When corroded reinforced concrete structures are repaired it is often difficult to decide whether the steel should be cleaned or cut out and replaced. This report looks at the effects of wire brushing, powered wire brushing and grit blasting on mild steel reinforcing bars suffering from either general or localised corrosion. The generally corroded bars were produced by atmospheric exposure at marine and industrial locations whereas the locally corroded bars were taken from a bridge deck. The pitting resulting from localised corrosion is classified as either coarse or fine. The specimens, after cleaning, were embedded in two concrete mixes, one without added chloride and one with 0.5 per cent chloride ion by weight of cement. The half cell potential of the steel was monitored at regular intervals for a year to determine whether or not the steel was corroding. The results showed that wire brushing and powered wire brushing are not effective for cleaning locally corroded steel and would not prevent corrosion from continuing in a repair. Grit blasting was usually successful for steel with coarse pits but not for steel with fine pits. This suggests that the safest practice would be to cut out and replace all pitted steel. The results for generally corroded steel show that the cleaning is only necessary where there has been exposure to chlorides. In this case steel should be cleaned by grit blasting. It is important to prevent chloride from entering repaired concrete since no cleaning process successfully prevented corrosion of pitted steel in concrete containing 0.5 per cent added chloride.
Samenvatting