Strength performance and enhancement mechanism of silty sands stabilized with cement, red mud, and phosphogypsum

Abstract

Reducing cement consumption by reutilizing solid wastes in soil stabilization and eliminating the residual by-product of cement hydration as much as possible could effectively improve the mechanical performance and economic benefits of problematic soils in underground engineering practices. This study employed red mud and phosphogypsum as additives to improve the engineering performance of cemented silty sands. A series of chemical, mechanical, and microstructural tests were conducted to investigate the optional mixing ratio of red mud and phosphogypsum to replace cement in silty sand stabilization, the strength improvement of silty sand with different total dosages of the composite binder (the mixture of cement, red mud, and phosphogypsum), the ratios of water to the composite binder, and curing ages compared with that stabilized with only ordinary Portland cement, and their mechanical performance enhancement mechanism. The results show that red mud and phosphogypsum could replace about 1/3 of cement consumption to the maximum in soil stabilization. The optional mixing ratio of cement: red mud: phosphogypsum for silty sand stabilization was 16:7:1. Compared with pure cement-stabilized silty sands, the silty sand stabilized with the composite binder achieved a superior mechanical performance at the initial age but a relatively slow increase over the curing age when the binder consumption was the same. The tensile and shear strength of silty sands stabilized with the composite binder were similar to that of only cement. The gradually disappeared calcium hydroxide and the downsized pores illustrated in microstructural observation implied that adding red mud and phosphogypsum in silty sand stabilization could not only compact the internal structure of the soil but also make up the defects of drying shrinkage and shrinkage cracking induced by the by-products of cement hydration. The results of this study can provide a reference for the resourceful utilization of red mud and phosphogypsum and for saving cement consumption in engineering practices.