Modeling Nanomechanical Behavior of Calcium-Silicate-Hydrate.

摘要

The Discrete Element Method (DEM) was used to model the nanomechanical behavior of Calcium-Silicate-Hydrate (C-S-H). The interparticle forces consist of the traditional friction and contact forces that operate in granular materials, with the addition of nanometerscale forces between gels, including van der Waals and ionic correlation forces. The contact normal forces were based on the Hertz contact law. The van der Waals attractive forces were calculated based on Hamaker's equation. The ionic correlation forces, generated from the negative charges on the C-S-H gel surface and the ion species in the pore solution, were calculated using Monte Carlo (MC) simulations. The particles are spherical with diameters of approximately five nano-meters. Virtual nanoindentation was performed to evaluate the elastic modulus and hardness of C-S-H nanoparticle assemblies. Both elastic modulus and hardness, calculated from DEM, were much smaller than the results from nanoindentation experiments for corresponding C-S-H nanoparticle packing densities. By using a higher rotational stiffness, both bulk modulus and hardness increase and they match well with the experimental data, pointing to the possibility that the morphology of C-S-H is far from a perfect sphere and interlocking between particles provides significant strength to C-S-H. These studies show that the elastic modulus of a C-S-H matrix increases with increased packing ratio and rotational resistance, and its hardness increases with increased packing ratio, cohesion, rotational resistance and shear friction coefficient. The studies also show that the elastic properties of an individual C-S-H nanoparticle have little effect on the elastic modulus and hardness of the C-S-H matrix. The studies suggest that increasing packing density of the C-S-H nanostructure is a favorable way of making the C-S-H matrix stiffer.