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Warm Mix Asphalt (WMA) Update

Thomas Bennert, Ph.D. Research Professor

Rutgers University Center for Advanced Infrastructure

and Transportation (CAIT)

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Presentation Outline

National Perspective New Jersey Perspective Moving Forward – Other Uses

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WMA Benefits

Reduced Emissions and Fumes Reduced Energy Consumption Improved Workability Extending Paving Window Cold Weather Paving Compaction Aid/Improve Compaction Quality

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WMA Technologies

In 2005

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WMA Technologies

At the end of 2012

+

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Technologies Currently Marketed in U.S. Material Processing (LEA) Organic Additives (Waxes, Zeolite) Chemical Additives (Surfactants) Foam Processing (Water Injection, Zeolite) Hybrid Systems (Water+Surfactant)

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Information on Technologies

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More Information WMA Best Practices,

3rd Edition Technologies Stockpile Handling Burner Adjustments Aggregate

Drying/Baghouse Temps

Drum Slope/Flighting RAP Usage Placement Changes

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NATIONAL PERSPECTIVE

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Researching WMA on National Level - NCHRP

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NCHRP Project 9-43 Appendix to AASHTO R35

to conducting WMA specific mixture design Requires designing the WMA,

with RAP and WMA technology, at anticipated temperatures

Uses Superpave guidelines Includes performance testing,

coating and workability evaluation

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NCHRP Project 9-47A

Evaluated 14 in-place and newly constructed WMA projects – all having companion HMA Various technologies Evaluated loose mix performance Field density Field performance (limited to the time frame of the

project < 5 years)

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Fuel Savings Comparative fuel usage reported for 15 projects

representing six WMA technologies Theoretical calculations indicate a 50°F reduction in

production temperature should result in an 11% reduction in fuel usage

Observed savings ranged from a 15.4% increase to 77% reduction, with an average savings of 24%

Heat losses and other inefficiencies believed to account for increased savings over theoretical calculations

Energy can also be conserved by simply using dryer aggregates!

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Preliminary Data from NCHRP 9-47A

Project Technology Average Production

Temp. F

Average Fuel

Usage, DTH/ton

Reduction, %

Walla Walla, WA

HMA 325 0.278 NA AQUABlack Foam 285 0.218 21.6

Rapid River, MI HMA 300 0.271 NA Advera 269 0.187 31.0 Evotherm 3G 269 0.225 17.0

Baker, MT HMA 298 0.157 NA Evotherm DAT 252 0.137 12.7

Griffith, IN HMA 300 0.226 NA Ultrafoam GX2 277 0.209 7.5 Evotherm DAT 256 0.212 6.2 Wax 268 0.201 11.1

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NCHRP 9-47A – Lab Findings

Same in-place densities as HMA Lab rutting higher for WMA than HMA TSR’s – 40% of time lower, rest the same Lab stiffness lower for WMA than HMA Lab fatigue resistance better for WMA than HMA Slightly better resistance to low temperature

cracking for WMA in lab

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NCHRP 9-47A – Field Findings Projects 2.5 to 5.5 Years Old (3 200 ft sections) All sections showed some distress No cracking in 1 or 5 projects Max crack length 1310 ft (St. Louis) – Zeolite Max rutting of 6 mm (0.24 inches)

Projects < 1 Year old (3 200 ft sections) No cracking in 5 of 6 projects No rutting in 3 of 6 projects Max crack length of 14 ft Max rutting of 2.5 mm (0.1 inches)

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NCHRP 9-47A – Mix Design

All field projects evaluated used a “drop in” method for WMA

Project also looked at AASHTO Appendix to R35 Average optimum AC% decreased almost 0.3%

for WMA compare to HMA Lower rutting resistance for lab-produced material

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NCHRP 9-47A - Summary Continue to use “drop in” procedure Reduction in AC% is resultant of extra

compactability due to WMA - tricking gyratory Superpave mixes dry enough already

Field showed excellent rutting resistance although lab testing does pick up initial differences Do these differences quickly disappear with in-

service life?

