Dual-Layer Paving Is First Choice - page 3 of 3
One train – two machines
Once the logistics is well organized, precise high-grade paving is assured by the intelligent technology of the Wirtgen machines.
The texture curing machine TCM 1800 from Wirtgen
The sub-processes are divided between two machines. The bottom-layer paver - a Wirtgen SP1500 - is equipped with dowel bar and tie bar inserters, while the top-layer paver uses a finishing beam and super smoother to produce a level surface.
Both slipform pavers feature an intelligent control system ensuring a perfect paved result. The surface is subsequently finished as desired by a texture curing machine of type TCM 1800.
Intelligent dowel bar and tie bar inserter
The integrated dowel bar and tie bar inserter is one of the technical highlights of the SP 1500 from Wirtgen. Dowel bars and tie bars are inserted in the pre-compacted wet concrete at freely determined intervals by these two fully automatic vibrating components.
The process for inserting the dowel bars is quite ingenious: Because the dowel bar inserter can move in the direction of paving, it can remain in position over the transverse joint until the vibratory insertion process is complete, while the slipform paver continues to advance uniformly.
The entire procedure is monitored electronically to assure that the dowel bars are positioned correctly.
For the projects described here, the dowel bars were typically positioned in the middle of the finished concrete surfacing, i.e. at intervals of 14-15 cm and exactly as specified by the regulation ZTV Beton (Additional technical contract conditions and guidelines for the construction of roadway surfacings made of concrete).
A closed, even and homogeneous surface was then assured by a finishing beam and super smoother integrated in the top-layer paver.
So that roadways can be paved with maximum surface accuracy, three of the four contractors use specially developed sensors to adjust the height of the front metering screed.
These sensors continuously measure the filling level of the concrete in the compaction zone and adjust the height of the front metering screed accordingly.
This ensures that the amount of concrete delivered to the compaction zone is exactly as required. Dirk Böttcher, Project Manager for Eurovia Beton, explains the advantage:
This relieves the paver operator, particularly when the top-layer concrete is to be paved as a thin layer.
The TCM 1800 texture curing machine applies a combination of surface retarder and dispersion to the exposed aggregate concrete freshly paved.
Curing is a further aspect of great importance when paving exposed aggregate concrete. The TCM can be fitted with brooms or combs to give the concrete a defined texture. This is unnecessary when placing exposed aggregate concrete.
The retarding agent delays the setting and initial hardening of the concrete surface (approx. 1 mm) for a limited time, while the dispersion prevents the concrete surface from drying out and cracking. As soon as the concrete has cured sufficiently to be driven over, the surface is brushed to expose the coarse aggregate.
An additional dispersion is then applied to the brushed surface. Exposing the coarse aggregate gives the concrete pavement the required non-skid properties which are subsequently of high importance for traffic safety.
The non-woven material on the subbase prevents reflective cracking being transferred from the subbase to the concrete surfacing. In this way, Eurovia was able to reliably pave concrete in two layers over a width of 15.25 m and a length of 5.3 km on the A1 near Lübeck using the slipform pavers SP 1500 L / SP 1500 from Wirtgen.
Max Bögl had some 70 people working simultaneously on the A9 project. In addition to the two machine operators of the two Wirtgen SP 1500 slipform pavers, the team on site included ground staff, as well as the operators of the concrete mixing plant and the truck drivers.