AASHTO M 156:13(2017) Standard Specification for Requirements for Mixing Plants for Hot-Mixed, Hot-Laid Bituminous Paving Mixtures. I-lopper or batcher-type weigh system that delivers asphalt mixture directly to the truck. Fully automatic batching equipment with a digital recording device to save batch weights for project tickets.
4.2.5. The weighing system used to determine the net weight shall have a printing system used in conjunction with automatic batching and mixing systems. All printing systems should be approved by the engineer.
4.2.6. Verify adequate installation of the net weight scale mechanism or device by the manufacturer to ensure acceptable performance and operation.
4.2.7. Provide information on the project tickets as required by the Agency or specifier.
4.2.8. Certify the accuracy of the weighing system by an approved registered scale service person at least once every six months or whenever the plant is moved or relocated. Verify by an independent calibrated or certified scale the accuracy of the weighing system at the beginning of project production and thereafter as directed by the engineer.
4.2.9. Plants using batch scales shall maintain ten certified 50-lb (25-kg) standard test weights at the plant site to check batching accuracy.
4.3. Equipment for Preparation of Asphalt Binder:
4.3.1. Tanks for storage of asphalt binder must provide adequate capacity to ensure proper continuous circulation between the storage tank and proportioning units during the entire operating period.
4.3.2. The circulating system for the asphalt binder must have adequate capacity to provide proper continuous circulation between the storage tank and proportioning units during the entire operating period.
4.3.3. Storage tank capacity must ensure continuous operation of the plant and uniform temperature of the asphalt binder when it is introduced into the aggregate. Metering devices must be calibrated accurately to within 1 percent of the actual weight being measured and shall be accessible for measuring the volume of binder material at any time. Any additives based on liquid volume should be interlocked with the plant to result in a plant shutdown during no-flow conditions.
4.3.4. A sampling valve must be provided in the asphalt binder feed lines connecting the storage tanks to the asphalt binder control unit. The valve shall be located in such a manner as to allow for maximum safety to the person drawing the sample. A sampling valve should also be provided on each individual tank.
4.3.5. Any tank used for storing polymer-modified asphalt binders should be equipped with an agitation system to ensure the liquid asphalt is maintained in a homogenous state without separation.
4.3.6. The mechanisms used to introduce WMA additives to asphalt mixture at the mixture plant should be capable of uniformly feeding and metering the additive. WMA additives typically consist of additives added at the binder production facility, dry material added through cold feeds, or water injection. Depending on the type of WMA process, the plant should be equipped with automatic controls to monitor the feed system and interrupt plant production if there is an interruption in the feed process. Equipment used to produce WMA should be approved by the engineer prior to mixture production.AASHTO M 156 pdf download.