Australia’s infrastructure pipeline isn’t confined to roads. As populations grow, and air travel costs plummet, airports around the country are upgrading their runways.
Airport pavements have highly stringent requirements, exceeding those for roads and other public infrastructure.
In the Australian Airports Association Airfield Pavement Essentials report, Dr. Greg White says pavements for airports are not fundamentally different to those for roads or other applications.
According to Dr. White, the principles for design, construction and maintenance are essentially identical.
The physical characteristics of a plane however place a unique set of demands and stresses on airport pavements.
Aircraft are very heavy. The average-sized Boeing 737-800, for example, has a maximum takeoff weight of 80,000 kilograms. They also have high tyre pressure and are less tolerant than cars to weak or bumpy surfaces.
SAMI Bitumen Technologies General Manager, Sebastien Chatard, says the binder supply and technology companies have invested significant time and resources into developing airport-grade polymer modified binders.
“Bitumen properties change over time, lighter fractions within the material are lost through evaporation and exudation, surface oxidisation causes the material to harden and lose durability ,” Mr. Chatard says. “The surface eventually loses aggregate particles that present as debris, and the aggregate loss affects the pavement’s functional integrity.”
The wearing course of an airport pavement must be able to resist plastic deformation due to its constant subjection to the high shearing stresses of aircraft movements.
According to Mr. Chatard, polymer modified binders are commonly adopted by airport contractors for this reason, as the polymeric additive promotes thermal stability, resistance to oxidation and increase in durability.
“Bitumen mixtures engineered with polymers have therefore been widely adopted in order to reduce the risk of pavement failure under demanding loading of aircraft tyres.”
Mr. Chatard recommends the company’s SAMIfalt B380 binder for runway and taxiway applications. He says because the binder was developed by blending specialty polymers with harder grade bitumen, it provides a combination of resilience and durability benefits, prolonging overall life expectancy.
“SAMIfalt B380 is a low to medium polymer modified binder specifically engineered for use in asphalt mixes requiring high workability, with excellent deformation and fatigue resistance,” Mr. Chatard says.
According to Mr. Chatard, a section of taxiway at Sydney’s domestic airport was paved in 2006 with dense graded AC14 and AC20 asphalt mixes, in which SAMIfalt B380 was used as a binder.
“Wheel tracking laboratory testing is extremely important when dealing with very heavy traffic situations, like those at an airport,” says Mr. Chatard.
“We took samples from the Sydney airport mix and tested them at SAMI’s in-house National Association of Testing Authorities accredited laboratory for wheel tracking and resilient modulus.”
Mr. Chatard says the tests revealed significant resistance to groove closure, with a 1.7-millimetre rut depth for the AC14 and a 1.2-millimetre rut depth for the AC20.
“The SAMIfalt B380 binder also has significant storage stability and remains homogenous under prolonged hot storage conditions,” Mr. Chatard says.
“This allows the binder to be transported and stored for long periods and, unlike other polymer modified binders, it’s not susceptible to phase separation.”
According to Mr. Chatard, SAMIfalt B380 is one of the multiple SAMI products suitable for airport applications. He names SAMIfalt EME high modulus asphalt and SAMIfalt Multigrade Plus as other examples.
“The base course of an airport pavement has to be stiff enough to withstand very high loading stresses,” Mr. Chatard says.
“A high modulus asphalt containing SAMIfalt EME bitumen works well under those conditions.”
According to Mr. Chatard, since being developed at the beginning of 1990s in France by the parent company Colas, EME binders have been extensively used in airports pavements all over Europe.
“SAMIfalt EME binders are manufactured with the aid of a blowing column under controlled conditions in order to obtain unique rheological properties,” Mr. Chatard says.
“When combined with high modulus asphalt, the overall pavement’s stiffness and rut resistance increases, which is crucial for heavily used runways.”
Mr. Chatard says SAMIfalt Multigrade Plus, an un-modified bitumen, was used for taxiway rehabilitation works at Sydney Airport, Port Macquarie Airport and at the RAAF HMAS Albatross base at Nowra in NSW.
“The Multigrade Plus has better temperature susceptibility than standard bitumen and is process designed to provide improved crack and rut resistance,” Mr. Chatard says.
“It is manufactured to meet the Australian Standard specification AS2008: Multigrade 1000 and improves the durability performance of asphalt.”
As airlines add additional flights to their schedules and plane ticket prices drop to an all-time low, Australian runways require a bitumen binder capable of withstanding the stress.
“SAMIfalt binders facilitate mass transit without the expected wear-and-tear of standard bitumen,” Mr. Chatard says.
“If you’ve been a on a plane in the last few years, it’s likely you’ve been landing on SAMI bitumen.