Mesoscale modelling of triaxial concrete fracture: The role of aggregate shapes
Qingchen Liu, Deheng Wei, Yixiang Gan
Abstract
• Triaxial tests of concrete are modelled, focusing on effects of aggregate shapes. • Similar to the uniaxial strength, rougher aggregate improves the triaxial strength. • A scaling law between triaxial strengths and confining pressures is encountered. • Local stress, damage and crack are used to explain the universality. Effects of aggregate shape have become one of the research focuses on mesoscale concrete fracture. Most relevant findings are achieved from simple uniaxial tests without considering the more complex and realistic stress sustained by filed-scale engineering structures. To this end, mesoscale modelling using the finite element method (FEM) is conducted to investigate the three-phase concrete fracture behaviour subjected to triaxial compression with the presence of confining pressure. The realistic aggregate shape, characterised by the fractal dimension, is generated to emphasise the effects of aggregate morphology on the concrete strength under varying confining pressures. Quantitative evidence from a microscopic perspective on local stress, damage evolution, and crack patterns is provided to support macroscopic observations. As a result, similar to uniaxial tests, rougher aggregate with the higher fractal dimension leads to greater compressive strength of concrete. With increasing confining pressure, this effect can be amplified. We further find that the data for uniaxial-strength-normalised triaxial strength and confining pressure of concrete specimens with various aggregate shapes are well-calibrated with experimental results and can collapse onto a single universal curve. As microscopic evidence shows, the heterogeneity of stress distribution for aggregate shapes, which deviates from each other at initial loading, finally converges. Local damage exhibits a universal competition between the ITZ and aggregates, with increasing fractal dimension of aggregates, under varying confining pressures, and explains the occurrence of the scaling law in the relationship between triaxial compressive strength and confining pressure. The same competition extends to macro-cracks and is reflected in crack volume (or area) and cluster size. This study presents a pioneering effort in systematic mesoscale modelling under triaxial loading, shedding new light on the effects of the aggregate shape on the strength of concrete-like composites.