## 3 Results and Discussion
### Effect of Initial pH  
To simulated the uptake of Cl\({}^{-}\) in the pore solution of normal or carbonated cement-based materials (pH = 7-13.5), chloride uptake of CAL-60 at different pH conditions was conducted, as shown in Figure 6. Chloride uptake of CAL-60 in NaCl solution with different pH. The adsorption of Cl\({}^{-}\) on CAL-60 at pH = 7, 8, 10, 12 and 13 were 95.5 mg/g, 99.7 mg/g, 100.4 mg/g, 102.5 mg/g and 106.0 mg/g, \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{\(\mathbf{Q_{m,ex}}\)} & \multicolumn{3}{c}{**Langmuir Isotherm**} & \multicolumn{3}{c}{**Freundlich Isotherm**} \\ \cline{3-8}  & & **Qm.\(\mathbf{\alpha_{c}}\)** & **k\(\mathbf{l_{L}}\)** & **R\({}^{2}\)** & **k\(\mathbf{f_{F}}\)**(mg-g\({}^{-1}\))** & \\  & & **(mg-g\({}^{-1}\))** & **(L-mg\({}^{-1}\))** & **R\({}^{2}\)** & **(L-mg\({}^{-1}\))**/n** & **I/n** & **R\({}^{2}\)** \\ \hline CAL-60 & 137.929 & 211.324 & 0.01185 & 0.972 & 7.89054 & 0.56491 & 0.922 \\ CAL-70 & 124.890 & 182.117 & 0.01279 & 0.968 & 7.40587 & 0.55328 & 0.913 \\ CAL-80 & 117.921 & 174.903 & 0.01217 & 0.970 & 7.01206 & 0.55201 & 0.921 \\ CAL-100 & 110.340 & 160.914 & 0.01381 & 0.977 & 7.68250 & 0.52628 & 0.920 \\ CAL-120 & 98.144 & 155.960 & 0.01043 & 0.967 & 5.27952 & 0.57350 & 0.925 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Experimental data of Cl\({}^{-}\) uptake on CAL samples at equilibrium and fitting parameters achieved from Langmuir isotherm and Freundlich isotherm. Figure 5: The effect of initial Cl\({}^{-}\) concentration on Cl\({}^{-}\) adsorption on CAL and nonlinear fits achieved using Freundlich isotherm and Langmuir isotherm ((a) CAL-60; (b) CAL-70; (c) CAL-80; (d) CAL-100; (e) CAL-120). respectively. It seems that the adsorption capacity of CAL-60 increased slightly with the enhancement of pH value. Moreover, the final pH of the mixture at equilibrium was almost in a stable range (pH = 11-12), which was favorable to maintain the alkaline environment of cement-based materials. Figure 7. XRD patterns of CAL-60 and CAL-60 samples after adsorption of Cl\({}^{-}\) under different pH conditions (N refers for CaAl-NO3\({}^{-}\) type LDH; H refers for Hydrocalumite) shows the XRD results of CAL-60 and CAL-60 samples after adsorption of Cl- under different pH conditions. Compared with the pristine phase of CAL-60, hydrocalumite (Ca\({}_{2}\)Al(OH)\({}_{6}\)Cl:2H\({}_{2}\)O,PDF#31-0245) was indexed in the samples collected after adsorption of Cl\({}^{-}\) with different pH values. The d\({}_{002}\) value was varied accordingly from 0.87 to 0.79 nm correspondingly, which was related to the change of interlayer anions of CAL. As previously reported, hydrocalumite-like LDHs had a higher solubility than hydrotalcite-like LDHs [37]. During the adsorption of Cl\({}^{-}\) on CAL (Equation (6)), the calcium metal ion, soluble aluminum (Al(OH)\({}^{4-}\)[37; 38] and hydroxyl ion released due to the incomplete dissolution of CAL by the following reaction (Equation (7)), and the dissolution was faster at lower initial pH of solution, which will increase the pH value of solution as shown in Figure 6. But OH\({}^{-}\) will compete with Cl\({}^{-}\) adsorption at higher initial pH [39] (Equation (8)), resulting in a decrease in the pH of the solution.