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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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Journal ArticleDOI
TL;DR: The results showed that ettringite precipitation is an effective and reliable method for sulphate removal.
Abstract: In the present study, ettringite precipitation was theoretically and experimentally evaluated as a means of sulphate removal. The results showed that ettringite precipitation is an effective and reliable method for sulphate removal. Synthetically prepared samples which were simulated to total wastewaters originating from the textile industry (sulphate concentration of 0.06 M) and to dye bath effluent (sulphate concentration of 0.22 M) were subjected to ettringite precipitation using the systems with Na2SO4–AlCl3–Ca(OH)2–NaOH, Na2SO4–AlCl3–Ca(OH)2, and Na2CO3–Na2SO4–AlCl3–Na(OH)2. An equilibrium model involving precipitation more than one solid phase and with ionic strength correction was used to predict the sulphate removal efficiency as well as solution composition. The optimum pH for ettringite precipitation in all systems was found to be around 12.0. By the application of the method, 0.06 M initial sulphate concentration was reduced down to 60 mg/L for synthetically prepared samples and 325 mg/L for re...

21 citations

Journal ArticleDOI
TL;DR: The spontaneous crystallisation of ettringite from combined calcium hydroxide (Ca(OH)2) and aluminium sulfate (Al2(SO4)3) solutions was investigated in the presence and absence of three different kinds of polycarboxylate superplasticisers as mentioned in this paper.
Abstract: The spontaneous crystallisation of ettringite from combined calcium hydroxide (Ca(OH)2) and aluminium sulfate (Al2(SO4)3) solutions was investigated in the presence and absence of three different kinds of polycarboxylate superplasticisers. The crystallisation period was limited to 10 s only to study the initial crystals, which provide the anchoring sites for most admixtures in cement. It was found that, in the absence of polycarboxylate polymers, only few, but large (l ∼ 3·5 μm), hexagonal, prismatic ettringite crystals exhibiting numerous defects on their surfaces were formed. However, when polycarboxylate polymers were present during the crystallisation, then the crystal sizes decreased to ∼ 0·5–2·1 μm. Generally, crystal sizes were found to decrease with increasing specific anionic charge of the same kind of polycarboxylate polymer. Apparently, polymers exhibiting a higher affinity to the crystal surfaces of ettringite inhibit its growth more strongly and produce smaller crystals. Furthermore, the spec...

21 citations

Journal ArticleDOI
15 Nov 2016-Fuel
TL;DR: In this paper, the surface of coal fly ash (FA) was studied using SEM, TEM, XRD and particle size measurements of non-treated FA compared to treated FA with acidic or neutral aqueous solutions, revealing the mullite skeleton as well as Ti and Fe species.

21 citations

Journal ArticleDOI
TL;DR: In this article, the stability of Supersulphated Cement (SSC) was investigated at 95°C when subjected to relative humidities of 100, 53 and 11% of water vapour.
Abstract: The stability of Supersulphated Cement (SSC) is investigated at 95°C when subjected to relative humidities of 100, 53 and 11% of water vapour. Previously [1] investigations at 25, 50, 75°C under the same conditions of humidity reported the stability of ettringite, one of the initial hydration products. At 95°C, decomposition of ettringite, is found at all humidities and is rapid at 100% relative humidity. The hydration products of cement pastes at a water cement ratio of 0.27 were determined by thermogravimetry (TG) and X-ray diffraction (XRD). The formation of the hydragarnet, plazolite is recorded during the decomposition/dehydration process enhanced by possible carbonation. Rehydration studies on the products after storage for up to 9 months were carried out using distilled water and the samples tested for ettringite content. It is concluded that ettringite in SSC is inherently unstable at 95°C.

21 citations

Journal ArticleDOI
Baohong Guan1, Wenbin Lou1, Qingqing Ye1, Hailu Fu1, Zhongbiao Wu1 
TL;DR: In this article, conduction calorimetry was applied to investigate the early hydration of calcium aluminate cement (CAC)/flue gas desulfurization (FGD) gypsum paste, supplemented with the determination of setting times and analysis of hydrates by X-ray diffraction.
Abstract: The use of by-product gypsum is an important alternative in concrete design. In present experiment, conduction calorimetry was applied to investigate the early hydration of calcium aluminate cement (CAC)/flue gas desulfurization (FGD) gypsum paste, supplemented with the determination of setting times and analysis of hydrates by X-ray diffraction (XRD). It was found that different profiles of heat evolution rate were presented depending on the CAC/FGD gypsum ratio. Two distinct exothermic peaks, associating with CAC hydration and ettringite formation respectively, appeared when the FGD gypsum content was less than 20%. Hydrate barrier mechanism was introduced to explain the difference in induction periods of the pastes with or without FGD gypsum. It is concluded that the blending of FGD gypsum accelerates the hydration of CAC for the quick formation of ettringite and generates greater hydration heat from per gram of pure CAC for the high exothermic effect of ettringite formation. The dissolution and diffusion of gypsum plays an important role of reacting controller during the hydrations of the pastes with FGD gypsum. The modified hydration process and mechanism in this case is well visualized by means of calorimetry.

21 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023244
2022439
2021175
2020161
2019166
2018143