This paper was presented at the `Strategic investment alternatives for sutainable roadway materials' session. A comparative evaluation of the Superpave volumetric mix design system technology, with the well-established Marshall mix design method, was completed for the three main Toronto Tranpsortation urban pavements hot-mix asphalt types: HL 1 high stability frictional surface course; stone mastic asphalt (SMA) surface course; and HL 8 (HS) high stability binder course. Practical Ontario experience has indicated that superpave mixes tend to be rather coarse and have a lower asphalt cement content than Marshall mixes. Performance graded asphalt cements (PGAC) were selected to reflect the Toronto climate and traffic conditions: 58-22 in HL (HS); 64-28 in HL 1; and 70-28 in SMA. The Superpave and Marshall mixes were tested using the Nottingham Asphalt Tester (NAT) for resilient modulus, fatigue endurance and permanent deformation (rutting) resistance. The Marshall method HL 1, SMA and HL 8 (HS) mixes used by Toronto Transportation were quite close to applicable Superpave volumetric mix design system optimal mixes. It is also clear that these three main Toronto Transportation hot-mix asphalt types have been optimized to meet the urban heavy traffic requirement of rutting resistance while still maintaining adequate durability. This Superpave mix design experience, for mixes of known good field performance under heavy urban traffic conditions, is of considerable importance to the overall hot-mix industry. The adoption of Superpave technology must be evolutionary and reflect considerable Marshall and practical hot-mix asphalt experience. (A)
Abstract