Effect of Pre-Loading on the Corrosion of Reinforcement in RC Beams

Abstract

Corrosion in RCC structures is a major durability problem, especially in marine environments.The loading history or the presence of loads, which is the scenario in RC structures in everyday use, has a ignificant effect on the corrosion process. These loads lead to the formation of micro or macro cracks, which accelerate corrosion and lead to localized failure of the elements. This experimental study focuses on chloride-induced corrosion of five RC beam specimens of dimensions 150 mm x 150 mm x 700 mm. Reinforcement detailing and concrete mix proportions used are the same for all the beams tested. Beam B1 is the healthy beam which is neither corroded nor subjected to sustained or pre-loads. Beams B2, B3 and B4 have been subjected to 25%, 50% and 75% of the ultimate load capacity of the beam B1respectively before subjecting them to corrosion. Beam B5 is pre-loaded to 50% before sustained load of 1% is imposed during corrosion. The corrosion process is accelerated using a 20V DC power supply and wet-dry cycles. All the beams are corroded for 15 days. Results indicate that corrosion is affected by the level of pre-load applied to the beam. In addition, corrosion led to a change in the mode of failure from brittle shear to ductile flexure type in the pre-loaded beams. The amount of corrosion has been measured using gravimetric weight loss. It was found that the load-carrying generally decreased with increasing amount of corrosion of the beams, with exceptions in beams B3 and B5, which are due to the localized nature of corrosion induced by the chlorides and the failure of the gravimetric loss method to include this effect in its formula. Also, the combination of pre-load of 50% with a sustained load of 1% in the case of B5 caused greater loss in the load-carrying capacity than in B3, in which only a pre-load of 50% is applied. This is attributed to the phenomenon of self-healing and reduction in crack widths upon the removal of loads in the case of B3 which is not subjected to any sustained load while corrosion. Finally, the ultimate strengths of the tensile bars of the beams were found to be decreasing with decreasing load-carrying capacities of the beams.