Clay-gypsum mortars: The influence of binder and sand ratios

• Development of eco-friendly clay-based and clay-gypsum-based mortars. • Gypsum partial substitution improves mechanical performance while maintaining the environmental benefits. • Propose a low-carbon solution for prefabricated wall panels. Prefabricating building elements minimizes material waste and enhances quality control. This study proposes a new formulation of clay-based mortars foreseen to produce prefabricated coating panels. The effect of the binder:sand ratio (1:2, 1:3 and 1:4, in volume) and clay replacement by gypsum (5 %, 10 % and 20 %, in volume) is assessed. The investigation focused on key properties, including workability, flow table consistence, setting time of the fresh mortars, linear shrinkage, bulk density, and flexural and compressive strengths of the hardened mortars. The clay content demonstrates a proportional impact on dimensional variation, with linear shrinkage exceeding 2 % in mortars with high clay content. Gypsum partial substitution has a small effect on fresh mortar properties, but it significantly reduces setting time and enhances mechanical performance. In mortars with different sand contents, replacing clay by 20 % gypsum increases compressive strength by 320 % and flexural strength by 685 %. Therefore, these optimized clay-gypsum mortars seem to have the potential for producing environmentally friendly prefabricated coating panels.