## 2 Development of Conductive Mortar
### Results and Discussions
#### 2.2.2. Resistivity Characteristics  
The resistivity was measured for 90 days in a dry condition at a lab temperature of 23 \({}^{\circ}\)C after the cup-shaped mortar specimens were made. Figure 3a shows the resistivity variations of the general mortar and four proposed conductive mortar specimens with an admixture ratio of 100% for 90 days. Since the moisture content is reduced over time, resistivity tends to increase for all specimens due to reduced moisture content. Zeolite and geopolymer have even higher resistivity than general mortar after 90 days; the higher the admixture ratio, the higher the resistivity for these materials after 90 days, as shown in Figure 3b. As discussed in Section 2.1.1, these materials have higher mesopore and lower micropore volumes than activated carbon and bentonite; moisture can quickly increase or decrease induced by highly developed mesopores. This means that resistivity can promptly increase in dry conditions, as shown in Figure 3. Since SACP requires sufficient and sustainable moisture inside the concrete structures, these materials are not proper candidates. On the other hand, activated carbon has lower resistivity than general mortar over 90 days, which means that it can maintain the humidity inside the mortar well. Bentonite has a similar resistivity level to general mortar after 90 days. In addition, increasing the amount of these materials helps to decrease resistivity, especially for activated carbon. Thus, these materials can hold moisture inside the mortar for a long time and can be considered conductive materials. After 90 days, all specimens were immersed in tap water for 24 h. We took out the specimens and measured the resistivity for 21 days to check whether the humidity was well maintained. This test aims to identify whether the proposed conductive mortar can  
Figure 3: Resistivity variations during the 90 days after mortar specimens were made (an admixture ratio of 100% for conductive mortars) (**a**) and resistivity after 90 days at different admixture ratios (**b**). Figure 2: Specific surface area (**a**) and micropore and mesopore volumes (**b**) of admixtures and sand. hold humidity for a long time. Figure 4 presents the resistivity change over 21 days. Geopolymer and zeolite quickly reduce resistivity after immersion; they quickly dry out and return to their original dry state in 21 days due to well-developed mesopores. Again, these materials have higher resistivity than general mortar. Considering that sustainable CP is important, quick increase and decrease characteristics are improperly used as the conductive mortar. However, large resistivity reductions are observed for the specimens with bentonite and activated carbon, and these materials have resistivity lower than general mortar. In addition, the resistivity is well maintained over 21 days, which means that the moisture is well maintained inside the mortar. In particular, activated carbon shows excellent performance with low, sustainable resistivity for a long time. In addition, specific surface area, total micropore volume, and average pore size play a role in determining the resistivity, as Table 2 and Figure 2 are compared with Figures 3 and 4; the micropore volume and pore size are key factors in the resistivity while specific surface area is somewhat related. The same procedures were repeated for the specimens with both admixtures and chemical agents. Various combinations of admixtures and chemical agents were made, and resistivity was measured. As mentioned before, sodium hydroxide (NaOH), calcium hydroxide (CaOH), lithium hydroxide (LiOH), and sodium chloride (NaCl) were selected as chemical agents. Sodium hydroxide, calcium hydroxide, and lithium hydroxide are strong alkali components, and sodium chloride has high electrical conductivity. Specimens with an admixture ratio of 50% were used for this study.