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These days, highways surfaced exclusively with concrete or asphalt are something of a rarity in Germany, particularly in its more densely populated regions. Hybrid roads are built instead, depending on the structural requirements and the predicted traffic volume - as was the case with the A5 near Karlsruhe. Bickhardt Bau AG, general contractors, is rehabilitating a 2.3-km stretch of this roadway using a variety of Wirtgen Group machines from its concrete and asphalt segments.

The A5 around Karlsruhe is one of the most heavily travelled highways in Germany: It handles up to 140,000 vehicles a day, 15 per cent of them being heavy-duty trucks. The roadway along this stretch of highway was over 30 years old in places, and forced to bear steadily rising volumes of traffic. It came as no surprise that this section needed resurfacing.

Wirtgen Group machines were deployed at all critical phases of the project: A tractor-towed stabiliser from Wirtgen paired with a compactor from Hamm provided for optimal compaction of the subbase. Most of this section of road was then paved in concrete with slipform pavers from Wirtgen. Immediately thereafter, asphalt pavers from V?gele and tandem rollers from Hamm built the adjacent asphalt approach and exit roads, as well as a 100-m stretch near a bridge. Thanks not least to the Wirtgen Group?s reliable and efficient technologies, the crews succeeded in completing their work sections on schedule.

Building the foundation
The old concrete roadway was removed over the entire stretch. The subbase then had to be stabilised in spots and completely repaved to meet water protection requirements. A Wirtgen WS 250 tractor-towed stabiliser together with a Hamm 20-t compactor built the 30 cm-thick stabilised subbase.

With its powerful milling and mixing rotor, and high material throughput - resulting from an optimised material flow in the mixing chamber - the tractor-towed stabiliser was capable of thoroughly and efficiently blending the soil. The H 20i compactor followed behind and quickly compacted the layer, giving the subbase the required level of compaction and degree of penetration. An easy job for the Hamm compactor, thanks to its high compaction and static linear load of over 60 kg/cm.

Dual-layer concrete paving
A non-woven fabric was laid out on top of the base course to bridge cracks and for water drainage. The SP 1500 slipform paver, often referred to as a ?rolling road factory,? went to work on top of it, placing a 27 cm-thick layer of noise-reducing, durable and skid-resistant exposed aggregate concrete of strength class C30/37 across a width of 12.50 m and 15.00 m. The special feature of the concrete surface is the fact that it comprises two layers of different compositions, which however are placed wet-in-wet in a single paving process.

The bottom layer is 22 cm thick, followed by the 5-cm top layer made with locally available gravel (grain size 0/32). The double broken and double screened chipping in the top-layer concrete has a maximum grain size of 8 mm. Combined with this is a significantly higher cement content. Such a roadway structure tangibly reduces material costs.

For this type of construction, the components for the two process steps are divided between two machines in the paving train: The first SP 1500, the bottom-layer paver, is equipped with dowel bar and tie bar inserters that automatically insert these reinforcements into the bottom-layer concrete at defined intervals. The second SP 1500, the top-layer paver, follows directly behind with the finishing beam and super smoother. This finishing equipment lends the concrete section the specified high degree of evenness.

Finally, the TCM 1800 texture curing machine from Wirtgen provides the surface finish. By applying a surface retarding agent, the setting and initial hardening of the concrete surface (approx 1 mm) can be delayed for a limited time and a curing dispersion applied to prevent the concrete surface from drying out and cracking. What is more, the TCM 1800 can give the concrete a defined texture, if desired. The team from Bickhardt Bau worked around the clock to pave the concrete, with logistics being one of the greatest challenges they faced: Two different materials were required that had to be available at the right time, in the right quantity and in the right place. Paving foreman J?rg Ackermann, who has 25 years of experience in the business, described the situation as follows: ?Dual-layer concrete paving can be compared to a planetary gear, in that it has many parts, all of which are important to the successful functioning of the whole. The Wirtgen paver sets the pace. It is the sun gear.? The team paved the concrete - 7,500 cu m in total - in just over 2.5 days. Incidentally, this was not the only slipform paver from Wirtgen at the job site: An SP 500 paver was in use at two other locations. It paved a 600 m long, additional turning lane directly adjacent to the 12.50 m wide concrete profile.

Asphalt paving
Johannes Foos, construction foreman for the customer (Karlsruhe Regional Administrative Authority), has a very definite opinion on the use of concrete and asphalt: ?Concrete is the right building material for this heavily trafficked highway, and the most sustainable. However, most of the approaches and exits handle significantly less traffic, so stone mastic asphalt is the material of choice for them. It bears enough of a load that it doesn?t get brittle, but the load is not so high that it causes wheel ruts.?

