Hot-mix asphalt is the paving material used to produce blacktop, a durable pavement commonly applied to highways, runways, parking lots, and residential driveways. Asphalt is produced at specialized facilities where various mixtures of aggregate are heated and dried, combined with liquid asphalt cement (also known as bitumen), and either stored in insulated silos or loaded into trucks and transported to a job site.

Aggregate heating and drying is accomplished with various types of dryers, depending on whether a batch or continuous process is used. The continuous-mix process uses aggregate drum dryers, which are designed to heat and dry measured quantities of gravel, sand, and other fillers by tumbling the damp contents down the length of a rotating drum.

While tumbling, the aggregate is continuously exposed to a stream of hot air that is generated by a burner located at one end of the drum. Hot, dry aggregate eventually reaches the far end of the drum and exits, while additional cold, damp aggregate is continuously added to the other end. The removal of ambient moisture is necessary to insure that the asphalt cement, applied afterwards, will properly adhere to the aggregate.

Continuous mix aggregate drum dryers can process up to 500 tons of aggregate each hour, which consumes a great deal of energy in both heating and rotating the drum.  Efficient drum design and optimization of the drying process are essential in reducing energy consumption and operational costs for any hot-mix asphalt facility.

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Astec, Inc., headquartered in Chattanooga, Tennessee, is a market leader for hot-mix asphalt equipment, technology, support, and training for customers across the globe. Astec designs and manufactures a complete line of continuous- and batch-process hot-mix asphalt facilities and soil remediation equipment.