The carbonation of concrete is the prime deterioration factor in reinforced concrete (RC) structures. During carbonation, the atmospheric CO₂ penetrates the concrete and lowers its alkalinity. The problem in predicting carbonation is difficult to address, and a reliable probabilistic carbonation assessment is required to consider different variables such as the concrete quality, the chemistry of the reinforcing steel, and the quality of finishing materials. In the present study, we have used different finishing materials on concrete to minimize the effects of carbonation with a field survey and accelerated conditions. In one experiment, the measurement of the thickness of the concrete cover and the application of the finishing materials were done on-site, whereas, in the other experiment, these were done under accelerated conditions. The carbonation depth and the coefficient of silk wallpaper (SWP) were reduced by half in an accelerated 5% CO₂ experiment compared to the plain ordinary Portland cement (OPC), owing to the external physical barrier that reduces the penetration of CO₂ through the pores of the concrete. We found that carbonation did not reach the embedded rebar even after 100 years when SWP finishing material was used. The probability model predicted that 51 years would be required for OPC and water paint (WP) to reach a 30% onset of corrosion initiation through accelerated carbonation, while SWP would require 200 years.

Concrete structures are economical and typically durable when exposed to a variety of environmental conditions. However, carbonation results in a reduction of the durability of reinforced concrete members because it damages the passive film surrounding the reinforcement, which accelerates corrosion processes and may ultimately lead to premature failure of the members. Predicting service life is complex because it depends strongly on changes in materials and environmental conditions. Existing carbonation models predict the service life based on deterministic theories. In this study, deterministic and probabilistic methods are applied to study concrete carbonation in the presence of repair materials using the maintenance periods and repair cost according to the coefficient of variation (COV) of the carbonation depth of each repair material. Water-based paint, organic alkaline inhibitor, inhibiting surface coating, and corrosion-inhibiting mortar (IM) were used as repair materials. An accelerated carbonation experiment using 20% ${\mathrm{CO}}_2$ was performed for 5 days, and then the repair materials were applied on the concrete surface. Then the samples were put back in the carbonation chamber and carbonation depth was measured after 7, 14, and 28 days. Based on the COV value, the carbonation depth and maintenance periods were predicted. These were used as parameters for the probabilistic life-cycle cost (LCC) model. Results showed that carbonation inhibition was best when the repair was done using IM. Cost results obtained from deterministic and probabilistic models were compared. When the probabilistic model is applied, the repair cost is evaluated as a curve, unlike with the deterministic model. The probabilistic model reduces the maximum cost by 50% compared to the deterministic model. As the COV decreased (indicating better quality concrete), the probabilistic model results approached those of the deterministic model evaluation.

Concrete carbonation damages the passive film that surrounds reinforcement bars, resulting in their exposure to corrosion. Studies on the prediction of concrete carbonation are thus of great significance. The repair of pre-built reinforced concrete (RC) structures by methods such as remodeling was recently introduced. While many studies have been conducted on the progress of carbonation in newly constructed buildings and RC structures fitted with new repair materials, the prediction of post-repair carbonation has not been considered. In the present study, accelerated carbonation was carried out to investigate RC structures following surface layer repair, in order to determine the carbonation depth. To validate the obtained results, a second experiment was performed under the same conditions to determine the carbonation depth by the Finite Difference Method (FDM) and Finite Element Method (FEM). For the accelerated carbonation experiment, FDM and FEM analyses, produced very similar results, thus confirming that the carbonation depth in an RC structure after surface layer repair can be predicted with accuracy. The specimen repaired using inhibiting surface coating (ISC) had the highest carbonation penetration of 19.81, while this value was the lowest for the corrosion inhibiting mortar (IM) with 13.39 mm. In addition, the carbonation depth predicted by using the carbonation prediction formula after repair indicated that that the analytical and experimental values are almost identical if the initial concentration of Ca(OH)₂ is assumed to be 52%.