#1 wma background and overview
DESCRIPTION
Warm Mix Asphalt training documents provided by the National Center for Asphalt Technology (NCAT) for classes held June 26 & 27, 2013 in California, sponsored by the California Asphalt Pavement Association (CalAPA).TRANSCRIPT
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Overview
Use of WMA in the USA
WMA Categories
Opportunities & Challenges with WMA
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Warm Mix Asphalt WMA definitions
asphalt mix produced with special technologies at temperatures 30 to 70°F lower than typical HMA
Asphalt mix produced at temps below 275 F
Lower temperatures result in…
Less energy to produce asphalt mixes thus reduced cost
Fewer emissions from asphalt plants
Less fumes and odors for paving crew and neighbors
Better workability at lower temperatures
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2003
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WMA Categories
1. Organic Additives
2. Chemical Additives
3. Asphalt Foaming Technologies
a. Foaming additives
b. Water Injection Systems
4. Combinations of above
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WMA Categories 1. Organic Additives
Sasobit (Sasol)
SonneWarmix (Sonneborn)
Rediset (Akzo Nobel) – also contains chemical additives
Bitutech PER (Engineered Additives)
LEADCAP (KICT-KUMHO Petrochemical)
Thiopave (Shell)
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WMA Categories 2. Chemical Additives (Surfactants)
Evotherm (MeadWestvaco)
Cecabase RT (Arkema Group)
HyperTherm/QualiTherm (QPR)
ECOBIT (All States Materials Group)
Revix (Mathy)
Typical dosage rates of 0.2 to 0.5% of the binder
Many of the WMA Chemical Additives provide anti-stripping additive compounds
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WMA Categories 3. Asphalt Foaming Technologies
a. Foaming Additives (Zeolites)
Advera (PQ Corp.)
Aspha-min (Eurovia)
Foaming Additive rates are typically 0.25 to 0.30% by weight of mix
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WMA Categories 3. Asphalt Foaming Technologies
b. Water Injection Systems
Accu-Shear (Stansteel)
AquaBlack (Maxam)
AquaFoam
Double Barrel Green (Astec)
Eco-Foam II (AESCO/MADSEN)
HGrant Warm Mix System (Herman Grant Co.)
Meeker Warm Mix
Terex WMA System
Ultrafoam GX2 (Gencor)
Most water injection foaming systems add 1 to 2% water by weight of binder
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WMA Categories 4. Combinations
Rediset (Akzo Nobel)
Low Emission Asphalt (McConnaughay)
Combined foaming and chemical additives
Mix production temperatures are typically lower than other WMA processes
What are the most popular WMA Technologies?
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Estimated WMA Production
0
5
10
15
20
25
30
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2009 2010 2011
WM
A U
sage
(%
)
State
Other Govt.
Non-Govt.
77.9%
19.6%
2.3% 0.2%
Water-injection foaming
Chemical additive
Foaming additive
Organic additive
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WMA in 2011 (NAPA)
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Economics of WMA
Water-Injection systems cost $30k to $80k.
Assuming $50k cost, 150,000 tons/yr., 5-year depreciation, then foamed WMA cost about 7ȼ/ton.
If only 1/3 of production is WMA, then cost is 21ȼ/ton.
Popular WMA additives are reported to increase cost by $2 - $3/ton of mix.
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Energy Savings with WMA
Fuel savings for WMA is proportional to the temperature reduction.
Most contractors report burner fuel usage decrease of about 10 to 15%.
Savings will range from $0.10 to $0.80 depending on fuel type and temperature decrease.
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Reduced Emissions with WMA
Especially noticeable at load-out
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Better Work Environment
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Improved Compactability
Compaction of asphalt mixtures to specified density criteria is one of the most important aspects of quality construction that affects the long-term performance of the pavement.
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Potential WMA Density Benefit
Some contractors use WMA primarily for a density benefit.
Data from NCHRP 9-47A indicates WMA test sections have only an average density 0.17% higher than companion HMA sections.
In a typical PWL specification, even that small improvement can impact the density pay factor and translate to a benefit of up to $1 per ton.
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Overlaying a Crack Sealed Pavement
Overlaying pavements with joint/crack sealant causes moisture trapped in & beneath sealant to expand
Expansion causes bumps in overlay that do not roll out, results in poor ride and density
WMA has been used to solve this problem
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Better Workability? Most, but not all,
contractors report WMA improves workability
Some also report finish to be better, especially joints.
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Long Haul Distances Haul times with WMA
from 1 to 3 hours reported
Generally successful in achieving target density
Crusting / lumps of mix reported on a few jobs
Some contractors use normal mix temperatures so the WMA technology is just a compaction aid
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Cold Weather Paving Several example projects
using WMA to pave in near freezing temperatures have been reported in trade literature.
Use Multi-cool program to estimate time available for compaction
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Plant Concerns with Initial use of WMA
Lower production temperatures could lead to:
Less efficient burner operation
Incomplete drying of the virgin aggregates
Condensation in the baghouse
Increase amperage on motors
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Lab Tests on WMA Nearly all WMA produced to date have used HMA mix
designs
Lower mix temperatures cause less asphalt adsorption for some aggregates that can change volumetric properties.
Lab tests for rutting and moisture damage potential for WMA commonly yield less favorable results compared to HMA
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Combining WMA and RAP
WMA technologies can improve the ability to properly coat aggregates and RAP during production
Improved workability
Lower production temperatures will reduce plant aging of binders which may allow for increased use of RAP without grade bumping
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Summary of Potential Economic Benefits w/ WMA
Energy savings
Improved density? → higher pay
Improved smoothness? → higher pay
Increased RAP contents?
Longer hauls/extended paving season
Eliminate other mix additives?
Liquid anti-strip agents
Odor scavengers/masking agents
Fibers for drain-down?
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Other Resources www.warmixasphalt.com
NAPA (www.asphaltpavements.org)
Warm Mix Asphalt: Best Practices, 3 rd Ed. (QIP-125)
ncat.us all NCAT reports can be downloaded
FHWA-NHI Webinar
Special Mixture Design Considerations and Methods for Warm-Mix Asphalt
Course Number FHWA-NHI 131137
Free, 2 hours