Composite-improved loess with fly ash-based solid waste materials

Loess is the primary material used for engineering construction on the Chinese Loess Plateau. To address environmental issues posed by solid waste and the poor engineering properties of loess, solid waste materials from power plants were utilized to enhance loess, thereby achieving comprehensive resource utilization. In this study, the utilization of solid waste materials to improve loess is examined, and their properties, microstructure, and stabilization mechanism at different maintenance times are investigated. First, orthogonal tests were conducted on the unconfined compressive strength (UCS) of loess specimens containing cement, fly ash, and solid waste material A to derive the optimal composite proportioning scheme. Subsequently, a series of mechanical, hydraulic, and durability tests was conducted on the cured loess to evaluate the effect of the composites on the loess. The results showed that fly ash-based composites effectively enhanced the mechanical properties of loess during compression, bestowing the loess with enhanced impermeability and durability. The UCS of the improved loess specimens reached 8.25 MPa after 28 d of maintenance, while the permeability coefficient decreased to 1.01 × 10 -8 cm/s. The strength loss index of the specimens was 95.02% after 96 freeze-thaw cycles. Finally, microscopy tests were conducted to reveal the physical and chemical mechanisms by which the composites improved the loess. The composites produced numerous new gels that fill the internal pores of the loess and strengthen the connections between soil particles, resulting in a denser and more stable internal structure. The proposed methodology utilizes solid waste materials from power plants, such as fly ash, as amendment materials for secondary use and in situ abatement of loess, thereby offering environmental and economic benefits.