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.
Risk Management in Engineering Construction Project
Warm Mix Asphalt research and performance
1.
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
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
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
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
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
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
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).