Ground improvement of collapsible soils for building foundations using alkali-activated copper industry wastes

This is the authors' abstract. We don't add key points for this paper.

This study investigates the potential of copper industry byproducts, Mineral Processing Tailings (MPT) and Copper Smelting Slag Waste (CSSW), as alkali-activated binders for stabilization of collapsible soils as a ground improvement technique in building foundation applications. These problematic soils are particularly prone to excessive settlement upon wetting and pose threats, if not treated, to existing buildings. Soil specimens were prepared by incorporating 5–20% waste content, were activated with potassium hydroxide (3–9 M), and cured for up to 91 days. Mechanical properties were evaluated using unconfined compressive strength (UCS), Brazilian tensile strength (BTS), wave velocity, activator absorption, and collapsibility index (Ic), supported by microstructural analysis using scanning electron microscopy (SEM). While MPT exhibited slightly superior mechanical performance, both binders proved highly effective in soil stabilization. At 28 days of curing, specimens stabilized with 20% MPT and CSSW activated with 9 M KOH achieved relative UCS improvements of 87% and 86%, reaching 1.67 MPa and 1.55 MPa, respectively. The same 28-day specimens showed similar improvements in BTS (88% and 86%) and wave velocity (79% and 78%), while the collapse index decreased from 7.2% in the untreated soil to 0.11% (MPT) and 0.20% (CSSW), effectively eliminating collapse potential. Microstructural analysis indicated that the formation of denser matrices and reduced pore connectivity contributes to improved resistance to collapse upon wetting. Statistical analyses, including aligned rank transform, identified waste type, dosage, and activator concentration as key performance influencers. Separately, regression analysis revealed a strong correlation between improved submerged tensile strength and collapse reduction, underscoring the critical role of interparticle bonding in mitigating saturation-induced settlement. Overall, the findings demonstrate that copper industry wastes can be valorized as effective geopolymer stabilizers, reducing collapsibility and enhancing strength while providing a sustainable and effective solution for improving the performance of collapsible soils in building foundation systems.