External steel plates are sometimes bonded to concrete using an epoxy adhesive to strengthen existing structures. The durability of such systems is being investigated by TRRL (transport and road research laboratory), both by exposure trials and by monitoring the performance of a strengthened bridge. Reinforced concrete beams, 3.5 m long and externally reinforced with a mild steel plate, have been exposed to a coastal environment. The performance of two different resins were investigated. The beams were plated either before or after being loaded to produce flexural cracking. They were maintained under load during exposure and loaded to failure after 1 and 8 years. The plates were then removed from the beam and examined. Some light corrosion was observed on the plates bonded with resin l but this did not adversely affect the structural performance of the plated beams. The performance of beams plated with resin ll was less satisfactory. The beams exposed with the resin under load failed during the first 3 months of exposure due to debonding between the resin and the concrete. On the beams exposed with the resin unstressed, corrosion of the plates occurred because moisture had penetrated from the edge of the plates along the interface between the steel and the resin. This resulted in some debonding of the plate after 8 years of exposure, and caused premature failure of the beams during the load tests to failure. The condition of plates examined on a bridge after 13 years in service were found to be generally satisfactory except in areas where de-icing salts had penetrated the resin-steel interface and caused corrosion. (Author/publisher) For other reports on this subject see IRRD 247075 and 813190.
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