# Optimization and Hydration Mechanism of Ecological Ternary Cements Containing Phosphogypsum
## 3 Results and Discussion
### Thermodynamic Analysis
#### 3.2.2 Simulation and Calculation Base on GEMS  
The phase evolutions of the hydrate pastes under different curing conditions calculated by the GEMS software are shown in Figure 10. It can be seen that the CH and C-S-H gels in the ECP hydration products increased with the continuous hydration, while the C\({}_{3}\)S and H\({}_{2}\)O decreased. Up to the age of 28 days, C\({}_{3}\)S and OH were still present, indicating that the hydration reaction had not been completed. In the test of ECP-1 and ECP-2, a little PG participated in the hydration at the early stage, but by the later stage of hydration, it was completely hydrated. In the test of ECP-3 and ECP-4, there were some FA mineral phases that still existed in the later hydration stage. This could be due to only part of the PG having been dissolved and hydrated with the C\({}_{3}\)A and C\({}_{3}\)S in the cement. The [SiO\({}_{4}\)]\({}^{2-}\) and [AlO\({}_{4}\)]\({}^{5-}\) networks in the FA vitreous had not depolymerized yet, and mainly participated in the reaction by the means of physical filling [25]. At the late hydration stage,  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Speces Parameters** & **C\({}_{3}\)S** & **C-S-H-jen** & **Portlandite** & **H\({}_{2}\)O(I)** \\ \hline \(\Delta_{\text{f}}\)H\({}^{\text{O}}\) & kJ/mol & \(-\)2931 & \(-\)2723 & \(-\)985 & \(-\)286 \\ \(\Delta_{\text{f}}\)G\({}^{\text{O}}\) & kJ/mol & \(-\)2784.33 & \(-\)2480.81 & \(-\)897.01 & \(-\)237.18 \\ V\({}_{\text{m}}\) & 10\({}^{-6}\) m\({}^{3}\)/mol & 72.4 & 106 * & 33.1 & 18.1 \\ M & kg/mol & 0.22833 & 0.19132 & 0.07409 & 0.01802 \\ \hline \hline \end{tabular}  
* Note: The molar volume of CSH is calculated according to chemical formula C\({}_{1.67}\)SH\({}_{4}\) instead of C\({}_{1.67}\)SH\({}_{2.1}\) since the early age’s CSH is under 100% relative humidity.  
\end{table}
Table 6: The thermodynamic database of PC’s hydration phases.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Phases** & **Formula** & **log K\({}_{50}\)** \\ \hline (Al-) ettrineticolumn{1}{c}{} & Ca\({}_{6}\)Al\({}_{2}\)(SO\({}_{4}\))\({}_{3}\)(OH)\({}_{12}\bullet\)26H\({}_{2}\)O \(\rightarrow\) 2 Al(OH)\({}_{4}\)\({}^{-}\) + 6 Ca\({}^{2+}\) + 26H\({}_{2}\)O + 4 OH\({}^{-}\) + 3 SO\({}_{4}\)\({}^{2-}\) & \(-\)44.9 \\ C\({}_{4}\)AsH\({}_{14}\) & Ca\({}_{4}\)Al\({}_{2}\)(SO\({}_{4}\))(OH)\({}_{12}\bullet\)6H\({}_{2}\)O \(\rightarrow\) 2 Al(OH)\({}_{4}\)\({}^{-}\) + 4 Ca\({}^{2+}\) + 6H\({}_{2}\)O + 4 OH\({}^{-}\) + SO\({}_{4}\)\({}^{2-}\) & \(-\)29.26 \\ Friedel’s salt & Ca\({}_{4}\)Al\({}_{2}\)Cl\({}_{2}\)(OH)\({}_{12}\bullet\)4H\({}_{2}\)O \(\rightarrow\) 2 Al(OH)\({}_{4}\)\({}^{-}\) + 4 Ca\({}^{2+}\) + 4H\({}_{2}\)O + 4 OH\({}^{-}\) + 2 Cl\({}^{-}\)SO\({}_{4}\)\({}^{2-}\) & \(-\)27.27 \\ Nitrate-AFm & Ca\({}_{4}\)Al\({}_{2}\) (OH)\({}_{12}\)(NONO)\({}_{3}\bullet\)4H\({}_{2}\)O \(\rightarrow\) 2 Al(OH)\({}_{4}\) + 4 Ca\({}^{2+}\) + 4H\({}_{2}\)O + 4 OH\({}^{-}\) + 2 NO\({}_{3}\)\({}^{-}\) & \(-\)28.67 \\ CH & Ca(OH)\({}_{2}\rightarrow\) Ca\({}^{2+}\) + 2 OH\({}^{-}\) & \(-\)5.2 \\ C-S-H\({}_{1}\) & Ca\({}^{2+}\) + SiO\({}_{3}\)\({}^{2-}\)\(\rightarrow\) CaSiO\({}_{3}\)\({}^{O}\) & 2.9 \\ C-S-H\({}_{2}\) & Ca\({}^{2+}\) + HSIO\({}_{3}\)\({}^{2-}\)\(\rightarrow\) CaHthe pozzolanic activity of FA [26] was gradually activated and participated in the reaction, resulting in the existence of some FA at the age of 28 days.  
Meanwhile, due to the interaction between the sulfate ions and C\({}_{3}\)S and the addition of PG having delayed the initial hydration of C\({}_{3}\)S, the addition of gypsum had a promoting effect on the hydration of C\({}_{3}\)S, which mainly resulted in the changing of the C-S-H morphology and the increase in ionic strength. Ettringite (AFt) crystals inhibited the formation of Al\({}^{3+}\) ions in the pore solution and enhanced the hydration mechanism of C\({}_{3}\)S. Accordingly, the hydrate equilibrium system was more complicated at the middle stage and later stage.