a). The corresponding maximum build-up thickness is then about 88 mm as shown inFigure 7.24b. Obviously, because the contractor cannot benefit from the stiffening causedby compaction, the work has to be done in more than one layer.20011501005000(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 towait before applying the second 70 mm layer. After the second layer has been applied, thefirst layer must carry the stress caused by the total build-up thickness of 150 mm. FromFigure 7.24b, one can determine that the required flow resistance is 3.0 Nm. In Figure7.24a, one can determine that the flow resistance of the shotcrete will reach that value at 3hours. Unfortunately, at this time the first concrete load will no longer be pumpable and asecond truck must be ordered by the contractor.In determining the waiting period, it was assumed that the FCAR is the same aftershooting and pumping as before pumping. Figures 7.25 and 7.26 show examples of freshconcrete aging rates (slope of lines) before and after pumping and also after shooting, forconcretes cast with and without air-entraining agents, respectively. In these figures, onecan see that the FCARs are similar for all concretes; the steps between the three lines arecaused by pumping or shooting compaction. One can also see on these two figures that thetorque viscosity (h) does not change significantly with time or because of the pumping orshooting operations.12Time (hours)(a)12 34In place g (Nm)3EFigure 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 SHOTCRETEThe hypothetical examples of Sections 7.6.2 show some of the advantages of using theconcept of a temporary high initial air content. This concept is a good way to enhance theIpumpabilityu. The “shootability” is also enhanced by the compaction. The commondilemma of the conflicting requirements for pumpability vs. shootability no longer existswith this concept.It has been shown that the concept of a temporary high air content (initial air content up to25%) 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 wayto avoid the use of accelerators for achieving build-up, since accelerators can have veryharmful effects both on crew health and on the concrete properties, especially durability.163D Cast—— OPump—AShot-= LI652100 15 30 45Time (mm)60 75 90164___4 ICast0 PumpA ShotFigure 7.26: Effect of time, pumping and shooting(7.12APS)3OL3SF-AF (without AEA)on rheological properties of mixAs explained in Chapter 6, special care should be taken by those who wish to adopt thisconcept because in working with high air content mixtures, one has to deal withcompressible materials, as opposed to non-air-entrained concretes which have littlecompressibility. Some types of pumping equipment would not be able to handle high aircontent mixtures, or would have significantly reduced pumping rates even if the flowresistance of the concrete is low (or if the slump is high). Thus special care should beexercised in selecting the appropriate pumping equipment for high air content mixtures.3E65z2100 15 30 45 60Time (mm)75 90165CHAPTER -8-EFFECT OF MIX COMPOSITION ON SHOTCRETE PROPERTIES8.0 INTRODUCTIONIn the previous chapters, it was shown that the initial value of the flow resistance, thetorque viscosity, the value of the fresh concrete aging rate (FCAR) and the relationshipbetween stiffening and compaction can be used to predict some important parametersrelated to pumpability and shootability. Up to now, however, the effect of mixcomposition on these properties has not been considered. This issue, as well as the effectof mix composition on hardened shotcrete properties is considered in this chapter. First,the influence of mix composition on the rheological properties of fresh shotcrete isanalyzed. Then, the influence of pumping and shooting on compressive strength withrespect to compaction is examined. Also, the durability is discussed, in terms of the deicersalt scaling resistance. Finally, the production of high performance shotcrete by usingsuperplasticizers or by using the concept of a high initial air content is considered.8.1 EFFECT OF MIX COMPOSITION ON RHEOLOGICAL PROPERTIESMix composition affects the values of the initial rheological properties (flow resistance andtorque viscosity at 15 minutes of age), and also the values of the fresh concrete agingrates. The variables considered in this analysis include: the cement type, the type andaddition rate of superplasticizers (SP), the water-cement ratio (W/C), the use of airentraining agents (AEA), and the presence of steel fibers.Table 8.1 presents the results of different tests carried out on 58 concrete mixes. Thesetest results include the air content, the slump measured at the age of 15 minutes, the initialvalues of g and h (at 15 minutes), the fresh concrete aging rate (FCAR calculated from 15to 90 minutes) and the compressive strengths at 7 and 28 days (average of 3 cylinders of100 nm-i x 200 mm). The exact compositions of these mixes are available in Appendix E.Rheometer test results are available in Appendix G.Table 8.1: Air content, slump. . h. FCAR. and compressive sirengthMix identification Air Slump g h FCAR 7d 28d(%) (mm) (Nm) (Nm.s) (Nm/h) (MPa) (MPa)(3.26A)40T1-AWM 14.2 50 2.1 0.5 - 19.5 -(5.18A)38T1SF-BMF 8.4 10 3.1 0.5 3.0 35.0 49.9(5.19A)38T1SF-AMF 20.5 200* 0.5 0.3 .07 17.9 24.2(5.20A)35T15F-AM 7.0 30* 4.1 0.4 1.0 - -(5.25A)33L1SF-AM 14.2 15 3.2 0.6 0.8 42.3 46.6(5.27A)30L1SF-AM 12.5 100 1.3 0.3 1.4 23.9 33.8(5.31A)33L1SF-AM 5.0 5 2.9 0.9 1.0 50.3 56.7(5.31E)35T3SF-AM 14.8 210 0.8 0.3 0.6 35.2 46.6(6.1A)35T3SF-AM 13.5 170 0.5 0.4 0.1 20.6 29.8(6.1E)35T3SF-AM 12.7 230 0.5 0.7 0.6 35.8 49.7(6.2E)33L1SF-AM 5.3 150 0.9 1.0 0.4 46.1 75.9(6.2F)33L1SF-B 5.0 155 0.8 1.0 0.6 53.9 68.1(6.7E)33L1SF-A 4.5 80 1.6 0.9 1.0 65.7 79.7(6.7F)33L15F-C 8.0 165 0.7 1.0 0.7 64.3 75.4(6.8E)33L1SF-D 14.6 280 0.0 1.0 0.0 38.8 56.6(6.15A)3OT1SF-AMF 14.0 210 4.2 0.7 2.2 - 31.7(6.16A)27T1SF-AM 16.0 70 1.3 0.5 0.9 40.3 52.1(6.21E)25L5SF-A 6.7 90 1.7 0.9 1.9 62.7 84.3(6.21F)25L1SF-A 5.0 95 2.8 0.7 1.0 66.0 90.7(6.21G)25L3SF-A 7.4 230 0.5 2.0 0.7 72.0 87.8(6.21H)25JMSF-A 6.7 105 2.4 1.4 1.5 58.7 81.3(6.23A)25L5SF-A 7.8 180 1.0 1.3 0.9 62.3 80.4(6.24A)2SL5SF-C 12.0 240 0.1 1.1 0.1 54.0 66.0(6.24B)25L1SF-C 7.5 160 1.0 1.0 0.6 67.1 83.5(6.24C)25L3SF-C 9.0 270 0.1 1.0 0.1 54.0 64.3(6.30A)25L3SF-AF 10.5 230* 1.0 2.5 - - -(7.6A)26L3SF-AF 5.5 200 3.1 1.2 - - -(7.8A)26L3SF-AF 12.0 260 0.7 2.8 0.1 47.4 63.5(7.12A)3OL3SF-AF 4.9 100 1.6 1.3 2.3 64.6 83.3(7.19A)3OL1SF-AF 4.0 140 2.3 1.9 3.8 65.1 80.7(7.20A)3OL1SF-AP 3.8 50 5.1 0.1 1.1 51.7 79.4(7.23E)33L1SF-AF 8.5 260 0.5 1.3 0.1 41.0 -(7.26A)3OL1SF-CF 6.8 110 1.7 1.6 0.8 51.2 76.5(7.27A)3OT1SF-AM 13.9 60 1.6 0.2 0.6 42.7 48.3(7.29A)3OT1SF-AM 16.1 115 1.1 0.2 1.5 23.2 32.6(8.3A)3OT1SF-DN 25.0 160 0.7 0.3 0.1 - -(8.4A)3OT1SF-DNF 25.5 160 1.1 0.3 1.6 - -(8.5A)3OT1SF-D 14.0 270 0.3 0.6 0.0 57.6 76.5(8.9A3OT1SF-DF 10.0 210 0.6 0.8 1.7 67.9 92.3* estimated slump (continued on next page)166167Table 8.1 (continued): Air content slumnMix identification Air Slump g h FCAR Str.7d Str.28d(%) (mm) (Nm) (Nm.s) (Nm/h) (MPa) (MPa)(8.11A)3OT1SF-D 8.1 170 0.5 0.6 0.8 72.1 85.0(8.16A)25T1SF-CF 9.2 225 1.0 3.1 - 73.0 93.4(8.16B)25T1SF-CF 9.2 255 0.5 1.5 0.1 - -(8.16C)25T1SF-CNF 22.8 260 0.3 0.6 0.1 23.2 31.0(8.16E)41L1SF-CF 9.0 240 0.6 2.2 0.1 71.3 -(8.18T41L1SF-AW 3.0 70 1.5 0.2 0.8 45.0 61.7(8.19A)25T1SF-C 8.0 250 0.5 0.8 0.2 78.0 97.4(8.21E)33T1SF-E 3.0 130 1.2 0.9 1.4 - 87.3(8.21F)33L1SF-E 2.9 210 0.5 0.9 0.5 - 88.8(8.23A)25T1SF-CNF 21.4 175 0.9 0.5 0.3 36.1 40.2(8.23B)25T1SF-CNF 19.2 175 1.3 1.0 2.2 - -(8.23E)3OT1SF-E 3.8 135 1.0 1.1 0.8 75.5 96.0(8.23F)3OL1SF-E 4.2 110 1.3 1.0 1.0 58.5 85.8(8.24T)41L1SF-AWF 3.4 120 2.3 0.2 2.2 34.2 50.7(8.251y??L1SF-E 3.2 115 0.7 0.2 0.1 38.7 61.1(8.27E)52L1FA**W 3.4 115 1.2 0.4 0.1 22.7 34.1(8.30A)48L1FA**W 4.8 30 2.3 0.3 0.2 28.3 39.6(8.30B)54L1FA**W 4.6 60 1.3 0.2 0.3 23.8 33.2* estimated slump** fly ash instead of silica fume8.1.1 Relationships between g, h and FCARThe mixes in Table 8.1 can be divided in four different groups: Plain (no fibers and noAEA used), Fiber (with steel fibers but no AEA), Air (with AEA but no fibers) and Air-Fiber (with steel fibers and AEA). Figure 8.1 shows that there is no clear relationshipbetween the g and h values for these four groups. One can see, however, that when highdosages of air-entraining agents are used, the viscosity is always below 1 Nm.s, which isgood from a pumpability point of view. These strong reductions in viscosity caused by theuse of air could probably be explained by a phenomenon similar to “dilution” (air can beseen as a fluid of very low viscosity): the resulting viscosity would then depend on therespective proportions of the two fluids.h FflAR nd comnressive strength1686541310h (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, onecan see (Figure 8.3) that the FCAR is generally higher for high values of g, although