The road body serves to transfer the load and to prevent penetration of water and thus erosion. It reduces the danger of frost and, depending on the type of surface finish, the development of dust. The course structure of simple roads has the following pattern (beginning with the bottom course, ending with the top, as shown in Fig. 3.14):
• Transition course. This serves to prevent interpenetration of the subsoil with the foundation or bearing bed (base course) in cases where there is poor subsoil bearing capacity. The various possibilities include lime stabilization, stabilized foreign matter, wool (fleece. [expensive]), beaten layers, branch layers (only small surfaces possible).
• Foundation course. In an effort to contain costs, local materials such as uncombined gravel and sand and crushed rock should be used whenever possible. The degree of consistency in bearing capacity, which is required in the construction of major roads, is not usually possible with minor rural roads.
• Bearing bed (base course). There is often no distinction made between a foundation course and a base course, particularly when the latter is an uncombined layer using
course as per Fig. 3.17 " calculation as per nomogram (Fig. 3.15) Figure 3.14. Road body of different types of rural roads.
the same materials as for the foundation course. The term "base course" often is used for a layer above the subgrade, whereas pavement also means "bearing bed".
The following are other types of bearing beds:
• Stabilized bearing beds. Local and centralized mixing procedures for tar and cement are well known (mixed in place and mixed in plant). Cement-stabilized gravel paths also have proven their worth. The proportion of cement should be 50-70 kg/m3 with an appropriate homogeneous grading curve. It is also important to use the prescribed water content and to mix thoroughly to ensure optimum durability. In any case, the meteorological conditions at the time of laying the bed, such as wind, air humidity, and sunshine, are also important. If meteorological conditions are bad, works must be stopped. Dry weather demands the moistening of the stabilized bearing bed. It is also possible that separation during transport or application will impair the quality. Otherwise, the result can be a compact surface that will be prone to cracking.
• Hot-mix bearing beds. The minimum thickness should be 6 cm at least, because anything less can lead quickly to damage, as indeed can too precise a thickness of the subgrade surface, which is technically possible.
• Concrete pavement. The application thickness together with the sliding moulding finish should be 15-16 cm. Concrete paving has shown itself to be exceptionally long-lasting and maintenance-free. If the subsoil has good bearing properties and the concrete slab can be laid directly, the construction costs can be quite low. On the other hand, if the concrete pavement is laid out on top of subsoil with poor bearing properties or insufficient homogeneity, uneven settling may occur when heavier loads move across it, reducing the road's practicability or even ending it altogether (should the slab be subject to subsidence).
• Pavement. This serves to seal the road and prevent water penetration. It is intended as a wearing course, i.e., to bear the direct brunt of abrasion wear caused by spike tyres, horseshoes, drip damage in forests, contamination by the passage of livestock.
As far as simple roads are concerned, the following types of pavement are commonly used:
• water-bound clay wearing course on unbound gravel and sand bearing bed;
• cutback pavements, as a flexible cover on unbound gravel, possibly with cement stabilization;
• sealing coat, requiring a minimum of two courses for an acceptable result.
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