The growing volume of traffic in Germany inevitably generates more noise. A high potential for minimizing this noise lies
in the construction materials for road pavements. Porous concrete eliminates part of the rolling noise directly at its point
of origin. The pioneering efforts made by VÖGELE contributed substantially to paving porous concrete in an economical
way. A research project near Düren, Germany, furnished proof of its efficiency.

The pavement must be sealed in order to prevent water from penetrating to lower areas. That was one of the problems to be solved for porous concrete paving. Another one is the special tack coat needed and, although one of the most low-noise pavement materials, the short in-service life of porous concrete pavements experienced so far made its economical use rather impossible.

Modified VÖGELE SUPER 1800. The tank with special agitator is the first element in the process of tack coat spreading. Tracks with “spikes” allow the paver to pass over the tack coat without causing damage. Example of Pavement Design 2-Layer concrete pavement made up of porous concrete and PCC bonded by tack coat.

“Low-Noise Traffic” project set up
A great deal of time and effort were needed before these problems were under control from the technical point of view. VÖGELE engineers focussed their research and development work on an efficient paving process which eventually was found. From the very beginning, the noise generated by tyres rolling on the road surface at 40km/h or higher for cars and 70km/h or higher for lorries was identified as the dominant source of traffic noise. Therefore, the Federal Road Research Institute (BaSt) together with a number of firms, among them VÖGELE, set up “Leistra”, a common project for “Low-Noise Traffic”. The project’s aim is to reduce noise directly at its point of origin, in fact at the interface between the vehicles’ tyres and the road surface. Its target is developing and testing road pavements reducing noise emission by up to three dB(A). As far as pavement materials are concerned, the BaSt experimented with noise-reducing mastic asphalt, porous asphalt and classical concrete. Alternative measures to minimize traffic noise are pretty expensive. 2800km of noise barriers have been installed so far throughout Germany. The building of new roads in future is closely linked to these costly noise protecting installations. “Reducing traffic noise with the aid of noise barriers is good, but preventing noise completely or preventing it to a considerable extent is better” says Angelika Mertens, Parliamentary Secretary of State in the Federal Ministry of Traffic and Transport, explaining why the government is so interested in “Leistra”.

On the B56 highway near Düren, German contractor F. Kirchhoff Strassenbau GmbH & Co. KG paved various construction materials on a test section using a VÖGELE SUPER 1800 paver (pave width 7.5m). Sensors were installed to measure noise emission.

Low-noise road pavements
“Initial research findings indicate that the noise generated at the interface between the vehicles’ tyres and the road surface can be reduced significantly with the technical means available today” says Dr Peter Reichelt, project manager at the Federal Road Research Institute (BaSt). As far as both cost and noise reduction are concerned, porous concrete is the most promising construction material. To find a technical solution for its paving, however, was a hard nut to crack. VÖGELE have carried out numerous trials on their premises at Mannheim, Germany, until their pavers started laying porous concrete on public roads.

The special tack coat for porous concrete caused problems at first. This tack coat needs to be applied by the paver together with the porous concrete in a single pass. A series paver on tracks was modified by VÖGELE for this purpose. The engineers installed an additional tank with agitator into the machine. This tank suited to filling from the side as work proceeds helps avoid paver stops. To prevent the tack coat from being damaged by the tracks as the paver moves on, track shoes were replaced with a sort of “spikes”.

Remarkable results
The SB 250 High Compaction Screed in TVP2 version is ideally suited to concrete paving. Tamper speed, extra weight for the screed, tamper shield and set-ups of pressure bars and tamper bars can be perfectly adjusted to match the porous concrete. Although the Federal Road Research Institute does not publish detailed results until noise emission measurements on the B56 highway near Düren are completed, the trend is quite clear: all instruments measuring noise recorded substantially lower levels compared with conventional roads, as project manager Reichelt confirmed. Laying porous asphalt or porous concrete may differ from standard operations, but the problem of paving can be regarded as solved from the technical point of view, also thanks to VÖGELE.