Engineers fight to stop global warming from ruining roads
The 2010-2011 floods in Australia wreaked devastation and damage across Queensland, claiming 33 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 hard lesson in the importance of weatherproofing Queensland’s most vulnerable roads, to ensure that future floods lead to fewer people being cut off.
Since then, Queensland has used a process called foamed bitumen stabilization. This injects small amounts of air and cold water into the hot bitumen, the sticky black substance typically used for road surfaces.
The bitumen then expands and forms a water-resistant layer. The result is a stronger yet flexible road surface or pavement that is better able to withstand flooding.
“It was actually tried and tested on Queensland roads during Tropical Cyclone Debbie in 2017,” says Caroline Evans, chair of the World Road Association’s (PIARC) Climate Change and Road Network Resilience Committee. ).
“When the waters receded, the sidewalks were still intact, so they didn’t need to be fully rehabilitated afterwards.”
Foamed bitumen stabilization has also been applied to other roads as part of Queensland’s move to make its roads more flood resistant 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. It has built 1,000 km of foamed bitumen road surfaces so far and “continues to develop foamed bitumen techniques”, according to its transport department.
It’s one of many technologies that authorities are testing on the streets around the world. From roads blocked by landslides in Nepal, washed away coastal highways in the United States, collapsed bridges in Kenya to melting ice roads in Canada – an increasingly unstable global climate threatens to disrupt transportation networks essential.
Yet it also inspires a lot of innovation.
One of the biggest problems with roads is their vulnerability to high temperatures. Extreme heat can soften pavement, leading to more cracking, buckling, and rutting or surface depressions.
The exact effects 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 road failure and the road can actually fail in 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-shielded pavements could reduce the surface temperature by up to 10°C,” says Ms Evans.
It 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 are often a lack of greenery.
Before the 2020 Olympics, Tokyo tested sun-blocking paint coating developed by construction company Nippon Corporation, a member of the Cool Pavement Society. It says that by the end of 2020, solar heat-blocking paint had been applied to almost three million square meters of the country’s road surfaces.
Although such coatings can protect the road surface, they could make life more uncomfortable for pedestrians. Research conducted in the United States has shown that reflective road surfaces radiate significant amounts of heat to the roadways.
The cost of doing nothing will be high. If measures to combat rising temperatures and increased rainfall are not taken, then the repair and maintenance invoice roads across Africa could reach $183 billion by 2100, according to a study by the University of Colorado.
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 control costs would be to “look at targeted sections of vulnerable roads” rather than immediately looking to upgrade 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 aren’t always justified. Low-traffic roads can be built from low-emitting materials like soil, and laid by human workers rather than heavily polluting machines, Mokoena says.
Low-volume roads also present “an opportunity to use recycled materials and waste materials for construction, which would otherwise go to landfills; these are generally associated with lower emissions”.
Alternative materials are particularly important given the lack of sandwhich is commonly used in road construction.
“The use of waste and recycled materials will likely present a cheaper locally available alternative material to modify bitumen to withstand the distresses associated with…higher temperatures,” says Georges Mturi, Principal Investigator at CSIR South Africa. .
Recycled tires have been 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 trial, “we are continuing construction and trials to also demonstrate the different 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 comes in, it’s something that can be used,” says Refiloe Mokoena.
Further research may be needed to find alternatives to bitumen and plastic which, after all, are both petroleum by-products.
In addition, there are “low fruits” that can be taken advantage of, says Mokoena.
These include 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 testing and design stages, Ms. Mokoena points out that many other technologies exist and have been tested. What is needed now is the impetus of industry and governments to generalize them.