Concrete paving with inset slipform pavers can build roads that last for as long as four decades
Highways, arterial roads, airport runways or even railway tracks without ballasts all have one thing in common: concrete.
Wirtgen has offered machines for inset slipform paving of these extremely resilient and hardwearing concrete roads and runways and the production of monolithic concrete profiles for more than 35 years.
Automated construction of these roads that deliver a long service life and resistance to deformation is a persuasive proposition for road construction.
Planned precision
The following workflow is typical for inset concrete paving projects. First, trucks unload the concrete in front of the machine. Depending on requirements, the concrete can also be placed from the side via a belt conveyor or by a placer/spreader (WPS) in front of the paver. The pre-placed concrete is then evenly distributed by a spreading auger or a spreading plough.
Next, high-frequency vibrators consolidate it directly in front of the paving mould. The integrated hydraulic or electric vibrators also remove excess air from the concrete. As the Wirtgen paver moves forward, the slipform mould shapes the profile to the specified width, thickness and form.
Inset slipform pavers offer paving widths of up to 16 metres and can pave thicknesses of up to 45 cm. The machine maintains its forward motion throughout the paving process at a paving speed in the range of 1 to 2 metres per minute.
Depending on the paving project requirements, a dowel bar inserter can be integrated in the machine to insert dowels into the concrete parallel to the paver’s direction of travel as specified in the reinforcement plan.
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As well, central tie bars or side tie bars can be inserted into the paved concrete at right angles to the paving direction. They serve not only as reinforcement, but also for connecting the slabs that are created by cutting joints precisely above the reinforcing elements. This ensures any cracking that may occur as a result of stress and temperature fluctuations is controlled in such a way that it occurs at the right location within the concrete surface.
The oscillating beam used for smoothing the concrete surface at right angles to the direction of paving is mounted behind the slipform mould. The grinding movement produces a small roll of concrete in front of the oscillating beam that fills any smaller holes in the concrete surface. After this, a super smoother can be used to smooth the surface again.
The right grip
Texture curing machines begin their work immediately after the smoothing of the concrete road surface by the oscillating beam and the super smoother.
These texture curing machines give the paved concrete the desired texture and apply a solution that prevents premature drying of the surface and edges.
The required surface texture is produced by using a brush, a burlap cloth or artificial turf. Automatic crown adjustment and a film unwinder for the application of a protective film round off the equipment of the texture curing machines.
Two layers, one pass
Roadbuilders are able to complete two-layer concrete paving with either one or two slipform pavers.
When only one paver is used for two-layer concrete paving, the bottom layer concrete and top layer concrete are paved in a synchronous operation by a single machine with two sets of concrete paving equipment. The bottom layer and top layer concrete are paved “wet-in-wet,” regardless of the weather or site conditions.
When two pavers are used for two-layer concrete paving, the bottom layer concrete and top layer concrete are paved by two separate slipform pavers. Synchronous coordination of the two machines for the realization of “wet-in-wet” paving is much more demanding when using this option.
The main advantage of using two slipform pavers rather than one is the machine weight. This is because the distribution of the overall operating weight between two separate machines may be relevant for the paving workflow on the construction site.
Perfectly even surfaces
Wirtgen slipform pavers are built on a rigid and torsion-free machine main frame. The slipform moulds themselves also have a rigid frame to prevent unevenness of the paved concrete slabs.
The heavy oscillating beam ensures a consistently smooth surface without ridges or ruts. The super smoother, then produces the final surface evenness by a combination of longitudinal and lateral oscillation. Levelling and steering parameters are communicated to the Wirtgen machine’s control system via a physical stringline or stringless systems like Wirtgen’s smart AutoPilot or 3D systems. The interaction between mature machine technology and equipment configurations precisely tailored to the paving requirements assure perfect evenness of the concrete road surface.
Concrete road surfaces have a long service life of 30 to 40 years, according to Wirtgen.
