JOB REPORT

Asphalt and concrete for the traffic artery.

Combined paving of asphalt and concrete

It is Austria’s main traffic artery: with a length of 301 km, the A1 motorway – the so-called “Westautobahn” – leads across the alpine country from Salzburg to Vienna. Because of the tremendous traffic volume of up to 84,000 passenger cars and 18,000 trucks per day, it was decided to gradually expand the motorway to three traffic lanes. One of the sections to be upgraded is located close to the town of Linz, where traffic congestions are the order of the day. The 19.7 km long stretch was expanded using a truly remarkable construction method: the new pavement structure was to include both, bituminous and concrete layers.

To protect the subgrade from detrimental influences like ingressing water, a Super 1900 road paver from Vögele placed an erosion-proof asphalt layer on top of the hydraulically bound base layer. The asphalt layer was compacted by two tandem rollers from Hamm, namely an HD O75K combination roller and a DV O6V Super.

The concrete was placed by two Wirtgen slipform pavers in two layers of 14.75 m width each. The 20 cm bottom layer, consisting of recycled concrete, was placed by an SP 1600, while an SP 1500 paved the 8 cm upper layer of washed concrete. The two machines produced between 600 m and 700 m of dual-layer concrete pavement per day, using some 2,500 m³ to 3,000 m³ of concrete mix. The bottom-layer paver inserted dowel bars at 5 m intervals, every 25 cm on the main lane and every 50 cm on the fast lane and hard shoulder, transverse to the pavement.

A retarder followed by a film-forming agent to prevent evaporation were sprayed on the freshly paved concrete surface. A small grader with broom brushed the desired washed-concrete texture into the pavement. The pavement’s peak-to-valley depth of 1 mm, combined with a distance between peaks of less than 10 mm, minimizes rolling noise, improves tyre adhesion and consequently increases safety on the A1.