Experimental Study on the Preparation and Properties of Alkali-Activated Slag-Based Flow Solidified Soil

To promote the resource recovery and utilization of construction spoil and to prepare flowable solidified soil with tunable properties and excellent construction adaptability, locally sourced construction spoil from Jinan was used as the primary raw material. A slag-based solidifying agent composed of cement, slag, fly ash, and desulfurized gypsum was prepared, together with a composite alkaline activation system consisting of calcium hydroxide and anhydrous sodium sulfate. The effects of solidifying-agent content, alkaline activator dosage, and slag-to-fly ash proportion on the workability, mechanical properties, and permeability of the flowable solidified soil were systematically investigated. The results show that solidifying-agent content significantly affects the material properties. As the content increased from 10% to 30%, the 28-day compressive strength increased from 0.94 MPa to 5.43 MPa, while the permeability coefficient decreased substantially; the best flowability occurred at intermediate contents. As the alkaline activator dosage increased from 1.8% to 4.8%, the slurry flow spread decreased from 214 mm to 193 mm and the bleeding rate decreased from 2.4% to 0.3%, while the 28-day compressive strength increased from 0.68 MPa to 0.92 MPa, indicating that alkaline activation markedly improves the water-retention capacity and mechanical properties of the solidified system. The slag-to-fly ash proportion regulates material performance through the synergistic effects of physical filling and chemical reactivity. Increasing the fly ash content improves slurry flowability but adversely affects strength development. These results provide experimental evidence and a theoretical basis for mix-proportion optimization and subsequent engineering application of alkali-activated slag-based flowable solidified soil.