Evaluation of Durability of Clay Stabilized with Philippine Quarry Dust-Based Geopolymer

High-plasticity clays (CH) are widely recognized in geotechnical engineering for their poor engineering behavior, including low shear strength, high compressibility, and swelling potential, yet their presence in infrastructure projects is often unavoidable. This study investigates a sustainable alternative to ordinary Portland cement (OPC) by evaluating the durability of soil–geopolymer mixtures (SGMs) incorporating quarry dust (QD), an industrial by-product from sand and gravel operations in the Philippines. Durability assessment was emphasized due to the country’s tropical climate, marked by alternating wet and dry seasons that may accelerate deterioration of stabilized soils. QD was activated using sodium silicate (SS) and sodium hydroxide (SH) and blended with CH to form SGMs. Index property tests were conducted to characterize raw materials and identify optimal mix proportions. After 28 days of curing, specimens were subjected to wetting–drying (WD) cycles consisting of 5 h of water submersion and 42 h of oven-drying at 70 °C. Mass loss and surface degradation were evaluated by brushing in accordance with ASTM procedures. The SGMs exhibited an average mass loss of 6.83% after 12 WD cycles, satisfying the Portland Cement Association (PCA) criterion of less than 7.00% for stabilized clays. These results demonstrate that QD-based geopolymers are a viable and sustainable stabilizer for CH soils in tropical environments.