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National Perspective

On-going research building on these findings Moisture Damage Established Long Term WMA Pavement

Performance sections Short-term aging in plants Long-term aging in the field

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NJDOT PERSPECTIVE

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NJDOT Perspective Conducting both laboratory research and pilot

program evaluation Laboratory Research Polymer Degradation Appendix R35 for NJ mixes General rutting and fatigue cracking performance

Pilot Program Plant produced WMA and companion HMA Rutting, fatigue, stiffness, and moisture damage

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Polymer Degradation?

Drop in molecular weight represents a degradation in polymer

WMAT 1 Polymer Peak Binder Peak

Mn Mw Mn Mw

Original 2 2 2 2

RTFO at 133°C 2 2 2 2

RTFO at 163°C 2 2 2 2

WMAT 2 Polymer Peak Binder Peak Mn Mw Mn Mw

Original 2 2 2 2

RTFO at 133°C 2 2 2 2

RTFO at 163°C 2 2 2 2

PG 76-22

(Control)

Polymer Peak Binder Peak

Mn Mw Mn Mw

Original 2 2 2 2

RTFO at 133°C 2 2 2 2

RTFO at 163°C 2 2 2 2

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Molecular Weight Polymer Peaks

Drop in molecular weight represents a degradation in possible polymer

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Molecular Weight Results

All binders showed a reduction in Molecular Weight going from 133C to 163C (current RTFO standard) conditioning 42% for Evotherm 13% for Sasobit 29% for normal 76-22

Evidence that reduced production temperatures may help in reducing polymer degradation

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NJDOT – Appendix to R35

Looked at NJDOT Approved JMF’s @ 2 RAP contents Normal (315F mixing) Advera, Sasobit, Evotherm (275F mixing) 0 and 25% RAP contents

Determined Optimum asphalt content Rutting resistance, fatigue resistance, and TSR

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NJDOT - Appendix R35

For virgin mixes, an average 0.45% reduction in optimum AC% was found Function of extra “lubricity” in the mixture due to

the WMA technology For 25% RAP mixes, no change was found Does this mean the 25% RAP mixes were under-

asphalted if same level of “lubricity” occurred in both mixes?

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How to Ensure Not Under-Asphalted in Field

Allow mix to cool, or condition, at expected and slightly lower compaction temperatures Example: Sampled from back of truck at 280oF,

allow to cool to 265 to 260oF prior to gyratory compaction

Reduce low end of allowable air voids to 2.5% (currently 3 to 5% during production) Specify no adjustment (taking out AC%) to

increase compacted air voids

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NJDOT Appendix to R35

Mixture Performance - Rutting Rutting resistance in similar for WMA mixtures –

HMA mixtures higher All WMA mixtures achieved higher Flow Number than minimum required for respective traffic level <3 N.A.

3 to < 10 3010 to < 30 105

≥ 30 415

Minimum Flow Number

Traffic Level, Million ESAL's

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NJDOT Appendix to R35

Mixture Performance – Fatigue Cracking When using WMA, all fatigue cracking results

improved 0% RAP at HMA temperatures were found to be

statistically equal to 25% RAP at WMA temperatures Based on optimum AC% found during mixture design 25% RAP WMA were approximately 0.5% higher in asphalt

content

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NJDOT Appendix to R35

Mixture Performance – Moisture Damage (T283) Moisture Damage Resistance: TSR values were all found to meet the minimum 80%

requirements 2 just under but would meet requirements when considering

repeatability of test Tensile strengths lower for WMA mixtures

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NJDOT WMA Specification (Pilot)

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NJDOT Pilot Projects

Seven (7) WMA projects were evaluated from 2012 paving season – 4 Evotherm, 4 Foamed Rt 40 – 9.5M64 Rt 130 – 12.5M64 I295 – 12.5M76 Rt 184 – 12.5M64 (3 sections) (WMA-SMA) - Fiberless (WMA-SMA) (WMA-SMA) - Fiberless

