When Copenhagen Motor Ring Road M3 was built in the seventies, slightly less cement ended up going into the lower road base of the pavement than the original recipe called for. But that mistake turned out to be an ingenious one. COWI, NCC and the Danish Road Directorate are now reviving the old technique and formulating a new mathematical description, inter alia simulating how this type of semi-rigid pavement reacts to different types of weather and traffic load.
It is the Danish Road Directorate's hope that in the future cement-stabilised bases will be used on Danish motorways and other roads carrying heavy traffic, to which semi-rigid pavements are best suited. Christian Busch, Project Manager at COWI, explains:
"We noted that certain roads, where the upper asphalt layers were on top of the cement-stabilised course, lasted longer than corresponding pavements with only asphalt-bound layers. But given that the roads were designed using a methodology that can only be regarded as outdated these days, we had to create a proper design basis if we were going to put that kind of pavement into service again."
The pavement, similar in many respects to the old one from Ring Road M3, has been tested in Sweden in 2003 and goes into service in 2006 on two test sections near Herning, where they will be continuously monitored. During the spring additional large-scale laboratory tests will be conducted in Poland. Most recently the concept has been presented as part of the European ecoserve networking project, targeting a general reduction in co2 emissions from all phases of the road construction process, like the production of chippings and binders and the use of residual products.
Instead of stabilising the road with cement, fly ash can be used too, as can ground blast-furnace slag or naturally occurring binders like volcanic ash. Compared to asphalt, which is really a high-viscosity liquid, the cement-stabilised base course is more deformation-resistant. The pavement is better able to withstand the traffic stresses that produce rutting and roughness in the wheelpaths, as well as being cheaper than asphalt and potentially attractive in environmental terms. By Christina Tækker, cht@cowi.com Published: 24.04.2006