Title: Effects of Carbide Slag and CO2 Curing on Physical Properties of Gypsum Plaster
Author(s): Yuli Wang, Yanchao Tian, and Junjie Wang
Publication: Materials Journal
Appears on pages(s): 169-178
Keywords: carbide slag; CO2 curing; compressive strength; gypsum plaster; softening coefficient; water resistance
Gypsum plaster is widely used in buildings for different purposes, but the low strength and weak water resistance of gypsum limit its application. To improve the properties of gypsum plaster, the effects of carbide slag (which is a waste material) and CO2 curing on the physical properties of gypsum plaster were investigated. The compressive strength and softening coefficient (or water resistance) of different samples were tested. The related mechanisms, mineral characterization, and microstructure were studied through differential thermal analysis-thermogravimetry (DTA-TG), X-ray diffraction (XRD), and scanning electron microscope (SEM) tests. The gypsum powder, carbide slag, and water were mixed together and then pressed into a disc sample under a compression pressure of 3 MPa in a cylinder mold. The disc samples were then cured in a CO2 chamber with 70% relative humidity under 25 ± 2°C for 24 hours. The results show that the replacement of 30 to 50% gypsum with carbide slag can increase the compressive strength of gypsum plaster by more than 100%, and at the same time, the softening coefficient or water resistance could be improved by more than 400%. The results from DTA-TG, XRD, and SEM show that the main minerals in the blended gypsum plaster are CaSO4·2H2O and CaCO3. The reaction between the carbide slag and the CO2 formed CaCO3, which increased the compactness, compressive strength, and the water resistance of the blended gypsum plaster. Except for the improved physical properties, the use of carbide slag can reduce the environmental impact by fixing CO2.