Empa scientists have developed a new formula for concrete elements to pre-stress themselves.
According to the team led by Giovanni Terrasi, Pietro Lura and Mateusz Wyrzykowski, this could open the door to more cost-effective and material-saving architecture.
More than ten billion tons of concrete are produced worldwide every year and this implies harmful emissions and huge energy requirements. Cement, the binding agent in concrete, is alone responsible for up to 8% of the global CO2 emissions.
Replacing concrete is not an easy task, as the building material simply offers too many advantages.
The Empa team has now developed a self-prestressing concrete technology to make concrete elements leaner, yet durable and stable, so that materials consumption is reduced.
Pre-stressing is generally used when a concrete element has to withstand very high loads – for instance, beams, bridges or cantilevered structures.
In a conventional pre-tensioning technology, the reinforcements or tendons – usually made of steel – are anchored on both sides of the element before the concrete is cast, put under tension and released again after the concrete has set.
This makes the concrete more stable.
There is one catch however: Steel is susceptible to corrosion and so the concrete layer around the pre-stressing steel must have a certain thickness.
One solution lies in using carbon ﬁber-reinforced polymers (CFRP) to replace steel reinforcement.
Because CFRP does not corrode, it is possible to produce signiﬁcantly leaner concrete components with almost same structural properties.
Nevertheless, very expensive prestressing beds are required and the anchoring of CFRP bars is much more complicated than that of steel.
The Empa team has now succeeded in completely dispensing with anchoring on both sides of the concrete element, as the concrete self-expands as it hardens.
As a result of this expansion, the concrete puts the CFRP bars in its interior under tension and thus automatically prestresses itself.
In lab tests, Empa’s self-prestressed CFRP concrete elements showed they could bear loads comparable to those that were conventionally prestressed – around three times more than a non-prestressed CFRP concrete element.
“Our technology opens up completely new possibilities in lightweight construction,” says Wyrzykowski.
“Not only can we build more stable structures, we also use considerably less material.”
Image and content: Empa