Predicting the impact of water transport on carbonation-induced corrosion in variably saturated reinforced concrete

TL;DR

The paper addresses carbonation-induced corrosion in reinforced concrete under variable moisture by developing a coupled framework that merges moisture transport in bulk and cracked concrete, saturation-dependent corrosion currents, and a diffusion–reaction carbonation model within a phase-field fracture description. Implemented as a fully implicit finite-element solver, the approach solves for moisture saturation, CO$_2$ concentration, and calcium hydroxide concentration while capturing crack-driven permeability enhancement and moisture-controlled corrosion. Validation against drying/wetting experiments and carbonation tests across cracked and uncracked specimens demonstrates accurate replication of water transport and humidity-dependent carbonation, including the accelerating effect of cyclic wetting/drying and the reduction in time to corrosion initiation when cracks are present. The framework provides a robust tool for service-life predictions of reinforced concrete and can be extended to include sorption hysteresis and chloride-induced corrosion, among other extensions.

Abstract

A modelling framework for predicting carbonation-induced corrosion in reinforced concrete is presented. The framework constituents include a new model for water transport in cracked concrete, a link between corrosion current density and water saturation, and a theory for characterising concrete carbonation. The theoretical framework is numerically implemented using the finite element method and model predictions are extensively benchmarked against experimental data. The results show that the model is capable of accurately predicting carbonation progress, as well as wetting and drying of cracked and uncracked concrete, revealing a very good agreement with independent experiments from a set of consistent parameters. In addition, insight is gained into the evolution of carbonation penetration and corrosion current density under periodic wetting and drying conditions. Among others, we find that cyclic wetting periods significantly speed up the carbonation progress and that the induced corrosion current density is very sensitive to concrete saturation.

Figures (8)

• Figure 1: The comparison of wetting and drying sorption isotherm. Curves estimated using Eq. (\ref{['Isotherm']}) with the experimentally-calibrated values of $\alpha$ and $\beta$ given in Table \ref{['tab:tableParam']}.
• Figure 2: Simulation of the drying test of Baroghel-Bouny1999: (a) geometry of the cross-section of the cylindrical cement paste specimen, and (b) comparison of predicted and experimentally measured water mass loss in time (expressed in percents of the original water mass content).
• Figure 3: Simulation of the wetting test of Zhang2022: (a) Geometry of the cross-section of the mortar specimen with two embedded steel wires, with the inset figure showcasing how the gradual change in porosity reported by Zhang2022 is accounted for; and (b) comparison of the evolution of the predicted and experimentally measured water saturation ratios in the vicinity of the upper steel wire.
• Figure 4: Simulation of the wetting test of Michel2018 -- cross-section of the concrete samples containing a single crack.
• Figure 5: Simulation of the wetting tests of Michel2018 of concrete samples with a single crack. Contours of simulated saturation ratio and experimentally measured envelope of water distribution (black line) after a time of (a) 0.03 h, (b) 1 h, (c) 2 h, (d) 3 h, (e) 5 h, and (f) 7 h.