The volume of traffic on Germany’s motorways is growing from year to year and with it the associated noise emission. At the same time, new residential areas are being built ever closer to carriageways and motorways. Demand is thus increasing for road surfaces that are as quiet as possible and also minimize traffic noise at high speeds. In September 2007, a modern VÖGELE SUPER 2100-2 paver of German contractor Matthäi, with an SB 250 Fixed-Width Screed built up to 12m, played a key role in the construction of a test section for optimizing porous asphalt. On the heavily trafficked A61 motorway, the paver laid four different kinds of porous asphalts for a long-term test under real conditions.

The contract was let by the State Roadworks Office of North Rhine-Westphalia (NRW). The state authority has been involved in the development of new asphalts to minimize noise emission for years now within the scope of the “Low-Noise Traffic” project. Four porous asphalts with different compositions were selected for the 6km test stretch on the A61, a section whose surface course was due for rehabilitation anyway. Over the next few years, these four asphalts will undergo regular evaluation in terms of durability and noise reduction properties.

A comparison of 4 types of asphalt

The SUPER 2100-2 first paved a reference mix (porous asphalt according to the state of the art) on a 1.5km stretch. Mixes containing new rubber-modified binders, with granules made from recycled old tyres, were then used on the next two sections, each also 1.5km long. On the final 1.5km stretch, an overlay was paved of porous asphalt containing an additive for enhanced bonding properties. The paving team did not notice any differences when placing the four mixes with the SUPER 2100-2, in other words, the paver handled the porous asphalts without problems. However, the required number of subsequent roller passes was different in each case as the mixes displayed differing compactability. The layer of 4.5cm was dimensioned 1cm thicker than usual for conventional wearing course of porous asphalt, as previous investigations had shown that thicker layers improve noise minimization.

12m screed had its debut in North Rhine-Westphalia

The project also represented a debut: this was the first time an asphalt paver with a 12m wide screed had been used in North Rhine-Westphalia (NRW). Stefan Ehlert, engineer and Project Manager at the NRW State Roadworks Office, explained the specification: “Porous asphalt must always be paved in full-road width without joints, in order to ensure that water drains away properly.” The material properties of porous asphalt are ideal for large pave widths. For many mixes, a high degree of precompaction by the paver is desired. Here, however, the opposite is the case. In order to obtain the required voids content, the SUPER 2100-2 worked with vibrators set to minimum compactive effort only. And the rollers following behind the paver also only compacted the layer in static mode. For this contract, Matthäi combined their SUPER 2100-1 paver with a SB 250 Fixed-Width Screed in TP1 version. The screed with a basic width of 2.5m was built up to 10.5m with fixed bolt-on extensions and a 0.75m hydraulic extension on either side. This way, the screed was variable enough in terms of width to pave spandrels and connections between lanes.

A wide screed needs a powerful paver

A wide screed always requires a high-performance tractor unit. This is why the powerful SUPER 2100-2 was used on the A61. With a maximum pave speed of 25m/min., this machine yields highest productivity especially when paving wearing course. The SUPER 2100-2 comes with an engine rated at 182kW. Despite its high power output, the paver is extremely quiet thanks to effective noise insulation. A feature of particular importance when handling large widths: proportional control provided for conveyors and augers guarantees a constant head of mix in front of the screed, thus providing for excellent pavement results.

First class service

The team from Matthäi was extremely satisfied with its SUPER 2100-2. The quality of the asphalt layers proved excellent, the paver performed perfectly, there were many practical details and they could always rely on prompt customer support. Jörg Gattkowski, the forman on site, put it this way: “Our partner in the WIRTGEN Group was the WIRTGEN Hamburg branch. Those people know their products and the requirements in practice inside out. Based on their comprehensive know-how they provide a prompt service, always friendly and always highly competent. This allowed my asphalt crew to work economically and efficiently with the VÖGELE paver and the HAMM rollers.”

New surfacing up to 10 decibels quieter

The wet late summer of 2007 could not endanger the schedule for completion of the project. 75,000 tonnes of asphalt were laid according to schedule and meanwhile traffic flows again on the A61 motoway. It is expected that all four mixes will reduce noise emission much more than other porous asphalts. The NRW Roadworks Office estimates that there will be an initial decrease in noise levels by 8 to 10 decibels, which would be a 50% reduction compared with the motorway’s former surfacing. Together with the Federal Road Research Institute (BASt), the NRW Roadworks Office will be conducting studies over the next 10 to 15 years in order to see how things go in terms of noise levels and structural durability. The analyses will show which mix, in the long run, displays the best properties and is best suited to render our heavily trafficked motorways quieter and minimize traffic noise nuisance for residential neighbourhoods.

SB 250 Fixed-Width Screed

The SB 250 Fixed-Width Screed combines with a variety of VÖGELE tractor units. This screed allows tractor units with a basic width of 2.5m to make use of the advantages offered by VÖGELE Fixed-Width Screed Technology – high compactive effort at large pave widths. The SB 250 has a basic width of 2.5m and builds up with both fixed and hydraulic bolt-on extensions to a maximum width of 13m.

Pave Widths: from 1.5m to 13m

Basic Width: 2.5m

Crown Control: mechanical from -2% to +3%

Compacting Systems: screed available in the versions TV, TP1, TP2 and TVP2

Screed Heating: screed plates, tamper bars and pressure bars heated electrically by heating rods

Dimensions for Transport (Basic Screed)

Width: 2.5m

Depth: 1.14m

Setting the Trend: Porous Asphalts

The main properties of porous asphalts: they reduce traffic noise and create good conditions for water draining away from carriageways. Their characteristic is a very high content of coarse grains bonded with the aid of an extremely viscous bitumen featuring long molecule chains. This creates voids to absorb the noise generated by tyres rolling on the road surface. Water also drains away better through these voids and aquaplaning, water spray and glare for car drivers are greatly prevented. It is because of these properties that porous asphalt is also called “whisper” asphalt or drain asphalt. A bitumen seal known as the SAMI layer (Stress Absorbing Membrane Interlayer) prevents water from seeping into the underlying layers.

Job Site Details

Paving porous asphalt on a 6km test section of the A61 motorway between Miel and Meckenheim junctions near Bonn, Germany

Length of section: 6km

Width of section: 12m

Paving Details

Pave width: 12m

Layer thickness: 4.5cm

Paving Material

Four different mixes, each of them paved on a 1.5km stretch

Stretch 1: ungrooved mastic asphalt (as a reference mix)

Stretches 2 and 3: mixes with new rubber-modified binders

Stretch 4: porous asphalt with a bond improving additive

Equipment

SUPER 2100-2 with SB 250 Fixed-Width Screed in TP1 Version