A Comparative Study of Wet Flue Gas Desulfurization Gypsum with Natural Gypsum: Physicochemical and Geotechnical Properties

• WFGD gypsum was characterized and directly compared to natural gypsum. • Cement-free WFGDG bricks showed high durability under wet-dry cycles. • WFGDG exhibited superior density and geotechnical properties. • WFGDG bricks were more resilient than natural gypsum under harsh conditions. • WFGDG offers a sustainable and cost-effective alternative for building materials. In this study, wet flue gas desulfurization gypsum (WFGDG) was characterized in terms of elemental composition, morphology, mineralogy, and geotechnical properties, and they were compared to those of natural gypsum. Cement-free bricks made from both raw materials were also evaluated using compression tests, wet-dry cycles, and toxicity characteristic leaching procedures. The results revealed that the reflection peaks corresponding to calcium sulphate (CaSO 4 ) with a 90% concentration were more prominent in WFGDG than in natural gypsum. WFGDG and natural gypsum density were 2.43 g/cm 3 and 2.30 g/cm 3 , respectively. For natural gypsum, the maximum dry density and optimal moisture content were 1093 kg/m 3 and 13.5%, respectively. For WFGDG, these values were 1425 kg/m 3 and 18.5%. For curing temperatures ranging between 40 to 100°C, WFGDG bricks reached a maximum strength of 2.3 MPa at 40°C, whereas CG bricks achieved the optimal strength of 6.1 MPa at a curing temperature of 80°C. However, WFGDG bricks outperformed natural gypsum bricks in the wet-dry cycle test, indicating its suitability for application in harsh environments. According to SANS 10145, WFGDG can also be used as a Class III mortar with a minimum strength requirement of 1.5 MPa. The current study contributes to the ongoing discourse about sustainable building materials by emphasizing the advantages of using WFGDG in terms of both environmental and economic.