Field Test of Reinforcement Corrosion in Concrete


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Title: Field Test of Reinforcement Corrosion in Concrete

Author(s): P. Fidjestol and N. Nilsen

Publication: Special Publication

Volume: 65


Appears on pages(s): 205-222

Keywords: beams (supports); cathodic protection; chlorides; corrosion; cover; cracking (fracturing); field tests; galvanic corrosion; marine atmospheres; offshore structures; reinforced concrete; reinforcing steels; sea water.

Date: 8/1/1980

The use of large offshore concrete structures for oil and gas production created several questions regarding the behaviour of reinforced concrete in a marine environment. Some of these questions concerned corrosion of exposed and embedded steel. This study reports the up-to-date results and conclusions from a test program which has been running since December 1976. A total of 70 reinforced concrete beams, some of them cracked, are submerged in the sea on the West Coast of Norway. All specimens have been monitored intermittently by electrochemical methods, and some specimens were removed and broken open after 18 months of exposure. From the analysis of the current test results it is concluded that many of the questions posed regarding reinforcement corrosion in marine concrete may be laid to rest. There are clear indications that corrosion in cracks in the cover, galvanic corrosion of exposed steel coupled to embedded steel, excessive consumption of current in cathodic protection systems and pitting due to penetrating chlorides are problems which in the long run will cease to have any significance. This encouraging result is due to inhibition of oxygen flux to the reinforcement, and this has as a direct consequence that the free corrosion potential of the embedded steel after 6-18 months stabilize at a very low value, (typically -900 mV Vs. Ag/AGC1). Then the steel is in an active state of corrosion at an extremely low rate (< 10 um/year). It seems that the crack-width criteria which are currently enforced are overly conservative, and future efforts should include re-evaluation of current codes.