We were hired recently to oversee the repair of an elevated train platform. The contractor on the job has removed much of the delaminated concrete from the deck, but he doesn't plan to undercut the exposed rebar. He says that the underside of the rebar hasn't corroded so there's no reason to remove concrete from beneath the bars. He plans to wire brush or sandblast the rust off the top of the bars, then place the repair concrete. I would feel more comfortable if the rebar were undercut so that the repair concrete is mechanically anchored to the deck. Which method is correct?
The International Concrete Repair Institute addresses this subject in their "Guide for Surface Preparation for the Repair of Deteriorated Concrete Resulting from Reinforcing Steel Corrosion." The guide recommends undercutting all exposed corroded rebar, regardless of whether the corrosion is believed to be limited to the top surface of the bar. The rebar should be undercut at least 3_4 inch or 1_4 inch more than the largest aggregate in the repair material, whichever is greater. If noncorroded rebar is exposed during concrete removal, these bars do not need to be undercut as long as their bond to the concrete has not been broken.