Reinforcement with a sustainability profile
Reuse, less need for material transport and an extended service life all make deep stabilisation a resource-efficient improvement method.
The Helgeland coast extends over both sides of the Arctic Circle. It is one of the most beautiful natural locations in Norway, and probably the whole of Europe. Visitors encounter sandy beaches, steep cliffs and thousands of islands, many of which are listed as World Heritage Sites by UNESCO.
During the past autumn, Skanska has worked together with its subcontractor, Grevlingen & Co AS, on improvement works in the area; in total, four road sections have been given a new, reinforced base course.
“These are low traffic roads with poor bearing capacity, deep ruts and overhangs,” says Tor Jakob Sandvik, Production Manager at Skanska Industrial Solutions in Norway.
The poor state of the roads lay behind the decision to carry out deep stabilisation. This is a method that involves the base course being recreated by milling the existing asphalt and the underlying layer before adding new aggregate and foamed bitumen to the existing road structure.
“We milled the road down 20 cm and then mixed new, crushed rocks with the milled material, and added bitumen corresponding to 8 litres/m2,” explains Tor Jakob Sandvik.
The surface was then planed and compacted, before it was time to take care of the asphalting a couple of days later. The upper layer consists of an Agb16 with Nypave 190 HT as binder, and the volume of asphalt is approximately 110 kg/m2.
In view of the geographical location and the changing weather conditions, the logistics represented a major challenge. All of the bitumen was supplied from the Nynas depot in Holmsund in Sweden, and they had to make sure that the temperature was sufficiently high all the way.
Grevlingen & Co AS was responsible for the actual deep stabilisation.
“We used a very powerful machine, the Wirtgen WR250, which breaks down and homogenises the road material to be used in the deep stabilisation process on site. It’s also equipped with a system that foams the bitumen during milling,” says Grevlingen’s CEO Jarle Ståhl.
“As the project was undertaken on islands off the Helgeland coast, it took a great deal of planning, not least because we had to wait for high tide so that the boats could transport the equipment.”
When the base course is reinforced with the deep stabilisation recycler, the starting point is that the existing material from the road is to be reused. The old asphalt is therefore mixed with parts of the base course plus a suitable amount of crushed rock.
Jarle Ståhl emphasises the importance of the material being well-graded and containing sufficient fine aggregate.
“Foam bitumen works best in the fine aggregate. Together, they both form a kind of mortar that holds together the larger crushed rocks and give the base course its unique properties; it becomes stronger and more flexible, with less water-sensitivity and a longer service life. Furthermore, the actual construction time is short and efficient.”