Microscale fracture analysis of concrete interfacial transition zone based on digital image correlation

Abstract

Interfacial transition zone (ITZ) is a critical weak link between aggregate and mortar, significantly influences the overall fracture behavior and mechanical performance of concrete. However, the fracture behavior of ITZ is difficult to measure, so that simulation lacks reliable parameters. This study investigates the fracture performance of ITZ by microscale three-point bending test using scanning electron microscopy (SEM) and digital image correlation (DIC), revealing localized deformation and microcrack evolution in ITZ. Wavelet packet analysis enhances maximum principal strain analyzed by DIC to quantify micro-damage before failure stage. Phase-field fracture model is developed to simulate ITZ-driven crack propagation in concrete, incorporating experimentally measured ITZ parameters. Results show that ITZ defects drive early microcrack nucleation, leading to brittle macroscopic failure. The fracture energy G_f of ITZ is determined as 0.02969 N/mm, reflecting its low toughness due to high porosity and weak bonding. The fracture process zone (FPZ) of ITZ can be characterized by regions with high wavelet packet signal energy, which is consistent with results analyzed by DIC. Simulations neglecting ITZ effects overestimate toughness, indicating the critical role of ITZ in post-peak behavior. The integration of SEM-DIC, wavelet packet analysis, and phase-field fracture model provides mechanistic insights into the interplay between the microscale fracture behavior of ITZ and the macroscopic response of concrete.