What are roads made of? A pavement materials engineer explains the science behind the asphalt you drive on
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May 10, 2024
Mansour Solaimanian, Associate Research Professor, Larson Pennsylvania Transportation Institute, Penn State -
The Conversation
While on the road, you’re probably thinking more about your destination than the pavement you’re driving over. But building roads requires a host of engineering feats, from developing the right pavement materials to using heavy equipment to lay them down. The better they’re built, the longer roads last and the fewer construction delays drivers have to endure.
Asphalt binder is refined from crude oil. From crude oil, refiners first extract gasoline, kerosene and oil, and what remains at the bottom becomes the asphalt. Portland cement is manufactured using several different ingredients, including limestone, sand, clay, silica and alumina.
Engineers compact the mixture of asphalt binder and aggregates together at an elevated temperature, about 300 degrees Fahrenheit (150 degrees Celsius), which glues the aggregates together into the final product, called asphalt concrete.
Hydration bonds the cement to the aggregates to make the product, called Portland cement concrete, stronger. With this process, there’s no external heating involved.
Pavement structure
Asphalt concrete’s pavement structure typically has three main layers: the base layer, the intermediate layer and the surface layer.
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