New Durability Concept for FRP Reinforcing Bars RESA new time-to-failure concept has been developed for glass fiber-reinforced polymer (GFRP) reinforcing bars in concrete. A series of bars is tested in highly alkaline water-saturated concrete at 23, 40, and 60°C (73, 104, and 140°F). The failure line of the material over time is described by a slope and the strength after 1000 hours of loading. Characteristic (5th percentile) values of the tensile strength for a specific design service life and a defined environment can be calculated. The concept allows for potentially much higher design values than do existing codes and guidelines, but without compromising safety. The concept applies to any fiber-reinforced polymer reinforcing bar, and it has been internationally accepted and adopted by fib.