Low temperature – low emissions

Vögele and Hamm machines build road using low-temperature asphalt

Karlsruhe | A leader in occupational safety

Strict conditions for paving in the auto tunnel under Karlsruhe's Kriegsstrasse: To reduce emissions, the Schleith-Züblin consortium was allowed to use only construction equipment fitted with diesel particulate filters (DPF), and required to use low-temperature asphalt (LTA).

As proven team players, the Vögele pavers and Hamm tandem rollers met all the requirements as well as delivering efficient, high-quality paving.

Downtown Karlsruhe has been undergoing complete reconstruction in the Kriegsstrasse area since 2019. The existing wide through highway is being transformed with a landscaped streetcar line, avenues of trees, bike lanes, and plenty of space for pedestrians. A subway line is also being built, with through auto traffic being rerouted into a mile-long tunnel.

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Job details

  • Job:
    Paving two tunnel tubes in widths of 17.4 and 22.3 feet with low-temperature asphalt
  • Customer:
    KASIG (Karlsruher Schieneninfrastruktur-Gesellschaft mbH)
  • Contractors:
    Kriegsstrasse Tunnel Consortium comprising Schleith, Züblin and Martin Paschmann Asphaltbau GmbH
  • Wirtgen Group machinery deployed:
    Two VögeleSUPER 1800-3i pavers, three Hamm rollers (DV+ 90i VT-S combination roller, DV+ 70i VV-S tandem roller, HD 14i VO compact tandem roller)

Protection of the paving crew

Comprehensive exhaust gas aftertreatment systems on the machines and the use of low-temperature asphalts are key elements in protecting the paving crew from fumes, emissions and high temperatures, and also help reduce work stress.


Low-temperature asphalts

Low-temperature asphalts (LTAs) are paved at temperatures around 86°F lower than hot asphalts. That not only reduces emissions. Experts believe that LTAs are also highly resistant to deformation – an important consideration on busy roads like the Karlsruhe auto tunnel route. There are major challenges in terms of paving and compaction. Vögele pavers and Hamm rollers demonstrate their strengths in meeting them too.

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SUPER 1800-3i: The powerful paver

Ensuring rapid, continuous paving

On the Karlsruhe project, special waxes were used to make sure the mix could be compacted even at lower temperatures. A key challenge in this is that LTAs solidify rapidly when their temperature falls below a critical level. So it's important to lay and compact the mix as quickly as possible, and without interruption. Vögele pavers like the SUPER 1800-3i are the ideal choice for efficient, continuous paving.

Efficient material conveying

With their powerful yet delicate material conveying and distribution capabilities, Vögele pavers achieve high paving capacities, enabling them to lay even low-temperature asphalts in high quality.

Heated auger frame

Vögele's patented heated auger frame is located where the material falls onto the spreading auger and is distributed crosswise. The surface of the frame is heated uniformly, so not even low-temperature asphalt will stick to it.

Electric screed heating

The electric screed heating system ensures that the other components in contact with the material, such as screed plates and compacting units, are also heated constantly. This ensures a uniform surface texture, as well as helping to reduce soiling of the machine components.

High degree of precompaction

Another crucial factor, alongside neat and precise paving inside the tunnel, was precompaction. The AB 500 and AB 600 extending screeds were deployed on the Karlsruhe job. Both are equipped with tamper bar and vibratory compaction units that enable the pavers to achieve a high degree of precompaction. That means fewer subsequent rolling passes are needed.

Useful AutoSet Plus automatic functions

The automatic functions of the ErgoPlus 3 operating concept greatly enhanced the efficiency and quality of paving. The higher viscosity of LTAs compared to hot-mixed asphalt (HMA) also affects the determination of the rolling dimension. Using the AutoSet Plus “Save paving programs” function, the paver operator could store successfully applied paving parameters and retrieve them for reuse at the push of a button.

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A challenge for Hamm tandem rollers: final compaction

Much narrower time windows than for hot paving

The time window available until final compaction is reached is much narrower when using LTAs than for hot paving. The low-temperature asphalt concrete used in Karlsruhe was workable for a long time, but then solidified abruptly. This rigidity makes compaction more difficult, and represents a major difference compared to conventional HMA. Because of the narrower time window, the rollers have to work very close to the paver, and in short, regular lines. This allows them to apply a lot of compaction energy in the short time available. As a result, LTAs can be compacted homogeneously over the entire road by the dynamic use of vibration and oscillation.

Thermal aprons: When operating combination rollers – like the DV+ 90i VT-S,here – thermal skirts prevent the tires from cooling down quickly.

“The sudden increase in rigidity is further proof that keeping to the right time window is key to high-quality compaction.”

Engineer Christian Riede (Dipl. Ing.), supervising site manager for general contractor Schleith, and coordinator of the asphalt works

First pass with the DV+ 90i VT-S combination roller

When compacting the asphalt concrete base and binder course, the medium-heavy (9 metric ton) DV+ 90i VT-S was used for the first pass. It compacted the mix, which was initially prone to heaving, with its pneumatic tires first. They knead and roll the material without heaving, and also provide good precompaction.

The kneading action of the tires at the rear creates a dense structure, and the drum on the front then provides the necessary evenness.

For final compaction, an HD 14i VO compact tandem roller, with vibratory and oscillating drums, was also deployed.

The roller approaches the paver at an angle, so avoiding undulations.

The anti-slip control (ASC) ensures high traction in any situation.

Final compaction with tandem rollers

The 4.5 metric ton HD 14i VO compact tandem roller and the DV+ 70i-VV-S pivot-steered tandem roller worked as a team during final compaction to rapidly apply the compaction energy. When paving an exposed asphalt surface course, it is generally important to quickly press and compact the marginal areas as soon as the asphalt is sufficiently resistant to deformation. This was not necessary in the Karlsruhe auto tunnel thanks to the slot drains that had already been installed.


Everybody happy

Paving LTA is still new for many contractors. There’s a lack of empirical data, specially with regard to the material’s behavior during compaction. The teams from Martin Paschmann Asphaltbau GmbH and Schleith GmbH continuously monitored the density using an isotope probe, and confirmed it in downstream lab tests. In summary: Vögele pavers and Hamm rollers are the ideal choice for producing a homogeneously compacted road even when using low-temperature asphalt.

“The measurements, and the downstream lab tests, confirm that we had laid a high-quality, homogeneously compacted road using the Vögele pavers and Hamm rollers.”

Engineer Christian Riede (Dipl. Ing.), supervising site manager for general contractor Schleith, and coordinator of the asphalt works

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