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

Thank you

Questions??

jsignore@berkeley.edudjjones@ucdavis.edujtharvey@ucdavis.edu