The bubbles give the water in concrete enough room to expand as it freezes. The bubbles also protect the surface of the concrete from chemicals used to melt ice. Such qualities make air-entrained concrete a good material for roads and airport runways. It costs more than ordinary concrete. But it is often cheaper to use, because it cuts the amount of time the concrete must be protected in cold weather.
Lightweight concrete weighs less than other kinds of concrete.
Builders make it in two ways. They may use lightweight shales, clays, pumice, or other materials instead of sand, gravel, and crushed rock. Or they may add chemicals that foam and produce air spaces in the concrete as it hardens. These air spaces are much larger than the air spaces in air-entrained concrete. How concrete is made Materials.