influência de nanopartículas de carbonato de cálcio na formação de etringita tardia em pastas de cimento submetidas à cura térmica

Abstract

The delayed ettringite formation (DEF) is a pathology resulting from the occurrence of internal sulfate attacks on the cementitious matrix, mainly affecting precast parts produced via steam curing and structures with large concrete mass, which generates a high heat of hydration. The search for improving the durability of cement products has led research to explore the incorporation of supplementary materials in this matrix, such as silica, metakaolin and CaCO3 nanoparticles. This study aims to evaluate how the presence of calcium carbonate in the nanometer scale interferes in the DEF and other phases of thermally cured Portland cement pastes. Pastes were produced by replacing the cement with CaCO3 (5 wt%) and adding CaSO4 (3 wt%). Pastes were characterized at 1, 7, 28, 90 and 180 days of hydration by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA / DTG). The results indicated that the thermal cure affected the microstructure of the pastes, favoring the decomposition of the primary ettringite and containing the dissolution of the portlandite. In addition, all pastes were carbonated, which favored the reactions involving CO3 2- ions and monosulfoaluminate, allowing the formation of monocarboaluminate and delayed ettringite. Such mechanism was intensified by the carbonation of pastes and the presence of CaCO3 nanoparticles.