Introduction The performance of a reinforced concrete repair depends signifcantly on the condition of concrete in the reinforcement vicinity and on the quality of (re-)encapsulation. The extent of concrete removal prior to repair must be adjusted in accordance with the degree of contamination and the nature of distresses affecting the member or structure. Question When corroded reinforcing steel is encountered in a repair, should the bar be undercut? How far should the bar be exposed along its length? Answer Concrete should be removed around the reinforcing bar, leaving in all directions a clear distance of at least 1/4 in. (6 mm) plus the dimension of the repair material maximum size aggregate. In addition, concrete removal along the reinforcing bar shall continue until the bar is essentially free from corrosion products. Discussion When a portion(s) of the electrically continuous reinforcing bar is exposed to a chloride-free repair material and the rest of the bar remains in contact with chloride-contaminated and/or carbonated concrete, corrosion in areas adjacent to the repair may be accelerated. This condition is often referred to as the “ring effect” or “halo effect.” Hence, when corrosion problems are encountered in a repair, the chloride ion concentration and the depth of carbonation in the existing concrete should frst be determined. The decision to undercut the reinforcing bar should be made based on the chloride ion concentration and/or extent of carbonation in the surrounding concrete. There is a high risk of continuing corrosion whenever, at the reinforcing steel level, the acid-soluble chloride content by weight of cement exceeds 1% (ASTM C114) or cement paste is carbonated. Signifcant contamination may require the removal of existing concrete surrounding the bar.
Summary When corroded reinforcing steel is encountered in a repair, surrounding contaminated concrete should be removed and the bars should be undercut and exposed along their entire affected length. References 1. ICRI, “Guide for Surface Preparation for the Repair of Deteriorated Concrete Resulting from Reinforcing Steel Corrosion (ICRI 310.1R-2008) [formerly No. 03730],” International Concrete Repair Institute, Rosemont, IL, 2008, 12 pp.ACI 364.6T pdf download.