Briefing: Assessing gravel roads for upgrading to bituminous standard

At the stage of upgrading a road from a gravel wearing course to a bituminous standard, and in the interest of reducing costs, the existing gravel wearing course is usually incorporated as a sub-base layer in the new bituminous road. The biggest technical challenge during the upgrade design is in assessing the strength of the existing wearing course in situ. In addition to this, a decision has to be undertaken as to whether to reprocess the existing wearing course before it is incorporated into the new pavement or to leave the layer undisturbed so as to benefit from the consolidation under continual traffic action that will have taken place during the gravel stage of the road. Moreover, if a decision is undertaken to process the wearing course, another question arises - how deep should the reprocessing be? The decision taken at this stage has a significant impact on the cost and performance of the upgraded road. This note offers guidance on how to assess an existing wearing course and interpret the results in order to assist road engineers in making a more informed decision. It further discusses common errors and assumptions made during assessment that lead to inappropriate measures being undertaken.