Combination of Asphalt and Cement for a High Load-bearing Capacity
Special material Densiphalt® paved near to Dusseldorf central bus station.
When it came to carrying out pavement reconstruction of its central bus station, the municipality of Dusseldorf (Germany) decided to strike out in a new direction. In the area of the bus stops, contractor A. Frauenrath Bauunternehmen GmbH paved a special material known as Densiphalt®, creating a pavement which can durably stand up to the high weight from heavy busses. SUPER pavers thus placed an asphalt layer with a high voids content, which was then filled with a cement mortar. The bonding of these two materials lends the semi-rigid surfacing a high load-bearing capacity.
Bus stations and other traffic areas which are almost exclusively used by vehicles weighing tonnes are particularly prone to signs of wear such as ruts. It was for this reason that an innovative method was selected for the reconstruction of the Dusseldorf central bus station. Known under the name of Densiphalt®, this mix was developed especially for asphalt areas exposed to high loads. The paving process involves a surfacing of semi-rigid nature due to the combined use of asphalt and cement, able to withstand extreme weights. This property is achieved by paving a wearing course with a high voids content. The voids are then filled with a modified cement mortar.
Roadworks began in the conventional way
At the central bus station, only the areas of the bus stops were to be paved with the semi-rigid Densiphalt®. But before placing the innovative material on the job site in Dusseldorf, the access road running in parallel with the bus station was reconstructed in the conventional way. The new pavement of this highly trafficked road, too, was designed for heavy usage. 34cm crushed-stone base was laid first, followed by 14cm asphalt base of a material type AC 32 TS. For the binder course, 8.5cm thick, a mix type AC 22 HS BM was used and stone mastic asphalt for 3.5cm wearing course. The asphalt layers were paved with a wheeled SUPER 1603. The roadworks turned out to be a bit complicated by the fact that the job had to be carried out alongside the tram platforms. The overhead lines in that area also demanded a high degree of attention and precision when supplying the paver with mix from feed lorries.
Grade and slope control with a multi-cell sonic sensor
As far as grade and slope control was concerned, the paving team used the roadway’s existing left-hand lane as a reference. A multi-cell sonic sensor tracked the lane and transmitted collected data to NIVELTRONIC Plus®, the System for Automated Grade and Slope Control. This non-contacting sonic sensor from the VÖGELE range of products is provided with 5 sensor cells emitting 5 sound cones for grade control. Out of these five measurements, the two measurements with the greatest deviation from the specified grade are ignored. This allows, especially in municipal areas, to achieve paving results of highest precision.
Conventional base and binder courses also when paving Densiphalt®
When the conventional roadway was finished, building of the Densiphalt® area began. For Densiphalt®, the pavement design in terms of asphalt layers is more or less identical with conventional paving. Only base and binder courses may be somewhat thinner. For the central bus station in Dusseldorf, 10cm asphalt base was placed and 8cm binder course. For asphalt paving, the contractor’s team used a tracked SUPER 1600-2 with AB 500-2 Extending Screed in TV version. The pave width in each case was 3.2m.
Paving the Densiphalt® surfacing
Once the first two asphalt layers had been placed, Densiphalt® was paved in a thickness of 5cm. A wheeled paver type SUPER 1603-2 was on the scene to lay the porous asphalt with a high volume of voids. It is important in this context that the screed operates with the lowest possible precompacting effort, in order to realize the required voids content of 25 to 30% by volume. This, however, has a considerable influence upon the screed’s angle of attack. In order to avoid a too large angle, the paver’s Screed Assist feature can be used, which is of high benefit on applications like the one in Dusseldorf. Screed Assist is available as an option for all SUPER pavers.
The VÖGELE Screed Assist feature lowers the weight
When activating the Screed Assist function from the screed operator’s or the paver operator’s ErgoPlus® console, a reduction in screed weight is initiated by regulating the pressure of the hydraulic rams. The screed thus becomes lighter and its angle of attack decreases. The pressure for Screed Assist, too, can be set via the display panel on the ErgoPlus® console – a fast and simple operation.
Filling with modified cement
Once the asphalt surfacing with a high voids content had been placed, the modified Densiphalt® mortar was applied and spread manually with squeegees. The semi-rigid surfacing could take loads after just a few hours. After about 72 hours, Densiphalt® reaches 65% of its final rigidity and can be opened to traffic.
New SUPER pavers for the contractor’s team
As the contracting company did not yet have VÖGELE machines in its equipment pool for long, the job in Dusseldorf was one of the first occasions for the paving team to work with the SUPER 1600-2 and SUPER 1603-2 pavers. “The whole team is very happy with the user-friendly technology,” said paver operator Hans-Peter Schuren. “Getting to grips with the new machines was easy. The ErgoPlus® operating system and NIVELTRONIC Plus® for automated grade and slope control make light work of our job!”