Sensor-packed footbridge demonstrates efficacy of flax construction

Flax is a very useful crop, being used in everything from e-racers to campers. With concrete being such a major contributor of carbon emissions, a team led by the Eindhoven University of Technology (TU/e) is researching whether it could also be used as a greener alternative building material, and to this end has constructed a sensor-packed footbridge to prove its efficacy.

The project is named the Smart Circular Bridge and builds on previous research by TU/e. It involves a team of five universities, seven companies, and three municipalities, and is located in the city of Almere, the Netherlands. The bridge can be used by pedestrians and cyclists and spans 15 m (roughly 50 ft). It's rated to safely hold the weight of up to 275 people at a time.

The build process for the main structure of the bridge is totally unlike constructing a standard bridge and involves the flax being laid on top of blocks of polyurethane, which lend the bridge its basic shape. A vacuum infusion process is carried out to remove all the air, with a resin then poured onto it all to hold the entire structure together. Finally, it's left to cure for around a day or so.

The bridge's decorative railings, meanwhile, were produced by robotically weaving flax fiber and are deliberately intricate, to underline the aesthetic and technical possibilities of flax.

"The first Smart Circular Bridge in Almere uses around 3.2 tonnes of flax fibers, mainly from French production," explained the TU/e press release. "The fibers, woven into mats, are impregnated with a polyester resin. In the first Smart Circular Bridge, 25 percent of this resin is based on biomass. For the coming bridges, the goal is to increase this share to about 60 percent. To achieve this goal, waste products from biodiesel production and recycled PET bottles are used. Innovations in the project include not only the development of a suitable resin that can handle the residual moisture of the flax fibers, but also the development of a cobalt-free accelerator. One of the advantages of this composite material is that flax is a fast-growing plant – compared to wood, for example."

The bridge is currently in use and is being continuously monitored with almost 100 integrated sensors that ensure it can withstand general wear and tear and changing seasons. The sensors can pick up any deformations and if a predefined limit is reached, the researches will receive an alert. In a neat touch, the data can be viewed on a public website.

Going forward, the Smart Circular Bridge is just the first of three bridges that will be made using flax over the next few years – with the second planned for the Netherlands, and the third slated for Germany.

Sources: Smart Circular Bridge, TU/e