What is the difference between cement and concrete, and asphalt, tar, and blacktop?
Cement is made from limestone, clay and sand pulverized into a fine powder. When cement is mixed with water, it can bind sand and gravel into a hard, solid mass called concrete. Asphalt is a dark brown or black cementitious material which is a natural constituent of most crude oils. Tar or coal tar is a similar material produced from bituminous coal. Blacktop is a mixture of stone (about 95%) and liquid asphalt/tar (5%). The two are mixed at about 300 degrees in order to coat the stone and give the mix workability for compacting and placing. After cooling, the liquid asphalt hardens and acts as a heavy glue or mastic to hold the stones together.
