Getting Good Compaction

307-213-0223 [email protected] © Mike Robinson, PE307-213-0223 [email protected] © Mike Robinson, PE

Getting Good Compaction

California Asphalt Pavement Association – Sacramento, October 27, 2016


First, some terminology…

Compaction is how hard you try

Density is what you may or may not get


And some history…

Method Spec


Compaction relative to lab-compacted


Compaction relative to theoretical max (Rice)


Compaction Specifications

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Mix Design Air Voids

% of Rice

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% of Laboratory

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% of Test Strip

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In-Place Air Voids


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


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


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)


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


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


Suitable support is required


Uniform support is important


Equipment


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


Don’t kid yourself


The right conditionsUse Multicool


The right methods


A few basics

The right tack at the right application rate


A few basics

Control the mix


A few basics

Keep the rollers close to the paver


A few basics

10-12 impacts per foot


A few basics

Monitor lab properties, temps, mix behavior


Subgrade / Base / Bottom Lift

Compacted HMA

Paving the First Pass

Longitudinal Joints


Paving the First Pass



Paving the Second Pass

Compacted HMA



Raking the Second Pass

Compacted HMA



Raking the Second Pass

Compacted HMA

Steel Drum Roller


Photo courtesy of James Signore

Don’t rake the joint


Roll from the hot side


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


Need to test


Quality Control

Keep deleterious materials out of the mix


Employ qualified individuals


Thin Overlays


• 1” overlay, 70 degrees, 15 mph wind, 300o

mix temp – less than 9 minutes to compact


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?


10 – 12 impacts per foot

70 fpm * 5 passes * 12 impacts/ft / 90% efficiency = 4,700 vibrations per minute


ALL of the rolling has to be completed in less than 9 minutes

And remember…


Greater influence of underlying layers for nuke gauges


Thin cores can be difficult


And yet density is still critical


Intelligent Compaction

Image courtesy of Sakai


But the mapping is very helpful

Image courtesy of Topcon


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


Put your sole into it


Mike Robinson LLC

101 Upper Canyon Loop

Ten Sleep, WY 82442

307-213-0223

[email protected]

Getting Good Compaction

Engineering

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