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Asphalt Concrete Mix Design and Construction

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Hot Mix Asphalt Concrete (HMA)Mix Designs

• Objective:

–Develop an economical blend of aggregates and asphalt that meet design requirements

• Historical mix design methods

–Marshall

–Hveem

• New

–Superpave gyratory

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Requirements in Common

• Sufficient asphalt to ensure a durable pavement

• Sufficient stability under traffic loads

• Sufficient air voids

–Upper limit to prevent excessive environmental damage

–Lower limit to allow room for initial densification due to traffic

• Sufficient workability

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Place pre-heated aggregate in bowl and add hot asphalt

Mixing

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MixingPlace bowl on mixer and mix until

aggregate is well-coated

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Example of typical full-size compactors.

Compaction

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% binder

VMA

% binder

VFA

% binder

%Gmm at Nini

% binder

%Gmm at Nmax

% binder

DP

% binder

Va

Blend 3

Selection of Design Asphalt Binder Content

HMA PLANT OPERATION

Types Of Plants

BATCH DRUM MIXER

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Basic Purpose Of HMA Plants

To produce a quality hot asphalt mixture that contains the desired proportions of asphalt and aggregate and meets all specifications.

Batch planttypical layout

Storage Silo

Batch TowerDryer

Conveyor BeltAggregate Bins

Burner

Asphalt Storage

Hot elevator

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Batch Plant

Batch Tower

Pug Mill

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Burner - Batch Plant

Drum Mixer Planttypical layout

Storage Silo

Dryer

Conveyor BeltsAggregate Bins

Burner

Asphalt Storage

Drum Dryer Mixer

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Temperature Profile in Drum Mixer

Dryer For Drum Dryer Mix Plant

Dryer For A Drum Mixer Plant

Aggregate Entry Point

Small Drum Mixer Plant

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Plants are computer controlled

HMA PLACEMENT

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To Be Covered

• Hauling

• Placement

• Compaction

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Different types of trucks are Used

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Self Propelled Paver

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Self Propelled Paving Machine

THE BASIC PRINCIPLE HAS NOT CHANGED

MUCH

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Self Propelled Paving Machine

HMA Flow

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COMPACTION

GOOD COMPACTION

LEADS TO GOOD

PERFORMANCE

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Reason For CompactionReason For Compaction

• To prevent further compactionTo prevent further compaction

• To provide shear strength or resistance to To provide shear strength or resistance to

ruttingrutting

• To ensure the mixture is waterproofTo ensure the mixture is waterproof

• To prevent excessive oxidation of the asphalt To prevent excessive oxidation of the asphalt

binderbinder

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Temperature is critical

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Vibratory Roller

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Pnuematic Roller

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Steel Wheeled Roller

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Extracting A Core

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Questions - ?