ABSTRACT
Over the last 20 years, flue gas desulfurization gypsum (FGD gypsum) has become a valuable and widely used substitute for a natural raw material to produce plasters, mortars, and many other construction products. The essential advantages of FGD gypsum include its high purity and stability, which allow for better technical parameters compared to natural gypsum, and, until recently, its low price and easy availability. This FGD gypsum is obtained in the process of desulfurization of flue gases and waste gases in power plants, thermal power plants, refineries, etc., using fossil fuels such as coal or oil. The gradual reduction in energy production from fossil raw materials implemented by European Union countries until its complete cessation in 2049 in favor of renewable energy sources significantly affects the availability of synthetic gypsum, and forces producers of mortars and other construction products to look for new solutions. The gypsum content in commonly used light plaster mortars is usually from 50 to 60% by mass. This work presents the results of tests on mortars wherein the authors reduced the amount of gypsum to 30%, and, to meet the strength requirements specified in the EN 13279-1:2008 standard, added Portland cement in the amount of 6-12% by mass. Such a significant reduction in the content of synthetic gypsum will reduce this raw material's consumption, thus extending its availability and developing other solutions. The study presented the test results on strength, density, porosity, pore size distribution, and changes in the microstructure of mortars during up to 180 days of maturation in conditions of increased relative humidity. The results show that decreased porosity and increased mechanical strength occur due to the densification of the microstructure caused by the formation of hydration products, such as C-S-H, ettringite, and thaumasite.
ABSTRACT
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.