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Getting Good Compaction
California Asphalt Pavement Association – Sacramento, October 27, 2016
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First, some terminology…
Compaction is how hard you try
Density is what you may or may not get
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And some history…
Method Spec
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Compaction relative to lab-compacted
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Compaction relative to theoretical max (Rice)
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Compaction Specifications
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Mix Design Air Voids
% of Rice
100
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% of Laboratory
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% of Test Strip
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In-Place Air Voids
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Why Worry?
NCAT Report 16-02
• Decreasing in-place air voids improves performance
• 1% decrease in air voids:– 8 - 44% improvement in
fatigue
– 7 - 66% improvement in rutting
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Why Worry?
NCAT Report 16-02
• 1% decrease in air voids can extend service life by 10% (conservatively)
• Increasing the required minimum density can save nearly 10% in net present value
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All it takes is…
• The Right Mix
• On the Right Substrate
• Using the Right Equipment and the Right Methods
• Under the Right Conditions
(thanks (or apologies) to the pavement preservation folks)
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The Right Mix
• Lift thickness AT LEAST three times the nominal maximum aggregate size
• Appropriate for the loading
– Balance rut resistance against durability and fatigue resistance
– Keep workability in mind
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NOTE• You can change
– The aggregate requirements
– The grading
– The natural sand content
– The fracture content
– Voids in Mineral Aggregate
– The laboratory compaction effort
– The target air voids
– The binder type / grade
– The target field density
– Etcetera – one mix does not fit all
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Suitable support is required
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Uniform support is important
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Equipment
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Pneumatic Rollers
• Compact with shear
– Bottom up instead of top down
• Don’t bridge high spots like steel drums
• Have a tendency to introduce more variability into nuclear gauge results
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Don’t kid yourself
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The right conditionsUse Multicool
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The right methods
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A few basics
The right tack at the right application rate
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A few basics
Control the mix
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A few basics
Keep the rollers close to the paver
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A few basics
10-12 impacts per foot
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A few basics
Monitor lab properties, temps, mix behavior
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Subgrade / Base / Bottom Lift
Compacted HMA
Paving the First Pass
Longitudinal Joints
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Paving the First Pass
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Subgrade / Base / Bottom Lift
Paving the Second Pass
Compacted HMA
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Subgrade / Base / Bottom Lift
Raking the Second Pass
Compacted HMA
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Subgrade / Base / Bottom Lift
Raking the Second Pass
Compacted HMA
Steel Drum Roller
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Photo courtesy of James Signore
Don’t rake the joint
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Roll from the hot side
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The right specs
• Need to suit the project
• Need to define acceptance criteria
• Need to assess conformance
Be very careful when cutting and pasting or using blanket referrals to other agency specifications
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Need to test
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Quality Control
Keep deleterious materials out of the mix
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Employ qualified individuals
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Thin Overlays
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• 1” overlay, 70 degrees, 15 mph wind, 300o
mix temp – less than 9 minutes to compact
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Higher paver speed
300 tph * 2,000 lb/ton / 60 min/hr / 145 pcf / 12’ wide / 1” deep = 70 feet per minute
Optimum paver speed for ride quality – 45 fpm?
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10 – 12 impacts per foot
70 fpm * 5 passes * 12 impacts/ft / 90% efficiency = 4,700 vibrations per minute
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ALL of the rolling has to be completed in less than 9 minutes
And remember…
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Greater influence of underlying layers for nuke gauges
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Thin cores can be difficult
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And yet density is still critical
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Intelligent Compaction
Image courtesy of Sakai
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But the mapping is very helpful
Image courtesy of Topcon
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So how do we succeed?
• Forget the “one size fits all” mentality –
– Agencies / consultants / designers / producers / contractors
• Obtain knowledge and guidance if necessary
• Adjust to fit
– The project
– The conditions
• Evaluate and correct as necessary
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Put your sole into it
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Mike Robinson LLC
101 Upper Canyon Loop
Ten Sleep, WY 82442
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