Nanogranular Nature of CSH: Experimental Confirmation by Nanoindentation

Hydration of cement materials is accompanied by the formation of calcium silicate hydrates (CSH). Accordingly, the hydration process is completed in the early, middle, and late periods, leading to the formation of two types of CSH phases: of low density (LD) and high density (HD). Usually, under normal conditions, LD CSH is formed in the middle period, while the formation of HD CSH predominates in the later stage. In using the nanoindentation method, it becomes possible to explain the nanogranular nature of the CSH gel, which is characterized by the contact forces of the CSH gel particles for these phases. Studies of cement stone samples at W/C = 0.21 and at the content of hydrothermal SiO₂ nanoparticles in the combined additive 0.000006 wt.% and multilayer carbon nanotubes (MCNT) 0.00004 wt.% for cement showed that the effect of nanoparticles on the structure of the CSH gel becomes more pronounced, since the volume fraction of the LD phase of the CSH gel with a low packing density of nanogranules becomes significantly lower than the fraction of the HD phase with increased hexagonal packing density of nanogranules.