Parametric Study of Cohesive ITZ in Meso-scale Concrete Model

Modelling of concrete at the meso-scale provides an effective way to analyse the effects of its constituents on damage initiation and evolution, leading to better understanding and predicting structural integrity. Majority of works to date focus on models calibration and validation with experiments in either tension or compression, leaving open the question of how such models perform under complex stress states. This work presents a modelling approach that includes all key constituents of the concrete meso-structure: coarse aggregates, represented by inclusions with elastic-brittle behaviour, mortar (including cement, sand and fine aggregates), represented with plastic-damage behaviour, interfacial transition zones (ITZ) between aggregates and mortar, represented by zero-thickness cohesive interfaces, and air voids or pores. Tension and compression experiments with mortar specimens are conducted to obtain its plastic-damage constitutive law. Similar experiments with concrete with several aggregate volume fractions are conducted to obtain stress-strain behaviours for further calibration of cohesive laws and model validation. Numerical simulations show that the proposed approach with pre-calibration of mortar behaviour leads to very good agreements between the predictions of the concrete meso-structural models and the experimental results under both tension and compression. The calibration of ITZ cohesive laws is performed by a parametric study of the effects of critical stress and fracture energy on the predicted stress-strain curves and fracture patterns. The results are used to propose a practical set of ITZ cohesive parameters.