Bond behaviour improvement between infra-lightweight and high strength concretes using FRP grid reinforcements and development of bond strength prediction models

Abstract

The structural performance of a newly developed lightweight and thermally efficient alternate of normal concrete (NC) i.e. infra-lightweight concrete (ILC) had been under question due to its low elastic modulus, surface roughness, and cracking. In the present study, the structural performance of ILC has been improved by using a layer of high strength concrete (HSC) on each side of the ILC. As the efficiency of the ILC-HSC composite structure depends on the bond between them, therefore, an extensive study has been performed to assess and improve the bond strength in two parts. In the first part, shear (push-out) and tensile (pull-off) bond strength tests have been conducted on ILC-HSC specimens which revealed that the interfacial bond strength is weaker than the weakest material i.e. ILC550. Hence, the bond strength has been improved by carbon and glass fiber-reinforced polymers (CFRPs and GFRPs) with two different grid dimensions i.e. 25 mm and 38 mm in the second part. Test results indicated that both the CFRPs and GFRPs significantly improved the bond strengths and this improvement depends on the reinforcement ratios. Maximum bond strength has been achieved for GFRP-25 reinforced ILCs where shear and tensile bond reinforcement ratios of 0.492% and 0.445% increased the shear and tensile bond strengths by 331% and 456% respectively as compared to un-strengthened specimens. In addition, the comparison of experimental shear bond strengths with five commonly used prediction models revealed the inaccuracy of all the presently available models. Moreover, there is no prediction model available for tensile bond strength prediction. Therefore, two new prediction models have been developed for shear and tensile bond strengths. The comparison of experimental results with developed models has revealed the accuracy and applicability of these models for both the un-strengthened and FRP strengthened ILC-HSC composite structures.