Influence of aluminum enrichment zone on chloride ion penetration resistance in rubber cement-based materials

The incorporation of waste rubber into cement-based materials has garnered significant attention as an innovative solution to both environmental and construction challenges. This study investigated the formation and impact of an aluminum enrichment zone (AEZ) near rubber aggregates, which enhances chloride ion (Cl^-) penetration resistance in rubber cement-based materials (RC). The AEZ, consisting of tricalcium aluminate (C₃A) and its hydration products, is positioned outside and at a certain distance from the rubber-cement interfacial transition zone (R-C ITZ). The AEZ exhibits higher aluminum content and a broader distribution in its lower region compared to the upper region. The formation of this AEZ is attributed to the hydrophobic nature of the rubber, the upward movement of free water following air bubbles, and the early hydration of C₃A. The presence of the AEZ around the rubber aggregates decreases the porosity of the R-C ITZ, improving the Cl^- penetration resistance of RC. The effects of the AEZ and R-C ITZ are integrated into an ellipsoidal interfacial transition zone (EITZ). Establishing the relationship between the Cl^- permeability coefficient of the EITZ and the rubber aggregate content and particle size. Furthermore, an EITZ finite element model with uneven interface thicknesses was developed, enabling accurate prediction of the Cl^- penetration process in RC under an electric field. © 2025 Elsevier Ltd.