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Warm Mix for a Cold Climate

Warm Mix for a Cold Climate. Update on Colorado DOT’s 2007 WMA Project on I-70 2009 Rocky Mountain Asphalt Conference and Equipment Show. Colorado DOT 2007 WMA. Project Summary Asphalt Mixture Details WMA Specification Summary Construction Highlights WMA Performance Monitoring

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Warm Mix for a Cold Climate

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  1. Warm Mix for a Cold Climate Update on Colorado DOT’s 2007 WMA Project on I-70 2009 Rocky Mountain Asphalt Conference and Equipment Show

  2. Colorado DOT 2007 WMA • Project Summary • Asphalt Mixture Details • WMA Specification Summary • Construction Highlights • WMA Performance Monitoring • Conclusions

  3. CDOT WMA Project Summary • Project Location:I-70, 70 miles west of DenverMountain terrain – elev. 8,800’ to 11,100’

  4. CDOT WMA Project Summary West Portal of Eisenhower-Johnson Memorial Tunnel on I-70 WMA Job started here and continued down to Town of Silverthorne

  5. CDOT WMA Project Summary • Climate35”+ annual precipitationover 200” annual snowfall150 - 200 freeze/thaw cycles per year • Cool summer conditions (construction) July – at lowest elevation on the projectWinds avg. 8-21mph

  6. CDOT WMA Project Summary • Traffic30,000 AADT, 10% trucks, 4.85M ESALS (10-yr.) • Extreme winter conditions (truck chain area) • Winter 2007/8 Stats: • Snowed 65 of 76 days between 12/1 & 2/14 • 128 chain-days total for 2007/8

  7. WMA Specification Summary • SAME mix design for WMA and for HMA • 3 additives – Advera-WMA, Sasobit, Evotherm • ~1000 tons each, ~1 mile for each section • Control mix placed each night prior to WMA section • Three lanes each direction, WMA in middle lane • WMA sections placed nearly adjacent toeach other to ensure similar site conditions

  8. Project Mixture Details • Project scope of work:Mill surface distress 2.5” and fill with 2.5” HMAThick existing pav’t (12”+ HMA over R75 fill) • Superpave dense graded mix specified - ½-inch nominal max (CDOT SX-mix) - PG58-28 binder- 75 gyration design- Volumetric Acceptance for pay (Voids, VMA, AC, mat density, joint density)

  9. Project Mixture Details • Contractor’s mixture design with CDOT approval • Project called for standard mix design with no WMA additives during design- Fine graded mix design by Everist Materials aggregates from crushed river rock- Production targets established: Voids = 3.6% (+/-1.2% tolerance) VMA = 16.8% (+/-1.2% tolerance) %AC = 6.3% (+/-0.3% tolerance) • Average bid prices $66/ton WMA, $48 HMA (~38%+)

  10. Construction Highlights • WMA produced and tested at 250 °F HMA produced and tested at 280 °F • Same roller configuration used • WMA Density per Spec (92%-96%) andWMA Volumetric pay factors “set to 1” and after discussions at pre-pave meetings

  11. Advera-WMA feed system - Similar to Sasobit feed system - blown in like SMA fibers

  12. Evotherm injected into AC feed line here Advera-WMA and Sasobit blown in here

  13. Advera-WMA Sasobit

  14. Same haul, placement and compaction equipment used for WMA as for HMA sections WMA ~240°F behind the paver – no fumes

  15. Construction Highlights - Field Data All values are averages of multiple tests except as noted Spec 92-96% * Per Specifications - minimum delivery temp for control HMA was 280 °F (actual temp not recorded) Target plant production temp for WMA mix was 250 degrees for all sections

  16. Construction Highlights – Lab Data Design 6.3% 3.6% 16.8% 39 NOTE: Samples compacted immediately at temps on previous slide

  17. Interpreting Hamburg Data Failure if more than 4mm in 10,000 cycles NOTE: CDOT does not typically run Hamburg on 75 Gyration mixtures Failure due to plastic flow is typical below the 100 gyration level

  18. Construction Highlights – TSR and Hamburg Data * Average of other control mix tested on the job. -TSR samples compacted immediately at temps previously stated-Hamburg samples cooled and shipped to Denver where they were all reheated for compaction to standard temperature (280 degrees)

  19. FHWA Mobile Asphalt Mixture Testing Laboratory and TFHRC Data

  20. Dynamic Modulus E*Master Curve (from Asphalt Mix Performance Tester)

  21. I-70 Flow Number, Fn, from AMPT689 kPa (100 psi) – Deviator Stress69 kPa (10 psi) – Confining Pressure

  22. WMA Performance Monitoring • NCAT under contract for WMA project support- field data collection during construction- long term tracking (3+ years)- interim and final reporting • First condition evaluation was in October, 2008

  23. WMA Performance MonitoringResults from First Annual Evaluation • Rutting less than 5mm in all sections • Transverse cracking is occurring but is relatively sparse and is occurring similarly in both control and WMA sections (3 to 4 cracks per mile)Some transverse cracks stop or are shorter in the WMA sections. • Weathering, raveling and other distresses were rare with workmanship problems likely the cause • Excellent performance in all sections at this time

  24. Conclusions • WMA decreased voids in lab compaction • WMA field compaction comparable at lower temps • TSR Lower, but passing, in two of three WMA sections • Hamburg data may be inconclusive – will rely on actual field moisture performance for these test sections • Early WMA performance equal to HMA on the job: - no rutting, moisture damage or early distresses • Due to harsh site conditions, we anticipate useful performance data within 3 years • Confident that WMA facilitates cold temp. placement • Will use more WMA in this corridor if performance is comparable to HMA

  25. Questions, Please Anticipating Warmth in the future

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