Thermal performance of eco-efficient gypsum–desert sand blocks: applicability in hot–dry and cold climate regions

The development of green building materials aims to replace conventional construction components with sustainable and environmentally friendly alternatives. This study investigates the feasibility of incorporating desert sand as a partial replacement for gypsum plaster in the production of composite plaster blocks. Five mixtures (B1–B5) were prepared with desert sand replacement levels of 0%, 20%, 40%, 60% and 80%. The raw materials were physically and chemically characterised prior to mixing, and three specimens were tested for each mixture. The experimental program evaluated both physical properties (bulk density and porosity) and a comprehensive set of thermal properties, including thermal conductivity, thermal diffusivity, specific heat capacity, thermal effusivity and thermal resistance, along with the proposed Insulation Efficiency Index (IEI). Results indicated that increasing desert sand content enhanced density and reduced porosity, while thermal conductivity nearly doubled (0.45–0.92 W/m·K), leading to a ∼52% reduction in thermal resistance. Conversely, thermal diffusivity and effusivity increased, highlighting improved thermal inertia, whereas specific heat capacity decreased. The IEI confirmed a decline in insulation efficiency per unit mass with higher sand substitution. Overall, gypsum–desert sand composites demonstrated potential as sustainable and resource-efficient materials, with gypsum-rich mixes favouring insulation and sand-rich mixes enhancing thermal inertia, making them particularly suitable for construction in hot-arid regions with abundant desert sand.