UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Durability of spray applied glass fibre reinforced polymers externally applied to concrete subjected… Dolan, Kyle 2006

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

Item Metadata

Download

Media
831-ubc_2006-0176.pdf [ 12.41MB ]
Metadata
JSON: 831-1.0063276.json
JSON-LD: 831-1.0063276-ld.json
RDF/XML (Pretty): 831-1.0063276-rdf.xml
RDF/JSON: 831-1.0063276-rdf.json
Turtle: 831-1.0063276-turtle.txt
N-Triples: 831-1.0063276-rdf-ntriples.txt
Original Record: 831-1.0063276-source.json
Full Text
831-1.0063276-fulltext.txt
Citation
831-1.0063276.ris

Full Text

DURABILITY of SPRAY APPLIED GLASS FIBRE REINFORCED POLYMERS E X T E R N A L L Y APPLIED to CONCRETE SUBJECTED to a SIMULATED MARINE ENVIRONMENT by K Y L E D O L A N B.A.Sc , The University of British Columbia, 2001 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE F A C U L T Y OF GRADUATE STUDIES (Civil Engineering) THE UNrVERSITY OF BRITISH C O L U M B I A April 2006 © Kyle Dolan, 2006 ABSTRACT Across Canada and around the world the need for rehabilitation of aging infrastructure is becoming a growing problem. Two major causes of this deterioration are corrosion of the reinforcing steel and increased service loads. Traditionally steel jackets and reinforced shotcrete have been utilized as repair materials, but these materials have many downfalls, such as the corrosion of steel and high unit weights. In recent years the use of fibre reinforced polymers for rehabilitation and strengthening of structures has become common practice. More recently, a new technique of applying these materials has been developed at UBC. The technique utilizes compressed air to pneumatically apply resin and short fibres to the surface of concrete resulting in an isotropic composite. These initial studies proved the material to perform as well as, or better than unidirectional fibre reinforced wraps and jackets. The durability of the material is unproven. The research described within this thesis evaluated the durability of sprayed glass fibre reinforced polymers (SGFRP) applied to concrete substrates subjected to a marine environment. The S G F R P material was applied at various thicknesses and fibre contents to small concrete cylinder and beam specimens. The intent of the study was to evaluate these materials as a structural coating and a protective coating. The cylinder specimens were coated, exposed to an accelerated marine environment for 175 days, and evaluated against control specimens to determine the effects of preloading and the marine exposure period. The application of coating was found to greatly increase strain capacity and the fracture toughness of the concrete when loaded in compression. The beam specimens were coated on the underside of each beam, exposed to an accelerated marine environment for a maximum of 175 days, and evaluated against control specimens to investigate the effects of the exposure period, and various coating thicknesses. 11 The study illustrated that the efficiency of the S G F R P application decreases as the coating thickness increases. The ultimate load carrying capacities of the beam specimens was found to decrease after the 175 day exposure period. The findings of the study suggest that Sprayed FRP material would perform well when used for retrofit of concrete structures. In addition to performing well structurally, these materials are lightweight and relatively easy to apply. However, further research should be carried out to evaluate the durability of Sprayed FRP materials prior to commercial use. 111 TABLE OF CONTENTS Abstract ii Table of Contents iv List of Tables ". vii List of Figures ix List of Symbols xii Acknowledgements xiii Chapter 1 Introduction 1 1.1 Background 1 1.2 Objective 4 Chapter 2 Literature Review 2.1 FRP Composites 5 2.2 Glass Fibre Vinyl Ester/Polyester Composites 9 2.2.1 Polyester Resin 10 2.2.3 Vinyl Ester Resin 11 2.2.4 E-Glass Fibres 13 2.3 Theoretical Bonding Mechanisms 14 2.3.1 Wetting and Adsorption 14 2.3.2 Interdiffusion 15 2.3.3 Chemical Reactions 16 2.3.4 Electrostatic Attraction 16 2.3.5 Mechanical Interlock 17 2.4 Spray Applied FRP Coating Application System 17 2.5 Durability of FRP Composites in Marine Environments 19 2.6 FRP - Concrete Bond 23 2.7 FRP - Concrete Bond Durability 26 2.8 Durability of Steel Reinforced Concrete 29 2.8.1 Mechanisms of Steel Corrosion in Concrete 30 2.8.2 Chloride Attack 32 2.8.3 Factors Influencing Chloride Diffusion 33 2.8.4 Service Life Estimates of Reinforced Concrete Structures 33 2.9 Use of FRP to Restrain Steel Corrosion Activity 34 2.10 FRP Confinement 36 2.10.1 Durability of FRP Confinement 39 2.11 Development of Spray Applied GFRP at UBC 40 2.12 Literature Review Summary 44 Chapter 3 Lab Program 3.1 Introduction 46 3.2 Test Parameters 46 iv 3.2.1 Cylinder Strengthening Test Program 46 3.2.2 Beam Strengthening Test Program 47 3.3 Materials 47 3.3.1 Concrete 47 3.3.2 Resin 48 3.3.3 Fibres 49 3.3.4 Catalyst 49 3.4 Concrete Specimens 49 3.4.1 Casting Concrete Specimens 49 3.4.2 Curing Concrete Specimens : 50 3.4.3 Surface Preparation 50 3.5 Coating Application 50 3.6 Exposure Program 53 3.7 Testing Program 55 3.7.1 Test Specimens 55 3.7.2 Cylinder Strengthening Testing Program 56 3.7.3 Beam Strengthening Testing Program 57 3.7.4 Visual Evaluation 59 3.7.5 Fibre Content Testing 59 3.7.6 Chloride Ion Penetration Testing 60 3.8 Analysis of Test Data 60 3.8.1 Cylinder Strengthening 60 3.8.1 Beam Strengthening 61 Chapter 4 Experimental Results 4.1 Visual Evaluation of G F R P Coating Surface 62 4.1.1 Visual Evaluation of G F R P Coating Surface Prior to Exposure 62 4.1.2 Visual Evaluation of G F R P Coating Surface After Exposure 62 4.1.3 Visual Evaluation of The Concrete FRP Substrate After Failure 65 4.1.4 Visual Examination of Specimen Series 1A and 2A after Preloading 67 4.2 Test Specimens Concrete Fresh Properties 67 4.3 Cylinder Strengthening Program Test Results 67 4.3.1 Concrete Hardened Properties 67 4.3.2 Cylinder Series 1A and 2A 68 4.3.3 Cylinder Series 1B and 2B 71 4.3.4 Cylinder Series 1C and 2C 73 4.3.5 Summary of Cylinder Strengthening Test Results 75 4.4 Beam Strengthening Program Test Results 75 4.4.1 Beam Series 1 75 4.4.2 Beam Series 2 77 4.4.3 Beam Series 3 80 4.4.4 Beam Strengthening Program Test Results Summary 82 4.5 Fibre Content Test Results 82 4.6 Chloride Ion Penetration Test Results 83 Chapter 5 Discussion of Results 5.1 General Comments 85 5.2 Discussion of Cylinder Strengthening Test Results 86 5.2.1 Performance of Control Series 87 5.2.2 Performance of the S G F R P / Concrete Composite Cylinders 87 5.2.3 Effects of Coating Thickness 90 v 5.2.4 Effects of the Exposure Period 92 5.2.5 Effects of Preloading Prior to Exposure 93 5.3 Discussion of Beam Strengthening Test Results 94 5.3.1 Failure Modes Overview 95 5.3.2 Effects of Coating Thickness 98 5.3.3 Effects of the Exposure Period 102 5.4 Fibre Content Test Results Discussion 104 5.5 Chloride Ion Penetration Test Results Discussion 105 5.6 Comparison of Test Results with Published Data 106 5.6.1 Cylinder Strengthening Test Results 106 5.6.2 Flexural Load Test Results 108 5.7 Comparison of Results - Flexural and Compressive Load Testing 109 Chapter 6 Conclusions and Recommendations 6.1 General Conclusions 110 6.2 S G F R P Materials and Application Techniques Conclusions 110 6.3 Cylinder Strengthening Program Conclusions 111 6.4 Beam Strengthening Program Conclusions 112 6.5 Recommendations 113 Chapter 7 References 115 Appendixes 119 Appendix A 119 Appendix B 124 vi LIST OF TALBES Table 2.1 Orientation Factors Derived for Constrained and Unconstrained Composites after Bentur and Mindess 9 7 Table 2.2 Performance of Various Composites as Reported by Malvar et a l . 2 22 Table 2.3 Summary of Select Lab Studies That Evaluated the Use of FRP to Restrain Corrosion Activity 35 Table 2.4 FRP Confinement Durability Studies Findings 40 Table 2.5 Results of Laboratory Tests on Full-Scale Bridge Girders after Banthia eta l . 6 41 Table 2.6 Comparison of the Benefits of S G F R P and Various Wrap GFRP Schemes External Confinement after Banthia and Boyd 42 Table 2.7 Summary of Findings Based on Research Completed by Johnson 2 3 43 Table 3.1 Concrete Mix Proportions 48 Table 3.2 Mechanical Properties of Reichold Resins 48 Table 3.3 Properties of Advantex Glass Fiber 49 Table 3.4 Summary of Concrete Test Specimens 55 Table 3.5 Coating Details Cylinder and Beam Specimen Series 55 Table 3.6 Cylinder Test Specimens 56 Table 4.1 Results of Visual Examination of S G F R P Concrete Interface After Failure 66 Table 4.2 Measured Fresh Properties 67 Table 4.3 Control Series Test Results 68 Table 4.4 Cylinder Series 1A and 2A Test Results 69 Table 4.5 Cylinder Series 1B and 2B Test Results 71 Table 4.6 Cylinder Series 1C and 2C Test Results 73 Table 4.7 Cylinder Strengthening Test Results Summary 75 Table 4.8 Beam Series 1 Test Results 76 Table 4.9 Beam Series 2 Test Results 78 Table 4.10 Beam Series 3 Test Results 80 Table 4.11 Beam Strengthening Program Test Results Summary 82 Table 4.12 Fibre Content Test Results 82 Table 4.13 Chloride Ion Penetration Test Results 83 Table 5.1 Flexural Test Results - Control Samples 98 Table 5.2 Beam Series 1 Test Results 101 Table 5.3 Exposure Program Test Results 103 viii LIST OF FIGURES Figure 2.1 Stress - Strain Behaviour of FRPs after Banthia8 5 Figure 2.2 Stress Profile Along a Fibre in a Matrix as a Function of Fibre Length after Bentur and Mindess 9 6 Figure 2.3 Safe Bridge Structural Upgrade after Banthia et a l . 7 9 Figure 2.4 Linear Polyester after Peters 1 3 10 Figure 2.5 Unsaturated Linear Polyester after Peters 1 3 10 Figure 2.6 Vinyl Ester Resin Structure after Peter 1 3 12 Figure 2.7 Balance of Horizontal Forces at the Solid Liquid Interface after Hull and Clyne 2 15 Figure 2.8 Molecular Entanglement after Hull and Clyne 1 2 16 Figure 2.9 Chemical Reactions after Hull and Clyne 1 2 16 Figure 2.10 Electrostatic Attraction after Hull and Clyne 1 2 17 Figure 2.11 Mechanical Interlock after Hull and Clyne 1 2 17 Figure 2.12 Chopper Gun Application System after Rubin 1 7 18 Figure 2.13 Appearance of G F R P Surface After Immersion in Water at 60 C for 210 Days after Nishizaki and Meiarashi 1 9 21 Figure 2.14 Bond Test Specimens after De Lorenzis et a l . 2 7 25 Figure 2.15 Effects of Vapour Pressure Build Up after Emmons 3 0 28 Figure 2.16 The Corrosion Process after Hansson 3 5 30 Figure 2.17 Typical Stress Strain Response of FRP Confined Concrete after Harries and Kharel 4 2 38 Figure 3.1 Pneumatic Application of Polyester Resin / Glass Fibre Composite 51 Figure 3.2 Rolling Out the G F R P Composite to Fully Saturate the Glass Fibres and Remove Air Voids 52 Figure 3.3 The Finished Product, a 5 -6 mm Uniform Isotropic Coating 53 Figure 3.4 Schematic Diagram of Compressive Loading Test Set Up 57 Figure 3.5 Schematic of Flexural Loading Test Set Up 58 ix Figure 4.1 Flexural Beam Testing Program Sample Series 1: Typical Surface Condition of S G F R P Composite Prior to Exposure 63 Figure 4.2 Flexural Beam Testing Program Sample Series 1: Typical Surface Condition of S G F R P Composite after 180 Exposure Cycles 64 Figure 4.3 Flexural Beam Testing Program Sample Series 1: Typical Surface Condition of S G F R P Composite after 525 Exposure Cycles 64 Figure 4.4 Typical S G F R P Concrete Interface After Failure 65 Figure 4.5 Typical Stress Strain Response Control Series 68 Figure 4.6 Typical Stress Strain Response Samples 1A and 2A, No Cracking Evident in Concrete Prior to Exposure 70 Figure 4.7 Typical Stress Strain Response Samples 1A and 2A, Cracking Evident in Concrete Prior to Exposure 70 Figure 4.8 Typical Stress Strain Response Series 1B 72 Figure 4.9 Typical Stress Strain Response Series 2B 72 Figure 4.10 Typical Stress Strain Response Series 1C 74 Figure 4.11 Typical Stress Strain Response Series 2C 74 Figure 4.12 Typical S G F R P Strain Distribution Series 1 76 Figure 4.13 Typical Load versus Midspan Displacement Relationship Series 1 77 Figure 4.14 Typical S G F R P Strain Distribution Series 2 79 Figure 4.15 Typical Load versus Midspan Displacement Relationship Series 2 79 Figure 4.16 Typical Load versus Midspan Displacement Relationship Series 3 81 Figure 4.17 Typical Load versus Midspan Displacement Relationship Series 3 81 Figure 4.18 Chloride Ion Penetration Test Set Up Schematic 84 Figure 5.1 Compressive Loading Stress Strain Responses 88 Figure 5.2 Proposed Stress Distribution after Toutanji4 6 89 Figure 5.3 S G F R P Stress Strain Response after Banthia and Boyd 7 93 Figure 5.4 Typical Load versus Midspan Displacement Plot Series 1 96 x Figure 5.5 Typical Strain Distribution Plot - Series 3 97 Figure 5.6 Effects of Coating Thickness on the Ultimate Load at Failure 99 Figure 5.7 Comparison of Typical Load versus Midspan Deflection Plots 100 Figure 5.8 Load versus Midspan Deflection Series 1 102 Figure 5.9 Load Carrying Capacity versus Exposure Period 104 xi LIST OF SYMBOLS ffrpu rupture stress of FRP E f r p frp modulus of elasticity e f r p u rupture strain of FRP ac tensile strength of the composite a m tensile strength of the matrix V m volume fraction of the matrix at tensile strength of a fibre V f volume fraction of the fibres Y g g l o b a l e f f i c i ency fac to r W a work of adhesion y surface energy T g glass transition temperature 8i lateral strain of a confined specimen E| lateral elastic modulus f°°c compressive strength Ruit ultimate load at failure fi lateral stress E| lateral elastic modulus EI lateral strain of a confined specimen ACKNOWLEDGEMENTS This thesis could not have been completed with out the support and technical assistance of my supervisor Dr. Banthia of UBC and Mr. P.T. Seabrook of Levelton Engineering. The technical support and assistance of the lab staff at UBC and Levelton Engineering are also . greatly appreciated. Financial funding was provided by ISIS Canada, NSERC, and Levelton Engineering. xiii CHAPTER 1 - INTRODUCTION The research described within this thesis was carried out to evaluate the durability of sprayed glass fibre reinforced polymers (SGFRP) applied to concrete substrates subjected to a marine environment. The spray applied glass fibre composite material was applied at various thicknesses and fibre contents to concrete cylinders and beams. The basic intent of the study was to evaluate the performance of the material both as a structural strengthening coating and a protective coating. Cylinder specimens were subjected to 525 exposure cycles consisting of 4 hr submersion in saline water followed by a 4 hr drying at room temperature. The specimens were subjected to compressive testing at the end of exposure period to evaluate the effects of the exposure. The intent of the cylinder strengthening program was to evaluate the durability of the SGFRP confinement with respect to a marine environment. The beam specimens were subjected to the same exposure sequence as the cylinders specimens. The samples were tested at various ages to evaluate the effects of the length of the exposure period. The beams were tested in three point loading to induce failure at the SGFRP concrete substrate bond. The intent of the program was to evaluate the performance of the SGFRP -concrete substrate bond. An in depth literature review was also completed that reviewed the issues surrounding the lab study. The findings of the research program could also be applied to exposure conditions involving the use of de-icing salts. 1.1 Background The need for rehabilitation and strengthening of aging infrastructure is becoming a growing problem across Canada and worldwide. Currently in Canada, an estimated 30,000 bridges and 5000 1 parking garages are need of rehabilitation or replacement1. Two major causes of the deterioration are increased service loads, inadequate code provisions of the past and corrosion due to the ingress of chlorides. Accelerated corrosion rates may be due to harsh exposure conditions, low cover, poor quality concrete, poor placement techniques, or a combination of the above. The decision of whether to repair or replace these structures is based upon life cycle costs. Traditional materials used for such applications are steel jackets and reinforced shotcrete, but these materials have many problems associated with their use. Corrosion of steel and the high unit weights being two of the major downfalls of these materials. In recent years the use of fibre reinforced polymers for rehabilitation and strengthening of structures has become common practice. The majority of the work done has utilized wraps and jackets consisting of continuos unidirectional glass and carbon fibres2. A big advantage of composite materials is the large number of epoxies, resins, and fibres available making it possible to design different composites to fulfill the structural and durability requirements of an application. Composite materials offer many other advantages including high strength/weight ratio, excellent corrosion resistance, high stiffness/weight ratio, and low thermal conductivity1,3. FRP materials have also been shown to reduce the ingress of chlorides and reduce corrosion rates when applied to reinforced concrete4 , 5. The durability of reinforced concrete structures is an enormous problem today. The use of FRP wraps has been introduced as a repair alternative to structures damaged by corrosion of reinforcing steel. In a lab environment, FRP wraps have been proven to provide two benefits, increase in strength and reduction of corrosion rates. It has been shown that corrosion rates can be greatly reduced by the application of FRP wraps to concrete specimens in a lab environment. The application of the wrap reduces the ingress of chlorides and slows the electrochemical corrosion5. 2 Full scale structures do not behave the same as lab specimens. The concept of sealing a full scale structure is not probable, nor is the concept of depleting the corrosion process of moisture and oxygen, resulting in a stoppage of corrosion. However, the coating of such structures prior to chloride levels reaching concentrations required for corrosion appears feasible. If the structures can be coated, before chloride concentration becomes too high, the service life of the structure may be extended by many years. Such a coating has the ability to greatly reduce the ingress of chlorides, only if the FRP/concrete is durable, if the interface fails the chlorides will simply be able to migrate underneath the coating. A new technique of applying glass fibre reinforced polymers to concrete has been developed at the University of British Columbia. The method was first developed and studied by Banthia et a l . 6 , 7 and further studied by Boyd3. The technique utilizes compressed air to pneumatically apply the resin and short fibres to the surface resulting in an isotropic composite consisting of short fibres randomly orientated in a 2-d plane. These initial studies have shown that the spray applied material performs as well, or better than unidirectional wraps and jackets when applied externally to concrete 1 , 3 | 6 | a n d 7 . However, very little work has been carried out to assess the durability of these systems. Given the excellent performance of the spray applied FRP composites as a structural coating in recent studies conducted at UBC and the low cost associated with the material, it seemed logical that the material be evaluated further. Therefore, this research program was carried out to assess the performance of this retrofit system in a simulated marine environment both as a structural and/or protective coating. The findings of the research program could also be applied to exposure conditions that subject SGFRP concrete composites to de-icing salts. 3 1.2 Objective The objective of the study was to evaluate the effectiveness of SGFRP composites with respect to long term durability of the SGFRP concrete system subject to a marine environment. The material was evaluated as a protective and a structural coating. The program was broken up into two separate programs as follows; • Strengthening of concrete cylinders with variable thickness SGFRP coatings and evaluation of the effects of an accelerated marine exposure. The specimens were tested to failure in compression. • Strengthening of concrete beam specimens with the application of variable thickness coatings on the tension face and evaluation of the effects of an accelerated marine exposure. The specimens were tested to failure in flexure. The objectives of the Compressive Testing Program were as follows: • To characterize the stress strain response of concrete cylinders confined with SGFRP coatings, and to evaluate the effects of coating thickness, preloading, and accelerated marine exposure on the stress vs. strain response. The objectives of the Flexural Testing Program were as follows: • To characterize the stress response of concrete beams with SGFRP coatings on the tension face of the member. Furthermore, to evaluate the effects of coating thickness and accelerated marine exposure period by the variation of the stress strain responses. The overall objective of the compressive and flexural testing programs was to evaluate the feasibility of using glass fibre polyester spray applied composites to externally reinforce and protect concrete structures subjected to marine environments. 