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Round the clock paving

Round-the-clock paving by the Bickhardt Bau team on

the A5 near Karlsruhe-Durlach where the paver hit the

mark on this job: its great flexibility enabled the concrete

paver to quickly be reconfigured as required after 1 km.

When the two layers of concrete have been paved,

a surface retarding agent is uniformly applied to the

freshly smoothed surface by a Wirtgen texture curing

machine (TCM) which matches the paver. Depending on

the prevailing climatic conditions, the coarse aggregate

is exposed by brooming the surface just a few hours after

placing the concrete pavement. The result is a non-skid

surface with a large number of profile peaks and a tex-

ture which durably minimizes tyre noise.

Four typical projects highlight the advantages of this

method and show which features of the SP 1500

(four-crawler model) / SP 1500 L (two-crawler model)

from Wirtgen are of benefit.

Three of the projects concerned the rehabilitation

of concrete roadways between 30 and 40 years old. The

fourth project, in Saxony-Anhalt, involved the rehabili-

tation of a stretch of highway with alkali-silica reaction

(ASR).

• 4.5-km rehabilitation of the A1 near Trier (Rhineland-

Palatinate) by Berger Bau

• 4.8-km rehabilitation of a section of the A9 with ASR

near Weissenfels (Saxony-Anhalt)

by Max Bögl

• 2.3-km rehabilitation of the A5

near Kar l s ruhe (Baden-

Württemberg) by Bickhardt Bau

• 5.3-km rehabilitation of the A1

near Lübeck (Schleswig-Holstein)

by Eurovia Beton

Dual-layer paving –

High quality at lower

material costs

Cost-efficiency is one of the factors

fueling the boom in dual-layer

concrete paving . This method tan-

gibly reduces the cost of construc-

tion, as the bottom-layer concrete

and the top layer of exposed aggre-

gate concrete are designed to meet

different requirements.

On the A1 near Trier, Berger Bau

used the SP 1500 to pave a 20 cm-

thick bottom-layer concrete pave-

ment with 360 kg cement per m³

concrete and a maximum aggregate

size of 22. Meanwhile, the 6 cm-

thick top-layer concrete comprised a high-grade material

mix with 420 kg cement per m³ concrete and 2/8 double

broken and double screened chippings.

Material logistics is a challenge

The biggest challenge with this method lies in the logis-

tics: Two different materials are needed and must be

available in the right place at the right time and in the

right quantities, since they need to be placed

wet-in-wet.

The bottom-layer concrete is dumped directly in front

of the paver. The top-layer concrete is delivered to the

second machine via a conveyor. To this end, the concrete

is either filled directly from the truck into a material

hopper or intermediate container – each contractor uses

its own process here.

The further procedure is then the same in all cases:

Conveyors and a chute at the end of the conveyor dump

the top-layer concrete on the fully compacted bot-

tom-layer concrete behind the first paver.

A sufficient supply of both concrete grades is essential

to assure the success of the paving work.

Christoph Hofmeister, Head of Division at Max Bögl,

sees logistics has the biggest challenge when paving

concrete in two layers:

“For the project on the A9, we had a steady

stream of 45 articulated trucks carrying between

6,500 t and 7,000 t of sand,

gravel and chippings every day

during the paving phase, in

addition to 27 trainloads of

cement.

“This is equivalent to

roughly 750 t of binder. It is cur-

rently the largest mobile plant

in the world. Building this con-

crete roadway meant orchestrat-

ing a complex system of ma-

chines, material, weather,

ambient conditions – and

people.

“To assure the project’s

Christoph Hofmeister, Head of

Division at Max Bögl

Round-the-clock paving by the

Bickhardt Bau team on the A5 near

Karlsruhe-Durlach

Contractors World International Vol 7 No 5

17