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Hamburg Wheel Track Test for Moisture Sensitivity &
Rutting
James M. Signore, PhD, PEPrincipal InvestigatorUCPRC, UC Berkeley
CalAPA Conference 2014
Presentation
• Why Hamburg Wheel Track?
• Equipment Requirements
• Testing – how, best practices, troubleshooting, lessons learned…
• Performance principles
• Conclusions
Moisture Sensitivity
• Caltrans needs reliable quick means of assessing moisture sensitivity and rutting
• Concerns about variability and duration of CT 371/T 283
• HWTT as second test
Moisture Sensitivity
Pavement Interactive.org
How does it show up?
HWTT T 324 vs IDT CT 371Test Issue T 324 CT 371 / T 283
Test Time 6 hours Multiple days
Specimens 4 cores (6 in. dia.) 12 cores (4 in. dia.)
Compaction Method Superpave Gyratory Superpave Gyratory
Specimen Preparation Cut ‘flats’ on cores Environmentally treat
6 cores
Analysis Machine produced –
pass or fail
Calculations required,
wet and dry strength
What’s Required?
• HWTT Machine ~$60K-$70K
• Superpave Gyratory ~$35K-$40K
including molds
• Rock Saw
HWTT Models
Operation
Test Specimen Fabrication
• Superpave Gyratory compaction of specimens to 7% ± 1% air void content
• Cut ‘flat’ to fit into test molds
Test Specimen Fabrication• Superpave Gyratory Compactor
Test Specimen Fabrication
• Hamburg Testing Fixture – cut ‘flat’ on cores
Fabrication/Test Variability
• Mix temperature into SGC
• Heating of the compaction plates
• Limit time from oven to start of compaction reduces heat loss
• Preparation and placement of specimens in HWTT
• Time specimen is in water and temperature of water
• Temperatures of prepared specimens placed in HWTT
Cox et al 2013
Concept behind HWTT – and other wheel trackers
“Inflection Point”
Performance Possibilities
Rut Depth
Cycles
Theoretical
“Rut Resistant”
Inflection Point
0.5 in.
Superpave Section 39Test Requirements
• Taken from 10/17/14 edition
Production TestingType A and RHMA-G
Section 39-2.01D(5) Quality Control and Assurance
Type A
Section 39-2.02B Mix DesignType A
Section 39-3.01Quality Control and Assurance
RHMA-G
Section 39-3.02 Mix DesignRHMA-G
Maximizing Usage of HWTT
• Arm/wheel weight calibration
• Rut depth measurement – ensure measured equals actual
• Cutting of flats – tightness in mold
• Air void requirement is broad
• Water bath temperature
HWTT Performance Assessment
Test should correctly identify rut-prone and moisture sensitive mixes
Additional benefit of test would be capability to rank mixes
Performance
• Put in closeup pics…
Performance
Performance
Performance – Rut Depth
SIDE VIEW OF CORES
Wheel Movement
Max or Average?
PerformanceStrong Performing Mix (lab and field)
Performance Variability
Rut DepthMaximum versus Average
One side fails both sides fail
Performance
• “Some mixes that used to pass may (will) not pass anymore”
• Adjust mix design based on results
• See as pass/fail – Given variability, assess confidence in mix based on how ‘well it passes’
Summary
• Hamburg here to stay
• Minimize variability and maximize success within your control
• Can be effective tool to assess mix performance
Acknowledgments
• Dr. Rita Leahy – CalAPA
• Dr. David Jones - UCPRC
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