RAS Research Update
Dr. Richard Willis
National Center for Asphalt Technology at Auburn University
March 11, 2014
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
5
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)
7
% 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
8
Deleterious Materials
• Material retained on #4
sieve
• AASHTO
– Total deleterious < 3%
– Lightweight < 1.5%
• Some states < 0.5%
• Cleaner stockpiles =
better mixtures
9
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
14
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
16
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?
17
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?
19
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
20
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
Research Plan Outline
• Phase I
– Volumetrics of 5% RAS Mixture & Temperature
Study
• Phase II
– Volumetrics of Alternate RAS Breakdown Mixtures
– Investigation of results and additional testing
• Phase III
– Performance testing of all mixtures
Phase I
• Lab mixed lab compacted 5% RAS Mixture
– Based on Lee County Road Section 24
– Volumetric samples mixed at:
350°F, 325°F, 300°F, 275°F, 250°F, & 225°F
– Aged and conditioned at 25 °F below mixing
temperature
Aggregate Stockpile
Calera Limestone 820s
Shorter Sand
EAP Baghouse Fines
Hydrated Lime
Oxford PCRAS
Blend Percentages
L-24
5% RAS
64%
63%
30%
30%
0%
1%
1%
1%
5%
5%
Phase I - Results
Effects of Mixing Temp. on Volumetrics of 5% RAS Mixture
%Gmm of Samples
98%
97%
96%
95%
y = 0.0002x + 0.9133
R² = 0.593
94%
225
250
275
300
Mixing Temperature (°F)
325
350
Phase II
• Volumetrics of Alternate RAS Breakdown
Mixtures
– 5% RAS equivalent recovered shingle aggregate
– 5% RAS equivalent recovered shingle binder
– Control mixture matched to Lee County Road
159 Section 19 (L-19)
Phase II – 5% RAS Aggregate
• Mix design equivalent to original 5% RAS
design BUT uses recovered shingle aggregate
and fibers instead of whole shingles
Phase II – 5% RAS Binder
• Mix design similar to original 5% RAS design
BUT no shingle aggregate or fibers were used
– Other blend percentages were divided by 95% to
maintain aggregate structure
• Recovered RAS binder was added equivalent
to the amount of binder from 5% RAS
– 100% binder activation and blending assumed
Phase II – Control
• 0% RAS in Mix Design
• Matched to Lee County Road 159 Section 19
• Same aggregates and similar gradation to
the other mixtures
Stockpile
Control (L-19) RAS Binder* RAS Aggregate 5% RAS
Calera Limestone 820s
74%
66.3%
63%
63%
Shorter Sand
25%
31.6%
30%
30%
EAP Baghouse Fines
0%
1.1%
1%
1%
Hydrated Lime
1%
1.1%
1%
1%
Whole Oxford PCRAS
0%
0%
0%
5%
Recovered RAS Agg.
0%
0%
5%
0%
Further Investigations
• Dry Mixing 5% RAS Samples
– Three mixed for one minute
One washed and graded
One aged for two hours
– One mixed for two minutes
– Large Shingles still visible loosely coated with
fines
– Color change between un-aged and aged sample
Further Investigations
• Shingles still visible and intact
+#4
+#16
Further Investigations
• Fine aggregate color change
Un-aged
Aged
Conclusions
• Temperature Study
– Temperature has a significant impact on volumetrics
– The 5% RAS mixture has high variability due to either
the aggregate stockpiles, the inclusion of RAS, or both
• Alternate Mixtures
– RAS aggregate and fibers had a slightly lower binder
content (6.2%)
– Control mix, 5% RAS and RAS binder mixtures all had
approximately 6.4% optimum binder content
Conclusions
• Further investigations
– Dry mixing experiment indicated that during
mixing little to no blending occurs
– The color change may indicate that activation
may be more prevalent during the aging of the
mixture
Thank you!
NCAT report 13-07: RAS
Characterization: Best Practices
www.ncat.us
37
J. Richard Willis
(334) 844-7301
willi59@auburn.edu