Macrocell Activity in Slightly Chloride-Contaminated Concrete Induced by Reinforcement Primers

Patch repair systems are usually composed of a primer (or paint) for the reinforcement, a bond bridge, and a repair mortar to restore the initial geometry. This system is said to induce an enhancement of the corrosion activity of the adjacent nonrepaired zones if they still contain a certain amount of chlorides. In the present paper, the action of the steel primers on the galvanic effect toward unrepaired zones was studied. Four protection mechanisms were selected: repassivation, inhibition, barrier, and cathodic protection. Small beams were fabricated with an embedded, continuous bar in the top part and a segmented one that enabled the monitoring of the corrosion potential and the corrosion rate of each segment when disconnected, and the macrocell or galvanic activity between segments in repaired interfaces and nonrepaired zones. The results after submitting the beams to different humidity conditions show that the primers were mainly effective in the first month after repair and sometimes they may have enhanced the anodic activity at the interfaces between repaired and nonrepaired zones. At long term, primers based on the barrier mechanism showed better performance than simple concrete or the other primers. The study was possible because corrosion currents were measured in parallel with galvanic current. Each current, separately, cannot give enough information of the developed processes.