Roads are essential infrastructure, but they're made with nonrenewable materials and have a significant carbon footprint, which opens up recycling opportunities.
Over 94% of paved roads in the U.S. are made with asphalt. It's a dirty fuel product that requires high temperatures to manufacture and was responsible for around 22 million tons of planet-warming carbon dioxide pollution annually between 2009 and 2019.
However, transportation agencies have begun recycling some of this material when roads need to be broken down and repaved. The product is called reclaimed asphalt pavement, or RAP, and it helps reduce emissions and conserve natural resources, according to a report shared by The Conversation.
In 2021, 95% of asphalt mixtures reclaimed from old pavement were put back into use on repaved roadways, saving over 2.8 million tons of CO2 in the process.
This led civil engineering researchers from the University of Tennessee, Knoxville, to examine more thoroughly the long-term safety and durability of RAP compared to new pavement materials, the report explained.
The study focused on the frictional properties of RAP in terms of road safety, especially during wet conditions. It shared that nearly 75% of weather-related auto accidents occurred on wet pavement.
Asphalt is generally the combination of a sticky, petroleum-based binder and aggregates, such as crushed stone, gravel, or sand.
To recycle asphalt, contractors use a milling machine to grind up old pavement surfaces and then blend them with new binders and some additional aggregates to ensure some level of performance.
Pavement friction is the force that resists motion between a vehicle's tires and the pavement surface, the report detailed, and understanding how RAP performs in this regard is essential to road safety.
The researchers developed a two-step process to examine the frictional properties of RAP aggregates, as they're essential to skid resistance.
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Absolutely 💯 It involved a mechanical inspection of the RAP, where it was crushed to expose the material's inner surfaces. That was followed by chemical analysis, where a solvent was used to dissolve the asphalt, revealing the aggregates for closer inspection.
The results are helping engineers determine if RAP mixes are safe for curving roads or intersections and understand how much of the recycled mix can be safely used.
"We hope our research will lead to solutions that reduce carbon emissions, conserve natural resources and keep roads safe over time," the report added.
Other studies have explored using plastic waste as a component in new asphalt to help reduce the need for mining new materials and reduce waste, while the development of permeable and porous road surfaces can help reduce the danger of flash floods.
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