scapa warm mix asphalt best practices 2016
TRANSCRIPT
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Engineering Properties, Emissions
and Performance of Warm Mix
Asphalt Technologies and Best
Practices
SCAPA Winter Conference 2016
Brian D. Prowell, Ph.D., P.E.
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2003 NCAT Study
Objectives • Evaluate Warm Asphalt Technologies
for U.S. Paving Practices
– High production
– Rapid Turn-over to traffic
• Potential Concerns
– “Curing” Time
– Increased Potential for Moisture Damage
– Binder effects
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Seeing is Believing!
First U.S. WMA Test Section
February 2004 Hot Mix 314 F Warm Mix 254 F
138.1 pcf 138.5 pcf
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Benefits of WMA
• Paving Benefits
– Compaction aid
– Cold-weather paving
– Longer haul distances
– Use of higher percentages of RAP
– Less restriction, potentially more production in
non-attainment areas
– Specific pavement rehabilitations
• Reduced Fuel Usage
• Reduced Emissions
• Improved Working Conditions
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NCHRP 9-47A Sites
Dry Freeze
Wet No Freeze Dry No Freeze
Wet Freeze
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Mix Design
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WMA Mix Design
AASHTO Appendix to R30:
• Perform design with WMA
additive or lab foaming
device
• Mixing temp. based on
coating
• Compaction temp based
on gyrations to 92% Gmm
• Rutting evaluation
None of the NCHRP 9-47A field projects were designed
with the Appendix to R30
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Research Plan
• To compare results with field results,
samples batched to match average of
field extracted gradation for
mix/technology
• Determine optimum asphalt content
• Evaluate coating and compactability at
laboratory optimum AC%
• Evaluate TSR and FN (lab opt. AC%)
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Making Foamed Asphalt in the Lab
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Binder Absorption
• Binder absorption observed to be less
for WMA vs. HMA for early TX project.
• Percent binder absorption calculated
knowing Gmm, AC%, Gb, and Gsb.
• Comparisons:
– WMA to HMA
– Lab to Field
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Loop 368 One-Year Cores
Warm Mix
Hot Mix
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Binder Absorption WMA - HMA
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
Pe
rce
nt
Bin
de
r A
bso
rpti
on
Dif
fere
nce
(W
MA
-H
MA
), %
Field
Lab Ver.
Field Avg. -0.11%; Lab Avg. -0.17%
Asphalt absorption similar after 1-2 years
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The Last Great Quandary: Selecting
Production Temperatures
• In many cases HMA produced too hot
– Excessive temperatures age/stiffen binder,
making compaction more difficult
• Many WMA suppliers wish to minimize
temperatures to maximize fuel savings and
offset cost of additives
• Some Agencies specify maximum
temperatures for “warm mix” regardless of
other production considerations
• RAP and RAS?
SC-M-408 specifies 220 – 285 °F
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Production Temperatures
AASHTO Appendix R30
• Based on Ross Count coating test after
90 seconds mixing with planetary mixer
• NCHRP 9-43 research completed with
planetary mixer
• Concern more common bucket mixer
may not provide adequate mixing or
may need different time.
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Ross Count
94.0
95.0
96.0
97.0
98.0
99.0
100.0
101.0
Co
atin
g, %
Field
Lab
Foaming processes resulted in slightly less coating. Can coat with bucket mixer
WMA 90 seconds
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SGC Compactability Ratio
• Compactability Ratio used to assess
proposed WMA compaction
temperatures
• Ratio of number of gyrations to 92%
Gmm at 30°C (54°F) below production
to proposed compaction temperature
• Supposed to be less than 1.25
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SGC Compactability Ratio –
Compaction Temperature
88.0
89.0
90.0
91.0
92.0
93.0
94.0
95.0
96.0
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75
In-p
lace
De
nsi
ty, %
of
Gm
m
SGC Compactability Ratio
Opt. AC% Draft AASHTO R35
Field AC%
0.74% decrease in AC%
0.90% decrease in AC%
0.39% increase in AC%
0.17% increase in AC%Sample tested at 250F,Field production avg. 273F
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Tensile Strength Ratio
0
0.2
0.4
0.6
0.8
1
1.2
TSR
Field
Lab
Mix verification from both MI and FL resulted in lower Opt. AC%
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WMA vs HMA Tensile Strength
2-2.5 year cores
0
2
4
6
8
10
12
Same Lower Higher
11
1
1
Nu
mb
er o
f C
om
par
iso
ns
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WMA vs HMA Tensile Strength
