# Analysis of the Effect of Capillary Water Absorption on the Resistivity of Cementitious Materials
## 3 Results and Discussion
### Hydration Products  
In order to make the test results more prominent, the samples of JZ group and the three samples with the largest admixture content (FA-4, SL-4, SF-3) were, respectively selected to analyze the hydration products. Figures 11 and 12 show the TG-DTG curve of cement paste. It can be seen from the figure that when the DTG curve has an endothermic peak, the TG curve has a relatively obvious mass loss. The position of the endothermic peak of the slurry is the same, and there are three peak intervals: 70-350 \({}^{\circ}\)C (dehydration and decomposition of hydration products such as C-S-H, Ettringite, and Monosulfate (AFM)), 350-470 \({}^{\circ}\)C (dehydration and decomposition of hydration products Ca(OH)\({}_{2}\)), and 600-730 \({}^{\circ}\)C (decomposition of carbonate) [37]. The content of chemically bound water and  
Figure 10: Pore volume distribution of cement mortar. Ca(OH)\({}_{2}\) in the slurry can be quantitatively analyzed based on the TG-DTG curve [38], and the specific method is as follows. \[m(H_{2}O)=m_{A}+m_{B}+m_{C}\frac{M_{H_{2}O}}{M_{CO_{2}}} \tag{1}\]  
\[m(Ca(OH)_{2})=m_{B}\frac{M_{Ca(OH)_{2}}}{M_{H_{2}O}}+m_{C}\frac{M_{Ca(OH)_{2}}}{ M_{CO_{2}}} \tag{2}\]  
In the above equation, \(m_{A}\), \(m_{B}\), \(m_{C}\) are the weight loss rate (%) of the sample in the range of 70-350 \({}^{\circ}\)C, 350-470 \({}^{\circ}\)C, and 600-730 \({}^{\circ}\)C, respectively; m(H\({}_{2}\)O is the content of chemically bound water (%); m(CaOH\({}_{2}\)) is the content of Ca(OH)\({}_{2}\) (%); M is the relative molecular mass, and the relative molecular masses of H\({}_{2}\)O, CO\({}_{2}\) and CaOH\({}_{2}\) are 18, 44 and 74, respectively. Figure 13 shows the calculated results of Ca(OH)\({}_{2}\) and the chemically bound water content of the sample. It can be seen from the figure that the content of Ca(OH)\({}_{2}\) in the four groups of samples is significantly different: JZ > SL-4 > FA-4 > SF-3. This well confirms the analysis in the Section 3.3, because the mineral admixture mixed with the cement hydration product (Ca(OH)\({}_{2}\))'s secondary hydration reaction, the consumption of Ca(OH)\({}_{2}\) content. As a result, the content of the mineral admixture mixed group Ca(OH)\({}_{2}\) is lower than in the JZ group. At the same time, the secondary hydration reaction and the filling effect of mineral admixtures together increased the number of gel pores or transition pores, reduced the number of large and capillary pores, and increased the tortuosity of pores,  
Figure 11: TG curve of cement mortar slurry. Figure 12: DTG curve of cement mortar slurry. so that the resistivity of the specimen after capillary absorption in the mineral admixture group was increased compared with that in the JZ group. The SF reaction activity was the highest among the three mineral admixtures, and the secondary hydration effect was the most significant, resulting in porosity of the SF group decreasing significantly. The percentage of gel pores and transition pores increased (as shown in Figure 10). In addition, the chemical binding water content of the sample with mineral admixtures decreased compared with that of the JZ group. This is the result of the comprehensive action of two factors. First, the content of cement clinker is reduced after cementing material replaces cement, resulting in a substantial reduction in the content of chemically combined water generated by cement clinker [39]. Second, compared with the JZ group, although the total amount of chemically combined water generated by cement clinker is greatly reduced after the addition of mineral admixture, the formation space of the cement clinker phase hydrate after the addition of mineral admixture is larger than that in the JZ group, and the surface of mineral admixture particles also provides a place for the non-uniform precipitation and generation of cement clinker hydration products, which promotes the hydration of the remaining cement clinker [40; 41; 42].