Producing long-lasting road surfaces

07 October 2020

Austroads has published the findings of inspections and binder ageing performance studies associated with two sprayed seal trial sites constructed in South Australia and New South Wales.

Austroads sprayed seal trial sites near Coober Pedy in South Australia and Cooma in New South Wales were established to evaluate the performance of seals constructed using various grades of polymer modified binders (PMBs), from their placement through to long-term service.

Ross Guppy, Austroads’ Transport Infrastructure Program Manager says the trial sites, constructed in 2011-12, were a significant investment but the research has been invaluable in Australasia’s quest to produce reliable long-lasting road surfaces.

“Flexible granular pavements protected by sprayed seal surfacings are the backbone of Australia and New Zealand’s road networks.”

“Austroads member agencies collectively purchase more than $600m worth of bituminous binders each year which are used to build and maintain our road network. PMBs are used extensively in sprayed seals with up to 40% of reseals in some jurisdictions incorporating their use.”

“This work builds on previous work commissioned by Austroads, and reviews how the test sections of road have performed after six to eight years of service. It included visual assessments of the sites, surface texture depth measurements and an investigation into the properties of the field aged binders,“ Ross said.

The visual assessment found that the performance of the Coober Pedy trial site was generally good. Some isolated areas of stripping and areas of bleeding were mainly due to a degradation of the pavement structure. All trial sections, constructed using different types of PMBs and bitumen, appeared to be showing similar, satisfactory performance. Further monitoring of the Coober Pedy site is required so that variations in the performance of the different binders can be observed.

Several sections of the Cooma trial site were showing severe distress after six years of service, while other sections appeared to be performing well. Widespread cracks throughout the site had reflected through from the cement stabilised pavement underneath. This widespread distress eventually led to the entire site being resealed shortly after the inspection.

The findings of this research will help ensure our test methods and technical specifications are robust and performance based, and validate models and calculations used in pavement design.

Sand patch texture depth measurements were conducted at both sites. Information about the changes in seals’ texture depth was used to validate a recently developed seal voids parameter. This work found that the new seal voids parameter, initially derived using data obtained in New Zealand, could reasonably predict the traffic-loading induced reduction in seal voids.

Samples of the binders collected during construction and after different periods of service were tested to provide information about reductions in binder elasticity and binder hardening over time. The research found that the hardening of PMBs was influenced by a complex process involving the hardening of the base bitumen and softening of the polymers in the binder.

The viscosity properties of aged C170 bitumen samples obtained from the trial sites were compared with an Australian seal life model. The model could not accurately predict the age hardening of bitumen at the Coober Pedy site.

Infrared spectroscopy tests showed that in many cases PMBs oxidised noticeably less than bitumen.

The authors concluded that further in-depth studies are required to evaluate the true effect of ageing on the performance of binders. More complex rheological tests (e.g. repeated loading tests) appear to be needed to develop a durability performance test for PMBs in the Austroads PMB specification (ATS3110).

Download: Inspections of Polymer Modified Binder Trial Sites and Ageing Properties of Binders, 

Join us for a webinar on Tuesday 17 November 1-2pm AEDT with Young Choi, Steve Patrick and John Esnouf to learn more about findings of the research.

No charge but registration essential. Can't make the live session? Register and we'll send you a link to the recording.

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Source:  Austroads -

Date of Original:  29 September 2020

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