Numerical study of the effect of ITZ on the failure behaviour of concrete by using particle element modelling

Abstract

The interface transition zone (ITZ) is the weakest area in the concrete three-phase medium, which directly affects concrete strength, stiffness, and durability. Because the ITZ has small-scale characteristics, conventional testing methods cannot be used to study its effect on concrete strength. The objective of this paper is to study the mechanism of ITZ in the process of concrete failure by means of a mesoscopic numerical model, and propose an efficient numerical simulation method for improving the numerical simulation in terms of concrete micromechanics. First, the random irregular aggregates are generated by PFC2D (Particle Flow Code in two-dimensions), and the percentage of aggregates is verified by image processing technology. Next, the contact properties of different media of concrete are defined by using the flat-joint model; based on this, the numerical simulation of Brazilian splitting test (BST) and uniaxial compression test (UCT) is carried out, and the simulation results are compared with the physical test data to verify the model. Finally, after processing the uniaxial compression and tensile test numerical simulation by using the proposed method, it was found that when the strength of ITZ is at least 70% of the strength of cement mortar, concrete can be regarded as a two-phase medium comprising aggregate and cement mortar; thus, ITZ can no longer be considered the weakest area.