COUPLED MODEL OF FRACTURE SEEPAGE AND DISSOLUTION IN CONCRETE INTERFACE TRANSITION ZONE CONSIDERING THE INFLUENCE OF MICROSTRUCTURE

A micro-scale numerical model was established for the coupled fluid flow and chemical dissolution in the interfacial transition zone (ITZ) of concrete fracture. The microstructure of ITZ was modeled by the quartet structure generation set. The evolution of fluid velocity and solute concentration were simulated by the lattice Boltzmann method with double distribution functions. The accuracy in dealing with the convection-diffusion and reaction-diffusion problems were verified by two classical examples. Finally, the fluid flow and dissolution coupling mechanism of ITZ fracture were discussed considering the effects of seepage velocity, Ca(OH)₂ content and Ca(OH)₂ arrangement. The results showed that the wall corrosion happened quickly under the faster initial flow velocity, resulting in the acceleration of overall porosity increase. As to the Ca(OH)₂ content, the higher Ca(OH)₂ content in ITZ could add the contact area between the ITZ wall and fluid, which increased the dissolution access and lead to larger Ca²⁺ concentration in the fracture. In addition, when the dissolved Ca²⁺ cannot migrate in time, the dissolution of Ca(OH)₂ will be restrained. In conclusion, the coupled fluid flow and dissolution process of ITZ fracture was controlled by both the comprehensive action of Ca(OH)₂ content and Ca²⁺ concentration. For different arrangements of Ca(OH)₂, the results showed that microstructure of ITZ affected the relative permeability, which was the largest in horizontal growth, followed by uniform growth, and the smallest in vertical growth under a steady dissolution.