Mix Designs with RAS
Dr. Richard Willis
National Center for Asphalt Technology at Auburn University
Asphalt Shingle Recycling Forum
November 8th, 2013
1
Background
• Mix design
considerations
– Binder
Quantity and quality
– Aggregate
Quantity and quality
– Volumetrics
Air voids
Voids in mineral aggregate
Voids filled with asphalt
Dust
2
Things to Consider
RAP
• 3 – 6 % asphalt binder
• 94 – 97% stone
RAS
•
•
•
•
3
19 – 36% asphalt
2 – 15% fibers
20 – 38% mineral aggregate
8 – 40% mineral filler
What Affects Mix Design and
Mixture Quality?
•
•
•
•
4
Shingle type
Shingle gradation
Shingle quantity
Deleterious materials
Shingle Type
Manufacturer’s Waste
Post-Consumer
• New shingles with less
oxidation
• No contaminants
• No asbestos
• Commonly 20-40 years
old
• Oxidized asphalt
• Nails and other
deleterious materials
• Might contain asbestos
– Must conform to EPA’s
NESHAP and other local
requirements
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Shingle Gradation
• Oversized shingles affect
– Asphalt mobilized
– Mixture consistency
State
Percent Passing
½”
3/8”
Texas
100% 95%
Missouri
-100%
GA/VA/AASHTO 100% -Iowa
100% 98%
Oregon
100% 90%
South Carolina 100% --
#4
---90%
-70.0 – 95.0%
No. 100
-----15% Max
No. 200
-----7% Max
6
Minnesota
90%
--
--
100%
--
Shingle Aggregate Gradation
Sieve Size
3/8 in (9.5 mm)
No. 4 (4.75 mm)
No. 8 (2.36 mm)
No. 16 (1.18 mm)
No. 30 (600 μm)
No. 50 (300 μm)
No. 100 (150 μm)
No. 200 (75 μm)
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% Passing
100
95
85
70
50
45
35
25
• RAS Aggregate must be
accounted for in new
mix design
• AASHTO – Assumes
gradation
• Does it matter if your
RAS has a different
gradation?
RAS Quantity
• Most states use between 3 – 5 percent RAS
• AASHTO Recommendations
– If greater than 30 percent is shingle binder, must
evaluate the blended binder to ensure
performance grade (MP 15-09)
– Possibly effected by grind size
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Deleterious Materials
• Material retained on #4
sieve
• AASHTO
– Total deleterious < 3%
– Lightweight < 1.5%
• Some states < 0.5%
• Cleaner stockpiles =
better mixtures
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Deleterious Materials
• Example specification
(TEX-217-F Part III)
– Oven dry sample
– Sample 1000 g = WT
– Weigh Pan and pour
sample over pan
– Magnet on pan catches
metal pieces in shingle
– Weigh metal pieces = M
Deleterious Materials
•
•
•
•
Sieves Used: 3/8”, No. 4, No. 8, No. 30
Shake sample for 10 minutes
Discard – No. 30 material
Test material retained on each sieve for deleterious
materials (wood, paper, plastic, felt paper)
– Manual separation
• Weigh material removed from RAS for each sieve
– Deleterious materials on 3/8” sieve =N3/8
Deleterious Materials
• P = percent of deleterious matter by weight
• M = weight of material retained by magnet, g
• N# = weight of deleterious substance on sieve,
g
Design Considerations
• How do I determine the specific gravity of the
RAS?
• How much binder is in the RAS?
• How much of that binder am I actually
getting?
13
Shingle Specific Gravity
•
Peregrine et al., 2011
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How Much Binder is in the RAS?
• Chemical extraction vs. Ignition Oven
– Chemical Extraction:
Do I get all of the RAS?
– Ignition oven:
Do I burn off other organic matter?
• AASHTO – Must use chemical extraction
• Virginia – Developed ignition oven correction
factor
15
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Shingle Binder Contribution
Organization
AASHTO
Alabama Department of Transportation
Iowa Department of Transportation
Missouri Department of Transportation
Texas Department of Transportation
Oregon Department of Transportation
How Much RAS Binder Is
Available for Mix?
Shingle Binder Availability
100 of RAS binder
66.7 percent of RAS binder
100 Percent of RAS Binder
100 Percent of RAS Binder
100 Percent of RAS Binder
What’s the truth?
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What Can Affect Binder
Availability?
• Size of RAS
• Where is the RAS
introduced
• Aggregate temperature
18
• Binder temperature
• Mixing time
• Moisture content!
Schroer 2009
AASHTO Methodology
1. Perform volumetric mix design on a mix
which contains all components but RAS
2. Perform a second mix design on a RAS
mixture
1. RAS added at ambient temperature to aggregate
1. Should I heat the RAS overnight at 140F and then
preheat for two hours at mix temp?
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3. Determine the difference between the
optimum asphalt content of virgin and RAS
mixtures, Δ
AASHTO Methodology
4. If Δ is positive, RAS is contributing binder
5. Multiply the percentage of shingle binder in
the RAS by the percent RAS in the mix = total
available binder
6. Divide Δ by total binder available
7. Correct shingle asphalt binder availability
factor
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Limitations of Methodology
• Assumes
– Differences in virgin and RAS mix is only due to
shingle binder and not
Fibers
Aggregate
21
Townsend et al., 2007
Performance Grade
• When using high amounts of reclaimed
binder, do I need to use a softer virgin binder?
• Blending charts
22
Performance Grade
• Challenge:
– How do I determine the Performance Grade?
– Too stiff for water controlled DSRs
– BBRs can be difficult to make
23
Are Volumetrics Enough?
• Rutting
– Flow number
– Hamburg
– Asphalt Pavement Analyzer
• Cracking
24
– Energy ratio
– Semi-circular bend (low and intermediate)
– TSRST or IDT Creep Compliance
– Overlay Tester
– Beam fatigue or S-VECD
Thank you!
NCAT report 13-07: RAS
Characterization: Best Practices
www.ncat.us
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J. Richard Willis
(334) 844-7301
willi59@auburn.edu