Low temperature – low emissions

Vögele and Hamm machines build a carriageway with reduced-temperature asphalt.

Karlsruhe | At the vanguard of occupational health and safety

Strict specifications for paving the road tunnel under Karlsruhe’s Kriegsstrasse road: in order to reduce emissions, the Schleith/Züblin consortium was permitted to use only construction machinery with a diesel particulate filter (DPF) and reduced-temperature asphalts.

As tried and tested team players, Vögele road pavers and Hamm tandem rollers not only satisfied the specifications, but also ensured efficient, high-quality paving.

The centre of Karlsruhe around the Kriegsstrasse road has been undergoing a complete rebuild since 2019. This former wide thoroughfare is to become a landscaped tram track with avenues of trees including cycle paths and plenty of space for pedestrians. At the same time, an underground train line is being built and through traffic is being diverted into a road tunnel 1.6 km long.

Job details

Order:
To pave low-temperature asphalt in two tunnel bores, one 5.3 m wide and the other 6.8 m wide
Client:
KASIG (Karlsruher Schieneninfrastruktur-Gesellschaft mbH)
Contractors:
The “Tunnel Kriegsstrasse” consortium made up of Schleith and Züblin, plus Martin Paschmann Asphaltbau GmbH
Wirtgen Group machines used:
Two Vögele SUPER 1800-3i-type pavers, three Hamm rollers (DV+ 90i VT-S Combined Roller, DV+ 70i VV-S Tandem Roller, HD 14i VO Compact Tandem Roller)

Protecting the paving crew

Comprehensive exhaust emissions after-treatment on the machines used, together with reduced-temperature asphalts, are key measures for protecting the paving crew from vapours, emissions and high temperatures, as well as for reducing workload.

Reduced-temperature asphalt

Reduced-temperature asphalts have a paving temperature some 30 °C below that of hot asphalts. This does more than just cut emissions. Experts assume that reduced-temperature asphalts also have particularly high resistance to deformation – an important feature for roads with heavy traffic such as the Karlsruhe road tunnel. Such mixes present significant challenges for paving and compaction, but here too, Vögele pavers and Hamm rollers play to their strengths.

SUPER 1800-3i: the powerful paver

Rapid, continuous paving guaranteed

On the Karlsruhe project, special waxes ensured that it was possible to compact the mix, even at low temperatures. The particular challenge: this kind of asphalt hardens the instant a critical temperature is undershot, so it is important to pave and compact the mix as quickly and continuously as possible – Vögele pavers such as the SUPER 1800-3i are the ideal choice for continuous, efficient paving in this instance.

Efficient material handling

With their powerful, gentle material handling and distribution, Vögele pavers achieve high laydown rates and can consequently pave even reduced-temperature asphalts in high quality.

Heated centre auger bearing box

The heated centre auger bearing box, already patented by Vögele, is located where the material drops onto the auger and is distributed crosswise. As this surface is heated evenly on Vögele pavers, no material - not even reduced-temperature asphalt - sticks to it.

Electric screed heating

Electric screed heating ensures that the other components which come into contact with the mix, such as screed plates and compacting systems, are also heated to a constant temperature. This guarantees a smooth surface structure and incidentally reduces contamination of the machine components.

High degree of pre-compaction

In addition to clean, accurate paving in the tunnel, pre-compaction was another key factor. AB 500 and AB 600 Extending Screeds were used in Karlsruhe. Both are equipped with the compacting systems tamper and vibrators, enabling the pavers to achieve a high degree of pre-compaction and allowing the number of subsequent roller passes to be reduced.

Helpful automatic functions from AutoSet Plus

The ErgoPlus 3 operating concept and its automatic functions considerably increased the efficiency and quality of paving. The higher viscosity of reduced-temperature asphalt compared to a hot mix also has an impact on the specification of the amount of subsequent compaction by rolling. Using the automatic “Save paving programs” function of AutoSet Plus enabled the paver operator to save paving parameters once they had been used successfully and then call them back up for the next session at the touch of a button.

Challenge for Hamm tandem rollers: final compaction

Much smaller time windows compared to paving with hot mix

The time window available for achieving final compaction is much smaller for reduced-temperature asphalt than for paving with hot mix. Although it was possible to process the reduced-temperature asphaltic concrete used in Karlsruhe for a relatively long time, it then suddenly became hard. This stiffness makes compaction work more difficult and is a key difference from conventional hot asphalt. The smaller time window means that the rollers have to work particularly close to the paver in short, regular runs. This enables them to generate a great deal of compacting power in the short amount of time available, allowing reduced-temperature asphalt to be compacted dynamically, using vibration and oscillation, and homogeneously across the entire carriageway.

Thermal aprons: when combined rollers, like the DV+ 90i VT-S in this case, are used, thermal aprons stop the tyres cooling down quickly.

“The instant rise in stiffness once again proves that use of the correct time window is a key factor in the success of high-quality compaction.”

Christian Riede, Senior Construction Manager at contractor Schleith and coordinator of the asphalt work

First pass with the DV+ 90i VT-S Combined Roller

The medium-weight (9 t) DV+ 90i VT-S was used for the first pass to compact the base and binder courses made of asphaltic concrete. The roller first used its pneumatic tyres to compact the material, which is initially sensitive to pushing. The tyres knead and roll the material without pushing it and also achieve a good degree of pre-compaction.

The kneading action of the tyres (rear) generates a dense structure, whilst the drum (front) ensures the required evenness.

An HD 14i VO Compact Tandem Roller with one vibrating drum and one oscillating drum was also used for final compaction.

The roller approaches the paver at an angle to prevent the formation of humps.

Traction control ensures a high level of traction in every situation.

Final compaction with tandem rollers

The 4.5 t HD 14i VO Compact Tandem Roller and the centre pivot-steered DV+ 70i-VV-S Tandem Roller worked as a team to deliver compaction energy quickly for the final compaction step. When paving the free asphalt surface course, it is generally important for the edges to be compressed and compacted quickly - as soon as the asphalt has sufficient resistance to deformation. However, this was unnecessary in the Karlsruhe road tunnel, as the slot gutters had already been installed.

Positive summing-up by all those involved

Paving reduced-temperature asphalt is still new to a lot of people. There is a lack of empirical values - especially with regard to material characteristics during compaction. The crews from Martin Paschmann Asphaltbau GmbH and Schleith GmbH continuously checked density using an isotope probe and had the values confirmed again in subsequent laboratory tests. In summary: Vögele pavers and Hamm rollers are the ideal choice for generating a homogeneously compacted carriageway, even when using reduced-temperature asphalt.

“Both the measurements and the laboratory tests carried out subsequently confirmed that we produced a high-quality, homogeneously compacted carriageway using Vögele pavers and Hamm rollers.”

Christian Riede, Senior Construction Manager at contractor Schleith and coordinator of the asphalt work