Multiscale lattice Boltzmann-finite element modelling of chloride diffusivity in cementitious materials. Part I: Algorithms and implementation

•A multiscale method is proposed to estimate chloride diffusivity in concrete.•The 3D structures of cement paste, ITZ, mortar and concrete are generated.•The lattice Boltzmann method is used as micro-scale solver.•The finite element method is selected as meso-scale solver.•The upscaling between micro-scale and meso-scale simulations is performed.

Chloride diffusivity in cementitious materials depends on both the environmental conditions and the evolution of their underlying microstructures over a wide range of length scales. Part I of this two-part investigation presents the algorithms and implementation of a hybrid lattice Boltzmann-finite element method that combines the advantages of lattice Boltzmann method and finite element method to estimate the chloride diffusivity in cementitious materials. Lattice Boltzmann method is used as micro-scale solver to predict the time-dependent chloride diffusivity in cement paste and interfacial transition zone (ITZ), the microstructures of which are generated from the HYMOSTRUC3D model. Finite element method is selected as meso-scale solver for estimating the chloride diffusivity in mortar and concrete, which are modelled as three-phase composites consisting of aggregate, matrix and ITZ, respectively. The upscaling between the micro-scale and meso-scale simulations is accomplished by using the volume averaging technique. The representative elementary volume (REV) of cementitious materials at a lower scale is determined with a numerical-statistical approach. Chloride diffusivity in the REV of cementitious materials at a lower scale is considered as input to predict the chloride diffusivity in cementitious materials at a higher scale. The developed multiscale lattice Boltzmann-finite element modelling scheme enables to acquire a meso-scale solution, i.e. chloride diffusivity, while still capturing the micro-scale information. The simulation results and validation are presented in detail in Part II.