Abstract
The electrical resistivity of concrete has considerable effect on the accuracy of estimated corrosion rate of reinforcement in concrete by non-destructive testing. Therefore, the quantitative evaluation of the electrical resistivity of concrete is important to achieve advanced maintenance of concrete.
It was studied by previous researches that the electrical resistivity of concrete is affected by water to binder ratio, the types of binder, the replacement ratio of mineral admixtures, and chloride ion. However, the results of these studies were qualitative evaluation, because the mechanism and the direct influential factors of the electrical resistivity of concrete were not considered in these studies. In particular, the effect of chloride ion on the electrical resistivity of concrete remains undefined.
In this study, the electrical resistivity of hardened cementitious pastes using various mineral admixtures and adding sodium chloride is measured by four-electrode technique. Furthermore, the electrical resistivity of pore solution and the porosity were measured, and the tortuosity of pore structure was calculated based on the experiments. The relationship between the electrical resistivity of hardened pastes and the direct influential factors, which are the electrical resistivity of pore solution, the porosity, the tortuosity, and others, was studied.
From the experimental results, the electrical resistivity of hardened pastes with sodium chloride was bigger than those without sodium chloride. The electrical resistivity of hardened pastes could not be evaluated only by porosity or the electrical resistivity of pore solution. On the other hand, the tortuosity could evaluate the electrical resistivity of hardened pastes without sodium chloride. Therefore, it was considered that the electrical resistivity of hardened pastes with sodium chloride had a lot of influence from other factors. The estimated value of the electrical resistivity of hardened pastes was calculated by the equations based on the electrochemical theory, using porosity, tortuosity, and the electrical resistivity of pore solution. The effect of other factors was quantified by comparing the experimental value of the electrical resistivity of hardened pastes and the estimated value of those. As the results, the effect of other factors on the electrical resistivity of hardened pastes had good correlate with ion strength of pore solution. Hence, it was estimated that the other factor was the electrical action between the ions in pore solution and the pore surface of hardened paste.
