Impact of free water on strain rate response of concrete in compression with a fully coupled DEM/CFD approach

The impact of water content on the dynamic behavior of concrete under the uniaxial compression state at the mesoscale was examined in this study. Extensive two-dimensional (2D) dynamic investigations into the impact of free water on dynamic strength and fracture of concrete of low porosity were performed. The effects of strain rate, fluid saturation and fluid viscosity were investigated in depth. The behavior of fully and partially fluid-saturated concrete was simulated using a mesoscopic pore-scale hydromechanical model based on a unique fully coupled DEM-CFD approach. To generate a fluid movement, the model featured a network of channels in a continuous area between discrete elements. In partially wet concrete, a two-phase laminar fluid flow (air and water) in pores and cracks was proposed. For accurate liquid/gas content tracking, the location and volume of pores and cracks were taken into account. On specimens of a simplified spherical mesostructure that mimicked concrete in both dry and wet conditions, a series of dynamic numerical simulations with varying strain rates were run. The particle fragmentation was disregarded. The dynamic compressive strength increased with the strain rate, fluid saturation and fluid viscosity. The pore fluid pressures slowed a fracture process because of the fluid confinement in pores, which resulted in increased concrete strength.