#1 wma background and overview

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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).

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#1 wma background and overview

  1. 1. 1
  2. 2. 2OverviewUse of WMA in the USAWMA CategoriesOpportunities & Challenges with WMA
  3. 3. 3Warm Mix Asphalt WMA definitions asphalt mix produced with special technologies attemperatures 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
  4. 4. 42003
  5. 5. 52012
  6. 6. 6WMA Categories1. Organic Additives2. Chemical Additives3. Asphalt Foaming Technologiesa. Foaming additivesb. Water Injection Systems4. Combinations of above
  7. 7. 7WMA Categories1. Organic Additives Sasobit (Sasol) SonneWarmix (Sonneborn) Rediset (Akzo Nobel) – also contains chemicaladditives Bitutech PER (Engineered Additives) LEADCAP (KICT-KUMHO Petrochemical) Thiopave (Shell)
  8. 8. 8WMA Categories2. 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 binderMany of the WMA Chemical Additives provideanti-stripping additive compounds
  9. 9. 9WMA Categories3. Asphalt Foaming Technologiesa. Foaming Additives (Zeolites) Advera (PQ Corp.) Aspha-min (Eurovia)Foaming Additive rates are typically 0.25 to 0.30% byweight of mix
  10. 10. 10WMA Categories3. Asphalt Foaming Technologiesb. 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 waterinjection foamingsystems add 1 to 2%water by weight ofbinder
  11. 11. 11WMA Categories4. Combinations Rediset (Akzo Nobel) Low Emission Asphalt (McConnaughay) Combined foaming and chemical additives Mix production temperatures are typicallylower than other WMA processesWhat are the most popularWMA Technologies?
  12. 12. 12Estimated WMA Production051015202530352009 2010 2011WMAUsage(%)StateOther Govt.Non-Govt.77.9%19.6%2.3% 0.2%Water-injection foamingChemical additiveFoaming additiveOrganic additive
  13. 13. 13WMA in 2011 (NAPA)
  14. 14. 14Economics of WMA Water-Injection systems cost $30k to$80k. Assuming $50k cost, 150,000 tons/yr.,5-year depreciation, then foamedWMA cost about 7ȼ/ton. If only 1/3 of production is WMA,then cost is 21ȼ/ton. Popular WMA additives are reported toincrease cost by $2 - $3/ton of mix.
  15. 15. 15Energy Savings with WMA Fuel savings for WMA isproportional to the temperaturereduction. Most contractors report burnerfuel usage decrease of about 10to 15%. Savings will range from $0.10 to$0.80 depending on fuel typeand temperature decrease.
  16. 16. 16Reduced Emissions with WMA Especially noticeable at load-out
  17. 17. 17Better Work Environment
  18. 18. 18Improved Compactability Compaction of asphaltmixtures to specifieddensity criteria is one of themost important aspects ofquality construction thataffects the long-termperformance of thepavement.
  19. 19. 19Potential WMA Density Benefit Some contractors use WMA primarily for a densitybenefit. Data from NCHRP 9-47A indicates WMA test sectionshave only an average density 0.17% higher thancompanion HMA sections. In a typical PWL specification, even that smallimprovement can impact the density pay factor andtranslate to a benefit of up to $1 per ton.
  20. 20. 20Overlaying a Crack Sealed Pavement Overlaying pavementswith joint/crack sealantcauses moisture trapped in& beneath sealant toexpand Expansion causes bumps inoverlay that do not rollout, results in poor rideand density WMA has been used tosolve this problem
  21. 21. 21Better Workability? Most, but not all,contractors reportWMA improvesworkability Some also report finishto be better, especiallyjoints.
  22. 22. 22Long Haul Distances Haul times with WMAfrom 1 to 3 hours reported Generally successful inachieving target density Crusting / lumps of mixreported on a few jobs Some contractors usenormal mix temperaturesso the WMA technology isjust a compaction aid
  23. 23. 23Cold Weather Paving Several example projectsusing WMA to pave in nearfreezing temperatureshave been reported intrade literature. Use Multi-cool program toestimate time available forcompaction
  24. 24. 24Plant 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 motors24
  25. 25. 25Lab Tests on WMA Nearly all WMA produced to date have used HMA mixdesigns Lower mix temperatures cause less asphalt adsorptionfor some aggregates that can change volumetricproperties. Lab tests for rutting and moisture damage potential forWMA commonly yield less favorable results comparedto HMA
  26. 26. 26Combining WMA and RAP WMA technologies canimprove the ability toproperly coat aggregatesand RAP during production Improved workability Lower productiontemperatures will reduceplant aging of binderswhich may allow forincreased use of RAPwithout grade bumping26
  27. 27. 27Summary of PotentialEconomic 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?
  28. 28. 28Other 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 andMethods for Warm-Mix Asphalt Course Number FHWA-NHI 131137 Free, 2 hours

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