4 CHAPTER 2 - LITERATURE REVIEW 2.1 FRP Composites FRP composites consist of high strength fibres including carbon, glass, or aramid embedded in a polymeric matrix. Epoxy, vinyl ester, and polyester are typical resins used. A composite material is defined by Banthia8 as follows: A material that is the combination of two or more chemically dissimilar materials separated by an interface. The resulting product has overall properties which are superior to those of the individual constituents. The stress strain behaviour of a composite material is illustrated in Figure 2.1. Stress Fibre * rupture / Eft,, — Matrix £frpu Strain Figure 2.1: Stress - Strain Behaviour of FRPs after Banthia8. Figure 2.1 illustrates that the mechanical behaviour of the composite is determined by the mechanical behaviour of its components. In a composite material the matrix and the reinforcing phases share the load. The tensile strength of a composite can be approximated by the law of mixtures: Gc = Om Vm + JgOfVf 5 where <jc refers to the strength of the composite in tension, <j„, refers to the tensile strength of the matrix, Vm refers to the volume fraction of the matrix, or refers to the strength of the fibre in tension, Vf refers to the volume fraction of the fibres, and yg is the global efficiency factor for the fibre phase taking into account the effects of the fibre length and orientation7. The critical fibre length in a composite with discontinuous fibres, L, is defined as the minimum length of fibre required to develop a stress in the fibre from loading that is equal to the stress capacity of the fibre9. Figure 2. 2 illustrates that I must be significantly greater than L to develop a stress along a significant length of the fibre that reaches the tensile strength of the fibre. Figure 2.2: Stress Profile Along a Fibre in a Matrix as a Function of Fibre Length after Bentur and Mindess9 From the trapezoidal stress profiles provided in the above figures the following equations were derived for the fibre efficiency factors: l - l c for I > L ni = -21 for / < lc m tju 1 / 2<T/« 2 lc 6 The fibre orientation factor takes into account the difference between the orientation of the fibre and the applied load. Table 2.1 presented by Bentur and Mindess9, which presents orientation factors derived for constrained and unconstrained composites. A constrained composite orientation factors are based on the assumption that deformation only occurs in the direction of the applied load and deformation occurs in two directions in an unconstrained composite9. Table 2.1 Orientation Factors Derived for Constrained and Unconstrained Composites after Bentur and Mindess9 Fibre Orientation Orientation E1 Fficiency Factor Unconstrained Constrained Aligned, 1-D 1 1 Random, 2-D 1/3 3/8 Random, 3-D 1/6 1/5 The advantages of FRP materials over conventional external steel reinforcement as outlined by Banthia et al 7. are as follows: • excellent corrosion resistance; • light weight; • high strength; • very high strength/weight ratios; • excellent corrosion resistance; • electromagnetic neutrality; • good fatigue resistance; • low coefficient of thermal expansion; • endless number of ways that fibers and polymers can be combined to suit the specific needs of an application; • use of FRPs provides a high structural efficiency; • low density of the material resulting in little physical effort to complete applications. 7 Externally bonded FRP reinforcing methods are beginning to see wide spread usage. The recently developed Design Manual, "Strengthening Reinforced Concrete Structures with Externally -Bonded Fibre Reinforced Polymers," developed by ISIS Canada (2001) provides excellent guidelines for using externally bonded FRP composites10. The guide covers design techniques, application techniques and quality control and assurance issues. The American Concrete Institute committee 440R, "State of the Art Report on Fiber Reinforced Plastic (FRP) Reinforcement for Concrete Structures," and 440.2R, "Guide for the design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures,"11 also present guidelines and methods. However, these manuals do not include design considerations based on the long term durability of externally bonded FRP composites. FRP composites have been utilized to effectively provide external shear reinforcement, flexural reinforcement, and effective confinement on reinforced concrete. Numerous projects have been carried out both on lab specimens and on full scale structures. The seismic upgrading of the Oak Street Bridge in Vancouver, B.C. utilized GFRP wraps. Additional reinforcement was applied to the columns and beams of this structure The Safe Bridge in Victoria, B.C. was strengthened utilizing the spray applied GFRP system developed at UBC 7 . Figure 2.3 illustrates the application process. The safe bridge upgrade was completed at a cost of $32/ft2. 8 Figure 2.3: Safe Bridge Structural Upgrade after Banthia et al.7 2.2 Glass Fibre Vinyl Ester / Polyester Composites The composite system used throughout the lab program discussed in this paper was a glass fibre embedded in a polyester resin matrix. Vinyl ester resin was utilized as the coupling agent to ensure a strong bond between the FRP composite and the concrete substrate. The glass fibre polyester resin matrix was chosen because these materials are relatively inexpensive and have been shown by other researchers to perform well when applied to structurally reinforce concrete 1 ' 3 a n d 8 . Vinyl ester resin was chosen as a coupling agent because again it had been shown to perform well by others3. It should be noted that other coupling agents, such as the commercially available Atprime 2 are available that outperform vinyl ester, but safety concerns associated with this material make its use not practical in a university lab setting. 9 Both vinyl ester and polyester resins belong to the thermo set family of polymers. During condensation polymerization a chemical reaction occurs that results in cross linking of the chains of the polymers together causing the material to become rigid. The mechanical properties of resin are dependent upon the length and density of the cross links and the properties of the molecular units that make them up12. 2.2.1 Polyester Resin Polyester resins generally have good chemical resistance and mechanical properties. The low cost of these resins is an added advantage. A linear polyester chain is produced by the reaction of a difunctional acid and difunctional alcohol, (Figure 2.4). I! II H ^ O - C - R - C - O ,B4 r "OH Figure 2.4: Linear Polyester after Peters13 Unsaturated polyester is a commonly utilized in the production of composites. The term unsaturated refers to the reactive double bonds that exist along the entire polyester chain, which is the location of the cross links, that provide the rigidity and high elastic modulus of the cured resin, (Figure 2.5). O O O H O II II II I II HO ( C - R - C - 0 - R ' - 0 - C - C = C - C - 0 - R ' - 0 )nH I H Figure 2.5: Unsaturated Linear Polyester after Peters13 10 The building blocks of an unsaturated polyester resin can be easily modified to alter the mechanical and environmental properties of the resin to suite the requirements of a given application. The chemistry of unsaturated polyesters provides for an endless number of possibilities. The other main factor that dictates the properties of unsaturated polyester is the level of curing as noted previously. In order to optimize the properties the resin it is essential to ensure that complete cross-linking occurs. Improper curing will result in a resin with reduced mechanical properties and chemical resistance13. Unsaturated polyester resins are utilized in a number of applications including: boats, building panels, automotive parts, and aerospace products. These resins can also be formulated to be highly resistant to chemical exposure and utilized for applications in corrosive environments. Unsaturated polyester resin may also be formulated to be a flame retardant. 2.2.3 Vinyl Ester Resin Vinyl ester resins have exceptional durability and mechanical properties. The structure of vinyl ester is quite different from that of unsaturated polyester. Vinyl esters commonly used are principally methacrylated epoxies, which are produced by the chemical reaction between methacrylic acid and a bisphenol epoxy resin1 3, (Figure 2.6). 11 Figure 2.6: Vinyl Ester Resin Structure after Peters13 Vinyl ester has a networked epoxy backbone, which provides excellent mechanical properties, thermal stability, and improved toughness and resilience. The epoxy resin building blocks can be easily altered allowing the properties of the resin to be modified to meet the environmental and mechanical requirements of an application. The epoxy backbone exhibits excellent acid resistance, which combined with fewer ester linkages per molecular weight results in an excellent chemical resistance. The low ester content results in a higher hydrolysis resistance than the polyester resins1 3. The excellent durability properties of vinyl ester resins make them highly advantageous for applications in corrosive environments. Vinyl ester resins can also be formulated to be flame retardant materials, which can be accomplished in two ways: use of either organic or inorganic additives, or reformulation of the resin to include halogen in the chemical composition. However, it should be noted that generally additives have a negative effect on the mechanical and or durability properties of the resin1 3. 12 2.2.4 E- Glass Fibres E-glass fibres, (E stands for electrical) are the most commonly used fibres because of their low cost. They are amorphous materials based on silica (Si0 2) with additives of oxides of calcium, boron, sodium and aluminum. E-glass fibres have good mechanical, electrical and weathering properties12. The atomic structure of a fibre determines its modulus and strength. Glass fibres have isotropic properties12. The advantageous properties of glass fibre as outlined by Hull and Clyne 1 2 are as follows: • high tensile strength; • heat and fire resistance; • chemical resistance; • thermal stability To improve the glass fibre matrix bond, fibres are coated with a "sizing" coupling agent when they are manufactured. The coupling agent acts to improve the durability and mechanical strength of the bond. Unprotected glass fibre when exposed to moisture can suffer from leaching of the components of the glass fibre resulting in a weak porous surface. Therefore, deteriorating the fibre matrix bond strength12. Coatings are also available that decrease the strength of the interfacial bond resulting in a composite that illustrates increased toughness at failure. The improved toughness is due to fibre pull out at failure. However, these weaker bonds are more susceptible to attack. 13 2.3 Theoretical Bonding Mechanisms Bonding mechanisms contribute to the performance of a composite material. In the case of concrete FRP composites the bond is crucial at the fibre matrix interface and at the concrete FRP interface. Bond strength is controlled by wetting, chemical reactions, electrostatic attraction, and mechanical keying12. At the concrete FRP interface mechanical keying and chemical bonding have been attributed by many authors to be the dominant bonding mechanisms1 4"1 6. The bond strength at the fibre matrix interface is controlled by chemical bonds 1 2 , 1 3. 2.3.1 Wetting and Adsorption Wetting occurs when two materials come into contact at the atomic scale. Generally one of the materials is liquid. The process of wetting results in van der Waals forces, which provide an adhesive force. The process can be quantified by thermodynamics. The Dupre equation12 quantifies the work associated with adhesion. Wa = yn + Jh - Ysl Where: Wa = work of adhesion; y = surface energy; The subscripts s, I, v refer to solid, liquid, and vapor respectively. ,The degree of wetting between a solid and liquid is dependent upon the contact angle 6, which is derived from the equilibrium of horizontal forces at the contact surface. The balance of horizontal forces results in the derivation of the Young equation. 14 Ysv = yivCosO +ysi Therefore, if 9 = 0° complete wetting occurs and if 6 = 180° no wetting occurs, (Figure 2.7). 134 The interface region (a) Figure 2.7: Balance of Horizontal Forces at the Solid Liquid Interface after Hull and Clyne12 2.3.2 Interdiffusion Diffusion occurs at the interface between two polymer materials. Coupling agents (that are often polymers themselves), such as those applied to glass fibres, result in the diffusion of free chain ends of the polymer matrix and the coupling agent resulting in chain entanglements. These entanglements increase the strength of the fibre matrix bond. (Figure 2.8) 15 V//://////////////////A //////////////////////A Figure 2.8: Molecular Entanglement after Hull and Clyne 1 2 2.3.3 Chemical Reactions Chemical reactions may also occur at the interface between the adjacent materials adding to the strength of the bond. These bonds may be covalent, ionic, or metallic, (Figure 2.9). Figure 2.9: Chemical Reactions after Hull and Clyne 12 2.3.4 Electrostatic Attraction The attraction force of oppositely charged material adjacent to each other at the interface will result in adhesion. Some coupling agents utilized on glass fibres result in electrostatic attraction between the fibre and the matrix, (Figure 2.10). 16 /////////////////////// + + + + + + + + + + + Figure 2.10: Electrostatic Attraction after Hull and Clyne12 2.3.5 Mechanical Interlock Mechanical interlock refers to the keying together of the bonded materials due to surface roughness present on the solid materials. Mechanical interlock is the dominant bonding mechanism at the concrete FRP interface, (Figure 2.11). This bond is directly controlled by the quality of the surface preparation. Figure 2.11: Mechanical Interlock after Hull and Clyne 1 2 2.4 Spray Applied FRP Coatings Application System This technique is by no means a new method, however limited work has been done with this technology for the application of composites to concrete. The spray application machine consists of four simple components: a catalyst pump, a resin pump, a chopper gun, and a spray gun. The equipment used for the program was manufactured by Magnus Venus, (Figure 2.12). The fibre is 17 cut to length in the chopper gun and pneumatically shot into the catalyst resin stream and projected onto the surface resulting in a 2-D isotropic material. Figure 2.12: Gun Application System after Rubin17 The resin and catalyst are pumped down separate lines and mixed within the spray gun assembly. The catalyst pump is controlled by the main resin pump. The catalyst pump's stroke length can be adjusted to modify the resin/catalyst ratio. The fibre length and content can be easily altered by the operator. The operator has the ability to increase, or decrease the number of blades within the chopper gun assembly. A decrease in the number of blades results in an increase in fibre length and vice versa. The design of the machine allows the operator to have great control and flexibility as noted above with respect to fibre content, fibre length, catalyst content, and coating thickness. The operator controls the thickness by regulating the number of passes, overlap between passes, and the rate at which the gun is traversed across the surface. Therefore, allowing the operator to produce coatings with very different mechanical properties for different applications with ease. Densified lay-up Roving 18 At low fibre volumes very good saturation of the fibres occurs and a minimal amount of material is lost to rebound. However, if the fibre volume and or length is increased the degree of fibre saturation decreases. Therefore, resulting in an increase in the amount of rebound. 2.5 Durability of FRP Composites in Marine Environments FRP materials produced for construction applications have been shown to deteriorate in a marine environment by numerous researchers. The majority of FRP composites utilized in civil construction applications are produced in environments where curing temperature and application pressure are not controlled as strictly as in industrial applications. The resultant composites have a lower glass transition temperature and degree of cure or polymerization18. Such a composite would therefore, not be as durable as a FRP composite manufactured under controlled environments and the durability of these materials when subjected to civil engineering applications is an issue that must be addressed. The literature currently available all agrees that carbon fibre composites are more durable than glass fibre composites. Many studies have concluded that glass fibres may not be that durable18"23. However, recent studies carried by ISIS Canada to evaluate the condition of GFRP reinforcing bars embedded in concrete showed that in service GFRP reinforcing bars are performing very well to date 2 4" 2 6 . Microscopic and physico-chemical analysis carried out concrete core sample taken from six bridges that have been in service for five to eight years to investigate the degradation of the GFRP reinforcing bars, the concrete, and the concrete GFRP interface. The studies found no signs of deterioration of the GFRP bars. Therefore, given that glass fibres are much cheaper than carbon fibres, as part of this study a further review to understand the mechanisms that cause the deterioration of glass fibre reinforced polymers was undertaken. 19 Accelerated lab testing programs have shown that glass fibre composites break down when exposed to, freeze/thaw cycles, wet / dry cycles, or submersed in neutral water, saline water, and or alkaline water. Numerous researchers have found the deterioration rates are accelerated at high temperature18"23. The break down of GFRP composites in moist environments has been attributed by Kshirsagar et a l . 1 9 to the following factors: • damage to the polymer matrix; • damage to the fiber matrix interface by leaching of the chemical coupling agent used to coat the fibre surface especially at elevated temperatures; • damage to the glass fibres due to surface etching and leaching out of some of the constituents of the fibre. The damage to the polymer matrix may be reversed upon drying as is the case with hydrolysis, but polymer swelling caused by water adsorption is not reversible and may lead to the development of stresses in the composite resulting in debonding of fibres from the matrix. A decrease of the glass transition temperature of polymers occurs as a consequence of water plasticization21. Water plasticization occurs most efficiently when water can interact with resin through hydrogen bonding, which causes an increase in free volume2 2. The durability of a polymer is dependent upon the glass transition temperature, (Tg) of the polymer23. The physical properties of amorphous polymers such as creep, chemical reactivity, flow, and diffusion are dependent upon the relaxation of polymer segments22. The rate of relaxation is dependent upon the temperature of the polymer with respect to its glass transition temperature. Therefore, such a composite would not be as durable as a FRP composite manufactured under controlled environments. 20 Nishizaki and Meiarashi19, carried out a study to evaluate the long term effects of water on GFRP materials. The material tested was a vinyl ester glass fibre composite. Exposure conditions evaluated were immersion in water and atmosphere conditions. Both conditions were evaluated at 40°C and 60°C. Samples submersed in water at 60°C showed the greatest rate of weight decrease and reductions in bending strength. The surfaces of the GFRP materials showed evidence of fine cracks at fibre matrix interface. Fibre prominence was also visible, (Figure 2.13). Figure 2.13: Appearance of GFRP Surface After Immersion in Water at 60°C For 210 Days after Nishizaki and Meiarashi19 Examination of the GFRP surface after exposure with a SEM by the authors revealed that the cracks visible with the naked eye were localized around the glass fibres, which suggests that cracks in the matrix will form were the resin is thin or tiny voids are present. The authors attributed weight reduction to chemicals being dissolved from the surface of the glass fibres and the remaining styrene within the matrix being dissolved1 9. Interfacial cracks are also often attributed to differences in coefficients of thermal expansion between glass and the polymer. 21 Malvar et al . 