Summit Materials, and its subsidiaries, produces and sells hot mix asphalt (HMA) using the latest processing technologies. Asphalt consists of quality aggregates, recycled asphalt pavements (RAP), recycled asphalt shingles (RAS), and liquid asphalt (binder). Mix designs formulated in specific proportions are delivered, placed, and compacted in accordance with local specifications and state regulations.
Step 1: Aggregates
All asphalt production starts with aggregate production. Once the correct aggregates are produced they are stored either in piles or silos according to the needs of the location and the materials (See our aggregates page for how aggregates are produced).
Step 2: Cold Feed Bins
The aggregates are then sorted into unheated bins. These bins sit on top of variable grates and the conveyor system that accurately measures and sorts the aggregates needed for the requested mix. Once measured the aggregates are fed into the drying drum.
Step 3: Drying Drum
The drying drum rotates such that the aggregates are tumbled through a hot air stream. There are two types of dryers: (1) parallel flow and (2) counter flow. Parallel flow is when the aggregates move in the same direction as the air flow. Counter flow is when the aggregates flow counter to the air flow. There are two different types of plants. At this point, in a drum plant, asphalt cement is added to the aggregates in the drum to mix the cement with the aggregates. However, in a batch plant, the asphalt is mixed one batch at a time so that the asphalt cement is not added in this step. Instead, the aggregates are moved to a tower where they are separated into various sizes and temporarily stored in hot bins. Then, when the correct amount of aggregates is created, the aggregates are discharged into a pugmill and asphalt cement is then added to the mix. Next, regardless of the production method, the hot mix is weighed and loaded onto trucks. It can also be stored for a short period of time in silos. Additionally, during this process, the emission control system works to capture and recycle the remaining aggregate particles in order to ensure that emissions are reduced as much as possible.
Step 4: The Emission Control System
When hot air passes through the aggregates inside the drying drum the air picks up dust and fine sand particles. These particles are picked up by the emission control system so that they do not enter the atmosphere.
Step 5: Storage
If the asphalt is not used right away, asphalt storage will be needed. Asphalt is stored in tanks that meet stringent regulatory guidelines for spill prevention. Storage silos might also be required depending on the type of drum used and the amount produced. Drum mix plants must have silos since they produce asphalt continuously. Batch plants do not require a silo, but often have them to increase plant production. Storage silos are insulated and may be heated to prevent heat loss. A mix may be stored in a silo for a few days.