This database for hydrothermal conditions contains thermodynamic data for crystalline calcium silicate hydrate phases which can form in the temperature range 100-300 °C. This hydrothermal database has been developed specifically for cement systems reacted at  above 100°C and is fully compatible with the Cemdata18 database for Portland, calcium aluminate, calcium sulfoaluminate and blended cements. It is available in GEMS program formats, and includes thermodynamic properties based on the summary work of Hirsch and Lothenbach (2024). It should not be used if you study the hydration of cements, as these hydrothermal phases are generally more stable than the ill-crystalline C-S-H, we observe in such systems.

To use the zeolite database in GEMS-PSI package, please download it to your hard disk and perform the following steps:

1. Unzip the downloaded zip file (contains a directory named "hydrotherm ") into a temporary directory, e.g. as /Tempfiles/hydrotherm
2. Find where you have GEMS installed (on Windows, usually under C:\Users\"your name"\GEMS3\Gems3-app\Resources\DB.default directory. Under Linux, this may need a root password.
3. Copy all files (but not the folder) from /Tempfiles/zeolite21 into the DB.default directory.
4. Start GEMS and create a new project. In the "Selection of Independent Components..." dialog, turn on "Kernel(Nagra-PSI)" and "hydrotherm". This will link the hydrothermal database files as a specific extension to the kernel PSI database.
5. Select Independent Components to form the system and click "Ok" to proceed as usual.
6. If used together with Cemdata18, be aware that that C-S-H will be less stable than the crystalline calcium silicate hydrates at ambient conditions

The thermodynamic data for the hydrothermal system are described in detail in:

• T. Hirsch, B. Lothenbach (2024) Phase stabilities and thermodynamic properties of crystalline phases in CaO–SiO₂–H₂O above 100 °C. Cement and Concrete Research, 177, 107412.

Application of the dataset:

• Mingione, S., Jansen, D., Winnefeld, F., Churakov, S., Lothenbach, B. (2025) Effect of temperature on the solubility of xonotlite. Cement and Concrete Research, 188, 107732