2 0 carried out a durability study to evaluate the performance of various GFRP composites. The resins evaluated included: polyester, vinyl ester, phenolic, and epoxy. The same glass fibre was utilized for all of the studies. The exposure periods ranged from 28 days to 18 months. The specimens were evaluated based on the loss in flexural and tensile strengths and the change in the glass transition temperature. The exposure programs included: submersion in oxygen rich water at 38°C for 12 months, oxygen and salt water spray at 38°C for 12 months, cold freezer at -20°C for 9 months, salt fog tank at 35°C for 28 days, 12 months and 18 months, dry heat oven at 35°C for 90 days, and ultraviolet exposure unit at 70°C for 90 days. The authors concluded that the salt water exposure caused the greatest deterioration of the tensile and flexural strength of the materials. The material performance in the salt fog tank exposure has been summarized in Table 2.2. Table 2.2: Performance of Various Composites as Reported by Malvar et al. Resin Vinyl ester I Exposure Period (Salt Fog Tank) Reported Loss of Tensile Strength, % 28 days 12 18 months 6 Vinyl ester II 28 days 6 18 months 8 Polyester I 28 days minimal 18 months 19 Polyester II 28 days minimal 18 months 12 Phenolic I 28 days 24 18 months 28 Epoxy-Polyamide 28 days 26 18 months 39 The results reported by Malvar et a l . 2 0 clearly show that the performance of the vinyl ester and polyester resins is superior to that of the phenolic and epoxy-polyamide tested. 22 The deterioration of glass fibre reinforced polymers in moist environments occurs by degradation of the polymer matrix, the fibre matrix interface, and break down of the glass fibres. Glass fibres are susceptible to dissolution, which a process that occurs at the interface of the glass fibre and results in the formation of a silicon hydroxide gel by-product. The resulting gel layer is less dense than the glass fibre structure, therefore making it more permeable material resulting in an acceleration of the degradation process2 3. Generally the durability test results presented in published literature vary due to test variables such as material composite, exposure programs, and test methods. The findings do however support the need for standardized tests to evaluate the durability of these materials. Such data sets are required, so that degradation factors for these different materials can be determined and incorporated into the design process. The performance of these materials must also be further quantified so that it is possible to better optimize the use of these materials. 2. 6 FRP - Concrete Bond The bond of the FRP to concrete substrate is the critical link. The bond is crucial to ensure that the concrete substrate and FRP act as a composite. If deterioration or premature failure of the FRP concrete bond occurs the benefits of the FRP composite application will not be maximized. This is the case whether the laminate application is for structural strengthening, or to prevent, or restrain corrosion of reinforced concrete section. Numerous studies have been carried out to evaluate the performance of the FRP concrete bond 1 5 , 2 7" 3 1. The studies noted above used a series of different test types, materials, and exposure variables. Therefore, it is the author's opinion the results are highly variable and due to the different test methods are not entirely applicable to design methods or direct comparison. 23 Test procedures reviewed include: pull off testing to induce pure shear failure, or tensile failure of the bond, and flexural testing to induce a combination of shear and tensile failure at the interface. Chajes et a l . 1 5 conducted a series of pull off tests and made the following conclusions: • Bond strength is significantly affected by surface preparation. Of the methods tested, mechanical abrasion or sandblasting provided the best bond. • Use of ductile adhesives is not recommended. • If the failure mode is governed by shearing of the concrete, the ultimate bond strength is proportional to the square root of the concrete compressive strength. Review of FRP concrete bond research revealed that the majority of the testing completed has tried to determine minimum bond development lengths and develop models to predict the distribution of stress at the FRP concrete interface. It has been suggested that this research is driven by numerous studies that have illustrated premature debonding of FRP laminates during loading due to: shear cracking, sheet peeling due to flexural cracking, concrete shear delamination, and glue bond failure15. One such study was conducted by De Lorenzis et al. ^.The researchers conducted a series of bond tests utilizing CFRP material. The CRFP material was applied to the tension face of beam specimens, (Figure 2.14). 24 J4,' 2" (Both Sides) 10° 10" 8" Hinge 21" ^ ~M Saw Cut 42° 10" 4 ' BL 4 C , t t . < 7 V -7 e H ' 4" ' MONITORED UNBONDED S I D E 48' Figure 2.14: Bond Test Specimen after De Lorenzis et al. 3 0 The specimens were loaded in flexural to evaluate the effects of: bonded length, concrete strength, number of piles, ply width, and surface preparation. The researchers were able to characterize the stress distribution at the bond interface during failure and noted progressive failure of the bond on specimens with 8 in and 12 in bonded lengths. The specimens with 4 in bonded lengths failed suddenly. The authors attributed the progressive failure to the increased bond length. The authors concluded that the results of the test program suggested that the length of the bond did not affect the bond failure load, which suggests that an effective length exists beyond which no stress is transferred until debonding occurs. The researchers found that failure occurred at the concrete-25 epoxy interface and that the thickness of the FRP coating affects the bond failure load, however it was not found to be a linear relationship. The researchers also found that samples that had a chiseled surface performed much better than those with a sandblasted surface30. The findings presented by De Lorenzis et a l . 3 0 are generally in agreement with those presented by Nakaba et al. 2 8 , Helmueller et al . 2 9 , and Bizindavyi and Neale 3 1. Therefore, an account of their findings will not be presented here. It should be noted that the research efforts in the area of concrete FRP bond has developed to the stage were numerical models have been developed to better understand and predict the stress distribution at the FRP concrete substrate interface 2 8 , 3 1 . However, research that evaluates the durability of this interface is not readily available. 2.7 FRP - Concrete Bond Durability The durability of the concrete - FRP interface is dependent upon the durability of the chemical and mechanical bonds at the interface. The concrete - FRP interface is subject to both mechanical and environmental damage. To ensure that a concrete - FRP bond is durable, proper surface preparation and correct adhesives must be used. The bond strength of concrete FRP composites has been shown to be dependent upon surface preparation of the concrete substrate by many researchers H 2 9 ' 3 0 . A proper bond is essential to ensure that the applied FRP is fully engaged during loading11. Peeling or premature debonding often occurs at stress concentrations at cracks in the substrate concrete. 26 Premature debonding may be the result of poor surface cleaning, water ponding on the surface at the time of coating application, lack of proper adhesive use, and / or issue associated with the mismatch of the chemical and mechanical properties of concrete and FRP materials3 2 , 3 3. Holt and Mack 3 2 broke environmental damage mechanisms into three systems: internal influences, interfacial influences, and external influences. The internal and interfacial influences have been noted. • Internal Influences: • chemical activity; • electrochemical activity; • alkali content and ph level; • stress levels; • moisture infiltration; • transportation of solutions; • Interfacial Influences: • moisture entrapment; • moisture diffusion; • selective transport of chemicals; • thermal and elastic mismatch; FRP coatings are impermeable to liquid and vapour water. Concrete is a porous material and allows the movement of moisture through it in both in the vapour and liquid forms. If the application of a FRP coating results in the entrapment of excess moisture within the concrete substrate this can result in premature debonding to due moisture build up and the deposit of deleterious materials and 27 salt crystals at the concrete FRP interface. The deleterious materials may attack the adhesive materials or may result in the accelerated deterioration of the substrate concrete 3 2 , 3 3. The application of an FRP surface coating may also cause increased internal pore, pressures due to temperature change, ice crystal growth, and, or salt crystal formation resulting in failure at the interface, (Figure 2.15). Figure 2.15: Effects of Vapour Pressure Build Up after Emmons33 Limited specific data about the performance of concrete FRP bond utilizing vinyl ester resin as an adhesive is available. However, a specific study was carried out at UBC by Johnson 2 3, which evaluated the performance of this system with respect to an alkaline environment. The overall performance of the system would not be considered excellent. Other studies are available based on different materials and similar environments, but again are not directly applicable. One such study was carried out by Rajan et a l 1 4 who concluded that wet - dry cycling led to the adsorption of moisture by adhesives at the concrete FRP interface. Evaluation of the bond after limited exposure revealed bond strengths that were in the range of 85% of the control specimens. 28 The issues that contribute to the failure of the concrete FRP are often related and appear to work together. Many of the issues associated with the durability of the FRP - concrete interface are associated with were encountered by the researchers and designer who developed externally bonded steel plates. For example, steel plates are generally not bonded to more than 50% of the concrete surfaces on structures that are subjected to large amounts of moisture, and or wetting -drying cycles. The plates are bonded to a limited amount of the surface area to provide a path for vapour and moisture transfer, such that moisture and salts do not get trapped and the concrete steel interface and deteriorate the concrete, and or the bonding agent31. Surprisingly, many researchers applying FRP externally to concrete have not reviewed this research, or if they have, simply disregarded it. It may be suggested that such findings can be disregarded to due the improved adhesives available today, but such a statement does not address the fundamental issues relating the physical mismatch between FRP permeability to moisture in both the liquid and vapour forms. An improved adhesive simply drives the failure from the adhesive concrete interface into the concrete, which by no means addresses the poor performance of the concrete substrate. 2.8 Durability of Steel Reinforced Concrete The durability of reinforced concrete infrastructure is becoming a large problem in Canada. The major cause of distress is the corrosion of the reinforcing steel in these structures. The corrosion of the reinforcing steel is the direct result of the ingress of chlorides from the surrounding environment into the concrete. The two predominant sources of deicing salts in our region are deicing salts utilized on our roads in the wintertime and exposure to marine environments. 29 Highway structures, such as bridge decks and columns are very susceptible to chloride attack. The deicing salts utilized in the winter time being the major source. Many concrete columns are continuously subjected to deicing salts because of their proximity to road ways34. Marine structures are also very susceptible to chloride attack. The chloride sources are sea water and marine air35. 2.8.1 Mechanisms of Steel Corrosion in Concrete To better understand the factors that influence the performance of a reinforced concrete structure, the mechanisms of steel corrosion in concrete must be understood. Concrete is an alkaline environment. The pore water solution is rich in hydroxides, resulting in a pH of around 12-13. The highly alkaline condition leads to a passive layer forming on the steel surface, which prevents the corrosion of the reinforcing steel 3 6. During the service life of the concrete the passivating layer can be broken down. The two main causes are chloride attack and carbonation37. Once the passivating layer is broken down corrosion may occur. The corrosion of reinforcing steel within concrete is an electrochemical process. The corrosion process is governed by the transfer of electrons from one species to another consisting of two half-cell reactions; an anodic reaction, which produces electrons, and a cathodic reaction, that consumes electrons, (Figure 2.16) 30 -ANODIC DISSOLUTION OF IRON Figure 2.16: The Corrosion Process after Hansson38 For steel embedded in concrete the anodic reactions are 3 8: 3Fe + 4H 20 => Fe 3 0 4 + 8H + + e~ 2Fe + 3H 20 => Fe 2 0 3 + 6H + + 6e" Fe + 2H 20 => HFe02*+ 3H + + 2e~ Fe => F e + + +2e" The cathodic reactions are most likely38: 2H 20 +02 + 4e~ 40H-2H + + 2e" => H 2 The occurrence of the cathodic reactions depends on the availability of 0 2 and the pH of the concrete surrounding the steel surface37. 31 If the pH is reduced the electrochemical process will proceed resulting in the rust, (oxides of iron with varying compositions) on the reinforcing steel, which has two detrimental effects. Rust has a volume several times greater than the iron it consumes resulting in large tensile stresses developing in the parent concrete, which may lead to cracking and spalling. Effectively reducing the cross section of the reinforcing steel and decreasing the load carrying capacity.38 2.8.2 Chloride Attack Chloride may be present in concrete because of two causes: present at the time of casting, and ingress from the surrounding environment after the concrete is cast. Generally today, chlorides are not cast into concrete, but this is not the case for many older structures. The chlorides may be due to: • addition of chloride rich set accelerators; • use of contaminated aggregates; • use of seawater for mixing. Some external sources of chlorides are: • sea water spray and direct wetting; • road deicing salts; • chloride rich chemicals in industrial applications. Before corrosion can occur, the chloride levels must reach a threshold value. The three means by which chloride ions can penetrate concrete are capillary absorption, hydrostatic pressure, and diffusion. Ingress of chlorides by diffusion is the principal mechanism36. Chloride Diffusion of chlorides is the movement of chloride ions due to a concentration gradient. The process is governed by Fick's first law that states the chloride flux is proportional to the concentration gradient. The process of chloride diffusion occurs through the pore water in saturated concrete35. 32 Chloride Permeation is driven by pressure gradients. This is applicable to concrete structures in a marine environment, where one face of the structure may be subjected to hydrostatic pressure40. Chloride Absorption is driven by moisture gradients. Concrete surfaces exposed to marine environments in the tidal zone undergo wetting and drying cycles. The sea water containing chlorides is drawn into the surface though capillary suction. Generally the depth of drying is small, so absorption will not bring the chlorides to the level of the reinforcing steel in the concrete, unless the concrete is of extremely poor quality or the cover is extremely minimal37. 2.8.3 Factors Influencing Chloride Diffusion Porosity and w/cm ratio both affect chloride diffusion rates, but a direct relationship between porosity and diffusions coefficients is difficult to define. When concrete specimens are exposed to a different variety of environmental conditions for long periods of time it becomes even harder to define such relationships39. More definite relationships have been determined between w/cm and diffusion rates. An increase in w/cm for a given cementing material has been shown to increase the effective diffusion coefficient. Supplementary cementing materials have been shown to decrease chloride diffusions rates, due to the alteration of the pore structure39. 2.8.4 Service Life Estimates of Reinforced Concrete Structures The service life of an existing steel reinforced concrete structure is dependent upon the in-service environmental conditions and the chloride concentration level. The initiation of corrosion is dependent upon the depth of carbonation and the chloride concentrations. Tutti37 subdivided the deterioration of reinforced concrete structures into the initial stage and the propagation stage. The initiation stage refers to the period of time required for carbonation to occur, or chlorides to ingress and reach a level at which corrosion begins to occur or a marked increase in corrosion rates occurs. The propagation stage refers to when the reinforcing steel is actively corroding. The time 33 frame of the initiation stage is dependent upon the rate of carbonation and the rate of chloride ingress. Tutti37 stated that the rate of carbonation is dependent upon the ambient concentration of C0 2 , the C 0 2 adsorption capacity of the concrete, and the impermeability of the material against CO2. The rate of chloride ingress is the other dominant factor which controls the length of the initiation stage. The propagation stage is controlled by the rate at which the reinforcing steel is corroding. The corrosion rate is controlled by the availability of oxygen, relative humidity of the concrete, and temperature after the initial levels of chlorides are present to initiate corrosion. 2.9 Use of FRP to Restrain Steel Corrosion Activity Recent lab studies 5 , 4 1 have been carried out to evaluate the benefits of externally applied FRP to reinforced concrete to restrain corrosion rates. The objectives of the studies were to determine the effects of the application of FRP wraps to small scale and large scale steel reinforced concrete columns damaged by accelerated corrosion rates in a laboratory setting. The repaired columns were subjected to further corrosion and destructive testing to characterize the mechanical response and the effects of the application of the FRP wraps to constrain corrosion. The application of such FRP wraps has been shown to increase the strength of corrosion damaged concrete and retard the rate of corrosion after repair. These benefits of the application of FRP wraps to corroding columns have been attributed to the following attributes of the FRP repair: • Low permeability properties of the FRP, therefore, a reduction in the supply of water and oxygen5. 34 • The physical confinement provided by the FRP wrap may impede the growth of the corrosion products, therefore arresting the corrosion rates41. • The physical confinement provided by the FRP may be sufficient to control the mechanical response of the column, therefore the mechanical response of the columns is not affected by further reduction of the area of the reinforcing steel5. The details of select Lab studies on this topic are summarized in Table 2.3. Table 2.3: Summary of Select Lab Studies That Evaluated the Use of FRP to Restrain Corrosion Activity Parameter Lab Study Demers et al.4 1 Lee et al.5 Specimens 152 X 305 mm plain and steel reinforced concrete cylinders 305 mm diameter full scale steel reinforced concrete columns 305 mm x 1016 mm full scale steel reinforced steel columns Corrosion Mechanism electrolysis in salt water galvanstastic accelerated corrosion by impressing a current through the reinforcement cage and subjected to wet/dry cycling Repair Technique application of TYFO S Resin and woven glass and aramid fibres fabric application of Pre-impregnated Replark Type 30 CFRP sheets The reinforced concrete specimens in both studies were subjected to accelerated corrosion regimes prior to repair and subjected to further accelerated corrosion after the application of the FRP repair. Demers et a l 4 1 determined: • Corroded and repaired specimens show an increase in strength of 40% over uncorroded unstrengthed specimens. • The structural performance of the corroded and repaired specimens was not compromised when the samples were subjected to subsequent post repair corrosion. Lee et al. 5 determined: 35 • Corroded and repaired specimens increased the load carrying capacity of the corroded columns by 28%. • The application of the CFRP wrap impeded the post repair corrosion rates by 50%. • The structural performance of the repaired columns was not comprised when the samples were subjected to subsequent post repair corrosion. 