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Contractors World

 
Contractors World - AFRICA
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construction, demolition, mining and quarrying industries.

 
Contractors World AFRICA - 2016 Vol 7 No 5

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Dual-Layer Paving Is First Choice

Wirtgen SP 1500 efficiently paves exposed aggregate concrete on four job sites

Four job sites, four contractors, four German states, one paving method: Dual-layer concrete paving with the slipform paver SP 1500 from Wirtgen.

Swayed by the numerous economic and technical advantages, more and more planning engineers are opting for this technology when rehabilitating concrete highways. Namely, dual-layer concrete paving.

This is because noise-reducing non-skid exposed aggregate concrete pavements can be placed most economically with this method. The concept is to pave a bottom-layer concrete on a high-grade subbase with a high load-bearing capacity. This layer is normally 20 – 24 cm thick. It is then overlaid with a top layer of exposed aggregate concrete which is normally between 5 and 8 cm thick.

At pave speeds of around 50 m/h, Berger Bau achieved daily outputs of 500 m per day on the A1 near Trier with the Wirtgen SP 1500 train. A conveyor deposits the top-layer concrete on the pre-compacted bottom-layer concrete behind the first paver, where it is directly paved by the second concrete paver.

At pave speeds of around 50 m/h, Berger Bau achieved daily outputs of 500 m per day on the A1 near Trier with the SP 1500 train from Wirtgen

There are different types of concrete

The slipform paver places the two concrete grades wet-in-wet in a fully automated process.

At pave speeds of around 50 m/h, Berger Bau achieved daily outputs of 500 m per day on the A1 near Trier with the SP 1500 train from Wirtgen

The requirements in respect of compressive strength, bending tensile strength and indirect tensile strength are the same for both the bottom layer and the top layer of exposed aggregate concrete.

The composition of the concrete can, however, differ with regard to the grading curve, maximum aggregate size, cement content and requirements to be met by the mineral aggregate.

While around 350 kg cement suffice per m³ in the bottom-layer concrete, 420 kg cement per m³ are required in the top layer of exposed aggregate concrete.

Coarse aggregate, i.e. material > 2 mm in size, is particularly important in the top layer of exposed aggregate concrete. Only double broken and double screened chippings which meet high demands in terms of angularity, grain shape and resistance to polishing are used in order to ensure that the concrete surfacing retains its noise-reducing properties and remains skid-resistant and durable in the long term.

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