Evaluation of Bond Characteristics of CFRP / GFRP with Concrete

Abstract

Strengthening of RC structures using different retrofitting materials has shown a substantial growth in construction industry since last decade. Fiber Reinforced Polymer (FRP) application includes a binding material (adhesive) which transfer the load on concrete to FRP. If this binding material fails to transfer the load then FRP cannot be used upto its full potential. Therefore, local Bond failure with delamination between concrete and FRP becomes one of the critical factor responsible for the performance of the structural elements. Fewer efforts have been made to understand the bond characteristics between concrete and FRP. Experimental and analytical studies provide results to predict bond characteristics between FRP and concrete. The main objective of the present study is to evaluate the bond characteristics of Glass Fiber Reinforced Polymer (GFRP) and Carbon Fiber Reinforced Polymer CFRP with concrete of different grades by changing thickness of FRP and adhesive mix proportion i.e. base to hardner proportion. The behavior of specimens subjected to bond failure is presented in this project. An experimental investigation is carried out on plain concrete specimens with different FRP fabric applications. Three grades of concrete M20, M30 and M40 are used for casting plain concrete specimen. Total 54 specimens are cast, out of which each set of 27 specimens are applied with GFRP and CFRP. From 27 specimens of GFRP, 3 sets of 9 specimens are applied with GFRP 900 gsm, GFRP 1200 gsm using 2:1 proportion of base to hardner and GFRP 900 gsm using 1:1 proportion of base to hardner. Similarly, another 27 specimens are divided in 3 sets of 9 specimens and are applied with CFRP 400 gsm, CFRP 300 gsm using 2:1 proportion of base to hardner and CFRP 400 gsm using 1:1 proportion of base to hardner. For each parameter 3 specimens are prepared. Average of 3 specimens are presented in the report. Specimens prepared for evaluating bond strength are subjected to direct tension. For applying direct tension on the specimen a special loading frame is fabricated. Measurements of displacement, strain on FRP, at every load interval are recorded during testing. Based on the test results presented in this project, it is observed that grade of concrete has no significant effect on the bond strength of concrete and FRP. GFRP 900 gsm applied with 1:1 proportion of base to hardner gives better results in terms of debonding strength compared to different GFRP and CFRP variables. For adhesive, base to hardner proportion of 1:1 is more efficient compared to 1:2 proportion of base to hardner.