Developments in defining exposure classes for durability design and specification

Durability design and service life modeling of concrete structures rely on environmental exposure classes based on the prevailing deterioration mechanisms. International standard environmental exposure classes, for example, those found in the fib Model Code 2010 and ISO 22965-1:2007 are predominantly based on European environmental conditions. Although these exposure classes are more suited to the prescriptive design for durability, they may also be adapted to performance-based design. For more complex design philosophies such as limit state design using partial factors, the generalizations of the standard exposure classes cannot be suitably employed and therefore a more rigorous characterization of the exposure environment is required. The standard exposure classes in the fib Model Code 2010 as well as various national codes from different regions of the world are critically reviewed, and their limitations highlighted. Based on the review, updates to the standard exposure classes for inclusion in the fib Model Code 2020 are proposed. This paper summarizes the work of TG8.8 WP3 (Commission 8: Durability, Task Group 8.8: Common approaches, Working Party 3: Exposure Zones) and represents the view of the Working Party members.