Warm Mix Asphalt
CEE597 Pavement Construction & QC
Outline
• What WMA does
• WMA technologies
• WMA benefits
• WMA issues
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HMA Mixing & Placement Temperatures
Hot Mix Asphalt
350°F
Standard Mixing Temperature
300°F • Dry aggregate
• Coat aggregate with asphalt
250°F
Standard Placement Temperature
200°F • Lower viscosity
• Good workability
150°F
100°F
50°F
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Basic WMA Premise
Reduce the viscosity of the mix during
production so that complete aggregate
coating can occur at a lower temperature.
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Resulting WMA Benefits
• Reduced plant fuel consumption
• Reduced emissions
– At the plant
– Fugitive emissions
• Reduced viscosity during construction
– Better compaction
– Longer haul distances
– Cold weather paving
• Same viscosity during operation
– Sasobit: greater viscosity at high temps
CEE597 Pavement Construction & QC
Typical Temperatures
Hot Mix Asphalt Warm Mix Asphalt
350°F 350°F
Plant Mixing
300°F 300°F
250°F 250°F
Construction
200°F 200°F
150°F 150°F
100°F 100°F
50°F 50°F
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WMA Technologies
• Plant foaming technologies
– BP WAM-Foam
– ASTEC Double Barrel Green
• Material foaming technologies
– Aspha-min (Hubbard Construction)
– Advera (The PQ Corporation)
– Low energy asphalt (McConnaughey)
• Additives
– Sasobit (Sasol)
– Evotherm (MeadWestvaco)
– Revix (Mathy Construction/Ergon)
– Rediset (Akzo-Nobel)
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WAM Foam
• Kolo Veidekke (Norway)
• 2-stage process
– 1st stage: softer binder
– 2nd stage: harder binder
foamed
• Needs plant modification
• Proprietary
photo from Kolo Veidekke website
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ASTEC Double Barrel Green
See the video:
http://www.astecinc.com/video/green/DB_Green.htm
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Aspha-Min
• Eurovia (France)
• Zeolite
– Minerals that have a
micro-porous structure
– Biggest use: detergent
• Aspha-Min
– Synthetic zeolite
– Crystalline hydrated
aluminum silicates
• 21% moisture in pores
• When heated the water
foams the asphalt
– Moisture lubrication
• Add to mix
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Aspha-min Zeolite
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Advera
• PQ Corporation
• Zeolite
• Advera
– Synthetic zeolite
– Crystalline hydrated
aluminum silicates
• 18-21% moisture in pores
• When heated the water foams
the asphalt
– Moisture lubrication
• Add to mix
– 0.25% by weight of mix
(5 lbs per ton)
Pictures from a presentation by Annette Smith of the PQ Corporation
(http://76.12.53.242/submissions/42_20071227_Annette%20Smith%20-%20Advera.ppt)
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Sasobit
• Sasol International (RSA)
• Fischer-Tropsch wax
– From coal gassification
– Melts at 216-221°F
– Long chain aliphatic carbon
(40-120 carbons)
• Melted sasobit = lubrication
picture from GraniteRock
• Add to binder or mix
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Sasobit: Effect on Binder Viscosity
0.35
1000
0.3
Viscosity at 135 °C [Pas]
Viscosity at 60°C [Pas]
800
0.25
600
0.2
400
200 0.15
Viscosity at 60°C
Viscosity at 135°C
0 0.1
0 1 2 3 4
Fischer - Tropsch Hard Wax in Pen 70/100 [wt.%]
From Prem Naidoo Sasol Wax Presentation
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Evotherm
• MeadWestvaco
• Asphalt emulsion
– Added at 5% of asphalt
content
– It is 85% water and 15%
chemical package
• Capable of very low
mix/compaction
temperatures (140°F)
• Need more
Evotherm/ton of mix
than asphalt binder
because of 70%
emulsion
Pictures from MeadWestvaco website
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WMA Costs
WAM Foam Aspha-min Sasobit Evotherm
Equipment $30,000- $0-$40,000 $0-$40,000 minimal
modification $70,000
Royalties or $15,000 1st yr $0.60/lb $0.80/lb 7-10%
material $5,000/plant/yr more than
$0.30/ton binder
Cost/ton $0.30 * $3.60 $1.30–$2.60 $3.50-$4.00
* Not including installation cost and royalty
Note: the market for WMA is still developing. Producers are still working to
establish their price point. Prices will change and likely go down in the future
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WMA Benefits: Emissions
• Importance depends on environmental situation
• Direct benefit to the producer is necessary
• In USA:
– Economic or regulatory incentives to reduce
emissions exists but is limited
– Plants can generally meet BACT without WMA
• In Iceland:
– Incentive to adopt WMA remains low until emission
limits are lowered
Map from the EPA Green Book Nonattainment Areas for Criteria Polluntants
(http://www.epa.gov/air/oaqps/greenbk/mapnpoll.html)
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Benefits: Energy Consumption
