Development of a more versatile approach to flexible and flexible-composite pavement design

The current UK pavement design standard deals with the use of a limited number of materials in a restricted range of design options. The versatility of this method needs to be increased to give the highway engineer a wider choice of materials and design configurations. The increased versatility will lead to more economic designs by allowing new materials, recycled materials and a wider range of secondary aggregates and binders to be used. It will also enable stronger foundations, incorporating hydraulically bound materials, to be used with reductions in the thickness of the more expensive surfacing layers. In addition, separate design methods are currently used for flexible and flexible composite pavements and many designs currently being submitted for road schemes reside in a 'grey' area that involve pavement structures with material layers that are not covered directly by the current methods. Often there may be more than one way of estimating pavement life depending whether either fully flexible or flexible composite pavement design methodology is used. This can lead to ambiguities and therefore, a more versatile approach is required to deal with these difficult areas, and at the same time help to deliver more sustainable and economic pavement construction. This report describes the modifications to the current design method to improve its versatility. This modified method predicts pavement layer thicknesses that are compatible with existing methodology and methods of characterizing materials. As a result, the modified method could be introduced with little disruption. The method will facilitate more prudent use of natural resources and assist in the protection of the environment in line with Government Policy.