Nanomechanical characterization of cement-based pastes enriched with SiO2 nanoparticles

Microstructural and nanomechanical surface properties of cement based pastes were experimentally investigated. Samples were prepared from CEMI42.5 cement, with water to cement ratio equal to 0.5 and enriched with SiO2 nanoparticles (d = 14 nm), with low concentration ranging from 0% up to 0.5% (by weight of binder). X-rays diffraction (XRD) patterns revealed a linear increase of crystal size of calcium hydrate (CH) products with the addition of nanoparticles, while scanning electron microscopy (SEM) images showed a denser microstructure with more defined grains for the higher SiO2 nanoparticles concentration. Atomic force microscopy (AFM) studies of samples after the grinding/polishing process indicated a strong dependence of surface roughness with the CH crystallite mean size and the materials mechanical properties. Finally, statistical analysis of nanoindentation mapping data revealed a decrease of elastic modulus with the increase of nanoparticles concentration.