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Recycled Asphalt Pavement:
Breaking Down BarriersAudrey Copeland
National Asphalt Pavement Association
Asphalt Pavement Alliance ConferenceMarch 12, 2012
It’s a given…
Must consider recycled materials to remain competitive
– with concrete, and
– mitigate material cost variability
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High RAP is defined as more than 25% RAP by weight of mix.
3‐15
‐10
‐5
0
5
10
15
20
25
30
35
40
2004 2005 2006 2007 2008 2009 2010 2011
Percen
tage Cha
nge in Produ
cer P
rices In
dexes
(PPIs)
Change in Producer Price Indexes for Construction Materials
Asphalt paving mixes &blocks
Source: Bureau of Labor Statisticshttp://www.agc.org/galleries/news/PPI.Tables.201201.pdf
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Source: Bureau of Labor Statisticshttp://www.agc.org/galleries/news/PPI.Tables.201201.pdf
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Asphalt Production Cost Categories
0
10
20
30
40
50
60
70
80
90
100
Material Plant Production Trucking Lay Down
Perc
ent (
%) o
f Cos
t
Greatest Potential for Cost Savings isin the Materials Category
Life Cycle Cost Using RAP 11" AC vs. 9" PCC
Top Barriers to High RAP Use
1. FEAR - Overly Conservative Specifications
2. Insuring Performance
3. Using high RAP with Superpave mix design – meeting volumetric requirements
4. Concerns about quality of the RAP as a material input
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Common BarriersAgency/Specifications• Quality Concerns• Consistency of RAP• Binder Grade and
Blending• Mix Design Procedures• Meeting Volumetric
Requirements• Durability• Use with Polymers
Industry• State Specifications• Control of RAP• Dust and Moisture
Content• Increased QC
Conservative Agency Specifications
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Current Guidelines
• AASHTO M 323 Standard Specification for SuperpaveTM
Volumetric Mix Design
• Calls for virgin binders that may be more expensive, hard to get• Blending chart analysis is time-consuming!
Recommended Virgin Asphalt Binder Grade Percent (%) RAPNo change in binder selection < 15Select virgin binder grade one grade softer than normal 15 – 25Follow recommendations from blending charts > 25
State of Deployment 2009Reclaimed Asphalt Pavement
States that Usemore than 20% RAP
• The amount of RAP used in HMA/WMA increased by 10%. – Assuming 5% liquid asphalt in RAP, this represents over 3
million tons (19 million barrels) of asphalt binder conserved.
• The average percent RAP used in mixes has increased from about 16% to 18%.
• 96% of the contractors/branches reported using RAP and over 86% of these contractors reported excess RAP.
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How far have we come?The Industry from 2009 to 2012
Room to Grow…• Our comfort level with RAP is less than 20% by weight of
mix.
• Still 5 to 10% RAP that can be used under existing specs. We can go further!
• Based on research*, Indiana found they could increase specification to allow up to 20% RAP with no binder grade change.– Cost savings of about $1.25 per ton of asphalt mixture. – Based on the amount of asphalt mixtures produced in
2010, this can result in savings of $125 million.*McDaniel,etal.InvestigationofLow‐ andHigh‐TemperaturePropertiesofPlant‐ProducedRAPMixtures.PublicationNo.FHWA‐HRT‐11‐058,FederalHighwayAdministration,Washington,DC,2011.http://www.fhwa.dot.gov/publications/research/infrastructure/pavements/11058/11058.pdf
RAP Percentage Based on Binder
• Historically, agency specs limit RAP based on RAP percentage by weight of total mix or weight of aggregate.
• With high RAP contents, the primary issue is amount of binder replacement.– Impacts binder properties & may impact binder choice
• Determine contribution of RAP binder toward total binder in the mix, by weight.– Typically specified as “70% of binder content must be
virgin” or “no more than 30% binder content can come from RAP or RAP & RAS”.
