Wednesday, 10 July 2019
A new Austroads technical study has proposed merging four grades of polymer modified binders (PMBs) into two in the Australian specification, after extensive testing revealed comparable PMB grades showed similar performance in asphalt and sprayed seals.
“Reducing the number of PMB grades will simplify technical specifications in each jurisdiction,” says Robert Urquhart, Principal Technology Leader, ARRB and author of the study. “Production costs should also be cheaper as fewer tanks will be needed to store different products.”
PMBs are increasingly used in road construction as they resist permanent deformation and cracking better than conventional bitumen. The Specification Framework for Polymer Modified Binders (AGPT/T190) currently includes binder grades for use in asphalt (A grades) and sprayed seal applications (S grades).
This study, Performance of Asphalt and Spray Grade PMBs in Sprayed Seals, compared the difference between samples of S20E and A20E grade PMBs, and S25E and A15E grade PMBs, to determine whether using comparable asphalt and spray grade PMBs influenced sprayed seal performance. The same binders were tested in asphalt in 2017-18, where it was found that S20E and A20E grade PMBs, and S25E and A15E grade PMBs, performed very similarly in laboratory tests.
“For this study, samples of each PMB underwent four laboratory tests, which investigated the ability of each binder to initially wet aggregate during construction, retain aggregate when a sprayed seal was first subjected to traffic in the presence and absence of water, and resist traffic‑induced cracking,” says Robert.
Results concluded that the representative S20E and A20E grade PMBs, and S25E and A15E grade PMBs, performed very similarly and effectively in all tests.
It is therefore proposed to merge these PMBs into two binder grades for use in both asphalt and sprayed seal applications, in an updated version of AGPT/T190. A combined S20E/A20E grade could include properties currently specified for an A20E grade PMB, and a combined S25E/A15E PMB grade could include properties currently specified for an A15E grade PMB.
AGPT/T190 will not be updated until other Austroads projects, proposing a new testing device, have been completed and industry has been consulted.
Specification requirements have been proposed for the merged grades.