Monotonic and cyclic bond responses of steel bar with steel-polypropylene hybrid fiber reinforced recycled aggregate concrete

Abstract

The bond failure between steel bars and concrete is the main reason for the strength degradation and deformation increase of structures in service. In this study, the bond behavior of steel bars with steel-polypropylene hybrid fiber reinforced recycled aggregate concrete (HFRAC) under monotonic and cyclic loadings was investigated. The acoustic emission (AE) technique was applied to monitor the bond response and the inner damage evolution of specimens during the loading process, and the microstructure of HFRAC was analyzed through the scanning electron microscope (SEM). The hysteresis curves, failure modes, bond strength degradation rate, and energy dissipation capacity, were systematically investigated by considering the effects of water-cement ratio, recycled aggregate replacement ratio, steel fiber volume fraction, and polypropylene fiber volume fraction. Experimental results demonstrated that there was more obvious degradation in the bond strength for the HFRAC specimens under cyclic loading, compared with that under monotonic loading. In the case of cyclic loading, the bond strength was degraded with the increase of the number of cycles, and the degradation rate increased quickly with the increase of the displacement amplitude. Moreover, the analysis of AE parameters measured on steel bar bonded recycled aggregate concrete (RAC) and HFRAC specimens, including the AE hits, AE energy, localization of AE events, and average frequency, was performed. Results showed that the AE technique could effectively monitor the bond damage of HFRAC specimens at different stages. A good correlation between the results of AE parameters analysis and the cracking process of specimens was confirmed. Based on the Weibull cumulative distribution function, the bond-slip models of steel bars with HFRAC under monotonic and cyclic loadings were proposed by considering the coupling effect of hybrid fibers and recycled coarse aggregates.