Corrosion products of reinforcing bars embedded in concrete

Chloride-induced reinforcement corrosion in RC structures has attracted a lot of attention recently. Such corrosion finally leads to cracking along the reinforcing bars on account of the expansive nature of the oxidation products. In order to evaluate the critical corrosion that causes the onset of these cracks, it is important to better understand the composition and properties of the corrosion products formed within concrete. From a study of corrosion products formed in bars embedded in concrete and bare bars exposed in a marine environment over a period of 5 years it was found that crystalline magnetite, goethite and lepidocrocite make up only 30% of the rust formed within concrete, as compared to about 45% for uncovered bars. Further, using a model proposed here, the ‘equivalent volume expansion ratio’ was estimated to be between 2.9 and 3.2. From these results and non-linear FEM analysis, it was found that the loss of only several micrometers of the bar could lead to the formation of longitudinal cracks.