| The ettringite formation and conversion in alite-sulphoaluminate cement paste were studied through the test of liquid composition and DTA, SEM, XRD. The results show that the solution is highly supersaturated with respect to ettringite, which leads to a large nucleation rate. The subsequent growth of the nuclei must result in the formation of a mass of fine ettringite crystal particles which surround the aluminum-bearing particles. After one day the ettringite converts to monosulphate.Monosulphate has two resources: ettringite converts to monosulphate and C4A3S|- hydrates to monosulphate. The curing condition affects the formation and the conversion of ettringite. The rate of ettringite formation is accelerated when the temperature is elevated. At higher hydration temperature, the ions diffuse rapidly, the adsorption of SO3 by C-S-H gel is decreased and the solubility of gypsum is increased. Consequently the formation amount of ettringite in the cement paste cured at the higher temperature than that in the cement paste cured in normal temperature.After cured in water for 50 days, secondly ettringite in the paste was detected. The amount of secondly ettringite is affected by the curing condition. |
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