Discrete Element Modelling of Damage Evolution of Concrete Considering Meso-Structure of ITZ

The mechanical properties of interfacial transition zones (ITZs) have traditionally been simplified by reducing the stiffness of cement in previous simulation methods. A novel approach based on the discrete element method (DEM) has been developed for modeling concrete. This new approach efficiently simulates the meso-structure of ITZs, accurately capturing their heterogeneous properties. Validation against established uniaxial compression experiments confirms the precision of this model. The proposed model can model the process of damage evolution containing cracks initiation, propagation and penetration. Under increasing loads, cracks within ITZs progressively accumulate, culminating in macroscopic fractures that traverse the mortar matrix, forming the complex, serpentine path of cracks. This study reveals four distinct displacement patterns: tensile compliant, tensile opposite, mixed tensile-shear, and shear opposite patterns, each indicative of different stages in concrete's damage evolution. The widening angle of these patterns delineates the progression of cracks, with the tensile compliant pattern signaling the initial crack appearance and the shear opposite pattern indicating the concrete model's ultimate failure.