We stopped by Granite Construction's open house at their Swan Road aggregate and hot asphalt plant just east of the Tucson airport.
Granite quarries sand and aggregate on the 800 acre site that is crushed, heated, dried, and mixed with a small amount of oil to create asphalt for roads. They also recycle old asphalt and mix up to 15% of it with new asphalt. A million tires are ground up each year to be added to asphalt mixtures to make softer surfaces for playgrounds, jogging paths, etc.
In the picture on the right, crushed rock goes up the conveyor into the cylindrical chamber in upper center, where it is heated to 380 degrees before being mixed with oil and cooled slightly before being loaded into trucks. The asphalt contains about 95% rock and only 5% oil.
The aggregate is heated by burning used oil - you know, the oil drained from your car engine at Jiffy Lube.