theresults aie quite scattered. A more detailed analysis based on mix composition with respectto g, h and FCAR is needed and is presented in Sections 8.1.3 and (Nm.s)0 1 2 3 40 1 2 3 4Figure 8.2: Relationship between FCAR and h (all mixes)169Figure 8.3: Relationship between FCAR and g (all mixes)8.1.2 Relationship between initial flow resistance and slumpFigure 8.4a shows that there is a good relationship between the slump and the flowresistance (g). For low workability (low slump), the flow resistance seems to be higherfor mixes with fibers. This may explain why the workability of fiber reinforced concretein not properly estimated by a slump test for stiff mixes. The spread of the results isreduced when one compares the slump to the real intercept on the abscissa (g’ on Figure8.4b) compared to g, especially for mixes with fibers. The increase in real g’ at lowangular speed for fiber mixes might be caused by some sort of fiber pull-out on freshconcrete.64Iz‘—‘200 1 2 3 4 5 6g (Nm)60Slump (mm) Slump (mm)(a) (b)Figure 8.4: Relationships between the slump and g (a) or g’ (b)1708.1.3 Effect of cement-superplasticizer combinationsThe compatibility between cements and superplasticizers was not the main objective of thisstudy. However, some results were obtained on this topic during the preliminary study onmix composition. This analysis shows some trends which might be important for furtherstudies 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 firstpart of the mix identification [e.g.: (6.7F)] is written below the bar charts. These mixesare in the “Plain” category (no fiber and no AEA). At the top of the bar charts, the lettersrepresent the type of superplasticizer, with the corresponding addition rate (in 1/rn3)justunder 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 ofsuperplasticizer for this particular cement and WIC ration (0.33); however, the flowresistance and the FCAR are affected. From these results, superplasticizer D is the bestoption because it produces a more workable and stable mix (with respect to aging) thansuperplasticizers A and E, which are the two worst in combination with this cement at thiswic.A B C D E W/C =(O.33)2 (12.9) (16.3) (12.5) (12.8) (13.5) Cement = LiEki II[I 8flrnJhj(6.7F) (6.2E) (6.7F) (6.2E) (8.2iF)Figure 8.5: Effect of superplasticizer type and dosage on g, h and FCARThe effect of cement type has been studied with two different superplasticizers: SP A andSP C. Figure 8.6 is similar to Figure 8.5 except that the top letters and numbers representthe cement-superplasticizer combination. These mixes are also in the Plain category. Fromthe results of Figure 8.6, it is obvious that SP C works better with all cements than doesSP A. It is possible to produce more workable concretes with cements L5 or Ti, withlower addition rates of superplasticizer C, than with cements Li or L3. 3M refers to aspecial cement usually used to inject cracks. It has a very high specific surface whichexplains the high amount of SP used. This cement was not used beyond this test.171Li-A L3-A L5-A L5-A JM-A(16.2) (17.5) (8.9) (10.5) (21.1)01W/C=(025)(6.21F) (6.2iG) (6.2iE) (6.23A) (6.2iH)Li-C L3-C L5-C Ti-C w,c = (025)(17.5) (i7.2) (13.9) (16.1) SPC(6.24B) (6.24C) (6.24A) (8.i9A) FCAR (Nm/h)Figure 8.6: Effect of superplasticizer type and dosage on g, h and FCARThese few results show the importance of the cement-superplasticizer combination on thevalues of the initial rheological properties and on the FCAR. Superplasticizers C and Dproduce the best results: i.e. they give better initial workability with smaller addition ratesand they are also more stable with respect to aging. They were used to cast the low WICshotcrete 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 fibersFigure 8.7 is similar to the two previous figures, except that the dosage of air-entrainingagent is shown under the dosage of superplasticizer (if applicable). Also, the air contentmeasured 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 stillproduce workable concrete (mixes D and DF, compared to mixes DN and DNF in Figure8.7). The use of air also considerably reduces the viscosity; this is more pronounced atlow 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 causesa 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 compatiblecement-superplasticizers combination. It also shows the importance of the FCAR and notonly the rheological properties initial values. Since this study was not performed to studyspecifically these variables, no general conclusion can be made.172D D DF DN DNF(13.8) (13.1) (14.0) (8.0) (13.1)(2.8) (3.2) •(8.5A) (8.11A) (8.9A) (8.3A) (8.4A)(14.0) (8.1) (10.0) (25.0) (25.5)v1c= oCe=T1(8.16E) (8.16C) (8.23A) (8.23A)(9.0) (22.8) (21.4) (19.2)WIC = 0.25Cement = TiSP = CFigure 8.7: Effect of W/C and superplasticizers on g, h and FCARD DN(13.1) (8.0)(2.8)D g(Nm)C h (Nm.s)• FCAR (Nm/h)g(Nm)h (Nm.s)FCAR (Nm/h)2I03210CNF(14.4)(2.9)CNF(9.8)(1.5)CF CF CF CNF(15.9) (17.0) (17.1) (9.5)(3.3)i1 &j(8.16A) (8.16B)(9.2) (9.2)C AM(12.5) (8.5)(3.2)(6.7F) (7.27A) (8.I1A) (8.3A)(8.0) (13.9) (8.1) (25.0)4 nCF AMF DF DNF3 (16.3) (10.5) (14.0) (13.1)(3.1) (3.2)(7.23E) (6.15A) (8.9A) (8.4A)(8.5) (14.0) (10.0) (25.5)No fiberWith fibersFigure 8.8: Effect of AEA and fibers on g, h and FCAR173120602008.2 EFFECT OF MIX COMPOSITION ON HARDENED PROPERTIESAs mentioned earlier, the term high performance shotcrete could refer to any shotcretewith exceptional properties: high strength, high durability or even high shootability. Thislast property was discussed in Chapter 7. The issues of strength and durability are nowconsidered. Detailed results of tests carried out on hardened shotcrete are available inAppendix H.8.2.1 Compressive strengthTable 8.1 shows the compressive strengths (at 7 and 28 days after casting) of all mixesbefore pumping and shooting. These results are in agreement with the usual relationshipbetween compressive strength, air content and W/C. Figure 8.9 presents these resultsgraphically: the compressive strength increases when the air content and the W/C arereduced. Three categories of concrete with different W/C are represented by the shadedlines.40Figure 8.9: Relationship between air content, W/C and compressive strengthThe 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. Thecompressive 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 thin0 4 8 12 16 20 24Air content (%)174line. One can see that the compressive strength after shooting is independent of the initialair content before pumping, and depends exclusively on the WIC. This last statementimplies that the concept of high initial air content is appropriate to produce high strengthshotcrete. The strength is detemtined only by the WIC used. A strength of 105 MPa wasobtained after shooting on a mix with an initial air content of 21.4%, with a correspondingstrength before pumping of 40 MPa. In this case total compaction increased thecompressive strength by more than 160%.8.2.2 Absorption testThis test is routinely carried out on shotcrete and should give an indication on the overalldurability of the shotcrete, especially for the dry-mix process. In this case, the skill of thenozzleman who constantly adjusts the amount of water in the mix may affect theabsorption of the in-place shotcrete. For the wet-mix process, this relationship is not soclear.120* I wic = 0.25 0.30 0.35i 0 AIpump 11 0O LShot • A•A W/C=038 035OW/C =033-030Q WIC = 0.27-0.250 4 8 12 16 20 24Air content (%)Figure 8.10: Effect of pumping and shooting on compressive strengthTable 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 dependsmostly on the W/C, and to a lesser degree on the presence of AEA. Results from theabsorption tests, as for the results from the compressive strength test, can be compared tothose of the cast-in place concrete of the same composition as mentioned in Section 1.5.i:o604020C)091758.2.3 DurabilityThe durability of wet-mix shotcrete was discussed in Chapter 1. It is more difficult toprotect wet-mix shotcrete against deicer salt scaling than against internal freezing andthawing. That is, if the concrete or shotcrete is resistant to deicer salt scaling (ASTM C-672), it will be resistant to internal freezing and thawing (ASTM C-666); the opposite isnot necessarily true.It is well known that the frost resistance and the scaling resistance of concrete dependprincipally 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 airvoid spacing factor (ASTM C-457), which is important for frost resistance. For scalingresistance, a low spacing factor (L) is a necessary but not sufficient condition: the concretemust also possess a low W/C (usually below 0.45) and must have been cured properly.Table 8.2: Absorption test resultsMix identification Boiled absorption Density Permeable voids(%) (%)(7.19S)30L3SF-AF 4.57 2.43 10.57(7.27S)3OT1SF-AM 3.76 2.23 8.05(7.29S)3OT1SF-AM 4.73 2.34 10.49(8.4S)3OT1SF-DNF 4.61 2.40 