# Pore Solution Chemistry of Calcium Sulfoaluminate Cement and Its Effects on Steel Passivation
## 3 Results and Discussion
### Pore Solution Analysis
#### 3.1.3 Comparison with PWE  
The chemical composition of the pore solution was compared with the data from literature to evaluate the validity of the method applied. To enhance the effectiveness of comparison, the pore solution for published data should be extracted from pastes produced by cements with similar chemical composition and w/b ratio. It is difficult to find cases in which the contents of all oxides are similar, so the contents of Na\({}_{2}\)O and K\({}_{2}\)O are set as the index, because their contents are the result of cement alkalinity, and the alkalis elements are the main components in the pore solution. The chemical compositions of the pore solutions are summarized in Table 7. Despite the differences between the figures of ESL and PWE from literature, the results acquired by ESL, allowing for the slightly different composition in cement, are acceptable. Additionally, [PERSON] [33] has concluded the variation range of sodium and potassium in pore solution as a function of alkali content. When Na\({}_{2}\)O (wt%) = 0.20-0.31%, the Na concentration is in the range of 120-180 mmol/L. When K\({}_{2}\)O (wt%) = 0.20-0.47%, the K concentration is in the range of 180-340 mmol/L. It is clear that the concentrations of Na and K in this work belong to these ranges. Thus, the ESL method employed in this study is capable of providing valid data.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Cement Composition**} & \multicolumn{5}{c}{**Concentration (mmol/L) (1)**} \\ \cline{2-6}  & **Na\({}^{+}\)** & **K\({}^{+}\)** & **Ca\({}^{2+}\)** & **SO\({}_{4}\)\({}^{2-}\)** & **OH\({}^{-}\)** \\ \hline This study & & & & & \\
28 days, w/b 0.5 & 135.8 & 221.0 & 0.8 & 1.8 & 451.3 \\ Na\({}_{2}\)O\% = 0.28\% K\({}_{2}\)O\% = 0.35\% & & & & & \\ \hline [PERSON] [34] & & & & & \\
28 days, w/b 0.5 & - & 320.0 & - & - & 510.0 \\ Na\({}_{2}\)O\% = 0.32\% K\({}_{2}\)O\% = 0.60\% & & & & & \\ \hline [PERSON] [2] & & & & & \\
28 days, w/b 0.58 & 89.4 & 216.6 & 1.0 & - & 320.0 \\ Na\({}_{2}\)O\% = 0.19\% K\({}_{2}\)O\% = 0.54\% & & & & & \\ \hline \end{tabular} \({}^{(1)}\) It is assumed that the concentration of an element is equal to the concentration of the corresponding ion, so all the data can be recorded in ionic form.  
\end{table}
Table 7: Summary of chemical analysis of pore solutions (OPC).  
Figure 2: Raman spectrum of a standard solution and the leaching solution. (**a**) standard solution, (**b**) leaching solution.  
Table 8 lists chemical compositions of pore solutions for CSA. Since few experiments were conducted to analyze the pore solution of CSA, the examples were chosen despite of different cement types and w/b ratios. The differences between the ion concentrations obtained by ESL and the published data are significant, as illustrated in Table 8. All the ions, other than hydroxide, are the result of ESL show higher values. Based on the comparison of OPC systems in Table 7, the ESL should be a reliable method to study the pore solution. The significant differences in Table 8 may be attributed to the different cement type and w/b applied in every case. The hydration of CSA requires higher amount of water than OPC [35]. When the w/b is low, e.g. 0.5, the cement cannot completely hydrate, so there are more ions present in the pore solution.