The 2010-11 Australian floods spread devastation and damage across Queensland, with 33 people losing their lives and causing billions in losses across the state. The floods also damaged 19,000 km of roads, including those needed for emergency and delivery vehicles.
It was a stark lesson in the importance of waterproofing Queensland’s most vulnerable roads, to ensure that future flooding means fewer people are cut off.
Since then, Queensland has been using a process called foamed bitumen stabilization. This injects small amounts of air and cold water into the hot bitumen, the sticky dark substance typically used for road surfaces.
The bitumen then expands and forms a waterproof layer. The result is a stronger yet flexible road or pavement surface that is better able to resist flooding.
“This was tested on Queensland roads during Tropical Cyclone Debbie in 2017,” says Caroline Evans, chair of the World Road Association’s (PIARC) road network resilience and climate change committee.
“When the waters receded, the pavements were still intact, so they didn’t need to be completely rehabilitated afterwards.”
Foam bituminous stabilization has also been applied to other roads as part of Queensland’s move to make its roads more resistant to flooding and is proving more cost effective than traditional asphalt.
Queensland faces considerable challenges as it has the longest state-controlled road network of any Australian state or territory with over 33,300 km of roads. So far, it has built 1,000 km of foamed bitumen road surfaces and “continues to develop foamed bitumen techniques,” according to its transport department.
This is one of many technologies that authorities are testing on streets around the world. From roads blocked by landslides in Nepal, washed-out coastal highways in the US, collapsed bridges in Kenya, to melting ice roads in Canada, an increasingly volatile global climate threatens to disrupt essential transportation networks.
However, it is also inspiring a great deal of innovation.
One of the biggest problems with roads is their vulnerability to high temperatures. Extreme heat can soften pavements, leading to more cracks, sags, and ruts or depressions in the surface.
The exact effects depend on local conditions, says Refiloe Mokoena, a research engineer with the Council for Scientific and Industrial Research (CSIR) in South Africa.
“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 the color of the streets and reflect solar radiation.
“Some of these heat protection flooring could reduce surface temperatures by as much as 10°C,” says Ms Evans.
This can also help reduce “heat island” effects, he adds, where cities are much warmer than surrounding regions because buildings can block airflow and there is often a lack of vegetation.
Ahead of the 2020 Olympics, Tokyo tested a sunlight-blocking paint coating developed by construction company Nippon Corporation, a member of the Cool Pavement Society. It says that by the end of 2020, paint that blocks solar heat had been applied to almost three million square meters of the country’s road surfaces.
While these coatings can protect the road surface, they can make life more inconvenient for pedestrians. Research conducted in the US showed that reflective road coatings radiated significant amounts of heat upwards.
The cost of doing nothing will be high. If action is not taken to combat rising temperatures and rainfall, Africa’s road repair and maintenance bill could reach $183 billion by 2100, according to research from the University of Colorado.
Ms Evans believes that while there is widespread international interest in alternative technologies for roads, the difference between countries is in the level of funding available to invest in the technologies.
One way to keep costs in check would be to “look at specific vulnerable road sections” rather than immediately looking to improve an entire road network, he says. This could include more preventative maintenance in certain areas, which would be cheaper than later repairs.
Expensive, high-tech materials and processes are not always guaranteed. Low-traffic roads can be built with low-emission materials like earth and laid by human workers instead of heavy-polluting machinery, says Ms Mokoena.
Low-volume highways also present “an opportunity to use recycled and waste materials for construction, which would otherwise go to landfills; these are often associated with lower emissions.”
Alternative materials are particularly important given the scarcity of sand, which is commonly used in road construction.
“Using waste and recycled material will likely present a cheaper, locally available alternative material to modify bitumen and withstand the difficulties associated with…higher temperatures,” says Georges Mturi, Senior Research Scientist at CSIR South Africa.
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The recycled tires were tested on a stretch of road in Gauteng, South Africa, where the material showed no heat cracks. According to Mr. Mturi, who participated in the test, “we are continuing with more construction and testing to also demonstrate the various ways of using waste and recycled materials in road construction.”
Other materials could include recycled plastic and glass. It may not seem obvious that such substances can withstand high temperatures and heavy traffic, but “depending on the form the material is presented in, it is something that can be used,” says Refiloe Mokoena.
More research may be needed to find alternatives to shoe polish and plastic, which are, after all, petroleum by-products.
In addition, there are some “low fruits” that can be taken advantage of, says Ms. Mokoena.
These include regular maintenance of stormwater infrastructure and thus improved drainage and planting of trees alongside roads to shade sidewalks.
While many potential innovations to improve road resilience are still in the testing and design stage, Ms. Mokoena points out that many other technologies exist and have been tested. What is needed now is the push from industry and governments to generalize them.
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