Lindetorpsvägen 7, Stockholm, Sweden
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Göteborg Landvetter Airport was opened in 1977. It is Sweden’s second largest international airport with about 90 direct flights and nearly seven million passengers per year. The rapid increase in traffic places great demands on the technical performance of the runways, and ongoing improvement measures are carried out according to a carefully prepared maintenance plan.
A few years ago the taxiways were renovated and late this spring it was time to apply a new surface course to parts of the runway. Considering the age of the runways and the need to install transducers for a new ice warning system, the airport owner, the state-owned company Swedavia, decided to replace the underlying layers as well.
“This type of work requires extensive planning and differs considerably from other resurfacing projects. In particular, it involves tight timeframes, a large number of work phases and rigorous safety and quality requirements. Everything has to fall into place,” says Tobias Pålsson, Quality Manager for the project at Skanska.
The fact that the work takes place after dark is another challenge, since the first aircraft must be able to take off and land at 6 a.m. In order to prepare for the unexpected, backup plans were drawn up which could be deployed if necessary. For example, there was always a mobile crane on site that could remove machines in case of malfunction.
Skanska began planning for the renovation in October 2018. In addition to coordination meetings with airport management and the company that was installing the new ice warning system, considerable time was spent evaluating different binders.
“We tested several binder grades and asphalt mixtures with most of the available methods,” Pålsson recounts. "All mixture types were tested and evaluated on the basis of the customer’s requirement for a dense and stable surface with a long service life. As this was a costly project involving many parties we really wanted to use the best products."
The extensive renovation was carried out in May and concerned the middle section of the runway: a stretch of just over 1,500 m with a width of 40 m – a total of about 67,500 m2. All work was carried out at night using four milling machines, two large paving machines, two shuttle buggies, two asphalt plants, 25 dump trucks and other equipment. Skanska’s workforce amounted to almost 100 people.
”We milled off 120 mm from the existing runway surface and replaced it with new asphalt layers amounting to about 20,000 tons,” Pålsson explains. ”First we applied a 100 mm binder course (AC) in two layers with Nynas Endura Z3 as a binder, and then a 20 mm thin layer as a surface course with our own special emulsion Duraflex, which is also manufactured by Nynas.”
It is important that the surface course fulfils its function of protecting the base layers from water while simultaneously offering good friction. In addition, it should be quick and easy to replace, thus facilitating maintenance. This explains why, a few years ago, Landvetter opted for a thin layer surface course, after learning of the positive results at Kastrup Airport in Copenhagen.
In the case of binder courses, it has been found beneficial to use a modified binder providing stiffness, such as Nynas Endura Z3 lower down in the structure in order to improve stability.
“Technically, we could have used a standard bitumen (70/100), but we chose a polymer-modified bitumen to ensure the highest quality renovation. It’s important not to forget that asphalt gets very hot in such wide, open spaces, reaching as much as 55 °C in the summer, so a highly modified stiff binder prevents deformation,” Pålsson concludes.