Blacktop, also known as asphalt concrete, is a mixture of stone aggregate and liquid asphalt. The liquid asphalt binds the conglomeration together and allows the hardened result to conform to the contours of the surface underneath.
Over 90 percent of the blacktop mixture is stone aggregate. Aggregate collectively refers to materials such as gravel, sand or stone powder that are quarried and crushed. Aggregate can also be manufactured as a byproduct of steel, copper or tin processing.
The rest of the blacktop mixture is liquid asphalt. The liquid asphalt in blacktop glues the stone aggregate together, forming a smooth surface when it hardens. When heated, it has the consistency of tar, and liquid asphalt hardens like cement.
Approximately 70 percent of the highways in the United States and over half of the country’s interstates are paved with blacktop. It is also used as a driveway cover, but due to its pliability (which helps seal it to the ground), it is susceptible to damage from tire wheels, ladders and even high-heeled shoes. Blacktop is also vulnerable to stripping, cracking and aging.