Drawn barrier: 3D printing at large

Groningen's new southern ring road is ready. The 12-kilometer road is important for traffic to and from the city, as well as for traffic passing through Groningen.
Road safety is guaranteed by BKB Infra's more than 40 kilometers of towed barriers, which, thanks to the flowing lines, not only provide a calmer image for road users, but also lift the project aesthetically to a higher level.

BKB Infra is considered the specialist in the realization of towed barriers. "We have been involved in the Aanpak Ring Zuid, as the project is officially called, since 2017," says Laurens Bogerd, commercial manager at BKB Infra. "At the time, Combinatie Herepoort was still in doubt between a prefabricated barrier or a pulled barrier, but because of the complex phasing of the project and the aesthetic requirements, a pulled barrier was preferred. What we are doing is a kind of 3D printing wholesale. Using our slipform paver, we create a concrete barrier from concrete mortar in one pass in a smooth line. We are not bound to a fixed length and can start wherever we want. Especially with complex phasing like here in Groningen, this is of great added value."

Complex phasing

Approach Ring South is characterized by a complex phasing of four clusters. "Within those four clusters, work was also phased. For us, that meant a very fragmented project, in which we had to pull a section of barrier on demand each time. Sometimes it involved only 1,000 meters, other times several kilometers," Laurens looks back. "In 2020 we made the first work, in the summer vacations of 2024 the last kilometers. The beauty of this technique is that you don't see the phasing reflected in the end result. That's different with a prefab barrier. Then you can't skip a phase, but everything has to be placed consecutively, while we can rotate a barrier between two other ends without any problems. And that is what happened here on a large scale. Especially in 2024, where the combination connected the four separate clusters - the Vrijheidsplein, the Julianaplein, the sunken section and the Europaplein."

Special finishing

On the design of Groningen's new southern ring road, the architect has overwhelmingly left his mark, Laurens knows. "The works of art are beautifully designed and richly decorated. Furthermore, the project is characterized by organic forms and flowing lines with a high level of finishing. The shape of a barrier is determined by law, but with a drawn barrier we are able to underline precisely those intended organic lines.   

Normally the barrier is finished with a fine broom stroke, here everything has been sanded and chipped. Furthermore, the saw cuts serving the contraction joints and expansion joints were rinsed clean and we applied a special curing compound that looks less spotty." In the free field, contraction joints were applied every 3.5 meters and an expansion joint was provided every 80 meters, while in the sunken position BKB Infra incorporated a slot joint every 25 meters in the drawn barrier, so that the slots could dilate and the barrier would not be crushed.

GPS unit

BKB Infra has a long track record in barrier pulling. Since the first project in the combi tunnel in Nijverdal in 2012, BKB Infra's pulled barrier concept has taken off. "We know better than anyone else how to convert the preconditions and requirements into a ready-made solution," Laurens emphasizes. "We can also meet specific fire safety requirements. We adjust the mixture we use for the drawn barrier accordingly, so that it gives the fire resistance of a structure an extra boost." BKB Infra's Wirtgen SP25i slipform paver is equipped with a GPS unit. "This allows us to determine the design height of the barrier directly from a 3D design and pour it onto the road in a smooth line. In this way, unevenness in the subway can be absorbed very easily."

Also in the flat plane

A slipformpaver is supplied from the manufacturer with a standard mold. BKB Infra adapted and further developed these in-house. Laurens: "Meanwhile, we have a range of about sixty unique moulds, including six variants for a barrier construction, so that we can offer a suitable solution for every situation. That makes us unique and versatile in terms of deployment. Between operations, we divert to other projects elsewhere in the country. With our machine we also pour in the flat, such as bicycle paths in a range from 2 to 4.5 meters wide. Besides hopping back and forth between the four clusters at Aanpak Ring Zuid, in between we also regularly worked on other projects in Groningen, such as a bicycle path in Beerta. We are well represented in the province." 

For Combinatie Herepoort, BKB Infra pulled the last 6 kilometers of barrier during the summer vacations, completing the unique project. "An achievement cast in concrete that our men can be proud of!"