402.01  Description

402.02  General

402.03  Scales

402.04  Thermometers

402.05  Storage

402.06  Calibration

402.07  Computerized Plant System

402.08  Polymer Binders

402.09 Water Injection System for Warm Mix Asphalt


402.01  Description.  This specification consists of the minimum requirements for an asphalt concrete mixing plant to produce asphalt concrete mixes according to Department specifications.

Ensure asphalt concrete mixing plants conform to the requirements of ASTM D 995 in addition to the following.

402.02  General.  If more than one kind of asphalt binder is to be used concurrently, separately store each kind.

Ensure that the adjustments for total and proportional feed are continuously variable and capable of being locked at any position.

Use batch plant hot bins that have an oversized material discharge pipe of not less than 6 inches (150 mm) in diameter.  Ensure pipes discharge material at points outside the plant operation and do not create a hazard or discomfort.

In batch plants, use a non-tilting asphalt binder bucket with a loose sheet metal cover.  Ensure that the length of the discharge opening or spray bar is not less than three-fourths the length of the mixer and that it discharges directly into the mixer.  Ensure that the asphalt binder bucket, its discharge valve or valves, and spray bar are fully jacketed or heated.  Use jackets that drain efficiently and ensure that all connections are constructed to not interfere with the efficient operation of the asphalt binder scales.  Use an asphalt binder bucket with a capacity of at least 10 percent greater than the weight of asphalt binder required in any batch.  Ensure that the plant has an adequately heated, quick-acting, nondrip, charging valve directly over the asphalt binder bucket.

402.03  Scales.  Use scales and test weights that conform to the regulations of the Ohio Department of Agriculture.  Seal scales as often as the Laboratory directs to ensure their continued accuracy.  Seal test weights at least every 3 years at places designated by the Ohio Department of Agriculture.  Equip the plant with one 50-pound (20 kg) test weight for each 400 pounds (200 kg) of the maximum batch weight with a minimum of ten test weights.

Provide a truck scale or recording batch plant scales for the purpose of obtaining the net weight of each load of asphalt mixture as required in 401.21.

Use truck scales that indicate the total weight within 20-pound (10 kg) increments and have a rated capacity of at least 10 percent greater than the largest load weighed.  Provide a platform large enough to receive the largest truck used for a single weighing.

Use batch plant scales that have a capacity of at least 10 percent greater than the largest weight required for any one batch.

402.04  Thermometers.  Equip the plant with an adequate thermometric instrument, clearly legible from the mixer operator’s station, to monitor the temperature of the asphalt binder.  Locate the sensing element or unit in the feed line near the charging valve at the mixer.  Where a pyrometer is used, connect the indicator to the thermocouple by a weatherproof extension wire.

Also, equip the plant with either an approved dial-scale, mercury-actuated thermometer; an electric pyrometer; or other approved thermometric instrument so placed at the discharge chute of the dryer as to register automatically or indicate the temperature of the heated aggregates.

402.05  Storage.  Provide storage bins capable of storing hot asphalt concrete mixtures up to 24 hours.  Insulate or heat storage bins if mixtures are stored for more than 8 hours.  Ensure that the system is capable of maintaining the required temperature without creating hot spots within the stored mixture.  In addition, if hot asphalt mixtures are stored from 8 to 24 hours, then introduce a silicone admixture into the asphalt binder at the rate of 1 fluid ounce per 5000 gallons (1 mL/640 L).

402.06  Calibration.  Calibrate the plant for each combination of aggregate, reclaimed asphalt concrete pavement, and asphalt binder type/content for the mixtures to be produced.  Ensure that the calibration is accurate within 1.0 percent.

402.07  Computerized Plant System.

A.      General.  Produce all asphalt concrete in a plant with a computerized plant system approved by the Laboratory.  Ensure that the computerized plant system’s monitoring device for the asphalt binder content is capable of being locked or sealed.  After initial calibration of the plant, the Department may lock or seal the asphalt binder content monitoring device.

Ensure that all printouts contain the following information:

1.      Date.

2.      Time.

3.      JMF number.

4.      Moisture content of the reclaimed pavement.

5.      Percent asphalt binder in the reclaimed pavement to the nearest 0.1 percent.

6.      Percent virgin asphalt binder to the nearest 0.1 percent.

7.      Percent total asphalt binder calculated to the nearest 0.01 percent.

Ensure that all printouts are preapproved by the Laboratory and are turned over to the DET at the end of the project or the end of the production year.

