For dense graded asphaltic concrete, enough voids in the mineral aggregate (VMA) should be provided to allow room between the aggregate particles for sufficient bitumen to provide cohesion, durability and fatigue resistance. In addition some 2 per cent air voids should remain after construction and trafficking. The packing characteristics of the aggregates determine the VMA. While a number of factors influence this packing, one of the influences is the overall shape of the gradation curve of the aggregates. Specified gradation curves close to the Fuller maximum density curve tend to create an asphaltic concrete with insufficient VMA, so should be avoided. The specifications for the gradation curves of a number of countries are examined and it is concluded that Transit New Zealand would be wise to retain generally the gradations they have specified for the last quarter century. (a) For the covering entry of this conference, please see ITRD abstract no. E212706.
Samenvatting