Effects of Asphalt Modification of Paste–Aggregate Interface on the Transport and Mechanical Properties of Concrete

Abstract

The addition of polymer emulsion in cement paste improves concrete impermeability. However, a high polymer emulsion content (usually 10%–20% of the mass of cement) is typically required to significantly improve the performance of concrete, which might increase material costs and decrease the compressive strength of concrete. This study seeks to develop a better method for improving concrete impermeability without significantly decreasing the concrete strength at a relatively low polymer emulsion content. In this study, the aggregates were pretreated with asphalt emulsion to concentrate hydrophobic asphalt film in the interfacial transition zone (ITZ). The effects of asphalt emulsion-coated aggregate (ACA) on the transport and mechanical properties of concrete were investigated. The aggregates were pretreated with asphalt emulsion at dosages of 0.1%, 0.4%, 0.7%, and 1.0% mass of the coarse aggregates, and the replacement percentages of normal coarse aggregates (NCA) by ACA were 10%, 30%, 50%, 70%, and 90%. Water absorption (WA) by capillarity, compressive strength, and stress-strain curves were obtained. The porosity and microhardness of ITZ around ACA were also investigated. The results indicated that the porosity of ITZ within 20 μm of the aggregate surfaces increased over two times, and its microhardness decreased by approximately 30% when the coated asphalt emulsion content increased to 0.7% and 1.0%, thus decreasing the concrete strength by approximately 20%. The WA rate was influenced by the mutual effects of the hydrophobicity of asphalt film and increased porosity in ITZ. The proper replacement percentage of NCA by ACA (30%) improve concrete impermeability and reduce concrete brittleness without significantly decreasing the concrete strength at a relatively low asphalt emulsion content (0.4% mass of coarse aggregates).