Selection of a Critical Chloride Level for Full Probabilistic Modelling

In 2022, a working party (fib TG 8.9.3) was formed to try and better develop critical chloride (Ccrit) distributions for use in modelling new structures and assessing existing structures. The authors of this paper are leading TG 8.9.3. and are in the process of writing a Bulletin (the Bulletin) that will detail how Ccrit values have been developed since the 1970s. The Bulletin notes that chloride-induced corrosion initiation modelling based on Ccrit is not intended as a sole durability assessment tool for structures exposed to chloride. It is recognized that voids and moisture at the bar can control corrosion activation virtually independent of chloride content, but in most cases sufficient voids and moisture are present so that the arrival of adequate chloride triggers corrosion activation of the reinforcement. So, durability verification by modelling restriction of chloride penetration, so that the concentration at the bar is less than that commonly found to cause corrosion, seems appropriate. This empirical approach was first fully detailed in fib Bulletin 34 A key part in the empirical model is the ‘adequate chloride to trigger corrosion activation’ Ccrit. Although Ccrit has a wide distribution and has different distributions in different environments and concrete compositions, its use in modelling provides greater design flexibility and improved confidence compared to the Deemed-to-Satisfy (DtS) rules included in most codes. Because of the limitations in DtS provisions, modelling provides more effective designs by incorporating specific criteria for a broad range of exposures, materials, and construction methods. This paper proposes that a lower bound for Ccrit distributions for a range of materials and exposures can be developed from published papers. This paper includes Ccrit distributions for steel fibres, carbon steel (above and below water), high tensile steel, galvanized steel, and stainless steels. These are expected to be recommended in the Bulletin.