Wednesday, 9 October 2019
Austroads has published the results of a study to test the long-term performance of polymer modified binders used in sprayed seals in Australia.
The resistance of non-modified bituminous binders to premature ageing has been assessed in Australasia using the durability test in the Australian/New Zealand specification AS/NZS 2341.13. This test, however, cannot assess the ageing performance of polymer modified binders and uses some equipment that can no longer be obtained.
“Austroads commissioned research into developing a long-term ageing or durability test for polymer modified binders based on test equipment that’s widely available,” said Dr Young Choi Senior Technology Leader, ARRB and lead author of the report. “We focused on using international devices, namely the pressure ageing vessel and the dynamic shear rheometer, to firstly age and then test binder samples.”
Austroads’ member agencies collectively purchase over $600 million worth of bituminous binders annually to build and maintain the Australasian road network. Up to 40% of roads resealed in some jurisdictions involve polymer modified binders, which enable constructed seals to be more resistant to cracking and other types of wear.
In 2011-12, two Austroads sprayed seal trial sites were established at Coober Pedy in South Australia and Cooma in New South Wales to provide field-related information about current and future polymer modified binder grades to be included in the Australian polymer modified binder specification AGPT/T190.
“To conduct the study, we collected unaged samples of binders from the two trial sites and artificially aged them using a pressure ageing vessel for between 30 and 72 hours. Field-aged binder samples were also collected between three to six years after the trial sites were constructed,“ Dr Choi said.
“We used dynamic shear rheometer stress ratio tests and Fourier transform infrared spectroscopy tests to investigate the differences between laboratory and field aged samples, and found that both sets of samples had broadly similar properties.”
Results obtained for samples from the Coober Pedy trial site indicated that pressure ageing vessel times of 52 and 80 hours were equivalent to binders aged in the field for three and six years, respectively. The results for Cooma, which has a less harsh climate, indicated that 23 hours of laboratory ageing were equivalent to six years of field ageing.
“These results will help us assess the longevity of polymer modified binders under the different climactic conditions found in Australia and New Zealand,” said Dr Choi.