Influence of Aggregates on Shrinkage-Induced Damage in Concrete

Abstract

Hardening stresses are generated as concrete hardens when the volume shrinkage of the concrete mortar is restrained by the aggregates. In the early stages of concrete curing, random cracking tends to occur because the structural strength of a concrete structure is relatively low and is likely exceeded by the concrete shrinkage-induced hardening stress. This is the primary cause of the initial damage in concrete. To investigate the initial damage in concrete, an exponential model for strain hardening is combined with a spline interpolation method to characterize the anisotropic hardening process in a three-phase structure that consists of aggregates, cement mortar and an interfacial transition zone (ITZ). A nonlinear analysis using a stress/strain softening damage model is then performed to analyze the characteristics of the shrinkage-induced initial damage in the concrete and the influence of the aggregates on the structural damage. To calculate the magnitude of the initial damage in concrete, damaged and undamaged concrete specimens are subjected to uniaxial loads. The results show that the shrinkage-induced damage initiates at the surfaces of aggregate particles and in the ITZs and then propagates into the cement mortar. The initial damage to the concrete is influenced by the volume fraction and geometric characteristics of the aggregate. These characteristics are analyzed using a random aggregate model and compared with computed tomography images of a cross section of concrete.