2.10 FRP Confinement It is well known that external confinement provided by FRP coatings improves the load carrying capacity and ductility of concrete loaded in compression. The improvement in these mechanical properties has been shown to be proportional to the level of external confinement. The carrying capacity and strain capacity of the FRP wrapped concrete increases as the level of confinement increases4 2"5 3. FRP jackets provide passive confining pressure. The confinement force is generated by the transverse dilation of the concrete contained by the confining FRP. FRP confining materials retain variable levels of stiffness during the axial loading period until failure; resulting in a continuously increasing level of confinement during loading. The mechanics of FRP confinement have been outlined by Toutanji48, who calculated the lateral stress f| applied to concrete by the FRP confinement as follows: fi = Eu where: ei = the lateral strain of the confined specimens E| = the lateral elastic modulus and is calculated as follows: R 36 where: E f = the elastic modulus of the fiber t = the thickness of the fiber R = the radius of the cylinder The equation presented above is based on static analysis, equilibrium of forces, and deformation compatibility of the materials48. Numerous other studies have shown that FRP wraps are an effective system capable of providing confinement to concrete. Therefore, resulting in increased ductility, lateral and axial strain capacities, and ultimate load capacity when loaded in pure compression 7 4 2 5 2 . A study carried out by Banthia and Boyd 7 concluded that sprayed GFRP (SGFRP) performed better than equivalent FRP wraps. The increase in concrete load carrying capacity and strain capacity has been shown to increase with the increasing FRP jacket strength and stiffness46. Pessiki et a l . 4 7 concluded that to limit concrete dilation, a FRP jacket must be significantly stiff to provide significant confining pressures at relatively low levels of strain. Numerous lab studies carried out have characterized the mechanical responses of carbon, glass, aramid, and hybrid fibre systems. The results of the lab studies are highly variable due to the variables associated with these systems. Such variables are: fibre type, fibre orientation, fibre content, resin type, bonding agent, and coating thickness. Systems in which the fibre type is the only variable, conclude that carbon fibres perform remarkably better than glass fibres45,47(Figure 2.17). 37 E-GIass 0.015 0 .010 0.005 0 0.005 0.010 0.015 Figure 2.17: Typical Stress Strain Responses of FRP Confined Concrete after Harries and Kharel45 Harries and Kharel 4 5 quantified the level of confinement provided by FRP into three simple categories as follows: 1. Lightly confined: the jacket does not provide an increase in the peak axial load, however they provide a large increase in the strain capacity. Failure occurs at the rupture strain of the jacket. 2. Heavily confined: the jacket does provide a significant increase in the peak axial load resulting in larger dilation strains. The failure is very brittle, and no post peak load carry capacity is observed. 3. Moderately confined: the failure mode falls between the two described above. The lab program earned out by Banthia and Boyd 7 showed that the SGFRP performed better than an equivalent GFRP wrap as noted above. The levels of confinement provided by the various systems in study are best quantified by the method put forth by Harries and Kharel 4 6. The GFRP spray material provided moderate confinement, while the various GFRP wrap systems provided light confinement. The spray applied GFRP coated cylinders exhibited a higher level of toughness, than the wrapped cylinders. 38 The authors attributed this to individual fibre pullout at failure due to the nature of the composite produced by the spray method. However, review of the findings of research carried out by Harries and Kharel4 5, and the mechanics of confinement as explained by Toutanji49, may suggest that the high level of toughness reported by Banthia and Boyd 7 be attributed in addition to the nature of the composite the overall stiffness of the confinement layer. The overall stiffness of the confinement layer being dependent upon the FRP confinement material mechanical properties and the thickness of the confinement layer. Sprayed GFRP has a lower stiffness than typical wrap applied GFRP 7 . 2.10.1 Durability of FRP Confinement The benefits of FRP coating to provide confinement to axially loaded concrete specimens, both full scale and lab scale, have been well documented and proven to be highly effective. The highlights of these studies are discussed in the previous section. However, these materials have not yet seen widespread use because of the questions surrounding the durability of the FRP materials and the FRP concrete composite. Test data with respect the durability of these systems is limited and the bulk of data available is based on accelerated laboratory test results. The test results available include data on: aramid, e-glass and carbon fibres, combined with numerous epoxies and resins, subjected to varying environments including wet dry in saline water, neutral water and alkaline water, freeze/thaw cycles, and extreme temperatures17 ,18. The studies noted above suggested that the FRP concrete confined systems that were exposed to accelerated weathering conditions showed a decrease in the measured compressive strength and ductility of the system. The results of the studies relevant to the exposure program earned out in the lab portion of this thesis have been presented in Table 2.4. 39 Table 2.4: FRP Confinement Durability Studies Findings Authors Fibre Resin Exposure Program Findings Micelli et a l . i a Carbon Epoxy Immersion 15% NaCl solution for 120 days Similar fc 34% reduction in the ultimate axial strain 23% reduction in the ultimate axial strain Glass 17% reduction in fc 50% reduction in the ultimate axial and hoop strain Toutanji and Balaguru4 9 Carbon Epoxy 300 cycles of 4hr wet, 2h dry in water containing 35g of salt per liter. Average air temperature 35°. Minimal reduction in f c Up to a 13% reduction in the ultimate axial strain Glass 10% reduction in fc Minimal reduction in ultimate axial strain Kshirsagar et a l . 5 0 Glass Epoxy Submersed in neutral pH water at a temperature of 66°C for 333 days 36 % reduction in f c 68 % reduction in the ultimate axial strain 69 % reduction in the ultimate lateral strain | Kshirsagar et a l . 5 0 attributed the reduced strength to deterioration of the glass fibre. The authors also attributed the reduced strain capacity to moisture and temperature induced strains and moisture diffusion in the FRP wrap resulting in polymer matrix swelling. The deterioration process was shown to be accelerated at higher temperature. The findings presented above illustrate the variable durability performance of FRP materials in moist environments, which further suggests that standardized test methods are required to evaluate the durability of concrete FRP systems. 2.11 Development of Spray Applied GFRP at UBC Spray applied GFRP (SGFRP) applied to concrete has been the topic of much research at UBC in recent years. The first application of spray applied GFRP (SGFRP) was earned out by researchers at UBC utilizing workers and equipment from a manhole lining manufacturer in the Lower Mainland. The initial study included retrofitting small undamaged and damaged concrete beams with SGFRP and mechanical testing to evaluate the properties of the SGFRP 6 . The 40 findings of this initial study were very promising and led to UBC carrying out further research and later purchasing their own spraying machine. The application of the coating drastically increased the load carrying capacity and fracture toughness of the beams. Since this first study, numerous studies have been carried out that evaluated the materials performance with respect to reinforcing concrete specimens to provide confinement, shear reinforcement, and tensile reinforcement. The material has been successfully applied in the laboratory and on full scale structures in the field. The second phase of the research included strengthening of reinforced concrete beams3. The research earned out by Boyd 3 showed that the SGFRP performed very well with respect to increasing the load carrying capacity and fracture toughness of steel reinforced and unreinforced concrete beams. The study compared the performance of spray applied GFRP and wrap GFRP material and found that spray performed much better than the wrap on full scale bridge girders that were tested. Table 2.5 illustrates the excellent performance of the spray applied GFRP. Table 2.5: Results of Laboratory Tests on Full-Scale Bridge Girders after Banthia et al6 Retrofit Type In itial Stiffness, kN/mm rPeak Load Ultimate Moment Capacity, kN-m Absorbed Energy to Peak Load, N-M None 6.69 214 237 11,559 Wrap 7.67 284 323 31,644 Spray 9.00 419 470 34,095 In addition to destructive testing of GFRP concrete composites Boyd 3 conducted a significant amount of research to optimize the SGFRP application system. Boyd 3 found that the optimum fibre length to be 48 mm at a fibre content by volume of 19%. Boyd based his optimization criteria on the performance of the composite when tested in tension and the application performance. The application performance was based on amount of rebound and the consolidation characteristics of the composite. 41 The application of SGFRP to provide external confinement to concrete columns has also been earned out at UBC 7 . The study involved the testing of both small and large scale specimens. The study found that SGFRP material performed as well or better than equivalent GFRP wraps as illustrated in Table 2.6. Table 2.6: Comparison of the Benefits of SGFRP and Various Wrap GFRP Schemes External Confinement after Banthia and Boyd7 Test Series Fibre ^Number of Increase in Increase in Orientation Layers Peak Load, % Fracture ^ ^ ^ ^ ^ ^ ^ ^ Energy, % Control Not coated None Wrap A 0-90u 1 69 978 WrapC + 45 u 1 18 464 WrapE + 45u/0-90u 1-1 64 1160 Spray 2-D random Not applicable 64 911 The Safe Bridge application in Victoria, B.C., was the first application of the SGFRP retrofit system on a full scale structure1. SGFRP was applied to externally reinforce shear deficient concrete channel beams. The application program was very successful and load testing of the bridge before and after application illustrated the benefits of the coating application. The measured strains in the reinforcing steel during loading were greatly reduced by the application of the SGFRP material. Visual examination and monitoring of intelligent sensing devices embedded in the repair suggest that the SGFRP retrofit is performing well to this date5 2. Johnson 2 3, has carried out the only durability study prior to this research program. The exposure program evaluated the performance of spray and wrap applied polyester glass fibre composites externally adhered to the tension face of small concrete beams and subjected to a moist alkaline and neutral environment. The samples were submersed in alkaline water for 30, 60, and 90 days. The variables included: exposure conditions and prestressing on the concrete specimens. Specimens were tested in flexural and the cracking load, ultimate load, fracture energry, midspan deflection, and initial stiffness were measured and compared to evaluate the performance of the 42 specimens. The author concluded that the glass/polyester laminates concrete composite beams performed very well when the samples were kept dry and exposed to room temperature. However, long-term exposure to moisture and alkaline environment is detrimental to the ductility and fracture energy of the glass/polyester laminates concrete composite beam 2 3. Table 2.7 provides a summary of the applicable findings of the study completed by Johnson 2 3. Table 2.7: Summary of Findings Based on Research Completed By Johnson Specimen and Exposure Conditions Fracture Energy, Nm Deflection, mm Days Exposed Days Exposed 60 90 60 90 SGRFP reinforced concrete beam exposed to water at room temperature 32.0 28.0 1.43 1.03 SGRFP reinforced concrete beam exposed to water at room temperature 30.1 26.7 1.32 0.96 SGRFP reinforced concrete beam exposed to water at room temperature and post-tensioned 34.9 31.6 1.63 1.18 SGRFP reinforced concrete beam exposed to water at room temperature and post tensioned 25.2 27.5 1.2 1.02 The concrete strengthening programs earned out by researchers at UBC illustrate the benefits and excellent performance of the SGFRP material when used to strengthen un-reinforced and reinforced concrete structures. The SGFRP system has been proven to be an excellent method of applying external reinforcement to concrete structures. However, the durability of the system is still in question. The results of the durability study carried out by Johnson 2 3 are not encouraging. However, the performance of the coating to date on the Safe Bridge is promising and suggests the long term durability of the SGFRP retrofit system may be acceptable, but more data is still needed to properly understand the durability issues surrounding the use of the SGFRP repair systems. 43 2.12 Literature Review Summary Ultimately all of the material presented in the literature review relates to the durability of GFRP reinforced concrete structures in a marine environment. Many of the mechanisms of deterioration noted are interrelated and make it difficult to study these effects individually. The literature review suggests that the application of GFRP materials to concrete is a plausible repair method that should be very durable provided the repair is properly designed and executed. A review of concrete repair technology should be the first step in ensuring that a FRP repair is durable. Reinforced concrete repair is not a new technology. The practice of repairing concrete structures with externally applied steel epoxy bonded plates and a cementitious material is well understood and common practice. To ensure that FRP repairs are durable, the principles of concrete repair most not be forgotten. Determining the cause of distress and designing a repair that addresses the deterioration mechanisms determines the success of a repair and an external repair is only as good as the substrate it is bonded to. MacDonald et a l . 5 3 outlined the necessary steps to ensure a durable repair. These steps are as follows: • identify the causes of distress; • establish the severity of the interior and exterior environments; • evaluate alternative repair techniques • develop repair techniques and select an appropriate system; • select repair materials and develop specifications; • execute work in accordance with specifications. The steps to a durable repair are the fundamental issues surrounding the durability of a GFRP reinforced concrete structure. In order for the GFRP concrete composite to be durable an understanding of the deterioration mechanisms, the behaviour of the individual materials, and the behaviour of the GFRP reinforced concrete composite structure must be understood. Therefore, 44 the lab study described in the following Chapter was carried out in hopes of providing information with respect to the SGFRP concrete interface and the performance of the SGFRP - concrete system. 45 CHAPTER 3 - EXPERIMENTAL PROGRAM 3.1 Introduction The experimental portion of this program evaluated the performance of concrete-SGRFP composites subjected to a simulated marine environment. To evaluate the concrete S G F R P composite a series of concrete lab specimens were cast and coated with S G F R P . Fibre content, coating thickness, and exposure period were the variables. The specimens were exposed to a simulated tidal zone environment consisting of wet/dry cycling in saline water. The test specimens consisted of a series of concrete cylinders and concrete beams. The samples were coated, exposed and tested to characterize the stress -strain response of the concrete spray applied G F R P composites and the effects of a simulated marine environment on these parameters. 3.2 Test Parameters 3.2.1 Cylinder Strengthening Test Program The effects of the following parameters were evaluated: 1. Coating thickness; 2. Exposure to a simulated tidal zone; 3. Effects of preloading prior to exposure. The cylinder specimen sample series were each labeled with a Series number and letter. The number refers to the coating thickness and fibre content. The letter refers to the exposure regime. The Series are as follows: Series 1 A, 2A, 1B, 2B, 1C, 2C • 1-1-3 mm coating thickness • 2 - 3-5 mm coating thickness • A - Preloaded prior to being subjected to 525 exposure cycles 46 B - Exposed to 525 exposure cycles C - No preloading and no exposure cycles. Example Series 1 A 7 Indicates 1- 3 mm coating, indicates preloading prior to exposure 3.2.2 Beam Strengthening Test Program The effects of the following parameters were evaluated: 1. Coating thickness; 2. Fibre content; 3. Exposure to a simulated tidal zone; 4. Length of exposure; Resulting in three series of specimens as follows: • Series 1: 1-2 mm low fibre content S G F R P coating; • Series 2: 3-5 mm low fibre content S G F R P coating; • Series 3: 6-8 mm high fibre content S G F R P coating. 3.3 Materials 3.3.1 Concrete Ready mix concrete was utilized to cast the samples. The concrete was a typical mix with a specified 28 day compressive strength of 30 MPa. The choice to use ready mix concrete was made to ensure uniformity of concrete between the samples. The mixture proportions as reported by the supplier are given in Table 3.1. 47 Table 3.1: Concrete Mix Proportions Material . Quantity 20 mm aggregate, kg/m J 715 14 mm aggregate, kg/m J 385 Sand, kg/m d 812 Cement, kg/m J 235 Flyash, kg/m" 40 Water, kg/m J 237 Water Reducing Admixture, mUm6 1300 Air Entraining Agent, mL/m'3 180 3.3.2 Resin Two separate resins were utilized for the lab program: vinyl ester and polyester. The vinyl ester resin was utilized as the bonding agent to improve the bond of the S G F R P to the concrete substrate. The polyester was utilized for the matrix of the composite. Reichold Inc manufactures both resins. The properties of the resins as supplied by the manufacturer are given in Table 3.2. Table 3.2: Mechanical Properties of Reichold Resins Mechanical Property Polyester Vinylester Flexural Strength, MPa 97 148 Flexural Modulus, x 10 3 MPa 4000 3600 Tensile Strength, MPa 62 85 Tensile Modulus, x 10 3 MPa 4100 3400 Tensile Elongation @ Break, % 1.7 4.0 The polyester resin was chosen because of its relatively low cost. Given that this was the first durability program of such, the decision was made to start with the most economical system. The vinyl ester was chosen for the coupling agent due to its improved performance over polyester as noted by Boyd 3. 48 3.3.3 Fibres The fibres used for the program were Owen Comings Advantex 360 RR continuous gun roving. The Advantex Glass Fiber has improved corrosion resistance with respect to traditional E-glass fibres due to a special sizing. The mechanical properties of the fibres as provided by the manufacturer are provided in Table 3.3. Again, the glass fibre was chosen because of its relatively low cost. Table 3.3: Properties of Advantex Glass Fiber Mechanical Property Value Density, g/cms 2.62 Diameter urn 11 Tensile Strength, MPa 3100-3800 Elastic Modulus, MPa 80 -81 Elongation at Break, % 4.6 3.3.4 Catalyst The catalyst utilized for the program was Methyl Ethyl Ketone Peroxide, (MEKP), given the product name Luperox DDM-9. The material is manufactured by Ashland Chemical Canada Ltd. 3.4 Concrete Specimens Preparation 3.4.1 Casting Specimens The concrete specimens were all cast from one batch of ready mix concrete. The cylinder specimens were cast utilizing cardboard "handi forms". The "handi forms" were placed in rov and braced with a wooden form to ensure that they maintained their shape during concrete placement. The concrete was placed in the moulds in one lift and consolidated utilizing a pencil vibrator to ensure proper consolidation of the concrete. 49 Panels 450 mm by 450 mm by 88 mm were cast and later saw cut to make the beams for the flexural loading test program. It was decided to cast panel specimens in order to make it easier to apply a coating of uniform thickness, therefore decreasing variability. 3.4.2 Curing Specimens The concrete specimens were stripped after 48 hr and placed in a water bath until an age of 28 days at which time they were removed and stored in a dry location under laboratory conditions. 3.4.3 Surface Preparation The concrete surfaces were thoroughly treated prior to application of the S G R F P . An angle girder equipped with a cup stone wheel was used to roughen the surface and remove approximately 0.5 mm from the surface of the concrete. The grinding was followed by washing with a 2000 psi water wash to remove all of the debris from the surface of the concrete. The samples were allowed to dry thoroughly prior to the application of the coating. 