The conveyor leads to a metal drum, lower left, where the virgin rock particles are heated. Then, they’re combined with recycled asphalt and a hot petroleum tar called asphalt binder. Asphalt binder is basically the “scrapple” of petroleum — the dense base left over after refineries distill all the other oils needed for products like gasoline, kerosene and jet fuel. (WBEZ/Katherine Nagasawa)