Warm Mix for a Cold Climate
Update on Colorado DOT’s2007 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• Climate
35”+ 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• Traffic
30,000 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
Advera-WMA and Sasobit blown in here
Evotherm injected into AC feed line 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
Mix Type
FieldProperty Control
7-24-07AdveraWMA Control
7-26-07Sasobit Control
8-13-07Evotherm
Low AirTemp. (°F)
54 54 50 50 36 36
MixDelivery
Temp. (°F)* 280+ 260 * 280+ 235 * 280+ 243
Mix TempAt Screed
(°F)* 243 * 230 * 235
MatDensity
(% Max. Theoret.)
93.8 93.3 95.7(single
data point)
93.2 93.7 94.7
All values are averages of multiple tests except as noted
* 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
Spec
92-96%
Construction Highlights – Lab Data Mix
Type
LabProperty
Control
7-24-07AdveraWMA Control
7-26-07Sasobit Control
8-13-07Evotherm
Results are from the CDOT QA lab – QC results were comparable
AC (%) 6.23 6.38 6.41 6.32 6.04 6.38
Voids (%) 3.1 1.8 3.0 2.4 3.6 2.2
VMA (%) 16.5 15.7 16.5 15.9 16.3 15.8
Stability 36 34 35 36 35 34
NOTE: Samples compacted immediately at temps on previous slide
Design
6.3%
3.6%
16.8%
39
Interpreting Hamburg Data
NOTE: CDOT does not typically run Hamburg on 75 Gyration mixtures
Failure due to plastic flow is typical below the 100 gyration level
Failure if more than 4mm in 10,000 cycles
Construction Highlights – TSR and Hamburg Data Mix
Type
LabProperty Control
7-24-07AdveraWMA Control
7-26-07Sasobit Control
8-13-07Evotherm
TSR Results are from the CDOT QA lab. 80% min. for design, 70% min for productionHamburg Results from CDOT Euro Lab. Max rut 4mm in 10,000 cycles for production
TSR (%) 100 83 *97 111 94 80
Hamburg(mm rut)
9.0 9.5 16.0 10.0 10.0 13.5
Hamburg(cycles)
9,700 5,100 7,650 9,400 9,650 7,750
HamburgStrippingInflection(cycles)
7,800 3,300 5,000 5,700 8,400 6,200
* 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)
M320 ContinuousPerformance Grade
M320, Table 2Performance Grade
Additive Rate, by wt of binder
Base 59.9 – 30.359.9 – 30.3 58 – 2858 – 28
Sasobit 64.2 – 29.264.2 – 29.2 64 – 2264 – 22 1.5%
Aspha-Min 61.1 – 30.961.1 – 30.9 58 – 2858 – 28
Advera 60.7 – 30.460.7 – 30.4 58 - 2858 - 28 4.33%
Evotherm No Data Obtained Due to ScheduleNo Data Obtained Due to Schedule
FHWA Mobile Asphalt Mixture
Testing Laboratory and TFHRC Data
I-70, Frisco, CO
10
100
1000
10000
100000
1.E-09 1.E-07 1.E-05 1.E-03 1.E-01 1.E+01 1.E+03 1.E+05
Reduced Time, sec
E*,
MP
a
Control MixAdveraSasobit
Dynamic Modulus E*Master Curve
(from Asphalt Mix Performance Tester)
0
100
200
300
400
500
600
700
800
900
Control Advera Sasobit Evotherm
Flo
w N
um
ber
, cy
cles
36° C 42° C 48° C
I-70 Flow Number, Fn, from AMPT 689 kPa (100 psi) – Deviator Stress
69 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