Post-fire bond behaviour of reinforcement in concrete considering different bonded lengths and position of rebars

Abstract

RC structures can be subjected to accidental fire load during their service life, which can have a strong negative effect on the bond strength. A reliable assessment of the bond behaviour after a fire event is essential to judge whether the fire affected structure is safe for further usage or does it require retrofitting or replacement. Until now, rather limited research has been carried out to understand the post-fire bond behaviour of reinforcement in concrete. This work reports and discusses the results of an experimental study on the post-fire (residual) bond behaviour carried out using beam-end-specimens, which simulate the boundary conditions closer to reality compared to conventional pull-out-specimens. The standard fire scenario is employed to expose the rebar to fire from one-side and three-sides for simulating the boundary conditions of a slab and a beam respectively. The specimens are subjected to fire for the target fire exposure duration and allowed to cool down naturally. An unconfined pull-out test is carried out thereafter to obtain the post-fire bond behaviour. The investigations reported here were carried out to study two aspects: (i) influence of concrete cover on the residual bond behaviour of the rebar placed at the corner of the specimen, and (ii) influence of bond length on the residual bond behaviour of rebar placed at the edge or in the corner. The test results highlighted the strong influence of fire on bond behaviour, with approx. 50% reduction in the bond capacity and even stronger reduction in bond stiffness just after 30 min of standard fire exposure. This is attributable partly to the material degradation and partly to the high thermal gradients and associated cracking.