Estudo de variáveis de ensaio que influenciam os resultados de ensaios de resistividade elétrica volumétrica

Abstract

Concrete quality control is commonly based on evaluating its consistency in the fresh state and its mechanical resistance to compression in the hardened state. In special cases, apparent porosity, wear resistance, expansion due to the alkali-aggregate reaction, resistance to attack by chloride ions, resistance to carbonation and resistance to attack by sulfates are controlled. In most cases, such control occurs by destructive methods. In the case of resistance to the entry of aggressive agents, chloride ions, CO2 and sulfates, for example, there is the possibility of evaluating the quality of the concrete through the electrical resistivity test. The surface resistivity test is widely used to study structures in situ, while the volumetric test is restricted to tests on specimens for concrete quality control. There is little data on the variables that affect these tests, especially the volumetric method. In this context, and in this work, some of the variables of the volumetric electrical resistivity test are analyzed in equipment developed at the Federal University of Minas Gerais that uses alternating current. The results indicate that the use of dry steel wool promotes adequate contact between the electrodes and the sample. Immersion in water for at least 2 hours and in a humid chamber for more than 11 hours leads to saturation of the specimen and guarantees the same measurement condition. When using alternating current, the use of frequencies in the range of 10 Hz to 210 Hz does not seem to influence the volumetric electrical resistivity results. Keywords: volumetric electrical resistivity, concrete, quality control.