Bitumen gets a new specification

18 Aug rss print

After a comprehensive review and consultation process, the Australian Standard AS 2008–2013 Bitumen for pavements was published on 18th November, 2013. This is the fourth iteration of the standard, with the original published as AS A10 in 1938 and the most recent version of the standard published in 1997.

Many of the changes implemented in the updated specification reflect the evolving bitumen supply situation in Australia. The advent of imported bitumen has introduced complexity into specification compliance testing due to the unavailability of Australian Standard (AS) test methods in international laboratories. The differences between AS test methods and the more widely used American Society for Testing and Materials (ASTM) test methods has made the interpretation of results from international supply refineries problematic. Consequently, the new AS 2008 allows for the use of two ASTM test methods – D92 Standard test method for flash and fire points by Cleveland Open Cup and D2872Standard test method for effect of heat and air on a moving film of bitumen (Rolling Thin Film Oven Test). There are significant differences between the AS and ASTM test methods for performing the Rolling Thin Film Oven (RTFO) treatment, therefore the values obtained for post-RTFO properties will differ depending on which test method has been used. This has been accommodated in the standard by specifying different limits for post-RTFO properties depending on the test method utilised.

In the case of Flash Point determination, both the Australian method AS 2341.14 and the international method ASTM D92 are considered to be similar enough that they share a specification limit of 250°C minimum.

A new parameter, Mass change (% mass) has been introduced to the specification, with both AS 2341.10 and ASTM D2872 test methods approved for use. This parameter indicates the change in mass of a given bitumen sample before and after the RTFO treatment. Unfortunately, AS 2341.10 does not currently refer to weighing the samples before or after treatment, however this will be rectified in the next iteration of the test method, which is currently underway.

The bitumen grades covered by the specification have also changed to reflect the types of bitumen now available in Australia. Class 50 has been removed from the specification and two new grades, Class 240 and Class 450 have been included. Additionally, multigrade bitumen grades M500 and M1000 have been incorporated into the specification – they were previously specified in an Austroads specification AG:PT/T190. This is a sensible alignment, as the test methods required for multigrade bitumen are the same as those used for normal paving grade bitumen.

Standards Australia has reviewed a number of bitumen-related specifications and test methods. In early November, AS 2341.14–2013Determination of flashpoint of bitumenwas published and a draft version of AS 2341.2 Determination of dynamic (coefficient of shear) viscosity by flow through a capillary tube was made available for comment on the Standard Hub until 6th December 2013.