This paper presents the results of long term experiments with reinforced concrete blocks with controlled-width cracks placed along a central reinforcing steel bar. Ponding allows for cyclic or continuous exposure to a 5% NaCl solution to imitate a marine environment. Crack widths ranging from 0.25 mm to 1 mm (0.01–0.04 inch) and polarization levels ranging from −430 mV to −640 mV vs the Saturated Calomel Electrode (SCE) are used. Results suggest that cathodic protection with moderate polarization levels may be of limited benefit in the presence of cracks aligned lengthwise to the rebar independent of crack width. Specimens without protection experience corrosion after only a week of exposure. The 5.5 year-long tests revealed that current densities in the order of 8–19 mA/m2 were required to achieve cathodic protection. Selected specimens were autopsied to examine their condition, revealing the presence of corrosion in the central bar at the crack location. The results are evaluated as to implications on the practical applicability of cathodic protection to marine structures.
The chloride-induced corrosion of steel in reinforced concrete structures, especially in marine environments, can seriously limit service life. It is common today to design bridges to achieve a minimum 75-year service life, and the primary design approach to that end has been to improve the quality of concrete to make it less permeable and increase the clear concrete cover.1 Both steps greatly extend the time to initiation of corrosion; however, the added cover places construction constraints, and some high performance concretes may be more susceptible to cracking, requiring special handling with associated risk and cost.2
These cracks in concrete structures can cause major localized durability problems because chloride ions' transport to the reinforcement is greatly enhanced. Chloride concentrations of about 2.4 kg/m3 have been found at the steel/concrete interface in cracked concrete locations in some bridges built with low permeability concrete, compared to about 0.24 kg/m3 or less steel/concrete interface in sound concrete locations.3 Thus, early corrosion in high performance concretes is likely to develop mainly at crack locations with the resulting higher corrosion current densities.4 For this reason, durability performance in cracked concrete and alternative corrosion control methods including cathodic protection (CP) and cathodic prevention (Cprev) are becoming a dominant concern in modern design.5,6
