Bond strength at high temperatures

Synopsis This paper deals with the bond strength of steel and concrete at high temperatures because, although bond strength is of major importance in the determination of the behaviour of concrete structures in fire, there is no detailed information available on this problem. For this reason a test apparatus was developed which enabled pull-out experiments to be carried out on cylindrical concrete specimens with short embedment lengths. During the tests the slip at the non-loaded end of the concrete specimen and the pull-out force were reassured. In the temperature range 20 to 800°C the pull-out system enabled two different types of experiment to be carried out: force–slip measurements at thermal steady state and at non-steady state conditions. In these experiments normal-weight concrete made with Portland cement and siliceous aggregate and three different types of reinforcing steel (ribbed steel bars, plain round bars and deformed prestressing bars) were used. Differences between the results for the different types were noted, especially between the ribbed steel and plain round steel bars.