A New Reactive-Transport Modeling Framework for Simulating Pore Solution Chemistry at Localized Imperfections Along Steel-Concrete Interface

Abstract

The variability and uncertainty associated with chloride thresholds for corrosion initiation in reinforced concrete structures can be partly explained by the presence of localized defects and imperfections along steel-concrete interface such as elongated cracks, pores, gaps, crevices, and mill scale. It has been demonstrated in prior research that pore solution in these imperfections might be different from that of the bulk pore solution, and this difference may create the necessary conditions for the breakdown of the passive film. These studies showed that the chemistry of the pore solution, in particular pH and Cl-/OH-, within localized defects provide more favorable conditions for depassivation than the bulk concrete pore solution. Local acidification and increase in Cl-/OH- within these defects were observed, albeit to different degrees. Defect geometry has been found to be a critical parameter affecting local acidification and the increase in Cl-/OH-. However, chemical composition of the pore solution, reactions between corrosion products and the ionic species in the pore solution and changes in transport properties within the defect due to accumulation of solid corrosion product have also been shown to affect the process. Due to these complications, it is challenging to study these effects experimentally, hence numerical investigation techniques are required. In order to better understand the processes that take place within local defects along the steel-concrete interface a reactive-transport modeling framework is developed. The model incorporates finite element analysis (FEM) with thermodynamic/kinetic modeling of cementitious systems. The FEM module is responsible for modeling multiphysics phenomena such as corrosion, mass transport, heat transfer, phase flow and kinetics, while thermodynamic module is used to model chemically complex reaction computations based on Gibbs Energy Minimization (GEM) theory. A non-iterative operator splitting technique in a time marching scheme is used for uncoupling the multiphysics phenomena from reaction equations. The framework is able to analyze complex chemical systems including processes that take place in cementitious materials and as a result of corrosion reactions. The presentation will highlight the main components of developed framework and demonstrate its functionality though case studies and hypothetical simulations.