Got Density?
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Transcript of Got Density?
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Got Density?
Asphalt Pavement Assn. of IndianaWinter Conference
December 2010
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Why measure density?
• Surrogate for other properties– Strength– Durability– Permeability
• Easy and fast
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Rutting vs. Air Voids
0
5
10
15
20
25
30
35
40
Rutting, mm
Low Medium High
Relative Air VoidsRef: WesTrack
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Rutting vs. Air Voids
-200
-150
-100
-50
0
0 2 4 6 8 10 12
Air Voids, %
Dep
th,
mm
Within Wheelpath Between Wheelpath Original
Ref: Mn/ROAD
1/2” Rutting in One Year
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Fatigue vs. Air Voids
0
0.5
1
1.5
2
2.5
3
4 5 6 7 8
Avg. Air Voids, %
Est
imat
ed F
atig
ue L
ife
0.60%
1.20%
1.80%
Ref: WesTrack
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Permeability
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Permeability
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Retained Penetration vs Air Voids
10
100
4 6 8 10 12 14 16
Air Voids
Ret
ain
ed P
enet
rati
on
, %
Ref: NCAT Text Book
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0
10
20
30
40
50
60
7 8 9 10 11 12
Air Voids
Pavem
en
t L
ife
Red
ucti
on
, %
SHA Survey Literature WSPMS
Pavement Life vs. Air Voids
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Getting Density
• Lift Thickness
• Temperature
• Compaction Support
• Equipment
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NCHRP Report 531
• Relationships of HMA In-Place Air Voids, Lift Thickness, and Permeability (NCHRP 9- 27)
• Recommended minimum lift thicknesses:– 3 X NMAS for fine-graded mixes– 4 X NMAS for coarse-graded mixes
• Thin lifts cool faster– less time available for compaction
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MultiCool
• FREE Software for Computing Compaction Window– Base Temp– Weather Conditions– Lift Thickness– Mix Temp– Latitude
• Available at www.hotmix.org
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MultiCool
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Temperature
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0 5 10 15 20 25 30 35 40 45 50 55 60
Time, minutes
Tem
per
atu
re,
F
1.5" 2" 3"
80OF Surface & Air Temperature, 5 mph wind
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150
175
200
225
250
275
300
0 5 10 15 20 25 30 35 40 45 50 55 60
Time, minutes
Tem
per
atu
re,
F
1.5" 2" 3"
50OF Surface & Air Temperature, 5 mph wind
Temperature
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150
175
200
225
250
275
300
0 5 10 15 20 25 30 35 40 45 50 55 60
Time, minutes
Tem
per
atu
re,
F
1.5" 2" 3"
30OF Surface, 40OF Air Temperature, 15 mph wind
Temperature
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Compaction Support
Weak!!!
Weak SupportLeads to Poor Compaction!
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Compaction Support
Strong!!!
Strong SupportHelps Compaction!
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Balancing Production
• Balance of plant production, trucking, paver speed and rollers
• Slow and steady wins the race– Speeding up to get rid of trucks not
recommended.• Hurts ride• Non-uniform compaction
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Joint Density
• Controlling segregation important
• Proper joint construction important
• Sealers
• Echelon paving
• Joint density specification
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Longitudinal Butt Joint
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Notched Wedge Joint
12”
1” minimum
Max Agg. Size
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Notched Wedge Joint Attachment
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Joint Rolling - Unconfined Edge
First Pass - Steel Wheel Rollers Inside of edge ~ 6”
Second Pass - Steel Wheel Rollers Overhang edge 3-6”
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3” - 6” off joint3” - 6” on joint
Longitudinal Joint
Hot M
at
Cold
Mat
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Longitudinal Joint
1/2 - 3/4 “ overlap
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Longitudinal Joint
Unrolled
Rolled
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Minimizing Joint Problems
• Minimize Joints
• Pave in Tandem!
• May Require More Lane Closures
• But, It Minimizes Return Trips!
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Final Quiz
Q - What is the maximum number of rollers needed on a paving project?
A - Whatever it takes to get density.
2
3 41
5
6
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The Future is Bright!
• Better Tools to Help Us!
• Oscillatory Compaction
• Intelligent Compaction– GPS Location– Mat Stiffness
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Don’t Forget Quality
• Diamond Achievement Commendation
• Diamond Quality Commendation
• Diamond Paving Commendation