A molecular dynamics study of calcium silicate hydrates-aggregate interfacial interactions and influence of moisture

Abstract

The interface properties between hydrated cement paste (hcp) and aggregates largely determine the various performances of concrete. In this work, molecular dynamics simulations were employed to explore the atomistic interaction mechanisms between the commonly used aggregate phase calcite/silica and calcium silicate hydrates (C-S-H), as well as the effect of moisture. The results suggest that the C-S-H/calcite interface is relatively strong and stable under both dry and moist conditions, which is caused by the high-strength interfacial connections formed between calcium ions from calcite and high-polarity non-bridging oxygen atoms from the C-S-H surface. Silica can be also adsorbed on the dry C-S-H surface by the H-bonds; however, the presence of water molecules on the interface may substantially decrease the affinities. Furthermore, the dynamics interface separation tests of C-S-H/aggregates were also implemented by molecular dynamics. The shape of the calculated stress-separation distance curves obeys the quasi-static cohesive law obtained experimentally. The moisture conditions and strain rates were found to affect the separation process of C-S-H/silica. A wetter interface and smaller loading rate may lead to a lower adhesion strength. The mechanisms interpreted here may shed new lights on the understandings of hcp/aggregate interactions at a nano-length scale and creation of high performance cementitious materials.