The historical development of the traditional Marshall and the modern gyratory-based, performance-related asphalt mix design procedures is described.
New Zealand is progressively adopting performance-related specifications and implementing performance contracts for road maintenance and construction. Thus, in 2002, asphalt mixes sourced from a range of asphalt manufacturers located around New Zealand were subjected to a comprehensive laboratory testing regime, to determine their volumetric- and performance-related properties, such as modulus.
Two sets of asphalt specimens were created, using either Marshall or gyratory compaction procedures, based on existing mix designs. They were then tested by AUSTROADS APRG18 procedures and equipment to provide performance-related data.
The Marshall mix design procedure is inadequate for the needs of performance-related specifications, so the AUSTROADS APRG18 asphalt mix design procedure, based on gyratory compaction of test specimens, should be adopted in New Zealand.
As an interim step, the New Zealand Supplement to the AUSTROADS Guide to the Structural Design of Pavements should be modified to incorporate the results of this research, namely that the range of stiffness moduli for typical dense-graded asphalt mixes used on New Zealand roads is 1400 MPa to 3300 MPa.
Keywords: aggregate, asphalt, bitumen, CAPTIF, gyratory test, Marshall test, mix, New Zealand, pavement, pavement design, pavement mix, road, testing, traffic