This paper reports on the fundamental changes made to the aggregate gradings of dense mix asphalt used for medium to heavy duty pavements in South Australia. The changes result from a redefinition of nominal size to better reflect designated mix sizes and the flow on from this to a theoretical grading curve. The objective was to reduce their susceptibility to rutting through good stone on stone contact and provide appropriate layer thicknesses in relation to mix size. Reported are two aspects from the changes made, firstly the resistance to change out of comfort zones and the practical problems encountered with accompanying lessons learnt. Many trials fell short of expectations due to resistance to change away from fine mixes, and the practical difficulties in obtaining suitable sand and aggregate fractions from quarrying sources. The field trials of September 1996 are reported, as well as the method of introduction into the specification of Transport SA and practical implications such as sand fractions for adequate compaction. Laboratory performance testing such as resilient modulus, fatigue and wheel tracking results are provided. Use of these mixes on large scale projects and laboratory testing has provided pleasing results, and further laboratory testing and field monitoring is required to establish fatigue resistance and pavement life. (A)
Abstract