Avaliação da resistividade elétrica superficial e da resistência à compressão em concretos com diferentes tipos de cimentos, submetidos a ataque por sulfatos

Abstract

Corrosion is a pathological manifestation arising from the percolation of aggressive physical and chemical agents through the pores of concrete, which can reach the passivating layer of steel reinforcement in reinforced concrete. As the phenomenon occurs, the surface electrical resistivity of the concrete changes, indicating the possibility of a decrease in its durability and useful life. Thus, surface electrical resistivity is a parameter used to monitor corrosion in concrete, which is very sensitive to its microstructural characteristics, especially in relation to the connectivity and distribution of its pores. The objective of this study is to establish a correlation between the aggressiveness of the environment, evaluated according to exposureto different levels of magnesium sulfate, and the surface electrical resistivity (RES) of the concrete over time. RES measurements were carried out on test bodies from two series of concrete samples produced with CP III 32 RS and CP V ARI RS cements, and water/cement ratios, 0.65; 0.50 and 0.45 for exposure to wetting and drying cycles in an aqueous medium with magnesium sulfate solution. The surface electrical resistivity was monitored using WENNER's non-destructive methodology. Research shows that one of the factors that affect the electrical resistivity of a concrete element is the water/cement (w/c) ratio, used in the preparation phase. The more saturated the pores were and the greater the number of pores and larger diameters, the higher the w/c ratio, with a decrease in surface electrical resistivity. According to measurements carried out at three ages (42, 70, 112 days), the changes showedan increase in surface electrical resistivity over time and a reduction in electrical conductivity in the pores.