# Analysis of the Effect of Capillary Water Absorption on the Resistivity of Cementitious Materials
## 3 Results and Discussion
### Effect of Capillary Water Absorption on the Resistivity of Cement Mortar
It can be seen from the figure that the changes in the capillary water absorption resistivity of each group of specimens show two stages of rapid decrease and slow decrease, and tend to be stable; in stage I, in the early stage of capillary water absorption, a saturated area appeared at the bottom of the specimen, forming a large number of conductive paths, and the resistivity decreased rapidly. In stage II, after capillary water absorption reaches a certain level, water diffuses to the unsaturated region on the upper part of the specimen. At this time, capillary water absorption has little influence on the pore connectivity of the specimen, and it is difficult to form more conductive channels, so the resistivity decreases slowly until it is stable [34]. (Figure 8 shows the cross-section of the specimen after 36 days of capillary water absorption). In addition, by comparing Figures 5-7, it can be observed that after FA or SL incorporation, the capillary water absorption and resistivity of the specimens with water absorption time are similar to those of the JZ group, while the specimens with SF incorporation are different. The resistivity of the specimens in the SF group decreased relatively gently with the increase in capillary water absorption time. The stage I process was significantly shorter than that of the other three groups. The resistivity of the samples doped with 5%, 10%, and 20% SF in the dry state was 41.3%, 37.5%, and 35.7% of that of the JZ group, respectively. However, after 36 d capillary water absorption, the resistivity of the SF group was 3.69, 6.45, and 10.39 times higher than that of the JZ group, respectively. The resistivity  
Figure 5: Changes in water absorption and resistivity of cement mortar with different FA contents over time: (**a**) Macroscopic damage; (**b**) Partially enlarged drawing. Figure 6: Changes in water absorption and resistivity of cement mortar with different SL contents over time:(**a**) Macroscopic damage; (**b**) Partially enlarged drawing. of specimens in the SF group was significantly higher than that in the FA group and SL group after capillary water absorption. The capillary water absorption mass (g) and t\({}^{1/2}\) (s\({}^{1/2}\)) of each group were linearly fitted according to the capillary water absorption data measured in the previous 6 h, and the fitted equations and the capillary water absorption coefficient data of each group were obtained, as shown in Table 4. It can be seen that the capillary water absorption coefficient of each group decreased after the addition of mineral admixtures compared with the reference group. With the increase in mineral admixture, the secondary hydration effect causes the internal pore structure of the specimen to be refined continuously, the degree of tortuosity increases, the internal pore connectivity becomes more difficult, the capillary absorption coefficient decreases continuously, and the capillary absorption coefficient of the SF group is the smallest. This explains the relatively gentle change in the second stage of capillary absorption in the SF group, and with the increase in the mineral admixture substitution, the SF group, being due to higher reactivity. The porosity of the specimens was significantly reduced (as shown in the Section 3.3), and the number of internal conductive pathways decreased significantly compared to other groups. Finally, the resistivity changes during the water absorption process are more gentle compared to the other groups. To a certain extent, it can be considered that the larger the initial water absorption rate, the lower the resistivity after capillary water absorption. Based on the above test results, the pore structure diagram of the cement mortar in the dry state and after capillary water absorption is given in Figure 9. In the dry state, the pore of the specimen is equivalent to the capacitance, which cuts off the conductive path, there is no connected pore inside the specimen, and the cement matrix is almost non-conductive, so the resistivity of the specimen is large.