Combining the American and European mix design approaches: utilization of NCHRP performance indicators for analysis of CEN-test results

In the Netherlands, the functional approach described in the 2008 European Asphalt Concrete standards was selected, specifying mixtures by their stiffness, fatigue resistance, permanent deformation, moisture sensitivity and limited composition data. The requirements for the functional specifications were based on the existing experience with a large number of mixes. Since the introduction of the standards, unexpected developments like improved performance in all functional tests with increasing RAP content, led to questions about the predictive quality of the laboratory determined functional characteristics for field performance and the potential causes of a mis-match between lab and practice. These questions led to a large, long term project in the Netherlands (NL-LAB) in which the functional characteristics are determined in the process of construction projects. They are determined on (I) material mixed and compacted in the lab, (II) mixed in the plant and compacted in the lab and (III) mixed in the plant and compacted in the road. These tests will eventually provide insight in the effect of mixing and compaction. The pavement sections are monitored in time, to allow the link with pavement performance. The sections will be sampled during their service life to see changes occur in their functional properties. For the road industry, that tries to guarantee pavement performance by accurate selection of materials, the possibility of design information based on both laboratory and in situ results would be beneficial.
Two mixes for base layers with different mix compositions and amounts of RAP are analysed using formalistic expressions originating from Design Guide Level II for estimation of various performance indicators. This project uses expressions to analyse the differences between the mixes in the three cases described above. It addresses the possibility of utilizing these expressions during preliminary mix design to guide the selection of mix composition parameters towards a desired optimum.