Hot on hot - HAMM tandem rollers for InLine Pave work
Conventional blacktop paving comprises three processes: laying the base course, laying the binder course and laying the surface course. Now there is an interesting new alternative. For some time now VÖGELE, the market leader in asphalt pavers, has been offering the new, revolutionary "InLine Pave" process. This combines the laying of binder and surface courses into one process. Tandem rollers behind the InLine Pave train compact the asphalt. An analysis of this final compaction showed that dynamic compaction using oscillation gave the best compaction results. This was conclusively demonstrated during construction of the 5.5 km B178 (n), around 80 km south-east of Dresden, using HAMM tandem rollers.
The local highways department at Bautzen explicitly requested the use of "compact construction techniques" for the build, as this system drastically lowers costs and the consumption of resources. "With this technology it's important that both types of asphalt are delivered at the right rate, to the appropriate quality and in the required quantity. If all this is done correctly, the costs can be halved right from the very first metre", enthused one of the responsible engineers at STRABAG – the contractor – concerning the efficiency of the VÖGELE process.
Oscillation wins – both commercially and technically
An additional increase in cost-effectiveness comes with the use of HAMM oscillation rollers. These compactors use the advantages of dynamic compaction and achieve the required degree of compaction in no time at all.
This added value was put to good use during construction of the B178. Right behind the paver, two HAMM DV 90 tandem rollers compacted the asphalt perfectly. Adviser Gerd Lenz from HAMM explains more: "We carried out a series of tests on this site to compare the compaction results of a DV 90 with oscillation against those of a DV 90 with vibration. The analysis showed that oscillation compaction is by far the best method for use with the InLine Pave process." This is why the team only used the DV 90 with oscillation during dynamic compaction for this particular building work.
In this application, the reasons for the superiority of the oscillation as compaction method lie in the configuration of the two layers. Whilst a conventional asphalt pavement has surface and binding courses that are 8 cm and 4 cm thick respectively, the relevant figures for two-layer applications are 10 cm and 2 cm. "The relatively thin surface course would be impacted so hard during vibration compaction that the material would shift", claims Gerd Lenz. He explains: "Under certain conditions the course bonding can even be destroyed. The conditions are much the same as when compacting thin-layer paving, which can also only be compacted statically or by using oscillation." HAMM oscillation rollers reduce these risks. Compaction can be done dynamically and rapidly to give a perfect texture with excellent skid resistance properties.
Oscillation: effective, quick, low-impact
Vibration or oscillation: what are the differences between the two compaction methods? Traditionally, vibration rollers are fitted with a circular vibrator in the roller drum. Depending on the rotational speed and mass of the vibrator, centrifugal forces of varying strengths are created and transferred vertically to the ground via the vibrating roller drum. If the material is sufficiently compacted after a certain number of passes, any more exposure to vibration will lead to damaging particle destruction or undesirable loosening of the compacted layer.
The conditions in oscillation technology are quite different: here, a moment is generated by weights spinning in the same direction about the roller drum. The moment changes its direction of force once per revolution of the weight and generates a horizontally oscillating movement of the roller drum. This means that shear forces orientated forward and backward are directed into the asphalt. Thus, the resulting vibratory loads are only about 10% of the level that occurs in the vibration process. Furthermore, the roller drum always maintains contact with the asphalt. This permanent load contributes to a quick and even compaction. In all, the reduced vibratory load mean the process is extremely effective and low impact, not least on the machine.
DV 90: a guarantee of high productivity
Back to the InLine Pave construction near Dresden. There, the DV 90 VO oscillation roller achieved the required degree of compaction after three passes. The oscillation roller drum was working at 42 Hz and generated a compaction force of 167 kN. Thanks to their staggering productivity, the two DV 90 all-wheel-drive tandem rollers were able to keep up effortlessly with the pace of construction on the 7.5 m wide road surface.