Abstract: Industrial waste residue combined with cement is of remarkable economic and environmental benefits in solidifying soil by enhancing soil strength and improving residue utilization. A ternary gel system composing fly ash, desulfurized gypsum, and cement is applied to solidify loess in this research. CaOH₂ and NaOH are selected as activators of the composite curing agent. Through orthogonal experiments, the influence degree of each component of the composite curing agent on unconfined compressive strength is examined, and the optimum mixing ratio is determined. On this basis, the impacts of loess water content, water-cement ratio, and early strength agent on the strength of the solidified loess are investigated and compared with those of cement-improved loess. Result shows that the strength growth rate solidified by the composite curing agent in middle and late age is higher than that of cement-improved loess, with the 90 day strength amounting to 6.85 MPa, equivalent to that of cement-improved loess with 20% cement mixing ratio. When the water content of composite solidified loess is about 20%, the strength reaches to the maximum at all ages. Triethanolamine and sodium silicate can be used as early strength agent for the composite solidified loess. In addition, XRD diffraction pattern and SEM microstructure verified the curing principle and strength law.

Key words: fly ash, desulfurized gypsum, composite solidified loess, unconfined compressive strength, orthogonal experiment, XRD test, SEM microstructure