INFLUENTIAL FACTORS ON ELECTRICAL RESISTIVITY OF HARDENED CEMENTITIOUS PASTE

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.セメント系硬化体の電気抵抗率は、電気化学的非破壊検査の精度や電気化学的補修工法の効果に影響を及ぼす。このため、硬化体電気抵抗率を定量的に評価する手法が必要とされているが、その現象メカニズムや影響因子に着目し検討を行った研究例は少ない。そこで本研究では、電気化学的理論に基づく硬化体電気抵抗率と各影響因子の関係式に、実験より定量した各影響因子を用い硬化体電気抵抗率の推定を行った。その結果、硬化体電気抵抗率の測定値と推定値の差がイオン強度と強い相関を示したことなどから、両者の差は細孔溶液中イオンと細孔表面間における電気化学的現象に起因していると推察された。