Resistivity of concrete

Abstract

Cement, a main composition of concrete, is the major contributor to the greenhouse effect. During the production of cement, a significant amount of carbon dioxide is released to the environment. As the world is moving towards a more sustainable environment, the durability of concrete becomes a concern. The durability of concrete can be improved with proper quality control and resistivity measurement is one of the methods used to indicate the quality of concrete. Because of the importance of resistivity, the present study is to achieve a better understanding of the electrical resistivity of concrete. The effect of various concrete mixtures to concrete resistivity is examined in this study. For the evaluation, surface resistivity is measured on 150mm concrete cubes. The concrete mixtures involves different combination of paste volume, W/C ratio, curing condition and supplementary cementitious materials / fillers. The supplementary cementitious materials are pulverised fuel ash (PFA), condensed silica fume (CSF) and the filler is limestone fines (LF). While PFA and CSF are used as cement replacement, the LF is used for the substitution of cement paste. The results have indicated that the electrical resistivity is affected by the paste volume, W/C ratio, curing condition and the combination of PFA, CSF and LF. Concrete resistivity increases as a result of a decrease in paste volume. A strong correlation exists between the W/C ratio and the surface resistivity. The R^2 = 0.9211 and 1 for 30% and 34% paste volume respectively. Also, the curing condition affect the moisture content of the concrete. The surface resistivity is higher for a drier surface. With the addition of PFA, CSF and LF, the surface resistivity increases significantly. The present study also examines the correlation between surface resistivity and different concrete properties such as compressive strength, moisture content, water penetration and rapid chloride penetration. The results shows that there is a strong correlation between surface resistivity and compressive strength for plain mixtures with R^2 = 1. However, this correlation decrease with the addition of other cementitious materials. As a result, the correlation would be better for a separated resistivity curve for different cementitious materials. The surface resistivity and the water penetration only has a moderate correlation. For plain mixtures, the correlation value is R^2 = 0.6814. R^2 = 0.7069 is the correlation value for concrete mixtures with PFA and CSF. Finally, there is a strong relationship between rapid chloride penetration and the surface resistivity. The surface resistivity is inversely proportional to the rapid chloride penetration with a correlation of R^2 = 0.9472.