Sustainable soil stabilization using calcium sulfoaluminate cement and phosphogypsum

Various additives, including fly ash, lime, fibers, and slag, have been extensively examined to improve soil stabilization properties and achieve targeted performance standards. Among these, Calcium Sulfoaluminate (CSA) cement has garnered significant attention for its environmentally friendly profile as compared to ordinary Portland cement (OPC), alongside its rapid strength development and high durability. This study investigates the effects of substituting CSA with phosphogypsum (PG) to enhance the compressive strength of sand while addressing the recycling potential of waste produced from phosphorus manufacturing. The chemical composition of PG was analyzed using X-ray fluorescence (XRF) and X-ray diffraction (XRD), revealing calcium sulfate hemihydrate as the primary component, along with impurities such as fluorine, phosphorus, silicon, and sulfur compounds. Standardized mixture compositions containing 3%, 5% and 7% CSA and 10% water were prepared, with CSA partially replaced by PG at substitution rates of 10%, 20%, 30%, 40%, and 50%. Uniaxial compressive strength (UCS) and ultrasonic pulse velocity (UPV) tests were performed at curing intervals of 3, 7, 14, and 28 days to evaluate the influence of PG on soil stabilization properties. Additionally, scanning electron microscopy was used to analyze the microstructural changes underlying the observed strength gain. The results demonstrate that substituting 30% of CSA with PG yields the highest compressive strength after 28 days of curing, indicating the optimal replacement level. These findings highlight the dual benefits of improved soil stabilization performance and sustainable recycling of industrial byproducts, offering practical implications for eco-friendly construction and waste management practices.