3.5 Coating Application The coating application consisted of three steps: brush application of the bonding agent, pneumatic application of the polyester resin and chopped glass fibre, and rolling out of the G F R P layers to fully saturate all of the fibres, remove any voids, and ensure a uniform coating thickness. For Cylinder Series 2 the coating was applied in layers and rolled out utilizing a grooved aluminum roller before the application of each successive layer as shown in Figures 3.1 -3. 3. 50 51 Figure 3.2: Rolling Out the GFRP Composite to Fully Saturate the Glass Fibres and Remove Air Voids 52 Figure 3.3: The Finished Product, a 5-6mm Uniform Isotropic Coating The beam specimens utilized for the flexural testing program were coated in a similar manner. Panel specimens were coated on one face and then sawn into beams utilizing a water cooled diamond blade. This ensured that coating with a uniform thickness and fibre content was achieved for each of the series. 3.6 Exposure Program The exposure chamber was set up indoors in the laboratory in order to maintain a nearly constant air and water temperature for the duration of the exposure. The samples were placed vertically in two non-insulated plastic tanks. At the beginning of the exposure period one tank was filled with salt water with a NaCl content of 4 grams/L, so that the specimens 53 were completely covered. The other tank was left dry. The tanks were covered to prevent evaporation of the water from the system. Initially the salt content was determined by weighing the mass of the salt added and measuring the volume of water. The volume of water within the system was kept constant for the duration of the testing program. Water lost due to evaporation was replaced throughout the test program. It was assumed that salt was not lost from the system, therefore, the total salt content would not change. The saline water was replaced after 250 cycles. The NaCl content was tested after 375 cycles and 525 cycles and found to be 4.36 and 4.3 grams/litre respectively. The content was tested by method of evaporation. The system was then equipped with two pumps capable of transferring the water from one tank to the other in approximately 15 minutes. The pumps were hooked up to electronic timers that were programmed to allow the system operation to be completely automated. The cycle period for the samples was 4h dry followed by 4hr submersed; three cycles per day. The exposure periods were as follows: • Cylinders: • Series A,B 525 exposure cycles; • Series C 0 exposure cycles. • Beams all series: • 0, 180, 360, and 525 exposure cycles. One exposure cycle is defined as four hours submersed followed by four hours dry. No external air flow or heat was applied to the samples to dry them during the drying period, the tank was simply drained. 54 3.7 Testing Program Two separate testing programs were carried out: compression testing of cylinders and flexural testing of beams. The purpose of the cylinder strengthening program was to evaluate S G F R P performance when applied for external confinement. With compressive loading, the S G F R P -concrete bond is not the critical component with respect to the structural performance of the composite. The beam strengthening program was carried out to evaluate the performance of the S G F R P - concrete substrate bond. Concrete beam specimens coated on the tension face were tested in flexure to assess the effects of the exposure period on the performance of the bond. 3.7.1 Test Specimens The test specimens were cast from single load of ready-mixed concrete as discussed in Section 4. The details of the specimens cast for each of the three testing programs are given in Table 3.4. Details of the two coatings applied are given in Table 3.5. The coating thickness measurements given in Table 3.6 are the design values. Actual measured thickness values are presented in Chapter 4. Table 3.4: Summary of Concrete Test Specimens Test Program Sample Type Quantity Cylinder Strengthening 200 X 400 mm cylinder specimens 30 Beam Strengthening 450 X 450mm X 88 mm panels; saw cut into beams 80 X 80 x 350 mm 14 Table 3.5: Coating Details Cylinder and Beam Specimen Series Series Target Coating Thickness Fibre Content 1 1 - 2 mm 26 % by mass 14 % by volume 2 3 - 5 mm 26 % by mass 14 % by volume 3 6 - 8 mm 29 % by mass 16 % by volume 55 3.7.2 Cylinder Strengthening Testing Program The variables evaluated in this portion of the testing were: Exposure Period : • Testing of mature cylinders after 0 and 525 exposure cycles. Effects of axial preloading: • Samples from each series were preloaded prior to exposure. Coating thickness: • Series 1 and 2 Coating thicknesses were applied. The details of the specimen sets are provided in Table 3.6. Table 3.6: Cylinder Test Specimens Series Coating Preload, 80% of expected Exposure Period, cycles Identification Thickness, mm ultimate strength 1A 1 - 2 Yes 525 2A 3 - 5 Yes 525 1B 1 - 2 No 525 2B 3 - 5 No 525 1C 1 - 2 No 0 2C 3 - 5 No 0 Control 0 No 0 The axial preloading variable was included to facilitate conditions that structures are subjected to during a service life. The testing was carried out in UBC's structures lab utilizing the Baldwin Universal Testing machine equipped with a digital data acquisition system. The testing was carried out in accordance with ASTM C469. The combined compressometer-extensometer utilized for the testing was designed to incorporate two linear variable differential transducer (LVDT) mounted on either side to measure the vertical displacement and two LVDTs mounted to measure the horizontal displacement at the mid height location of the sample. The purpose of the compressometer-extensometer was to isolate the displacement of the testing machine from 56 that of the samples. The compressometer rings were attached to the sample at approximately 65mm from the top and bottom. The extensometer was not attached to the sample, but rather to the compressometer, therefore, not constraining the displacement at mid height from occurring (Figure 3.4). Note: Arrows indicate locations of LVDTs. T I Figure 3.4: Schematic Diagram of Compressive Loading Test Set Up The test data were analyzed to determine the effects of the variables with respect to change of initial stiffness, ultimate load at failure, ultimate strain at failure, shape of the stress - strain curve, and fracture toughness. 3.7.3 Beam Strengthening Testing Program The flexural testing program was carried out to evaluate the performance of the S G F R P -concrete bond. Beam specimens with S F G R P coatings applied on the tension face were loaded in 3 point bending in accordance with ASTM Test Method C1018. The midspan deflections were measured utilizing a Japanese Yoke equipped with two LVDTs (Figure 3.4) Notes: The large arrows indicate restraint points and red small arrows indicate strain gauge locations. The strain gauges were mounted at 0 mm, 25 mm, 75mm, and 125 mm from the center of the beam (Figure 3.5). 57 "S * * * T ? * f Figure 3.5: Schematic Diagram of Flexural Loading Test Set Up The samples were notched at the mid point on the top surface to cause failure to occur at the center of the span. The purpose of the notch was to prevent failure by crushing of the concrete as the beam deflected. Therefore, isolating the performance of the S G F R P and S G F R P concrete interface from that of the concrete beam. The intended failure mode was failure of the concrete in tension at the notch location, followed by failure of the bond initiating at the stress concentration in the G F R P located below the crack in the concrete at midspan. Therefore, causing the failure to propagate along the bond line from the center point outwards as the deflection of the beam increases. The initial control specimens were instrumented with strain gauges on the bottom face of the S G F R P to measure to strain distribution within the material. The purpose of strain gauges was to relate the debonding mechanisms to the concrete failure, beam deflection, load, and FRP strain. 58 Testing of Beam Specimen Series 1, 2, and 3 (Table 3.5) was carried out after 0,180, 360, and 525 exposure cycles. The toughness, initial crack strength, maximum load, maximum deflection, and interface condition after the exposure were the parameters used to evaluate the effects of exposure on the bond. 3.7.4 Visual Evaluation The G F R P concrete composite system was visually examined for both the cylinder and beam specimen series. Prior to exposure the coating surface was examined to determine the general characteristics of the surface including color and irregularities. The surfaces were re-examined after the exposure period. The failure surfaces in the G F R P were examined after failure and limited sample sections of these failures were analyzed to quantify the amount of fibre pullout versus fibre fracture at the rupture point in the coatings. The concrete GRFP interface was also examined on select number of cylinder and flexural beam specimens. The interfaces were examined to determine, if there were any trends with respect to the amount of substrate material that remained bonded to the failed G F R P coating and for any visual signs of deterioration in the concrete paste at the interface due to the exposure period. 3.7.5 Fibre Content Testing Fibre content testing was carried out in accordance with ASTM D2584: Ignition Loss of Cured Reinforced Resins. The thickness of the coating on each specimen was also measured. For the beam specimens, this was measured at two locations at the center point of the beam. The measurements were taken with a set of calipers accurate to 0.01mm. The average of the two readings was reported as the coating thickness. The cylinder specimens were measured at four locations mid height on the 59 specimens. The coating was removed in these locations after testing to allow for the measurements. Again a set of calipers was used to take the measurements. 3.7.6 Chloride Ion Penetration Testing Chloride ion penetration testing was carried out to evaluate the effectiveness of the coating with respect to the penetration of chlorides. Testing was carried out in accordance with ASTM C1202 on two samples. Two mature concrete beams were coated with GFRP. The first coating contained glass fibres in a polyester resin matrix and the second sample contained only the polyester resin. 300 mm concrete cores were taken from a coated concrete beam using an electric coring drill equipped with a four inch diameter water cooled diamond tipped core barrel. 3.8 Analysis of Test Data 3.8.1 Cylinder Strengthening During testing the load and the horizontal and vertical displacements were digitally recorded. The following Calculations were carried out: • Compressive Stress, (MPa); • Axial Strain, (mm/mm): change in length/ distance between the top and bottom rings of the compressometer; • Lateral Strain, (mm/mm): change in diameter/ diameter, mm; • Axial Stiffness,' (GPa): Microsoft excel linear curve fitting option was utilized to carry out this task. The curve was fitted to the linear portion of the stress vs. strain curve yielding the chord modulus; • Fracture Toughness: The area under the stress - strain curve was calculated for both the axial and lateral strains. 60 3.9.2 Beam Strengthening Calculation of the Fracture Toughness (area under the load vs. deflection curve) was carried out. The calculation was conducted in the same manner as for the cylinder. The measured load values were normalized to account for the slight variation in the size of beam specimens that resulted from the saw cutting preparation. The standard procedure to account for this variation is the calculation of the flexural stress. Therefore, the formula provided in ASTM C78 to calculate flexural stress; R = Pl/bd 2, was the basis of the normalization factor, which is as follows: N = b,d,2/b sd s 2 where: N = normalization factor; b| = average specimen width of the sample set in mm, at the fracture; di = average thickness of the sample set in mm, at the fracture; b s = average width of the test specimen in mm, at the fracture; d s = average depth of the test specimen in mm, at the fracture; The range of the factors was from 0.8 to 1.2. 61 CHAPTER 4 - EXPERIMENTAL RESULTS 4.1 Visual Evaluation of GFRP Coating The coatings were visually examined before, during, and after the exposure period. The concrete S G F R P interfaces were also examined after failure. 4.1.1 Visual Evaluation of GFRP Coating Surface Prior to Exposure The GFRP coating surfaces were initially a translucent light pink colour. The surfaces were quite irregular and the resin coating covered all of the fibres that were on the surface layer. The surfaces appeared free from porosity and were impermeable. However, during the grinding of the flexural specimens control series for the strain gauge application, small air voids became visible in the coatings. The number of voids was found to be quite minimal and no pattern was evident in the air voids on these polished surfaces. The cylinder sample Series 1A and 2A were also visually examined after the preloading was carried out. No notable changes in the coating surface were visual. 4.1.2 Visual Evaluation of the GFRP Coating Surface After Exposure The GFRP concrete specimens that were not exposed exhibited no major change in coating appearance over time. The colour and visual appearance of the coatings remained unchanged. The G F R P specimens that were placed in the exposure tanks changed colour within the first three exposure cycles. The surface colour of the coating became chalky and the appearance was somewhat milky. Over the length of the exposure, the surface gradually became faded and the surface fibres became prominent. The surfaces of the Cylinder Series A and B appeared to be identical after the exposure period, both showing similar amounts of fibre prominence. 62 After the samples were removed from the exposure tank and allowed to completely dry, a milky white film was left on the surface of the samples. The colour of the film was much lighter than when the samples were in the tank. The colour of the resin was noted to have faded slightly during the exposure, which has been attributed by numerous other researchers to be the result of moisture adsorption by the GFRP. The flexural beam specimens were examined and photographed after 180, 360, and 525 exposure cycles. There was no visible evidence of deterioration of the concrete GFRP bond on these specimens. The deterioration of S G F R P as indicated by the degree of fibre prominence increased as the exposure age increased, (Figures 4.1 - 4.3). Figure 4.1: Flexural Beam Testing Program Sample Series 1: Typical Surface Condition of SGFRP Composite Prior to Exposure 63 Figure 4.2: Flexural Beam Testing Program Sample Series 1: Typical Surface Condition of SGFRP Composite after 180 Exposure Cycles 4.1.3 Visual Evaluation of The Concrete FRP Substrate After Failure The testing of the flexural specimens was conducted after 0, 180, 360, and 525 exposure cycles allowing for the examination and photographing of the bond surface after varying lengths of exposure (Figure 4.4). The exposure period did not affect the appearance of the interface after failure. The visual bond evaluations were based on the percentage of the bond failure that was cohesive versus adhesive. The degree of cohesive failure varied a large amount between the test specimens. The results were compared with respect to the effect of coating thickness and exposure period. No noticeable trends were evident. The results of the visual survey are provided in Table 4.1. The percentages presented in Table 4.1 were based on the visual survey made by the author. The failure pattern in the substrate concrete was similar for all three series of specimens. The failure occurred in the surface paste and no coarse aggregate pop out was visible. The failure in the paste was limited to a depth of approximately 1.0 mm. Figure 4.4: Typical SGFRP Concrete Interface After Failure 65 Table 4.1: Results of Visual Examination of SGFRP Concrete Interfaces After Failure Sample Number of Exposure Visual Estimate of Bond Failure Identification Cycles Modes, % Adhesive Cohesive 1A 0 Failure occurred in GFRP 1B 0 80 I 20 1C 0 Failure occurred in GFRP 1A 180 15 1B 180 20 1C 180 15 1A 360 15 1B 360 15 1C 360 15 1A 525 Failure occurred in GFRP 1B 525 Failure occurred in GFRP 1C 525 80 20 2A 0 60 40 2B 0 90 10 2C 0 50 50 2A 180 50 50 2B 180 85 15 2C 180 20 80 2A 360 85 15 2B 360 70 30 2C 360 15 85 2A 525 55 45 2B 525 55 45 2C 525 60 40 3A 0 90 10 3B 0 70 30 3C 0 55 45 3A 180 40 60 3B 180 80 20 3C 180 60 40 3A 360 40 60 3B 360 65 35 3C 360 60 40 3A 525 40 60 3B 525 25 75 3C 525 10 90 A limited number of bond interfaces were also examined on the cylinder specimens. The specimens in which the jacket ruptured and pulled away from the concrete at failure made it possible to examine the interface. During the failure of the concrete cylinders in many cases the failed G F R P jacket had large pieces of concrete well bonded to it. These pieces were up to 5 - 6 mm thick and contained coarse aggregates. The geometry of the concrete still 66 attached to the jacket after failure appeared to coincide with the failure pattern of the concrete, rather than the exposure period. 4.1.4 Visual Evaluation of Specimen Series 1A and 2A after Preloading Cylinder series 1A and 2A were coated, preloaded, and subjected to 525 exposure cycles. All samples were intact and free from visible cracking prior to loading. No visible damage was noted in the S G F R P coating as noted previously. However, the preloading did result in some minor cracking in concrete near the top and bottom edges of the coating on Samples 1A-1, 1A-2, 2A-2. 4.2 Concrete Fresh Properties The results of the fresh properties tests are given in Table 4.2. Table 4.2: Measured Fresh Properties Fresh Property Measured Value Slump, mm 100 Air Content, % 3.4 Ambient Temperature, U C 18 Concrete Temperature, U C 22 4.3 Cylinder Strengthening Program Test Results 4.3.1 Concrete Hardened Properties A series of test cylinders that did not under go coating was tested to determine the mechanical properties of the concrete. Compressive strength test results are provided in Table 4.3. 67 Table 4.3: Control Series Test Results Sample I.D. f c MPa Maximum Lateral Strain \d/d Maximum Axial Strain •\L/L Axial Modulus GPa Fracture Energy Nm Modulus 1 36.3 0.0079 0.0071 25.6 450.8 Modulus 2 38.1 0.0016 0.0019 28.2 447.5 Modulus 3 28.8 0.0013 0.0012 25.7 140.4 Refer to Figure 4.5. for a typical stress strain response of the control series specimens. The complete set of stress vs. strain plots is provided in Appendix A. E • /' / // 1 Lateral Strain i -J Axial Strain -0.01 -0.005 0 0.005 0.01 Strain Figure 4.5: Typical Stress Strain Response - Control Series The control series specimens exhibited a typical linear axial and lateral stress vs. strain response and very low levels of lateral and axial strains at failure. 4.3.2 Cylinder Series 1A and 2A Cylinder Sample Series 1A and 2A were subjected to axial preloading prior to exposure. Initially the axial preload was intended to be 80% of the expected ultimate strength of the 68 sample. However, due to the variability associated with the coating thickness and performance, this was not possible. Unfortunately the ultimate strength and coating thickness could be determined only after the specimens were loaded to failure. The test results are given in Table 4.4. Table 4.4: Cylinder Series 1A and 2A Test Results Sample Coatinij Ultimate Maximum Maximum Axial Fracture Preload Exposure I.D Thickness Strength Axial Strain Axial Modulus Energy MPa Cycles mm MPa C P A Strain GPa Nm with coating 1A-1 2 30.3 0.005 0.0021 19 295.4 38.9 525 1A-2 1.5 24.2 0.0058 0.0033 23.7 495.6 36.1 525 1A-3 3.5 38.9 0.0048 0.0035 22.2 742.6 35.4 525 2A-1 1.5* 33.9 0.0024 0.0016 26.6 251.1 34.5 525 2A-2 3.5 31.7 0.0031 0.002 23.8 416.6 28.3 525 2A-3 5.5 42.4 0.0079 0.0071 25.9 1088.5 33.2 525 * Actual coating thickness was 3.5 mm, but a localized flaw reduced thickness at location of coating failure to 1.5 mm The samples that showed cracking in the concrete after preloading performed very poorly when loaded to failure after the exposure period. Typical stress strain plots are presented in Figure 4.6 and Figure 4.7. The complete set of stress strain responses is provided in Appendix A. The samples that were cracked prior to exposure show very little increase in strain capacity, or fracture toughness, and a decrease in load carrying capacity, when compared to the uncoated control specimens. 69 L i . IE V." fc u 45 40 35 30 25 20 15 10 5 0 -0.008 T 1 " ' ' "' Lateral Strain T | - — if— - — ! Axial Strain -0.006 -0.004 -0.002 0 St ra in 0.002 0.004 0.006 0.008 Figure 4.6: Typical Stress Strain Response Series 1A and 2A, No Cracking Evident in Concrete Prior to Exposure 40 35 30 25 20 w £ 15 o. E o 10 5 Q. CO -0.008 Lateral Strain w Ji# Axial Strain -0.006 -0.004 -0.002 0 Strain 0.002 0.004 0.006 Figure 4.7: Typical Stress Strain Response Series 1A and 2A, Cracking Evident in Concrete Prior to Exposure Notes: The dark curves represent the stress vs. strain response after exposure and preloading. The gray curves represent the preloading stress vs. strain response. 