Australia’s 2010-11 floods spread devastation and damage across Queensland, killing 33 people and causing billions in damage across the state. The floods also damaged 12,000 miles (19,000 km) of roads, including those needed for emergency and delivery vehicles.
It was a clear lesson in the importance of weatherproofing Queensland’s most vulnerable roads to ensure future flooding results in fewer people being cut off the road.
Since then, Queensland has employed a process known as foamed bitumen stabilization. It involves injecting small amounts of air and cold water into hot bitumen, the sticky dark substance typically used for road surfaces.
The bitumen then expands and forms a water-repellent layer. The result is a stronger yet flexible road surface or sidewalk that is better able to withstand flooding.
“This was tried and tested on Queensland roads during Tropical Cyclone Debbie in 2017,” says Caroline Evans, Chair of the World Road Association (PIARC) Committee on Climate Change and Road Network Resilience.
“When the water receded, the sidewalks were still intact, so they didn’t have to be completely rehabilitated afterwards.”
Foamed bitumen stabilization has also been used on other roads as part of Queensland’s effort to make its roads more flood resistant and is proving to be less expensive than traditional asphalt.
Queensland faces significant challenges as it has the longest state-controlled road network of any Australian state or territory, with over 33,300km of roads. So far it has built 1,000 km of foamed bitumen road surfacing and, according to its transport department, is “continuing to develop foamed bitumen techniques”.
This is one of many technologies that authorities are testing on roads around the world. From roads blocked by landslides in Nepal, flooded coastal highways in the US, collapsed bridges in Kenya to melting ice roads in Canada, an increasingly volatile global climate threatens to disrupt vital transportation networks.
But it also inspires many innovations.
One of the biggest problems of roads is their vulnerability to high temperatures. Extreme heat can soften sidewalks, which can lead to more cracks, buckling, and ruts or surface depressions.
The exact impact will depend on local conditions, says Refiloe Mokoena, a research engineer at the South African Council for Scientific and Industrial Research (CSIR).
“There are so many variables that determine a road failure, and the road can actually fail in many different ways.”
One solution is heat shields. These are special coatings and tiny hollow ceramic particles that lighten road paint and reflect the sun’s rays.
“Some of these heat shield coatings could lower the surface temperature by up to 10°C,” says Ms Evans.
This can also help reduce “heat island” effects, she adds, where cities are much warmer than surrounding regions because airflow can be blocked by buildings and there’s often a lack of greenery.
Ahead of the 2020 Olympics, Tokyo is trialling a solar-blocking paint coating developed by construction firm Nippon Corporation, a member of the Cool Pavement Society. It said sunscreen paint had been applied to almost three million square meters of the country’s road surfaces by the end of 2020.
While such coatings could protect the road surface, they could make life more uncomfortable for pedestrians. Research conducted in the United States has shown that reflective pavement coatings radiate significant amounts of heat upwards.
The cost of doing nothing will be high. Unless action is taken to combat rising temperatures and heavier rainfall, the cost of repairing and maintaining roads in Africa could reach $183 billion by 2100, according to a University of Colorado study.
Ms Evans believes that while there is widespread international interest in alternative road technologies, the difference between countries lies in the level of funding available to invest in the technologies.
One way to keep costs under control would be to “look at targeted sections of at-risk roads,” rather than immediately trying to improve an entire road network, she says. This could include increased preventative maintenance in certain areas – which would be cheaper than after-the-fact repairs.
Expensive, high-tech materials and processes are not always justified. Roads with little traffic can be built from low-emission materials like earth and laid by people instead of heavily polluting machines, Ms Mokoena says.
Low-volume roads also represent “an opportunity to use recycled and waste materials in construction that would otherwise be destined for landfill; these typically have lower emissions.”
Alternative materials are particularly important given the scarcity of sand commonly used in road construction.
“Using waste and recycled material is likely to provide a cheaper, locally available alternative material to modify bitumen to withstand the stresses associated with…higher temperatures,” says Georges Mturi, a senior research scientist at South Africa’s CSIR.
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Recycled tires were tested on a stretch of road in Gauteng, South Africa, where the material showed no heat cracking. According to Mr Mturi, who was involved in the trial, “We are continuing with further construction and testing to also demonstrate the various possibilities of using waste and recycled materials in road construction.”
Other materials could be recycled plastic and glass. It may not seem obvious that such substances can withstand high temperatures and heavy traffic, but “depending on the shape of the material, it’s something that can be used,” says Refiloe Mokoena.
More research may be needed to find alternatives to bitumen and plastic, both of which are by-products of petroleum, after all.
Additionally, there are some “deep-lying fruits” that can be exploited, Ms. Mokoena says.
This includes regular maintenance of stormwater infrastructure to improve drainage, and planting trees along roads to shade sidewalks.
While many potential innovations to improve road resilience are still in the testing and construction stages, Ms. Mokoena points out that many other technologies exist and have been tried. What is needed now is industry and government pressure to spread it further.
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