Modelling deterioration of structural behaviour of reinforced concrete beams under saline environment corrosion

In the assessment of existing structures the likely future deterioration of strength and stiffness is of interest. For reinforced concrete beams one of the most important influencing factors is the loss of reinforcement cross-sectional area at critical locations. Because corrosion is a long-term process for well-designed structures, there is only limited field experience available on which to draw and with which to make empirical rules. The considerable research effort in corrosion of reinforcement in concrete structures has focused mainly on the rate of migration of chloride ions from the environment through the concrete to the corroding steel surface. This will estimate the time before reinforcement corrosion becomes significant but does not provide the rate of structural deterioration. In the present paper a method is proposed for estimating structural deterioration, based on evidence that (a) reinforcement corrosion causes internal damage to and loss of bond with the surrounding concrete and (b) chloride diffusion is influenced by stresses set up in the concrete by external loading. Both these factors affect the rate of chloride migration locally and hence the amount of corrosion and material strength loss at any point in time. The proposed method is outlined and an example application given. Reasonably good agreement between the results of the proposed procedure and the few experimental results was obtained.