Hydrostatic compression and pressure phase transition of major Portland cement constituents – Insights via molecular dynamics modeling

The complex composite material cement paste (CP) is under high pressures in underwater applications and when impact loading occurs. The mechanical behavior of cement paste to hydrostatic compression results from mechanical deformations of each phase, including unhydrated and hydrated minerals. Molecular Dynamics was used to study the atomistic deformation of individual unhydrated cement phases with increasing hydrostatic pressures. The pressure-specific volume Birch-Murnaghan equation of state (EoS) and the bulk modulus at zero pressure were determined for each phase. Results show that the bulk modulus and compressibility are pressure dependent. For tricalcium silicate (C₃S), dicalcium silicate (C₂S), and tricalcium aluminate (C₃A), the bulk modulus increases, while the volume compression decreases with increasing pressure. The C₃S and C₃A phases are stable during hydrostatic compression and exhibit isotropic behavior. The C₂S phase is not stable and shows anisotropic behavior. These results explain the effect of unreacted cement clinkers on cement paste mechanical behavior under high pressure based on the response of individual phases.