grip
The grip describes the size of the frictional resistance or the power transmission between the vehicle tires and the road. Essentially, these are driving and braking forces as well as lateral forces from cornering. The grip conditions on a road have a significant effect on the safety of traffic. Dry road surfaces all have relatively high grip values. If the road surface is wet or icy, the grip values drop sharply depending on the speed driven and the surface texture. In the field of road construction, the property of grip is an important characteristic when recording and assessing the condition of new or existing road surfaces. Therefore, the grip is checked with the help of different measuring devices .
Influencing factors
The grip of a road surface is influenced by various factors:
- Water film thickness on the road surface ( aquaplaning )
- Roughness of the road surface
- Tire condition and properties
- Driving speed
functionality
The roughness in the contact area between the road and the tire is decisive for grip. This property is also called “sharpness”. Smooth or polished road surfaces cannot guarantee this roughness and must be roughened or renewed using suitable measures. The aggregate used for the top layer should be broken and as resistant to polishing as possible. Furthermore, it must be ensured that the bitumen content is kept low in order to avoid "over-greasing" the asphalt surface.
Initial grip
When producing new road surfaces, it is important to develop a sufficient initial grip . Shortly after their production, new surface layers made of asphalt may have insufficient grip, because there is still a thin layer of unbound bitumen on the surface that covers the aggregate below. By rolling in sand or chippings directly during production (so-called blunting , chipping or sanding ) the roughness of the surface is increased and the required initial grip is guaranteed. After a while, the overlying layer of bitumen is removed so that the aggregate is exposed.
In the case of concrete roads, the surface roughness must also be created during manufacture. For this purpose, measures such as stripping with a steel brush in the transverse direction or with artificial turf are used. There is also a thin layer of cement glue on the surface of the concrete road, which is worn off over time.
literature
- S. Velske, H. Mentlein: Road construction technology . Werner Verlag, Düsseldorf 2002, ISBN 3-8041-3875-6 , p. 260 ff .
- E. Straube, K. Krass: Road construction and road maintenance . Erich Schmid Verlag, Berlin 2005, ISBN 3-503-09067-3 , p. 263 ff .