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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 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 • Conclusions
CDOT WMA Project Summary • Project Location:I-70, 70 miles west of DenverMountain terrain – elev. 8,800’ to 11,100’
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
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
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
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
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)
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%+)
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
Advera-WMA feed system - Similar to Sasobit feed system - blown in like SMA fibers
Evotherm injected into AC feed line here Advera-WMA and Sasobit blown in here
Advera-WMA Sasobit
Same haul, placement and compaction equipment used for WMA as for HMA sections WMA ~240°F behind the paver – no fumes
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
Construction Highlights – Lab Data Design 6.3% 3.6% 16.8% 39 NOTE: Samples compacted immediately at temps on previous slide
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
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)
FHWA Mobile Asphalt Mixture Testing Laboratory and TFHRC Data
Dynamic Modulus E*Master Curve (from Asphalt Mix Performance Tester)
I-70 Flow Number, Fn, from AMPT689 kPa (100 psi) – Deviator Stress69 kPa (10 psi) – Confining Pressure
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
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
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
Questions, Please Anticipating Warmth in the future