The introduction of the European Union's climate change legislation and the intended use of renewable energy sources instead of fossil fuels will significantly reduce the production of flue gas desulfurization (FGD) gypsum used as the raw material for gypsum mortar plasters' production. This has forced mortar producers to look for alternative materials, including gypsum-cement composites. This work investigated the mechanical strength and linear extension of four gypsum-cement mortars with the gypsum content reduced to 30%. The authors showed that the cement admixture of 6 to 12% introduced into the prepared mortars resulted in the formation of gypsum-cement mortars, which fulfill the requirements of the EN 13279-1:2008 standard concerning mechanical strength. This publication took into account the use of scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffractometry to characterize the chemical and phase composition of the mortars up to 180 days of dry air curing and increased relative humidity (RH) conditions. The formation of thaumasite, ettringite, and mixed ettringite-thaumasite phases was interesting because of their deleterious effect on the durability of plaster mortars.
Keywords: ettringite; expansion; gypsum–cement mortars; mechanical strength; thaumasite.