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How does asphalt mixing plant work?

An asphalt mixture plant is an assembly of mechanical and electronic equipment where aggregates, recycled materials or other additives are blended, heated, dried and mixed with binder to produce asphalt mixture meeting specified requirements. The plant may be stationary (located at a permanent location) or portable (moved from contract to contract). There are numerous types of plants, including batch plants, continuous mix plants, parallel-flow drum plants, counter flow drum plants, and double barrel drum plants to name a few. In general, however, the majority of plants may be categorized as either a batch plant (Figure 3-1), or a drum mix plant (Figure 3-2) and the information presented in this chapter covers these two types of plants. In the batch-type mixing plant, hot aggregate, recycled materials and binder are added in designated amounts to make up one batch. After mixing, the asphalt mixture is discharged from the pugmill in one batch. In the drum-type mixing plant, the aggregate and other materials are dried, heated, and mixed with the binder in the drum in a continuous process. Regardless of the type of mixing plant, the basic purpose is the same. That purpose is to produce an asphalt mixture containing proportions of binder and aggregate that meets all of the specification requirements.