Topic
Ettringite
About: Ettringite is a research topic. Over the lifetime, 2702 publications have been published within this topic receiving 67056 citations. The topic is also known as: woodfordite.
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TL;DR: In this paper, the effect of fly ash and the hemihydrate form of calcium sulfate on the properties of CSAC was studied and the results suggest that the use of Fly Ash in the presence of anhydrite accelerates the formation of a strong ettringite-rich matrix that firmly accommodated unreacted fly ash particles, both synergistically contributing to a dense microstructure.
111 citations
TL;DR: In this paper, the effect of sodium sulfate content and curing duration on the binder structure of activated slag cements was evaluated, and the most significant changes upon curing at advanced ages observed were growth of the AFt phase and an increase in silicate chain length in the C-A-S-H, resulting in higher strength.
111 citations
TL;DR: In this article, the authors show that the expansion that can be associated with delayed ettringite formation is driven by processes occurring within the paste and not by the formation of ettricite at aggregate interfaces.
Abstract: Cement pastes were cured at 80°C and examined by scanning electron microscopy, X-ray microanalysis and X-ray diffraction immediately or after storage in water for various periods at 20°C. Ettringite began to form a few days after the heat treatment, as very small crystals thinly dispersed throughout the paste in close admixture with C-S-H. It subsequently recrystallized in cavities typically 5-10 μm in size formed by dissolution of clinker grains or in other ways. There were no indications that this latter process disrupted the surrounding material. The results favour the view that the expansion that can be associated with delayed ettringite formation is driven by processes occurring within the paste and not by the formation of ettringite at aggregate interfaces.
111 citations
TL;DR: In this paper, the authors used CEM I with two w/c ratios (0.45 and 0.60) to characterize the possible altered zone and to identify the mechanisms of degradation under such conditions.
110 citations
TL;DR: In this paper, the possibility that oxyanions such as arsenate, borate, chromate, molybdate, selenate and vanadate might substitute for sulfate in the ettringite structure has been explored.
Abstract: Long-term batch leaching studies of composites of lignite combustion and gasification ashes with a calcium-based scrubber waste have shown the prominent formation of an ettringite structure phase, accompanied by reductions in solution concentrations of potentially hazardous elements such as boron and selenium. The possibility that oxyanions such as arsenate, borate, chromate, molybdate, selenate and vanadate might substitute for sulfate in the ettringite structure has been explored. There are literature reports of fully substituted borate, chromate and selenate [ettringites]*, and of two minerals with partial borate for sulfate substitution. X-ray diffraction phase pure products with chromate and selenate, substituted completely for the sulfate in ettringite, and with arsenate, borate and vanadate partially substituted for sulfate, have been synthesized at room temperature by mixing soluble Ca, Al and sulfate sources and maintaining a pH> 12 with NaOH additions. Attempts to substitute substantial amount of molybdate for sulfate were unsuccessful. The resulting phases were characterized chemically by ICAP spectrometry, ion chromatography and thermal analysis, and for phase purity and unit cell size by XRD. The speciation of the oxyanions in the substituted [ettringite] were confirmed by FTIR spectrometry. In solid solutions, the sulfate/oxyanion ratio was greater in the precipitated solid than in the synthesis solution. Chemical analyses of the [ettringites] did not give simple stoichiometries analogous to Ca6Al2(SO4)(OH)12 ·26H2O. Because nonstoichiometry can be attributed to numerous possibilities for charge balance and defects, structural formulae of the oxyanion substituted [ettringites] could not be established.
110 citations