A Five-Phase Mesoscale Numerical Analysis Method for the Sulfate Attack Process on Recycled Aggregate Concrete

Abstract

Concrete made using recycled aggregates may become less durable due to sulfate attack. In this study, the degradation of recycled aggregate concrete (RAC) under external sulfate assault was investigated using a mesoscale numerical analysis method. A random convex polygon aggregate model with five phases—(1) aggregate, (2) aggregate–old bonded mortar interface transition zone (ITZ), (3) old bonded mortar, (4) old bonded mortar–new bonded mortar ITZ, and (5) new bonded mortar—was established using a self-compiled program in order to take into account the heterogeneity of RAC. The aggregate was considered an impervious phase, but the four other phases were considered pervious. In the model, the only chemical byproduct was the ettringite that causes expansion. The proposed method for modeling sulfate attack on RAC was validated by experiments. Sulfate diffusion, the impact of ITZ thickness, water:cement ratio, and surface sulfate content were investigated. The simulation results showed that (1) there was limited influence of surface sulfate ion concentration on the rate of sulfate erosion in RAC, (2) water:cement ratio has a significant impact on sulfate resistance in RAC, and (3) the sulfate attack procedure is largely unaffected by ITZ thickness.