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State of California, Department of Transportation - page 8 / 52

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Recycled Asphalt removed from an

Pavement (RAP) - Old asphalt concrete pavements that have been

existing

roadway

and

stockpiled.

During

production

the

RAP

is

crushed, screened and proportioned with heated virgin aggregates, hot asphalt binder and

then mixed in an asphalt plant. Batch plant and continuous different manners and each application will be covered later

mixing plants handle in this manual.

RAP

in

Cold Storage - This refers to how the virgin aggregate is handled and fed to the asphalt plant (batch or continuous mix) prior to being heated in the drier drum. The following systems are the most commonly used: 1) Rectangular open bins fed by a loader from the top. 2) Stockpiles separated by large bulkheads, feeding aggregates onto a belt located in a tunnel under each stockpile. 3) Multiple storage silos, with adjustable gate openings deliver aggregates to a collection belt. Before being fed to the drier, Caltrans requires that aggregates be separated into 3 or more sizes and stored separately.

Cold Feed Low-Flow Interlocks - Each cold feed bin shall be equipped with a device that monitors the depth of aggregate between the troughing rollers. The device will automatically shut the plant down whenever the depth of aggregate drops 30 percent below the target depth. A small time delay, usually 10 seconds or less, is allowed and set into the plant controller at the time of CT 109. This device shall be in good working condition and functioning properly whenever the plant is operated.

Cold Feed No-Flow Interlocks Each cold feed bin shall be equipped with a second device located either in the stream of aggregate beyond the belt or where it will monitor

movement of the automatically and shall be in good operated.

belt by detecting revolutions of immediately shut the plant down

the tail pulley. when there is no

The flow.

working

condition

and

functioning

properly

whenever

device shall This device the plant is

Scalping Screen - A large rectangular vibrating screen, typically placed after the collection belt and before the weighbelt. The screen openings allow the largest size aggregate through and remove all oversized materials, including tree roots and clay balls. A scalping screen is usually placed in the cold feed system of continuous mix plants.

Rate of Flow Indicators All asphalt meters and aggregate belt scales, at continuous mixing plants, shall be equipped with rate-of-flow indicators that show the delivery rates for aggregate and asphalt binder.

Weighbelt - A weighing system that is designed to continuously determine the weight of material flowing over the scale at any given time. Combined aggregates are fed from a collection belt, onto another conveyor belt (weighbelt) and over an in-line belt weigher, also known as a “weighbridge”. The plant controller calculates the amount of aggregate being fed to the drier drum using the mass of material on the weighbridge and the belt speed. An indicator located in the control room displays the rate at which the material is flowing, usually in tons per hour.

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