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Production of cold asphalt

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

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Cold asphalt

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