10.60(8.5S)3OT1SF-D 4.26 2.40 9.87(8.9S)3OT1SF-DF 3.60 2.41 8.38(8.11S)3OT1SF-D 3.68 2.39 8.46(8.18S)41L1SF-AW 5.19 2.41 11.88(8.19S)25T1SF-C 2.23 2.38 5.18(8.23S)25T1SF-CNF 3.35 2.40 7.77(8.24S)41L1SF-AWF 6.40 2.37 14.25(8.25S)??L1SF-E 6.32 2.37 14.11(8.30S)54L1FA-W 6.63 2.29 14.25A few shotcrete mixes were tested for deicer salt scaling resistance according to ASTM C666. The weight of scaled-off particles (kg/rn2) and the visual estimation of thedeterioration (rating 0 = no deterioration, rating 5 = very severe deterioration) arepresented in Table 8.3. The air void parameters of these concretes were also determinedaccording to ASTM C-457. The most important characteristics of the air void system [the176hardened air content, the specific surface (c and cx*) and the spacing factor (L and L*)1are 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 shotcreteASTM C-39 ASTM C-457 ASTM C-672Mix identificationInitial Final Air a L a* L* Loss of Visualfresh air fresh air (%) (mm-1) (jim) mm-1) (pm) weight rating(%) (%) (kglm2)With AEA(5.20S)35T1SF-AM 7.0 4.5 4.2 11.8 450 16.8 385 3.46 3(5.25S)33L1SF-AM 14.2 2.0 5.0 13.4 366 14.5 353 2.72 3(5.27S)3OL1SF-AM 12.5 2.6 3.7 12.9 465 15.6 425 0.23 1(6.1S)35T3SF-AM 13.5 2.4 3.2 14.5 433 15.3 422 1.29 2(8.23S)25T1SF-CNF 21.4 4.8 3.7 19.4 306 24.5 272 0.02 0Without AEA(8.18S)41L1SF-AW 3.0 3.0 4.8 9.1 610 9.1 610 3.52 3.5(8.24S)41L1SF-AWF 3.4 1.2 3.8 9.0 588 11.9 512 5.69 3.5(8.25S)??L1SF-E 3.2 1.2 2.8 5.8 776 11.1 573 8.96 5(8.30S)54L1FA-W 4.8 2.0 4.9 8.2 621 8.8 606 32.0** 5* without large air voids (see Appendix H for details)** after 15 cyclesThe mixes cast without air-entraining admixtures have very poor scaling resistance; theirspacing factors are around 600 urn and they also have higher W/C ratios. For mixes castwith AEA, there is a direct relationship between the characteristics of the air void systemand the initial air content before pumping and shooting. The scaling resistance is improvedwith the use of AEA as well as by a decrease in W/C. Even for air contents as high as21%, it is difficult to produce spacing factors in the range of 230 .trn as required in theCanadian 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 airentraining adrnixtures. The scaling resistance is strongly affected by the W/C. A loss ofweight of 1 kg/rn2 is often used as a maximum limit for good scaling resistance. Only theshotcrete with W/C less than 0.30 satisfies this limit. However, the use of cement type 30and a W/C of 0.35 is probably acceptable (1.29 kg/rn2 weight loss). Thus, wet-mixshotcrete 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 stabilityproblems (high spacing factor even when starting with a very high air content probably177because of the loss of small bubbles during pumping), a high initial air content is not initself sufficient to protect the wet-mix shotcrete against scaling.400.45 0.40 0.35 0.30Water-cement ration (W/C)0.25Figure 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 wasavailable 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 particules0.08 kg/rn2), it might be possible that at a W/C of 0.25, air is not required for durability asis the case for some cast-in-place concretes of the same W/C.178SUMMARY AND CONCLUSIONSDuring this study on the rheology of high performance shotcrete, a new apparatus (UBCrheometer) was developed to measure the rheological properties of the fresh shotcrete. Thetraditional method of using superplasticizers to produce workable low water-cement ratiomixes, and a new method consisting of using a high amount of air-entraining agent wereused to cast several low water-cement ratio shotcrete mixes. A laboratory concrete pumpwas also developed to pump and/or shoot several of these mixes. A model based onrheological behavior was then developed to predict pumpabiity and shootabiity.The UBC rheometer is a new automatic apparatus which measures the rheologicalproperties of fresh concrete or shotcrete. It measures the flow resistance and the torqueviscosity, which describe the fundamental behavior of fresh concrete or shotcrete. Thisbehavior is similar to the Bingham model. The rheological properties can be determinedeither by sampling the freshly mixed material or on the-in-place shotcrete by shootingdirectly into the rheometer sampling bowl. This apparatus was found to be precise andreliable.The values of the flow resistance and the torque viscosity are affected by the mixcomposition. It was observed that these properties, especially the flow resistance, changewith 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 definedproperty is also affected by the mix composition, especially the cement type, and the typeand 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 useddirectly to predict the pumpability of high performance concrete mixes. However, is hasbeen possible to verify that the pumpability and the pumping pressure of these mixes canbe predicted by measuring the values of the flow resistance and the torque viscosity. Thefresh concrete aging rate also affects the period of time during which a particular mix willremain pumpable. Stability problems related to bleeding and/or segregation were notobserved on low water-cement ratio mixes containing sffica fume.179Important fundamental relationships were obtained between the rheological properties andthe shootability which was defined and estimated in terms of the maximum build-upthickness. It was found that the build-up thickness is directly proportional to the value ofthe flow resistance of the in-place shotcrete. Compaction caused by the shooting processincreases the in-place flow resistance proportionally. By knowing this last relationship (airloss during pumping and shooting), it is thus possible to predict the maximum build-upthickness by measuring the properties of the shotcrete before pumping. By measuringthese properties at different times and by determining the value of the fresh concrete agingrate, it is also possible to estimate the minimum required waiting period between twosuccessive applications.High performance shotcrete can be produced by reducing the water-cement ratio. Thiscauses a reduction of workability which can be overcome in different ways. The mostcommon way, referred to as the “traditional method”, consists of using superplasticizersto 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 improvethe workability. In both cases the requirements of pumpability and shootability must besatisfied in order to allow one to apply the shotcrete.It was found that the above requirements can be expressed in terms of rheologicalproperties. For pumpability, the flow resistance must not exceed a certain limit whichdecreases when the value of the viscosity increases. There is also a limit for torqueviscosity below which not even a mix with no flow resistance can be pumped. Forshootability, the higher the in-place flow resistance, the better the shootabiity. Mixes withno flow resistance do not remain in place after shooting. Practically, there is a minimumvalue of flow resistance below which the shooting operation is not efficient. The torqueviscosity does not influence the build-up thickness.These requirements are in conflict in terms of flow resistance: pumpability requires a lowflow resistance while shootability requires a high flow resistance. One can define awindow for the values of the flow resistance within which the pumping and shootingoperations can be carried out properly. The width of this window is affected by the torqueviscosity: for high viscosity, the maximum allowed flow resistance is reduced(pumpability requirement). For this reason, the conflicting requirements of pumpabilityand shootabiity are more severe for mixes with high torque viscosity.180It was shown in this study, that low water-cement ratio mixes made according to thetraditional method (use of superplasticizers only) are very viscous when fresh. Thesemixes must have less flow resistance (higher slump) in order to be pumped. Because oftheir high superplasticizer content, it is difficult to adjust their flow resistance: in the fluidstate, small changes in the superplasticizer content produce major changes in flowresistance. The fresh concrete aging rate is reduced when high dosages ofsuperplasticizers are used. Lowering the water-cement under 0.30 is not easy with thismethod unless special shooting methods are used, such as downward shooting or byusing 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 fewresults on practical mixes used on real jobsites, it seems that a high fresh concrete agingrate 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 enhancethe pumpability by reducing both the flow resistance and the torque viscosity. Theshootability is also enhanced by the compaction during pumping and shooting whichbrings the flow resistance back to a level corresponding to the same concrete made withoutair. The common dilemma of the conflicting requirements for pumpabiity vs. shootabilityno longer exists with this concept, for two reasons:• First, by reducing the torque viscosity, the use of air allows one tomaintain a wider window for the acceptable values of the flowresistance, as opposed to the use of superplasticizers only.