Asphalt

Asphalt is a viscoelastic, black or dark-brown material used primarily as a binder-aggregate mix for pavements. In road construction, the term commonly refers to asphalt concrete, a mixture of mineral aggregates bound together with bitumen, the viscous binder. In some markets, bitumen or asphalt binder is distinguished from the finished asphalt pavement. Naturally occurring asphalt deposits and refined bitumen are both used in industry.

Composition and production: Bitumen typically accounts for 5–25% of the mix by weight; aggregates such as gravel, crushed rock, and sand make up the remainder. The materials are heated and blended in asphalt plants to produce hot-mix asphalt (HMA). Cold-mix formulations use asphalt emulsions or foamed binders. Warm-mix asphalt uses additives or processes to reduce production and compaction temperatures, lowering energy use and emissions.

Types and applications: Hot-mix asphalt is standard for high-traffic roads, while warm- and cold-mix variants are valuable for maintenance, low-temperature construction, or recycling. Applications include road and highway surfaces, airport runways and taxiways, parking areas, and sometimes roofing products or waterproofing membranes in construction.

Performance and sustainability: Asphalt is durable and waterproof, with properties that depend on temperature and traffic. Modifications with polymers, rubber, or rejuvenators can enhance elasticity, aging resistance, and rutting performance. Recycling is common: reclaimed asphalt pavement (RAP) can be reused in new mixes, reducing material needs and energy consumption. Environmental considerations include emissions from heating and the management of fumes and runoff.