Experimental study on fracture behaviour of concrete after low-cycle reciprocating loading

Abstract

To fully understand the fracture behaviour of concrete after low-cycle reciprocating loading, a series of experiments are carried out using compact tension specimens. An improved wedge splitting device for adaptive loading is proposed to relieve the brittle unloading process during the concrete fracture tests. Due to the additional springs, the complete stress–strain curves representing concrete fracture are measured and recorded, including the evolution of micro-cracks, damage accumulation, and ultimate fracture stages. Moreover, a group of specimens is designed to split directly under quasi-static loading for comparison. Both the measured load–strain curves and load-CMOD curves are given and analysed to determine the fracture toughness and fracture energy with the double-K fracture model. The results show that the reciprocating loading changes the failure pattern and that more failures occur around the coarse aggregates, causing the relative ratio up to over 160%. When subjected to a limited number of low-cycle reciprocating loadings, concrete generates more micro-cracks or damage that result in an earlier crack initiation and a lower critical force, as well as a smaller fracture energy. Meanwhile, the measured values of the initiation force, the initiation toughness and the unstable toughness increase slightly because the weaker bond zones have accomplished fracture, and the rest performance of concrete specimen is mainly determined by the properties of coarse aggregates. The results indicate that the bearing capacity of concrete decreases and the deformation becomes more brittle as concrete undergoes reciprocating loading.