Hidratação do cimento portland na presença de elevados teores de fíler dolomito com diferentes finuras

Abstract

Due to the growing demand for cements and the need to reduce CO2 emissions during their production, new cements containing high levels of filler and additional cementitious materials have been investigated. The limestone filler in partial replacement to cement is one of these alternatives, observing the adoption of increasing levels in cement from different countries, including Brazil, with the recent approval of the NBR 16697 standard. However, the use of dolomitic limestone as a filler is still it is not widespread and the formation of hydration products from the reaction of dolomite limestone fines - as present in southern Brazil, with high MgO content - in Portland cement pastes is still little known. Although the performance of limestone filler has been investigated in the past, in terms of durability, the formation of thaumasite is still poorly studied in Brazil, as most international publications report that thaumasite develops at low temperatures, in the range of 5º and 15ºC. Thus, this research sought to investigate the cement hydration products in the presence of dolomite, looking for the formation of thaumasite. A dolomite filler with 20% MgO was adopted, used in contents of 0%, 15%, and 35% to replace cement, with D50 of 10 µm, 6 µm and 4 µm. The pastes were cured at temperatures of 5ºC and 20ºC. The research results indicate that, in relation to rheological behavior, all cement pastes with dolomite incorporation showed better homogeneity compared to pastes without the presence of dolomite, and that the 35% filler content had the highest viscosity rate. The analysis by isothermal calorimetry showed that the presence of dolomite showed a nucleation and dilution effect, reducing the hydration heat of the pastes. In the results of resistance to compression, it was identified that the pastes submitted to a temperature of 5ºC showed the best mechanical performance. As for the different levels of dolomite, they did not present significant differences, and the 4µm fineness showed the best packaging in microscale, also showing higher strength values. The XRD detected the presence of thaumasite only at a temperature of 20ºC, indicating the possibility of formation of this mineral at higher temperatures.