Elastic modulus of recycled aggregate concrete: a multiscale-multiphase modeling approach

Concrete is a multiscale, multiphase composite material whose elastic properties are challenging to predict, particularly when recycled aggregates are used. The inclusion of recycled aggregates introduces greater heterogeneity due to residual mortar, microcracks, and variable material properties, all of which complicate modeling efforts. Growing demand for concrete, scarcity of natural aggregates, and the environmental impacts of cement production have increased interest in recycled aggregate concrete (RAC) from construction waste as a sustainable alternative. However, RAC often exhibits reduced mechanical performance due to residual mortar, pre-existing microcracks, and variability in particle properties. While numerous experimental and numerical studies have explored the elastic modulus of RAC, existing theoretical models remain limited. Most simplify concrete as a two-phase system of mortar and aggregate, overlooking the influence of cement paste and hydration products. Poisson's ratio is commonly neglected, despite natural and recycled aggregates generally exhibiting different values. This study presents a multiphase and multiscale computational framework for predicting the elastic modulus of RAC. The model integrates nanoscale, microscale, and mesoscale interactions using the Mori-Tanaka and Generalized Self-Consistent schemes, incorporating cement paste and clinker hydration products and investigating the influence of differences in Poisson's ratio between natural and recycled aggregates on the predicted elastic modulus. The framework was validated in two stages and demonstrated good agreement with experimental results, with errors below 10%. A parametric study was performed, showing that the macroscale elastic response is governed primarily by the aggregate volume fraction and elastic stiffness, while the influence of Poisson'ratio is comparatively small.