Nanomechanical investigation of the effects of nanoSiO2 on C–S–H gel/cement grain interfaces

In this paper, nanoindentation and viscoelastic modulus mapping were employed to study the influence of nanoSiO2 on the properties of the interface between C–S–H gel and cement grains. The interface width measured by modulus mapping was around 200 nm as compared to a rough estimation of less than 5 μm by nanoindentation, due to the fact that 2 orders of magnitude increase in spatial resolution can be achieved with modulus mapping. Although the influence of nanoSiO2 on the interface width was not significant, its impact on nanomechanical properties of the interface was marked. The data suggest an improvement of modulus and hardness of the interface by nanoSiO2 in early age. This interface, which could be regarded as a layer surrounding cement grains, become denser by the addition of nanoSiO2.