Nanoscratch study of the modification effects of nanoSiO₂ on C-S-H gel/cement grain interfaces

The modification effects of nanoSiO₂ on properties of the interface region between cement grain and C- S- H gel in cement-based composites are investigated by means of the nanoscratch technique. The nanoscratch test involves driving a Berkovich diamond tip across the interface boundary perpendicularly and recording the lateral force while the normal load applied to the indenter is kept constant. The coefficient of friction (COF), defined as the ratio of lateral force to normal load, indicates an interfacial width close to 200 nm, which is irrelevant to the addition of nanoSiO₂. However, the COF value within the interface region decreases significantly if nanoSiO₂ is incorporated. The decreased friction between the indenter and the interface is mainly attributed to the reduction of adhesion friction, because the addition of nanoSiO₂ has a densification effect on the interface. This study further confirms that nanoSiO₂ addition is beneficial for the formation of a denser layer surrounding the unhydrated cement particles in early hydration ages.