A collaborative partnership between SAMI Bitumen Technologies and Brisbane City Council has confirmed the benefits of emulsion stabilisation technology.
Future infrastructure demand will be directly affected by population growth, broader economy shifts, technological change and the need for environmental sustainability, according to Infrastructure Australia.
Ensuring the road network meets future demand is more complex than simply building new roads.
Extensive work is required to maintain existing roads through improving road base strength and resilience.
Given the inter-connected nature of public policy, improving that performance while also meeting public expectations requires increasingly collaborative relationships between industry and government.
lulian Man, SAMI Bitumen Technologies Technical Services Manager, says collaboration across a diverse set of stakeholders is integral to ensuring Australia’s future infrastructure sustainability.
“SAMI is consistently working with asset owners to find cost-effective ways to improve road performance,” Mr. Man says.
In 2017, SAMI partnered with Brisbane City Council (BCC) to develop and trial emulsion-stabilised granular road material.
SAMI developed the material for BCC at its in-house lab, before BCC lay the material on a council road for detailed monitoring and performance testing.
“The BCC trial was designed to confirm SAMI’s belief that using emulsions to stabilise aggregate road material is more effective for workability and performance in the presence of moisture, due to the better coating of the aggregate particles,” Mr. Man says.
“SAMI has undertaken significant research in this space, and the partnership with BCC gave us the opportunity to translate that research into real world application.”
Traditionally, the practice of strengthening granular material for road base involved treating the material with a cementitious or bituminous binder, but SAMI is seeking alternatives.
“Cement or lime treated materials are often used to stabilise the base material, which results in cracking that is then reflected into the surface, whereas bitumen stabilised bases are more flexible and not as prone to cracking,” Mr. Man says.
“Bitumen stabilised base courses can be made with either foamed bitumen (FTB), or bitumen emulsion (ETB).
“Both applications work to reduce the viscosity of bitumen, which allows the binder to be mixed with cold, moist aggregate material.”
Mr. Man says foam bitumen is the more commonly used stabiliser in Australia, despite emulsion having a greater stabilising effect.
He adds this is due to emulsion’s ability to coat both the fine and coarse aggregate of the base material.
“Coating both aggregates results in a more moisture-resistant material, which in turn increases pavement life,” he says.
“Additionally, emulsions are easier and safer to handle during transport, storage and mixing.”
According to Mr. Man, preliminary work was undertaken at SAMI’s lab in 2017, with granular-base coarse material from BCC’s Bracalba Quarry.
Researchers investigated the performance of the emulsion stabilised material using multiple residual binder contents.
“We also wanted to highlight how emulsion-treated base can yield higher stiffness, and therefore better deformation resistance, at a lower binder content than foamed bitumen,” Mr. Man adds.
Work was also undertaken to assess how the ETB mix reacted to stockpiling, for a period of up to two weeks post manufacture.
“The ability to have access to stockpile-able emulsion-stabilised granular materials offers more flexibility to contractors,” Mr. Man says.
Generally, when using cement or hydrated lime stabilised materials, the material should not be stockpiled.
“This presents a big risk to contractors when using fixed plant mixed stabilised materials, especially when dealing with factors like variable weather and plant breakdowns, which are out of their control,” Mr. Man says.
Following assessment, SAMI and BCC’s Asphalt and Aggregate Branch discussed a suitable place to trial the application and monitor the ETB’s ongoing performance.
“The final decision was to use ETB in the rehabilitation on Abbott Street in Camp Hill, which was undertaken in July 2018,” Mr. Man says.
Mr. Man says the Abbott Street trial is still in progress, with monitoring supported by the BCC’s Asset Management Branch.
“This involves extracting cores out of the road base for resilient modulus testing at SAMI’s lab, which measures the increase in stiffness over time,” he says.
BCC is also undertaking Falling Weight Deflectometer (FWD) measurements to monitor the strength of the stabilised pavement.
“FWD testing shows that maximum deflection has decreased over time, indicating the pavement is becoming stiffer,” Mr. Man says.
“For example, FWD testing in August 2018 indicated that the overall pavement was performing like a weak granular pavement, whereas by July 2019, the pavement was performing more like a bound pavement.”
Mr. Man says that so far, the trial is confirming emulsions application as an alternative to other methods of material stabilisation.
“The emulsion stabilisation process is safer, environmentally friendly and lacks the complexity associated with other types of stabilisation, as it is carried out in a simple pugmill at ambient temperature,” Mr. Man says.
“Plus, the cost of producing ETB is significantly lower than FTB, as less binder is required to achieve the same performance.”