• Second, the compaction allows a recovery of the flow resistance aftershooting. This particular effect also allows one to apply a thicker layerof shotcrete: after shooting, it is possible to obtain an in-place flowresistance which would have prevented pumping.Special care must be taken by those who want to try this concept because in working withhigh air contents they will have to deal with a highly compressible material, as opposed toa non-air-entrained concrete with little compressibility. Some problems might beencountered when using this concept of temporary high air content. During this study,because of an inadequate gate control sequence, some pumping rate reductions wereobserved. Some types of pumping equipment will not be able to handle high air contentmixtures or would have significantly reduced pumping rates even if the flow resistance of181the concrete were low (or if the slump were high). Thus special attention should be paid inselecting an appropriate type of pumping equipment for high air content mixtures.The concept of temporary high air content can be effectively used to produce highperformance shotcrete: this allows one to produce a low water-cement ratio shotcrete withenhanced pumpability, strength, and durability. It would probably be an excellent way toavoid the use of accelerators, which have adverse effects both on crew health and on theconcrete 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 aspectsof this technology.With respect to pumpability, it would be interesting to use different types of pumpingequipment in order to develop a more comprehensive understanding of this process. Theeffect of rheological properties on pumping pressure, pumping rate, the compaction-stiffening relationship, modification in the structure of the air void system, etc. should belooked at.Regarding shootability, because it is mostly related to the value of the flow resistance, itwould 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 testor similar in-situ static test and the flow resistance. With this tool, it would be easier tostudy 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 ofcast-in-place concrete of similar composition, it would be appropriate to study furtherthose properties which are closely related to the air content or to the quality of the air voidspacing 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” ofshotcrete as opposed to the traditional “art” of shotcrete.182Appendix A: MaterialsThis Appendix contains information on the material used to cast the concrete and theshotcrete mixes used in this study. The results of physical and chemical analysis carriedout on five cements, as well as those carried out on the silica fume and the fly ash, arepresented. Some information on the sand and the coarse aggregates used in the study isgiven, including the absorption, unit weight and aggregate gradings. Some information onthe admixtures used in the study are also presented. Finally, the physical and chemicalanalysis on superplasticizers, carried out at the Université de Sherbrooke (Sherbrooke,Québec), are given.183Physical and Chemical analysis of CementsPHYSICAL TESTSCHEMICAL TESTSCement:Tricalcium silicate (C3S: %):Dicalcium silicate (C2S: %):Tricalcium aluminate (C3A: %):Tetracalcium silicate (C4AF: %):Li L3 L5 Ti T349 62 53 63 5623 ii 21 13 186 8 2 6 79 7 13 ii iiCement: Li L3 L5 Ti T3Setting time (vicat: mm), initial: i 13 90 i23 - 6ifinal: 219 193 203 - i58Fineness (Blame: m2/kg): 422 532 4i8 448 509Passing 45 p.m (%): 97.3 97.0 93.9 -Autoclave expansion (%): 0.05 0.20 0.07 -Strength (MPa) at 3 days: 25.2 31.0 26.6 - 32.27 days: 34.6 - 33.6 - -28 days: 43.2 48.3 43.0 - 44.8CalciumOxide(CaO%): 63.4 63.9 6i.76 65.4 94.9Silicon oxide (Si02): 21.1 20.3 21.5 21.1 21.0Aluminiumoxide(Al302%): 5.2 4.54 3.27 4.44 5.0Iron oxide (Fe203 ): 4.14 2.46 4.17 3.68 3.7Magnesium oxide (MgO: %): 1.0 2.2 3.9 0.9 1.2Sulphur trioxide (SO3:%): 2.7 3.4 2.4 2.7 3.2Loss on ignition (%): 1.23 2.13 1.79 1.61 0.7Alkalies (Na20 + 0.658 K20: %): 0.49 0.48 0.55 0.38 0.48184Physical and Chemical Analysis of Silica Fume (SF) and Fly Ash (FA)PHYSICAL TESTS (grading)Sieve Silica fume Fly ash(.tm) (% passing) (% passing)100 100 9770 100 9350 99 8730 98 7420 96 6010 93 348 92 266 90 174 88 82 83 11 78 0CHEMICAL TESTSSilica fume Fly ashSilicon oxide (Si02%): 91.7 49.7Aluminium oxide (A1302%): 0.07 23.8Titanium oxide (Ti02%): 0.01 3.36Phosphorus oxide (P205%): 0.04 0.93Iron oxide (Fe203 %): 0.05 5.30Calcium oxide (CaO %): 0.09 8.51Chromium oxide (Cr0 %): 0.05 0.43Magnesium oxide (MgO %): 0.23 2.07Sodium oxide (Na20 %): 0.12 4.33Potasium oxide (K20%): 0.60 0.51Sulphur trioxide (SO3 %): 0.28 0.57Loss on ignition (%): 6.55 0.58185Absorption, unit weigth and gradings of coarse and fine aggregatesABSORPTIONsand:10 mm stone:UNIT WEIGHT (SSD)sand:10 mm stone:GRADINGS2642 kg/rn32697 kg/rn3Passing (%)Sieve sizeU.S. (metric) Sand 10 mm stone1/2 in. (12 mm) 100 1003/8 in. (8 mm) 100 98No.4 (5 mm) 100 4No. 8 (2.5 mm) 92 0No.16(1.25mm) 79 0No. 30 (630 jim) 53 0No. 50 (315 jim) 16 0No. 100 (160 jim) 5 0No. 200 (74 jim) 1 01.1%1.5 %186Admixtures information (from manufacturer)SUPERPLASTICIZER ACommercial name: Rheobuild 1000 (Master builders)Usual dosage: 650 to 1600 ml per 100 kg of cementChemical family: cement dispersing agentSUPERPLASTICIZER BCommercial name: Pozzolith 440-N (Master builders)Usual dosage: 650 to 1600 ml per 100 kg of cementChemical family: cement dispersing agentSUPERPLASTICIZER CCommercial name: Daracem 100 (W.R. Grace)Usual dosage: 350 to 1250 ml per 100 kg of cementChemical family: blend of sodium/potasium naphthalenesulphonate salts, lignosulphonate andhydroxycarboxylic acid salts concreteadmixtureSUPERPLASTICIZER DCommercial name: WRDA-19 (W.R. Grace)Usual dosage: 600 to 1250 ml per 100 kg of cementChemical family: naphthalene sulphonate formaldehydecopolymer concrete admixtureSUPERPLASTICIZER ECommercial name: SPN (Master Builders)Usual dosage: —400-1000 ml per 100 kg of cementChemical family: concrete admixtureAIR-ENTRAINING AGENT MCommercial name: MBVR (Master Builders)Usual dosage: 16 to 260 ml per 100 kg of cementChemical family: vinsol resinAIR-ENTRPJNING AGENT NCommercial name: DaRaVaiR (W.R. Grace)Usual dosage: 47 to 188 ml per 100 kg of cementChemical family: vinsol resinWATER-REDUCER WCommercial name: Pozzolith 100-N (Master Builders)Usual dosage: 200 to 325 ml per 100 kg of cementChemical family: cement dispersing agent187Test results on admixtureSUPERPLASTICIZER ACommercial name: Rheobuild 1000 (Master builders)% of solid: 44 %Density: 1.19Calcium oxide (CaO): 5.0Sodium oxide (Na20): 0.0Chemical family: naphthalene sulphonateSUPERPLASTICIZER BCommercial name: Pozzolith 440-N (Master builders)%ofsolid: 31%Density: 1.15Calcium oxide (CaO): 0.0 %Sodium oxide (Na20): 4.6 %Chemical family: blend of naphthalene sulphonate and lignosuiphonateSUPERPLASTICIZER CCommercial name: Daracem 100 (W.R. Grace)% of solid: 40 %Density: 1.2Calcium oxide (CaO): 0.0 %Sodium oxide (Na20): 5.4 %Chemical family: blend of naphthalene suiphonate and lignosuiphonateSUPERPLASTICIZER DCommercial name: WRDA-19 (W.R. Grace)% of solid: 40 %Density: 1.21Calcium oxide (CaO): 0.0 %Sodium oxide (Na20): 6.3 %Chemical family: naphthalene suiphonateSUPERPLASTICIZER ECommercial name: SPN (Master Builders)% of solid: 43 %Density: 1.2Calcium oxide (CaO): 0.0 %Sodium oxide (Na20): 5.0 %Chemical family: blend of naphthalene sulphonate and lignosulphonate188Appendix B: UBC Rheometer User DocumentationThis Appendix presents the UBC Rheometer User Documentation. It has been preparedby:Kevin Campbell,Stefano Dondonibus,Jeff Freisen,Einar Halbig andKevin Wong.I thank them for their work. The documentation does not contain the listings of theprograms because their use has been licenced.189UBC RheometerUser DocumentationDeveloped by:Kevin CampbellStefano DonadonibusJeff FriesenEinar HalbigKevin Wong190—Introduction! The rheometer is a computer-controlled device that tests the rheologiPumose cal properties of concrete (specifically shotcrete). This machine’s designis based on a modified Mark III’ rheoineter.This manual describes the hardware components, calibration procedure, and operation and set-up of the computer program that controls therheometer. Theory and specifics of the actual control and feed-backelectronics are not included in this manual, nor is a discussion of rheologyor such properties of concrete.The intended audience of this documentation is the user of therheometer.Conventions Computer-displayed material (screens, pmmpts, etc.) are displayedintheCourier typeface (what you are reading now).Responses that you are to type are shown in Bold Courier.The following keyboard conventions are observed:Symbol MeaninfKev<Eec> Escape key<Enter> Enter or Return key<Space> Space barcCntrl> Control key (pressed in conjunction with another key)<Break> Break keyAssumptions The reader is assumed to be familiar with fundamental DOS commands and concepts (directories, simple batch files, etc.).Hardware A schematic of the rheometer is presented in Figure 2.1. An IBMPC computer with a PCL-812PG A/D and D/A (analogue-to-digital‘.J’.J II IIJJI Ii II 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 importedinto a spreadsheet program. (please see Test Data Output).Motor control circuitry is contained in a grey box above thecomputer cabinet.