Giving concrete infrastructure a second life

© 2012 EPFL

© 2012 EPFL

Rather than just fixing corroding concrete infrastructure, Professor Eugen Brühwiler and his team of engineers have shown that it can be improved using ultra-high performance fiber reinforced concrete.

Today we tend to be all too quick to throw away clothes, furniture, or other belongings when they start to show signs of wear and tear or simply go out of style. We’re victims of the same mentality outside our homes, too, just on a larger scale. In an act of questionable sustainability, entire buildings are demolished to make way for newer, more sustainable ones. But when it comes to infrastructure, it’s not so simple. The throw-away mentality would dictate that we tear up and replace roads, bridges and railroad tracks when they begin to show signs of aging, such as corrosion or cracks. But surely a more sustainable, not to mention more cost-effective, solution would be to fix them, right?

I hate the term ‘to fix’,” says Professor Eugen Brühwiler, head of the Laboratory of Maintenance, Construction and Safety for Civil Structures and director of the recently concluded National Research Program 54 on the sustainability of the built environment. “We are interested in the question of how far we can take and use our existing built structures,” he explains. ’Fixing’ infrastructure, to him, is simply patching over defects without identifying their root cause. “Five years later, you have the same problem all over again - what a waste!” Rather than just being patched up, a road or a bridge should come out of any intervention improved. Over the years, Brühwiler and his collaborators have worked tirelessly to find strategies to do just that, and they’ve come up with a convincing solution: concrete!

Conventional concrete, composed primarily of cement, gravel, and water, cast around reinforcing steel bars and left to harden, is used widely in construction. Buildings, bridges, tunnels, walls, as well as roads and railroad tracks have been built with it for more than a century. The concrete Brühwiler proposes as a cure for many weaknesses civil structures suffer is of a different type, however: Ultra-High Performance Fiber Reinforced Concrete (UHPFRC). Though a mouthful, this novel formulation for concrete is actually quite simple: by adding a specific fraction of short, thin metal fibers to the powdery components, the resulting building material resists loads better than conventional concrete, and gravel can be eliminated from the mix. As a result, it is more dense, and thus becomes completely impermeable to water and gases, an extremely durable building material.

Corrosion, often implicated in the degradation of built structures, is most commonly caused by exposure of building materials to moisture. Thanks to its density and impermeability, the ultra-high performance fiber-reinforced concrete developed in Professor Brühwiler’s lab acts as a tight seal, protecting the structure’s interior. Thanks to significantly shorter hardening times, roads can be rehabilitated much faster than previously possible, saving time, money, and drivers’ nerves. And Brühwiler has already successfully demonstrated that with the right formulation, the concrete will stay put long enough to harden even when applied to steep slopes. But that’s not all. New structures can also be made lighter and with less raw materials, all without sacrificing performance. Imagine concrete bridges with elements only one fourth their current thickness.

The concept of high performance fiber reinforced concrete may not be entirely new, but the EPFL civil engineers have been able to position themselves successfully in the field. These experts are global pioneers in using fiber-reinforced concrete to repair and enhance existing civil structures. The economic and environmental benefits of their approach has struck a chord beyond our borders. As Brühwiler explains: “We are now attracting interest from abroad, where the frame of mind is much more focused on building costly new structures. Here in Switzerland, we have understood that we can get a lot more out of what we already have.”