Quiet as a whisper – thanks to porous asphalt DV rollers from Hamm compact trial section of porous asphalt

Traffic volumes on motorways around the globe have been increasing steadily over the years – and so have noise emissions. At the same time, new residential areas are built ever closer to arterial roads and motorways. It is therefore not surprising that there is an increasing interest in “quiet” road pavements that minimize rolling noises even at high driving speeds.

Porous asphalt is one approach to reducing the noise levels caused by traffic. In a reference project on the German A61 motorway, as many as five tandem rollers from Hamm’s DV series ensured the correct compaction of these special asphalt mixes.

Comparing four types of asphalt

Straßen.NRW is a state-owned enterprise which is responsible for planning, building and operating the motorways in North Rhine-Westphalia, the most heavily populated German state. Under the direction of this authority, four types of porous asphalt in different compositions were chosen for the six-kilometre long trial section: a reference mix was paved on the first stretch of 1,500 m in length. On the following two sec-tions of 1.5 km each, two different types of asphalt with new, rubber-modified binding agents were applied using granulated rubber material from scrap tyres. The pavement on the remaining 1.5 kilometres of the test section was produced from porous asphalt with an adhesion additive. Whilst the paving gang didn’t notice any differences when paving the four mixes using a Vögele Super 2100-2 paver, they became quite obvious during compaction. For one type of asphalt, for instance, the number of roller passes needed to be increased.

Incidentally, the surface course was paved at a layer thickness of 4.5 cm for all four types of asphalt mix, which is one centimetre more than is typical of porous asphalt surfaces. Research had shown that thicker layers are capable of reducing noise levels even better.

Material properties require more rollers

Porous asphalt design involves a number of important requirements in terms of compaction. For one, the void content – 22 percent after final compaction had been specified for the test section – needs to be ad-hered to with maximum accuracy, because it is a material property that is vital for the reduction of noise levels. That is why excess compaction needs to be avoided at all costs. The rollers therefore applied static compaction, and the screed in the Vögele paver was operated at the lowest possible vibrating power.

Temperature is yet another important aspect: porous asphalt cools down very quickly after paving due to its high void content. In addition, road markings were rolled into the warm asphalt on the A61 test section immediately after paving, which required additional machine capacity. Static compaction, faster cooling of the asphalt and the simultaneous application of road markings all led to a larger number of rollers being needed than with the paving of other types of asphalt.

DV series guarantees safety

When many rollers are operating in confined conditions, as was the case on the A61, DV rollers offer a tremendous increase in safety. Their driving and steering system “HI-DRIVE” makes sure that the driver’s seat rotates automatically when reversing the roller in automatic mode, thus ensuring that the driver is always seated in the direction of travel. This feature is gentle on the driver’s back, extremely comfortable – and extremely safe!

First-class service

The paving gang from contractor Matthäi – headquartered in the town of Verden in northern Germany – was highly satisfied with the Vögele and Hamm machines. The asphalt surface is of excellent quality, paved by superior machinery, and the service offered is first-class. Foreman Jörg Gattkowski puts it like that: “Our contact partners at Wirtgen Hamburg know their products and field requirements from the inside out. With their extensive know-how, they have supported us quickly, in a friendly way and with much expertise. That enables my asphalting gang to operate the paver from Vögele and the rollers from Hamm with economic efficiency.”

Annual check measurements

Traffic is moving again on the A61 motorway. It is expected that all four asphalt mixes will reduce the noise emissions to a much greater extent than other types of porous asphalt: experts estimate the initial reduction to be between eight to ten decibels, which equals a decrease by fifty percent of the felt noise volume when compared to the previous pavement. Straßen.NRW will carry out regular checks over the next 10 to 15 years to assess the pavements’ noise levels and functional properties. These analyses will show which one of the mixes will achieve the best results in the long term, and will make a valuable contribution towards making heavily trafficked motorways less noisy and therefore more environmentally compatible.