Effects of nanosilica on cement grain/C–S–H gel interfacial properties quantified by modulus mapping and nanoscratch

The modification effects of nanosilica, a widely used nanomaterial, on the cement grain/C–S–H gel interface of cement-based material at early ages are investigated. The mechanical properties, morphology, and chemical composition of the interface at nano-size are explored by quantitative modulus mapping based on scanning probe microscopy (SPM) and tribological nanoscratch coupled with scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS), for the interface in the form of an ultra-thin layer requires high spatial resolution techniques. The interface width as determined by the analysis on the variation of storage modulus and coefficient of friction (COF) is around 200 nm, which is irrelevant to the nanosilica addition; however, the incorporation of nanosilica improves the nanomechanical performance of the interface significantly. The densification of the interfacial region by nanosilica, which is mainly attributed to the pore refinement, is confirmed by morphological characterization. It has been proven by EDS analysis that Ca/Si ratio provides evidence for the location of the interface and the modification effects by nanosilica.