Empa engineers are continuing to test a concrete beam built in 1970 with steel reinforcement. After half a decade, the beam is showing no signs of weakness, says engineer Christoph Czaderski.
For half a century now, a long-term experiment has been running in Empa’s largest testing laboratory at the Dübendorf site. This involves a reinforced concrete beam manufactured in 1970 which was strengthened with a steel plate bonded to its underside and has since been subjected to a permanent load of just over six tons.
“After 50 years under 87 percent of the average breaking load, the epoxy resin bonding shows no weaknesses. Bonded steel plate reinforcements have thus passed the long-term test,” says engineer Christoph Czaderski, who has supervised the test in recent years.
fracture and fatigue tests in which their load limits were exceeded. The aim of the tests was to find out how well epoxy resin had proved itself as an adhesive for fixing a steel plate to a concrete beam. According to Czaderski, long-term tests show “practically no slip” in the adhesive joint after 50 years.
Retrofitting instead of new construction
The background to this work was that at the end of the 1960s, unusual crack formations appeared on various prefabricated shed roof elements made of reinforced concrete in a new industrial building in Kreuzlingen in Switzerlnad. These were discovered by a painter. In order to repair the damage, the elements were subsequently strengthened by gluing thin steel plates to the concrete surface.