Hydration products of C3A, C3S and Portland cement in the presence of CaCO3

The subject of this work is the effect of calcium carbonate on the hydration products of C(3)A, C3S and cement. Pastes made from C(3)A and C3S containing 0%, 10%, 20% and 35% w/w of chemical grade CaCO3, as well as pastes made from Portland cement containing 0%, 10%, 20% and 35% w/w limestone, were examined after 1, 2, 7 and 28 days of hydration. The hydration products in C3S and C(3)A pastes containing CaCO3, as well as in limestone cement pastes, were identified by means of powder diffraction. The effect of calcium carbonate on the hydration procedure was also recorded. It is concluded that in pastes containing CaCO3, either as a chemical reagent or as a limestone constituent, the ettringite's transformation to monosulfate is delayed, while calcium aluminate monocarbonate is preferably formed instead of monosulfate even at early ages. In addition, the hydration of C3S is accelerated and formation of some carbosilicate is observed. (C) 2000 Elsevier Science Ltd. All rights reserved.