Physical and Mechanical Properties of Foamed Lightweight Soil Incorporated with Desulfurization Ash

To promote the utilization of industrial solid waste in subgrade filling, this study investigated desulfurization ash foamed lightweight soil (DA-FLS) with a high ash content. Various binder proportions, target wet densities (600–1500 kg/m3) and activator types were used to examine molding behavior, unconfined compressive strength (UCS) and free swell. Among the activator systems tested, only the cement–GGBS–DA binder produced mixtures that could be demolded and subsequently tested. Mixes of cement and DA without GGBS, and mixes activated by RS-W-S, calcium hydroxide or carbide slag, gave slow molding or molding failure. Mix proportion, foam dosage and target density were not varied independently. Among the mixtures investigated, the 1:4:5 blend designed at 600 kg/m3 gave a measured wet density of 638.95 kg/m3. In the 1:4:5 foamed series, 28 d UCS increased with measured wet density and reached 3.3 MPa in the densest mix tested. For several types of cement-activated mixtures with a 1:4:5 mix ratio (design dosage of 600–800 kg/m3), the 28-day free vertical expansion rate remained below 0.7%. These low values of short-term expansion indicate the potential to meet the limit requirements for lightweight roadbed fill in the Chinese standard Specifications for Design of Highway Subgrades. This study provides a laboratory basis for the preparation of lightweight roadbed fill using high dosages of desulfurization ash, indicating that the material holds potential for further engineering evaluation.