Effect of high temperatures on gypsum-based composites

The behaviour of several gypsum-based materials at high temperatures was investigated. Three gypsum-based binders, pure gypsum, binary gypsum-lime binder and ternary gypsum-lime-silica fume binder were exposed to temperatures up to 1000 °C. From each binder paste (binder and water) and mortar (binder and mortar and silica sand) were prepared. The basic physical and mechanical properties of the materials after heating were measured. With the exception of gypsum-lime paste, all the materials performed well at temperatures up to 400 °C. Gypsum paste achieved the best residual strength at 1000 °C (about 30% of the original value). The volume changes could be effectively reduced by adding silica sand, but the strength of the mortars was about 10% lower than the strength of the pastes. The volume changes in mortars were three times less than the volume changes of the pastes. The presence of aggregates also prevents the disintegration of gypsum-based materials. The best resistance against high temperatures was found for pure gypsum materials. The ternary materials have similar residual strength to cement-based pastes and mortars, while the behaviour of the binary materials was significantly worse.