This study investigates the potential of waste gypsum (WG) as a sustainable substitute for natural gypsum (NG) in the production of ordinary Portland cement (OPC). The WG used was collected from construction site molds and originated from the hydration of Tunisian plaster. Cement samples were prepared by grinding clinker with 3 to 5 wt% of either WG or NG using a laboratory planetary ball mill (Powteq MG 200), producing waste gypsum cement (CMWG) and natural gypsum cement (CMNG), respectively.

To evaluate the suitability of WG, both gypsum types were characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), and differential scanning calorimetry/thermogravimetric analysis (DSC/TG). XRD results showed that NG consisted mainly of gypsum dihydrate, while WG contained a mixture of dihydrate and hemihydrate phases. Thermal analysis further confirmed a significantly higher hemihydrate content in WG. These differences could influence cement hydration and setting behavior.

Despite the mineralogical differences, mechanical testing revealed that the flexural and compressive strengths of CMWG were comparable to those of CMNG at all tested ages. This indicates that replacing natural gypsum with waste gypsum does not adversely affect the mechanical performance of the resulting cement.

Overall, the results demonstrate that WG, a construction waste byproduct, can be effectively utilized as a setting regulator in OPC. This substitution contributes to resource conservation and waste valorization without compromising the cement’s structural integrity, making it a promising step toward more sustainable construction materials.