Toward a Practical Approach to Experimental Evaluation of Cracking Behaviour of GFRP-Reinforced Concrete

The low modulus of elasticity and high tensile strength of Glass Fiber Reinforced Polymer (GFRP) reinforcing bars results in designs often governed by deflection and crack control at the serviceability limit state. Bond characteristics of GFRP bars – the manner and efficiency with which force is transferred to the bar from the surrounding concrete – significantly impacts the control of cracking provided by the bar. Unlike standardized steel reinforcing bars, GFRP bars are manufactured with a variety of surface preparations and conditions – each effecting bond. To address this in design, a bond coefficient – termed kb in this work – is adopted to normalize bond characteristics of different bars and permit the use of single design equations. This paper reports a pilot study of two simple test methods intended determine this coefficient. The ASTM D7913 pull-out test is suitable for rapidly determining relative values of kb. The non-standard prism tension test has the advantage of providing quantitative, in addition to qualitative comparison of cracking behaviour as it is affected by reinforcing bar type. The authors propose the evaluation of kb using ASTM D7913 but confirming the overall bond performance using a smaller number of prism tension tests. Preliminary results presented in this paper indicate that three of the four GFRP bars considered have better bond characteristics than the ASTM A615-compliant bars to which they were compared.