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State of California, Department of Transportation - page 39 / 52





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4) Combotronics Total Flow - This meter is very similar to the B & S Industries DigiFlow meter in appearance and operation. At this time, none of these meters are

in use in California.

  • 5)

    Mass Flow Meter (Coriolis Effect)

    • -

      This meter is very unique, as it has no moving parts. Liquid asphalt is pumped through one or more "U" shaped tubes. The meter determines the liquid flow rate from the action of the "U" shaped tubes when any liquid is pumped through them. Specific gravity and temperature correction is not a factor when this type of meter is used. The meter determines the mass being used, indicates the flow rate and displays the weight in pounds, tons, kilos, etc. Calibration of this type meter is accomplished by changing a "span number". If a remote or hand-held

The rectangular object in this photo( indicated by arrow) is the mass flow, Coriolis effect type meter.

device is needed to view the span number, it must be available at the control room whenever the plant is operating for Caltrans. A large number of asphalt suppliers have converted over to the mass flow, Coriolis effect type meter.

If liquid asphalt is proportioned as a percent of total dry aggregate weight ("outside the mix") and the asphalt content is to be 5 percent. 100 tons per hour of dry aggregate would require 5 tons per hour of asphalt binder, and so forth.

For continuous drum mixing plants, liquid asphalt is introduced about 2/3 of the way down the drum and mixed with heated aggregates. If the continuous drum mixing plant is equipped with a double drum, the asphalt is introduced into the outer drum and mixed with heated aggregate. For continuous pugmill mixing plants, liquid asphalt is introduced into the pugmill and mixed with the heated aggregates.

Temperature Control Asphalt binder shall be at a temperature of not less than 250 F and not more than 375 F when added to the aggregate. Proper asphalt binder/aggregate temperature is critical. Caltrans specifies that aggregate temperatures shall not exceed 325 F prior to the addition of asphalt. A temperature sensing device placed at the drum discharge shall measure the

temperature of

the AC

in the control


mixture and shall display the mix temperature on Aggregates that are heated to an excessive

a display located temperature can

prematurely harden asphalt during mixing. thoroughly with asphalt, and cool mix is

Under heated aggregates are difficult difficult to place on the roadway.

to coat Large

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