Comparative Study of GFRP and Steel Rebar Bonding in Concrete: Experimental Analysis and Crack Prediction

Abstract

The glass fiber reinforced polymers (GFRP) bars are considered as an alternative to steel reinforcement in certain structures cases due to their non corrosive aspect. Perhaps, they exist with different surface treatment helically wrapped (GFRP-HW) and sand coated (GFRP-S). Thus, each rebar type is performed by a particular bond behavior with the concrete and it affects the concrete crack formations. In the first part of this paper, an experimental and analytical study of the bond behaviour between the (GFRP), rebars and concrete were carried-out. Pull out test tests have been applied on concrete cylindrical slabs in order to identify experimentally the bond behaviour between the self-compacting concrete and GFRP. Various parameters were taken in account in this experimental study: the rebar diameters, the concrete age, and the rebar roughness. Based on the experimental results, the failure mode of the bond specimens, the variation of the bond load, and the bond-slip variation are analyzed. Two failure modes of the GFRP rebars were experimentally identified: the pull-out failure mode and the splitting one. According to the experimental data, it was proven that the GFRP-S rebars and the steel ones exhibit a more bond performant than that of the GFRP-HW rebars. In the second part, an analytical identification of the BPE and the CMR models was established. Subsequently, a tension tie model was extended analytically in order to predict the crack patterns of concrete elements reinforced with the GFRP rebars and steel rebars. The expressions of the cracking parameters issued from the tension tie model have been developed. It can be deduced that the GFRP-HW and GFRP-S reinforced concrete element exhibits a longitudinal strain less than that of the steel reinforcement case. Hence, the GFRP reinforced element undergoes cracks that are characterized by more important width measurements than those of the cracks deduced from the case of the reinforced steel element. Finally, the stress-strain analytical diagram of a GFRP tension member has been plotted and compared to the steel tension element.