Long-Term Performance
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Primary Performance Concerns
• Fatigue Cracking–Aging characteristics – virgin vs. RAP binder
• Low Temperature Cracking
• Durability (Raveling)–Moisture content
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Evaluating RAP Performance
• Long Term Pavement Performance SPS-5 sections–Virgin–30% RAP–Milled and non-milled surface–50 and 125 mm thick–Oldest is over 17 years
at Auburn University
SPS-5 Project Locations
at Auburn University
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Fatigue Cracking
29%
10%61%
Virgin performedsignificantly betterthan RAP
RAP performedsignificantly betterthan Virgin
Differencebetween Virginand RAPinsignificant
Longitudinal Cracking
15%
10%
75%
Virgin performedsignificantly betterthan RAP
RAP performedsignificantly betterthan Virgin
Differencebetween Virginand RAPinsignificant
Block Cracking
3% 1%
96%
Virgin performedsignificantly betterthan RAP
RAP performedsignificantly betterthan Virgin
Differencebetween Virginand RAPinsignificant
Raveling7%
15%
78%
Virgin performedsignificantly betterthan RAP
RAP performedsignificantly betterthan Virgin
Differencebetween Virginand RAPinsignificant
RAP Mix Performed As Well As or Significantly Better than Virgin Mix
Fatigue Cracking – 71%Longitudinal Cracking – 85 %Block Cracking – 97 %Raveling – 93 %
LTPP Study Results
Long-Term Performance of RAP in HMA
CA
AZ
CO
NM
TX
OK AR
LA
MO KY
AL GA
FL
VA
OH
MI
VTAK
MT
NV
MEWA
OR
UTKS
IDWY
ND
SD
MN
NE
WI
IAIL IN
MS
TNSC
NC
WV
PA
NY
CTNJDEMD
DC
MANH
PR
HI
RI
No significant difference in performance of virgin and recycled pavement sections.
Well-designed pavement with high RAP (35%) can perform well during life span.
Average age of virgin mixes is 11 years.For 30–50% RAP content, the average age ranges from 10–13 years.
“…in all 3 environmental zones, long term performance of RAP likely to be comparable to other treatments.”
RAP Publications from FHWA
http://www.fhwa.dot.gov/publications/research/infrastructure/pavements/11057/11057.pdfhttp://www.fhwa.dot.gov/publications/research/infrastructure/pavements/11021/11021.pdf
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“In summary, the performance data from LTPP SPS-5 shows that RAP and virgin HMA mixes used in overlays of flexible pavements showed approximately the same performance across a range of climates, traffic, and existing pavement conditions over a period of up to 17 years. This finding should give agencies confidence in specifying RAP mixtures for overlays when economic and other conditions warrant.”
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Long-term Performance of RAP Pavements
• High percentages of RAP have successfully been used for more than 30 years.
• Long-term performance of recycled asphalt pavements not well documented.
• Recycled asphalt mixtures designed using established mix design procedures and produced with appropriate QC/QA measures perform comparably to conventional mixtures.
Superpave Volumetric Requirements
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Binder Grade Selection
• For high RAP contents, the virgin binder Performance Grade (PG) may have to be lowered to account for the aged (stiff) RAP binder OR the RAP % is chosen based on a given virgin binder PG.
• Bumping a grade can increase cost & deter high RAP use?
• Blending charts• Standardized PG based on region
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RAP Aggregate Testing• Gradation - AASHTO T 30 Mechanical Analysis of
Extracted Aggregate
• RAP aggregates must meet the same quality requirements specified for virgin aggregates. –Coarse Aggregate Angularity (D 5821)–Fine Aggregate Angularity (T 304)–Flat & Elongated (D 4791)–Sand equivalent requirements (T 176) are waived for RAP aggregate. –Agency Specifications
•Source properties 26
Superpave Volumetric Mixture Design Requirements
DesignESALS (millions)
Required Density (% of Theoretical Max
Specific Gravity)
VMA (%), minimumVFA (%)
Dust-to-
binderratio
Nominal Max Agg Size, mm
Ninitial Ndesign Nmax 37.5 25.0 19.0 12.5 9.5
< 0.3 ≤ 91.5 70 -80
0.6 –1.2
0.3 to < 3
≤ 90.5
96.0 ≤ 98.0 11.0 12.0 13.0 14.0 15.0
65 -78
3 to < 10
≤ 89.0 65 -7510 to <
30≥ 30
VolumetricsDetermining Bulk Specific Gravity (BSG) Values
• VMA is a function of BSG of combined aggregate (RAP & virgin), BSG of compacted mix, and aggregate percentage.–Change gradation–Change amount of No. 200 material–Change surface texture or shape of fine aggregate fraction
• VFA is function of VMA and percent air voids in compacted mix
• Dust-to-binder ratio 28
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Asphalt Research Consortium (ARC)– FHWA Cooperative Agreement
• Determining binder properties without extraction and recovery
• Extraction techniques and properly determining RAP aggregate properties (i.e. Gsb, Gse)
• Monitoring field performancehttp://www.arc.unr.edu/
Maintaining Quality of RAP & Recycled Pavements
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Increasing RAP Use
The question we’re posing…• How much RAP can we
allow in the mix and meet specification and constructability requirements?
