High Compaction Technology
High Ppressure for the best roads one can imagine.
VÖGELE set standards in terms of compaction: perfected technology together with the ultimate in materials for manufacture of screed components guarantee the outstanding performance and reliability VÖGELE High Compaction is known for. RoadNews gives an insight into the screed, the unit crucial for both quality and density of a road pavement. Inside the screed operate the three compacting systems of tamper, vibrators and 1 or 2 pressure bars to bring about the highest degree of density a road paver can achieve.
Even when working with the VÖGELE tamper and vibrators alone, very good results are achieved in road construction. Unique, however, and to date unrivalled in terms of efficiency and final pavement quality is VÖGELE High Compaction Technology based on pressure bar(s) driven by pulsed flow hydraulics. It is the pressure bar(s), the core of VÖGELE HPC Screeds, that bring about high compaction of most varied construction materials and make a substantial contribution to the high-quality and economical building of roads. Read more on the next pages about VÖGELE High Compaction Technology, its method of operation and the range of applications.
1. The Tamper
For optimum precompaction
The tamper provides for optimum precompaction of the mix. Driven by eccentric shaft, the tamper bar packs the mix under the screed.
Terribly hard work
Correct set-up of the tamper in strict compliance with layer thickness and pave speed is crucial to ensure optimum handling of the mix by the overall system made up of tractor unit and screed. Two factors determine the compacting intensity: tamper speed and the length of the tamper stroke. For VÖGELE screeds, both of them can be set up precisely and adjusted to perfectly match the flow of mix, type of mix and layer thickness.
Correct set-up is crucial
The tamper speed is infinitely variable from the SUPER paver’s operator’s console. The higher the tamper speed, the higher the compacting intensity. In addition, 3 options exist for the length of the tamper stroke. Changing the tamper stroke requires no more than a few swift movements. Just loosen the screw connnection of the eccentric shaft and set your tamper to the desired stroke length. Depending on the thickness of the layer to be paved, select a tamper stroke of 2mm, 4mm or 7mm. For thin layers or ultra-thin overlays, the shortest tamper stroke of 2mm is recommended along with a very low tamper speed. For medium layer thickness typical for binder course and wearing course, best results are achieved with a stroke length of 4mm. And when it comes to paving thick layers of more than 12cm, the maximum tamper stroke of 7mm is the preferred choice for excellent compaction.
2. The Eccentric Vibrators
For an optimum grain size distribution
Compaction by the tamper is followed by the vibrating screed plates. The eccentric vibrators acting upon screed plates and screed frame and causing them to vibrate provide for an optimum grain size distribution, a vital precondition for a very smooth surface structure of the finished pavement. Just like the tamper, the vibrators, too, are infinitely variable in speed from the operator’s console and the vibrating intensity increases with an increase in vibrator speed. As to the vibrators, the same rule applies: for thin layers and a small grain size select a low vibrator speed. Depending on conditions on site, the preferred choice may be to even do without vibrators.
Vibrators for a smooth pavement surface
For medium layer thickness in the range between 3.5cm and 12cm, best results are achieved by a medium vibrator speed of some 2,000 revs/min. Thick layers when paving base course or combined base and wearing course, for instance, or when placing concrete in a single layer, call for a high vibrator speed. Depending on the type of screed, the maximum vibrator speed can be up to 3,600 revs/min. All screed types for standard compaction come with vibrators as a regular equipment. Vibrators, however, are also fitted in the HPC Fixed-Width Screed SB 250 in TVP2 version.
3. The Pressure Bar(s)
The innovative VÖGELE system achieves a high degree of density
The third and last compacting system installed in VÖGELE HPC screeds is 1 or 2 pressure bars. They are the core proper of VÖGELE High Compaction Technology, as only with their help can a very high degree of density be achieved.
Very close to the final density, under ideal conditions even the final density
The system requires a high pressure which, in SUPER pavers, is generated by pulsed flow hydraulics. This principle of operation is an innovation developed by VÖGELE (see box). The pressure bars P1 and P2 are the last elements in the process of compaction as a whole. Logically, they are located in the rear area of VÖGELE HPC screeds. Only in this location can the highest possible compacting intensity be achieved, as the mix is prevented from yielding to the front. Nor can it yield to the sides where it is confined by the screed‘s end plates.
The core of VÖGELE High Compaction Technology
VÖGELE HPC screeds allow the pressure to be so finely regulated that High Compaction Technology can be used even for paving pretty thin layers. The pressure for the pressure bar(s) is infinitely variable by pressure regulating valve from 40 bar to a maximum of 130 bar. As a general rule applies: the thicker your layer and the harder the mix is to compress, the higher needs to be the pressure selected for the pressure bar(s). Thus, thanks to HPC technology, perfect compaction even of thick layers is possible in a single pass. And with pressure bar(s) operating at a high pressure, even very thick concrete pavements or porous concrete pavements can be built in single-layer construction. The pressure bar(s) force the mix down until it cannot be compressed any more and the maximum of density is reached. In other words, until an equilibrium is attained between the force exerted by the pressure bar(s) and the counterforce by the compacted mix.
Pressing the mix down until an equilibrium of forces is reached
This allows not only to achieve a maximum of truth to line and level and evenness, but also to pave very economically. The calculation is simple: the higher the density produced by the paver, the less extra compaction is needed by rolling. But VÖGELE HPC Screeds with pressure bar(s) also do an excellent job on projects where, for technical or economical reasons, compaction by rolling is not recommended. And let us give another example of the cost saving potential VÖGELE HPC Technology offers to users: when paving asphalt in several layers, cost can be cut substantially by economy of mix.
More efficient paving
Expensive binder and wearing course materials need not be used for levelling out irregularities, as such irregularities do not exist due to the laying of a perfectly even base course. Thanks to this unique technology of pressure bar(s) driven by pulsed flow hydraulics, VÖGELE HPC Screeds in the versions TP1, TP2 and TVP2 bring about the highest degree of density a road paver can achieve.
The Facts: VÖGELE High Compaction Technology
The pressure bars P1 and P2 are the last elements in the process of compaction as a whole. Logically, they are located in the rear area of VÖGELE HPC screeds. Only in this location can the highest possible compactive effort be achieved, as the mix is prevented from yielding to the front. Nor can it yield to the sides where it is confined by the screed‘s end plates. A change from high compaction to standard compaction and vice versa can easily be made from the paver operator’s console. This allows use of the screed for most varied applications.
The element at the beginning of the process of VÖGELE High Compaction is the pulse generator as part of the pulsed flow hydraulics. It generates high-frequency pressure pulses. The pressure bar(s), in contrast to the beating tamper bar, remain in permanent contact with the mix, thus forcing the mix down for a prolonged period of time. Thanks to the high density achieved by the pressure bar(s), fewer passes are required for subsequent compaction by rolling.
High precompaction is essential for perfectly building up a pavement in layers and for a pavement profile true to line and level. When paving layers varying in thickness, VÖGELE High Compaction Technology provides that, although an identical pressure is applied across the screed width, the pressure bar(s) are forced down to varying depths. This way, an absolutely uniform density is produced.
For each compacting system installed in a VÖGELE HPC screed, separate control is provided. Fine control of the pressure for pressure bar(s) allows use of VÖGELE High Compaction Technology also for paving wearing course.