> 3 year cores
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Summary • Binder absorption less for WMA,
approx. 0.10% field; 0.16% lab. Binder
absorption the same after 1-2 years
• Recovered binder from cores not
different after 1-2 years
• Rutting performance similar
• NCHRP 9-47A recommends “drop-in”
approach for WMA where WMA
technologies are used with existing
HMA designs
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Field Performance
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23
Hall Street St. Louis, MO
Test Section
Field Rut Depth, mm
6 Months 26 Months 66 Months
Control 0.4 0.5 1.2
Evotherm™ 1.1 1.1 2.0
Sasobit® 0.8 0.8 0.5
Aspha-min® 0.3 0.5 1.7
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Layer(s) Prediction
Interval,
years
Mix Mean
Rut
Depth,
mm
Variance t-test p-
value
Sub-Total all
Asphalt
Layers
12 HMA 4.84 15.0 0.08
WMA 5.03 15.6
20 HMA 6.96 22.4 0.06
WMA 7.23 23.2
Experimental
(Surface)
Layer
12 HMA 1.65 0.36 0.16
WMA 1.80 0.67
20 HMA 2.22 0.65 0.14
WMA 2.45 1.31
MEPDG Predicted Rutting
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Summary of Observed and
Predicted Field Performance • No difference in opening times for WMA
vs. HMA
• Rutting
– < 5 mm of rutting for all sections after 2 years
– MEPDG predicts slightly more (0.2 mm) rutting
over life
– WMA performed well at accelerated loading
facilities
– Appears to be discrepancy between laboratory
predicted and observed field rutting
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Summary of Observed and
Predicted Field Performance • No evidence of moisture damage in field
projects, including saturated CA HVS
sections
• Cracking
– Very little observed after 2 years; similar for
WMA and HMA
– MEPDG predicts slightly more cracking for
HMA
– Where Level 1 data used, MEPDG predicts
less thermal cracking
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= +
+
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Fuel Savings
• Theoretical calculations indicate a 50°F reduction in production temperature should result in an 11% reduction in fuel usage
• Actual savings average 13% for average reduction of 50°F
• Based on preliminary analyses, savings distributed as:
– 14% from reduction in stack temperature
– 51% from reduction in mix temperature
– 37% from reduction in casing loss
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Best Practice: Reduce
Stockpile Moisture • Saves fuel – 2%
decrease = savings
of 0.48 gal/ton
• Drier aggregate in =
drier aggregate out,
reducing potential
for moisture damage
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Best Practice Benefit
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
Stockpile Moisture, % liters per ton of Diesel
2% Reduction in stockpile moisture
saves 0.58 gal. diesel per ton
Based on field data from fives sites.
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Reduced Emissions
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-30
-20
-10
0
10
20
30
40
50
60
70
-30 -20 -10 0 10 20 30 40 50 60 70
Re
du
ctio
n in
CO
2Em
issi
on
, %
Reduction in Fuel Usage, %
Fuel Usage Vs. CO2
Literature
NCHRP 9-47ALine of Equality
WMA D
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Reduced Emissions
NCHRP 9-47A data indicate:
• Reduced fuel usage = reduced CO2
• With one exception, NOx emissions
from WMA were lower than for HMA
• VOC’s significantly lower for parallel-
flow drum plant
• 50% reduction in SO2 with recycled oil
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Best Practice: Burner Tuning
• Elevated levels of CO and VOCs can
indicate incomplete combustion
• Stack emissions data indicate examples
of improperly tuned burners
• 32% fuel saving for HMA production at
one plant after tuning for WMA project!
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Worker Exposure • NIOSH uses Benzene Soluble Matter (BSM)
to measure worker exposure to asphalt
emissions
• In many cases, results for BSM below
detectable limits for both HMA and WMA –
hard to quantify benefits
• For NCHRP 9-47A, Heritage Research Group
used a more discriminative test for Total
Organic Matter
• Tests on 6 WMA and 2 HMA at 2 sites
showed WMA reduced exposure by 33 to
61%
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Summary • Warm Mix technologies most frequently used
as compaction aids and to improve coating
– Stiff mixes with polymer modified binders or higher
recycle content
– Longer hauls/cooler weather
– Can combine chemical and foaming technologies
• Warm mix technologies are a component of
asphalt’s sustainability
– Reduced fuel usage = reduced emissions
– Better for workers
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Contact Information:
Brian Prowell
Advanced Materials Services, LLC
(334) 246-4428
WWW.AdvancedMaterialsServices.com