Expansive clays pose significant challenges in civil engineering due to their high shrink–swell potential, which can compromise stability and cause structural damage. This study adopts a phased approach to develop effective stabilizer blends by integrating gypsum into industrial by-products, such as fly ash and slag, to enhance the durability of smectite-rich clay. In the first phase, gypsum-free blends were formulated to investigate the combined effects of additives and determine the optimal stabilizer content. The best-performing mix was then tested in a field implementation phase to validate its performance under real-world conditions. In the later phase, gypsum was incorporated and evaluated under wetting–drying (W–D) cycles to simulate environmental moisture fluctuations. The gypsum content was limited to avoid excessive sulfate reactions, particularly ettringite formation. An integrated framework, including strength testing, chemical assessment, and mineralogical analysis, was applied to unmodified, gypsum-modified, and gypsum-modified samples subjected to W–D cycling. Chemical treatment significantly improved strength, increasing the unconfined compressive strength (0.31 MPa) of untreated soil by about 6–8 times, with Class C fly ash and slag providing the best performance. The gypsum-modified blend retained ∼54 % of its initial strength after five W–D cycles, demonstrating improved resistance to moisture-induced deterioration. Mineralogical analyses indicated transformations such as smectite modification, ettringite formation, and calcite precipitation. These findings underscore gypsum’s role in enhancing the performance of expansive soils with moisture fluctuations and contribute to advancing stabilization strategies for resilient transportation infrastructure.
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