# 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  
Because in an underground environment, groundwater erosion on concrete through capillary action takes a long time, a longer capillary absorption test time of 36 d is chosen in this paper to restore the actual engineering situation as much as possible. Figure 4a,b show the resistivity of the cement mortar in the dry state and after 36 d of capillary water absorption, respectively. It can be seen in Figure 4a that in the dry state, the resistivity of the specimens in the JZ group is the highest, the resistivity of the specimens with admixture decreases to different degrees, and the resistivity of the specimens in the same group decreases with the increase of admixture. It can be seen in Figure 4b that after 36 d capillary water absorption, the resistivity of the specimens in the JZ group is the lowest, and the resistivity of the specimens doped with admixtures increases to different degrees. The resistivity of the specimens in the same group increases with the increase in the amount of admixture, and SF has the best effect on the resistivity of the specimens after improving water absorption. It can also be obtained from Figure 4 that after 36 d of capillary water absorption, the resistivity of specimens in the SF group decreases between 70% and 90%, while the resistivity of specimens in the other three groups decreases more than 90%, and the resistivity of specimens in the JZ group decreases the most, by 99.08%. The above phenomenon is related to the influence of mineral admixtures on the pore structure of cement mortar. Cemertitious material is a typical gas-solid-liquid three-phase composite, and its electrical conductivity is mainly determined by the solid phase formed by the aggregate and cementitious material, and the gas phase and liquid phase in the pores, of which the conductivity of the gas phase is the worst, and the conductivity of the solid phase is also poor; their electrical conductivity is negligible, so the liquid phase in the pores is a key factor in determining the electrical conductivity of cementitious materials [16]. In the dry state, the pores inside the specimens are almost free of water and are all gas phase, and their connectivity is poor. The number of pores in the JZ group specimens is larger and larger (as shown in the Section 3.3); thus, their resistivity is the largest, and after mixing with mineral admixtures, the pore size of the specimens is refined, the number of large pores is reduced, and the resistivity decreases. This phenomenon is more obvious with the increase in admixture, wherein the specimens mixed with SF have the lowest porosity; thus, their resistivity is the lowest. Under the effect of capillary absorption, the pores inside the specimen are partially connected by water, the liquid phase replaces part of the gas phase, the electrical conductivity is greatly enhanced, the resistivity drops rapidly, the internal tortuosity of the specimen in JZ group is worse than the other three groups, the difficulty of forming the conductive pathway is reduced, and the number is higher; thus, its resistivity after water absorption is the lowest after the addition of mineral  
Figure 4: The resistivity of cement mortar: (**a**) Resistance in dry conditions; (**b**) Resistance after 36 d of capillary water absorption. admixtures, as is the tortuosity of the pores inside the specimen. After the addition of the mineral admixtures, the degree of tortuosity of the internal pores of the specimens increased, the difficulty of forming conductive pathways increased, the number decreased, and the resistivity increased compared with that of JZ group. Figures 5-7 show the change curves of capillary water absorption and resistivity with time for cement mortar with different FA, SL, and SF contents, respectively.