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12/9/14
1
Construction of Quality Hot Mix Asphalt Pavements - 1 Day Course
PLANTS & PRODUCTION Bob Horan, P.E.
Senior Regional Engineer Mechanicsville, Virginia
Early Asphalt Plant
Plants and Production The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again.
Basic Functions of Plants
• Store component materials • Combine aggregates in proper propor7ons • Heat and dry aggregates • Add and mix liquid binder in proper propor7ons • Coat aggregates uniformly • Store mixture and load trucks without segrega7on
Reproduce the mix design !
Types of Facilities
• Batch • Con6nuous (drum-‐mix) • Combina6on Batch Plant
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Batch Plant Elements
Cold feed bins
Dryer
Asphalt storage tanks
Storage silos
Batch tower
Control room
RAP bin
Batch Tower Flow
Aggregates travel up hot elevator
Pugmill
Aggregate weigh hopper
Asphalt weigh bucket
HMA dispensed into truck Aggregate
from dryer
Across screen deck
Screens separate size
Hot bins
Drum-Mix Plant Drum-Mix Plant
Dryer/m
ixer
Storage silos
RAP bin
Cold feed bins
Asphalt storage tanks
Control room
3rd Generation Technology Batch Plant • More versa6le • More expensive • Sta6c weighing • Semi-‐permanent
Drum Plant • Less expensive • High output • Weighs moving, wet aggregate
• More portable
Batch or Drum-Mix?
• Both make quality mix • Choice based on business decision
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• Store Component Materials
Basic Plant Functions Horizontally Stockpiled Aggregate
Stockpile Contamination Avoid Contaminated Material
Paved & Sloped Area Covered Stockpiles
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Asphalt Binder Storage Vertical Asphalt Tanks
• Store Component Materials • Combine aggregates in proper propor6ons
Basic Plant Functions Cold Feed Bins
Ver6cal Dividers
Cold Feed Bins
Bin Feed is determined by:
Gate Opening
Belt Speed
Cold Feed Bin Belt
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Collector Belt
Feeder Dryer
Collector Belt
Belt Scale
• Collects material and transfers to dryer
Collector Belts/Conveyors
Cold Feed Bin
Plant Computer
Single Deck Scalping Screen
• Store materials • Combine aggregates in proper propor6on
• Heat and dry aggregates
Basic Plant Functions
Heat And Dry Aggregates
Aggregate Dryers • Gas or liquid fueled burner • Removes moisture from aggregate
• Surface and internal • Heat aggregate to produc6on temperature • “Super-‐heat” aggregate for heat transfer to cooler RAP being blended
Two Types of Dryers
Aggregate & Air
• Parallel-‐flow • Same direc6on
• Counter-‐flow • Opposite direc6on
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Parallel-Flow Drum-mixer Zones
Combustion Heating Drying Air
Liquid Feed
Hot Mix Asphalt
Mixing
Counter-Flow Drum-mixer Zones
Air
AC
Hot Mix Asphalt
Aggregate Combustion Heating Drying Mixing
Captures Dust From Plant & Silo
Evacuates Gases & Steam
Provides Air for Combus6on
Exhaust Fan
Emission Control Equipment Insufficient Drying
• Trapped moisture • Poor asphalt - aggregate bond • Tender mixes • Rapid heat loss after mixing • Asphalt content errors
Insufficient Heating
• Poor mixing – Rich and lean spot – Uncoated Aggregate – Poor compaction
• Insufficient heat transfer to RAP
• Store Component Materials • Combine aggregates in proper propor6ons
• Heat and dry aggregates • Add liquid binder in proper propor6ons
Basic Plant Functions
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• Store Component Materials • Combine aggregates in proper propor6on
• Heat and dry aggregates • Add liquid binder in proper propor6ons • Mix to coat aggregates uniformly
Basic Plant Functions 3rd Generation Technology
3rd Generation Technology
Basic Functions of Plants • Store component materials • Combine aggregates in proper propor7ons • Heat and dry aggregates • Add and mix liquid binder in proper propor7ons • Coat aggregates uniformly • Store mixture and load trucks without segrega7on
Stationary Silo Installations
1 2 3
Proper loading of trucks helps reduce segrega7on
Truck Loading
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Truck Loading
• Use mul6ple drops • Loading sequence:
• Front
1
25-7
5%
Truck Loading
• Use mul6ple drops • Loading sequence:
• Front • Back
1
25-7
5%
2
Truck Loading
• Use mul6ple drops • Loading sequence:
• Front • Back • Middle
• Always transfer in “bulk” 25-7
5%
1 2 3
Haul Trucks
• Clean, smooth beds • Approved release agent • No diesel!
• Insulated & tarped • Front, sides, bo]om • Thin overlays, long hauls, cold weather
• Store Materials • Combine aggregates in proper propor6ons
• Heat and dry aggregates • Add and mix liquid binder in proper propor6ons
• Mix and coat aggregates uniformly • Store mixture and load trucks without segrega6on
Basic Plant Functions Questions?