70 4.3.3 Cylinder Series 1B and 2B Test Results Series 1B and 2B were coated and exposed for 525 exposure cycles prior to testing, but unlike Series 1A and 2B these samples were not subjected to loading prior to exposure. The results of the compressive testing program are given in Table 4.5. Table 4.5: Cylinder Series 1B and 2B Test Results Sample I.D. Coating Thickness f c MPa With Maximum Lateral Strain Maximum Axial Strain Axial Modulus Fracture Energy Exposure Cycles mm coating GPa Nm 1B-1 3.4 38.1 0.0035 0.0025 28.9 442 525 1B-2 1.5 36.7 0.0086 0.0042 28.5 1043 525 1B-3 1.5 39 0.0052 0.0036 24.7 941.4 525 2B-1 4.5 38.1 0.011 0.003 25.2 537.1 525 2B-2 2 38.9 0.0139 0.0063 26.4 1399.2 525 2B-3 3 39.1 0.0067 0.0085 28 1244.2 525 Typical stress strain plots are presented in Figure 4.8 and Figure 4.9. The complete set of test results are provided in Appendix A. Both Samples Series 2B and 1B showed improved performance with respect to the control series Modulus. Samples Series 2B with an increased coating thickness showed an increased load carrying capacity, increased axial and lateral strain capacity, and improved fracture toughness. Samples Series 1B showed a minimal increase in load carrying capacity, however the axial and lateral strain capacities and fracture toughness increased greatly due to e coating application. 71 CO a > o o — — 40-, » ***"*^^-35 J 1 — ^0. 1 Lateral Strain I Axial Strain -0.015 -0.01 -0.005 0 Strain 0.005 0.01 0.015 Figure 4.8: Typical Stress Strain Response Series 1B 0. 2 o o -0.015 -0.01 -0.005 0 Strain — 46-— 40-\ — _ o _ — o f _ on - J C IO ~ -in I u ~ \ c Lateral Strain i 1 — , 0 I Axial Strain 0.005 0.01 0.015 Figure 4.9: Typical Stress Strain Response Series 2B 4.3.4 Cylinder Test Specimens Series 1C and 2C Cylinder Sample Series 1C and 2C were not subjected to any exposure cycles. The samples were stored in the laboratory at room temperature. The results of the compressive testing program are presented in Table 4.6. Table 4.6: Cylinder Series 1C and 2C Test Results Sample Coating fc Maximum Maximum Axial Fracture Exposure I.D. Thickness MPa Lateral Axial Strain Modulus Energy Cycles With Strain mm Coating GPa Nm 1C-1 3.5 36.2 0.0066 0.004 19.4 798.5 0 1C-2 2.5 35.8 0.0097 0.004 25.5 1598.4 0 1C-3 2 34.8 0.0091 0.0032 30.2 797 0 2C-1 3 34.8 0.009 0.0032 30.2 797 0 2C-2 3.5 38 0.007 0.004 26 1087.3 0 2C-3 2 33.4 0.0114 0.0034 28.9 854.9 0 Test specimens in Series 1C and 2C exhibited similar stress strain responses to those of the samples in Series 1B and 2B, which were subjected to 525 exposure cycles. A typical stress strain plots are presented in Figure 4.10 and Figure 4.11. The complete set of stress strain responses are given in Appendix A. 73 D-E —— __— 4 6 _ — , • * X T-_ ,n—«••• \ 1 — „ on IE m i \ — ~ 5_ "J Lateral Strain r— , — , _ g j Axial Strain -0.005 0 0.005 Strain Figure 4.10: Typical Stress Strain Response Series 1C 0 . 5 — — 49-" 1 " ~ Tnfl 8 * 1 1 ' . 2G_ 1 — .-J0. —- — -Lateral Strain j i — 1 — , Axial Strain -0.005 0 0.005 Strain Figure 4.11 Typical Stress Strain Response Series 2C 4.3.5 Summary of Cylinder Strengthening Test Results Results from the compressive testing of the cylinders have been tabulated and presented in Table 4.7. The complete data set is given in Appendix A. Table 4.7: Cylinder Strengthening Test Results Summary Sample I.D. Coating Thickness mm fc MPa Maximum Lateral Strain Percent Maximum Axial Strain Percent Axial Modulus GPa Fracture Energy Nm Axial Preload MPa Exposure Cycles Modulus 0 34.4 0.0036 0.0034 26.5 346.2 0 0 1C 2.7 35.6 0.0085 0.0037 25.0 1064.6 0 0 1B 2.1 37.9 0.0058 0.0034 27.4 808.8 0 525 1A 2.3 31.1 0.0052 0.0030 21.6 511.2 36.8 525 2C 2.8 35.4 0.0091 0.0035 28.4 913.1 0 0 2B 3.2 38.7 0.0105 0.0059 26.5 1060.2 0 525 2A 3.5 36 0.0045 0.0036 25.4 585.4 32 525 Note: The above values are the averages of three tests. 4.4 Beam Strengthening Program Test Results The flexural test specimens were tested at varying ages of exposure to determine the effects of the exposure conditions with time. The other variables investigated were coating thickness and fibre content. Beam series 1 and 2 had the same fibre content, but different coating thicknesses and series 3 had a thicker coating thickness and higher fibre content. 4.4.1 Beam Series 1 Series 1 had a fibre content of approximately 24% by mass and coating thickness between 0.5 mm and 2.0 mm. The samples were subjected to a maximum of 525 exposure cycles. The results from Series 1 are summarized in Table 4.8. 75 Table 4.8: Beam Series 1 Test Results Sample I Exposure Series I.D. :Cycles Normalized Load. kN Maximum Midspan Displacement, mm Fracture Toughness, Nm Coating Thickness, mm 1 - 5 2 5 525 8.1 2.05 8.7 1.2 1 - 3 6 0 360 8.1 0.97 7.0 1.7 1 - 180 180 7.4 1.57 8.7 1.2 1 - 0 0 7.9 1.53 8.2 1.3 Note: The above reported results are the average three tests. The control series was instrumented with strain gauges on the bottom face at 0, 25 mm, 75 mm, and 125 mm from the centre to monitor the strains in the S G F R P during loading. The strain in the S G F R P was plotted (Figure 4.12) at numerous load increments to illustrate how the strain within the S G F R P evolved as the failure of beam occurred. The load and midspan displacement were also plotted during loading. Typical results for all exposure ages have been presented (Figure 4.13). Also refer to Appendix B. The load 76 displacement plots were similar for all exposure ages, however, the data sets were quite variable (Figure 4.13). The majority of the samples failed at the concrete/SGFRP interface and exhibited similar load displacement relationships. However the specimens that failed with S G F R P fracture, 1A-0, 1A-525, and 1B-525 exhibited higher midspan displacements than the specimens that failed at the S G F R P interface. The failure mode was not influenced by the exposure period. 0.5 1 1.5 2 Midspan Displacement, mm Figure 4.13: Typical Load versus Midspan Displacement Relationship -Series 1 4.4.2 Beam Series 2 Series 2 had a fibre content of approximately 25% by mass and the coating thickness between 2.5 mm and 4.0 mm. The samples were subjected to a maximum of 525 exposure cycles. The results from Series 2 are summarized in Table 4.9. The test variables of Series 2 were the same as those of Series 1, except for coating thickness. 77 Table 4.9: Beam Series 2 Test Results. Sample Series I.D. Exposure Cycles Normalized Load. kN Maximum Midspan Displacement, mm Fracture Toughness, Nm Coating Thickness, mm 2 - 5 2 5 525 8.9 2.2 16.1 2.2 2 - 3 6 0 360 11.7 1.3 12.6 4.0 2 - 1 8 0 180 12.1 1.5 15.7 3.0 2 - 0 0. 13.3 1.7 19.1 2.5 Note: The above reported results are the averages of three tests. As with Series 1, the bottom face of the S G F R P coating in Series 2 was instrumented with strain gauges at 0, 25 mm, 75 mm, and 125 mm from the center of the beam to monitor the strain distribution within the S G F R P during loading for the control series (Figure 4.14). The load versus midspan displacement relationship was similar for all of the exposure ages. (Figure 4.15). The load versus deflection curves for Series 2 show an increase in load carrying capacity after failure of the concrete portion of the beam specimen. 78 Figure 4.15: Typical Load versus Midspan Displacement Relationship - Series 2 79 4.4.3 Beam Series 3 Series 3 had a fibre content of approximately 28% by mass and coating thickness between 6.0 mm and 8.0 mm. The samples were subjected to a maximum of 525 exposure cycles. The results from Series 3 are summarized in Table 4.10. Table 4.10: Beam Series 3 Test Results. Sample ID Exposure |Cycles Normalized Load, kN Maximum Midspan Displacement, mm Fracture Toughness, Nm Coating Thickness. mm 3 - 5 2 5 525 16.8 0.8 10.7 7.3 3 - 3 6 0 360 1.8.7 0.5 7.2 7.7 3 - 1 8 0 180 17.7 0.5 7.6 7.7 3 - 0 0 19.7 1.1 15.4 6.5 Note: The above reported results are the average of three tests. As with Series 1 and 2, the bottom face of the S G F R P was instrumented with strain gauges during loading to monitor the stress distribution across the S G F R P . Strain gauges were placed at 0 mm, 25 mm, 75 mm, and 125 mm from the center of the beam (Figure 4.16). The load deflection responses for all exposure ages were similar (Figure 4.17). 80 Distance From Center, mm Figure 4.16: Typical SGFRP Strain Distribution - Series 3 20 0 "•1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Midspan Deflection, mm Figure 4.17: Typical Load versus Midspan Displacement Relationship - Series 3 4.4.4 Beam Strengthening Program Test Results Summary The flexural test results have been summarized in Table 4.11. The complete data set is provided in Appendix B. The exposure period did not effect the performance of Series 1, but the ultimate load carrying capacities of Series 2 and 3 decreased after exposure. Series 2 had the highest fracture toughness on average. Table 4.11: Beam Strengthening Program Test Results Summary Samole Series I.D. Exposure Cycles Normalized 'Maximum Load, kN Midspan I Displacement, 'mm Fracture Toughness, Nm Coating Thickness, mm 1 - 5 2 5 525 8.1 2.05 8.7 1.2 1 - 3 6 0 360 8.1 0.97 7.0 1.7 1 - 180 180 7.4 1.57 8.7 1.2 1 - 0 0 7.9 1.53 8.2 1.3 2 - 5 2 5 525 8.9 2.2 16.1 2.2 2 - 3 6 0 360 11.7 1.3 12.6 4.0 2 - 1 8 0 180 12.1 1.5 15.7 3.0 2 - 0 0 13.3 1.7 19.1 2.5 3 - 5 2 5 525 16.8 0.8 10.7 7.3 3 - 3 6 0 360 18.7 0.5 7.2 7.7 3 - 1 8 0 180 17.7 0.5 7.6 7.7 3 - 0 0 19.7 1.1 15.4 6.5 4.5 Fibre Content Test Results Fibre content testing was carried out on three samples. The samples were taken from sheets of S G F R P material fabricated for this purpose. The results are given in Table 4.12 Table 4.12: Fibre Content Test Results Sample Ideftjfication Fibre Content. % Mass Fibre Content. % Vol. Coating Series 1 and 2 26.2 14 Coating Series 3 28.0 16 82 4.6 Chloride Ion Penetration Test Results The chloride ion penetration testing was completed in accordance with ASTM C1202. Unfortunately, the results were inconclusive due to the low conductivity of the S G F R P coating. The test results are given in Table 4.13. Table 4.13 Chloride Ion Penetration Test Results. Sample Identification Fibre Content, % Mass Resistivity, R ohm-cm Sample 1 0 12 Sample 2 26 11 The test setup is illustrated in Figure 4.18. 83 Data logger (records charge passed) S G F R P coating on face exposed to NaCl solution Figure 4.18: Chloride Ion Penetration Test Set Up Schematic 84 CHAPTER 5 - DISCUSSION OF RESULTS 5.1 General Comments The analysis is presented in two main sections where the results from the cylinder strengthening test program and the beam strengthening test program are discussed. The results from the compressive loading tests are similar to previous results obtained at UBC by Banthia and Boyd 7. The results of the current test program however, did not show a large increase in the load carrying capacity due to application of the sprayed FRP coatings. No work has yet been done with respect to the S F G R P concrete composite durability in a marine environment, except for work carried out recently by Johnson 2 3 as discussed in the literature review. The experimental program showed that the S F G R P system performed poorly when subjected to full time submersion in a water bath with a minimum pH of 12, for a maximum exposure period of 90 days. The test program was successful in accelerating the degradation of the material, but given the extremes of this environment the test results of this program may not be indicative of the long term performance of this material. The results of this research program suggest that concrete S F G R P composites will be quite durable with respect to tidal environments because the simulated marine exposure had minimal effect on the concrete S G F R P composites. The nature of the application system as discussed previously in this paper outlines the difficulty associated with applying a uniform coating to small cylindrical specimens such as the ones utilized in this program. The coating thickness varied around the circumference of the specimens, and from specimen to specimen. This led to large variations in test results. The beam specimens that were coated as panels and later sawn had much more uniform coating thicknesses than the cylindrical specimens. However, the inexperience of the 85 operator still resulted in varied coating thicknesses between panels. These specimens were coated on a horizontal plane and the specimen geometry was very forgiving, with respect to coating application. However, the irregularities of the concrete/SGFRP interface caused the results of this program to be variable. Although, both testing programs provided data that illustrated the changes in the load response of the various systems and the variables examined, results form both compressive loading results and flexural load test results are not consistent enough to apply them to the development of fundamental degradation models. 5.2 Discussion of Cylinder Strengthening Test Results The S G F R P concrete composite cylinders performed very well with respect to the exposure program variables. However, the results for the program were variable and made it somewhat difficult to quantify the effects of the exposure regime. The nature of the application system as discussed in Section 3.5 outlines the difficulty associated with applying a uniform coating to small cylindrical specimens such as the ones utilized for this program. The results for the program were variable, which made it difficult to quantify the effects of the exposure program. However, the benefits of the coating application are apparent. A brief review of the above test data revealed the following trends: 1. Coating thickness was the most influential variable; 2. The axial and lateral strain capacities of the concrete were greatly increased by the application of the S G F R P confinement; 3. The fracture toughness of the cylinder specimens was greatly increased by the application of the S G F R P confinement material; 86 4. Exposure period had no apparent effect on the mechanical performance of the coated cylinders; 5. The axial preloading caused damage to some of the concrete specimens prior to the exposure period; 5.2.1 Performance of the Control Series The stress strain response of the control series with no coating exhibited a nearly linear stress - strain relationship until failure and no post peak load increase was recorded for any of the specimens. The response curves were typical of normal strength concrete with normal weight aggregate found in literature56. The axial and vertical strain levels were very low at failure. 5.2.2 Performance of the SGFRP /Concrete Composite Cylinders The samples that had the externally applied S G F R P coating exhibited a stress strain relationship with two distinct portions. The initial linear portion of the curve, the slope of which is related to the elastic modulus, was the same as that for the control series and is attributed directly to the concrete properties. The second portion of the curve is attributed to the application of the S G F R P coating, which results in the S G F R P coating providing active confinement for the concrete cylinder during loading. This portion of the response was not exhibited by the uncoated specimens. This defines that the shape of the initial portion of the curve is predominately controlled by the properties of the concrete and the shape of the second portion of the curve is controlled predominately by the S G F R P coating (Figure 5.1). 87 45 Figure 5.1: Compressive Loading Stress Strain Responses As the crushing concrete expands laterally it transfers a lateral stress outwards into the S G F R P coating until the jacket exceeds its stress or strain capacity and ruptures (Figure 5.1). A graphical presentation of the stresses exhibited on the S G F R P jacket from the concrete core is presented in Figure 5.2. 88 FrEfrht 2R Fc^lfihR Fj=Efiht Figure 5.2: Proposed Stress Distribution after Toutanji : : 4 9 As discussed previously in Section 2.10 the stress applied to the concrete by the FRP confinement is: ft = Eid where: EI = the lateral strain of the confined specimens E| = the lateral elastic modulus and is calculated as follows: Eff E, = -R where: E f = the elastic modulus of the fiber t = the thickness of the fiber R = the radius of the cylinder 89 5.2.3 Effects of the Coating Thickness The level of confinement provided by the S G F R P coatings, as expected, appears to be dependent upon the coating thickness, which controls the ultimate stiffness of the S G F R P coating confinement as supported by the findings of Toutanji4 9. A thin S G F R P coating less than 2 mm did not provide any increase in the axial load capacity, or the ultimate axial or lateral strain capacities. The thicker S G F R P coatings ranging from 2 mm - 3.5 mm, however provided a large increase in the ultimate axial and lateral strain capacities, resulting in a large increase in the fracture toughness. The thick S G F R P coatings ranging from 4 - 5.5 mm provided a large increase in the ultimate axial and lateral strain capacities and an increase in the ultimate load The samples with coatings ranging from 2 - 3.5 mm exhibited minimal increases in peak load carrying capacity. The ultimate failure mode of these specimens was a rupture failure of the S G F R P coating. The rupture surfaces in the S G F R P coatings exhibited fibre pull out and fibre fracture. The failure mode was brittle. The behaviour exhibited by the specimens with coatings ranging from 2 - 3.5 mm can be explained after Harries et a l 4 5 : • The overall stiffness of the S F G R P coating "jacket" was not sufficient to restrain the lateral expansion of the concrete core at higher loading levels; • The "jacket" initially restrains the concrete cylinder, resulting in the slight increase in ultimate load carrying capacity, but as the level of lateral expansion in the concrete cylinder increases, the expansive forces exceed the resistance of the jacket. The lateral expansion continued until the strain capacity of the jacket was reached resulting in the jacket failing in a somewhat brittle fashion. 90 As noted above, the thick S G F R P coatings ranging from 4 - 5.5 mm provided a large increase in the ultimate axial and lateral strain capacities and an increase in the ultimate load, therefore, resulting in an even greater increase in the fracture toughness of the specimens. The second portion of the stress - strain response, controlled by the S G F R P coating showed an increase in load carrying capacity until failure, (Figure 5.1). The ultimate failure of these specimens was also very brittle. The rupture surface exhibited both fibre pull out and fibre fractures. The behaviour exhibited by the specimens with coatings ranging from 4 - 5.5 mm can also be explained after Harries et a l 4 5 . : • The overall stiffness of the S F G R P coating "jacket" was sufficient to restrain the lateral expansion of the concrete cylinder resulting in the increased load carrying capacity of the specimens; • The level of confinement provided by the "jacket" increased, as the lateral expansion of the concrete increased. This resulted in an increase in the stress in the S F G R P "jacket", further increasing until the ultimate stress capacity of the jacket material was reached, resulting in a very brittle failure. Therefore, the brittle failures exhibited by the S G F R P jackets can be attributed to the following factors: • A linear stress strain response and brittle behaviour of the S G F R P . • The overall stiffness of the S G F R P "jacket", which controls the deformability of the "jacket" and the level of stress within the "jacket" at failure. • The extremely brittle failure of the thicker "jackets" was due to the large level of stress within the jacket at failure. 91 5.2.4 Effects of the Exposure Period The cylinder specimens that were subjected the simulated tidal environment exposure for 525 cycles exhibited mechanical properties similar to those of the coated specimens without any exposure cycles. The stress strain response of the samples that were exposed to the 525 cycle exhibited ultimate axial loads and ultimate axial and lateral strains that were similar to those of the samples that were not subjected to deleterious conditions. The elastic modulus values were unchanged as well. Therefore, the fracture energy of the specimens was calculated to be similar for the two series. The variation between the results of the exposed and non exposed series was not notably larger than the (within test) variation exhibited by the two test series. These variations have been attributed to variations in the coatings thickness and local flaws such as voids. The exposure period however, did cause the visual appearance of the S G F R P coating to change. The change in colour of the coating is attributed to the absorption of moisture by the coating. The coating surface was also broken down by the saltwater resulting in fibre prominence. As noted by others 2 1 ' 5 0 glass fibre polyester resin composites do not exhibit excellent durability characteristics with respect to saltwater exposure. It is possible that the length of the exposure period was not sufficient in this test program, given that visual change in the S G F R P coating was noted, but the load response of the system did not change. The short wetting cycles may also have been insufficient to cause the glass fibre polyester resin composite to become completely saturated. It was expected that the exposure period would result in damage to the polymer matrix, damage to the fibre matrix interface, and damage to the glass fibres by etching. It is possible that plasticization occurred, but the effects may have reversed upon drying because the samples were tested in a dry state. 