Warm Mix Asphalt research and performance
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As Warm Mix Asphalt (WMA) moves into the mainstream, hear the latest research on WMA performance from the respected National Center for Asphalt Technology, which puts various pavement technologies to the test under live traffic on a test track in Alabama.
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Warm Mix Asphalt research and performance
- 2. 2 Outline Use of WMA in the USA WMA Benefits/Challenges NCHRP 9-47A- WMA vs. HMA Projects Evaluated Energy Usage, Emissions Mix Design Engineering Properties Short Term Field Performance Summary of Findings
- 3. 3 Warm Mix Asphalt A process or additive designed to reduce asphalt mix production temperatures by 30 to 70°F and maintain mix workability (non- sanctioned definition) A key part of the asphalt industry’s strategy for Sustainable Pavements Categories: foaming, chemical and organic additives
- 4. WMA Technologies Available in U.S. In 2005: 3 In 2014: +30 6
- 5. 5 Estimated WMA Production NAPA Surveys
- 6. 6 Economics of WMA Water-Injection systems cost $30k to $80k. Assuming $50k cost, 120,000 tons/yr., 5-year depreciation, then foamed WMA cost about 8 /tonȼ If only 1/3 of production is WMA, then cost is 25 /tonȼ Popular WMA additives are reported to increase cost by $2 - $3.5/ton of mix Some costs may be offset by energy savings and other benefits
- 8. 8 WMA Benefits/Challenges Benefits Reduced energy consumption Reduced emissions Extended haul distance Extended construction season Better work environment Challenges Performance vs. HMA Standardize Mix Design
- 9. 9 WMA vs. HMA NCHRP 9-47A
- 10. Location Route WMA Technologies Date Const. St. Louis, MO Hall Street Evotherm ET, Sasobit, Aspha-min May-2006 Iron Mtn., MI M95 Sasobit Sep-2006 Silverthorne, CO I-70 Advera, Sasobit, Evotherm DAT Aug-2007 Franklin, TN SR45 Astec DBG, Advera, Evotherm DAT, Sasobit Oct-2007 Graham, TX US 380 Astec DBG Jun-2008 George, WA I-90 Sasobit Jun-2008 Walla Walla, WA US-12 Maxam Aquablack Apr-2010 Centreville, VA I-66 Astec DBG Jun-2010 Rapid River, MI CR-513 Evotherm 3G, and Advera Jun-2010 Baker, MT Route 322 Evotherm DAT Aug-2010 Munster, IN Calumet Ave. Evotherm, Gencor foam, Heritage wax Sep-2010 Jeff. Co., FL, SR 30 Terex foaming system Oct-2010 Queens, NY Little Neck Pkwy Cecabase, SonneWarmix, BituTech PER Oct-2010 Case Grande, AZ SR 84 Sasobit Dec-2011 NCHRP 9-47A Projects
- 11. WMA &HMA Production Temperatures
- 12. 12 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%. Decreasing mix production temperature by 52°F resulted in an average fuel savings of 21 % (NCHRP 9- 47A)
- 13. 13 Emissions and Worker Exposure with WMA (NCHRP 9-47A) Stack emissions largely result of combusted fuel, reduced fuel should result in reduced CO2 emissions A 52°F reduction in temperature (21% reduction in fuel) in in a 20% reduction in CO2 emissions Worker exposures to respirable fumes during paving were significantly reduced Reduction in application temperature resulted in an average 36% reduction in TOM (total organic matter)
- 14. WMA Mix Design Appendix to AASHTO R35: Perform design with WMA additive or lab foaming device Mixing temp. based on coating, 95% coated, min. Compactability: SGC N92 at comp. temp. and 30°C below the comp. temp., Ratio N92≤ 1.25 Moisture susceptibility-AASHTO T 283, TSR ≥ 0.80 Rutting evaluation; Flow Number: AASHTO TP79, criterion depends on traffic None of the NCHRP 9-47A field projects were designed with the Appendix to AASHTO R35
- 15. 15 WMA Mix Design (NCAT Recommendation NCHRP 9-47 A) Complete volumetric mix design without the WMA technology/additive ( drop in approach) for selecting optimum asphalt content Check coating, compactability, moisture resistance and rutting resistance ( if required) using laboratory produced WMA
- 16. 16 In Place Densities TSR FN Engineering Properties HMA vs. WMA
- 17. In Place Densities (=) After ~2 YearsAfter Construction
- 18. TSR-AASHTO M323 (= or ↓)
- 19. FN Test Results- WMA vs. HMA Statistical Comparison 9 cases FN WMA lower than HMA 5 cases no statistical differences
- 20. 20 FN Criteria HMA&WMA Included in AASHTO TP 79-13 Traffic Level, Million ESALs Minimum FN (HMA) Minimum FN (WMA) <3 NA NA 3 to<10 50 30 10 to <30 190 105 ≥30 740 415
- 21. HMA Flow Number Results Traffic, MESALs Min. Flow No. <3 NA 3 to <10 50 10 to <30 190 > 30 740 Project Route Mix Heating FN Baker, MT Route 322 Reheated 98 Rapid River, MI CR-513 Reheated 199 Casa Grande, AZ SR 84 No 61 Jefferson Co., FL SR 30 No 414 Reheated 231 Queens, NY Little Neck Pkwy No 291 Munster, IN Calumet Ave. No 561 Walla Walla, WA US-12 No 332 Reheated 426 Centreville, VA I-66 Reheated 1855 HMA Fn Criteria
- 22. WMA Flow Number Results Traffic, MESALs Min. Flow No. <3 NA 3 to <10 30 10 to <30 105 > 30 415 Project Route Mix Heating WMA Additive FN Baker, MT Route 322 RH Evotherm DAT 58 Rapid River, MI CR-513 RH Advera 60 RH Evotherm 3G 65 Casa Grande, AZ SR 84 No Sasobit 46 Jefferson Co., FL SR 30 RH Terex Foam 127 No Terex Foam 157 Queens, NY Little Neck Pkwy No Cecabase 115 No SonneWarmix 123 No BituTech PER 128 Munster, IN Calumet Ave. No Evotherm 3G 177 No Gencor Foam 217 No Heritage Wax 314 Walla Walla, WA US-12 No Maxam Aquablack 200 RH Maxam Aquablack 227 Centreville, VA I-66 RH Astec DBG 439 NCHRP 9-43 Mix Design Criteria
- 23. 23 Field Performance of WMA vs. HMA
- 24. 24 Field Performance Evaluation Procedure Three 200-foot sections per mix Three 6” dia. cores from in right wheelpath, and four 6” dia cores from in between wheelpaths Cores used to determine the in-place density indirect tensile strengths, specific gravity, gradation, asphalt content, and the true binder grade for each mix.
