External steel plates bonded to the concrete surface using structural epoxy adhesives are sometimes used to strengthen existing structures. The durability of such systems has been investigated by TRL, both by exposure trials and by monitoring the performance of a strengthened bridge. Unreinforced 500mm long concrete beams and reinforced 3.5m long concrete beams were externally strengthened with mild steel plates, and exposed to high rainfall, industrial and coastal environments. The performance of two different resins was investigated (resin I: Ciba Geigy XD800 and resin II: Colebrand CXL 83). The beams were maintained under load during exposure. Load tests on the 0.5m beams were carried out after 1, 2, 10 and 19 years exposure and on the 3.5m beams after 1, 8, and 16 years exposure. The plates were then removed from the beams and examined. Some light corrosion was observed on the plates bonded with resin I but this did not adversely affect the structural performance of the plated beams. There was less corrosion on the plates which had been coated with an epoxy primer paint prior to assembly of specimens. The performance of beams plated with resin II was less satisfactory. Corrosion at the interface between the resin and the steel resulted either in failure during exposure or premature failure during the load tests. The durability of the bond with resin II has proved to be satisfactory on the Quinton bridge since plate bonding was carried out in 1975 except where the plates have been exposed directly to leakage of water and chlorides from the carriageway above. Tapping the surface with a steel hammer has proved to be a useful method for detecting debonding. At Quinton little debonding was identified during the most recent survey in 1993. (A)
Samenvatting