Warm-mix additive proportioning -
Proportion all ingredients by weight. The HMA plant process-controller must be the sole source of ingredient proportioning control and be fully interfaced with all scales and meters used in the production process. Ensure that the HMA plant process-controller utilizes the warm-mix additive as an integral ingredient of the HMA mix.
Weighing and metering devices used for the production of warm-mix HMA must meet the requirements of the Material Plant Quality Program (MPQP). When a loss-in-weight meter is used it must meet the requirements of the MPQP and the following:
1. Include at least one complete system re-fill cycle during each calibration test run.
2. Operate the device in a normal run mode for 10 minutes immediately before starting the calibration process.
3. Isolate the scale-system, within the loss-in-weight feeder, from surrounding vibration.
4. Check the scale-system, within the loss-in-weight feeder, for accuracy before and after the calibration process and daily during mix production.
5. For a dry ingredient delivery rate of less than one ton per hour use a 15 minute minimum test run size.
6. The unit's accuracy must comply with the limits of Table B, “Conveyor Scale Testing Extremes,” in the MPQP.
Dry ingredient additives for continuous production must be proportioned with a conveyor scale or a loss-in-weight meter. Dry ingredients for batch production must be proportioned with a hopper scale.
Liquid ingredient additive, including a normally dry ingredient made liquid, must be proportioned with a mass flow meter.
Produce warm-mix HMA by using either a continuous mixing or a batch type HMA plant.
Continuous Mixing Plant -
The HMA plant process-controller in conjunction with the measuring systems must be capable of varying all ingredient feed rates proportionate with the aggregate delivery, at all production rates and rate changes. Liquid warm-mix additive must enter the production stream with the binder. Dry warm-mix additive must enter the production stream at or before the mixing area.
When dry warm-mix additives are utilized at continuous mixing HMA plants, baghouse dust systems must return all of captured material to the mix.
HMA additive must be proportioned to within 0.2% of the target rate.
Batch Mixing Plant -
The metered liquid warm-mix additive must be placed in an intermediate holding vessel to then be added to the mix with the binder. Dry ingredient proportioning devices must be separate from metering devices for the aggregates and asphalt binder. Dry warm-mix additive must be proportioned directly into the pugmill or placed in an intermediate holding vessel to be added to the pugmill at the appropriate time in the batch cycle.
Zero tolerance for the HMA additive batch scale is ±0.01 percent of the asphalt binder batch weight. The indicated HMA additive batch scale weight may vary from the preselected weight setting by up to ±0.02 percent of the asphalt binder batch weight.
Production Data Collection
The HMA plant process-controller must produce an electronic log of production data. The log will consist of a series of snapshots captured at a maximum of 1-minute intervals throughout the period of daily production. Each snapshot of production data must be a register of production activity at that time and not a summation of the data over the preceding interval to the previous snapshot. The amount of material represented by each snapshot will be that amount produced during the 0.5 minute interval before and the 0.5 minute interval after the capture time. Collect and hold data for the duration of the contract and submit the electronic media to the Engineer, daily or upon request. The snapshot of production data must include the following:
A. Date of production,
B. Plant location,
C. Time of day the data is captured,
D. Mix type being produced,
E. Temperature of the binder and HMA mixture,
F. For a continuous mix operation, the rate of flow of the dry aggregate calculated from the wet aggregate flow rate as determined by the conveyor scale.
G. For a continuous mix plant operation, the rate of flow of the asphalt meter.
H. For a continuous mix plant operation, the rate of flow of warm-mix ingredient meter.
I. For a batch plant operation, actual batch weights of all ingredient.
J. The aggregate/binder ratio calculated from metered ingredient output.
K. The binder/warm-mix additive ratio calculated from metered output.
Electronic media must be presented in a Comma-Separated Values (CSV) format. Captured data, for the ingredients represented by production snapshot, must have allowances for sufficient fields to satisfy the amount of data required by these specifications and include data titles at least once per report.