VÖGELE and HAMM machines build a carriageway with reduced-temperature asphalt
The process of completely reorganizing the centre of Karlsruhe around the Kriegsstrasse has been going on since 2019: what used to be a wide road for through traffic is to become a generous space for pedestrians plus a landscaped tram track and an avenue of trees with cycle paths. 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. The client KASIG (Karlsruher Schieneninfrastruktur-Gesellschaft mbH) gave a high priority to protecting the paving team for the paving of the two tunnel bores (5.3 m and 6.8 m wide respectively). As a result, only rollers and pavers with diesel particulate filters were allowed to work in the tunnel. The use of low-temperature asphalts was also specified: as their paving temperature is approximately 30 °C below that of hot asphalts, they significantly reduce the pollution arising from vapours, emissions and high temperatures to which the paving team is exposed. Experts furthermore assume that reduced-temperature asphalts have a particularly high resistance to deformation. This is of particular benefit on such a heavily-used route as the Karlsruhe road tunnel.
Short window of opportunity for paving and compaction
A number of challenges is involved in processing this mix, however: on the Karlsruhe project, special waxes ensured that it was possible to compact the mix, even at low temperatures. However, this kind of asphalt hardens the instant a critical temperature is undershot, so the mix had to be paved and compacted as quickly and smoothly as possible. The contractor, Martin Paschmann Asphaltbau GmbH, used two VÖGELE pavers of the SUPER 1800-3i type and three HAMM rollers: a DV+ 90i VT-S-type Combination Roller, a DV+ 70i VV-S Tandem Roller and an HD 14i VO Compact Roller.
Efficient, powerful pavers required
In order to allow the rollers as much compaction time as possible, it was important for all the equipment on the job site to work together smoothly: in addition to steady transport of mix, continuous, efficient paving was also key. The SUPER 1800-3i machines played to their strengths here - with their powerful, gentle material handling and distribution, they achieve high laydown rates and can consequently pave even reduced-temperature asphalts in high quality. The so-called heated centre auger bearing box, already patented by VÖGELE, makes the primary contribution here; it is located where the mix drops onto the auger for distribution across the width of the machine. As on VÖGELE pavers, this surface is heated evenly, no material sticks to it - not even reduced-temperature asphalts. Electric screed heating furthermore ensures that the other components in contact with the mix, such as the screed plates and the compacting systems, are also constantly heated. This guarantees an even surface structure and incidentally reduces soiling of machine components.
A high degree of pre-compaction and automatic functions save time
In addition to clean, accurate paving, pre-compaction is another key factor. The AB 500 and AB 600 Extending Screeds were used in the Karlsruhe road tunnel, both equipped with tamper and vibrators as compacting systems. This allowed the pavers to achieve a high degree of pre-compaction and thus reduced the number of roller passes subsequently required. The ErgoPlus 3 operating concept also increased the efficiency and quality of paving: as the higher viscosity of the reduced-temperature asphalt compared to that of hot mix also had an impact on specification of roller dimension, the automatic functions of AutoSet Plus, among others, were especially helpful. Using the “Save paving programs” function enabled the paver operator to save the paving parameters once they had been used successfully and then call them back up at the touch of a button the next day or for the next section of the project.