Unconfined Compressive Strength and Microstructural Characterization of Loess Stabilized with Alkali-Activated Lithium Slag and Granulated Blast Furnace Slag

Loess subgrades commonly show low strength and pronounced collapsibility upon wetting. This study proposes an alkali-activated binder composed of lithium slag (LS) and ground granulated blast furnace slag (GBFS) for loess stabilization. An orthogonal experimental design was used to prepare loess specimens with varying total binder content, LS/GBFS mass ratio, activator solid content, and initial moisture content. Unconfined compressive strength (UCS) was measured at different curing ages, and complementary microstructural characterization was conducted to clarify the strengthening mechanisms and identify the optimum mix. The results indicate that alkali-activated LS–GBFS markedly increases UCS relative to untreated loess, converting the loose fabric into a dense and continuous cemented skeleton. The failure mode shifts from plastic shear/bulging to predominantly brittle splitting, reflecting enhanced stiffness and structural integrity. For the optimum mix, 7-day and 28-day UCS values are approximately 13 and 19 times those of plain loess, respectively, and the 28-day UCS across all mixes ranges from 485 to 2645 kPa, meeting typical subgrade strength requirements. The formation of dense amorphous gel and compacted aggregates provides the primary microstructural basis for strength gain and increased brittleness.