KNOW-HOW

Withstanding the pressure on the road.

How can roads absorb the tremendous loads induced by traffic?

One of the countless questions to be asked when planning the construction of a new road is, “What loads will the road actually need to cope with?” In addition to overall traffic frequency, road engineers are especially interested in the percentage of heavy traffic. For one vehicle weighing 30 tons will not apply the same load on the road pavement as 30 vehicles weighing one ton. Quite the opposite is true – as many as 160,000 passenger cars equal one single truck axle with a load of 10 tons. The road, and therefore the design of the different pavement layers, needs to be tailored to its future use.

To No. 1: Example of an inner-city asphalt road

Roads in residential areas, for instance, are usually trafficked by no more than a few trucks. The portion of the pavement bound with binding agents is therefore usually less thick. A 10 cm asphalt base layer is built on top of a 45 cm granular subbase that will protect the upper layers against frost. The uppermost layer of an asphalt road is the surface course which, in this example, has a thickness of 4 cm. The demands placed on a surface course include resistance to wear, excellent stability, and a skid resistant surface texture.

To No. 2: Example of a main road built in asphalt design

Roads linking villages and towns or heavily trafficked inner-city roads are exposed to medium to high loads. Such link roads are based on a 30 cm thick frost blanket and 16 cm asphalt base layer. These layers are followed by a 4 to 8 cm asphalt binder course, the main function of which is to safely divert the shear stresses caused by traffic into the lower pavement layers. It needs to prevent the pavement from heaving as a result of the dynamic forces generated by braking and accelerating vehicles. The topmost layer consists of a 4 cm asphalt surface course.

To No. 3: Example of a motorway built in asphalt design

Motorways are usually exposed to tremendous loads caused by high traffic frequency and a high percentage of heavy vehicles. The pavement structure of motorways is therefore based on thicker base layers, using mixes of crushed stone and particularly viscous bitumen. The frost blanket has a thickness of 45 cm, while the asphalt base layer is 22 cm thick. The layer thicknesses of binder course and surface course layers are similar to those of main roads.

To No. 4: Example of a motorway built in concrete design

Motorways are the main application of concrete in road construction. Unlike asphalt roads, concrete pavements combine the functions of surface course, binder course and parts of the base layers, and are resistant to plastic deformation. Concrete motorways typically consist of, for instance, an 18 cm frost blanket, 15 cm cement-stabilized base layer and 26 cm concrete surface.