Paved roads are a godsend for travelers and truckers alike. But potholes, frost heaves, and other perennial problems can ruin the ride and damage vehicles from bicycles to SUVs to delivery vans.

State and local governments spend lots of money each year to repair potholes. But shovelfuls of asphalt or tar often prove no match for the forces of nature – and traffic wear and tear.

Potholes often begin as microscopic cracks in the road surface. Bad weather, poor drainage, and heavy traffic can  cause that surface to loosen and wear away. Engineers are researching ways to better predict when and where potholes might open up, coming up with such novel solutions as sensor-embedded “smart” roads and self-healing pavement.

Early pothole detection systems

Luna Lu, a professor of civil engineering and director of the Center for Intelligent Infrastructures at Purdue University, leads a team that is testing the use of sensor-embedded “smart” road surfaces that could provide real-time information and allow transportation agencies to fix cracks before they become major pothole hazards. The research, undertaken in 2017 on a stretch of Indiana highways, recently has yielded an in-situ piezoelectric sensor system to monitor concrete as it cures, saving construction time and money.

Self-healing asphalt

In Great Britain, researchers at the Nottingham Transportation Engineering Centre are investigating the addition of capsules full of “asphalt rejuvenators” as a way of creating self-healing pavement. The idea – inspired by an episode of the Spanish version of TV’s MasterChef, in which a contestant used a technique to form spheres that resemble caviar when submerged in a liquid – could reduce the frequency of repairs and “hopefully help turn potholes into a distant memory,” write Alvaro Garcia, a lecturer in engineering at the University of Nottingham, and Brunel University London colleagues Juliana Byzyka and Mujib Rahman.

As they explain in their 2018 Conversation article, asphalt roads are composed of mineral aggregates that give structural stability, and bitumen, a viscous liquid that binds the other materials together. When cracks appear in the road, bitumen drains into the cracks and fills them. But bitumen is a very viscous liquid at normal temperatures, and the healing of the cracks can take weeks. With regular traffic, the rate of crack growth may occur at a faster rate than they are filled – allowing potholes to form.

To accelerate the “healing” of the road, the researchers looked at adding tiny capsules containing sunflower oil, or tall oil, a byproduct of paper production. The idea is that when roads start to crack, the capsules break open and release the oil within, softening the surrounding asphalt. This helps the asphalt stick back together more swiftly, effectively filling in cracks and preventing small defects from deteriorating. Garcia and his colleagues estimate their technique could delay the first potholes by at least five years.

Energy-harvesting roads

Meanwhile, Tech Briefs reported in 2017, researchers from Lancaster University and the University of California, Merced, are exploring smart roads paved with piezoelectric ceramics. When embedded in road surfaces, the tiles convert vehicle vibration into electrical energy.

In 2008, the East Japan Railway Company installed a footstep-sensing floor at Tokyo station, harvesting the crowd’s kinetic energy to operate ticket gates and display systems. Italy, in 2011, signed a contract to place piezoelectric crystals underneath a stretch of road on the Venice-to-Tieste Autostrada. Even a club in San Francisco has taken the technology to the dance floor, using energy-capturing panels to power lights .

Why not roads?

Piezoelectric devices create an electric shock, or charge, when compressed. The idea is that as cars roll over the sensors, the vibration creates electricity that can run through a wire to a battery, transformer, or central collection point on the side of the road.

The Lancaster University team, led by professor Mohamed Saafi, aimed to recover 1 to 2 megawatts per kilometer on a 1-mile stretch of test road in the U.K. and Italy under normal traffic volumes — approximately 2,000 to 3,000 cars per hour.

The energy produced will be stored in a battery to power street lamps, traffic lights, and electric car charging points, according to Saafi. The team’s biggest challenges: cost, durability, and compatibility with materials like asphalt. “The pavement must not affect the performance of vehicles in terms of gas consumption and safety,” Saafi told Tech Briefs.

Volts from jolts

Not everyone considers potholes a scourge, however. A decade ago, the National Science Foundation sponsored a Cambridge, Mass.-based team of engineers hoping to commercialize a novel shock absorber that could convert the bumps and grinds of wheels hitting potholes into electricity. This video explains how:

Filed under: Special Features

Tags: asphalt, highway construction, materials science, pavement, potholes, self-healing roads, sensors, sustainable materials, transportation engineering