Abstract
The influence of limestone powder (LSP) addition on the optimum gypsum (SO3) content for Portland cement with different Al2O3 content was investigated. When setting time, compressive strength and size stability were considered, the optimum SO3 content for cement having Al2O3 content of 3.5-7.2 mass% was varied from approximately 3 to 5 mass% positively depending on the Al2O3 content of cement. The influence of LSP addition on the optimum SO3 content was negligible. By the analysis of combined water, porosity, and phase composition by XRD/Rietveld method, at less SO3 content than the optimum content, with the increase of SO3 content, the cement hydration was promoted mainly in Ca aluminate and the compressive strength increased. At the more SO3 content, excess formation of expansive ettringite introduced more pores and compressive strength decreased. By the addition of LSP, the maximum compressive strength was obtained at lower SO3 content. This is attributed to the hydration acceleration for silicate minerals and increase of carbo-aluminate hydrates content. This effect was significant for cement with high C3A and C4AF content.
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