Waste rubber-modified sulfur-fly ash-sand composites as low CO2-emission cements

The by-product of oil desulfurization, sulfur, can be used as an eco-friendly material to replace cement. In this study, waste rubber-modified sulfur-fly ash-sand composites (WRMSFSC) were prepared by waste rubber, modified sulfur, fly ash, and sand. The effect of percentage of modified sulfur and waste rubber on the mechanical properties of WRMSFSC were investigated. The pore size distribution, mineralogy phases, microstructure, and thermal properties of WRMSFSC were characterized by NMR, XRD, FTIR, SEM, and DSC. Results indicated that the compressive and flexural bonding strength of WRMSFSC were enhanced with the increase of modified sulfur content. The flexural bonding strength of WRMSFSC containing only 2% of waste rubber increased by approximately 48.34%. Microscopic results showed that the number of macropores (>1 & mu;m) and capillary pores (0.1-1 & mu;m) in WRMSFSC were significantly reduced with the increase of modified sulfur content. The pore structure characteristic parameters were used to explain the mechanical properties of WRMSFSC. Analysis of the mechanical properties of WRMSFSC by response surface methodology (RSM) showed that the optimum modified sulfur and waste rubber content was 30% and 2%.