Stability in the system CaO–Al2O3–H2O

The solubility of AH3, CAH10, C2AH7.5, and C3AH6 was determined experimentally at 7 to 40 °C and up to 570 days. During the reaction of CA, at 20 °C and above initially C2AH7.5 formed which was unstable in the long-term. The solubility products calculated indicate that the solubilities of CAH10, C2AH7.5 and C4AH19 increase with temperature while the solubility of C3AH6 decreases. Thus at temperatures above 20 °C, C3AH6 is stable, while at lower temperature also CAH10 and C4AH19 are stable, depending on the C/A ratio. At early hydration times, CAH10 can be stable initially at 30 °C and above, as the formation of amorphous AH3 stabilises CAH10 with respect to C3AH6 + 2AH3. With time, as the solubility AH3 decreases due to the formation of microcrystalline AH3, CAH10 becomes unstable at 20 °C and above.