How does asphalt work, and where does it come from?

and our shopping trips depend on the stuff. Everything we buy at the store comes in via truck on those same roads, so without asphalt there wouldn't be anything to buy either. Millions of tons of asphalt are made and laid every year in the United States, yet we tend to take asphalt completely for granted. Let's take a look at how this essential material actually works and asphalt roads. Starts off with crude oil pumped out of the ground. The crew it oil ends up at an oil refinery,

and there it gets boiled. The refinery takes the crude oil vapor and captures it at different temperatures to separate the molecules into different groups. There are very short, lightweight molecules like propane and butane, with three or four carbons in the carbon chain. Gasoline molecules typically have ten carbons motor oil has twenty to fifty carbon atoms in the chain. The very longest chains, typically a hundred fifty carbons long, are asphalt. These are the heaviest molecules in crude oil.

Asphalt is black and solid at room temperature. You have to apply heat to turn it into a liquid. To make the hot mixed asphalt or h m A found on most roads, you start with a big, rotating, heated drum. Into your drum, you put gravel and sand and raise the temperature to three hundred degrees fahrenheit or so. Then you add five or six percent asphalt from the refinery

and mix until all the gravel is thoroughly coated. The drum dumps this hot mixture into the back of a dump truck and it gets laid by an asphalt spreading machine to make a road. After several hours, the mixture cools off, the asphalt solidifies, and you have a road. An interstate highway that handles thousands of cars and trucks a day uses a lot of asphalt. The layer of asphalt might be a foot thick sitting on top of

a gravel base up to two feet thick. A normal road through your neighborhood has only a few inches of asphalt in two layers. The base layer uses thicker gravel. The surface layer uses smaller pieces of gravel to provide a smoother surface that cuts down on noise and tends to repel water better. One interesting thing about asphalt is that it's recyclable. In fact, asphalt is the most recycled material by weight in the United States. Old asphalt can be ground up, reheated, and re mix to make new

asphalt in a process that's very efficient. So what's not to like? Asphalt is relatively inexpensive, easy to make, easy to lay, and it lasts a long time. About The only problem is the fact that it does wear out eventually. One obvious sign of this is the infamous pothole. Potholes more often arrived in the winter for two reasons. First, cold asphalt is more brittle than warm asphalt, so that's

more likely to crack. A hot asphalt road in the summers has some tendency to be self healing, but that's definitely not the case on a cold, dark winter night, so a small crack forms and lets water in. If that water freezes, it widens the crack. Since the asphalt layer is simply sitting on top of the gravel layer below. Eventually, a chunk of asphalts several inches thick, pops out when a heavy car truck passes by. Immediately you have a

four or five inch deep hole in the road. Cars driving over that hole quickly crushed the edges and make the whole bigger, and they scour out the gravel beneath the asphalt. Suddenly, in just a couple of days, you have a hole that's two ft around and a foot deep. It's a full blown pothole that can eat your tires and wreck your fancy rims. So what does the future hold? There is some discussion of replacing asphalt with glass roads.

The road would have a glass surface that protects banks of solar cells and l E d s. The l e ed s could display stripes and messages, and the solar cells could generate enough electricity to power the entire country. It'll be interesting to see if glass roads ever become a reality. For more on this and thousands of other topics. Because it has staff works dot com