A liquid-solid-chemical coupled mass transport model for concrete considering phase assemblages and microstructure evolution

Abstract

Concrete is a highly alkaline porous medium that is prone to chemical reactions with acidic environments. The ion transport coupled with chemical reactions between concrete and solutions in acidic environments (acid rain, acid groundwater, acid industrial water, etc.) is a major challenge to the durability design of such infrastructure. Here, a liquid–solid-chemical coupled mass transport model of concrete considering phase assemblages and microstructure evolution was developed to tackle this problem. The highly nonlinear evolution of phase assemblages was solved via chemical thermodynamics. Further analysis was conducted on the spatiotemporal relationship of microstructure evolution caused by reaction kinetics, and the dynamic porosity and ion adsorption capacity were taken into account in the mass transfer equations. Furthermore, the nonlinear non-homogeneous partial differential equations were solved via finite difference method. Finally, the proposed model was validated based on four different types of cement-based concrete. The results indicated that considering the chemical reaction between highly alkaline concrete and acidic environments was crucial for the transport of chloride ions. The migration depth varied up to twice under the influence of acidic solutions. This study builds a bridge between mass transfer and cement chemistry knowledge, and is expected to improve the accuracy of life prediction for reinforced concrete structures.