Behaviour of concrete beams with exposed reinforcement

Reinforcement corrosion is the principal cause of deterioration of reinforced concrete. It has been estimated that around £500 million is spent annually in the UK on concrete repairs. Of the alternative techniques available to extend the useful life of concrete structures, removal of concrete around affected reinforcement and subsequent reinstatement with a concrete or mortar remains the most commonly used. A detailed description of the changes in structural behaviour that arise when reinforcement is exposed is provided, based on principles of equilibrium of forces and compatibility of deformations. Results of 19 physical tests and of numerical modelling of beams with bonded and with exposed reinforcement are reported. Four different failure modes were represented in the study, namely flexure, shear, crushing of concrete on the tension face near the ends of the exposed length of bar, and end anchorage. Shear failures do not occur within the exposed length. A 50% loss in strength was found for a beam with 1.5% reinforcement, exposed over 90% of the span, but there was no loss in strength for a beam with 0.5% reinforcement exposed over a similar proportion of span. The numerical model is shown to predict strain behaviour and failure loads with good accuracy. The model is applied to specific examples to estimate loss of strength on exposure of reinforcement and to evaluate the length of bar which may be exposed without loss of ultimate strength.