1、Standard Specification for Requirements for Mixing Plants for Hot-Mixed, Hot-Laid Bituminous Paving Mixtures AASHTO Designation: M 156-13 American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001TS-2c M 156-1 AASHTO Standard Sp
2、ecification for Requirements for Mixing Plants for Hot-Mixed, Hot-Laid Bituminous Paving Mixtures AASHTO Designation: M 156-13 1. SCOPE 1.1. This specification covers requirements for plants producing hot mix asphalt (HMA) or warm mix asphalt (WMA) paving mixtures. It may be used as a basis for stat
3、e certification or inclusion of an asphalt mixing plant on an agencys approved list. Additional requirements may also be specified by the agency. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: R 66, Sampling Asphalt Materials T 19M/T 19, Bulk Density (“Unit Weight”) and Voids in Aggregate T 27, Siev
4、e Analysis of Fine and Coarse Aggregates T 30, Mechanical Analysis of Extracted Aggregate T 84, Specific Gravity and Absorption of Fine Aggregate T 166, Bulk Specific Gravity (Gmb) of Compacted Hot Mix Asphalt (HMA) Using Saturated Surface-Dry Specimens T 168, Sampling Bituminous Paving Mixtures T 2
5、09, Theoretical Maximum Specific Gravity (Gmm) and Density of Hot Mix Asphalt (HMA) T 283, Resistance of Compacted Asphalt Mixtures to Moisture-Induced Damage T 308, Determining the Asphalt Binder Content of Hot Mix Asphalt (HMA) by the Ignition Method T 312, Preparing and Determining the Density of
6、 Asphalt Mixture Specimens by Means of the Superpave Gyratory Compactor 3. TERMINOLOGY 3.1. batch planta manufacturing facility for producing asphalt paving mixtures in discrete production batches. Each batch includes specific proportions, by weight, of aggregate, asphalt binder, and other chosen ad
7、ditives. Each discrete batch is mixed and then discharged. 3.2. checka specific type of inspection or measurement performed on equipment or materials to indicate compliance with the stated criteria. Examples include (a) lime check, and (b) calibration check of cold feed system. 3.3. continuous mix p
8、lanta manufacturing facility for producing asphalt paving mixtures that continuously proportions the aggregate, asphalt binder, and other chosen additives into the mix by a continuous volumetric proportioning system without definite batch intervals. 2015 by the American Association of State Highway
9、and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2c M 156-2 AASHTO 3.4. drum mix planta manufacturing facility for producing asphalt paving mixtures that continuously proportions the aggregate, heats and dries it in a rotating drum, adds any chosen ad
10、ditives, and simultaneously mixes the material with a controlled amount of asphalt binder. 3.5. hot mix plantany of the plants listed above that produce HMA or WMA. 3.6. interlocka system whereby plant production will be interrupted when any one of the interlocked raw material constituents fails to
11、meet the targeted requirements established within the specifications or plant requirements. 3.7. modified batch planta manufacturing facility for producing asphalt paving mixtures that continuously proportions the aggregate, asphalt binder, and other chosen additives into the mix by weighted batches
12、. The modified batch plant will usually have the screen decks removed. 4. PLANT REQUIREMENTS 4.1. Prerequisite for Plant Approval: 4.1.1. Inspection of EquipmentThe plant owner or manager shall schedule an inspection of the plant facilities to determine compliance with this specification. The equipm
13、ent shall be maintained in a satisfactory operating condition and be capable of its intended function at all times during production. 4.1.2. Quality Control ProgramEach plant shall have an approved quality control program and have a designated person to administer the program. This program shall inc
14、lude the testing and control of the individual component materials and the final product produced at the plant. Operations shall be conducted in a manner so that a uniform product is produced that will meet specified requirements. 4.1.3. Certified Public Weighers or Certified Public ScalesState or f
15、ederal requirements should dictate plant requirements related to Certified Public Weighers or Certified Public Scales. 4.1.4. UniformityThe plant must be capable of producing homogenous asphalt mixtures even though the individual components include such diverse materials as various sizes of aggregat
16、e from stockpiles, reclaimed asphalt pavement (RAP), reclaimed asphalt shingles (RAS), asphalt binder, and other admixtures, as required by the mix design. 4.2. Weight Measuring Systems: 4.2.1. Furnish (at the contractors expense) platform scales to weigh bulk asphalt plant mixtures, regardless of t
17、he type of weight measuring system used for payment. 4.2.2. Ensure that the documentation for platform scales complies with state or federal requirements. Platform scales shall be certified at a minimum every six months, or at a frequency required by state or federal requirements. Platform scales sh
18、all be certified if they are moved or relocated. 4.2.3. Each platform scale system should be capable of taring truck weights with each load. 4.2.4. When not using platform scales, provide calibrated weighing devices that record the mixtures net weight delivered to the truck. Weighing devices shall b
19、e calibrated at a frequency specified by the state. The weight of produced mixture should be verified periodically by platform scales. A net weigh system will include, but is not limited to, the following: 4.2.4.1. Hopper or batcher-type weigh system that delivers asphalt mixture directly to the tru
20、ck. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2c M 156-3 AASHTO 4.2.4.2. Fully automatic batching equipment with a digital recording device to save batch weights for project tickets. 4.2.5. The
21、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 t
22、o 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
23、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
24、 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
25、 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 b
26、inder 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
