Construction of a two-storey, 2,200-square-foot learning and presentation centre on the campus of Technical University (TU) in Dresden, Germany began this summer. What makes this building interesting is the use of carbon fibre reinforced concrete.
Locally known as Carbonhaus and funded by the German Federal Ministry of Education and Research, this demonstration project claims to be a world-first.
Manfred Curbach, director of the Institute of Concrete Construction at TU Dresden, has been researching the inclusion of carbon fibre in concrete since the 1990s. Initial reaction was not encouraging.
“When we started publishing the first results on carbon concrete at that time, we were smiled at.”
Today, TU Dresden considers the Carbonhaus “a quantum leap in the history of construction.”
What is exciting researchers is that carbon fibre reinforcement polymers (CFRP) used in place of steel can extend the life of a structure, reduce structural weight, and reduce GHG and carbon emissions, all at a price comparable to steel. CFRP also opens up new design possibilities, demonstrated by Carbonhaus’ dramatic, double-curved roof and its seamless 24-metre expanse of concrete.
According to researchers, the majority of concrete used in construction today is in place only to protect steel reinforcements from corrosion. The resultant cracking and erosion over time can limit the life of both buildings and bridges. Carbon fibre, however, has extremely high corrosion resistance and does not degrade, thus extending the structure’s life. Therefore, less concrete is required in the project. This reduced need for concrete means fewer GHGs related to the construction process.
Since Carbon fibre also delivers tensile strength equal to steel at only 25 per cent of the weight, material handling is easier and installation costs are reduced. Carbon fibre’s strength-to-weight advantage over steel also means less steel production is required, which again reduces GHGs associated with the project.
The use of carbon fibre to strengthen concrete has been limited to date. However, at the 2016 International Conference on Fibre-Reinforced Polymer (FRP) Composites in Civil Engineering, engineers from EMPA (Swiss Federal Laboratories for Materials Science and Technology) presented proposals to take CFRP development further using pre-stressing. EMPA followed up in July 2020 with a patent for a new process that allows the concrete to pre-stress itself through expansion as it hardens, rather than using expensive pre-stressing beds.
“Pre-stressing is generally used when a concrete element has to withstand very high loads — for instance, beams, bridges or cantilevered structures,” EMPA said in a recent release. However, they explained because steel is susceptible to corrosion, the concrete layer around the pre-stressed steel must have a “certain thickness.”
Lightweight, pre-stressed CFRP concrete results in significantly leaner concrete components, according to EMPA.
“Our technology opens up completely new possibilities in lightweight construction,” says development team member Mateusz Wyrzykowski. “Not only can we build more stable structures, we also use considerably less material.”
No one, including Curbach, is under any illusion that CFRP concrete will quickly dominate the world of construction. Despite international interest expressed in his research and findings, the industry has a reputation for inertia and is slow to adapt to new technologies, particularly when they run ahead of the regulatory environment.
Engineers Mike Abell, Paulo Nolli and Stephen Tattershall outline some of the challenges facing widespread adoption of CFRP in concrete as a standard method of construction.
“Available software doesn’t really provide for this class of material, so a lot of customization is required in design and analysis. This creates a barrier to application which discourages engineers from applying the method.”
They add that since engineers and most jurisdictions aren’t familiar with the associated behaviour and modelling of carbon concrete, there would be challenges with permit approvals.
However, they agree with Curbach’s suggestion that even today without manufacturing scale, CFRP concrete could be cost-effective versus steel.
The steel and concrete industries are often the target of environmentalists because of their outsized contributions to global GHGs. Innovations like CFRP technology point to a new, hopeful direction.
John Bleasby is a Coldwater, Ont.-based freelance writer. Send comments and Inside Innovation column ideas to firstname.lastname@example.org.
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