• Importance depends on the type and
cost of energy
• Where fuel is expensive energy savings
could offset WMA cost
– Otherwise, the cost of WMA is greater than
the energy savings
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WMA Savings
Iceland Honolulu, HI Joliet, IL
Fuel source No. 2 Fuel oil Diesel Natural gas
Fuel to make 1 ton
2-3 gallons 2-3 gallons 2.5-3.5 therms
of HMA
Fuel Cost $2.50/gal $2.20-3.20/gal $0.70-0.80/therm
Fuel Cost to make
$5.00-$7.50 $4.40-$9.00 $1.75-$2.80
1 ton of HMA
Electricity to make
8-14 kWh 8-14 kWh 8-14 kWh
1 ton of HMA
Electricity Cost $0.02/kWh $0.1805/kWh $0.0445/kWh
Average energy
$5.15-$7.78 $5.84-$11.53 $2.11-$3.44
cost for 1 ton of HMA
20% savings with WMA $1.00-$1.50 $0.88-$1.80 $0.35-$0.56
50% savings with WMA $2.50-$3.75 $2.20-$4.50 $0.88-$1.40
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Benefits: Lower Viscosity
• Research and marketing has focused on
the environmental benefits
• Cost of compaction risks can far
outweigh WMA costs
• Viscosity reduction may provide the best
business case for WMA
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Benefits: Lower Viscosity
• Improved workability
– A higher quality construction
• More compaction per roller pass
– Fewer roller passes needed
• More workability/compaction for stiff mixes
– More quality for mixes with high RAP content
• Better compaction at lower temperatures
– Cold weather paving
– Increased haul distances
– Extended paving season in cold areas
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Sasobit: Compaction Effects
3.0% addition by weight of binder (1.5% is more common)
160 2,350
150
140 2,285
2,300
130 2,28
Temperature [ °C ]
2,27 2,27
2,26
120 2,250
Density [ g/ cm³ ]
2,23
100 2,200
85
79 78
80 2,15
70
2,150
66
60
60 2,100
40 2,050
20 2,000
1,975
0 1,950
0 1 2 3 4 5 6 7 8
Number of rolling cycles
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Reduced Compaction Temperature
HMA – no Sasobit
WMA – 1.5% Sasobit by weight of binder
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Cold Weather Paving
(37°F and windy)
Maryland SHA: Sasobit + 35% RAP mix
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Maryland SHA: High RAP Sasobit
• 35% RAP by weight of aggregate
• Compaction temperature = 270°F
• Mat characteristics
– Crew reported good workability
– More compaction per roller pass
– 92.6% Rice density with Sasobit
CEE597 Pavement Construction & QC
RAP and Sasobit
Material Costs Other Costs
Unit Cost Tons Cost Unit Cost Tons Cost
Milling Operation Plant Operations
Milling cost $0.00 1.00 $0.00 Energy cost $4.00 1.00 $4.00
Trucking $5.00 1.00 $5.00 Overhead $7.00 1.00 $7.00
RAP cost $5.00 Plant cost $11.00
Virgin Materials Trucking
Virgin aggregate $15.00 0.95 $14.25 Trucking $5.00 1.00 $5.00
Asphalt binder $400.00 0.05 $20.00 Trucking cost $5.00
Virign materials cost $34.25
Placement
Assumptions Crew $5.00 1.00 $5.00
1. Trucking at $80/hr, 1 hr cycle time Equipment $5.00 1.00 $5.00
2. milling cost included in job bid Placement cost $10.00
Total other cost $26.00
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RAP and Sasobit
RAP Virgin Material Other Total
Content Content Costs Costs Cost
0% 100% $34.25 $26.00 $60.25
5% 95% $32.79 $26.00 $58.79
10% 90% $31.33 $26.00 $57.33
15% 85% $29.86 $26.00 $55.86
20% 80% $28.40 $26.00 $54.40
25% 75% $26.94 $26.00 $52.94
30% 70% $25.48 $26.00 $51.48
35% 65% $24.01 $26.00 $50.01
40% 60% $22.55 $26.00 $48.55
45% 55% $21.09 $26.00 $47.09
50% 50% $19.63 $26.00 $45.63
Conclusions:
1. Using RAP with WMA could offer competitive advantage for contractors.
2. By changing the rules, agencies could lower the price of HMA.
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Grace Pacific: Multi-Lift Paving
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Testing and Demonstrations
• 10 years experience
• US and worldwide
• Lift thicknesses
– 1 to 3.5 inches
• Minimum ambient temperature = 37°F
• RAP content
– 0 to 45%
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Risk…
• WMA is a new technology
• Long-term performance?
– Oldest test sections are about 10 years old
– Accelerated pavement testing
• Uncertain use
– Investment in equipment modification,
materials and training
– Commitment?
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Industry Concerns
• Baghouses
• Plant Modifications
• Available Binder Storage Tanks
• Changing Behaviors
• Changing Paving/Compaction Procedures
• Costs
• DOT Acceptance
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DOT Concerns
• Costs
• Testing
• Long-Term Performance
• AASHTO Provisional Standard
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What is Next?
• Determine long-term performance
• Life cycle analysis
• Commitment to use by owner agencies
• Contractor expertise
• Price point from WMA producers