Experimental Study on the Properties of Nano-Silica Modified Fly Ash-Cement Composite Grouting Materials

Pursuing low-carbon development in green mining requires improving the efficiency of solid waste utilization. This study developed a high-strength green cement-based composite grouting material using silicate cement and fly ash as the primary cementitious materials, with its toughness enhanced by the incorporation of nano-silica (NS). Various testing methods, including slurry property and mechanical strength tests, as well as advanced techniques such as XRD and SEM, were employed to comprehensively analyze the effects of NS dosage on hydration products, working properties, setting time, and mechanical strength. The results demonstrate that adding NS effectively reduces the initial setting time of the fly ash-cement composite slurry. Moreover, as the NS dosage increases, the fluidity, hydration rate, and compressive strength of the composite slurry initially increase and subsequently decrease. At an NS dosage of 1%, the composite slurry achieves optimal performance, with a 1% increase in fluidity, a 5.9% reduction in initial setting time, and compressive strength improvements of 12.6% and 37.8% at 3 and 90 days, respectively. Microscopic characterization indicates that the addition of an appropriate amount of NS significantly enhances the volcanic ash effect, consuming substantial amounts of Ca(OH)2 and generating abundant hydrated calcium silicate products. In addition, the unhydrated NS can also play a filling effect, significantly improving the matrix's densification. These findings provide new insights into the development of cost-effective, high-performance green grouting materials for deep coal mine engineering, offering both theoretical and practical significance.