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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?