An asphalt plant is a plant used for the manufacture of asphalt, macadam and other forms of coated roadstone, sometimes collectively known as blacktop or asphalt concrete.

Asphalt plants for road construction
The manufacture of coated roadstone demands the combination of a number of aggregates, sand and a filler (such as stone dust), in the correct proportions, heated, and finally coated with a binder, usually bitumen based or, in some cases, tar,although tar was removed from BS4987 in 2001 and is not referred to in BSEN 13108/1. The temperature of the finished product must be sufficient to be workable after transport to the final destination. A temperature in the range of 100 to 200 degrees Celsius is normal.

An asphalt mix starts at the aggregate cold feed bins,  where different sizes of aggregate are stored. The aggregates are fed onto a conveyor at a specified rate  to ensure the proper volumes for the mix design.

Spraying truck with degreaser
  • Silos
  • Cold feed bins
  • Conveyor to dryer
  • Recycled asphalt feed bin
  • Baghouse
  • Pugmill
  • Cold feed bins
  • Control room
Recycled Asphalt Pavement (RAP) When a paved road is removed it can be ground up and fed into the asphalt plant as recycled asphalt.  When RAP is used, less liquid asphalt is required

Drying • The aggregate moves to a large dryer where it is heated up and any moisture is driven off as steam. • A baghouse is attached to the dryer to vacuum off any dust. Screening • Once the aggregate is dried it moves up and onto a vibrating screen. • It is screened to the specific sizes required for the mix design and stored in bins. Pugmill • Specific weights of each size drop from the bin into a pugmill. • A specific amount of liquid asphalt enters the pugmill with the dried stone.  • The pugmill mixes the stone with the liquid asphalt.  • The product is typically mixed at 150°C. Delivery • Once the mixing is complete the hot mix asphalt drops into the waiting truck. • For the best quality paving asphalt needs to arrive at the job site and be laid at 140°C. Storage silos Most asphalt plants have storage silos used to store hot mix asphalt to meet future customer needs.  Silos come in handy for large paving jobs.