# Analysis of the Effect of Capillary Water Absorption on the Resistivity of Cementitious Materials
## 2 Materials and Methods
### Test Method  
(1) Test material preparation: Test specimens of mortar strength and resistivity were made according to the Chinese standard: GB/T176/71-2021 \"Test Method for Cement mortar Strength (ISO Method)\". The size of cement mortar is 40 mm \(\times\) 40 mm \(\times\) 160 mm, and the strength test and resistivity test specimens are made, respectively. The electrical electrode of the resistivity test specimen is ordinary stainless steel mesh, and extends 20 mm out of the mortar surface for testing. The spacing between the mesh is 40 mm, and the distance between the two ends of the mesh is 20 mm from the end of the specimen. In the process of specimen pouring, four electrodes were inserted vertically into the bottom of the mold, and then the specimen was placed on the shaking table to vibrate and compact. To avoid water loss, the surface of the specimen was covered with a layer of plastic wrap immediately after the completion of vibration, and the specimen was demolded after being cured in the laboratory environment at 20 \({}^{\circ}\)C for 24 h, before being put into the saturated lime water solution at 20 \(\pm\) 2 \({}^{\circ}\)C for curing to the corresponding age. The molded specimen is shown in Figure 1.  
According to the mix ratio given in Table 2, six test pieces (three strength test pieces, and three resistivity test pieces) were made for each mixing ratio of cement mortar at the same time. The strength and resistivity test pieces of three strength test pieces and resistivity test pieces with the same ratio were tested. The average values of the three pieces were taken as the strength or resistivity test results of the test pieces under the mix ratio. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline  & **SiO\({}_{\mathbf{2}}\)** & **Al\({}_{\mathbf{2}}\)O\({}_{\mathbf{3}}\)** & **Fe\({}_{\mathbf{2}}\)O\({}_{\mathbf{3}}\)** & **CaO** & **MgO** & **SO\({}_{\mathbf{3}}\)** & **Na\({}_{\mathbf{2}}\)O\({}_{\mathbf{eq}}\)** & **TiO\({}_{\mathbf{2}}\)** & **f-CaO** & **D\({}_{\mathbf{50}}\)** \\ \hline C & 20.58 & 4.97 & 3.76 & 63.57 & 2.29 & 2.00 & 0.53 & - & 0.75 & 17.763 \\ FA & 55.7 & 28.39 & 4.695 & 3.424 & 0.751 & 0.885 & 0.949 & 1.15 & - & 7.911 \\ SL & 30.48 & 15.46 & 0.322 & 37.45 & 8.12 & 2.36 & 0.46 & 1.16 & - & 11.895 \\ SF & 93.7 & 0.329 & 0.0957 & 0.478 & 0.248 & 1.35 & 0.893 & 0.017 & - & 14.860 \\ \hline \end{tabular}
\end{table} 
Table 1: The chemical compositions of raw materials (calculated by mass fraction %). \begin{table}
\begin{tabular}{c c c c c c} \hline  & **Group** & **Cement** & **FA** & **SL** & **SF** \\ \hline JZ & & 100 & - & - & - \\ \hline  & FA-1 & 95 & 5 & - & - \\  & FA-2 & 90 & 10 & - & - \\  & FA-3 & 80 & 20 & - & - \\  & FA-4 & 70 & 30 & - & - \\ \hline  & SL-1 & 95 & - & 5 & - \\  & SL-2 & 90 & - & 10 & - \\  & SL-3 & 80 & - & 20 & - \\  & SL-4 & 70 & - & 30 & - \\ \hline  & SF-1 & 95 & - & - & 5 \\  & SF-2 & 90 & - & - & 10 \\  & SF-3 & 80 & - & - & 20 \\ \hline \end{tabular}
\end{table} 
Table 2: Mix proportions of cement mortar. (2) Compressive strength test: The compressive strength of the cement mortar specimens of corresponding age was tested according to the Chinese standard: GB/T17671-2021 \"Test Method for Cement mortar Strength (ISO Method)\". (3) Resistivity test: At present, the commonly used methods of concrete resistance testing are the Wenner method [21], double-probe method [22], embedded four probe method [23], impedance spectroscopy [24], and ASTM C1760-12 method, etc. The four-electrode method is widely used because of its simple test method, uniform test electric field, and small error [21; 22; 23]. Therefore, this paper chooses the four-electrode method using ordinary stainless steel mesh as the electrode; a DC voltage of 24 V was used during the resistivity test.