Effect of Gypsum on the strength of CSA treated sand

The conventional binding admixture for soil, Ordinary Portland Cement (OPC) has higher carbon footprint hence a new cement type namely Calcium sulfoaluminate (CSA) cement is examined as an effective alternate for OPC. Ye'elimite is the major constituent of CSA cement. The hydration of ye'elimite depends on the amount and reactivity of gypsum present. Depending on the amount of gypsum present, either monosulfate or ettringite is formed. Unconfined compressive strength (UCS) is used to measure the effectiveness of cementation. Since pure CSA is used in this study, the gypsum content is varied from 0% to 60% to find the optimum gypsum content. Optimum gypsum content is identified as the gypsum content which has higher initial strength and durable rate of strength gain with curing time. The results are then compared against OPC treated sand to examine CSA as an effective alternate for OPC. Scanning electron microscope (SEM) images and X-ray diffraction (XRD) technique are used to identify the type of hydration product formed.