Page 119 - RoadCem Manual - PCT BV
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5.2 In Situ Material as the Basis for the RoadCem method 5.2 1 General
Traditional pavement designs usually consist of a typical pavement structure shown in Figure 5.15.
Figure 5.15 Typical pavement structure.
SURFACING
The surfacing is the uppermost layer of the pavement and forms an interface with traffic and the environment. It normally consists of some kind of non-structural, impermeable bituminous surface treatment or a structural layer of premixed bituminous material (asphaltic concrete).
BASE
The base is the main load-bearing and load-spreading layer of the pavement and normally consists of natural gravel, gravelly soils, decomposed rock, sands and sand-clays. The granular materials are often stabilized with cement, lime or bitumen. On relatively highly trafficked roads, asphalt concrete and crushed stone may also be used.
SUBBASE
The subbase is the secondary load-spreading layer underlying the base and normally consists of a material of lower quality than that used in the base. This layer protects the subgrade and, importantly, acts as a construction platform and also provides a stiff platform against which the base can be adequately compacted.
SUBGRADE
The subgrade is the upper layer of the natural soil that supports the pavement structure. It may be undisturbed local material or soil imported from elsewhere and placed as fill. In either case, it is compacted during construction to give added strength. The ultimate strength characteristics of the subgrade dictate the type of pavement structure required, in terms of layer thickness and material quality, to reduce the surface load by traffic to a magnitude that can be supported without unacceptable permanent deformation and settlement.
Each of the components of a traditional approach pavement structure forms a part of a typical road cross section as shown in Figure 5.16.
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