The Swiss Federal Laboratories for Materials Science and Technology (Empa) (Dübendorf, Switzerland) released an update on its 50-year-old experiment involving a reinforced concrete beam strengthened with a steel plate bonded to its underside and subjected to a permanent load of 6 metric tons (6.6 tons). The goal of this experiment was to determine the adhesive properties of epoxy resin in fixing a steel plate to a concrete beam.
Empa engineer Christoph Czaderski, who has supervised the test in recent years, summarizes its results thusly: “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.”
According to Empa, the concrete beam was originally manufactured in 1970 along with five other identical specimens that all underwent different tests. However, those five specimens broke down due to static fracture and fatigue tests. By contrast, the beam that withstood the 50-year tests showed “practically no slip” in the adhesive joints, Czaderski reports.
The origins of the experiment go as far back as the end of the 1960s, when unusual crack formations were discovered on various prefabricated shed roof elements made of reinforced concrete in a new industrial building in Kreuzlingen, Switzerland. At the time, attempts were made to repair the damage and reinforce the concrete by gluing thin steel plates to its surface. But because these techniques had not yet been perfected, the elements did not have long-term stability.
Empa looked to address this issue with various fatigue tests and investigations that were initially intended to last a few months at most. And yet, 50 years have passed since then and the steel-plate strengthened concrete beam remains in Empa’s testing hall in Dübendorf. At first, Empa engineers feared that the reinforcing effect of the bonded steel plate might decrease over time due to creeping in the adhesive joint. However, no significant slipping in that joint has occurred, which Czaderski says is a “truly astonishing and extremely significant result.”
In a statement. Empa says its 50-year test is a typical example of its commitment to developing and researching new, simple, and inexpensive reinforcement methods using modern materials such as epoxy resins, carbon fiber reinforced plastics, and shape memory alloys.
Source: Empa, www.empa.ch.