Base course
|
Superstructure ceiling base course |
|
| Planum ▼ | ||
|
possibly solidified - - - - - - - - - |
Substructure (with dam position) |
|
|
possibly solidified - - - - - - - - - |
Underground | |
Base layers (outdated also called slab substructure ) are the subdivisions of the superstructure of the road structure in road and path construction . They carry the surface course ( road surface ) and a binder course for heavily used roads .
The creation of a base course requires that the subsoil is suitable, which means above all that it is stable, stable, profile-appropriate and level. The base courses are limited at the bottom by the subgrade .
A distinction is made between unbound and bound base courses.
Unbound base layers
The unbound layers include the frost protection layer, gravel and crushed stone layer and soil improvement. A technically outdated term for an unbound base layer is suitcase ( gravel suitcase , road suitcase ).
- Frost protection layer
Frost damage poses a major risk to the roads. Ice has a larger volume than water. If water penetrates the road and freezes there, it expands, displacing the stones of the road. This leads to a loosening of the grain structure , the road loses its stability . The consequences are particularly visible in the spring as “potholes” in the road surface.
To prevent this, a layer of frost protection is installed. It is the first, lowest base layer and has the task of draining off any water that may penetrate. Therefore it has to be particularly permeable to water. In addition, the selected aggregate must be frost and weather resistant, i.e. H. the rock must not be damaged by frost or rain, for example it must not crumble. In order to ensure the load-bearing capacity of the layer, a graded grain size distribution is selected. For example, gravel , sand , crushed stone , chippings and the possible mixtures from them are used, possibly recycled building materials or waste incineration ashes are added.
- Gravel and gravel base course
Gravel and gravel base layers differ only slightly from the frost protection layers. The main difference is the grading line bands , which allow only slight fluctuations in the grain size distribution.
- Soil improvement
Soil improvement is used on soils that are too moist, fine-grained and unstable. It is intended to improve the workability and drivability of the ground. To achieve this, either the proportion of coarse grain is increased, which is referred to as mechanical soil improvement. Or small amounts of fine lime (CaO) or hydrated lime [Ca (OH) 2 ] or hydraulic binders are mixed in.
Bound base layers
The bound layers include soil consolidation, bitumen-bound base layers, base layers with hydraulic binders and the road surface.
The resistance to mechanical and climatic stresses should be increased permanently by soil consolidation. The soil should be sustainable and frost-resistant. This is achieved by mixing in cement or white fine lime , which are known as binders . The choice of binder depends on the grain size distribution of the soil. Tar and bitumen were also used in the past .
Bitumen-bound base courses are also known as asphalt base courses . They consist of the minerals chippings, gravel or sand, and bitumen 70/100 or 50/70, sometimes also 30/45. Granulated asphalt is also increasingly used, which is removed from old roads and reinstalled after processing.
The base courses with hydraulic binders include hydraulically bound base courses (HGT) and concrete base courses.
Hydraulically bound base courses (HGT) consist of a graded grain structure 0/32 or 0/45, which consists of natural or artificial minerals such as chippings, gravel or sand. Cement, is used as a binder road binders or high-hydraulic lime. The layers are paved with pavers . After installation, they must be kept moist for at least three days. In certain cases, notches are made in the transverse and longitudinal direction. This “predetermined breaking point” prevents uncontrolled cracking.
Concrete base layers consist of concrete , an artificial rock made of cement, concrete aggregate or aggregate (sand and gravel or chippings) and water. It can also be used concrete additives and additives such. B. Liquefier or retarder. The concrete for the base layers is dimensioned according to DIN 1045 and must correspond to strength classes C12 / 15 or C20 / 25. Concrete base layers are installed by pavers with upright or towed formwork . The concrete must be kept moist after installation. Uncontrolled crack formation should be avoided by joints and dummy joints .
The pavements represent the top layer of the road structure and belong to the category of bound layers. A distinction is made between asphalt pavements, concrete pavements and cobblestones.
Norms
In Germany, the ZTV SoB-StB 04 serves as the basis for assessment for the base courses .
literature
- Additional technical contract conditions and guidelines for base courses in road construction , ZTV T-StB, 1995 edition, 2002 version, published by FGSV-Verlag, Cologne
- Additional technical contract conditions and guidelines for layers without binding agents in road construction , ZTV SoB-StB 04