Enhancing the mechanical behaviour of concretes through polymer modification of the aggregate-cement paste interface

A critical obstacle to the design of polymer-cement composites is its relatively large contents required for a significant improvement on concrete performances, which increased materials cost and decreased compressive strength. In this study, an asphalt emulsion, waterborne epoxy resin, and waterborne epoxy resin modified asphalt emulsion were used to pretreat aggregates for improving the toughness of concrete at relatively low polymer contents. The results showed that, for the model aggregate concrete, the partial replacement of polymer-coated aggregates could induce cracks and yielded better improvement in concrete toughness as compared to full replacement. However, the three-point bending tests showed the opposite results, compared with partial replacement, complete replacement of polymer coated aggregate increases the fracture energy which can be attributed to the interlocking effect of the gravel aggregate. The addition of water-based epoxy resin-asphalt emulsion composite emulsion showed the best improvement on concrete toughness. With 30% composite emulsion coated aggregate, concrete showed almost the same strength with 33% increase in concrete fracture energy. With 100% composite emulsion coated aggregate, concrete showed about 11.5% decrease in compressive strength, but 73.4% increase in concrete fracture energy. Increasing the polymer film thickness on the aggregate surface could significantly increase the energy consumption during the fracture process of concrete and improve its toughness.