The Performance of Reinforced Concrete Tunnel Linings, with and without Fibers, after Twenty Years of Service

This study investigates the contribution of fibers to the durability of reinforced concrete tunnel linings. Two cast-in-situ tunnels are herein analyzed after twenty years of service. Tunnel #1, made with plain concrete and steel rebar, has shown significant spalling at joints between two consecutive tunnel panels, caused by poor workmanship and construction details. Conversely, in Tunnel #2, close to Tunnel #1 on the same motorway, fiber-reinforced concrete (FRC) was used in combination with steel rebar. During the service life, the amount of FRC spalled from the cold joints of this lining has been significantly lower than the volume of concrete detached in Tunnel #1, despite the presence of the same type of joint. Thus, the addition of steel fibers to concrete mixtures can increase the material toughness, which in turn reduces concrete spalling. Hence, fiber-reinforcement enhances not only the durability but also the resilience of tunnel linings (i.e., Tunnel #2). Consequently, FRC represents a sustainable solution to extend the service life of structures, and to reduce the costs associated with the maintenance and renovation of tunnel linings.