92 5.2.5 Effects of Preloading Prior to Exposure The samples that were preloaded prior to the exposure period performed poorly under the exposure conditions. The initial intent of preloading the specimens prior to failure was to induce damage to the concrete/SGFRP interface and to the S G F R P coating itself. Therefore, accelerating the deterioration rate of the composite in the simulated tidal environment. However, the preloading appears to have damaged the concrete cylinders as well as the coatings, as evident by the reduction of the initial stiffness of the specimens after preloading. Therefore, the preload level was apparently too high. However, the review of the stress -strain response of the S G F R P material, (Figure 5.3) illustrates that the S G F R P material has a much lower elastic modulus than concrete. The proposed failure mode suggests that the concrete dilation transfers stress to S G F R P coating. Therefore, making it difficult to effectively isolate the damage of preloading to the S G F R P coating. Fig. 6. Stress-strain response of sprayed fibre reinforced polymer coupons with a 48 mm fibre. 0.000 0.005 0.010 0.015 Strain ( ) Figure 5.3: SGFRP Stress Strain Response after Banthia and Boyd 7 93 The reduction in the average maximum lateral strain for both of the sample series preloaded suggests that S G F R P coatings were damaged during the preloading operation. Unfortunately no samples were preloaded and re-tested without being subjected to the exposure period to isolate the effects of preloading from the effects of the exposure, but the samples that were only exposed did not exhibit the reduction in ultimate performance shown by those samples that were preloaded and exposed. 5.3 Discussion of Beam Strengthening Test Results The results of the flexural loads tests carried out on the beam specimens coated on the tension face were similar to those of previous study carried out at UBC by Johnson 2 3 . The S G F R P material applied on the tension face of the specimens acted as tensile reinforcement, thereby increasing the ultimate load carrying capacity and the measured midspan deflection at failure. The increase in ultimate load carrying capacity was proportional to the coating thickness. The benefits of the coating application were negatively effected by the deleterious exposure. Review of the above data suggests the following trends: 1. Ultimate load carrying capacity of Series 1(1-2 mm coating thickness) was not affected by the exposure period. 2. Ultimate load carrying capacity of Series 2 (3 - 5 mm coating thickness) and 3 (6 - 8 mm coating thickness) decreased due to the exposure. 3. The effectiveness of the coating to increase the load carrying capacity of the concrete specimens loaded in flexure was decreased by the exposure period. 4. The relationship between coating thickness and load carrying capacity is similar for exposed and unexposed specimens. 5. The exposure period didn't change the dominant failure mode of each specimen series. 94 No uncoated beam specimens were tested as part of this program. A large amount of data is readily available for concrete specimens cast from concrete with similar properties as the concrete utilized for this test program. Furthermore, since the purpose of this program was to quantify the performance of different concrete S G F R P coating thicknesses, and given that mild saline environments have been proven not to be detrimental to un reinforced concrete no tests were carried out on exposed uncoated concrete specimens. 5.3.1 Failure Modes Overview The sample geometry was chosen such that the failure of the specimens would occur at the S G F R P concrete coating interface. The samples were notched on the top half of the beam at midspan to a depth of approximately 45 mm. This geometry resulted in the first crack in the concrete section occurring at the midspan directly below the notch location. The crack propagated downward toward the bottom face of the concrete beam, resulting in a stress concentration at the S G F R P concrete interface at the crack mouth and an increased displacement rate. As the stress at the interface became larger than the shear capacity of the interface, debonding occurred at this location, reducing the stress concentration and resulting in a decrease in load. The debonding propagation continued until a point that had sufficient mechanical and or chemical bond to resist the debonding mechanism was encountered, resulting in an increase in the shear stress concentration until it became larger than the shear strength of the interface at this location, resulting in further debonding. The process continued until complete debonding occurred, (Figure:5.4). 95 Midspan Displacement, mm Figure 5.4 : Typical Load versus Midspan Displacement Plot - Series 1 The incremental nature of the debonding is also illustrated by the strain distribution recorded in the S G F R P . A typical stress distribution plot is shown in Figure 5.4. The strain gauges were located at 0, 25, 75, and 125 mm from midspan on the bottom face. The strain in the S G F R P was plotted at incremental load levels. The strain distribution pattern in the S G F R P during loading indicate the following: • Low levels of strain were measured across the bottom face of the S G F R P prior to the occurrence of first crack; • Large increase in the level of strain were recorded by the gauges at 0 and 25 mm locations after first crack; • Decrease in the strain concentration at midspan after initial debonding, and a corresponding increase in strain values 0, 25, 75 mm from midspan. It was generally noted that the strain values decreased outwards from the midspan. 96 The variation of the post break portion of the load - displacement responses and strain distributions observed during testing suggest that the chemical and mechanical bond at the interface was irregular, which may be attributed to the irregularities of the concrete surface. Review of Figure 5.5 illustrates that as the debonding occurred the stress distribution at the surface of the S G F R P is was symmetrical and became continually asymmetrical with debonding. The surface was mechanically roughened prior to S G F R P application with a grinder to remove any loose material; this was intended to improve the surface characteristics and improve the degree of mechanical interlock. However, all irregularities could not be removed from the concrete surface and hence a uniform bond strength could not be achieved. 97 5.3.2 Effects of Coating Thickness The specimens for the flexural testing were broken up into three sets based on coating thickness as follows: • Series 1: 0.5 - 2 mm; • Series 2: 2 - 4 mm; • Series 3: 5.5 - 8 mm. The effects of coating thickness are presented in Table 5.1 Table 5.1: Flexural Test Results - Control Samples Sample • Series I.D. Exposure Cycles Normalized Load,kN Maximum Midspan Displacement, mm Fracture Toughness, Nm Coating Thickness, mm 1-0 0 7.9 1.53 8.2 1.3 2 - 0 3 - 0 0 0 13.3 19.7 1.7 1.1 19.1 15.4 2.5 6.5 Note: The above values are the average of three tests. The measured midspan displacement and fracture toughness do not relate directly to the coating thickness. This is thought to be due to irregularities and variability of the concrete S G F R P interface, and the observed failure mode as noted previously. This is further illustrated by the variation in the complete set of load versus midspan displacement plots presented in Appendix B. The review of the complete data set suggests that the midspan displacement decreased as the coating thickness increased. However, the data does illustrate that the Series 2 had the highest calculated fracture toughness values. The values calculated from Series 3 test results are lower, which can be attributed to the lower midspan displacements recorded at failure. The initial failure of the Series 3 concrete S G F R P interfaces occurred at higher load levels, but the debonding rate was notably faster. 98 Analysis of the experimental data revealed a relationship between the coating thickness and the ultimate load carrying capacity of the system. The relationship developed utilizing the Trend Line Option of Microsoft Excel is as follows: Ru„= 5.7117 xln(t) +9.4111 where Rult = Ultimate Load at failure measured in kN; t = coating thickness measured in mm. The above relationship suggests that the benefit of increased coating thickness diminishes for high values of t. (Figure 5.6). 5.0 0.0 y = 5.7117Ln(t) +9.4111 R 2 = 0.8984 \ • • \ ^ • A X / • I I 1 1 , 1 1 1 2 3 4 5 6 7 8 9 t, m m Figure 5.6: Effects of Coating Thickness on the Ultimate Load At Failure 99 The load versus midspan deflection relationship was dictated by the coating thickness as follows: • The ultimate load carrying capacity of the specimens after failure of the concrete section was increased as coating thickness increased; • The initial drop in load carrying capacity after failure of the concrete section diminished as coating thickness increased. This is thought to be attributed to the increased stiffness of the thicker coatings. • The ultimate measured midspan deflection decreased for Series 3 (series with greatest thickness). This is thought to be due to the increased stiffness of the thicker coatings applied in Series 3. The above trends are illustrated in Figure 5.7. 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 Midspan Displacement, mm Figure 5.7: Comparison of Typical Load versus Midspan Deflection Plots The coating thickness also affected the ultimate failure mode of the specimens. The specimens in Series 2 and 3 all exhibited failure of the S G F R P concrete substrate bond, 100 however the specimens in Series 1, (coating thickness, < 2 mm), exhibited one of following three failure modes: 1. Debonding of the S G F R P coating from the concrete substrate. 2. A combination of Debonding of the S G F R P coating from the concrete substrate and rupture of the S G F R P coating; 3. Rupture of the S G F R P coating. The results of the Series 1 Flexural Tests are presented in Table 5.2. Table 5.2: Beam Series 1 Test Results Sample I.D. Exposure [Normalized Cycles Load. kN Maximum Midspan Displacement, mm Fracture Toughness. Nm Failure Mode Coating Thickness. mm 1 A - 0 0 6.0 0.5 0.46 3 0.5 1B - 0 0 10.0 2.07 18.4 1 1 1 C - 0 0 8.2 1.83 12.1 2 1 The review of the above data suggests the following: • The rupture of the S G F R P coating was a brittle failure mode resulting in a very low midspan deflection at failure and measured fracture toughness. • Failure modes 1 and 2 resulted in similar load midspan deflection relationships and fracture toughness. Rupture occurred in the S G F R P because the shear strength of the S G F R P concrete bond exceeded the tensile strength of the S G F R P coating. It was not possible to develop a relationship to determine the minimum thickness at which this will occur because of the variability of the S G F R P concrete bond. (Figure 5.8) 101 12 Debonding of of the S G F R P Failure Mode 0.5 1 1.5 . 2 Midspan Displacement, mm Figure 5.8: Load versus Midspan Deflection Series 1 5.3.3 Effects of the Exposure Period The exposure period negatively affected the performance of the S G F R P coating. The results have been summarized in Table 5.3. 102 Table 5.3: Exposure Program Test Results Sample Series I.D. Exposure Cycles Normalized :Load. kN 'Maximum Midspan Displacement, mm Fracture Toughness. Nm Coating Thickness, mm 1 - 525 525 8.1 2.05 8.7 1.2 1 - 3 6 0 360 8.1 0.97 7.0 1.7 1 - 180 180 7.4 1.57 8.7 1.2 1 - 0 0 7.9 1.53 8.2 1.3 2 - 5 2 5 525 8.9 2.2 16.1 2.2 2 - 3 6 0 360 11.7 1.3 12.6 4.0 2 - 1 8 0 180 12.1 1.5 15.7 3.0 2 - 0 0 13.3 1.7 19.1 2.5 3 - 5 2 5 525 16.8 0.8 10.7 7.3 3 - 3 6 0 360 18.7 0.5 7.2 7.7 3 - 1 8 0 180 17.7 0.5 7.6 7.7 3 - 0 0 19.7 1.1 15.4 6.5 Note: The above reported test resu ts are the average of three tests. Review of the above data revealed the following trends: • The performance of Series 1 was not affected by the exposure period. • The ultimate load carrying capacity of Series 2 and 3 was decreased by the exposure period and increased as the coating thickness increased. Series 2 showed a 40% reduction in ultimate load carrying capacity after 525 exposure cycles. Series 3 showed a 17% reduction in ultimate load carrying capacity after 525 exposure cycles; • No relationship between exposure period and the Maximum Midspan Deflection was apparent. • No relationship between the exposure period and the Fracture Toughness was apparent. The variability of the measured maximum midspan deflection and fracture toughness can be attributed to the variability of the S G F R P concrete bond strength. The reduction in ultimate load carrying capacity is graphically presented in Figure 5.9. 103 25.0 20.0 5.0 -I 0.0 J , 1 , , , 0 100 200 300 400 500 600 Number of Exposure Cycles Figure 5.9: Load Carrying Capacity versus Exposure Period The variation in the reduction of the measured ultimate load at failure can be attributed to variation in coating thickness between sample series and the variation of the S G F R P concrete interface strength. The load test results were normalized to account for the variation of the sample sizes. However, an overall trend in reduction of ultimate load carrying capacity is still evident Series 2 and 3. 5.4 Fibre Content Test Results Discussion The fibre content testing was carried out in accordance with ASTM D2584. The sets of samples were still tested: Sample 1 taken from Series 1 and 2 coatings had a fibre content of 26 % by mass and Sample 2 taken from Series 3 had a fibre content of 28% by mass. The 104 results of the Series 3 tests are what were to be expected. The results are similar to those of previous researcher at UBC, Boyd 3. Series 3 was sprayed with two strands of fibre being fed into the chopper gun. Series 1 and 2 were sprayed with one strand of fibre being fed into the chopper gun. Therefore, it would be expected that the fibre content of Series 3 would be significantly higher than that of Series 1 and 2. However, the application process was altered slightly for the application of 2 strands of fibre simultaneously. The adjustments were as follows: • Increasing the resin pump air pressure to increase the resin volume, therefore, reducing the amount of rebound. • Spraying of a layer of resin alone between the applications of the second resin fibre layer. The adjustments were made at the time to ensure that enough resin was applied to the surface to ensure complete saturation of the glass fibres. The adjustments in resin flow decreased the amount of rebound, however, visual observations during spraying noted that significant more fibre rebound was visible during two strand spraying operations. Therefore, the increased application rate of the resin and increased amount of rebound can be attributed as the causes of the lower than expected fibre content of Series 3 specimens. 5.5 Chloride Ion Penetration Test Results Discussion The results from this portion of the testing illustrated the extremely low permeability of the S G F R P coating material. The coulombs passed recordings were negligible for both concrete specimens coated with the resin only coating and concrete coated with glass fibre resin coating. 105 The rapid chloride permeability test (ASTM 1202) provides a rapid determination of chloride penetration resistance of concrete by measuring the electrical resistance of the concrete. The measured resistance is correlated to data from long term chloride penetration testing to quantify the chloride ion penetration resistance of the concrete. The extremely low values of coulombs passed recorded during this testing program suggest that very little moisture was able to penetrate the coatings during testing. The transfer of electrons is through the moisture in the concrete and coating, (both of these materials are poor electrical conductors). The direct results of the tests do not provide a reasonable numerical value to chloride resistance of the coated concrete, but the results do illustrate the low moisture permeability of the coated concrete tested in this program. Therefore, suggesting that chloride penetration of concrete can be greatly reduced by the addition of these coatings to the surfaces exposed to water borne chlorides. These coatings can therefore be used as effective protective coatings 5.6 Comparison of Test Results with Published Data 5.6.1 Cylinder Strengthening Test Results The application of the S G F R P coating to the concrete cylinders in this test program caused a marginal increase in the load carrying capacity. Results presented by Banthia and Boyd 7 , showed an increase in peak load of 55% for a coating application thickness of 3.5mm on 101.6 mm diameter by 203.2 mm samples. The samples in this program had a diameter of 200 + 12 mm, therefore the noted decrease in the ultimate strength improvement may be attributed to the reduction of the concrete specimen diameter/ coating thickness. Banthia and Boyd 7 also tested a series of large cylinders with a diameter of 190.6 mm and a height of 787.9 mm, resulting in a height/diameter ratio of 4. The increase in peak load due to the 3.5 mm coating thickness was 64 % for the large cylinders. Initial review of the test results presented suggests that the findings of the two test programs do not agree. However, the 106 difference of the results can be attributed to variation of specimen geometry as discussed below. The ratio of the specimen diameter/coating thickness was much larger for the small specimens tested by Banthia and Boyd 7 resulting in improved apparent performance of the S G F R P coating. As discussed previously Toutanji4 8 determined the lateral stress fi applied to concrete by the FRP confinement proportional to the inverse of the cylinder radius, R, therefore, as R increase, the effectiveness of the confinement decreases. The failure mode of the large specimen size tested by Banthia and Boyd 7 was a combination of compression and buckling failure. Therefore, resulting in the large apparent improved performance of the coated specimens because the S G F R P in this situation resisted the buckling forces as well as the lateral forces due to the compressive forces. AS a result, the moment on the specimen increased and flexural strengthening by the FRP became apparent. This idea is further supported by the variation in failure strengths of the small and large specimens tested in this study. The average compressive strengths of the uncoated specimens reported by Banthia and Boyd 7 were as follows: • small specimens 50 MPa; • large specimens 33 MPa. The lower value of compressive strength for the large specimens can be attributed to the above noted buckling failure and the decreased diameter/coating thickness. Durability studies carried out by other authors on GFRP has shown these materials to degrade with time when exposed to moist environments, or moist saline environments. As discussed in Chapter 2, numerous researchers 1 8" 2 3 , 5 0 found that the performance of these materials decreases with exposure. The researchers 5 0 attributed the break down of G F R P composites to the following factors: 107 • damage to polymer matrix; • damage to fibre matrix by leaching of the chemical coupling agent used to coat the fibre surface especially at elevated temperatures; • damage to the glass fibres due to surface etching and leaching out of some of the constituents of the fiber; • damage to the polymer matrix as in hydrolysis and plasticization may be reversible upon drying • polymer swelling caused by water adsorption resulting in the development of stresses in the composite causing debonding of fibres from the matrix. The samples in this exposure program had relatively short exposure period. The wet/dry cycles were 4 hours submersed in salt water followed by 4 hours dry. However, it may be plausible that the S G F R P material did not become fully saturated, therefore, no significant damage occurred to the S G F R P coatings other than hydrolysis and plasticization, which are reversible upon drying. Therefore, given that the specimens were dried every cycle, these degradation mechanisms would not been detected by the testing carried out in this program. 