Atomistic insights on the elasticity and Raman spectra of C-S-H from quantum-mechanical simulations

The strength of Portland cement is primarily due to the products of its hydration: Calcium silicate hydrates (C-S-H). The poorly ordered nature of these phases at the atomic scale is a limiting factor for the applicability of quantum-mechanical simulations relying on periodic boundary conditions (PBC). This is because large supercells are usually needed within PBC to capture the structural complexity of amorphous materials, with associated high, when not prohibitive, computational costs. Here, we devise a strategy to design small and symmetric PBC-compliant structural models of C-S-H with different Ca/Si ratios, allowing efficient quantum-mechanical atomistic simulations via the density functional theory (DFT). The mechanical and dynamical stability of the proposed models is assessed from DFT calculations. The effectiveness of the symmetric models in mimicking the actual disordered C-S-H phase is validated against experimental Raman spectra and bulk moduli.