HMA Characterization Permanent Deformation 1

Permanent Deformation

Senior/GraduateHMA Course

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Permanent Deformation

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Test Methods

• Gyratory Shear Compactors• Loaded Wheel Testers• Simple Shear Tester• Uniaxial and Triaxial

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Terms

• Uniaxial– Vertical axial load only – no confining

pressure• Triaxial

– Both vertical and horizontal pressure used•Horizontal pressure used to

simulate field conditions of lateral support

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Terms

• Creep– Static load applied over some time

interval•Usually 1 hour or more•Vertical deformation measured

• Creep recovery•Load removed and rebound of

material measured

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Terms

• Repeated loading– Step load followed by a rest period

•Load from 0.05 to 3 seconds•Rest

–From 0.6 to 1 minute– Typical = 0.1 second load & 0.9 sec

rest

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Terms

• Dynamic loading– Cyclic loading

•Can be all compression or include stress reversal

–Tension to compression cycles»Simulates stress reversal seen

in pavement as tire passes a point

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Loaded Wheel Testers

Asphalt Pavement Analyzer (APA)

Hamburg Wheel Tracking (HWT)

Purdue Wheel Tracker (PurWheel)

LCPC Wheel Tracker (LCPC)

Mobile Load Simulator (MLS) - 1/3 scale

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Asphalt Pavement Analyzer

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Asphalt Pavement Analyzer

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Asphalt Pavement Analyzer

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Typical APA Results

0

2

4

6

8

10

0 2,000 4,000 6,000 8,000 10,000Numbers of Load Cycles

APA R

ut

Depth

, m

m

Good HMA Poor HMA

Example of 5 mm Max Limit

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Loaded Wheel Testers

Parameters GLWT APA

Specimens 3 Beams 6 Gyratory

Air Voids, % 4 or 7% 4 to 7%

Load, N (lb) 445 (100) 445 (100)

Hose Press kPa (psi) 690 (100) 690 (100)

Conditioning dry wet or dry

Temperature, oC (oF) 35 to 60 (95 to 140) 40 to 64 (105 to 147)

No. of Cycles 8,000 8,000

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Asphalt Pavement Analyzer• Three stages in deformation vs passes

0

5

10

15

20

25

0 2,000 4,000 6,000 8,000 10,000

Wheel Passes

Per

man

ent

Def

orm

., m

m

Secondary

Tertiary

Primary

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Hamburg

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PurWheel

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PurWheel

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Loaded Wheel Testers

Parameters Hamburg PurWheel

Specimens 2 slabs 2 slabs

Air Voids, % 7 + 1% Varies Load, N (lb) 175 (385) 175 (385)

Wheel Steel Wheel Pneumatic tire 793 kPa (115 psi)

Conditioning wet or dry wet or dry

Temp., oC (oF) 25 to 70 (77 to 158) Variable

No. of Cycles 20,000 or 20 mm rut 20,000 or 20 mm rut

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LCPC (French unit)

www.lcpc.fr/LCPC/English/Presentation

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US Corps of Engineers Gyratory• Originated at the US Corps of Engineers

Waterways Experiment Station • Generally applicable to dense-graded mixes

– May not be strictly applicable to mixes that are not sensitive to bitumen content

• Can get Mohr’s circle information

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US Corps Gyratory (Old)

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US Corps Gyratory (New)

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Simple Shear Tester (SST)

• Simple Shear Tests– Permits controlled rotation of

principal axes of stress and strain– Assumes shear deformation rather

than densification is the primary rutting mechanism

9

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SST

Prepared sample

Computer control and chamber

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SST

Empty chamber ready for sample

Sample mounted in chamber and ready to test

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Uniaxial and Triaxial Testing

www.mts.com

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QUESTIONS ?