Effect of modified rubber powder on the mechanical properties of cement-based materials

There are two common problems in the application of rubber aggregate concrete (RAC). One problem is that the rubber aggregate floats easily, which leads to a reduction in the workability of the mixture and delamination of the matrix. Another problem is that the mechanical properties of RAC are greatly reduced after hardening due to the poor interfacial bonding between rubber and the cement matrix (R–C). In this study, a novel modification method of waste rubber powder (WRP) combining mechanochemistry action, ultrasonic energy accumulation and the coating effect was proposed. The particle size distribution, specific surface area, hydrophilicity, morphology and structure of rubber were characterized by a laser particle size analyser, scanning electron microscopy (SEM), etc. The distribution of WRP in the cement-based materials was determined. The interfacial bonding and microstructure of R–C were analysed by SEM. The compressive and flexural strengths of cement-based materials with different contents of rubber were studied. The results showed that the R–C interface was significantly improved, and rubber particles were uniformly distributed in the cement mortar. The particle size of rubber particles showed a standard normal distribution, the surface cracks and pores were filled and coated, and the hydrophilic angle decreased from 94.6° to 68.0°. The cracks and voids of the R–C interface disappeared, and the compressive and flexural strengths of the mortar increased by 70% and 50%, respectively. The R–C interface and the distribution of rubber particles were found to play a major role in influencing the mechanical properties of RAC.