Geo-mechanical performance of copper slag-infused hybrid geopolymer for stabilising sandy soils under static and cyclic loads

The rising demand for sustainable, high-performance ground improvement in transportation infrastructure has driven interest in geopolymer stabilization. Traditional stabilizers like Ordinary Portland Cement (OPC) contribute heavily to carbon emissions, while single-source geopolymers often face limitations in long-term performance. To overcome these issues, this study investigates the efficiency of a hybrid geopolymer treatment for sandy soil by incorporating alkali-activated copper slag with a small dosage of OPC to improve strength and stability compared with conventional OPC and single-source copper slag geopolymers. Unconfined compressive strength testing on 28-day cured specimens showed a remarkable 94.42% strength improvement in the hybrid-treated sample compared to the conventional stabilizer. Furthermore, static Consolidated Undrained (CU) triaxial and cyclic CU triaxial tests were performed to assess shear strength and deformation behavior under different confining pressures and cyclic deviatoric stress. The static CU test confirmed that the hybrid-treated soil displayed higher shear strength than untreated soil, with cohesion and internal friction angle increasing by 629.22% and 108.22%, respectively. Additionally, hybrid samples showed lower pore water pressure buildup and superior deformation resistance than untreated and OPC-treated soils. Under cyclic loading, the hybrid-treated specimens exhibited substantial reductions in plastic and elastic strains, with the 20% copper slag + 1.5% OPC mix offering the highest resilience against permanent deformation. The resilient modulus of this mix was 98.47% higher under high confinement compared with OPC-treated soil, highlighting its superior elastic performance. With limited studies on copper slag-based systems, this approach offers a promising solution for stabilizing sports infrastructure under repeated loading.