Production of cold asphalt
The
design and operation of cold asphalt plants are categorized as continuous type
and batch type. However, the continuous method is more common. The term
"cold asphalt" means that the stone materials are not heated in the
factory, but hot bitumen emulsion is injected into it. In these factories,
there are no burners, dryers, dust collectors, and grading screens.
However,
hot bins and storage silos for mixed materials may be available and optional.
Cold asphalt plants are simpler than hot asphalt plants. they are often mobile
and are prepared as prefabricated units. These plants can also be used to
produce cold bitumen with foam (Foamed Bitumen).
To
produce foamed bitumen, air is blown into the bitumen with the help of
pressurized nozzles. When the pressure is applied, the water expands along with
the air, resulting in foamed bitumen, which is used to cover cold asphalt
materials. In Continuous cold asphalt
plants, the materials are pre-graded and then enter the plant using calibrated
feeders. Then the aggregates with cement or hydrated lime, as a filler, are
weighed using a conveyor and then are poured into the mixer.
In a
continuous cold asphalt plant, pre-fabricated
one-size materials enter the plant using conveyor-shaped feeders with dedicated
pre-calibrated variable speed.
The
feeders are adjusted according to the percentage required in the final mix
specification and then the aggregates on the weigh belt conveyor are
fed. Before distributing the weight on the conveyor belt, cement, hydrated lime,
or filler is added to the collected feed using a silo and a weight loss system. Thus the conveyor measures the total weight of the wet
materials and the dry filler. Aggregates and the filler are continuously discharged
into a paddle mixer. This is a wide mixer with a rotating plate mounted at the
end of the drain. The resulting signal from the weighing conveyor constantly controls
the weight of the bitumen, emulsion, or injected bitumen in the mixer through
the spray strip.
The
cold mixture is discharged directly into the trucks using a conveyor or a
funnel. Direct loading of the truck includes an adjusted control system to
produce the specific amount required in the truck.
A
cold asphalt batch plant has a paddle mixer with drain at the bottom, instead
of a continuous mixer. It also has a bitumen weighing funnel instead of a
bitumen measuring system. In a cold asphalt batch plant each batch is made
separately, while in a continuous plant, the production of cold asphalt is
determined specifically by the size of each truck load or each silo capacity.
Continuous
unloading from a large funnel into the trucks is the same as continuous
production. Capacities up to 400 tons per hour are easily produced in cold
asphalt plants. However, to feed the plant, prefabricated aggregates of the
same size must be used. Also the performance of the final product of cold
asphalt is also limited. Further development of these cold asphalt plants is
currently underway.
Advantages of cold asphalt plants
•
Low cost of the initial equipment
•
Low cost of operation and maintenance
•
Low cost of the final mixture
•
Reducing environmental impact, because there is no need to heat and dry the
aggregates
•
simple design
•
Ease of adapting to mobile and prefabricated design
•
Ease of achieving high production capacities
•
Ability to produce small batches
•
Production without wasting materials
•
no need to store mixed materials
•
Ability to add RAP
Disadvantages and limitations of cold asphalt plant
· Prefabricated materials of the same size are essential,
otherwise the quality of the final mixture cannot be guaranteed.
· Limited performance of the cold asphalt final product
Read
more at:
Cold asphalt