Creep of lubricated layered nano-porous solids and application to cementitious materials

A variety of geomaterials, such as cementitious or clay-based materials, has on the nano-scale a layered microstructure that can contain fluid in its nano-porous space. The creep of such nano-scale basic units is what causes the macroscopic creep. Here, one nano-pore whose walls consist of two parallel infinite solid layers interacting through Lennard-Jones potential is studied. The authors evaluate numerically the energy barriers that such a system needs to overcome for the two solid layers to slide over each other and show how this sliding depends on the longitudinal and transverse forces applied to the layers. The energy barriers translate into a dependence of the apparent viscosity of the system on the disjoining pressure in a manner consistent with the microprestress theory. This result makes it possible to explain why the longtime creep of cementitious materials is logarithmic. The experimental data on how the long-term logarithmic creep of cementitious materials depends on the temperature and relative humidity is then considered. This model can capture the observed dependencies if not only the energy barriers induced by the interactions between layers but also the influence of the interlayer fluid, which is water in the case of cementitious materials, is taken into account. This fluid is modeled as a continuum with the same properties as the bulk fluid.