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
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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 Denver
Mountain 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 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
• 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 to
each other to ensure similar site conditions
Project Mixture Details
• Project scope of work:
Mill surface distress 2.5” and fill with 2.5” HMA
Thick 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%) and
WMA 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
Mix
Type
7-24-07
Control
Advera
WMA
54
Mix
Delivery
Temp. (°F)
Mix Temp
At Screed
(°F)
Field
Property
Low Air
Temp. (°F)
Spec
92-96%
Mat
Density
(% Max. Theoret.)
Control
7-26-07
Sasobit
8-13-07
Control
Evotherm
54
50
50
36
36
* 280+
260
* 280+
235
* 280+
243
*
243
*
230
*
235
93.8
93.3
95.7
(single
data point)
93.2
93.7
94.7
* 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
Mix
Type
7-24-07
Lab
Property
Control
Advera
WMA
Control
7-26-07
Sasobit
8-13-07
Control
Evotherm
Results are from the CDOT QA lab – QC results were comparable
Design
6.3%
AC (%)
6.23
6.38
6.41
6.32
6.04
6.38
3.6%
Voids (%)
3.1
1.8
3.0
2.4
3.6
2.2
16.8%
VMA (%)
16.5
15.7
16.5
15.9
16.3
15.8
Stability
36
34
35
36
35
34
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
Mix
Type
7-24-07
Lab
Property
Control
Advera
WMA
Control
7-26-07
Sasobit
8-13-07
Control
Evotherm
TSR Results are from the CDOT QA lab. 80% min. for design, 70% min for production
Hamburg 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
7,800
3,300
5,000
5,700
8,400
6,200
Hamburg
Stripping
Inflection
(cycles)
* 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
M320 Continuous
M320, Table 2
Performance Grade
Performance Grade
Base
59.9 – 30.3
58 – 28
Sasobit
64.2 – 29.2
64 – 22
Aspha-Min
61.1 – 30.9
58 – 28
Advera
60.7 – 30.4
58 - 28
Evotherm
Additive Rate,
by wt of binder
1.5%
4.33%
No Data Obtained Due to Schedule
Dynamic Modulus E*
Master Curve
I-70, Frisco, CO(from Asphalt Mix Performance Tester)
100000
1000
100
Control Mix
Advera
Sasobit
1.E-09
1.E-07
1.E-05
1.E-03
1.E-01
Reduced Time, sec
1.E+01
1.E+03
10
1.E+05
E*, MPa
10000
I-70 Flow Number, Fn, from AMPT
689 kPa (100 psi) – Deviator Stress
69 kPa (10 psi) – Confining Pressure
900
36° C
42° C
48° C
800
Flow Number, cycles
700
600
500
400
300
200
100
0
Control
Advera
Sasobit
Evotherm
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 Monitoring
Results 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
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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