Combined utilization of slag, fly ash, and polyacrylamide for sustainable saline soil improvement: a win-win strategy

Saline soils are always treated as waste materials due to the salt in the soil deteriorating the soil structure, decreasing the strength, and causing salt expansion. Especially for large-scale urbanization in developing countries, how to use the waste saline soils to realize resource utilization, decrease construction costs, and further reduce carbon emissions are the biggest problems for the researchers. Hence, in this research context, a novel solid waste additive composed of slag, fly ash, and polyacrylamide, referred to as SFP, was adopted to investigate its impact on saline soil’s improvement and reinforced mechanisms based on a highway project in Urumqi, Xinjiang, China. The investigation involved laboratory experiments and Scanning Electron Microscope (SEM) analysis, specific indicators presenting the Atterberg limits, salt expansion, Unconfined Compressive Strength (UCS), resistance to freeze-thaw (FT) cycles, and water stability. The results demonstrate that the SFP additive can increase the plasticity index of the stabilized soil. From the perspective of salt expansion and UCS, the optimal SFP content is determined to be 15%, resulting in a salt expansion rate of less than 1% and approximately a threefold increase in strength compared to unstabilized saline soil. Also, the SFP additive improved the soil’s resistance to freeze-thaw cycles and enhanced water stability. SEM analysis revealed that inorganic compounds underwent chemical reactions with ions in the soil, generating a substantial amount of hydration products. When combined with the polyacrylamide, a synergistic effect substantially improved the geotechnical properties of saline soil.