Therefore, in addition to total rehabilitation of the concrete roadway, the approaches and exits were also renewed as required by their degree of wear. Bickhardt Bau renewed the asphalt surface and binder courses, a total of some 12,000 sq m. The team further paved a 100 m long section in the region of a bridge with asphalt. The 14-cm base course (AC 32 TS) and 8-cm binder course (AC 16 BS) were paved in one day across a width of 10.30 m. These jobs were taken care of by a V?gele SUPER 1900-2 paver and a Hamm DV 85 VO tandem roller. After they finished their work, the road was surfaced with a mastic asphalt course.

High compaction meets the highest demands: The SUPER 1900-2 was equipped with an AB 600 TP2 extending screed for its work on the job site near Karlsruhe. Michael Fuchs, foreman of the blacktop crew, likes the screed because ?extending screeds from V?gele are more stable and display greater torsional resistance than other solutions.? The reason is the highly stable single-tube telescoping system, which helps to quickly and precisely set the correct paving width. Michael Fuchs maintains further that V?gele pavers simply ?produce a better pavement surface,? because the screed plates, tamper bars and pressure bars are heated particularly uniformly. But the SUPER 1900-2 has even more features for consistently delivering maximum quality, such as during material feed. Large, oscillating push-rollers ensure a smooth supply from the feed truck - a key prerequisite for maximum surface evenness. For leveling, Bickhardt Bau uses the NIVELTRONIC Plus System for Automated Grade and Slope Control, combined with the associated sensors from V?gele?s extensive line. As a result, there was no stringline along the short stretch between the concrete roadways. The adjacent slot channel on the first lane was used instead as a reference, being scanned by sonic sensors. NIVELTRONIC Plus together with a slope sensor took care of the rest.

V?gele SUPER 1900-2: Most user-friendly paver
Paver operator Pascal Reichmann has been working with the SUPER 1900-2 for five years already, and he is still thrilled with his machine. For him it is ?the most user-friendly paver on the market,? in part because of its well-designed details, the arrangement of the controls, the easily repositionable operating console, the swing-out seats and the extending sunshades.

Certified paver driver: Reichmann also is the proud owner of a ?paver driver?s license? or more precisely: He is a ?Certified Paver Operator.? Various providers offer specialised training classes at which paver operators can earn this certificate. Reichmann spent a week at V?gele in Ludwigshafen, Germany, for this purpose: ?We learned a great deal about the machines, safety, logistics and asphalt as a building material. I can apply what I learned there on the job every day.?

Hamm DV 85 VO: A roller with a view
Two DV 85 VO machines from Hamm were used on this project for final compaction. The pivot-steered tandem rollers are the ideal candidates for the job, because numerous corners and tie-ins had to be compacted on a relatively small surface area. From his positionable seat, roller operator Nikolaj Schneider always had an excellent view of the drum edge from the cabin.

But that is not the only thing he likes about the DV 85 VO: ?I?ve tried other rollers. But the ones from Hamm are always quieter than those of other manufacturers.? One reason is the good sound insulation. Another is the conceptual design of the machine, because Hamm has a strong focus on ?soft factors?, too, such as a low noise level inside the cab.

Schneider, a roller operator for over 20 years, also is a fan of the DV series water sprinkling system: ?I can adjust the precise volume of water, so that there is always enough water on the drum: Not too much, not too little.? The fine adjustment helps him and his roller to achieve premium-quality results. The machine displays high productivity in the process, because the precision adjustment minimises water consumption, meaning it is seldom necessary to stop and fill up. The two windows in the floor of the cabin give the operator a perfect view of the drum surface. He can check at any time to see if the drums are sufficiently sprinkled.

Quality thanks to oscillation
Not least, Schneider also likes the oscillation feature, and for good reason: During asphalt compaction for instance, this technology prevents over-compaction and particle destruction. What is more, it produces compact joints, without damaging adjacent, cold asphalt or concrete surfaces. And finally, but importantly, the oscillation rollers can also compact vibration-sensitive areas quickly and efficiently.

In other words, on bridges and ramps, above gas and water lines, and in the vicinity of railway structures or historic buildings, they have a clear advantage over classical vibration compaction - in terms of both compaction performance and quality.

Fast and reliable service
One prerequisite for successful project implementation is the reliability of the machines being used on site. For this reason, the daily maintenance of all his machines is essential to paving foreman Michael Fuchs. The construction team also performs all other maintenance work itself. ?We do maintenance pretty much exactly after every 500 hours.? Depending on how tightly the team is scheduled, the service crew from Bickhardt Bau even comes to a job site on occasion and carries out its work there.

They can do so because the Wirtgen Group product brands pursue the same strategy when it comes to maintenance and service. Maintenance points are easy to access and the work can be completed quickly, without any special tools.

Simple maintenance, meanwhile, is the best precondition for a long machine service life. And when asked what happens when a part fails nonetheless, paving foreman Fuchs replies unruffled: ?The Wirtgen Group?s service is really good. When we need a mechanic or spare parts on site, someone arrives in less than 2 to 3 hours.?