A versatile pore-scale multicomponent reactive transport approach based on lattice Boltzmann method: Application to portlandite dissolution

Abstract

A versatile lattice Boltzmann (LB) based pore-scale multicomponent reactive transport approach is presented in this paper. This approach is intended to capture mineral phase and pore structure evolution resulting from geochemical interactions applicable, for example to model microstructural evolution of hardened cement paste during chemical degradation. In the proposed approach heterogeneous reactions are conceptualized as pseudo-homogenous (volumetric) reactions by introducing an additional source term in the fluid node located at the interface adjacent to a solid node, and not as flux boundaries as used in previously proposed approaches. This allows a complete decoupling of transport and reaction computations, thus different reaction systems can be introduced within the LB framework through coupling with external geochemical codes. A systematic framework for coupling an external geochemical code with the LB including pore geometry evolution is presented, with the generic geochemical code PHREEQC as an example. The developed approach is validated with a set of benchmarks. A first example demonstrates the ability of the developed approach to capture the influence of pH on average portlandite dissolution rate and surface evolution. This example is further extended to illustrate the influence of reactive surface area and spatial arrangement of mineral grains on average dissolution rate. It was demonstrated that both location of mineral grains and surface area play a crucial role in determining average dissolution rate and pore structure evolution.