## 1 Introduction  
Electrical conductivity is a measure of how well a material accommodates the movement of an electric charge. It is the ratio of the current density to the electric field strength. Electrical resistivity is the reciprocal of conductivity. It is the is the opposition of a body or substance to the flow of an electrical current through it, resulting in a change of electrical energy into heat, light, or other forms of energy. Electrical resistivity in concrete is a reversed function of conductivity and is related to the diffusivity of ions in the pores [1]. The measurement of electrical resistivity is considered to be a very attractive method for evaluating the properties of geomaterials and for the quality control of concrete because such non-destructive testing (NDT) is simple, rapid, and cost-effective [2]. Particularly, electrical resistivity can be classified into two stages of durability, as proposed by [PERSON] [3], which are before and after steel corrosion and thus can be used as the barometer of durability during the latent period relating to the micro structure of the concrete as well as the corrosion progress period [4; 5; 6]. Electrical resistivity measurements as NDT in the concrete industry are employed for the following reasons: (i) to measure resistivity without damage; (ii) to save time and costs; and (iii) to obtain the results of the measurements in real time. Figure 1 shows the classification of the service life of a concrete structure into stages: (i) the initiation period; and (ii) the propagation period. In general, the initiation and propagation periods are strongly dominated by the chloride diffusivity and corrosion current density of the reinforcement, respectively, both of which are qualitative indices. However, these experimental data are not easy to obtain on site. As an alternative to these two indices, electrical resistivity can be measured relatively easily and used as a qualitative index for evaluating the corrosion rate of concrete and eventually predicting its service life [7; 8; 9]. Nevertheless, electrical resistivity measurements have many factors causing data interference. The chloride and water content in concrete may also have an effect on electrical resistivity [10]. Even so, electrical resistivity has some disadvantages because it is affected by several other factors, e.g., (i) the amount of cement paste; (ii) a water-cemetitious material ratio; (iii) curing condition; (iv) exposure temperature; (v) chlorides; (vi) moisture content; (vii) cement type, and the volumetric fraction of the cement paste; (viii) type and amount of admixtures; and (ix) quality and volumetric fraction of the aggregate [9]. When a current is applied, the electric field is dependent on the chloride concentration that has an effect on the pore water transfer [11; 12], and thus it is necessary to monitor the data on the change in electrical resistivity of concrete containing various chloride concentrations over time. Meanwhile, the electrical conductivity is not caused by the binding of electrons in an electrolyte solution but depends on the movement of charges. The resistance of the electrolyte solution is highly dependent on the concentration, while distilled water is generally an insulator and seawater is considered a high conductor. Therefore, when the chloride concentration increase, the electrical resistivity should decrease [13]. The decrease in resistivity between subsequent intervals of increasing chloride concentration decreased as the moisture content increased [14]. Since resistivity is measured by applying a current through the concrete and a potential difference is measured, increasing the chloride concentration of the pore water solution will improve the current conduction as ions help carry the current [15]. Nevertheless, it is rare to study the change in the electrical resistivity of concrete due to the effect of the chloride ions and carbonation.