Alkali carbonation of calcium aluminate cements: influence of set-retarding admixtures under hydrothermal conditions |
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Authors: | T. Sugama N. R. Carciello G. Gray |
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Affiliation: | (1) Department of Applied Science, Energy Efficiency and Conservation Division, Brookhaven National Laboratory, 11973 Upton, NY, USA;(2) Department of Mechanical Engineering, Massachusetts Institute of Technology, 02139 Cambridge, MA, USA |
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Abstract: | The preferential uptake of aluminium ions by lactone and carboxylic acid groups in glucuronic-6,3-lactone and gluconic acid suggested that these organic admixtures have a high potential as set-retarding admixtures of high-temperature calcium aluminate cement slurry. However, the liberation of abundant free calcium ions caused by the adsorption of aluminium ions by the admixtures, increased the carbonation rate of hydrated cement pastes after exposure to Na2CO3-laden water at 300 C. Using inorganic acid admixtures, such as boric acid and sodium tetraborate decahydrate, the retarding ability of colloidal Ca(BO2)2 ·nH2O and aluminium hydroxide yielded by the reaction between admixture and cement was less than that of the reaction products derived from organic acid admixtures. Although Ca(BO2)2 ·nH2O in hot Na2CO3 solution was converted into CaCO3, the rate of alkali carbonation was almost the same as that of admixture-free calcium aluminate cement pastes. |
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