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Summary of NJDOT WMA Pilot Studies Moisture Damage (T283) All projects had passing TSR values except 1 – both

HMA and WMA failed HMA = 74.5%; WMA = 42.4%

Rutting Resistance (Flow Number) HMA has shown higher rutting resistance, but similar

to NCHRP study, WMA mixtures met the minimum Flow Number per traffic level

Fatigue Resistance (Overlay Tester) All WMA except 1 project had superior Overlay

Tester results Was same project as failed TSR

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MOVING FORWARD – OTHER USES FOR WMA

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Emissions Reduction Looked at quantifying

emissions reduction at paver with and without WMA

Used portable emissions tester mounted to railing on back of paver (where workers would stand)

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Example of Typical Emissions at Paver (AR-OGFC on I-78)

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Rapid River, MI Evotherm™ 3G

Advera™ WMA

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Rapid River, MI Stack Emissions - % Reduction

Emission Advera™ WMA

Evotherm 3G

Condensables, lb/hr

83 67

CO2, % 11 6 CO, lb/ton 49 53 SO2, lb/ton 57 58 NOx, lb/ton 11 1 VOC, lb/ton 47 45

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THIN LIFT PAVEMENTS – PREVENTATIVE MAINTENANCE

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General Thin-Lift HMA Cooling (MultiCool 3.0)

100

125

150

175

200

225

250

275

300

325

0 5 10 15 20 25 30Time After Placement (minutes)

Tem

pera

ture

(F)

1-Inch Thick

2-Inch ThickAir and Pavement Temperature = 45F

8 minutes 25 minutes

Placed Immediately Over PCC

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REDUCTION OF CRACK/JOINT SEALANT SWELLING

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Paving Over Crack/Joint Sealants Due to high

temperatures associated with HMA, crack/joint sealants generally soften and swell causing bumps in pavement

Reducing temperatures below softening point can elevate problem.

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Paving over Crack Sealant

West Bend Airport – WMA with 20% RAP Photos c/o Payne and Dolan

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ELIMINATING FIBERS FROM SMA & OGFC MIXTURES

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Removing Fibers in WMA

Addition of fibers required to resist draindown of asphalt binder in gap-graded mixes

Complaints regarding handling issues and proper distribution of fibers in the mix

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Draindown Test (AASHTO T305)

1200 + 200 g 60 + 5 minutes Temperatures Plant 15 °C (27 °F) above

Criteria – max. 0.30%

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Draindown Laboratory Evaluation

325F with Fibers = 0.08% Draindown

325F without Fibers = 0.19% Draindown

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Draindown Laboratory Evaluation

290F without Fibers = 0.08% Draindown

255F without Fibers = 0.06% Draindown

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Draindown Results

Mixing TestingNormal SMA 325 325 0.08

WMA SMA #1 (No Fibers) 325 325 0.19WMA SMA #2 (No Fibers) 290 290 0.08WMA SMA #3 (No Fibers) 255 255 0.06

Mixture ID Percent Draindown

Temperature (F)

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WMA to Eliminate Fibers

WMA technology used to reduce temperatures and achieve density Reduction of production temperature increases

viscosity of binder Increased viscosity adheres to aggregate better

resulting in lower draindown

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Summary Enough national and regional research to indicate

WMA can perform as well as HMA Laboratory testing able to pick up differences but do

how long do these differences exist Continue to monitor sections in NJ

NCHRP 9-47A and NJDOT research indicates no need to have specific WMA mix design procedure Continue with “drop in” procedure

WMA also has potential to help with other specific needs in NJ Thin-lift mixes, eliminating fibers in SMA, reducing

emissions/odors of asphalt rubber mixtures

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Thank you for your time!

Thomas Bennert, Rutgers U. bennert@rci.rutgers.edu