jim signore: hamburg wheel track test
DESCRIPTION
A new arrival to California as part of the Caltrans move toward national “Superpave” specifications, the Hamburg Wheel Track test is intended to test the rut resistance and moisture sensitivity of asphalt pavements. Hear the latest research and practical lab applications of the HWT in California from the acclaimed Pavement Research Center.TRANSCRIPT
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