Synergistic Valorization of Ternary Industrial Solid Wastes for Sustainable Loess Stabilization: Mix Optimization, Strength Evolution, and Microstructural Mechanisms

This study investigates the mechanical properties and strength formation mechanism of loess solidified with a ternary blend of fly ash, lithium slag, and magnesium slag. The mix proportion was optimized using response surface methodology with a Box–Behnken design. Unconfined compressive strength (UCS) tests, digital image correlation (DIC), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were employed for evaluation. The optimal 7-day mix (15.926 wt.% fly ash, 10.158 wt.% lithium slag, and 6.427 wt.% magnesium slag) achieved a UCS of 0.974 MPa, while the 28-day optimum (16.064 wt.% fly ash, 10 wt.% lithium slag, and 2 wt.% magnesium slag) yielded 1.834 MPa. Strength development followed a quadratic nonlinear model at early age, shifting to a linear superposition model at 28 days. XRD and SEM revealed that strength enhancement originates from synergistic pozzolanic and hydration reactions under alkaline activation, producing C-S-H gel and ettringite (AFt) that fill pores and cement soil particles. The ternary system demonstrates effective utilization of industrial solid wastes for loess stabilization.