Recycled Asphalt Pavement: Breaking Down Barriers Recycled Asphalt Pavement: Breaking Down Barriers...

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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

High RAP is defined as more than 25% RAP by weight of mix.

3‐15

2004 2005 2006 2007 2008 2009 2010 2011

Percen

tage Cha

nge in Produ

rices In

(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

Asphalt Production Cost Categories

Material Plant Production Trucking Lay Down

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

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

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.

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

• 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

Primary Performance Concerns

• Fatigue Cracking–Aging characteristics – virgin vs. RAP binder

• Low Temperature Cracking

• Durability (Raveling)–Moisture content

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

Fatigue Cracking

10%61%

Virgin performedsignificantly betterthan RAP

RAP performedsignificantly betterthan Virgin

Differencebetween Virginand RAPinsignificant

Longitudinal Cracking

Block Cracking

Raveling7%

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

IAIL IN

CTNJDEMD

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

“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.”

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

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

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

29•29

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

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.

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

• 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

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

• Loader operator

• RAP feed system–Scalping screen–Sizing device

Efficient Operations

In the Plant

• Superheating of aggregate• Air flow• Baghouse• Warm mix

Insuring Quality

• Final mixture–Volumetric properties–Extraction & recovery–Gradation–Asphalt content–High-RAP

•PG grade of blended binder•Quality of Aggregate

• Performance Testing

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

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!

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

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: audrey@asphaltpavement.org

Recycled Asphalt Pavement: Breaking Down Barriers Recycled Asphalt Pavement: Breaking Down Barriers...

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