Contribuição ao estudo do uso de fluorsilicato de sódio em materiais cimentícios

Abstract

Cementitious material exposed to an environment with aggressive conditions will be subject to deterioration processes. Since the durability of structures is a current concern, several studies are looking for new perspectives to improve the properties of cementitious materials. The aim of this study was to evaluate the influence of the addition of sodium fluorosilicate in cementitious materials. The content of sodium fluorosilicate was 1.5% in relation to the cement mass. For the experimental analysis mortar samples were made with Portland cement CP V-ARI with different water/cement ratios (0.40, 0.55 and 0.70). The samples were characterized as compressive strength, hydration temperature, setting time, water absorption by immersion and by capillarity, voids index and specific mass. To evaluate the behavior of cementitious materials after exposure to an aggressive environment, exposure tests were carried out considering exposure to sulfate ions and in a carbonation chamber. The tests to characterize the action of sulfates were linear dimensional variation, mass variation, propagation velocity of ultrasonic waves, tensile strength, compressive strength, and sulfate ion content. To characterize the carbonation, phenolphthalein spray method was used to monitor the carbonation depth. The microstructure analysis of samples exposed for 15 months were carried out the tests of porosimetry through mercury intrusion (PIM), scanning electron microscopy (SEM) associated with energy dispersion spectrography (EDS), X-ray fluorescence spectrometry (XRF) and X-ray diffractometry (XRD). Pastes exposed to the respective aggressive environment was performed thermogravimetric analysis (TGA/DTG). The results indicated that there is influence of sodium fluorosilicate on the properties in the initial ages of the mortar, decreasing the absorption of water by immersion. However, sodium fluorosilicate can delay setting time, and therefore its dosage needs to be adjusted according to the purpose of use. Regarding deterioration mechanisms, there are no indications of alteration in the characteristics of the material subjected to the action of sulfates. The addition of sodium fluorosilicate is promising to reduce the carbonation rate of cementitious materials, due to the influence on porosity and the reduction of calcium hydroxide by the production of calcium fluoride.