Simulation of Mass Transfer of Calcium in Concrete by the Lattice Kinetic Scheme for a Binary Miscible Fluid Mixture

The lattice kinetic scheme (LKS) for a binary miscible fluid mixture was applied to the simulation of the mass transfer of calcium in concrete. Cement paste, a major component of concrete, is a porous medium with a complicated three-dimensional geometry. The structure of the model concrete was selected on the basis of experimental data obtained by high-intensity X-ray computed tomography. The LKS, an improved version of the original lattice Boltzmann method, was used to save computational memory and to maintain numerical stability. First, an unsteady convection-diffusion problem was examined, and the accuracy of the method and the error norms with various lattice resolutions were investigated. Next, the problem of the calcium current in concrete was simulated. Pressure drops in the concrete were calculated for various Reynolds numbers, and the results were compared with those of an empirical equation based on experimental data. Also, velocity fields and concentration profiles were obtained at a pore scale for a structure with inhomogeneous mass diffusivities. These simulations showed that the present method might be useful for predicting calcium leaching in concrete from the microscopic point of view.