Durability of precast concrete tunnel segments

In one-pass lining systems, the durability of tunnel structure is directly related to durability of concrete segments-acting as both the initial support and the tunnel final lining. In this paper, most-frequent degradation mechanisms-of concrete linings are discussed including chloride- and carbonation- induced corrosions, sulfate, acid and-freeze-and-thaw attacks, and alkali-aggregate reactions. Mitigation method for each specific degradation mechanism is explained. A durability factor specific to railway and subway tunnel known as stray current corrosion is presented. Mitigation methods for this specific corrosion together with coupling effects with other-conventional damage mechanisms are explained. Prescriptive approaches for durability design based on major codes and standards are explained and comparison is made between these methods. Exposure classes-as the main inputs to the prescriptive approaches are elaborated and requirements specified by the codes-and standards are presented and analyzed. The need to move on from prescriptive approach and embrace performance-based approaches for durability design of tunnel segmental lining is demonstrated and future studies are discussed.