# Analysis of the Effect of Capillary Water Absorption on the Resistivity of Cementitious Materials
## 1 Introduction  
Cement-based material is a typical porous material whose resistivity is closely related to its pore structure and pore water saturation [1; 2; 3]. In practical engineering, decreases in the resistivity of cementitious materials can lead to several problems, such as subway stray currents [4]. Studies have shown that the track insulation performance is excellent at the beginning of the metro opening [5], but with the dirty, wet, iron powder overlay or the aging of the surface of the operational insulation fasteners, the walking track current will leak into the surrounding soil and structures through the concrete roadbed, causing serious electrochemical corrosion of the main structure reinforcement and metal pipes along the line [6; 7]. In addition, the main structure of the subway is often in a groundwater-rich environment, and the pore water saturation of the concrete roadbed rises rapidly under the invasion of moisture, and the resistivity decreases sharply, increasing the hazard of stray currents [8]; the subway, as an underground, hidden and complex project, is moredifficult to renovate or repair [9]. Therefore, studying the preparation of highly insulating cementitious materials and their application in metro rail engineering is crucial. There are various methods to improve the insulation (resistivity) of cementitious materials, of which the most common application is the incorporation of mineral admixtures. Research on mineral admixtures to improve the resistivity of cementitious materials has made some progress in recent years; [PERSON] et al. [10] found that the resistivity of concrete could be increased by a factor of 2.2 after replacing cement with a mass of 30% fly ash. [PERSON] et al. found that the resistivity of concrete after replacing cement with 25% fly ash equivalent mass underwent a large increase [11]. [PERSON] et al. [12] found an eight-fold increase in 1800 resistivity after replacing cement with 10% silica fume of equal quality. [PERSON] et al. [13] replaced cement with 6% and 12% silica fume of equal mass at 0.5 water-cement ratios, and found that the mortar replacement rate was increased by 2.5 and 5 times for 6% and 12% silica fume replacement, respectively. [PERSON] et al. showed that the resistivity of concrete after replacing cement with 26% silica fume equivalent mass can be increased by 13.4 times and 17 times after 28 d and 60 d of curing, respectively [14]; [PERSON] et al. [15] found that calcined mar as a supplementary cementitious material was able to increase the resistivity of the mortar in a water-filled state. [PERSON], by comparing the effect of fly ash, slag, and partial high territory on the resistivity of cement mortar, found that the partial high territory has the best effect on the resistivity of cement mortar [13]. You found that the resistivity of concrete can be increased by 2.67 times after replacing cement with 15% silica fume of equal quality in experiment [16]. [PERSON] et al. [17] found that electrical resistivity increased with the increase in the slag replacement ratio, since the addition of slag would consume more conductive ions. [PERSON] et al. [18] tested the resistivity of fly ash mixed in the early stage by a non-contacting electrical resistivity meter, and found that concrete mixed with 25-50% had high early stage resistivity. It is worth noting that most scholars currently test the resistivity of cementitious materials in a water-saturated state, but in actual working conditions, due to the specificity of the environment in which the subway is located, the pore water saturation of cementitious materials will fluctuate greatly, especially in rainy weather or groundwater-rich areas.