Premiere: Two InLine Pave Trains Working "Hot to Hot"
Schedules for runway rehabilitations are always exceedingly tight. And the project at Rostock-Laage Airport was no exception. Here, though, a new approach was taken: two InLine Pave trains from VÖGELE were used to lay a new surface and binder course both "hot on hot" and "hot to hot" as a compact asphalt pavement. As a result, the contractor, Kemna Schwerin Tief- und Straßenbau GmbH, not only finished the job at record speed but also delivered maximum paving quality.
FOD – for an airport operator, that is like a red flag to a bull. The abbreviation stands for "Foreign Objects Damage" and describes the danger caused by small objects on the runway – from as little as 4mm in size they can destroy whole engines. This particular problem had arisen after bubbles – and subsequently cracks as well – had formed on the runway at Rostock-Laage Airport. This meant that large parts of the 2.5km-long runway had to be rehabilitated – and as quickly as possible, in order to minimize the disruption to flight operations.
The ideal solution: The InLine Pave process
"The compact asphalt pavement using the InLine Pave process looked like the ideal solution in this case", explained Bernd Kanscheit, an engineer at engineering consultancy Mecklenburgisches Ingenieurbüro für Verkehrsbau, Germany. "Firstly, InLine Pave gives you an excellent bond between layers – which prevents bubbles from forming. Secondly, the InLine Pave surface is very dense and low in voids, so neither water nor deicing agents can cause damage. Thirdly, we benefit from the very high compaction of the binder course in the InLine Pave process. It is higher than in conventional paving. That's particularly important to us here! After all, the characteristic load profile of the take-off and landing runway means we cannot expect post-compaction by vehicles.
In addition to the requirements on the asphalt, organizational aspects also made InLine Pave an ideal choice. For one thing, the binder and surface course could be laid rapidly in one pass. Secondly, the pavement was going to be laid in potentially cool autumn weather. In the InLine Pave process, however, the asphalt stores a great deal of heat. This ensures both correct compaction and slow cooling.
95,300 square metres in ten days
Once the go-ahead was given, the road construction contractor had ten days in which to mill off the 95,300m2 centre portion of the take-off and landing runway, lay the asphalt with a new profile, apply all the required markings and clean the whole surface. Flights at the airport, which is for both military and civilian use, were suspended during this period.
Before the pavers could get started, four WIRTGEN W 210 Large Milling Machines removed the asphalt. The Kemna team began to lay a level regulating layer of asphaltic concrete while the milling work was still going on. Using two VÖGELE pavers of type SUPER 2100-2, they established a layer 4 – 8cm thick that guarantees water drainage with a slope angle of 1.5% to each side. The grade and slope control was carried out in the longitudinal direction by scanning tensioned wires.
Kemna was already working "hot to hot" with the VÖGELE pavers. A quasi-jointless strip with a width of approximately 15m was laid on both sides, starting from the middle. On each outer edge the pavers then laid another strip 7.5m wide and a shoulder 3.4m wide.
InLine Pave permits a thinner surface course
On top of the sloped and very even level regulating layer the InLine Pave train then laid the binder course together with the surface course in a constant thickness. Unlike the previous pavement structure, the new surface course is only 2.5cm thick instead of 4cm. "We based our measurements of the surface course on the requirements of the German terms and guidelines for the construction of asphalt roadways (ZTV Asphalt StB). The operators of the airport were absolutely delighted with the savings this delivered in terms of surface course material", Kanscheit explained.
Minimizing the costs of future maintenance operations was also the reason for another technical requirement set by the airport operators: the landing runway was to have no longitudinal joint for 10m to the right and left of the middle, "because experience has shown that the maintenance intervals are the longest then," said Kanscheit. To ensure this functionality exactly, he put the compact asphalt pavement out to tender in combination with "hot to hot" paving.
An impressive premiere
Kemna completed the paving with two InLine Pave trains in just three days. On the first day the teams, each consisting of two pavers and a material feeder, worked in parallel on the outside edges of the landing runway, with each laying a 7.5 m-wide strip. The second day saw the premiere, when the binder and surface courses were laid "hot on hot" and "hot to hot" with VÖGELE InLine Pave. Starting from the middle of the runway, a 15m-wide compact asphalt pavement was thus created in a single pass – an impressive sight that was followed enthusiastically by everyone involved. On the third day, the final asphalt strip, 15m wide, was laid on the opposite side in the same procedure.
25,500 tonnes in three days
The changes in the pave widths of the screeds did not present any problem, because VÖGELE equip their InLine Pave trains with extending screeds. Anything between a pave width of 3m and 8.5m is possible. The screeds are extended and retracted hydraulically. This enabled the Kemna team to lay 5,900t of asphalt on each of three successive working days while meeting the high quality requirements of the customer. "The "hot to hot" joint is as good as invisible", said a delighted Torben Eymer, engineer and Site Manager. Planner Kanscheit added: "Samples show that there are no structural irregularities in the binder at the joint. And that's exactly what's required."
PowerFeeder MT 3000-2 Offset
Apart from the "hot to hot" paving with InLine Pave, there was another highlight to marvel at on the job site: the PowerFeeder MT 3000-2 Offset from VÖGELE ensured that both pavers were kept permanently supplied with material. With a pave speed of around 4m per minute and a pave width of 7.5m, the offset material feeder delivered some 400t/h of material to the pavers; including about 280t for the binder course and 120t for the surface course. This performance made a lasting impression.
The offset material feeder also came up trumps when it came to laying the 3.4m-wide – or should that be narrow – shoulder. "If the mix had been delivered directly by a lorry, the existing edge of the surface up to the shoulder would certainly have sustained damage. Thanks to the pivoting conveyor, though, the lorries were able to drive alongside. Not only did that enhance our quality, it also made us considerably quicker", said Site Manager Eymer in praise of the benefits of the offset material feeder from VÖGELE.
Kemna was able to wrap up the job within the tight timescale just ten days after getting started. "We thought of everything. The whole job went according to plan", a satisfied Torben Eymer concluded. After this premiere with a 15m-wide strip paved with the InLine Pave train, he was confident of one thing: "This technology has a great future, especially for large projects."
Ludwigshafen / Juli 2014