Effect of Portland Cement on the Selected Properties of Flue Gas Desulfurization Gypsum-Based Plasters

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.

A Study of the Influence of Cement Addition and Humidity on the Mechanical Strength and Microstructure of Flue Gas Desulfurization Gypsum–Cement Plasters

“…The increase in mechanical strength that occurs for most plasters (Figure 3) between 28 and 180 days may be attributed to the formation of ettringite, thaumasite, or a mixture of ettringite and thaumasite crystals (woodfordite). The authors' previous work described the formation of these phases in gypsum-cement plasters in conditions of increased humidity [25]. The possibility of a beneficial effect of the above stages on the mechanical strength of the tested mortars is consistent with the research results of Tesch and Middendorf [45], who showed that a small amount of formed ettringite or thaumasite did not result in deterioration of the mechanical properties and durability of gypsum-lime mortars.…”

“…The SEM image of plaster 30G/12C (Figure 11A), containing of cement, shows a higher compaction degree than the other three pla in porosity that occurs with the maturation of the plaster samples (28 ing to a more compact structure, was attributed to the increasing am products, mainly the C-S-H phase, which grow on the gypsum crys spaces between them (Figures 8B,C-11B,C). Figure 12 shows an example SEM image of the 30G/10C plaster a soning, with the characteristic structures of gypsum (G), the C-S-H thaumasite (Th) [25] marked, and the EDS spectra recorded for thes 13), confirming the presence of the phases mentioned above. XRD diffr ing the presence of thaumasite and/or mixed crystals of ettringite and 28 and 180 are provided in Figures 14 and 15.…”

“…XRD diffractograms confirming the presence of thaumasite and/or mixed crystals of ettringite and thaumasite at days 28 and 180 are provided in Figures 14 and 15. Detailed explanations of the formation of these phases were provided in an earlier publication by the authors [25].…”

“…The authors of the study [25] showed that it is possible to develop plasters containing approximately half as much gypsum binder, i.e., 30% by mass, which will also meet the requirements of the standard [11] thanks to the addition of Portland cement in the amount of 6-12% by mass. Despite the confirmed formation of expansive sulfate-clay and sulfatecarbonate-silicate phases in such plasters, their presence did not negatively affect the mechanical strength of the prepared gypsum-cement system [20,25].…”

Preparation and Performance Study of High-Strength and Corrosion-Resistant Cement-Based Materials Applied in Coastal Acid Rain Areas

“…The reason why FA, GBFS, SF and DG were selected as ACMs was that FA [27,28], GBFS [28], and SF [29] affect the hydration and microstructures of cementitious materials through their filling effect and pozzolanic reaction, thus effectively improving the performance of composite cementitious materials. The addition of DG [30] helps increase the number of ettringite (AFt) crystals and promote the development of strength. P•II 52.5 grade cement was purchased from China Huarun Cement Holdings Co., Ltd. (Shenzhen, China); FA, GBFS, and DG were purchased from China Baowu Environmental Science Shanxi Resource Recycling Co., Ltd. (Shanghai, China); and SF was purchased from China Aiken Silicone Co., Ltd. (Shanghai, China).…”