Considerations on the possible corrosion mechanisms of reinforced concrete structures and on the factors that control their kinetics

Abstract

It is well known that in normal circumstances steel remains passive in concrete, due to the highly alkaline pH, and that the passivity of the rebars guarantees the practically unlimited durability of reinforced concrete structures (RCS). However, a number of matters continue to cause controversy, with the risk of promoting the acceptance of behaviours or mechanisms that cannot be extended to all circumstances; for instance: a) that when carbonation is ruled out, concrete "always" imposes a highly alkaline pH on rebars. b) that in RCSs corroding active state, cathodic control by oxygen diffusion in the aqueous phase of the pore network is "usual", c) that the influence of galvanic macrocouples strongly conditions the rebar corrosion process, d) that the concrete coating "always" has a protective effect on rebars. e) that the initial grade of corrosion of rebars does not matter, since the concrete's great alkalinity guarantees their passivation. This paper presents results which demonstrate that the response of RCSs in the above cases is variable, at times contradictory, depending on the set of experimental conditions.