Molecular dynamics study on structural characteristics of amorphous C‐S‐H with different Ca/Si ratios

Abstract As the major hydration product of cement, hydrated calcium silicate (C‐S‐H) governs the overall performance of cement‐based materials. The molar ratio of CaO to SiO 2 (Ca/Si ratio) significantly affects the structure and properties of C‐S‐H. This study analyzed the effect of Ca/Si ratios (0.83–2.0) on the structural morphology evolution, bond lengths and angles, polymerization process, and nanoporosity of amorphous C‐S‐H, with the help of the ReaxFF force field. The results showed that the reacted C‐S‐H tend to form a fibrous network‐like morphology at low Ca/Si ratios, while the silicate chains are prone to accumulating at high Ca/Si ratios, forming a dense granular ovoid structure. Meanwhile, the Ca/Si ratio has no effect on the bond lengths and angles. In addition, the Ca 2+ ions can interrupt the silicate chains during hydration, which leads to a decrease in the average silicate chain length with increasing Ca/Si ratio. The porosity of C‐S‐H decreases from 59.3% to 54.3% when the Ca/Si ratio increases from 0.83 to 2.0. It can be deduced from these findings that the increase in the Ca/Si ratio decreases the compressive strength of cement‐based materials but increases their durability.