Transcript Warm Mix in a Cold Climate

Warm Mix for a Cold Climate
Colorado DOT’s
2007 WMA Project
CDOT WMA Background
• CDOT interested in assessing WMA
– Proper compaction achieved at other WMA trials
– Concerns about moisture susceptibility of mix
• WMA test sections installed to assess
performance in extreme mountain conditions
– Cold nighttime temperatures in our mountains
• Night Construction mandated when restricted
to one through-lane on I-70 west
CDOT WMA Site Information
• Project Location:
– I-70, 70 miles west of Denver
– Mountain terrain – elev. 8,800’ to 11,100’
CDOT WMA Site Information (2)
• Increasing Congestion in I-70 West Corridor
Critical to Industry and Tourism
CDOT WMA Project Summary
• Traffic
30,000 AADT, 10% trucks, 4.85M ESALS (10-yr.)
• Extreme winter conditions (truck chain area)
CDOT WMA Project Summary
• Climate
35”+ annual precipitation
over 200” annual snowfall
150 - 200 freeze/thaw cycles per year
• Cool summer conditions (construction)
July – at lowest elevation on the project
Winds avg. 8-21mph
CDOT WMA Project Summary
West Portal of Eisenhower-Johnson Memorial Tunnel on I-70
WMA Job ended here and began down in Silverthorne
Project Mixture Details
• Project scope of work:
– Mill surface distress 2.5” and fill with 2.5” HMA
– Thick existing pavement
• 12”+ HMA over R75 fill
• Superpave dense graded mix specified
– ½-inch nominal max (Colorado 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
– Fine graded mix design by Everist Materials
– Production targets
Voids = 3.6% (+/-1.2%)
VMA = 16.8% (+/-1.2%)
%AC = 6.3% (+/-0.3%)
• Acceptance testing also included Stability & TSR
Min. Stability allowed = 28, Min. TSR = 70%
WMA Summary
• SAME mix design for WMA from HMA
• CDOT spec based on NCAT’s WMA protocol
• 3 additives –
– Advera WMA
– Sasobit
– Evotherm DAT
• ~1000 tons each, ~1 mile for each section
WMA Summary
• 3 lanes each direction
– WMA in middle lane
• WMA sections placed nearly adjacent to
each other to ensure similar site conditions
• Testing by QC, CDOT, FHWA
• Data collection by NCAT per WMA protocol
– production and placement equipment, weather
conditions, compaction temps, etc.
Construction Highlights
• WMA pre-paving meeting was critical
– final additive placement order (who goes first!)
– I.D. key personnel – lots of visitors
– Safety precautions on site
– Test section paving hours each night
– Sampling/transport/testing plan
– Plant production details
Construction Highlights
• WMA produced at 250 °F, HMA at 280 °F
– Same for lab testing temperatures
• Same roller configuration used for all 4 mixes
Advera-WMA feed system Similar to Sasobit feed system
- blown in like SMA fibers
Evotherm DAT injected into
AC feed line here
Advera WMA and Sasobit
blown in here
Same haul, placement and compaction equipment
used for WMA as for HMA sections
WMA ~240°F behind the paver – no fumes
Construction Highlights
Mix Type
Control
7-24-07
Control
Advera
WMA
Property
7-26-07
Sasobit
Control
8-13-07
Evotherm
Results are from the CDOT QA lab – QC results were comparable
FHWA’s mix flow number, dynamic modulus and binder test data are pending.
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
Mat
Density
(% Rice)
~94
~94
~94
~94
~94
~94
TSR (%)
100
83
*97
111
94
80
Stability
36
34
35
36
35
34
9.46
9.79
17.31
10.49
10.10
14.86
Hamburg
(mm rut)
* Average of other control mix tested on the job.
Regardless of Hamburg Rut Depth, Moisture damage more prevalent in
the WMA samples than the control samples – see following pictures
Hamburg Advera WMA
CDOT Hamburg History:
75 gyration mixtures
typically fail Hamburg, but
fail primarily due to plastic
flow rutting rather than
stripping/moisture damage
CONTROL
ADVERA
Hamburg Sasobit
CONTROL
SASOBIT
Hamburg Evotherm DAT
CONTROL
EVOTHERM
DAT
WMA Monitoring
• NCAT under contract for WMA project support
– Field data collection during construction
– Long term tracking (3+ years)
– Interim and final reports
• Due to harsh site conditions, we anticipate
useful performance data within 3 years
Conclusions
•
•
•
•
WMA decreased voids in lab compaction
WMA field compaction comparable at lower temps
Hamburg moisture damage visibly more in WMA
Early WMA performance equal to HMA on the job
– No rutting, no early distresses
• Confident that WMA facilitates cold temp. placement
• Will use more WMA in this corridor if performance is
comparable to HMA
Questions, Please