What are roads made of? A pavement materials engineer explains the science behind the asphalt you drive on

(The Conversation is an independent and nonprofit source of news, analysis and commentary from academic experts.)

Mansour Solaimanian, 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.

I am an engineer who does research on materials used in roads. Scholars in my field are working to develop materials that can make roads stronger and last longer.

Road materials

So, what are roads really made of? The simple answer is that they are made of typical construction materials such as aggregates – soils and rocks – as well as asphalt binder and Portland cement, which act like glue to bond it all together.

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,...