• Be sure that the powerswitch is off whenever a test is notbeing run.• Ensure thai the auto/manual switch is in not in the centreposition, as this will cause the motor to run at full speed.The auto/manual switch should be at auto, and the speed dial shouldremain at the zero position during a test (the dial may be used for rotatingthe torque beam for calibration procedures with the auto/manual switchset to manual). Please refer to Calibration Procedure on page 5.The Motor and Speed SensingThe impeller is driven by a ooe half horsepower DC motor to whicha tachometer is attached so that accurate motor speeds may be read intothecomputer. ThereisaóO:lreduceratthispointsoastoprovidesmoother and more efficient motor use and speed change. This providesan excellent method of measuring speeds ranging from zero to inputtedmaximum speed and back to zero.Sm eflbeem191‘‘-“ometeilc mot{11/2 HP [SlIp r....,Control penn Ippcomputer1511 PC AT 286 WIPCI-B 12P5 cerd6OPG.er 16 D //ImpellerFigure 2.1 - Schematic diagram of the rheometer192Drive Gearing and Torque MeasurementAt this point the shalt travels down to the torque/beam device. Thereis a 1:1 gear ratio that drives the impeller by way of the torque/beam. Thebeam then actually turns the impeller shaft and its deflection, caused byforcing the impeller through the concrete, is measured by 4 strain gauges.The signal from the gauges is amplified 470 times prior to beingtransferred to the computer via a slip ring situated at the top of the shaft.The ImpellerAs the previous MKIII rheometer this new rheometer uses an Hshaped impeller that moves in planetary motion thereby assuring adifferent path through the concrete on every rotation. The gears leadingto the impeller are a 16DP20 gear at the impeller shaft and a 16DP45 gearat the driving shaft.The BucketThe 19.2 L bucket is placed on a platform that can be raised by crankinto the desired testing position. The platform is counter weighted and thesafety pin should be placed in the stop hole while the bucket is off theplatform and also while the test is being performed. The impeller shouldbe removed whenever loading or unloading the bucket, and for cleaning,so as to avoid damaging the sensing equipment.Program..The Selection Menu screen suiular to Figure 3.1 will appear when theOperation computer is turned on. You may:1. Press 1 to run the calibration program,2. Press2torunarheologytest,3. Press <EBC> to leave the menu and return to the DOSoperating system,4. Choose any other listed option in a similar manner.The Selection Menu can also be invoked from the DOS prompt bytyping the following (from any directory):RHEOLOGY <Enter>Note thai when option 2 (test program) is selected, a DOS batchfilewill set the current directory to CARHEOM..PARAM, and then run theprogram. This has the effect of telling the program to expect to find anyspecified parameter files (explained below) in the C:\RHEOM\PARAMdirectory. The program will expect to fmd parameter files in whateverdirectory it is run from193Selection MenuPlease press the number of your choice1- Calibrate2 - Run Test3 - Directory Map (Change Directory)4 - Copy/Move/Delete FilesEeC- Exit menu to DOSFigure 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 Parameteris a plain text file created by the user (in any text editor) that contains al Filesthe test information required from the user by the computer for a singletest. The information, or parameters, are read in by the computer, anddisplayed as “defaults,” or initial values. Repeated (identical or similar)tests on different shotcrete mixes can be run more easily by creating onesimple parameter file that is used for all mixes. Figure 2 shows thecontents of a typical parameter file (parameter meanings are explainedlater).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 theprogram is run (typically C:\RHEOM\PARAM)• The file must begin with a mix description: one line of textonly, no commas!• The values are all positive integers, and must each be enteredon a separate line with no commas• Parameters must be entered in the following order:Maximum SpeedSpeed IncrementSpeed DecrementInterval Between Increments/DecrementsNumber of Samples at Each Increment/DecrementFor information on how to use a parameter file, please refer to the TestProgram Operation on page 6.194To run the test program. choose 1 (Run Test) from the Selection Menu. Test ProgramFigure 3.4 shows the opening test program screen. OperationIf you have created a parameter file for this test; type the filename atprompt 1 shown in Figure 3.4. Do not include the .REO extension in thename. A parameter file named TEST1.REO was specified in thisexample.RHEOLOGY - Rheometer Test Program V2.l1. Parameter filename (<Enter> for defaults) : TEST1Figure 3.4 - Opening screen of Test ProgramIfyou do nothave a parameter file for this test, press <Enter> to usethe program default parameter values.Default ValuesEach prompt is presented in sequence as responses are provided, untilthe screen appears as in Figure 3.5. Each prompt requests a single value,and each prompt displays the default value in angle brackets ( c..>). Touse the specified default, just press <Enter> at the prompt. To use avalue different from the default, type a new value, and press <Enter>Parameter PromptsOnce parameters have been entered, they cannot be corrected, instead, the user must press <Cntrl> C and restart the test program. Atest may be halted at any time by pressing <Fl>.Prompt 2: Mix Identification CodeThis U) code is mandatory - there is no default value. This code willbe used as the output file name and must therefore conform to DOSfilename requirements. Do not add a file extension. The extension .DATwill be added to the filename automatically. Output files are written intothe directory C:RIJEOM by defaulL To change this default directoryto another, the program must be edited and re-compiled.195Figure 2- Contents of a typical parameter file.Calibration The Calibration Program allows for calibration (zeroing) of theProcedure torque-reading system. Calibration may only be required at the beginning of the test session, and is generally not required after each test. Theneed for manual calibration may be eliminated in future updates of theTest Program.To Calibrate the system:1. Run the Calibrate Program (Selection Menu option 1)2. Enter 0 for the speed3. Enter a maximum value of torque above O(say 300)4. Slightly rotate the very small brass screw on the white ceramiccomponent on the underside of the shroud covering the sensingelectronics (near the metal beam with strain gauges attached). Watchthe torque reading on thecomputer screen - rotate thescrew in the direction that getsthe reading as close to zero aspossible. One direction willmake the reading more negative;the other will make it morepositive. Refer to Figure 3.3 forlocation ofthe calibration screw.5.. Once a value of zero (or veryclose to it) has been set, press<Space> to return to theSelection Menu.Figure 3.3Location of calibration screw (barelyvisible on white ceramic block). A smalljewelers screwdriver is required for thecalibration.Type 10 cement with plasticizer250050025S70196RHEOLOGY - Rheometer Test Program V2.12. Enter mix identification code (for output filename) :MZX4BCurrent mix description :Test la - use on low air-content shotcrete3. New description or <Enter>4. Enter maximum speed (max. 4096) < 2200 >5. Enter speed increment < 175 > :1506. Enter speed decrement < 50 >7. Enter increment interval < 15 >8. Enter number of samples at each speed interval (Max. 100 ) < 50 > :75Figure 3.5 - Final screen showing all prompts, and some modified default values. The defaults were taken from a parameter filenamed TEST1 .REOPrompt 3: Mix DescriptionIn this example (Figure 3.5), a mix description was provided in theparameter file TEST 1 .REO. The user is given the option of changing thedescription, or of leaving it as is (default) by pressing <Enter>. It isimportant that no commas be used in the mix description.Prompt 4: MaxImum SpeedEnter this value as a positive integer. This value is the maximumspeed value that may be sent to the drive motor controller. This numberis in “internal units”, and is not the same as the speed read from the speedsensors.The maximum speed value actually sent to the motor controller maybe less than this number. If increments are 300 speed units each, and themaximum speed is set to 1000, the maximum speed value sent will be 900(3 x 300 = 900), and not 1000.Prompt 5: Speed IncrementThis positive integer represents the number ofinternal units the motorspeed is to be increased by at each interval.Prompt 6: Speed DecrementAnalogous to Speed Increment above.197Prompt 7: Increment IntervalA positive integer representing the amount of time (1 unit = 1/l8thsofa second) after the speed has been increased but before the samples aretaken. This time period allows the rotating parts to overcome inertialresistances that would affect the sample data.Prompt 8: Number of SaipplesThe number ofsamples taken (and averaged) at each speed setting areset 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). Feedrepresents the internal speed value sent to the motor controller. Speedrepresents the speed value read from the rheometer’s speed sensor, andTorque is the instantaneous (not averaged) torque value read from thestrain gauges and amplifier circuit. The value in parentheses to the rightof the Torque reading is the maximum torque value read thus far in thetest.Test DataThe rheometer has a built-in over-torquing safeguard: the systemwill shutdown ifthetorqueapproachesa value that would causepkzs&deformation of the sensing beam.RHEOLOGY - Rheometer Test Program V2.lTest Mix Identification : Test la - use on low air-content shotcreteName of output data file : MIX4B.DATMaximum speed : 2200Speed increment : 150Speed decrement : 50Increment interval : 15Samples per interval : 75Feed : 150Speed : 76Torque: 127 ( 235Figure 3.6 - 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.198Test Data Output Test data are written into a tab-delimited (e.g. data values areseparated by tab characters) data file in the directoxy C:\RHEOM. Thefile name is the Mix Identification Code (see prompt 2 information) witha DAT extension appended to it. Figure 3.7 shows a typical output datafile. The data are written in the order ofFeed, Torque, Speed. These datamay be easily imported into a spreadsheet for analysis. Each data file isalso time- and date-stamped.Timestamp : 03-21-1993 15:38:52Mix Identification : Test laMaximum Speed: 2200Speed Increment : 175Speed Decrement : 50Increment Interval : 15Number of Samples : 500 0 0175 .125 12350 .138 20525 .150 47700 .250 60875 .299 731050 .356 851225 .385 94250 .120 17200 .116 15150 .108 10100 .095 750 .099 30 .045 0Figure 3.7 . A typical output (.DAT) data file contents. The data files are easilyimported into a spreadsheet for analysis. Data are written in theoiler Feed, Torque, Speed.Performing This section assumes the reader is familiar with the Test ProgramA Test operation (see Program Operat.ion, Section 3). To perform a rheologytest:1. Turn on the computer and ensure power switch for the motorand controls is tamed off and the auto/manual switch is onauto.2. Ensure the rheometer is calibrated (see Calibration Procedure in Section 3).199Important: the motor power switch should be off wheneverthe rheometer is not being calibrated ora test is not being run.3. With the motor power turned off, remove the impeller (thisis important to prevent damaging the sensing beam whileinstalling or removing the testing bucket).4. Ensure the bucket elevator pin is installed to prevent thebucket elevatioh platform from rising when the bucket isremoved.5. Remove the test bucket, and fill with shotcrete to approximately 8 inches (203 mm), thus ensuring that the impeller isfully submerged.6. Place the test bucket on the elevation platform.7. Re-install the impeller, making sure it “clicks” into place (thelarge key on the end of the impeller shaft should take thetorque, not the small holding screw on the shaft sleeve).8. Remove the elevator pin, raise the platform and bucket usingthe hand crank, and re-install the elevator pin. The impellershould be submergedjust below the surface of the shotcrete.9. Turn the motor power on.10. Run the Test Program (see Test Program Operation on page6).Important: do not run too many tests on a single bucket ofshotcrete — the impeller does not agitate the mix all the wayto the bottom of the bucket, and mix hardening results.11. Once the test has completed, shut offthe power to the motor.12. Remove the elevator pin, lower the elevator platform andbucket, and replace the pin.13. Remove the impeller, the bucket, and wash everything down.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 theimpeller in the normal position (see Figure 5.1 la). The compositions of all mixes tested inthis small program are given in Table 5.2.1,210,80,60,40,20T50.38 (2500,200,200,70,5,5)1,210,80,60,40,200200ITorque (Nm)T50.38 (3000,100,100,50,5,5)5L___-i.——-iII’ ‘.d_. _._2 3 4 5Torque (Nm)(uIN)nboi9V£Z10rDB‘‘B‘.——.—...—.—....—.i•90z’0V’09’0Iz’T0V’09’0x’0z’I0z’oI”O9’08’oIz’T(‘‘o9’ooc’oog’ooo).si(Uif4J),nbio 1VZ10.—.II.T1II•h”-.——-....r.i•...I.II—I.•.;.(‘s’os’ooI’oo1’ooo)xsi(wN)nbioiI’£Z10—III—.——I—.—I——•—..-._.I—.—•.;‘9(‘‘oL’ooz’ooz’oosz).si•10z202FS.38 (3000,500,500,60,5,5)1,2110‘J,—1L,-0, -A,,(I1,110,0,Torque (Nm)T10.43a (2500,50,50,5,5,10)T10.43a (2500,50,50,5,5,10) all dots11I....40- ..0 1 2 3 4 5 6Torque (Nm)1,0,0,0,0,0 1 2 3 4 5 6Torque (Nm)203T10.43a (4000,300,300,30,5,3)UU •U—U UU U— — —— -.— —.— —. — —— —i— —n — —UI— •— — U-.— — —0 1 2 3 4 5 6 7Torque (Nm)T10.48 (2500,200,20,70,5,5)81,20,81,20,8II 0,6v’.-.- 0,4E 0,2—01,20,8U. U.U.. U—.U U. U— —UU U. —U——.U U. -I.I U! U-50 1 2 3 4Torque (Nm)T10.48 (3000,100,100,50,5,5)I.- i[•I.L!.__i41_ _____. iiT. —IU.UU0 1 2 3 4 5Torque (Nm)204T10.48 (300,500,500,60,5,5)....-I.I.—I.____________0 1 2 3 4 5Torque (Nm)T10.43b (2500,200,200,70,5,5)1,210,80,60,40,2010,80,60,40,20jIL•.-. ..., —.—.—. .—..., -.._____________0 1 2 3 4 5Torque (Nm)T10.43b (3000,100,100,50,5,5)1,210,8• 0,60,4E 0,20_______i!’.—.!.—iu.--:-i.iI—!•.•reiI0 1 2 3 4 5Torque (Nm)1’T1O.43b (3000,500,500,560,5,5)T10.43c (3000,100,100,50,5,5)2051,210,80,60,40,20.III.IU•1—U—1’II0 1 2 3 4 5Torque (Nm)T10.43c (2500,200,200,70,5,5)706050403020100‘IiU.. —U——.I I.U I.-. II. I • III.0 i 2 3 4 5Torque (Nm)0 1 2 3 4 5Torque (Nm)(uIN)nboiS10I•.—.—ILjL!0z’ov’o9’08’OI0z’o-‘0‘0Iz’IB———B—(D(oz’i’s’os’os’oosz)qrsi(uiK)nbioiI’Z10U—U•ULU—!T.;:ia.i——-U—1’.._JI.(6T’T’oI’os’oo’ooSz)901Appendix D: Pumping and shooting equipmentThis appendix presents some drawings of the laboratory concrete pump. Other details weregiven in section 6.1. The pump was designed by Conseption GSR (near Quebec City).20700313N31108£L_9/1OS310H91(noLt00SC2H1ESl/4—20NCX1/2SEC11ONA—A207/16’1.1WwIII6\f6H0(S111/16’ CN6’BOlTCIQ.Ei1Yx1Yx126HOLES011/16’8’BOLTCIRCLE—11/2’/\TWOOPENINGS/\1’wD1Nx7o\—/o.in’0.18----/I-.__—__091/2’-06.250’-._-——_-——_---—__.g.—---_____——___—.——_—SI-...•1__\/__T_LLriA43/8’V/—__FORORING2—258________________________W=197/8’____M=19.750SEC11OMA—AAFTER3.DINCANDACHDINc RE—COVERThEUSICf1NETUBE1H0.010’TIIO(JIESS OFHAR])CHROUE.212:3.ri?.R3/8’ TVP.1/32’ X 45 rrP.04IIIIII-___-___I IIII I0361’•— O363.10• Ti?.3/V 13/4’3 3/8’4.Appendix E: Mix compositionThis appendix presents the mix compositions and the results of some usual tests (Slump at15 mm, fresh air content and the compressive strength). The compressive strengths weremeasured on three cylinders or cores for the shotcrete. The results of other tests carried outon these mixes are presented in Chapters 6, 7 and 8 (including Figure 5.21).213214Ci C) ‘.0 ‘.0 00 ‘ oq q r’0 00 t- r- a — — ‘0 N00 I I I I I ‘.6‘- c ‘.0-‘.0 ‘0 ‘.0 ‘.0 in - C in r N ‘.0 N N ‘n cn inCflC 000-00N • C) in N 00 C C C) 0 N C) in C) in ‘.6 c Ifl 00 ‘ CCC)‘— “C in in fl C’ in C1) in ‘.0 ‘.0 C’1rC)n%CC)-4 -4 -4 -4 -4 -4—‘E E C) ,in in C)C) ©OininC)©C)0‘ r in ‘ N Cr) in in ‘-‘ ‘.000in in -4 C) -c’.-4Cl)Cr) Cr) Cr) C) C) ‘.0 c t’ ‘.000 C’ ‘.0 in in • -4 -4 -4 -4 -4-4 0’ 0’< OC)C)N’0N0000NC)0’’.00’’.0NC)NS%-::::_‘.0C CNin00 NCNlf4-a 00 ‘.0 N 0’ — 00 Cr) C C) in ‘n ‘.0 C) C) ‘.0 C Cr) 00 in Cr) 00 Cr) C) Cr) 00 NEC CC ‘ “1 00 ‘0 0’ ‘.0 Cr) 00 00 ‘.0 ‘.0 ‘.0 N Cr) Cr) in 00 in —4Ci Cr) N 0’ Cr) C)C)C)C’-4C)-4C)C)-4C)-4-4-4-4C)C)C)C)C)-4Cl) 0’ 00 0’-4 -4 -4 -4 -4 -4 -4 -4 -4 -4 -4 -4 -4 -4 -4 -4 -4‘—O in’.DC)C’ 4.-00inCr)i, , , , , , , , , , , , ,. , , , , , . , ,N ‘0 Cr) N Cr) 00 in C) N 00 C) 00 C) ‘ 00 Cr)qNN ’N C)J- r Cr) Cr) ‘j in in ‘I1. in in ir in i in in in in in in in in• Cr) C)00N’0C)C)C)0’N0000inC)’0(CEECr)’ Cr)”1 Cr) Jr).lc.)UL)L).)c)cuuC in in in ‘‘ Q c_) U U U U U ‘-. 1_f- E- EE E.E-- Cr)Cr)’ Cr) F F— F—E-E-C)oC)C)C)0000ininininC)C)C)C)CflinF-F-C)C)C)NN. inininNCr) r)r)C’< - -‘ ‘ —.‘ -‘ “‘ —‘ - ‘ - -‘ -‘ 2 ‘ ‘ . .