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TRANSCRIPT
Construction Compaction 1
Compaction of HMA Mixes
Background
Senior/GraduateHMA Course
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What you will learn
• Objective of Compaction• Engineering properties related to compaction• Factors affecting compaction
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Safety
• Watch your back!• Keep visual contact with roller operators!• Keep an eye on traffic! • Wear your safety vest!
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Typical Compaction Process
Paving Machine Vibratory Roller Pneumatic Roller
Steel wheeledRoller
TemperatureZones
300° - 240°F 240° - 190°F 170 - 150°F
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Definitions
• Density • Compaction • Pass • Coverage • Time available for compaction (TAC)
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Pass & Coverage DefinedW
idth
of m
at Pass1
Pass 2Make up Pass 5
Pass 3
Pass 4
This is a 5 pass pattern that provides 2 complete coverages.
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Time Available for Compaction
(TAC)
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Importance of Compaction
• Improve Mechanical Stability• Improve Resistance to Permanent
Deformation • Reduce Moisture Penetration• Improve Fatigue Resistance • Reduce Low-Temperature Cracking Potential
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Factors Affecting Compaction
• Properties of the Materials• Environmental Variables • Laydown Site Conditions
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Properties of the Materials
• Aggregate • Asphalt Binder • Mix Properties
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Compact effort increases due to
• Crushed content• Nominal maximum size• Hardness of the aggregate • Angularity of aggregate• Less natural sand• High dust content mixes• Note: Typically, HMA mixes will be harder to
compact.
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Hot Mix Compaction
• Asphalt binder holds particles together– Provides lubrication at high temperatures– Provides cohesion at in-service
temperatures• Limits air and water intrusion into HMA mat
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Environmental Variables
• Layer thickness • Air and base temperature • HMA mix laydown temperature • Wind velocity • Solar flux
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Tim
e f
or
Mat
to
Co
ol t
o 1
75
F,
Min
ute
s
HMA Mat Thickness, inches
0 1 2 3 4 5 6 7 8
50
40
30
20
10
0
Mix
B
as
e °F 3
00,
5
0 300
,
32
300
,
14 250
, 3
22
50,
1
4
250
,
50
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LOWHIGH
LOWHIGH
THINTHICK
Base Temperature
Mix Temperature
Major Factors Affecting Rolling Time
Mat Thickness
allows LESS time
allows MORE time
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Compaction Temperature Range
185 °F(85 °C)
300 °F(150 °C)
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Laydown Site Conditions
• Lift thickness versus aggregate size• Lift thickness uniformity• Base Conditions
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Questions?