Examining microstructural composition of hardened cement paste cured under high temperature and pressure using nanoindentation and 29Si MAS NMR

Microstructural composition of the hardened cement pastes are analyzed using nanoindentation and Si-29 MAS NMR after curing time periods of 7 and 28 days. Two curing conditions, room condition (20 degrees C with 0.1 MPa pressure) and an elevated condition (80 degrees C with 10 MPa pressure) are prepared to hydrate cement pastes [water to cement (w/c) ratio of 0.45]. The degree of hydration of the cement paste quantified using nanoindentation was compared with that from Si-29 MAS NMR. From nanoindentation of the hardened cement pastes, microstructural hydration products are characterized with respect to the corresponding modulus of elasticity. A hydration product, which has a relatively high modulus of elasticity over other known hydration products, was found in the hardened cement paste cured in elevated temperature and pressure. The effect of high pressure on the composition of the hydration product is discussed and it is hypothesized that the packing density of calcium-silicatc-hydratc (C-S-H) might increase when a cement paste is hydrated under high temperature and pressure.