The world’s first three-dimensional (3D) printed reinforced, pre-stressed concrete bridge recently opened as part of a new road project in Gemert, The Netherlands.
The bridge was printed at the nearby Eindhoven University of Technology (Eindhoven, The Netherlands). With the knowledge the researchers gained in this project, they say they are now able to design even larger printed concrete structures.
The bridge is the first civil infrastructure project to be realized with 3D concrete printing, according to the university. The bridge is 8-m long, with a clear span of 6.5 m, and 3.5-m wide. Developers tested the bridge by putting a load of 5 tons on it, significantly larger than the load the bridge is expected to actually carry.
The bridge is designed to carry cyclists for 30 years or more, with hundreds of cyclists expected to ride over the printed bridge each day. It is part of a large road construction project, led by BAM Infra (Gouda, The Netherlands) and commissioned by the province of North Brabant.
As part of the project, researchers say they successfully developed a process to incorporate steel reinforcement cables while laying strips of concrete. According to the researchers, steel cables are the equivalent of the reinforcement mesh used in conventional concrete. The steel cables are used to handle tensile stress because steel can handle tensile stress better than concrete, they say.
One of the main advantages of printing concrete is that much less concrete is needed than in the conventional technique—in which a mold, or formwork, is filled with concrete. By contrast, the printer deposits only the concrete where it is needed, which decreases the use of cement, the researchers explain. This reduces carbon dioxide (CO2) emissions, as cement production has a very high carbon footprint. Another benefit is that the printer can make any desired shape, whereas conventional concrete shapes tend to be unwieldy in shape due to the use of formwork.
Concrete printing also enables a higher production speed, since no formwork structures have to be built and dismantled—and reinforcement mesh does not have to be put in place separately. Overall, researchers say the printing process could eventually be three times faster than using conventional concrete techniques.
With the knowledge gained, the university researchers say they are now able to design and realize even larger structures. Their approach is to print elements that are assembled afterwards, because otherwise the maximum size of the structure would be limited by the size of the printer.
Source: Eindhoven University of Technology, www.tue.nl/en.