High-plasticity clays (CH) are widely known in geotechnical engineering for their undesirable characteristics. These characteristics include low shear strength, high compressibility, and swelling potential, yet their presence in infrastructure projects is often unavoidable. This study aims at investigating a sustainable alternative to ordinary Portland cement (OPC) stabilization by evaluating the durability performance of soil–geopolymer mixtures (SGMs) using quarry dust (QD), an industrial by-product from sand and gravel quarrying in the Philippines. Durability testing was considered essential in this study due to the tropical climate in the Philippines, which is characterized by alternating wet and dry seasons that can significantly affect the long-term performance of stabilized soils. The QD was activated with a combination of sodium silicate (SS) and sodium hydroxide (SH) and blended with CH to form SGMs. Index property tests were conducted to characterize the raw materials and determine optimal mix proportions. After a 28-day curing period, the SGMs underwent wetting–drying (WD) cycles, where each cycle consisted of 5 hours of submersion in potable water, followed by 42 hours of oven drying at 70°C. Mass loss and soil-cement degradation were assessed by brushing the sample surfaces with a wire brush and weighing the samples, in accordance with procedures recommended by the American Standard for Testing and Materials (ASTM). The results showed an average mass loss of 6.83% after 12 WD cycles, meeting the Portland Cement Association’s (PCA) requirement of less than 7.00% for stabilized clays. These findings support the use of QD-based geopolymer as an effective and environmentally sustainable stabilizer for high-plasticity clays, particularly in tropical regions where seasonal exposure cycles pose significant durability challenges.