Pavement

This report describes the results obtained during the second year of work (2015–16) into the development of a binder test that can rank the low temperature cracking performance of PMBs.

Studies conducted during the first year of work (2014–15) indicated that extensiometer force ratio tests could be used to rank the low temperature cracking performance of nine of the 13 binder grades included in the Australian PMB specification if binders did not break when subjected to a standard set of test conditions (i.e. test temperature = 10 °C, test speed = 0.5 mm/s and final sample displacement = 250 mm). As a number of hard PMB samples broke during extensiometer tests, investigations were conducted during the second year of work to determine if force ratio tests could be used to rank the low temperature cracking performance of the remaining four hard A35P, A25E S15RF and S18RF PMB grades. Studies were also conducted to determine if dynamic shear rheometer (DSR) stress ratio tests could be used to rank the low temperature cracking performance of both hard and soft PMB grades.

Seven PMB samples which represented the four hard PMB grades were subjected to varying extensiometer test conditions to find a set of conditions where the binders did not break during testing. The optimum test conditions for the characterisation of hard binders were found to be when tests were conducted using a test temperature of 20 °C and test speed of 0.1 mm/s. As no marked correlation was found between force ratio results determined at 20 °C and the fatigue life results obtained for a series of binders in asphalt at 10 °C, it appears that force ratio tests cannot currently be used to rank the low temperature cracking performance of A35P, S15RF and S18RF PMB grades.

An analysis of the results obtained in the first and second years of work indicated that force ratio tests that were conducted using standard test conditions were suitable for ranking the low temperature cracking performance of 10 of the 13 binder grades included in the Australian PMB specification.

A very reasonable correlation was found between the DSR stress ratio results obtained for a series of 27 different binders and the fatigue life results obtained for each of the materials in asphalt. Based on these results, DSR stress ratio tests appear to be suitable for ranking the low temperature cracking performance of all 13 binder grades which are included in the Australian PMB specification.