Comparative assessment of carbonation-ingress modelling in reinforced concrete structures with application to a cooling tower

Among the primary durability threats for reinforced concrete structures is carbonation-induced corrosion of reinforcement. Despite significant research efforts in the last decades, models for carbonation ingress are associated with large case-specific model uncertainties. Therefore, this study compares selected predictive models for carbonation of reinforced concrete. Two representative frameworks are examined: a widely accepted resistance-based approach of the fib Bulletin 34, and a detailed semi-mechanistic model, which makes it possible to reflect mixture of the concrete. Their performance is assessed in a case study on an existing cooling tower, which provides field data for calibration and validation. Deterministic analyses demonstrate that the different models yield consistent predictions, while probabilistic evaluation highlights the dominant influence of concrete cover and the significant roles of diffusion parameters and model uncertainty. The comparative results confirm that reliability-based approaches provide a more robust basis for durability design than purely deterministic evaluations, with case-specific updating of key parameters proving essential for accurate service-life assessment. On average, both the resistance and semi-mechanistic models seem to reproduce field carbonation depths with reasonable accuracy (about 10 mm versus a measured mean of 15 mm). Probabilistic reliability analysis then indicates that the durability target of βt=1.5 is reached after about 20 years of exposure.