Impacto do teor de água e de fino calcário no desempenho de matrizes cimentícias

Abstract

The main purpose of this research is to analyse the impact of the use of different water contents and the partial replacement of 30% of cement by calcium carbonate in the performance of cementitious matrices. The reason behind a partial substitution of cement by another compound is due to the possibility of presenting an alternative that meets the legislation requirements and, at the same time, minimizes the dependence on cement, since its production generates large emissions of carbon dioxide in the atmosphere. Limestone is a non-reactive material that has a positive effect on filling voids, because it has a smaller particle size distribution when compared with cement. In order to investigate the effects when 30% of the cement is replaced by calcium carbonate, different water contents of 13, 15 and 17% in relation to the mass of solids (cementitious binder, limestone and aggregate) were determined. The agglomerationof particles caused by the insertion of a material with smaller particle size was minimized with the use of dispersant additive, which was determined by its optimum quantity accordingly each water content given. The mortars were analysed in the fresh state by the tests of mass density, incorporated air content, consistency index and squeeze-flow. The latter was done on a non-absorbent surface and on a ceramic surface, both after 5 minutes of contact with their respective surfaces. In the hardened state, porosity, compression strength and tensile adhesion strength tests were performed. The compression and tensile adhesion tests were conducted at the age of 14 days after molding the specimens. The results show that the matrixes with the presence of fine limestone have a higher workability because they have presented higher consistency indices and spreads in the squeeze-flow tests. In addition, the partial replacement of cement has shown a more impactful effect on compression, with a reduction of 29.9% to 37.8% in its strengths. Regarding the tensile strength, there was a slight increase in the adhesion to the mixture with 17% of water (0.01 MPa), while for the other water contents, the minimum resistance required by standard were not achieved. Hence, the use of calcium carbonate in the manufacture of cementitious matrices can be advantageous, provided that the mechanical performance required for the desired use of the mortar is verified.