Influence of a Multifunctional Admixture on the Workability and Mechanical Properties of Gypsum-Sand Mortar

Gypsum-based mortars are common building materials, but their use is limited by low mechanical strength and an exceptionally rapid setting time. This study investigates the effects of a multifunctional, calcium carbonate-based powder admixture on a gypsum-sand mortar. A reference mortar was compared against a modified mortar, with fresh and hardened properties evaluated according to EN 13279-2:2014. The results show the admixture acts as a powerful plasticizer and retarder, reducing water demand for standard consistency by over 20% and extending the final setting time from 5 to 56 minutes. However, this significant improvement in workability was accompanied by a reduction in mechanical performance. At 28 days, the modified mortar exhibited a 51% decrease in flexural strength and a 17% decrease in compressive strength compared to the reference. The strength loss is attributed to the admixture’s retarding action and a slight increase in air content, which likely alter the gypsum crystal matrix. The findings highlight a clear trade-off between enhanced workability and mechanical strength.