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Defects due to human actions and accidents
Published in A. M. Sowden, The Maintenance of Brick and Stone Masonry Structures, 2020
The mortar was lime-based in the original construction but had been repointed in some places with materials based on ordinary Portland Cement (OPC) and in the areas where newer bricks had been used it was based on either OPC or high alumina cement. It generally reacted in sympathy with the surrounding bricks, but its function as a jointing material did not seem to have been significantly affected by the fire. The composition of the cementitious component had radically altered; over the years, the mortar had become sulphated due to the presence of smoke, but on heating this calcium sulphate dihydrate had converted into the drier bassanite or anhydrite form.
Stability study and mineralogical evaluation of clays for lignite mine
Published in T. Szwedzicki, Geotechnical Instrumentation and Monitoring in Open Pit and Underground Mining, 2020
S. Tangchawal, S. Phuvichit, V. Pisutha-Arnond
The quantitative evaluation for clay and non-clay mineral percentages is carried out using computer program. Only the oxide content as well as the selected mineral peak are used as input data for calculation of each mineral type value. Some minerals such as gypsum, siderite, bassanite, and dolomite are not used in the calculation process due to their erratic appearance and small peak shown on the X-ray graph. In the final determination, the percentages of clay and non-clay mineral are reported as the mineralogy results of the whole sample for each soil type.
Protective Coatings Based on Silsesquioxane Nanocomposite Materials
Published in Vikas Mittal, Polymer Nanocomposite Coatings, 2016
Bogdana Simionescu, Irina-Elena Bordianu, Magdalena Aflori, Florica Doroftei, Corneliu Cotofana, Mihaela Olaru
The X-ray measurements were performed for the qualitative phase identification for both limestones exposed to SO2 dry deposition. Moreover, different phases for carbonate, sulfite, and sulfate species have been identified for both limestones (Figure 9.16): Laspra: dolomite (D)–CaMg(CO3)2, calcite (C)–CaCO3, ankerite (A)–CaMg0.32Fe0.68(CO3)2; Repedea: calcite (C)–CaCO3, magnesian calcite (CM)–Mg0.1Ca0.9CO3, quartz (Q)-SiO2; Laspra, Repedea: hannebachite (H)–CaSO3–0.5 H2O; Laspra: gypsum (G)–CaSO4 −2 H2O, epsomite (E)–MgSO4 −7 H2O, bassanite (B)–CaSO4 −0.5 H2O; Repedea: gypsum (G)–CaSO4−2 H2O, kieserite (K)–MgSO4–H2O.
Chemical and Microscopic Investigation of Ancient Mortar and Plaster from the Middle Elamite Period Tepti Ahar’s Vaulted Tomb, Southwestern Iran
Published in International Journal of Architectural Heritage, 2020
Atefeh Shekofteh, Omid Oudbashi
The existence of bassanite and anhydrite in some samples (based on the SEM observation) may be explained by invoking the effects of temperature fluctuations. In fact, small particles of hemihydrate observed much more in plasters. Bassanite or calcium sulphate hemihydrate (CaSO4·0.5H2O) is an intermediate phase between gypsum and anhydrite. It occurs under two forms, α and β, that are classified according to the mode of preparation. Dry or wet dehydration of gypsum yields hemihydrates (α-, β-) with different thermal and re-hydration behaviors (Freyer and Voigt 2003) and with different physical properties. It is unclear whether the α- and β-forms differ in structure (Ballirano et al. 2001; Bezou et al. 1995; Bushuev and Borisov 1982; Kuzel and Hauner 1987). The α-hemihydrate occurs as well-forming transparent crystals with sharp crystal edges, mainly single crystals showing idiomorphic features and uniform straight extinction. The β-form occurs as microcrystals of varying orientation whose morphology is not obvious even at high magnification (Kelley, Southard, and Anderson 1941; Kybartienė, Leškevičienė, and Valančius 2012; Lewry and Williamson 1994a; Singh and Middendorf 2007). Then, the fluffy and broken shapes may have related to the β-form of calcium sulphate hemihydrate (Figure 6e,h).
Properties and reactivity of two oxidized and unoxidized South African Highveld fine coal rejects and their density-separated fractions
Published in International Journal of Coal Preparation and Utilization, 2023
K Mphahlele, R. H. Matjie, J. R. Bunt, R.C. Uwaoma
The percentages of total sulfur in the TEP and STEM samples presented in Table 3 are comparable because these FCR samples are derived from the same Highveld coal mines. However, its distribution across the density-separated fractions is expectedly more pronounced in the density-separated fractions of the TEP sample, correlating to a higher distribution of % ash yield (coal washability characteristics) of the same coal sample. This sulfur trend could indicate that other sulfur species in the TEP sample is associated with extraneous pyrite and sulfate minerals, while a near even distribution of sulfur is observed across all forms in the density fractions of the STEM sample. Sulfate sulfur was not detected in FI1.5 of the TEP sample, illustrating its complete association with extraneous minerals. Comparably, the lowest pyrite (FeS2) percentage was reported in the FI1.5 of the TEP sample, indicating the presence of inherent pyrite in both coal samples. These results are in agreement with those reported by Moyo et al. (2019) in their sulfur speciation in South African coals. Either inherent or extraneous pyrite in the FCR stockpile oxidizes and releases SO2, which reacts with CaO from transformed inherent/extraneous calcite to form bassanite (2CaSO4.H2O), which is not contained in the ROM coal during spontaneous combustion of pyrite (Riley et al. 2012). In the presence of water, bassanite could gain water molecules to form gypsum (CaSO4.2 H2O). Furthermore, organic S and organic Ca can interact with each other to form bassanite during the spontaneous combustion of pyrite (Rautenbach, et al. 2019; Matjie et al. 2016).