Construction costs of the upper pavement layers (roadbase and sub-base) are typically about 30 to 40 per cent of the total road construction cost. The work reported here concentrates on granular pavement materials, although many of the principles developed and described are applicable to the materials used in the lower layers (subgrade and fill). The limiting criteria (compacted strength, plasticity and grading) set out in traditional specifications for roadbase and sub-base materials are based on universal standards applied to all traffic levels. Where the materials fail to meet these criteria they are termed \"marginal\" or \"sub-standard\".
The fundamental principal, or message, that needs to be carried forward from this research is that appropriate road construction materials need to selected on a \"fitness for purpose\" basis and that this is related to the service performance expectations for the material. This approach needs to recognise
the impacts of the governing road environment (defined by the climate, hydrological regime, terrain, traffic, construction and maintenance standards) which may not be modelled through rigid adherence to specification testing. Many materials currently falling within the \"marginal materials\" definition will
certainly be appropriate as roadbase for many sealed secondary and feeder roads.
This report draws on information gathered on a range of representative \"marginal\" or \"non-standard\" materials and has been drafted as a summary document that highlights key issues, presents general
approaches and gives typical examples of use.
Cook, J.R.; Bishop, E.C.; Gourley, C.S.; Elsworth, N.E. Promoting the use of marginal materials. (2000)