Expansion of irregularly shaped aggregate induced by alkali-silica reaction: Insights from numerical modeling

Abstract

This study presents a homogenization approach to understand and simulate the heterogeneous expansion of irregularly shaped aggregate induced by alkali-silica reaction (ASR). The analysis employs a cubic representative volume element (RVE) containing a single reactive aggregate with an arbitrary shape embedded in a mortar matrix. At the aggregate level, ASR expansion is characterized by applying a homogeneous volumetric strain inside the internal structure of the reactive aggregate based on a first-order reaction kinetics. On the RVE scale, ASR expansion is formulated as a series of diffusion processes involving the formation of ASR products and their resulting expansion. By discretizing the RVE, a homogenization approach was proposed to link the homogeneous expansion rate at the aggregate level with the heterogeneous expansion strain at the RVE level. The model captures the heterogeneity of ASR expansion produced by reactive aggregate with arbitrary geometries by assigning anisotropic expansion capacity in different directions as a function of aggregate volume and size. The model was calibrated and validated using experimental data from literature. Results demonstrate that ASR expansion increases with aggregate size in the expansion direction for a given aggregate volume, and also with overall aggregate volume for a constant aggregate size in expansion direction. In addition, the simulations show that ASR-induced cracks in the mortar matrix initially form around the surface of reactive aggregate, particularly along the major axis (the direction of the maximum aggregate length) and around sharp corners of the irregularly shaped aggregate.