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