When Concrete learns to pre-stress itself

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A beam made of self-pre-stressed concrete with carbon fiber reinforced plastic (

A beam made of self-pre-stressed concrete with carbon fiber reinforced plastic (CFRP) as reinforcement. Image: Empa

Concrete is by far the most widely used building material in the world - and the trend is rising. Using a new type of concrete formula, an Empa team has succeeded in producing self-prestressed concrete elements. This innovation makes it possible to build lean structures much more cost-effectively - and save material at the same time.

Carbon Fibres instead of Steel

As early as in the 1990s, carbon fiber-reinforced polymers (CFRP) were used to replace steel reinforcement. Because CFRP does not corrode, it is possible to produce significantly leaner concrete components - with very similar structural properties. "But if you want to pre-stress these CFRP reinforcements in order to be able to build even thinner structures with a higher load-bearing capacity, you reach your limits," says Wyrzykowski. Very expensive pre-stressing beds are required and the anchoring of CFRP bars is much more complicated than that of steel. Thus, pre-stressed CFRP high-performance concrete is still not very widely used.

Expanding Concrete

The Empa team has now succeeded in completely dispensing with anchoring on both sides of the concrete element, as the concrete does the work by itself: Thanks to a special formula, the concrete expands as it hardens. As a result of this expansion, the concrete puts the CFRP bars in its interior under tension and thus automatically pre-stresses itself. In their laboratory tests, the researchers were able to show that the self-pre-stressed CFRP concrete elements could bear loads comparable to those that were conventionally pre-stressed - around three times more than a non-pre-stressed 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 consider-ably less material." The Empa researcher also envisions completely new fields of application: "We can easily pre-stress in several directions at the same time, for example for thin concrete slabs or filigree curved concrete shells," he says, looking to the future. These new applications are now being developed further in cooperation with industry partner BASF.

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Stephan Kälin
Phone +41 58 765 49 93

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