‘ ‘ ‘ ‘: I-%0\000CCC)ininininNNNC’N 00--I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I ICr) Cr) Cr) ininin ininininin ininin ininin’.0 ‘0’0’0’0’.0’.0’.0 ‘.0 ‘.0 ‘.0’.0’.0‘— - - %_, - %_, %_, %_, ‘— - - - %_, S/ \ ‘ % % % ‘215O’r ca Nrl rN cNC00 Q C N — C I I I I C O C C 00 \C 00 Ncq 00 C 00 0000 00 ‘,C 0000 00 N N N 00 \D N cCNN N— NN N \C) N 00 N N N ‘r N 00 — — I N cN %C C’ N Ifl \Q Ir - N‘‘E ‘D N — C N N ‘.C ‘.C ‘D N 0 N ‘CI I.fl I.fl N N:::; — — N — — — — — — — — — — ‘- — — — — — — — — — — — —-•I’ C Nrqc. C N 00 00 C C C N N 0000 N kfl %C N 00) - C rI 00 C N Ifl C — c Q, 0 N N 00 N 00 C N 00 — N •r C a “C N N— b C N N ‘C “C “C “C ‘r \C N c N C C - — — — C 00 00 C C — N ‘.n N —‘I ‘ ‘ “zl ‘ ‘I ‘j ‘j ‘ ‘Ij k(1 II Ifl Ifl ir ‘- --E C’Ir 00 - II’N 00 C C — C I N — C’ N N 00 NC— 00 C’ \C “C ‘.0 C ‘.0 N ‘. 00 00 N ‘.0 00 N N 00 N ‘f C C ‘.0 C’ ‘.0 0’, 1-c, C — .— .— — —‘ - — — — ——‘ C — C — ‘.0 ‘—‘ — ‘ — ‘-‘ — — — — —- C .- — C- — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — —00 C’ 1- C’ ‘.0 C C N’.CCC”, ‘.0E ‘. ‘.c c r’ .— c. ‘ c N C r’ ‘j- - r’i 00 — C a’ ‘.0 NC ‘.— N N N N N — N N N c’ (‘I’, N N ‘ - - ‘ - J- • c4 ‘J cv’, fl ‘-— — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — —%00’,00NN0000NN0000.-c..,1. ‘1• lfl Ifl kr ‘If tr ‘Ij• ‘If ‘If fl - ‘If ‘If If ‘If ‘If ‘If ‘If ‘If ‘If—C N 0’, 00 C ‘If N c N N ‘.0 ‘—‘ 0 0 ‘.0 C ‘.0 O N 00 N ‘.0 ‘r ‘.0 N 00 N ‘IfE00 It’, ‘If ‘If ‘If N ‘If N ‘.0 N N c c ‘If ‘If N N ‘, N - C C ‘— N C c” Il’, 0’- cfl “f ‘If ‘If ‘If ‘If ‘If ‘If ‘If ‘If ‘If ‘If ‘If ‘If If i ‘If t ‘If ‘If ‘If ‘If ‘If ‘If ‘If ‘If ‘If c,’-.L UQQQQ)QQQc.)L)uQQ‘ —— %-, U ‘—‘ U — — — — ‘— — .— 1— — —‘.- NNNNNNNNNN’.IC• ‘‘6’I <U’< —‘-‘4 QcI,<‘.0 — — — — e ‘If C ‘ 00 00 N N N 0’, C’ 0 C — c “0 ‘.0 ‘.0 N N N 0NNNNNNNNc\0\0o0O000——————NNNNNNNNNNNI I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I%0%0%0’.0’0’.D’.0’.C’.0NNNNNNNNNNNNNNNNNNNNNN%_ %__ - ‘- ‘— - ‘-‘ ‘— %__ - %_ - “- - \__ ‘— %_ ‘— ‘— - -216C \C — C C - C N In 00oo o6-’ 6oc c’_-’ ‘-rr-o6C N C N N C 0000 C’ %D In ‘n O 0000C. c’ - vN — tn N 0000 N 00 c - tn ‘C C 00 fl -‘Ifl c In N In Ifl N N 00 N ‘,C) N N c’ N t- N N C‘‘ In tc C1f) C In - N a C C C C C ‘n C.,-‘C C C ‘n C C I C In C ‘n ‘n CI ‘.C \ I N Ifl I N I C’ In C In I I c . N N C— — — .— c’ csI c’i ci cI — —P1 I( C N I’ oq 0 1— C—C9 — “ 00 CE CInInInnNrt-’:D::l — — — — — — — — — — — — — — — — — — — — — 0%sN— flInIn.— N Cfl 00 C’ — C1) C — t tin In In ‘n in ‘n - in ij- -) %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 in00 C 00 CI C, In N 0% ‘.0 N N ‘j ‘.0 In C% In In In — N In ‘.0 ‘.0 —.- 00N\0—N00’.0NN’%’.00000\0In00O00%f%NNN000%0%cP1 f% (% ‘lj 1j ‘j ‘Ij C% ‘1 ‘t ‘i-‘E — ‘.0 00 00 00 % In C1% — ‘It — in N ‘.0 C 0% ‘It C% N 0% C 00 C —C00InN0 000%1_cn 00%0%00InP1 IJ — C C C C—’ — — — In00, — — — — — — — — — — — — — — — — — — — — — — — — — —Cc%C N00C% N InIn0%00’.0- 0%c C0%000% — N N00c%O%—’.- ‘ ‘ ir’ i C j- in in ‘.o o r’.i N- C C — cl — ‘t ‘j- ‘o C .— 00 C C c ‘,c Nin t- , r in 1- In ci in in - In C’ C’ C C’ C’ N N N CI fl l% ‘.D \ ‘— - —— — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — —-;-,_ NCnN0000000%CC00c’Itini- ‘t’It1 In’1-InIn in1- InInIn-InInI-’It’It InInInIn’It‘.0 in — In c’1 0% N N C C c a ‘It N c% C N C In — N — N0% 00 ‘.0 N 0% C’ C’ c% N 0% ‘.6 .— — — In — c’% 0% 00 C In 0% 00 0% C ‘:1-‘It c% ‘It c ‘It It - ‘j- ‘It It - c% - ‘It ‘It ‘It ‘ItI ZZQ i I I II I: C C. < ‘6’’P’<0%<—’.C’.C\0’.0\00000000%0%0%n%N000000000000000000000000000000000000000000 00000000000000000000- -‘— ‘-, - -, - ‘— ‘— s__ ‘, ‘.- , ‘ - s__ ,e % % %.‘ %‘217000 N - .- ir ,- ‘D N r00 ‘D 0 - ‘n .- -i N óN , Q 00 fl C “C fl C) C C-Voqo00Q00000N00CflC0 N%-. ‘Z’C- c c j- j-—‘V000 kn0 fll•) N 0 N I — I— — — — — — —— nCl) ‘-‘() E — - ag- in— — — — ‘- —Cil 0-lfl ‘.C%CC) 0 00 N ef 0’ in ‘ Cr1 cq.1 0 0 - 0Ein N N “C “C N N N N —— 0 — NCl) “CJ ‘j ‘ ‘Cj ‘ Cr) in Cr) Cr) Cr)-‘ ON00inin”CC‘ E f)000N00 N N 00 0 C 0 N N ‘Ct “C 00Cl) ‘J — — — —— N — — — — — — — —, — — — — C-C- . — . —N N C N N—Cr) N —Cr)— 0 0 — C’ Cr) N —C in in 00 00 00 C N C C’ 0‘ ‘ .-i .- ‘ ‘ —i ‘ ..— N-00ccodoin in Cr) Cr) Cr) Cr) If) in in‘Ct ‘Ct ‘Ct in—00 —.— N - 00 N 0 N ‘-i “C N Cr) “CC) 0 00 00 0 “C ) Cr) in N N in 00 ‘CtN in j- 00 C) C) in in Cr) N N -—‘ N1)‘1 ‘Ct ‘Ct c’ ns.— — — — — — — — — — — — — —:N Cfl (i’) ‘Ct ‘ ‘Ct e—• C-. c-. Cr) ‘I’ Cr)< ,%‘‘ S ‘—‘ ‘—‘ -‘,—. ‘—S.-inCr)N0000NNNNN NNNNCrI I I I I I I I I I I I I I00 00 00 00 00 00 00 00 00 00 00 00 00 00‘ ‘ ‘ \00‘ICC,)Cl)*218Appendix F: Pressure bleed test resultsThis appendix presents the results of the pressure bleed tests carried on some mixes. Thedescription of the apparatus and the test procedures are presented in Chapter 6. Theanalysis of these results is also presented in Chapter 6.-.EPressure bleed test (7.20A)3OL1SF-AFPressure bleed test (7.23E)33L1SF-CF100.Qa.-.EEII“U. 20 40 60 80 100 120 140Time (mm)60 80 UTime (mm)O 120 140.E-.EE-.Pressure bleed test (7.26A)3OL1SF-CF100219I I60f-I_____0 20 40 60 80 100 120 140Time (mm)Pressure bleed test (7.27A)3OT1SF-AMI0 20 40 60 80 100 120 140Time (mm)Pressure bleed test (7.29A)3OT1SF-AM15012090603000 20 40 60 80 100 120 140Time (mm)220‘‘ 15EEEEEE-.12090603Pressure bleed test (8.3A)3OT1SF-DNPressure bleed test (8.5A)3OT1SF-D20 40 60Time (mm)7LGD°150120906030015012090603000 20 40 60 80 100 120 140Time (mm)Pressure bleed test (8.11A)3OT1SF-D0 20 40 60 80 100 120 140Time (mm)EEPressure bleed test (8.16A)25T1SF-CFTime (mm)Pressure bleed test (8.19A)25T1SF- C20 40 60 80 100 120 140Time (mm)Pressure bleed test (8.23A)25T1SF-CNF1501209060300221‘ n..E0 20 40 60 80 100 120 14000 20 40 60 80 100 120 140Time (mm)222-.Pressure bleed test (8.24T)41L1SF-AWF1512090603000 20 40 60 80 100 120 140Time (mm)Pressure bleed test (8.25T)??L1SF-E-D-I‘ ,nE‘ 2’15010010 20 40 60 80 100 120 140Time (mm)Appendix G: Rheometer resultsThis appendix presents the results of the rheometer tests carried out on the mixes presentedin Appendix E. The description of the apparatus and the test procedure are presented inChapter 5. These tests were carried out with the second torque measuring beam (7 mmthick) with the impeller in the deep position (see Figure 5.11 a). Results in grey wereobtained on pumped concrete while the results in black were obtained on the shotcrete(projected directly into the rheometer sampling bowl). These test results are discussedthroughout Chapters 6, 7 and 8.1.2110U.L0.60.”0.20‘ft(5.18A)38T1SF-BMFTorque (Nm)2231. 11 mmo 26 mmA 44 mmo 62 mmL.C.EpI I — I —0 1 2 3 4 5 6 7(5.19A)38T1SF-AMF‘:VEl 20 mmO 36 mmA 50 mmo 65 mm— 112 miii0 1 2 3 4 5Torque (Nm)224——C?E—(5.20A)35T1SF-AMF0 1 2 3 4 5Torque (Nm)(5.25A)33L1SF-AM1. 1 2 3 4 5Torque (Nm)(5.27A)3OL1SF-AMC?C?——C?______..r17 mmO 32 mmA 46 mmo 68 mm— 92 mm0 1 2 3 4 5Torque (Nm) (Nm)I:’(5.31A)33T3SF-AM225iirj rM——?E0 1 2 3 4 5Torque (Nm)(5.3 1E)35T3SF-AM1. 10 mm0 new 15 mmH3Omin1 2 3 5(6.1A)35T3SF-AM415 mm0 27 mm‘ 49 mmo 70 mm- 100 mmX 120 mm0 1 2 3Torque (Nm)226.—0 1(6.1S)35T3SF-AM2—-•&&.j1.:A3• 49 mm• 70 mmA 100 mm• 115 mm4 5Torque (Nm)(6.1E)35T3SF-AM1.21;‘— 00I-1 2 3Torque (Nm)I] 35 mmO 45 mm56 mm4—D2 3Torque (Nm)00 27 mmo 38 mm50 mmo 60 mm— 75 mmX 90 mm1 4227‘I,1,210,8H 0,60,4E 0,2—001 30 mmo 40 mmA 50 mmo 60 mm- 75 mmX 90 mmEl 20 mmO 30 mmA40 mmo 60 mm— 75 mmX 90 mmD 20 mmo 30 mmA 40 mmo mm- 60 mmX 75 mm+ 90 mm(6.2F)33L1SF-BjII1.20.0.6Av’— n.’.E 0.2—01,20,80 12 3 4Torque (Nm)(6.7E)33L1SF-A1434Torque (Nm)(6.7F)33L1SF-C1 2Torque (Nm)41.21E— 0xc01. 30 mmo 40 mmA 50 mmo 60 mm— 75 mmX 90 mm1 2 3Torque (Nm)4a 20 mm0 30 mmA 40 mmo 50 mm1.2 -—:__________-__-__1rj—cii-0-J-!.Q)A0 A__2 3 4 5 6Torque (Nm)(6. 16A)27T3SF-AMI,.LL.—5--— I —W ‘• -I- LAP.’4f%_ I7a 20 mmO 30 mmA 40 mmo 50 mm- 60 mmX 75 mm+ 90 mm—_‘-I-0 1 2 3 4Torque (Nm)(6.21E)25L5SF-A2291. c %)Co_2 3 4Torque (Nm)0 15 mmO 30 mm45 mmo 60 mm- 75 mmX 90 mm0 15 mmO 30 mm45 mmo 60 mm- 75 mmX90 miii5(6.21F)25L1SF-Af—g1I i———E——,,—X2 3 4 51.2 -1 -0.8 -0.6 -0.4 -0.2 -0 - (Nm)(6.21G)25L3SF-A_______4!_r-1LIx-x )1 2D 15 miii0 30 mmA 45 mmo 60 mm— 75 mmX 90 mm3 4Torque (Nm)230(6.21H)25JMSF-A1. 3 4 5Torque (Nm)El 15 mm0 30 mmA 45 mmo 60 mm- 75 mm1.21L i5 mm0 30 mmA 45 mmo mm New- 60 mmX 75 mm+ 90 mm_1 2(6.23A)25L5SF-A0 1 2 3Torque (Nm)——E1. J___0i:i i mm0 30 mmA 45 mmo 60 mm- 90 mm1 2 3Torque (Nm) —ci-jO0 3 4Torque (Nm)(6.24C)25L3SF-C15 mm0 30 mmA 45 mmo 60 mm- 75 mmX 90 mm15 mm0 30 mmA 45 mmo 60 mm— 75 mmX 90 mmxj’.-ri’-’1 2 3 4Torque (Nm)0 1 2 3 4 5Torque (Nm)2321. (Nm)• 35 mm• 48 mmA 65 mm• 80 mm• 95 mm- 110 mm0 1 2 3 4 5 6 7 8 9 10(7.8A)2513SF-AFTorque (Nm)1 2 3 4 5Torque (Nm)2331. mmO cast 30 mm• pump 30 mmA pump 45 mmshot 45 mill• shot 60 mmo i 2 3 4 5 6 7 8Torque (Nm)(7.19APS)3OL3CF-AFI’D Cast 15 mill0 Cast 30 mmA Pump 45 mill0 Pump 75 mmPump 80 mm• Shot 90 mm0 1 2 3 4 5Torque (Nm)6 7 8(7.20A)3OL1SF-AF1. 20 mill0 Cast 30 mmA Cast 45 mmIM0 1 2 3Torque (Nm)4 5 .—O——-—-—-0 1Torque (Nm)(7.26APS)3OT1SF-AM(7.29A)3OT1SF-AM0 1 2 3 4 5D Cast 15 mmo Cast 30 mm• Pump 30 mmo Pump 45 mm• Shot 45• Shot 60 mill0 1 2 3 4 5Torque (Nm).fI_Cast 15 mmo Cast 30 mmA Cast 45 mmo Cast 60 mm- Cast 75 mmX Cast 90 mm2 3Torque (Nm)2351. (Nm)(8.3A)3OT1SF-DN1. 