Synthesis of Calcium Silicate Hydrate in Highly Alkaline System

Zhu, Guangshan; Li, Huiquan; Wang, Xingrui; Li, Shaopeng; Hou, Xinjuan; Wu, Wenfen; Tang, Qing

doi:10.1111/jace.14242

Cited by 32 publications

(10 citation statements)

References 43 publications

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“…The main reaction product for these cements, an amorphous gel or gels (actually a mix of cementitious gels) appeared on the diffractograms as a hump stretching from 25° to 35° (2θ). According to the literature, the presence of a certain amount of alkalis can accelerate initial calcium silicate hydration from PC, favoring the precipitation of portlandite and C‐S‐H gel. The ash reacted well with the Ca(OH) 2 or with the alkalis to generate more cementitious gel that took Al and Na up into its structure, forming C‐(N)‐A‐S‐H‐like gels (Figures and ).…”

Section: Resultsmentioning

confidence: 99%

Hydration mechanisms of hybrid cements as a function of the way of addition of chemicals

et al. 2018

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In this study fly ash contents of up to 50% were used to produce binders with mechanical strength greater than or equal to type CEM I 42.5R cement (reference). The specific aim pursued in this research was to determine whether the procedure used to add the chemical activator (in solid or liquid form) can affect strength development in the cement or the nature of the reaction products formed. Two experimental procedures were deployed: (a) the chemical activator was dissolved in the mixing water; (b) the chemical activator was ground, as a solid, into the fly ash. The solid-state method induced slightly higher mechanical strength than when the activator was dissolved in hydration water. The way the chemical activator was added affected not only early age reaction kinetics, but also the nature and composition of the reaction products, the liquid state favoring the formation of phases AFt and AFm. K E Y W O R D Salkali activator, calorimetric, cement, fly ash, mechanical strength

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Section: Resultsmentioning

confidence: 99%

Hydration mechanisms of hybrid cements as a function of the way of addition of chemicals

et al. 2018

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“…Therefore, high temperature could promote the reaction speed of C-S-H formation, but meanwhile, impurities would be generated. Generally, heating at high temperature is a common method to produce C-S-H [28,29]. However, from the view of engineering application, RTC-S-H is a more promising material for environmental applications because much more energy could be saved when synthesized at room temperature than that of heating at high temperature.…”

Section: Characterizationsmentioning

confidence: 99%

Characterizations of calcium silicate hydrates derived from coal fly ash and their mechanisms for phosphate removal

Tian

Sasaki

2019

DWT

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Coal fly ash is an industrial waste generated from the thermal power plant and a large amount of it could be produced annually in the world, which can cause serious environmental problems. Reutilization of coal fly ash could be imperative to alleviate the environmental pressure. Thus, in the present study, coal fly ash was used as silicon source for the synthesis of calcium silicate hydrates (C-S-Hs) though the desilication process. Two kinds of C-S-Hs was synthetized at 100°C and room temperature respectively, with the fixed Ca/Si molar ratio of 1.2, and adopted as the adsorbents for phosphate. The properties of them were characterized using XRD, SEM, FTIR, TG-DTA as well as surface area and pore analysis. Compared to C-S-H synthesized from high temperature, the C-S-H obtained at room temperature possessed high purity and larger surface area. Therefore, synthesis by agitation at room temperature could be an alternative method to produce C-S-H materials from desilication liquid of coal fly ash, and this could save infrastructure cost and energy consumption. Both C-S-H materials have good ability to immobilize phosphate pollutant (higher than 100 mg•g-1). The specific mechanisms of phosphate removal using C-S-H include several steps: firstly, phosphate ion was immobilized by binding with Ca 2+ and forming aggregates, and the C-S-H structures were gradually corroded. Eventually, hydroxyapatite was formed after the C-S-H structure was totally destroyed.

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“…C‐S‐H is commonly synthesized through calcium oxide and silica fume or chemical grade silicon source as sodium silicate with calcium source of calcium nitrate under lower temperature and the research cycle is in a quite long time. Our previous studies have shown that C‐S‐H can be successfully synthesized in model solution, whose structure and components depend on many factors such as Ca/Si and temperature 20 . The thus‐synthesized C‐S‐H shows a potential prospect to be applied as seeds to accelerate cement hydration and as absorbent material for heavy metals in wastewater 21,22 .…”

Section: Introductionmentioning

confidence: 99%

“…Our previous studies have shown that C-S-H can be successfully synthesized in model solution, whose structure and components depend on many factors such as Ca/Si and temperature. 20 The thus-synthesized C-S-H shows a potential prospect to be applied as seeds to accelerate cement hydration and as absorbent material for heavy metals in wastewater. 21,22 This research endeavors to obtain high-efficiency utilization for real DSS generated from the pretreatment process of HAFA.…”

Section: Introductionmentioning

confidence: 99%

Effect of calcium to silica ratio on the synthesis of calcium silicate hydrate in high alkaline desilication solution

et al. 2020

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High alkaline desilication solution (DSS), a high volume byproduct from the pretreatment of high-alumina fly ash, was used as low-cost mother liquor for the synthesis of calcium silicate hydrate (C-S-H). Through the combined analysis of X-ray diffraction, thermogravimetric analysis, X-ray fluorescence, 29 Si MAS NMR, and Brunauer-Emmett-Teller, the relationship between chemical composition and structure of C-S-H synthesized under Ca/Si of 0.83:1 to 2.0:1 was investigated. Silicon conversion and yield of product have a positive correlation with Ca/Si. Sodium uptake in C-S-H is inhibited as Ca/Si increases. The formation of sodium in C-S-H transfers from "bound Na" to "mobile Na" and aluminum from tetrahedrally coordinated Al (IV) to octahedrally coordinated Al (VI). The increase of Ca/Si leads to shortening of silicate chain and formation of more dimers, which causes more water bound in C-S-H. The mechanism of calcium addition on silicate chain obtained from DFT calculation primarily results from more interlayer calcium occurrence to affect bridging tetrahedron and cationic bounding states reorganization. Reasonable control for Ca/Si momentously contributes to the adjustment for composition and structure of C-S-H synthesized in DSS.

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Synthesis of Calcium Silicate Hydrate in Highly Alkaline System

Cited by 32 publications

References 43 publications

Hydration mechanisms of hybrid cements as a function of the way of addition of chemicals

Hydration mechanisms of hybrid cements as a function of the way of addition of chemicals

Characterizations of calcium silicate hydrates derived from coal fly ash and their mechanisms for phosphate removal

Effect of calcium to silica ratio on the synthesis of calcium silicate hydrate in high alkaline desilication solution

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