Insights into the performance evolution of C–S-H under different temperatures and pressures by First-Principles

The thermal destruction or mechanical properties of hydrated calcium silicate gel are closely related to the concrete consumption industry. This work researched the structural or dynamics of Tobermorite14Å under the temperatures, pressures and both effects of DFT. Water molecules at D and E sites are dehydrated at about 473K. The dehydration of water molecules from C, D and E sites is observed at around 573K, 673K, 773K and 873K. Water molecules at all sites are dehydrated at approximately 973K. The MSD value of the oxygen atom increases gradually and the MSD curve jumps at about 573K and 973K. In terms of external pressure, the lattice parameter of Tobermorite14Å decreases slower than Tobermorite11Å along the a-axis, while it decreases faster along the c-axis. Silicon oxygen tetrahedron appears in the structure for the first time when the pressure is 40GPa. In respect to temperature and pressure, the dehydration of water molecules from D and E sites is found at about 473K under all pressure. When the temperature is 573K, 673K, 773K, 873K and 973K and the pressure is 20GPa, 40GPa and 60GPa, respectively, all sites of water molecules are dehydrated. The application of pressure will increase the MSD value of oxygen atoms and accelerate dehydration.