Smart Circular Bridge made of Bio-composite

Innovations for Climate Protection

May 2022

An old material is being rediscovered: flax has been with us for thousands of years in the form of clothing, sacks, and robust ship’s ropes. Now the plant fibres are experiencing a renaissance and could become the building material of the future. Combined with a special bio-resin, it can be made into a light and highly stable material with properties comparable to aluminium or steel.

The EU project “Smart Circular Bridge” shows what is possible with this innovative new material through the development of three bridges made from this so-called bio-composite. A first one has now been built, and two more will follow.

In times of climate change and dwindling raw materials, bio-composites offer a great opportunity for the construction industry, which has a huge CO₂ footprint and consumes vast resources. They hold enormous potential for a bio-based circular economy.

Interdisciplinary Teams Drive Development

The first “Smart Circular Bridge”, with a span of 15 metres, has been realised by an international consortium of 15 partners led by Eindhoven University of Technology in the Netherlands. The project team consists of five universities, seven innovative companies, and three municipalities.

The first bridge, installed at the Floriade international horticulture exhibition in Almere (Netherlands), opened on April 22. Two more “Smart Circular Bridges” for pedestrians and cyclists will be built in Ulm, Germany, and Bergen op Zoom, Netherlands, later in 2022 and in 2023 respectively.

Through this intensive cooperation between science, industry, and local authorities, a wide range of innovations is being launched.

Laboratory Tests to Understand Long-Term Behaviour

One focus of the Smart Circular Bridges research is understanding the long-term behaviour of natural fibre-reinforced composites, with the aim of using them in large-scale projects lasting several decades.

To this end, the bio-composites were investigated in laboratory tests regarding their tensile and compressive strength, as well as material stiffness under various environmental conditions such as UV radiation and moisture. Particular attention was given to fatigue strength and material ageing.

Real-Time Monitoring – On a Public Dashboard

A complementary aspect of the research is the structural health monitoring of the three bridges. The system used is similar to that applied in offshore wind farms, meaning the bridges are monitored continuously in real time rather than periodically inspected.

The monitoring system has two main tasks:

Ensuring structural safety, especially important when using relatively new materials in load-bearing structures
Providing continuous data to create a precise picture of the bridge’s condition and estimate its lifespan

Nearly one hundred sensors continuously generate large amounts of data about the material’s behaviour under real-life conditions. As with laboratory results, real-time data help verify finite element models and predicted material properties.

Data from the sensors are publicly accessible in real time via:
dashboard.smartcircularbridge.eu/

Monitoring with Three Types of Sensors and Artificial Intelligence

Fibre-optic sensors measure deformations in different directions. They are embedded within the bio-composite material. Even if one fibre breaks, data transmission continues via a second interface.
Temperature sensors provide comparative data to evaluate deformation patterns and are also located inside the bridge.
Acceleration sensors detect even minor vibrations and provide insights into movement caused by wind or dynamic traffic loads.

All measurement data are continuously recorded, initially processed on-site, then transmitted to a server and reduced. Using artificial intelligence, key parameters are extracted to describe the bridge’s condition. If a predefined threshold is exceeded, the system immediately triggers an alarm.

Monitoring builds upon earlier testing with large-scale models and allows continuous data collection under real-use conditions. Combined with materials research, it also enables estimation of the remaining service life.

The project aims to achieve a lifespan comparable to conventional glass-fibre reinforced polymer bridges, while offering the environmental benefits of bio-composites.

Material

The first Smart Circular Bridge in Almere uses about 3.2 tonnes of flax fibres, mainly from France. The fibres are woven into mats and impregnated with a polyester resin.

Currently: 25% bio-based resin content
Target for future bridges: ~60%, using biodiesel by-products and recycled PET bottles

Key innovations include:

Development of a resin compatible with residual flax moisture
Creation of a cobalt-free accelerator

Flax offers advantages as a fast-growing renewable resource. In addition, other natural fibres are available globally for high-performance bio-composites.

Construction

The bridge structure consists of:

A bio-composite deck
A bio-composite railing
Abutments with access ramps

The deck is a multi-cell rectangular box structure with continuous longitudinal webs.

Main dimensions:

Width: 3 m
Height: 0.9 m
Span: 15 m

Panel thickness:

Longitudinal webs: 15 mm
Soffit: 20 mm
Carriage surface: 25 mm

Structural calculations by Eindhoven University confirm that the bridge can withstand:

Permanent loads
Distributed traffic loads
A vehicle load of 2 × 25 kN axle

The abutments consist of sheet pile walls, two bored piles, and a steel beam support. Loads are transferred vertically via the beam and horizontally via sheet piles. Concrete slabs on sand beds provide access routes.