5.6.2 Flexural Load Test Results A recent study at UBC evaluated the performance of S G F R P with respect to a moist alkaline environment33. The results of this test program are different from those presented in this study as would be expected given the different variables examined. The test results presented by McKay 3 3 however, do illustrate the variability of the concrete S G F R P bond found in the study here. 108 5.7 Comparison Of Results - Flexural and Compressive Load Testing The simulated marine exposure caused minimal degradation to S G F R P concrete composite in both testing programs. The S G F R P confinement greatly increased the axial and lateral strain capacity of the concrete cylindrical specimens, the fracture toughness, and slightly increased the ultimate compressive strength in the case of the thicker coating applications. The marine exposure program did not decrease the overall performance of the S G F R P confined concrete columns. The S G F R P reinforced beam specimens performed well when tested in flexure. The application of the coating on the tensile face of the specimens increased the ultimate load at failure, maximum midspan deflection, and fracture toughness. Unlike compressive specimens, the marine exposure did cause the ultimate load carrying capacity of the coated beams to decrease. The overall reduction in ultimate strength does suggest that the strength of the S G F R P itself was decreased by the exposure period. The strength of the S G F R P interface may also have been decreased by the exposure period. However, visual observations of the interfaces of exposed and unexposed specimens did not support this concept. The S G F R P material itself was also not directly tested in tension to determine the effects of the exposure on the material itself. However, the results of the compressive loading portion of this study did not reveal any reduction in the performance of the S G F R P concrete composite. 1 0 9 CHAPTER 6 - CONCLUSIONS AND RECOMMENDATIONS 6.1 General Conclusion The research program presented in this paper was carried with the intent of evaluating the durability of sprayed polyester glass fibre reinforced polymer (SGFRP) applied to a concrete substrate and subjected to a simulated marine environment. The findings of the experimental portion of the research program are applicable to the design and execution of retrofit systems utilizing such a coating to externally reinforce concrete. However, the research completed in this program is a very small step towards what is required to property evaluate this repair system. 6.2 SGFRP Materials and Application Techniques Conclusions The polyester glass fibre reinforced polymer was pneumatically applied to the concrete surfaces with a chopper gun as discussed in Chapter 3. The polyester resin and glass fibres were applied in layers and rolled out to remove any air voids. The following conclusions were made: 1. The SGFRP material showed visual signs of deterioration resulting from the simulated marine exposure. Deterioration was in the form of colour change and fibre prominence. 2. The spray application system as utilized in this program is an excellent method to apply GFRP coating to concrete systems. An applied fibre content of 26 % by mass appears to be the optimum fibre content with respect to shoot ability and loss of fibre due to rebound. 3. The specimen geometry greatly affects the ease of application for the spray application method. The material was very easy to apply to flat surfaces, horizontal and vertical, but it was difficult to apply the material to the circular cylinder surfaces. Apply the fibres to the cylinders resulted in excessive rebound. It was also difficult to wrap the fibres to the shape of the curved surface. 110 6.3 Cylinder Strengthening Program Conclusions SGFRP was applied to concrete cylinder specimens that were subjected to 525 exposure cycles in a simulated marine environment and tested in compression to evaluate the performance of the coating. The following conclusions were made: 1. SGFRP when applied to provide external confinement to concrete cylinders results in a large increase in the strain capacity and fracture toughness. 2. The post peak load carrying capacity of concrete cylinder coated with 3-4 mm thick SGFRP coating is controlled by the low stiffness of the SGFRP "jacket". This apparent ductility is not a result of fibre pull out because SGFRP jackets thicker than 4 mm did not exhibit this post peak load carrying capacity, but rather depicted a linear increase in load followed by a brittle failure. 3. The 525 exposure cycles (approximately 6 months at 4 cycles/day, wet/dry) simulated marine exposure did not result in a loss of strength or strain capacity of the SGFRP confined concrete cylinders. 4. The SGFRP - concrete bond was still intact at the end of the exposure regime. 5. The failure mode of the unexposed and exposed SGFRP confined concrete cylinders were the same. The ultimate failure occurred when the SGFRP coating ruptured and debonded from the concrete. 6. The load capacity of concrete columns is not increased by the application of SGFRP confinement as illustrated by the outcome of the preloading exercise based on 80% preload capacity. 7. SGFRP confinement when applied to concrete does not increase the design working load of a specimen because the effects of the confinement are not evident until the specimens reach large displacements. This is further illustrated by the similarity in the initial portion of the stress strain curve for all specimens. 111 6.4 Beam Strengthening Program Conclusions 1. Concrete panels were cast and coated with various thickness SGFRP coatings on one face. The panels were then saw cut into beams and subjected to varying numbers of exposure cycles. The beams were tested in three point loading to evaluate the effects of the exposure period. 2. The effectiveness of SGFRP material to provide tensile reinforcement when bonded externally to the tensile face of concrete beams is dependent upon the coating thickness. 3. The efficiency of the SGFRP application decreases as the coating thickness increases. 4. The increase in midspan displacement, toughness, and the ultimate load carrying capacity provided by the SGFRP bonded to tensile face of a concrete beam is dependent upon the SGFRP concrete interface strength and the coating thickness. 5. The exposure period of 180, 360, and 525 8hr exposure cycles caused a decrease in the ultimate load carrying capacity of load carrying capacity of the SGFRP coated concrete beams. • Ultimate load carrying capacities of beams with 3 -5 mm coatings were as follows after exposure: o 90% after 180 cycles; o 67% after 525 cycles. • ultimate load carrying capacities of beams with 6 - 8 mm coatings were as follows after exposure: o 90% after 180 cycles; o 85% after 525 cycles; • The failure mode of the control and exposed specimens were similar. 6. The observed toughness of the SGFRP coated beams can be attributed to the incremental failure of the SGFRP concrete interface. 112 6.5 Recommendations The research program presented in this paper is only a small step towards evaluating the durability of SGFRP concrete composite. The results of the research are promising given that the most cost effective composite was used for this program. Further studies should be carried out to further evaluate the durability under marine conditions. Long term research should be carried out in conjunction with accelerated test programs, such that the data from each can be correlated. Furthermore, such data is required to develop degradation models. Ultimately such research should be focused with the intent of developing the optimum SGFRP concrete system. To optimize this retrofit technique the following research should be conducted. 1. Optimization of the spray application technique to minimize fibre rebound. 2. Evaluation of the benefits of increased curing temperature. It has been shown by researchers18 that elevated curing temperatures results in complete cross linking, which improves the mechanical properties and chemical resistance of unsaturated polyesters. 3. Durability studies to evaluate the performance of other adhesives, resins and protective coatings, such as gel coats utilized on boats. Such testing programs should include long term and accelerated testing programs, so that results from accelerated tests can be correlated to long term test data. 4. Long term field durability studies, so that these results can be compared with the results of accelerated lab exposure programs. Such studies should include programs to evaluate the deterioration of the concrete SGFRP interface, and the SGFRP material itself. 5. Accelerated durability studies to evaluate the effects of moisture movement within the concrete substrate, with regards the concrete SGFRP interface. 6. Evaluation of various surface preparation techniques. The technique utilized in this program resulted in highly variable performance of the concrete SGFRP interface. 7. Evaluations of the effects of environmental exposures with respect to the concrete - SGFRP interface. Such program should utilize direct shear testing to evaluate the transfer of stress at the concrete SGFRP. The transfer of stress at the bond can be assessed with the placement 113 of strain gauges on the SGFRP. Comparison of the stress distribution before and after the exposure period could possibly help better understand the mechanisms that cause deterioration of the SGFRP - concrete interface. 8. Application of the SGFRP coating to various structures with different geometry, loading conditions, and durability requirements, so that data can be collected with respect to the long term durability of these materials. 9. The data collected from various durability studies should be compiled, so that degradation models can be developed for design purposes. The limited studies completed to date all suggest that the strength of most of these materials is will deteriorate with time. However, this does not deem these materials as useless, but suggests a need to quantify this degradation and loss of property. 114 CHAPTER 7 - REFERENCES 1. N. Banthia et al, "Sprayed Fiber-Reinforced Polymers: From Laboratory to a Real Bridge." ACI, Concrete International. 11, (2002): 47-52. 2. Neale, K.W., and Labossiere, P., "State-of-the-Art-Report on Retrofitting and Strengthening by Continuous Fiber in Canada." Japan Concrete Institute 1 (1997): 25-39. 3. Boyd, A.J., "Rehabilitation of Reinforced Concrete Beams with Sprayed Glass Fiber Reinforced Polymer." Thesis Ph.D., University of British Columbia, 2000. 4. Debaiky, Ahmed S., Green, Mark F., Hope, Brian B., "Carbon Fiber-Reinforced Polymer Wraps for Corrosion Control and Rehabilitation of Reinforced Concrete Columns." ACI Materials Journal 2 (2002): 129-137. 5. C. Lee et al., "Accelerated Corrosion and Repair of Reinforced Concrete Columns Using Carbon Fibre Reinforced Polymer Sheets." Canadian Journal of Civil Engineering 27 (2000): 941-948. 6. N. Banthia et al., "Sprayed Fibre Reinforced Plastics (FRPs) for Repair of Concrete Structures," CSCE Advanced Composite Materials in Bridges and Structures, 2 n d International Conference (1996), 537-545. 7. Banthia, N. and Boyd, A.J., "Sprayed Fibre-Reinforced Polymers for Repair." Canadian Journal of Civil Engineering 27 (2000): 907-915. 8. Banthia, N, Civil 529 High Performance Materials in Repair and Rehabilitation of Civil Infrastructure Course Notes University of British Columbia (2002). 9. Bentur, Amon and Mindess, Sidney, Fibre Reinforced Cementitious Composites. Elsevier Science Publishers LTD, 1990. 10. ISIS Design Manual No. 4.." Strengthening Reinforced Concrete Structures with Externally - Bonded Fibre Reinforced Polymers." ISIS Canada, 2001. 11. ACI 440R-96. "State of the Art Report on Fiber Reinforced Plastic (FRP) Reinforcement for Concrete Structures," ACI Manual of Concrete Practice (2002). 12. Hull, D. and Clyne, T.W., An Introduction to Composite Materials Second Edition. New York: Cambridge University Press, 1996. 13. Peters, ST. , ed (1998), Handbook of Composites Second Edition. London, England: Chapman and Hall, 1998. 14. Sen, Rajan, Shahawy, Mohsen, Mullins, Gray, Spain, John, "Durability of Carbon Fiber-Reinforced Polymer/Epoxy/Concrete Bond in Marine Environment." ACI Materials Journal 1 (1999): 95-103. 15. M.J. Chajes et al., "Bond Force Transfer of Composite materials Plate Bonded CFRP Strips." ACI Structural Journal 2 (1996): 209-217. 115 16. Green, Mark F., Bisby, Luke A.„Beaudoin, Yves, Labossiere, Pierre,"Effect of Freeze-Thaw Cycles on the Bond Durability Between Fibre Reinforced Polymer Plate Reinforcement and Concrete." Canadian Journal of Civil Engineering 27 (2000): 949 -959. 17. Rubin, Irvin I., ed., Handbook of Plastic Materials and Technology. New York:: John Wiley and Sons, Inc. 1990. 18. Micelli, Francesco, Myers, John J. , and Murthy, Sharath S., "Performance of FRP Confined Concrete Subjected to Accelerated Environmental Conditioning." Proceedings Second International Conference on Durability of Fibre Reinforced Polymers (FRP) Composites for Construction (2002):87- 98. 19. Nishizaki, Itaru and Meiarashi, Seishi, "Long-Term Deterioration of GFRP in Water and Moist Environment." ASCE Journal of Composites For Construction 2 (2002): 21-27. 20. I I. Malvar et al., "GFRP Composites in Simulated Marine Environments." Proceedings Second International Conference on Durability of Fibre Reinforced Polymers Composites for Construction (2002): 191-201. 21. Wang, J . and Ploehn, J . , "Dynamic Mechanical Analysis of the Effect of Water on Glass Bead-Epoxy Composites." Journal of Applied Polymer Science 59 (1996): 345-357. 22. Chu, W., and Karbhari, V.M., "Characterization and modeling of Moisture and Alkali Effects on E-Glass/Vinylester Composites." Proceedings Second International Conference on Durability of Fibre Reinforced Polymers (FRP) Composites for Construction (2002): 359-369. 23. Johnson, Martin McKay, "Exposure Based Durability of FRP Strengthened Concrete." Thesis M.A.Sc, University of British Columbia, 2003. 24. Benmokrane, Brahim and Cousin, Patrice, "University of Sherbrook GFRP Durability Study Report - ISIS Project 5.17." ISIS Canada 2005. 25. Boulfiza, Mohamed and Banthia, Nemkumar, "University of Saskatchewan & University of British Columbia Durability Study Report - ISIS Project 5.17." ISIS Canada 2005. 26. Onofrei, Maria, "University of Manitoba Durability of GFRP Reinforced Concrete From Field Demonstration Structures - ISIS Project 5.17." ISIS Canada 2005. 27. Ferrier, E. and Hamelin, P.," Effect of Water Absorption on the Durability of Carbon FRP Reinforcement." Proceedings Second International Conference on Durability of Fibre Reinforced Polymers (FRP) Composites for Construction (2002): 99-111. 28. Kasumasssa Nakaba et al., "Bond Behavior between Fiber-Reinforced Polymer Laminates and Concrete." ACI Structural Journal 3 (2001): 359-366. 29. Eric J . Helmueller et al., "The Effect of Freeze-Thaw on Bond Between FRP Stay-in-Place Deck Forms and Concrete." Proceedings Second International Conference on Durability of Fibre Reinforced Polymers (FRP) Composites for Construction (2002):141-151. 30. De Lorenzis, Laura, Miller, Brian, and Nanni, Antonio, "Bond of Fiber-Reinforced Polymer Laminates to Concrete." ACI Materials Journal 3 (2001): 256-265. 116 31. Bizindavyi, L , and Neale, K.W., 'Transfer Lengths and Bond Strengths for Composites Bonded to Concrete." ASCE Journal Of Composites For Construction 4 (1999): 153-60. 32. Mack, Jaime K. and Holt, Erika E., "The Effect of Vapour Barrier Encapsulation of Concrete By FRP Strengthening Systems,." Proceedings International SAMPE Symposium and Exhibition 44 (II), 2182-2193. 33. Emmons, Peter H., Concrete Repair and Maintenance Illustrated. Kingston, Ma: R.S. Means Company, Inc. 1993. 34. C. Lee et al., "Accelerated Corrosion and Repair of Reinforced Concrete Columns Using Carbon Fibre Reinforced Polymer Sheets." Canadian Journal of Civil Engineering 27 (2000): 941-948. 35. Schueremans, L. and Van Gemert, D., "Service Life Prediction of Reinforced Concrete Structures, Based on In-Service Chloride Penetration Profiles." Durability of Building Materials and Components 8 (1999): 84-93. 36. Broomfield, John, P., Corrosion of Steel in Concrete: Understanding, Investigation and Repair. E & FN SPON, 1997. 37. Tuutti, K., "Service Life of Structures with Regard to Corrosion of Embedded Steel," Performance of Concrete In Marine Environments, ACI Special Publication 65 (1980): 223-236. 38. Hansson, Carolyn, M., "Comments on Electrochemical Measurements of The Rate of Corrosion of Steel In Concrete,." Cement and Concrete Research 14 (1984): 574-584. 39. McGrath, Patrick, F., "Development of Test Methods for Predicting Chloride Penetration into High Performance Concrete." PhD thesis, University of Toronto, 1996. 40. K.D. Stanish et al., 'Testing the Chloride Penetration Resistance of Concrete: A Literature Review," Department of Civil Engineering University of Toronto, Toronto, Ontario, Canada. 41. Marc Demers et al., "Use of FRP's For the Rehabilitation of Corroded Reinforced Concrete Columns." Proceedings Second International Conference on Durability of Fibre Reinforced Polymers (FRP) Composites for Construction (2002): 419^28. 42. Karabinis, A.I. and Rousakis, T.C., "Concrete Confined by FRP Material: A Plasticity Approach." Elsevier Engineering Structures Journal 24 (2002): 923-932. 43. Toutanji, Houssam and Deng, Yong, "Strength and Durability Performance of Concrete Axially Loaded Members Confined with AFRP Composite Sheets." Elsevier Composites Journal 33 (2002): 255-261. 44. Shi Zhang, Lin Ye and Mai, Yiu-Wing," A Study on Polymer Composite Strengthening Systems for Concrete Columns," Applied Composite Materials 7 (2000): 125-138. 45. Harries, Kent A., Kharel, Gayatri, "Behavior and Modeling of Concrete Subject to Variable Confining Pressure." ACI Materials Journal 2 (2002): 180-189. 117 46. Chaallal, Omar and Shahawy, Mohsen, "Performance of Fiber-Reinforced Polymer-Wrapped Reinforced Concrete Column under Combined Axial-Flexural Loading." ACI Structural Journal. 4 (2000): 659-668. 47. Stephen Pessiki et al., "Axial Behavior of Reinforced Concrete Columns Confined with FRP Jackets." ASCE Journal of Composites for Construction. 4 (2001): 237-245. 48. Toutanji, Houssam, A.,"Stress-Strain Characteristics of Concrete Columns Externally Confined with Advanced Fiber Composite Sheets." ACI Materials Journal 3 (1999): 397 - 404. 49. Toutanji, H. and Balaguru, P., "Durability Characteristics of Concrete Columns Wrapped With FRP Tow Sheets." Journal of Materials in Civil Engineering (1998): 52 - 57. 50. Kshirsagar, Sachin, Lopez-Anido, Roberto A., and Gupta Rakesh K., "Environmental Aging of Fiber-Reinforced Polymer-Wrapped Concrete Cylinders." ACI Materials Journal, 6 (2000): 703-713. 51. Attard, M.M. and Setunge, S., "Stress-Strain Relationship of Confined and Unconfined Concrete," ACI Materials Journal 5 (1996): 432-442. 52. Lin, Tiffany, T.Y., "Study of Structural Health Monitoring Process and Its Application on a Bridge with Innovative Sprayed Fibre Reinforced Polymer Repair." Thesis M A S c . , University of British Columbia, May 2006. 53. J.E. McDonald et al., "Selecting Durable Repair Materials: Performance Criteria -Summary," ACI Concrete International January 2002, 37-44. 118 APPENDICES Appendix A Conrtol Series, Uncoated, O Exposure Cycles 40 Axial Strain 0.004 0.006 0.008 0.01 Strain Sample Series 1A Preloaded and Subjected to 525 Exposure Cylces — 4 5 - . 40 Strain 120 Sample Series 2A Preloaded and Subjected to 525 Exposure Cylces Sample Series 2C 0 Exposure Exposure Cycles 46 0.01 Strain Sample Series 1B 525 Exposure Cycles - 4&_^ 40 008 Strain 1 2 2 Sample Series 2B 525 Exposure Cylces 123 Appendix B 124 Series 1 525 Exposure Cycles 12 T — 10 Midspan Deflection, mm Series 1 360 Exposure Cycles 0 * — n — , , , , | ° 0.2 0.4 0.6 0.8 1 1.2 Midspan Deflection, mm 125 Samples Series 1 0 Exposure Cycles 12 10 0 0.5 1 1.5 2 2.5 Midspan Displacement, mm Series 2, 525 Exposure Cycles 12 1 , 10 I o . , , _ , , 1 0 0.5 1 1.5 2 2.5 Midspan Deflection, mm 126 Series 2 0 Exposure Cylces Series 3, 360 Exposure Cycles 25 20 0.7 Midspan Deflection, mm Series 3, 180 Exposure Cycles 25 -i — _ 0-2 0.3 0.4 0.5 0.6 Midspan Deflection, mm 128 25 Sample Series 3 O Exposure Cycles Control 0.8 1 Deflection, mm 1 2 9 Sample 1B Strain Distribution 0 Exposure Cycles -9066-Distance From Center, mm Sample 2B Strain Distribution 0 Days Exposure 8606-, -150 -100 -50 0 50 100 150 Distance From Center, mm 130 Sample 3C FRP Strain Distribution 0 Exposure Cycles -7600-3QQQ Distance From Center, mm 131 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

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"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0063276/manifest

Comment

Related Items