- 25. Field Performance-New Projects Project Mix Rutting (mm) Cracking (m) Walla Walla, WA HMA 5 1 Maxam Aquablack 0 0 Centreville, VA HMA 3 1 Astec DBG 3 1 Rapid River, MI HMA 0 0 Evotherm 3G 0 0 Advera 0 0 Baker, MT HMA 1 0 Evotherm DAT 0 0 Munster, IN HMA 0 4 Gencor Foam 0 36 Evotherm 3G 0 0 Heritage Wax 0 0 Jeff. Co., FL, HMA 3 0 Terex Foam 3 0 Queens, NY HMA - 9 Cecabase <1 20 SonneWarmix - 5 BituTech PER - 5 Casagrande, AZ HMA 3 NA Sasobit 0 NA
- 26. 26 Summary Laboratory Performance Statistically equivalent as-constructed densities for WMA mixes compared to the corresponding HMA TSR -82% of mixes passed 0.8 minimum criterion; 6 mixes failed: 4 WMA and 2 HMA. Since all of the field projects performed well; adjusting the TSR criterion on plant mix samples should be considered FN results for WMA mixes lower than HMA ( 2/3 of the comparisons) FN criteria recommended in NCHRP Report 673 for HMA and NCHRP Report 691 for WMA seem appropriate for evaluating plant produced mixes.
- 27. 27 Summary Short Term Field Performance WMA and HMA had no significant difference in rutting No observed moisture damage in any HMA or in WMA section No apparent differences in density between HMA and WMA WMA and HMA cracking after to years- none or low severity and extend No significant differences in surface texture between HMA and WMA
- 28. NCHRP Project 9-47A NCHRP Report 779
Editor's Notes
- Where we are?
- 50000/(5X120,000)
- In summary, a comparative analysis shows that the WMA usage has increased from 2009, when a 5.4% was reported, followed by a 13.2 % in 2010 and a ~ 28% by 2011, which indicates that implementation of WMA has continued to grow. However, since the use of WMA is becoming a conventional practice, monitoring its usage is becoming more challenging. California 10% and 18% (2012)
- Rutting Potential, Moisture Susceptibility
- Evaluate engineering Properties of WMA and HMA Compare production and placement practices between WMA and HMA Comparison of early life field performance WMA-HMA This study has collected mix samples from 14 WMA projects across the USA. All of these projects also had conventional HMA mix that was produced and sampled along with the WMA mixes. At least one WMA technology was used for each project. The goals was to conduct test to determine engineering properties of WMA compare with HMA and to monitor short term performance of these sections. All of the WMA mixes used the “drop-in” approach to mix design, that is, the WMA technology was simply added to an existing approved HMA mix design with no other changes.
- The bottom line is that the amount of energy savings is directly related to the temperature reduction from HMA to WMA. Most well documented studies have shown fuel savings of 10 to 30%
- For laboratory produced mixes, aged for two hours at the observed field compaction temperature, maximum theoretical gravity and calculated binder absorption were generally lower than for field produced mix. In all cases, the binder absorptions of laboratory produced WMA were less than the binder absorptions of laboratory produced HMA. Overall, the optimum asphalt contents for the WMA mixes averaged 0.27 percent less than the HMA. The “drop-in approach” for WMA mix designs has worked well and avoids the potential of designing mixes with lower asphalt contents when using WMA. Therefore, mix designs should be conducted without the WMA technology
- Tensile strength ratio test was conducted in accordance with aashto M 323, Eighty-two percent of the mixes passed the standard 0.8 minimum TSR criterion. The six mixes that failed the criterion included four WMA and two HMA mixes. Since there are no replicates for TSR values, comparison of the WMA and HMA results was made using a paired t-test for all projects. The p-value of the paired t-test was 0.312, which indicates that overall TSR values of the WMA and HMA mixes are not significantly different. Given that warm-mix asphalt may be produced at significantly lower temperatures than hot-mix asphalt (with associated lower aggregate heating temperatures), moisture sensitivity,, should be closely monitored in mix-design and quality control/quality assurance testing.
- Graph summarizes the test results for all project, and it show wide range of resuts from approximately 1850 for the project in Virginia, to as low as 61 for the project in Arizona. It can also be observed that where WMA FN results are consistently lower than HMA FN results (even 36 when no statistical differences were found).