Degradation of Steel Girder Bridge Bearing Systems by Corrosion

Corrosion of anchor bolts in bridge bearings presents two principal problems: (1) failure of the anchorage due to loss of bolt shear strength, and (2) loss of bearing functionality due to the build up of corrosion products. Of Georgia’s 1500 steel girder bridges, 411 (27%) were found to be experiencing anchor bolt corrosion through routine bridge inspections. Field investigations were performed at eight bridges around Georgia. Anchor bolt corrosion was found to be locally accelerated, with necking occurring at the concrete interface. This degradation is primarily due to the formation of concentration cells with the alkaline concrete embedment and to crevice effects where the build up of soil and debris occurs at the anchorage. An experimental program was developed, including long-term in-solution exposures in addition to electrochemical testing. Results of long-term concentration cell experiments indicate corrosion rates up to 4.5mpy, 4 to 6 times that of the same bolt in an uncoupled state. Type 304, 316, 2101, and 2205 candidate stainless steels were investigated using cyclic polarization. Each alloy showed adequate corrosion resistance in the simulated bridge bearing environment, with Type 304 showing the least resistance to localized corrosion.