Effects of Cement Type, W/C Ratio, Specimen Size, and Curing Time on Concrete Electrical Resistivity

Chloride diffusivity and steel corrosion are two major factors in durability characteristics of concrete structures. It is possible to use the electrical resistivity (ER) of concrete as a measure of concrete's ability to resist the movement of ions within the material. In this study, surface electrical resistivity (SR) and bulk electrical resistivity (BR) of concrete cylinders were measured from 3 to 161 days for concrete mixes with four varying water to cement (w/c) ratios (0.45 to 0.60) and three distinct cement types. The study investigated the influence of important durability parameters such as cement type, long-term curing period, and w/c ratio on concrete electrical resistivity. In addition, the impact of cylinder size on SR of concrete was observed. The findings show that both SR and BR of concrete decrease with increasing w/c ratio except for concrete with cement Type-I/II, which showed a minor increase in resistivity with w/c ratio of 0.55. Concrete with Type-V cement showed the highest electrical resistance. Moreover, a strong linear relationship between the two types of resistivity was established, and a new equation was introduced in terms of cement type, w/c ratio, and long-term curing period. The correlation between SR and BR was validated by determining the mean absolute error (MAE) of the proposed equation for the three types of cement, which were 0.41 (Type-I/II), 0.65 (Type-III), and 0.35 (Type-V). For all three cement types, the mean absolute percentage error (MAPE) and coefficient of variation (COV) were within acceptable limits, and the 95% confidence interval (CI) indicated a small error margin for the proposed equation when estimating BR from SR using experimental data. Statistical analysis showed that the new equation was less reliable for Type-III cement than the other two types, possibly due to its rapid strength increase property.