Influência da mineralogia de fíleres carbonáticos na hidratação de cimentos ternários com argila calcinada oriundos da região amazônica

Abstract

One of the great contemporary challenges to mitigate CO2 emissions in the earth's atmosphere is the production of cements with reduced emissions of this gas that causes the greenhouse effect. Therefore, seeking to reduce the use of clinker in cement, new alternatives are tested, among these, the study of ternary compositions, such as LC3. The use of calcitic limestone is discussed a lot, but very little is said about the use of dolomitic limestone filler, due to the hypothesis that the magnesium present causes a negative impact. Thus, we sought to investigate the hydration of ternary compositions composed with carbonate fillers of different mineralogies and calcined clay from the Amazon region. The composition used is in accordance with the literature, being 50% clinker, 5% gypsum, 30% calcined clay and 15% limestone. Pastes with three types of carbonates were prepared for proper comparisons. In view of the climate in the states of the Legal Amazon, and its effect on the temperature of cement hydration, the produced pastes were cured at temperatures of 21 °C and 60 °C, and tested for 7, 28 and 91 days of age. The results showed that excess magnesium tends to react in the composition with the alumina of the cement, forming products such as brucite, at both temperatures, but with more evident formations at the temperature of 60 °C, according to DRX. When magnesium and alumina are mixed in excess, portlandite tends to be completely consumed, which may lead to problems in compressive strength. The paste containing magnesium carbonate and cement proved to be the ideal scenario regarding the amount of magnesium and alumina for hydrotalcite formation at both curing temperatures, being more intense at 60 °C. The dolomitic limestone used in LC3 showed results similar to the reference limestone, usually used as calcitic limestone, with compressive strength results above 30 MPa, without formation of brucite, hydrotalcite or thaumasite, with curves of calorimetry, thermogravimetry and product phases hydrates similar to each other. In view of the study carried out, it is possible to state that dolomitic limestone has the potential to be used as a dolomitic filler in LC3, under the boundary conditions of this study.