Construction Methods of Mesoscopic Models for Concrete and Quantitative Analysis of Mesoscopic Damage

Existing mesoscopic numerical models still exhibit shortcomings in terms of the aggregate geometric fidelity, interface transition zone (ITZ) characterization, and modeling efficiency. To solve these problems, this paper establishes a two-dimensional mesoscopic model and analysis method for concrete, considering randomly distributed convex polygons of aggregate grains and a three-phase structure comprising aggregate, mortar, and ITZ. An efficient random placement algorithm based on background meshing is proposed to enable rapid and accurate model construction. The effects of aggregate geometry, spatial distribution, and ITZ on mechanical properties and damage evolution have been systematically studied. A quantitative relationship has been established between damage energy and the decay of strength and stiffness, and damage quantification indices have been proposed. The damage rates of mortar and ITZ, along with the variation characteristics of the damage variable d_c at each stage, have been quantified. Neglecting the ITZ leads to overestimation of the peak strength and stiffness of concrete while exacerbating its post-peak brittle behavior. The most significant increases occur in both stiffness decay and damage growth at 90% of peak stress. A sudden change occurs at approximately 0.17% axial strain (corresponding to 80% of peak stress). This study offers a meso-scale foundation for understanding concrete failure and designing high-performance concrete.