Development and implementation of a new Australian asphalt mix design procedure

A new asphalt mix design procedure has been developed in Australia as a result of a joint program by transport authorities, ARRB Transport Research and the asphalt industry. The procedure is performance related, aims to produce mixes with improved service properties, is affordable, and is rapid and easy to use. The procedure is based on the outputs of a coordinated laboratory research program supported by an Accelerated Loading Facility (ALF) trial. Research indicated that the dynamic creep test suffered from a number of deficiencies and a wheel tracking test was introduced together with a refusal density test. Wheel tracking ranked the rutting performance of mixes in the same order as did a full scale ALF trial. A study of aggregate packing las indicated by particle orientation) was undertaken to assist in the selection of suitable laboratory compaction equipment. The new mix design procedure is arranged in three levels. During level one testing, a composition with suitable volumetric proportions is identified by selecting a target grading and materials combination, and then preparing a series of mixes, using a gyratory compactor, at binder contents that span the expected binder range. The volumetric properties of candidate mixes are assessed with respect to criteria related to the expected use of the mix and traffic level. For mixes to be used in heavily trafficked conditions, level two and (for very heavy traffic) level three testing is performed. This includes wheel tracking and refusal density testing. There are optional fatigue and moisture sensitivity tests. The mix design procedure is now entering its implementation phase and has the support of all State Road Authorities and industry. The new level 1 test methods are gradually replacing the existing ones such as Marshall and Hubbard Field. National agreement has been reached on the level 2 and level 3 tests but these are not routinely specified at present. As the implementation process continues it is expected that fine tuning of the methods and of the procedure will be required.