Análise da microestrutura de pasta de cimento Portland com tratamento térmico por meio de segmentação de imagens e ensaio de ultra-microdureza

Abstract

The knowledge of Portland cement hydration, the influence of mineral admixtures and the heat treatment in hydrated products formation is very important to the understand of the properties and of the microstructure of cementitious materials. The aim of this work was to analyze the influence of heat treatment on the properties of the Portland cement pastes made with low water/binder ratio through image analyses and ultra-microhardness test. The samples were prepared with Ordinary Portland Cement (CPV), water/binder ratio of 0,20 and 0,40 and 5%, 10%, 15%, 20% and 25% wt. silica fume. The specimens were cast at room temperature, and after a day, they were placed in a furnace for 24 hours, at 100°C, 200°C or 300°C. Scanning electronic microscopy, optical microscopy, ultra-microhardness test and X ray diffraction were realized. The heat treatment increased the speed of pozzolanic reactions and the hydration of the Portland cement pastes prepared with low water/binder ratio. Moreover, the greatest values of microhardness were finding in high temperatures. Silica fume particles were agglomerated damaging the pozzolanic reaction. Furthermore, the microstructure of Portland cement did not present changes due to the heat treatment and xonotlite crystals were not formatted.