Ensure that the computerized plant system prints “SIMULATE” on the ticket or printout whenever the computerized plant system is only simulating asphalt concrete production.

Ensure that the computerized plant system has an audible alarm system that notifies the plant operator when the amount of asphalt binder, aggregate, or reclaimed pavement being mixed into the asphalt concrete is outside the tolerances established by the Contractor’s Quality Control Manager.  Make appropriate adjustments when production is outside the tolerances.

B.      Batch Plants.  In addition to the requirements of 402.07.A, print the information on each weight ticket if the asphalt concrete is directly loaded into the truck or on a separate printout for every 16 tons (15 metric tons) or less of production if the asphalt concrete is loaded into a storage silo.  Ensure printouts contain the following additional information:

1.      Tare weight of the asphalt binder scale.

2.      Tare weight of the aggregate scale.

3.      Pounds (kilograms) of virgin asphalt binder.

4.      Pounds (kilograms) of virgin aggregate.

5.      Pounds (kilograms) of reclaimed pavement measured by a batch scale.

6.      Tons per hour (metric tons per hour) of reclaimed pavement measured by a belt scale.

C.      Drum Mix Plants.  In addition to the requirements of 402.07.A, print the information every 5 minutes during production.  Ensure printouts contain the following additional information:

1.   Tons per hour (metric tons per hour) of virgin asphalt binder.

2.   Tons per hour (metric tons per hour) of virgin aggregate.

3.   Tons per hour (metric tons per hour) of reclaimed pavement.

4.    Moisture content of the virgin aggregate.

402.08  Polymer Binders.  If an asphalt binder is modified by SBR polymer at an asphalt concrete mixing plant, equip the plant with an SBR polymer flow meter and monitoring system.  Obtain the Laboratory’s approval of the system before operating.  Demonstrate the system calibration to the District.  If the District waives the demonstration, provide a letter documenting calibration data for the flow system to the DET for each project.

For drum mix plants, introduce the SBR polymer directly into the asphalt binder line through means of an in-line motionless blender able to provide a homogeneous blend.  Locate a sampling valve between the in-line blender and the plant drum.

For batch plants, add the SBR polymer after the aggregate has been completely coated with asphalt binder.  Continue mixing for a minimum of 20 seconds after SBR polymer is added and long enough to provide a uniform mixture.

Use a 1-inch (25 mm) magnetic flow meter that employs balanced electrode plane technology.  Ensure that the flow meter has two grounding electrodes located in the same measurement plane as the sensing electrodes.  The flow meter does not require grounding rings if installed in nonmetallic piping.  No straight run is required in piping before or after the flow meter to maintain accuracy, except if located downstream of a pump or modulating valve.  Ensure that the totalizer displays a total volume measured and rate indication in any standard engineering units.  Ensure that accuracy is ±2.0 percent over flow range from 0.8 to 47.5 gallons per minute (3 to 180 L/min).  Install the flow meter in the piping downstream of all recirculation lines.  Provide a lockable sample valve downstream of the flow meter for calibration purposes.  Interface the flow meter with a data logging flow computer.  The flow computer shall produce printouts of the logged data every 5 minutes for a drum mix plant or every batch for a batch plant.  Include time, date, flow rate, and flow total in the logged data.  Flow rate is not necessary for batch plant production.

Balling or wadding of SBR polymer or uncoated aggregate indicates improper mixing.  Cease production immediately and until corrected to District satisfaction.

402.09 Water Injection System for Warm Mix Asphalt

When allowed by specification  use a Department approved water injection system for the purpose of foaming the asphalt binder and lowering the mixture temperature. Only use equipment that has been proven stable and effective thru project use on non-ODOT projects. Ensure equipment for water injection meets the following requirements:

1.  Injection equipment computer controls are in the plant control room and are tied to the plant computer metering.

2. Injection equipment has variable water injection control controlled by the plant operation rate and the water injection can never exceed 1.8% by weight of asphalt binder.

3. Water injection rate cannot be manually overridden by the plant operator once in the computer.

4. Injection equipment stops water flow when a control or equipment failure in the injection system occurs.

5. The water injects into the asphalt binder flow before the asphalt binder spray hits aggregate.  Do not allow water to touch aggregate before the binder spray.

6. Injection equipment includes water storage and pump control tied to the injection computer controls.

7. Water storage low water alarm installed in the control room.

8. Provide a PG binder sampling valve between the last piping tee on the tank side of the line and the injection equipment to sample PG binder before water is injected.

9. Provide a PG Binder sampling valve at the injection equipment to sample binder prior to spray.