Experimental and simulation study of rubber/cement paste interface modified by waste paint and silica in two stages

The processing of waste tires as one of the raw materials into rubber cement-based materials is gradually developing as an effective method for waste disposal, but the addition of rubber particles can adversely affect the mechanical properties of concrete, and a large number of studies have shown that the weak interfacial transition zone (ITZ) between rubber and cement matrix is one of the key factors limiting the material properties. To address this problem, this paper adopts a bottom-up investigation of the interfacial modification mechanism of rubber cement paste from molecular to macro scales, so as to evaluate the effects of one-stage and two-stage modification of the rubber surface using polyacrylic paint and silica powder on the mechanical properties of rubber-cement paste. Mechanical property tests show that the modified rubber cement paste increased the flexural strength by 13%-34% and the compressive strength by 12%-27% at 28 d age. Contact angle tests and SEM-EDS analysis verify the bridging effect of the modifiers on the interface between rubber and cement paste. Finally, molecular dynamics (MD) simulations reveal that the modified interfacial models have a maximum increase of 38% in pullout force and 71.8% in adhesion energy. Combined with RDF analysis, the modification mechanism is found to enhance interfacial bonding mainly through non-bonding interactions, which explains the mechanism of the one-stage and two-stage modifications from the molecular scale.