27、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 t
28、he 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 t
29、o 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 o
30、f 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. 4.4. Cold Aggregate FeedersA me
31、chanism that must be capable of uniformly feeding the aggregates into the dryer so that uniform production and temperature are assured. The mechanism must be capable of accurately blending aggregates from different storage bins. 2015 by the American Association of State Highway and Transportation Of
32、ficials.All rights reserved. Duplication is a violation of applicable law.TS-2c M 156-4 AASHTO 4.4.1. Cold bins for storing aggregates prior to proportioning should be monitored to assure that bins do not become empty or restricted. The bins shall be interlocked so that a production interruption wil
33、l occur if an interruption in supply of material from any cold feed occurs. Note 1The requirements of Section 4.4.1 do not apply to batch plants. 4.4.2. Adequate and convenient facilities must be provided for obtaining samples of the full flow of aggregate from each cold feed bin and from the total
34、of the bins. 4.4.3. Control shall be based on frequent samples from each component aggregate as well as samples taken from the combined cold aggregate feeders. 4.4.4. All plants are to be equipped with a means of diverting aggregate on the conveyor belt away from the dryer and into an empty haul tru
35、ck for cold bin calibration purposes. 4.5. Reclaimed Asphalt Pavement (RAP)/Reclaimed Asphalt Shingles (RAS)The recycled mixture shall be a homogenous mixture of RAP, RAS, or RAP and RAS material, virgin aggregate, hydrated lime (if required), asphalt binder, and any additives. If recycling capabili
36、ty is required, the plant shall be equipped with mechanical means for feeding the desired weight of RAP, RAS, or RAP and RAS into the mix. 4.5.1. RAP/RAS bins for storing material prior to proportioning should be monitored to assure that the bins do not become empty or restricted. The bins shall be
37、interlocked so that a production interruption will occur if any interruption in supply of material from any cold feed occurs. Note 2The requirements of Section 4.5.1 do not apply to batch plants. 4.5.2. Adequate and convenient facilities shall be provided for obtaining samples of the full flow of RA
38、P/RAS material from each RAP/RAS bin as well as samples from the combined RAP/RAS material. 4.5.3. Use a hot mix plant for the recycling process with necessary modifications to process the recycled material. The ratio of the RAP or RAS to virgin aggregate shall be controlled by weight. 4.5.4. For dr
39、um, modified batch plants, and continuous mix plants, use electronic belt weighing devices to monitor the flow of RAP or RAS and the flow of virgin aggregate. For batch type plants, the RAP or RAS proportion of the mix may be weighed in a weight hopper before incorporating into the pug mill. 4.5.5.
40、Equip plants with an interlocking system of feeders and conveyors that synchronize the RAP, RAS, or RAP and RAS material flow with the virgin aggregate flow. Ensure that the electronic controls monitor the flow rates indicated by the belt weighing devices and automatically maintain the desired ratio
41、 at varying production rates. Design the RAP/RAS feeder bins, conveyor system, and auxiliary bins (if used) to prevent the material from segregating and sticking. RAP should be screened prior to crossing the weigh bridge with a 2-in. or larger screen. 4.6. Emissions Controls for Dust Collector Fines
42、: 4.6.1. A dust collection system shall be provided. The system shall be made to waste the material so collected, or to return all or any part uniformly to the mixture. 4.6.2. Other emissions, such as smoke with the exception of water vapor, shall be controlled to be in compliance with applicable en
43、vironmental limits. 4.6.3. Control the dust collection as follows: 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2c M 156-5 AASHTO 4.6.3.1. When collecting airborne aggregate particles and returning
44、 them to the mixture, ensure the return system delivers all or part of the collected dust uniformly into the aggregate mixture and wastes the excess. The percentage of collected dust returned to the mixture is subject to the engineers approval. 4.6.3.2. When the collected dust is returned directly t
45、o the hot aggregate flow, interlock the dust feeder with the hot aggregate flow in order to maintain a constant, proportioned, and uniform flow. 4.7. Surge and Storage Systems: 4.7.1. Provide surge and storage bins as follows: 4.7.1.1. Ensure that bins for mixture storage are insulated and have a wo
46、rking seal, top and bottom, to prevent outside air infiltration and to maintain an inert atmosphere during storage. Bins not intended for storage may be used as surge bins to hold asphalt mixtures for part of the working day; however, empty these surge bins completely at the end of the working day.
47、Ensure that the batchers on top of the surge and storage bins function properly at all times via scheduled visual inspection by plant personal. 4.7.1.2. Ensure that surge and storage bins can retain a predetermined minimum level of mixture in the bin when trucks are loaded. All surge and storage bin
48、s shall have a heated gate system. 4.7.1.3. Ensure that surge and storage systems do not contribute to mix segregation, loss of homogeneity, lumpiness, temperature loss, draindown, or stiffness. 4.7.2. A plant may be permitted to store asphalt mixtures in a silo after prior evaluation and approval b
49、y the engineer. Use will conform with all limitations on retention time, type of mixture, heater operation, silo atmosphere, mix level, mix draindown time, or other characteristics set forth in the applicable specifications. 4.7.3. Approval of silos may be removed or restrictions may be applied if it is determined the silo contributes to segregation, does not maintain temperature, or fails in any other way to provide a homogeneous mix. 4.8. Mineral FillerWhen mineral filler is required as a mixture ingredient: 4.8.1. Use a separate bin and feed
