Noise-reducing asphalt places high demands on the execution

"The production of a surface layer with open-pored asphalt (OPA) is particularly challenging because the asphalt mix is very sensitive and the existing geometry makes seamless installation extremely difficult. Installation with staggered pavers requires the complete closure of one lane. We were therefore under enormous time pressure during the renovation of the busy BAB 40 motorway. In addition, we had to deal with different road cross-sections, so we had to map lane widths from 8.5 to 25 metres," explains project manager Kai Pusdrowski-Sales. As a new binder was being used for the first time, a test field was set up in advance to check the quality of the asphalt. The parameters for improving grip were also determined and defined.

A time window of exactly seven days was available for all the work, including resurfacing, removing and restoring the road markings, 1,400 metres of joint connections, exposing the edge of the carriageway and clearing work. The renovation began with the milling of around 95,000 square metres of asphalt surface layer at a maximum milling depth of 5.5 centimetres. Subsequently, an asphalt surface layer of SMA 8 S was produced on the structures along the route. An open-pored asphalt surface course of type PA 8 was then installed and immediately treated with high-pressure water jets. This process ensured immediate roughening of the surface and guaranteed the necessary grip right from the start. In addition, the carriageway transitions in front of and behind the bridge structures were constructed using mastic asphalt.

Surface treatment with high-pressure water jets

"Without high-pressure water jets, the speed limit of 80 km/h and a skid hazard warning would have remained in place on the newly completed section until the required initial grip had been established naturally after around four weeks. However, in recent years, it has become increasingly apparent, particularly on roads with open-pored surfaces, that this improvement in grip due to use does not occur, especially in the overtaking lanes. In some cases, it can take up to a year for the required limit values to be reached. The residents of this heavily frequented conurbation were not expected to put up with these restrictions, especially after the complete closure. The process had only been used once before in the UK for the installation of open-pored asphalt. We are proud that we were able to prove its practical suitability once again," explains project manager Kai Pusdrowski-Sales.

In addition to PORR Verkehrswegebau, sister companies PORR Gussasphalt, PORR Transport und Frästechnik and CMG Baulogistik Münster also contributed significantly to the success of the project. Thanks to flat hierarchies on the construction site, fast and direct communication with the client, Autobahn GmbH des Bundes - NL Rheinland, was also guaranteed at all times.

‘Our great advantage is that we can offer the complete service package from demolition to new construction from a single source and implement it with our own equipment. We completed all the work not only on schedule but also to the highest quality, and the route is now in excellent condition,’ concludes Pusdrowski-Sales.