The influence of limestone on cement hydration

EN specifications (EN 197) permit addition of up to 5 % limestone, mainly calcite, in "Portland cement", while worldwide much higher additions are used in special cements. However concerns exist about the performance of limestone-rich cements. These cannot begin to be addressed until the role of limestone is understood: is it a reactive admixture, or an inert filler or both? We show how calculations, supplemented by focussed experiment, can be used to elucidate the role of calcite in low amounts such that it is reactive. The findings presented in this paper demonstrate the power of modern thermodynamics as an adjunct technique for the study of paste mineralogy.