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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 eco-

nomically 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-lay-

er concrete behind the first paver, where it is directly

paved by the second concrete paver.

There are different types of

concrete

The slipform paver places the two concrete grades wet-

in-wet in a fully automated process. 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 ag-

gregate 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 re-

quired 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 con-

crete surfacing retains its noise-reducing properties

and remains skid-resistant and durable in the long

term.

Dual-Layer Paving Is

First Choice

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

Contractors World International Vol 7 No 5

16