The uppermost layer of the road is the asphalt surface layer. This layer bears the brunt of traffic and weather. Due to the high degree of mechanical and climatic damage, this surface generally needs to be renewed every 12 to 15 years. Particularly rough and abrasion resistant stone particles help to maximise the road surface's durability.
The main objective of the binding layer is to quickly and effectively transfer any thrust and vibration exerted on the road surface down into the lower layers. This provides protection for the surface layer from becoming over-stressed and distorting. This is particularly important in the case of high traffic intensities and sharply decelerating vehicles.
It is in fact the lowest asphalt layer which plays the important role of bearing the weight exerted on the road surface. The mixture of large chunks of stone, which makes up this layer, ensures that weight is evenly distributed across the ground surface and therefore increases the total load-bearing capacity of the road. If the road is properly maintained, then the base layer will last for up to 50 years.
In order to prevent frost damage, a frost-protection layer will often be laid below the asphalt layers. The loose mixture of gravel, sand, ballast or grit is extremely weather resistant, the mixture drains excess surface water which may collect beneath the road and therefore prevents cracks occurring due to frost forming and expanding in the upper asphalt layers.