Jim Signore: Hamburg Wheel Track test
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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.
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Jim Signore: Hamburg Wheel Track test
- 1. Hamburg Wheel Track Test for Moisture Sensitivity & Rutting James M. Signore, PhD, PE Principal Investigator UCPRC, UC Berkeley CalAPA Conference 2014
- 2. Presentation • Why Hamburg Wheel Track? • Equipment Requirements • Testing – how, best practices, troubleshooting, lessons learned… • Performance principles • Conclusions
- 3. 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
- 4. Moisture Sensitivity How does it show up? Pavement Interactive.org
- 5. HWTT T 324 vs IDT CT 371 Test 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
- 6. What’s Required? • HWTT Machine ~$60K-$70K • Superpave Gyratory ~$35K-$40K including molds • Rock Saw
- 7. HWTT Models
- 8. Operation
- 9. Test Specimen Fabrication • Superpave Gyratory compaction of specimens to 7% ± 1% air void content • Cut ‘flat’ to fit into test molds
- 10. Test Specimen Fabrication • Superpave Gyratory Compactor
- 11. Test Specimen Fabrication • Hamburg Testing Fixture – cut ‘flat’ on cores
- 12. 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
- 13. Concept behind HWTT – and other wheel trackers “Inflection Point”
- 14. Performance Possibilities Rut Depth Theoretical Cycles Inflection Point “Rut Resistant” 0.5 in.
- 15. Superpave Section 39 Test Requirements • Taken from 10/17/14 edition
- 16. Production Testing Type A and RHMA-G
- 17. Section 39-2.01D(5) Quality Control and Assurance Type A
- 18. Section 39-2.02B Mix Design Type A
- 19. Section 39-3.01Quality Control and Assurance RHMA-G
- 20. Section 39-3.02 Mix Design RHMA-G
- 21. 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
- 22. HWTT Performance Assessment Test should correctly identify rut-prone and moisture sensitive mixes Additional benefit of test would be capability to rank mixes
- 23. Performance • Put in closeup pics…
- 24. Performance
- 25. Performance
- 26. Performance – Rut Depth Wheel Movement Max or Average? SIDE VIEW OF CORES
- 27. Performance Strong Performing Mix (lab and field)
- 28. Performance Variability Rut Depth Maximum versus Average One side fails both sides fail
- 29. 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’
- 30. Summary • Hamburg here to stay • Minimize variability and maximize success within your control • Can be effective tool to assess mix performance
- 31. Acknowledgments • Dr. Rita Leahy – CalAPA • Dr. David Jones - UCPRC
- 32. Thank you Questions?? jsignore@berkeley.edu djjones@ucdavis.edu jtharvey@ucdavis.edu
Editor's Notes
- Once the core specimens are produced in the sgc, they are placed into the hamburg fixture. To make this work, flats are cut on the two cores so they make direct contact with one another.
- And what do we do with hamburg data – well, there are sensors in the machine that measure how much the rut depth in the HMA changes with each repetition of the wheel In concept, what happens is the red line. The rutting develops slowly (flat slope)and then the mix reaches a point where it starts to fail much faster. The idea here is that at the “knee” The mix is sufficiently failed so that moisture has reduced the stiffness and strength and durability of the mix so that it fails faster. The specs for this test are typically we want less than ½ in. rutting over 20,000 cycles. However, what we see in many mixes we’ve tested is much better performance. These mixes don’t reach the knee – I call these rut resistant mixes here – in green.
- “Good (bad) on the test = Good (bad) on the street”