Corrosion autopsy of a structurally unsound bridge deck

An investigation was performed on a 12-year old salt-contaminated, reinforced concrete bridge deck that had to be replaced because of its deteriorated condition. In this investigation, the electrical half-cell potential measurements and effect of chlorides present seem to be related to some threshold amount that changes the steel from a passive to an active state. Beyond this point, the amount of salt present has little or no effect except as it might infleunce the area of corrosion involved. The chaining or soundind of the deck to locate delaminated concrete performed the function very well but did not necessarily locate the corroded steel. From the observation of the type of cracking, it appeared that the final mode of distress was concrete fatigue. An investigation of actual concrete cover disclosed that there was reinforcing steel corrosion at depths greater than 3 in. It was determined that estimating the pit depth of steel by visually estimating the thickness of rust is not a very useful inspection technique. In this highly slat-contaminated bridge deck, no relation was found between variations in the chloride content of the concrete and the relative severity of the corrosion of the steel. /Author/