Modeling Nanoindentation of Calcium Silicate Hydrate

The discrete element method (DEM) was used to model nanoindentation of calcium silicate hydrate (C-S-H). The interparticle forces consisted of the traditional friction and contact forces that operate in granular materials, with the addition of nanometer-scale forces between gels, including van der Waals and electric double-layer forces. The contact normal forces were based on Hertz contact law. The van der Waals attractive forces were calculated on the basis of Hamaker's equation. The electric double-layer forces, generated from the negative charges on the C-S-H gel surface and the ion species in the pore solution, were calculated by using Monte Carlo simulations. The particles are spherical with diameters of approximately 5 nm. Both elastic modulus and hardness, calculated from the DEM, were much smaller than the results from nanoindentation experiments. The effects of interparticle forces on the elastic modulus and hardness were studied to explore possible reasons for the differences. The simulations give insight into the morphology of C-S-H nanoparticles and the interparticle forces between C-S-H nanoparticles.