Assessing Stray DC and AC Current-Induced Corrosion in Steel Fibre-Reinforced Concrete (SFRC) in Railway Tunnelling Construction

Abstract

This paper discusses the uncertainties surrounding corrosion prompted by stray direct current (DC) and alternating current (AC) interferences. The influence of railway stray DC interference was simulated through cyclic potentiodynamic (CP) polarization in a simulated concrete pore solution. Steel fibres exhibit excellent resistance to stray DC perturbations up to 1.0 V (vs. OCP or Open Circuit Potential) in the absence of chloride. However, when the electrolyte contains 0.6 mol/L chloride, a reduced DC perturbation of 0.4 V (vs. OCP) was sufficient to initiate pitting corrosion, indicating decreased corrosion resistance. The stray AC interference was simulated by applying an AC perturbation test to the embedded steel fibres which were polarized in simulated concrete pore solution as well. This approach allows for the effect of steel fibre orientations under stray AC interferences to be assessed. Following the AC interference test, the Tafel polarisation test shows a stochastic corrosion pattern in the embedded steel fibres. Notably, there is a significant reduction in the corrosion potential (E_corr) and a corresponding increase in the corrosion current density (i_corr) observed in one of the fibres. Ongoing research is being conducted to explore the stochastic corrosion phenomena identified in this research. Boundary element modelling (BEM) results show that the maximum voltage drops between steel fibres arranged in various configurations closely correspond to experimental measurements. The computer simulation approach applied in this study has the potential to further advance the development of more valuable predictive tools in forecasting the corrosion behaviours of reinforced concrete exposed to stray currents under complex built environments.