Asphalts

Asphalt (often called bitumen in technical contexts) is a viscous, black or dark brown material used mainly for paving and waterproofing. In road construction, asphalt typically refers to an asphalt binder combined with mineral aggregates to form asphalt concrete. Bitumen may occur naturally or be produced from refining crude oil.

Key forms include asphalt binder, asphalt concrete (hot-mix asphalt with aggregates), asphalt emulsion, and cutback asphalt (solvent-based). Polymer-modified asphalt improves elasticity; crumb rubber modifiers use recycled tires. Roofing asphalt is a harder, more viscous product used for shingles and damp-proofing.

Production involves refining bitumen from crude oil. For paving, the binder is heated and mixed with graded aggregates to produce hot-mix asphalt, placed hot and compacted. Emulsions are produced by dispersing bitumen in water with surfactants and used for cold applications. Cutbacks use solvents but are restricted due to emissions.

Uses and performance: The primary use is road surfaces—highways, local streets, parking lots, airfields—and roofing, waterproofing membranes, and sealants. Asphalt pavements are recyclable; reclaimed asphalt pavement (RAP) is reprocessed into new mixtures, reducing material demand and energy use.

Environmental and safety notes: Production and paving release fumes and particulates; processing is energy-intensive but recycling and warm-mix technologies reduce emissions. In many countries, asphalt production is regulated to control emissions. The modern industry advanced in the 20th century with refinements in binder technology and asphalt mixing.