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State of California, Department of Transportation - page 30 / 52

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Continuous Mix Plants

Production

capacity

for

continuous mixing AC plants may range from 100 TPH to 700 TPH. A high capacity plant running at 500 TPH can produce 42 tons of completed mix in 5 minutes. The

reason

for

this

example,

to

illustrate the potential for a quantity of asphalt concrete produced in a very short

large to be time

period.

With

this

type

of plant,

a

continuous flow of aggregates from the coldfeed bins is heated in a drier drum. The

aggregates are delivered in an as-used condition without any subsequent except for the removal of oversized rocks if a scalping screen is in place. aggregates have been heated to the desired temperature a continuous flow

screening, After the of asphalt

binder is introduced into the drier controls this continuous operation. completely automatic.

drum mixer or the pug mill mixer. A computer Caltrans specifications require this operation to be

Continuous Mixing Plant Types:

  • 1)

    Continuous drum mixing

  • 2)

    Continuous pugmill mixing

Storage Bins and Cold Feed Systems Individual bins are used to store different sized aggregates. Storage bins for continuous mix plants are basically the same as the ones used for batch plants,

with

a few exceptions.

the

#4 sieve) and

Fine bins (passing supplemental fine

aggregate

bins

vibrating

unit

must be equipped with a (bin vibrator) to prevent

material from hanging up in the bins.

Gates located at the bottom of the bins, feed controlled amounts of different aggregate sizes onto the collection belt. Gate openings can be adjusted to increase or decrease the discharge from each bin.

Anytime a cold feed bin gate opening has been adjusted the bin must be re-calibrated. When a change in material occurs, for example, coarse aggregate replaced with fine aggregate, the bin must be re-calibrated with the new material. Typically, bins are

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