2 3Torque (Nm)(8.3P)3OT1SF-DNCast 30 mm• Pump 35 mmA Pump 60 mmo Pump* 80 mmPump* 95 mmPump** 105mm• Shot 30 mm• Shot 45 mmA Shot 60 mm• Shot 75 mm- Shot 90 mm0 1 2 31’L_______I”,_______________Ii’,%—II’,_______‘j‘,W%.‘-,:..iL.%.#!‘Cast 15 mmo Cast 30 mmA Cast 45 mmo Cast 60 mm- Cast 75 mmX Cast 90 mm1.2ii0. 1 2 3Torque (Nm)2361. (Nm)(8-4APS)3OT1SF-DNF(8.4A)3OT1SF-DNFD CastO CastCasto Cast- CastX Cast15 mm30 mm45 mm60 mm75 mm90 mm0 1 2’I__AA_J—2’iAtA‘IA—A— —4--Cast 30 mmPump 30 mmA Shot 60 mm0 Pump** 90 mm0 1 2 3 4 5 6Torque (Nm)(8.5A)3OT1SF-DD Casto CastCasto Cast- CastX Cast15 mm30 mm45 mm60 mm75 mm90 mm0 1 2 3Torque (Nm)2371. 30 mm• Pump 40 mm—0 Pump** 135 mmA Shot 30 mm0 1 2 3 4Torque (Nm)5(8.9A)30T 1SF-DF0 CastO CastA Casto Cast- CastX Cast15 mm30 mm45 mm60 mm75 mm90 mm0 1 2 3Torque (Nm)——•r.0 1 2Cast 60 mmPump 55 mm• Shot 70 mm• Shot 90 mmA Block 145 mm0 Block 150 mm3 4 5 6 7 8Torque (Nm)2381.’Cast 15 mmO Cast 28 mmCast 45 mmo Cast 65 mm— Cast 90 mm0 1 2 3Torque (Nm)—E— PSI• 1400 PSI1600 PSI0 1850 PSI- 2100 PSI0 1 2 3 4Torque (Nm)(8.16A)25T1SF-CF1. 1 2 3 4 5Torque (Nm)2391. 1Cast 30 mmO Cast 45 mmA Cast 60 mmo Cast 75 mill— Cast 90 mm2 3Torque (Nm)0 1Cast 30 mmo Cast 45 mmA Cast 60 mmo Cast 75 mm- Cast 90 mm2 3Torque (Nm)(8.16E)25T1SF-CFD CastO CastA Casto Cast- CastX Cast15 mm30 mm45 mm60 mm75 mm90 mill0 1 2 3Torque (Nm)2401. (N)(8.11APS)3OT1SF-D1. r4d.‘i._AICast 45 mmG Cast 65 millPump 43 mm• Pump 58 mmA Shot 36 mm• Shot 50 mm+ Shot 61 mm0 1 2 3Torque (Nm)A2250 Psi• B1300 PsiA C 300 PsiO B*2250 Psi0 1 2 3 4 5Torque (Nm)(8.18T)41L1SF-AWTruckO TruckA Trucko Truck— TruckX Truck0 mm15 mm30 mm45 mm60 mm75 mm0 1 2 3Torque (Nm)2411.210.80.6p0. (Nm)(8.18TPS)41LT1SF-AW(8.18P)41L1SF-AW1. 02.—0.,0Pump• PumpA Pumpo PumpPumpPump15 mm30 mm45 mm60 mm75 mm90 mmi i IPump 60 mmTruck 60 mmShot 65 mm0 1 2 3 4 5Torque (Nm)(8.19A)25T1SF-CCast 15o Cast 30A Cast 45o Cast 60- Cast 75X Cast 90mmmmmmmmmmmm0 1 2 3Torque (Nm)242.—G—(8.21F)33T1SF-E(8.19APS)25T1SF-C1.21a? 30 mmo Cast 45 mmPump 30 mm• Pump 45 mm• Shot 30 mm• Shot 45 mm0 1 2 3Torque (Nm)(8.21E)33L1SF-ECastl5 mmO Cast 30 mmA Cast 45 mmo Cast 60 mm- Cast 75 mmX Cast 90 mm1. 1 2 3Torque (Nm)a?ii A,D Cast 15 mmO Cast 30 mmA Cast 45 mmo Cast 60 mm— Cast 75 mmX Cast 90 mm0 1 2 3Torque (Nm)2431. (Nm)(8.23APS)25T1SF-CNFTorque (Nm)(8.23B)25T1SF-CNF1. 30 mmo Cast 45 mmCast 60 mmo Cast 75 mm- Cast 90 mm0 1 2 3—..••....4.4.—..4444-.Cast 60 mmO Cast 75 mmPump 60 mm• Pump 75 mm- Shot 60 mm• Shot 75 mm1 2 3Cast 15 mmO Cast 30 mmA Cast 45 mmo Cast 60 mm- Cast 75 mmX Cast 90 mm0 1 2 3 4 5Torque (Nm)2441. CastCasto Cast- CastX Cast15 mm30 mm45 mm60 mm75 mm90 mm0 1 2 3Torque (Nm)Cast 15 mmo Cast 30 mmCast 45 mmo Cast 60 mm- Cast 75 mm0 1 2 3Torque (Nm)D Truck 0 mmO Truck 15 mmA Truck 30 mmo Truck 45 mm- Truck 60 mmX Truck 90 mm0 1 2 3 4 5Torque (Nm)245(8.24P)41L1SF-AWFTrucko TruckA Trucko Truck— TruckX Truck+ Truck30 mm45 mm60 mm75 mm90 mm105 mm120 mmPump 15 mm• Pump 30 mmA Pump 45 mmo Pump 60 mm --F-Jø—-.c i0 1 2 3 4 5Torque (Nm)(8.24TPS)41L1SF-AWF1. Truck 30 mmTruck 45 mmPump 30 mm• Pump 45 mm• Shot 35 mmShot 45 mm0 1 2 3 4 5Torque (Nm)(8.25T)? ?L1SF-E0 1 2 3Torque (Nm)2461. 45 mm• Pump 60 mmA Pump 75 mmo Pump 90 mmPump 105 mm0 1 2 3Torque (Nm)(8.25TPS)??L1SF-ETruck 90 mmO Truck 105 mmPump 90 mm• Pump 105 mmShot 90 mm• Shot 105 mm0 1 2 3Torque (Nm) Cast 15 mmO Cast 30 mmA Cast 45 mm t_____1•_2 3Torque (Nm)4 52471.21C?C? (Nm)1.21C?C? Seriesio Cast 30 mmCast 45 mmo Cast 60 mm— cast 75 mmX Cast 90 mm0 1 2 3(8.3OBPS)54L1FA-Wcast 75 mmo Cast 90 mmPump 75 mm• Pump 90 mm• Shot 75 mmShot 90 mm0 1 2 3Torque (Nm)248Appendix H: Hardened shotcrete test resultsThis appendix presents the results of several tests carried out on hardened shotcrete. Itcontains the results of absorption tests, scaling tests, and the results of the determination ofthe 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 Diy Saturated Masse Boiled Bulk Apparent Permeablemasse masse in water absorption density density voids(g) (g) (g) (%) (%)(7.19S)3OL3SF-AF-a 1102.0 1154.8 673.1 4.79 2.40 2.57 10.69(7.19S)3OL3SF-AF-b 931.8 972.4 573.2 4.36 2.44 2.60 10.17(7.27S)3OT1SF-AM-a 937.3 971.2 506.1 3.62 2.36 2.48 8.25(7.27S)3OT1SF-AM-b 993.7 1032.5 593.0 3.90 2.09 2.19 7.86(7.29S)30T1SF-AM-a 988.0 1039.4 596.9 5.20 2.35 2.53 11.62(7.29S)3OT1SF-AM-b 1035.8 1077.7 615.2 4.05 2.33 2.46 9.06(8.45)3OT1SF-DNF-a 1103.4 1147.9 669.9 4.03 2.40 2.55 9.31(8.4S)3OT1SF-DNF-b 952.0 1001.4 585.6 5.19 2.41 2.60 11.88(8.5S)3OT1SF-D-a 884.1 917.7 538.2 3.80 2.42 2.56 8.85(8.5S)3OT1SF-D-b 801.6 839.4 492.1 4.72 2.42 2.59 10.88(8.9S)3OT1SF-D-a 1061.0 1099.4 638.3 3.62 2.38 2.51 8.33(8.9S)3OT1SF-D-b 1160.9 1202.5 708.6 3.58 2.43 2.57 8.42(8.11S)3OT1SF-D-a 1394.5 1445.7 839.2 3.67 2.38 2.51 8.44(8.11S)3OT1SF-D-b 828.4 858.9 499.4 3.68 2.39 2.52 8.48(8.18S)41L1SF-AW-a 856.6 903.8 530.3 5.51 2.42 2.63 12.64(8.18S)41L1SF-AW-b 1125.1 1179.8 687.8 4.86 2.40 2.57 11.12(8.19S)41L1SF-AW-a 1679.9 1712.6 993.0 1.95 2.38 2.45 4.54(8.19S)41L1SF-AW-b 1673.8 1715.9 993.1 2.52 2.37 2.46 5.82(8.23S)25T1SF-CNF-a 1127.4 1167.6 679.3 3.57 2.39 2.52 8.23(8.23S)25T1SF-CNF 1252.0 1291.2 754.1 3.13 2.40 2.51 7.30(8.24S)41L1SF-AWF-a 991.1 1058.3 611.4 6.78 2.37 2.61 15.04(8.24S)41L1SF-AWF-b 1026.7 1088.6 628.9 6.03 2.37 2.58 13.47(8.25S)??L1SFEa* 922.4 979.6 564.8 6.20 2.36 2.58 13.79(8.25S)??L1SFEb* 977.8 1040.8 604.2 6.44 2.38 2.62 14.43(8.305)54L1FA-W-a 951.4 1013.7 571.6 6.55 2.29 2.51 14.09(8.30S)54L1FA-W-b 905.0 965.7 544.3 6.71 2.29 2.51 14.40249Scaling test results (ASTM C-672)The scaling tests were carried out according to ASTM C-672: 50 cycles of freezing andthawing 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 ofscaled off particles was recorded. Only the results every 10 cycles are presented except formix (8.30S)54L1SF-W where the test was stopped at 15 cycles.Sample Loss of Loss of Loss of Loss of Loss of Visualweight at weight at weight at weight at weight at rating at12 cycles 22 cycles 31 cycles 41 cycles 50 cycles 50 cycles(kg/rn2) (kg/rn2) (kg/rn2) (kg/rn2) (kg/rn2)(5.20S)35T1SF-AM-a 0.19 0.49 0.82 1.78 3.59 3.5(5.20S)35T1SF-AM-b 0.10 0.43 0.72 1.60 3.33 2.5(5.25S)33L1SF-AM-a 0.44 1.35 1.93 2.49 2.74 3(5.25S)33L1SF-AM.-b 0.66 1.49 1.95 2.45 2.70 3(5.27S)3OL1SF-AM-a 0.02 0.06 0.08 0.17 0.22 0.5(5.27S)3OL1SF-AM-b 0.04 0.15 0.24 0.42 0.54 1(6.1S)35T3SF-AM-a 0.02 0.08 0.21 0.53 0.76 2(6.1S)35T3SF-AM-b 0.26 0.72 1.07 1.54 1.82 2(8.18S)41L1SF-AW-a 0.16 0.78 1.48 2.31 2.88 3(8.18S)41L1SF-AW-b 1.23 2.12 2.76 3.64 4.16 4(8.23S)25T1SF-CNF-a 0.01 0.01 0.01 0.02 0.02 0(8.23S)25T1SF-CNF-b 0.01 0.01 0.01 0.02 0.02 0(8.24S)41L1SF-AWF-a 2.79 3.87 4.88 5.81 6.34 4(8.24S)41L1SF-AWF-b 1.18 2.01 3.01 40.1 5.03 3(8.25S)??L1SF-E-a 2.18 3.42 4.88 7.25 9.54 5(8.25S)flL1SF-E-b 0.97 2.38 4.06 5.58 7.96 4.5(8.30S)54L1FA-W-a 32.96 - - - - 5(8.30S)54L1FA-W-b 31.20 - - - - 5250Air 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 secondcalculation 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 airvoids. This new calculation usually reduces the spacing factor for air-entrained concrete butdoes not affect significantly the spacing factor for non-air-entrained concrete.Sample St N Sv Sp Ngb Svgb A a Lban A* a* L*(%) (mm-i) (pm) (%) (mm-’) (pm)(5.20S)35T1SF-AM-a 1600 123 52 496 18 32 3.3 12.6 492 1.3 28.0 336(5.20S)35T15F-AM-b 1600 173 82 403 7 16 5.1 11.3 408 4.2 13.4 378(5.25S)33L15F-AM-a 1500 175 78 404 5 12 5.2 12.0 393 4.4 13.7 370(5.25S)33L15F-AM-b 1500 201 72 442 1 2 4.8 14.9 342 4.7 15.2 338(5.27S)3OL1SF-AM-a 1600 141 62 500 8 20 3.9 12.1 475 2.7 16.9 406(5.275)3OL1SF-AM-b 1600 128 49 481 1 2 3.1 13.9 451 2.9 14.4 445(6.1S)35T3SF-AM-a 1600 169 63 449 2 6 3.9 14.3 381 3.6 15.6 365(6.1S)35T3SF-AM-b 1600 105 38 536 0 0 2.4 14.7 501 2.4 14.7 501(8.18S)41L1SF-AW-a 1600 130 75 531 0 0 4.7 9.2 587 4.7 9.2 587(8.185)41L1SF-AW-b 1600 128 77 588 0 0 4.8 8.9 634 4.8 8.9 634(8.23S)25T1SF-CNF-a 1600 192 57 530 4 11 3.6 18.0 342 2.9 21.8 310(8.23S)25T1SF-CNF-b 1700 222 57 454 6 15 3.4 20.8 276 2.5 27.4 239(8.24S)41L1SF-AWF-a 1600 105 46 407 3 9 2.9 12.2 493 2.3 14.7 450(8.24S)41L1SF-AWF-b 1600 100 76 403 4 24 4.8 7.0 678 3.3 9.8 574(8.25S)??L1SF-E-a 1600 132 139 488 17 93 8.7 5.1 693 3.1 13.3 488(8.25S)??L1SF-E-b 1600 95 70 490 8 19 4.4 7.2 746 3.2 9.1 685(8.305)54L1FA-W-a 1600 120 85 466 5 11 5.3 7.5 624 4.7 8.3 621(8.30S)54L1FA-W-b 1600 120 71 496 2 4 4.4 9.0 599 4.2 9.4 590S t: total number of stops (reading points)N: number of voids interceptedSv: number of stops on voidSp: number of stops on pasteNgb: number of large voids (>300jim) interceptedSvgb: number of stops on large voidsA: air content (%)a: specific surface (mm1)Lbarre: spacing factor (pm)A*: air content without large voids (%)a*: specific surface (mm1)without large voidsL*: spacing factor (jim) without large voids


Citation Scheme:


Citations by CSL (citeproc-js)

Usage Statistics



Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            async >
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:


Related Items