Effect of Red Gypsum Replacement on Water Absorption and Density in Gypsum Board Composites at Room Temperature

The paper investigates the performance of red gypsum (RG) as a partial replacement for natural gypsum (NG) in insulative gypsum composites. Five batches of samples with varying RG replacement levels (0–40%) were prepared with a constant water-to-binder ratio of 1.2 and cured at ambient indoor temperature. Water absorption (W_a) and capillary absorption (W_c) were calculated to assess the porosity of the composites. Additionally, density measurements were conducted to understand the effect of RG on particle arrangement within the composites. The results indicate that an optimal 10% RG replacement yields the lowest W_a and W_c values (63.5% and 59.3%, respectively) and increases density to 1251.3 kg/m³. This improvement in particle arrangement and porosity resistance suggests that a small fraction of RG addition at 10% enhances composite quality. However, higher percentages of RG lead to decreased density and increased porosity, suggesting that RG primarily acts as a filler and does not participate in the hardening process. These findings suggest that RG can be partially used with NG in gypsum composites, providing an environmentally friendly alternative for managing RG waste in landfills and improving the performance of gypsum boards. Future research could further explore the mechanical properties and long-term performance of RG replacement composites.