Methods and Practices on Reduction and Elimination of Asphalt Mix Segregation (2015) / Chapter Skim
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Pages 102-107
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From page 102... ...
103 • Links between test methods, training and certification programs, and segregation (Table C3) The conclusions are organized as individual tables for quick reference on how and where segregation occurs and how it can be reduced or eliminated: • During mix design and aggregate production (Table C4)
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From page 103... ...
104 Topic Categories Importance Specifications Method of detection Visual detection most used followed by temperature differences; no consistent use of temperature differences at this time. Disincentives Remove and replace most frequent disincentive Time needed for additional testing for segregation is a good disincentive; delays construction Percent within limits (PWL)
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From page 104... ...
105 Location Topics How to Reduce Segregation Comments Mix Design Gradation Limit gaps in the gradation Use gradation chart with all of Superpave sieve sizes plotted to see any gaps which can be minimized Bailey method of designing gradation helps minimize gaps Maximum aggregate size Use 9.5-mm maximum size aggregate mixes 12.5 mm or larger maximum size aggregate mix increasingly segregate with increases in maximum size aggregate Physically reblend mixes with larger maximum size aggregates when transferring mix from haul trucks to paver (examples: material transfer units; baffles at back of end dump bed to funnel mix) asphalt SMA and porous Increase additives to prevent drain down Occasionally segregate; asphalt separates (drains down)
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From page 105... ...
106 Location Topics How to Reduce Segregation Comments Mix Transport Truck types Belly dumps and live bottom: May help reblend mixes with lower levels of segregation Survey indicated these haul trucks help minimize segregate, but this benefit may be due to remixing, which occurs during transfer rather than truck type Truck options Tarps: Some indication they help manage temperature segregation Widespread use most likely because they limit flying debris Insulated truck beds: Help minimize temperature segregation Used by agencies in the colder regions of the country Used by agencies with long haul distances Material Transfer End dumps Use funnel-shape baffles at back of bed Forces mix to reblend as it flows through funnel into paver hopper Windrow elevators (pick-up devices) Deposit sufficient mix in windrow to keep optimum amount of mix supplied to screed Windrows commonly formed by belly dumps DO NOT "dribble" mix out in thin stream When next truck places more mix on top of "dribble," both mix and temperature segregation is produced Minimize segregation in haul truck bed Limited amount of segregation can be remixed by windrow elevators but more severe levels of segregation will still be transferred to the paver hopper Material transfer vehicles/devices Keep sufficient amount of mix in holding hopper and surge bin Keeps screed auger from being "starved" for mix DO NOT run surge bin low of mix Properly size surge bin to size of paver hopper Needed for proper operation of transfer units Make sure remixing augers in holding hopper or surge bin are running Easily overlooked during set up; needed for most successful reblending of mix DO NOT scrape down cold mix built up on sides of holding hopper or surge bin if the mix is too low This creates both mix and temperature segregation Pavers -- At Front Hopper Keep hopper at least half full If wings are flipped, then there is sufficient mix in the hopper to reblend any coarser aggregates deposited by haul trucks DO NOT let hopper run too low before flipping wings Creates end of truck segregation Moving mix Drag slats: ensure coarse aggregate stay on conveyors (may require retrofit)
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From page 106... ...
Abbreviations used without definitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005)
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From page 107... ...
TRANSPORTATION RESEARCH BOARD 5 0 0 F ifth S tre e t, N W W a s h in g to n , D C 2 0 0 0 1 A D D R ESS SER VICE R EQ UESTED NO N-PRO FIT O RG .
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