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HMA Compaction

Types of Rollers & the Compaction Process

Senior/GraduateHMA Course

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What you will learn….

• The different types of compactors• How compactors compact• Variables associated with compaction• How density is controlled in the field

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Types of Rollers

• Static Steel Wheel • Pneumatic – Rubber Tired• Vibratory

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How Do Rollers Compact?

By applying their load

over a given area!

(Contact Pressure)

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Static Steel Wheel Roller

• Contact Pressure • Operation

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Pounds per Linear Inch (PLI)

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Pounds Per Linear Inch (PLI)

• Example:– A 8 ton roller with two, 50 inch wide drums.– In this case, 60% of the mass is on the

drive drum and 40% is on the guide drum.– Calculate the PLI for each roll and for the

roller in total.

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Pounds Per Linear Inch (PLI)

• 8 tons x 2000 lbs/ton = 16,000 lbs.• For each drum

60% x 16,000 lbs. / 50 inches = 192 PLI

40% x 16,000 lbs. / 50 inches = 128 PLI • For total roller

16,000 lbs. / (50 +50) = 160 PLI

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Speed of Roller

• Speed kills compaction forces• Dwell time• Pressure, impact, manipulation

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Travel

Frictional force turns trailing drum

Non-Non-powered powered

drumdrumPowered

Drum

WW R

R

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Pneumatic Tired Rollers

• Wheel load• Tire design • Inflation pressure• Contact area

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Vibratory Rollers

• Amplitude • Frequency• Impact Spacing • Operation

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01-00 6 - 47

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Frequency, f = the number of hertz (cycles/s)--a single cycle is one full rotation of the eccentric weight. Frequency = 1/T

Amplitude, A = the maximum deviation from position at rest -- one-half the total movement.

Amplitude(A)

Time

U pD

ow

n

Time (T) For Full Cycle

Mo

vem

ent

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AMPLITUDE

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DIRECTION OF TRAVEL

FREQUENCY

Impact Spacing

High FrequencyLow Frequency

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Typical Compaction Process

Compactive Force PressureVibration

PressureManipulation

Pressure

TemperatureZones

300° - 240°F 240° - 190°F 170 - 150°F

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Compaction Variables

• Roller Speed • Number of Coverages• Rolling Zone • Rolling Pattern

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Typical Range of Roller Speeds(miles per hour)

Type of Roller Breakdown Intermediate Finish

Static Steel Wheel 2 to 3.5 2.5 to 4 3 to 5

Pneumatic 2 to 3.5 2.5 to 4 4 to 7

Vibratory 2 to 3.5 2.5 to 3.5 3 to 51

1 1 Operated in static modeOperated in static mode

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One Coverage

How many passes of the roller are How many passes of the roller are needed to cover the width of the mat needed to cover the width of the mat one time ?one time ?

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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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75 m

15 m

Typical Rolling Zone

Paver

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Test Strip Construction

• Simulating Actual Conditions • Establishing Roller Patterns • Calculating Effective Roller Speed

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1

4

2

3

5

6

CROWN2-lanes

One Roller Coverage

Drum Width = 72 inches

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How Many Repeat Coverages to Assure Density?

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Density

High

Low

DensityPassing

1 2 43 5 6

Roller Passes

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Balancing Production

Trucking Compaction

PavingHMA Facility

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Questions?