• Biggest impact can be made in processing and production.
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Issues to Consider when Increasing RAP
• Additional Processing & Quality Control (QC)–Mill Intelligently–Processing RAP–Stockpile Management
• Characterizing RAP
• Changing Binder Grade
• Plant mixing & temperatures
• RAP mixtures must meet the same mix design specifications required for virgin mixtures.
• Most State DOTs do not have additional means of determining the acceptability of high RAP mixtures.
Quality Control
Getting the RAP ready…
• Unprocessed RAP–Not subject to QC–Visual Inspection
• Processing RAP–Uniform size–Promotes final blend
consistency
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• Stockpiling–Conical–Well-maintained–Sample frequently
• Comprehensive QC testing–Absorption–Moisture content–Asphalt content–Gradation
Maintaining RAP Quality
Obtaining uniform gradation of RAP• RAP aggregate separation based on size
increases control and may reduce variability.
• Sizing of RAP materials–Screening is used to
separate sizes & control dust–Fractionation–Allows for adjustments for
variability to be made within the RAP
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Fractionated RAP (FRAP)
• Fractionation is processing and separating RAP into at least two sizes, typically a coarse fraction and a fine fraction.
Dealing with DustDust to Binder Ratio
• Big challenge in using higher RAP contents–Fills voids and reduces VMA
• Removing dust increases costs
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• Loader operator
• RAP feed system–Scalping screen–Sizing device
Efficient Operations
In the Plant
• Superheating of aggregate• Air flow• Baghouse• Warm mix
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Insuring Quality
• Final mixture–Volumetric properties–Extraction & recovery–Gradation–Asphalt content–High-RAP
•PG grade of blended binder•Quality of Aggregate
• Performance Testing
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Laydown and Compaction
–No special requirement/techniques•May require more attention than conventional mixes
–Mix Workability - Stiffer•Density
–Cooler temperatures•Reduced compaction times
RAP/RAS Publications
• Designing HMA Mixtures with High RAP Content: A Practical Guide, Publication QIP-124
• How to Increase RAP Usage and Ensure Pavement Performance, NAPA Publication PS 34
• Uses of Waste Shingles in HMA: State-of-the-Practice, Special Report 179
• Guidelines for the Use of Reclaimed Asphalt Shingles in Asphalt Pavements, Information Series 136
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Using RAP Effectively
• View RAP as a valuable resource.• Treat RAP as you would other ingredients.• Offer yourself maximum flexibility in using
RAP.• Learn what’s in RAP.• Monitor process and materials continuously –
keep it consistent.
What’s the national trend?
• The nation is comfortable using up to 20% RAP, but there’s room to use up to 30% or more.– Best opportunity to stabilize material costs.
• The use of RAS and interest in rubber is increasing.– Start with low amounts of RAS and maintain quality.
• The use of WMA in the industry has increased by almost 150%!– Consistency & best practices are key when combining
RAP, RAS, & WMA!
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The Most Important Things
• Build trust with your agency – help write specifications.
• Do your homework (before bidding) when it comes to RAP
• Processing, production, & construction best practices – avoid segregation– Pave & slope stockpile storage areas
• Communication with other industries –aggregate, binder suppliers
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Thank you for your hard work and effort to produce quality
pavements, improve transportation infrastructure, and
our economy.
For more information:Web: www.asphaltpavement.org
Email: [email protected]
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