Electrochemical realkalisation and combined corrosion inhibition of deeply carbonated historic reinforced concrete

Abstract

The electrode reaction and the change in composition and morphology of the rust layer on rebar surfaces after electrochemical realkalisation treatment are investigated by electrochemical measurement and scanning electron microscopy. The results show that the rust layer is gradually reduced following the sequence Fe³⁺→Fe²⁺→Fe⁰ through mechanisms postulated to involve proton exchange and dissolution–deposition. The realkalisation process can restore the alkalinity of the pore solution in carbonated concrete adjacent to cathodically polarised rebar and also reduce rust layers on rebar in severely carbonated concrete structures. However, though the alkalinity of pore solution is restored and the corrosion potential of the rebar in deeply carbonated concrete becomes more noble after cathodic polarisation, the rebar cannot repassivate while polarised. Thus, to assist in repassivation, additional inhibitor injection is proposed. The results demonstrate that the adjunction of inhibitor can limit the corrosion of the rebar. Therefore, the combination of inhibitor plus electrochemical treatment is likely to prolong the durability of deeply carbonated reinforced concrete structures.