ABSTRACT
This chapter gives a technical explanation of the major processed materials used in pavements: bitumen, asphalt and cement. It is noted that bitumen is sometimes called asphaltic cement or bituminous cement in North America. While bitumen can occur naturally, today it is most commonly produced as a residue during the distillation of natural crude petroleum where it is the highest boiling point fraction. Related materials are mastic, which is defined as a mixture of bitumen and sand or of powdered asphaltic rock and sand, softened by heat or by the addition of more volatile oils or bitumens. Bitumen is a thermoplastic adhesive which, when heated to about 150℃, readily attaches to pieces of stone. The main durability issue with bitumen occurs when it is used as thin spray covering a surface layer of stone. Such layers are directly exposed to the sun, and the loss of durability will directly cause a loss of stones from the surface layer. Tar is a bitumen-like material obtained by burning timber or coal. Pitch is produced by distilling tar. Asphalt is a mixture of bitumen, stone and (possibly) sand and some popular mixes are called asphaltic concrete, or bituminous concrete. Cement is made by burning limestone or dolomite to change their main constituent – calcium carbonate – to calcium oxide. Mixing cement, water and sand produces mortar. Adding stones to a mortar produces concrete.
