The term bituminous materials is generally used to denote substances in which bitumen is present or from which it can be derived. Bitumen is defined as an amorphous, black or dark-colored, (solid, semi-solid, or viscous) cementitious substance, composed principally of high molecular weight hydrocarbons, and soluble in carbon disulfide. For civil engineering applications, bituminous materials include primarily aphalts and tars. Asphalts may occur in nature (natural asphalts) or may be obtained from petroleum processing (petroleum asphalts). Tars do not occur in nature and are obtained as conden-sates in the processing of coal, petroleum, oil-shale, wood or other organic materials. Pitch is formed when a tar is partially distilled so that the volatile constituents have evaporated off from it. Bituminous mixtures are generally used to denote the combinations of bituminous materials (as binders), aggregates and additives.