Page 124 - RoadCem Manual - PCT BV

Figure 5.20 Examples of pavement failure and causes thereof
5.2.3 Pavement Structure Materials
When discussing pavement structure materials we can group them into a number of categories:
Naturally occurring materials
These include natural soils, gravel-soil mixtures and gravels. Little or no processing is required other than, possibly, loosening the In-situ material by ripping and breaking down (usually with a grid roller) or removing oversize particles. The cost of such materials is, typically, about 25% of crushed stone. Although crushing may occasionally be required.
Standard/traditional materials
These are defined as materials which meet traditional specifications, such as those of the American Association of State Highway and Transportation Officials (AASHTO). Such materials are tolerant of construction mishandling and adverse environmental conditions and will probably perform well in most cases.
An essential feature of most traditional specifications for standard materials is a requirement for strict compliance with limitations on particle size distribution (grading), plasticity index and aggregate strength. This is partly to avoid the use of any materials in pavement layers that are susceptible to the weakening effects of water and frost. Crushed rock and river-washed and fluvio-glacial gravels are thus the predominant materials used for building roads in temperate climates. The export of these practices to tropical and subtropical regions has meant that the potential of natural gravels, especially in the drier areas of such regions, have often been neglected.
Non-standard/non-traditional materials
These comprise any material that is not wholly in compliance with the specifications used in a country or region for a standard or traditional material, for example, as regards grading or PI. Nonetheless, it
124