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aggregate exceeds more than 1 %, the Plant Inspector should reject the material at the plant site and have the Contrctor make corrections to the plant processes.

Temperature Control

Proper

aggregate/mix

temperature

is

critical. Caltrans specifies that aggregate temperatures shall not exceed 165 C prior to the addition of asphalt. The temperature of the aggregate for Open Graded mixes

shall not exceed 135 C. sensing device placed at the

A temperature drum discharge

along

with

a

temperature

indicating device

shall be

displayed in the control room.

The burner control shown at the right automatically adjusts the damper position to maintain a preset maximum/minimum temperature entered by the plant operator. This system is also a chart recorder, recording the aggregate temperature during all hours of production.

Aggregates that are heated to an excessive temperature can prematurely harden asphalt

A temperature chart recorder is being used to document the aggregate temperature during all hours of production.

during mixing. Under heated aggregates are difficult to coat thoroughly with asphalt and cool asphalt mixtures are difficult to place on the roadway. Large fluctuations in temperature could indicate a moisture change within the stockpiles or a cold feed bin that has malfunctioned.

Asphalt mixtures that exceed the maximum allowable temperature, cold asphalt mixtures, asphalt mixtures that contain uncoated aggregates or asphalt mixtures that do no meet the minimum specifications should be rejected at the AC plant by the inspector.

The requirements for all Caltrans QC/QA project specify that an automatic continuous recording device be provided to document aggregate temperatures during all production. Caltrans specs require, when a recording type temperature indicator is used, it shall be maintained in a working condition.

Dust Collection Systems All continuous mixing plants have a small amount of fine aggregates carried out of the drum. In order to meet Federal, State and Local air quality regulations, dust collection systems must be used to capture dust and exhaust gases that would otherwise be released into the atmosphere. In addition, some dust control systems, (knock-out boxes, cyclones

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