The largest use of asphalt/bitumen is for making asphalt concrete for road surfaces and accounts for approximately 85% of the asphalt consumed in the United States. Asphalt concrete pavement mixes are typically composed of 5% asphalt/bitumen cement and 95% aggregates (stone, sand, and gravel). Due to its highly viscous nature, asphalt/bitumen cement must be heated so it can be mixed with the aggregates at the asphalt mixing facility. The temperature required varies depending upon characteristics of the asphalt/bitumen and the aggregates, but warm-mix asphalt technologies allow producers to reduce the temperature required. There are about 4,000 asphalt concrete mixing plants in the U.S., and a similar number in Europe.