ABSTRACT
This paper presents the results of a corrosion investigation on rebar embedded in concrete slabs which are exposed to sea water for more than 4 years. Corrosion potentials and polarization resistances were measured on the rebar. The w/c ratio varied between 0,40–0,75. Some of the slabs were prepared with cracks, 0,2–0,6mm in the cover surface. The Cl− and the OH− concentrations in the concrete were determined at the level of the rebar when the corrosion started. The results show that the w/c ratio was the dominant factor which controls corrosion on rebar in concrete. Initiation of corrosion is achieved, for a w/c 0.40, when the Cl/OH ratio is about 6.
The cracks are of minor importance for the corrosion initiation when the structure is totaly submerged. One explanation for this is that the cracks are sealed with brucit, Mg(OH)2, which is producced because of the high magnesium ion content in the sea water. Another explanation is that the oxygen content in the sea water is so low that the cathodic reaction will be prevented.
