The purpose of the asphalt plant is to mix aggregate, asphalt and other additives in the required proportion as per job mix formula and at high temperatures to produce a paving mixtures homogenized. This hot mix asphalt is used for the road construction.
There are basically two types (based on the design) of plants :
1. Batch Mix Plant (discontinuous type)
2. Drum Mix Plant (continuous type)
In the batch type plant, drying and heating of aggregates takes in a rotary drum and heated aggregates are weighed and screened in hot bins for proportioning before blending with binder in separate pugmill type mixer to make up one batch.
In the drum type plant, the heating, drying and blending of aggregates with the binder takes in the same drum where in feeding of aggregates and binders and output of hot mix asphalt is continuous. This type of plant give a higher level of production rate and easy and simple in using. They are cheaper than the batch type plant.
Regardless the type of asphalt mixing plant, the basic purpose is the same to produce the quality hot mix asphalt to be used for road construction.
The basic components of asphalt drum mix plant are the multiple cold aggregates feeder bins, a single deck scalping screen, the slinger conveyor, a rotary drum, a burner, load out conveyor, tank of asphalt, mineral filler Unit, fuel service tank, wet scrubbers and Control panels with insulated control cabin. This plant can be in a mobile (portable) and a stationary versions to meet the customer’s needs.
In the asphalt drum mix plant, various size virgin aggregates are stores in multiple feeder bins. Each compartment is fitted with manually operated gates and belt conveyor driven by the variable speed notor to preset the proportion of the aggregates to be removed from each container. Aggregates from all bins are received on gathering belt that transfer them to the single deck scalping screen for oversize material removal. The screened aggregate are then transfered to the rotary drum by a slinger conveyor. High pressure jet oil burner fitted at infeed side of the rotary drum dries and heats the aggregates in main zone of the drum. The heated aggregate then travel to the secondary zone, that is coating zone, where they are mixed with the pre metered binders ( asphalt & additives) to produce the hot mix asphalt. Then, the hot mix asphalt is transferred to the storage silos or directly transferred to the tipper by load out conveyor fitted with gob hopper. All plant operations are controlled from the control room with control panels.