Large stone asphalt mix design for heavy duty asphalt pavements

Abstract

The recent increase in traffic volumes and also axle loads on some of the major routes in South Africa has extended the traffic classes beyond the current highest design class. Additionally there is a strong lobby to increase the legal axle load to between 9 and 10 metric tonnes. There is also a tendency from overseas to use higher tyre pressures with new tyre types. One of the main reasons why the top size stone in mixtures has been limited to 26,5 mm is because the conventional mix design procedures cannot handle aggregates larger than 26,5 mm. A design method to incorporate the benefits of large stone mixes is urgently needed. Mix design, pavement design and pavement performance needs to be considered simultaneously and should not be independent functions as currently is so often the case. A mix design method must therefore be based on engineering properties, structural behaviour and long term performance.