How long can fiber reinforced polymer sustain concrete structures? A question that is answered by scientists

It is a fact that, in modern society, the majority of our infrastructure (buildings, bridges, tunnels, etc.) is made of ageing concrete. A cost-effective method of sustaining this infrastructure was recently developed: the external coating with fiber reinforced polymer (FRP) composites.

But we don’t know if it is a temporary patch or a durable solution. Some research efforts have looked into this question. A 13-year-long study published in Composites Part B finally finds out, taking us one step closer to the wide-spread utilization of this solution.

In the FRP-strengthening of concrete, glass or carbon fiber reinforced polymer (GFRP or CFRP) composites are bonded onto concrete using an epoxy adhesive. These sheets provide additional support and strengthen the concrete structures by protecting them from harsh environmental conditions, such as high moisture levels and temperatures. But the problem is, these same environmental conditions can potentially degrade the concrete-FRP bond as well, causing the FRP protection system to fail prematurely.

Professor Jaeha Lee from Korea Maritime and Ocean University, a lead researcher in the 13-year study, says, “The information available on FRP-concrete bond behavior following sustained loads in different environments is very limited, particularly for periods beyond two years.”

The researchers tested both CFRP and GFRP systems under various indoor and outdoor environmental conditions for change in a parameter called the debond onset strain. This is a measure of the deformation that occurs before failure - larger strains are usually preferred to forewarn failure.

The researchers found that environmental conditions had a significant impact on bond behavior. At the end of 13 years, larger reductions in debond strains were observed in outdoor beams than indoor beams. Further, the bond behavior varied between materials. Changes in debond strain were negligible in indoor CFRP beams, while in indoor GFRP beams, there was a notable decrease.

Professor Lee stresses the importance of such tests for future use stating: “If the long-term durability of concrete-FRP interfaces is evaluated, the use of this strengthening system is expected to increase with minimum investment. This will be great for affordably maintaining a safer city by minimizing the risk of collapse or damage of existing structures.”