STUDIES ON CONCRETE FRACTURE BEHAVIOUR UNDER MONOTONIC AND FATIGUE LOADING: EFFECT OF HETEROGENEITY

Abstract

The fracture behaviour of concrete is complex due to its inherent material heterogeneity. In quasi-brittle materials like concrete, a considerable damage region is developed ahead of the crack tip under loading. This inelastic zone ahead of the crack tip is called the fracture process zone (FPZ) and governs the quasi-brittle nature of the concrete. The existence of such non-negligible process zone is responsible for the exhibition of the size effect in concrete. It has been observed that the fracture process zone is strongly influenced by the nature of loading and material heterogeneity, thereby complicating the characterization of fracture behaviour. In view of this, the mechanisms of FPZ development and its characterization to address the size effect issues concerning material heterogeneity and loading conditions are important. Although the effects of specimen size on FPZ characterization are well explored, its response to varying aggregate sizes remains a topic of contention within the literature. Despite numerous investigations into the impact of material heterogeneity on concrete behaviour, the complexity of this phenomenon has led to conflicting findings. Therefore, there is a need for an extensive examination of heterogeneity influences concrete fracture characteristics under different loading conditions. Further, concrete structures often undergo repetitive loading during their service life. Even though the applied loads are much lower than the static peak load, the stiffness gradually decreases, ultimately leading to structural failure. It is important to note that the fracture characteristics in the presence of fatigue loading differ from static loading. In fact, the mechanisms underlying in concrete fracture under fatigue loading are highly complex. The complexity is further added due to variability in the material heterogeneity (aggregate size). Therefore, it is important to investigate the fracture behaviour of concrete under two different loading conditions with varying aggregate size.