Modular Asphalt Plant---III---" ...and it comes out....where?"

To begin the process, crushed stone is loaded into two large bins having a single conveyor below both discharge gates. Stone flows off this conveyor onto a small bucket elevator which drops it into the high end of the rotary drier. As the dryer drum turns, super heated air from the lower end's burner unit circulates completely around all the individual stones cascading down and around inside.

This process evaporates all water and heats the stone to allow the liquid asphalt applied later to completely coat each piece for maximum bonding of all particles in the mix. Heated stone leaving the drum is then carried by bucket elevator to the top of the screening unit.

Among the last units assembled were the pugmill, filter unit, and material elevators between major units. The pugmill is the business end of the plant. In its mixing chamber, the recombined stone mix is sprayed with a precisely measured amount of liquid asphalt while being mixed between two constantly rotating paddles. After sufficient mixing time, clamshell doors at the bottom of the mixing chamber open to release a measured amount of the product from the bottom of the chamber into a dump truck parked below for transport to the paving site. The stone is fed into the chamber at a constant rate, the asphalt spray is also constant, and the discharge gate openings are precisely timed to release only the amount of product which is properly mixed and ready for use. This is the "continuous mix" method which can achieve 100 tons per hour of peak production under ideal conditions. In contrast, a "batch-type" plant combines precisely measured amounts of aggegates and liquid asphalt into a mixing chamber for a specific mixing time and then releases the total amount of that mixture into the haul unit parked below. The mixing chamber is filled and then totally emptied in an on -going cycle, each complete cycle producing a "batch" of asphalt mix. Batch plants are classified according to the weight of a completed batch produced. Thus, batch plants are known as 1-ton, 2-ton, etc. Batch plants allow rapid changes of mix specifications between each small batch, but have limited production capacity in tons per hour. Continuous mix plants, however, can produce large quantities of a single mix specification per hour, making them more efficient for larger jobs over extended periods of time.

--Normand Dupuis EOC USNR-(Ret. )

Viewed from the screen unit catwalk, the rotary dryer unit is next in line, and the cold bins for feeding stone into the plant are behind the rotary dryer. The dry filtering unit for dust control is hidden behind the screen unit to the left of the rotary dryer. The top of the cold stone elevator protrudes above the dryer intake hopper.	The small buckets which carry a measured amount of crushed stone from the cold feed bins into the rotary dryer are clearly visible in this photo taken during placement of the cold elevator and before fitting of protective shielding.
This huge oil-fired burner unit superheats the air inside the rotary dryer to evaporate any water on the crushed stone. Water would prevent the liquid asphalt from binding the individual stones together. Replaceable furnace brick liners can be seen inside the nozzle. Really "Hot Stuff"!	Viewed behind the plant, the bag filter unit is connected to the exhaust from rotary drier. The smokestack is in the upright position for operation. The hot elevator which carries stone from the bottom of the rotary dryer to the top of the screen unit is seen on the right.
These hoppers are filled with crushed stone by either a wheeled front-end loader or a crane with clamshell bucket attachment. This starts the material flow through the plant which later results in the finished asphalt mix being discharged from the pugmill mixing chamber into a dump truck for transport to the paving site.	An NCBC truck crane lifts the pugmill mixing unit into position. This was the final major component in place. Once placed precisely in relation to the hot elevator from the weigh box unit, the plant was ready to begin shakedown testing.

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