A thinner bridge with enormous strength

It is almost as resilient as steel, has a long service life and makes especially thin structures possible: Ultra-high performance concrete, which is still only rarely used in Germany in spite of its positive properties. “This is a new material which behaves differently from conventional concrete,” explains Prof. Oliver Fischer of the TUM Chair of Concrete and Masonry Structures. “Germany has yet to introduce a set of regulations for its use.”

The material has been the subject of international research for years – including at the Technical University of Munich (TUM). The special thing about it: Its composition makes the material exceptionally dense, with almost no internal cavities that can be penetrated by moisture or salts which could damage the material. Ultra-high performance concrete is also much stronger, able to withstand four to five times the pressure which the conventional concrete currently used in bridge construction can take.

The bridge was commissioned and supported by the Tegernsee-Bahn GmbH (TBG) rail company. TBG CEO Heino Seeger explains why: “Tegernsee-Bahn actively promotes future-oriented forms of passenger rail traffic. This includes helping develop rail infrastructures in the best way possible. An intensive feasibility study on the use of the new material indicated essential design advantages for the pilot project. We are pleased to have been able to support TU Munich in this initial application for a railway bridge and to make yet another important contribution on behalf of the local Oberland region.”

Carbon fibers from the 3D printer

By making measurements during ongoing operations, the researchers hope to make important findings which will be incorporated among other things in the development of a future set of regulations for the application of the material, which – for example – also may be applied as a strengthening layer on existing concrete and/or steel bridges. The first measuring results confirm the design assumptions and structural analyses.

The ultra-high performance concrete owes its high density and strength to an exactly defined ratio of cement particles to fine additives and scaled granularity. Steel micro-fibers are another important component of the ultra-high performance concrete, providing higher tensile strength and ductility. When the bridge is bearing a load, tensile forces have to be safely transmitted much the same way as in a rope during a tug-of-war.

In their next step the engineers want to increase the tensile strength of the ultra-high performance concrete even further: For example, with short carbon fibers from the 3D printer. Not only can these fibers be easily arranged all in a single direction in the concrete, they also interface better with the material, providing higher load bearing capacity and a longer service life.