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Shakir Shatnawi, Ph.D., P.E.President, SHATEC ENGINEERING CONSULTANTS, LLC
(Former Caltrans State Pavement Engineer)sshatnawi@sbcglobal.net
916-990-6488
COST EFFECTIVENESS OF ASPHALT RUBBER INTERLAYERS
18th Annual Complete Streets and Technology
Conference – April 19, 2017
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Presentation Outline California Experience Asphalt Rubber Interlayers Composite Layering Systems Cost Effectiveness Discussion Final Remarks
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Chip Seal Interlayers (SAMI)
1960 1970 1980 1990 2000
Chip Seal (SAM)
Open-GradedHot Mix
Dense-GradedHot Mix
Gap-GradedHot Mix
California Experience with AR Products
2010
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Reduced Thickness of AR
Conventional Asphalt Rubber
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Thickness Equivalencies for Flexible Pavements
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Thickness Equivalencies for Composite Pavements
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Chip Seals Known as ARAM – Asphalt Rubber
Aggregate Membrane
A quality AR Chip Seal has the ability to resist reflective cracking
Can fill and bridge cracks
13 year old ARCS
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Asphalt Rubber Interlayers-Description
ARAM: Asphalt Rubber Aggregate Membrane SAM-R: Rubberized Stress Absorbing Membrane
ARAM and SAM-R are the same descriptions for asphalt rubber chip seal.
ARAMI and SAMI-R describe asphalt rubber chip seal interlayers.
California Design: ARAMI is assumed equivalent to 45 mm of HMA.
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Reflective Cracking CriteriaVon Mises Strains
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Interlayers (ARAMI/SAMI-R)
Increase reflective crack resistance
Can fill and bridge cracks
Provide thickness equivalencies
10 Year ARAMI
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Composite Layering Systems
Cape Seals
Two Layer System
Three Layer System
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Composite Layering System-System I: Cape Seal (Slurry/ARAM)
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19Composite Layering System-System II: Cape Seal
(Slurry/ARAM/Leveling Course)
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AR Cape Seals
ARAM overlaid by slurry seal
For residential streets
Have been used by local agencies since the mid 1980’s
NORWALK 1991
NORWALK 2010, 19 years after Cape Seal
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21Composite Layering System-System III: AR Overlay/ARAM/Leveling
Course (3 Layers)
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Three Layer System
ARAM overlaid by ARHM
For arterial streets
Have been used by local agencies since the mid 1980’s
Costa Mesa, 1989
Costa Mesa 2009, 20 years after Three Layer System
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Composite Layering System-System IV: AR Overlay/ARAM (2 Layer)
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Two Layer System
ARAM overlaid by ARHM or conv. AC
For arterial streets
Have been used by local agencies since the mid 1980’s
Azusa 2004
Azusa, After Two Layer System
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Layering System Cost Effectiveness
Initial CostLife Cycle Cost
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Example 1: Costa Mesa
Built in 1989 (Over 20 years ago)– Alt1: Conventional: Full Reconstruction
125mm AC/125mm AB Cost:$135K
– Alt2: 3-Layer System 45mm RAC-G/ARAMI/25mm AC Cost:$83K
Savings=$52K (40%) ARAMI allowed a reduction in thickness
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Example 2: I-5 Orange County
CS & OL Caltrans Project Alt1:Conventional-Cold plane 120 mm
– 75mm AC/Fabric/30 mm AC/PCC– Cost:$12Million
Alt2: 3-Layer System-Cold plane 85 mm– 30 mm RAC-O/ARAMI/45 mm RAC-G– Cost:7.3Million
Savings: $4.7 Million (40%) ARAMI allowed a reduction in thickness
28Life Cycle Cost Analysis (LCCA)Example Project
Project: – 2-mile long segment, two lanes each direction– AADT: 150,000 both directions.
Existing Pavement: – 150 mm distressed flexible pavement over an
untreated aggregate base.– Cracks over 3 mm
Rehabilitation Design: – 20-year service life based on reflective crack
retardation.
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Strategy Comparison
Strategy I: 105 mm Conventional HMA overlay.
Strategy II: 60 mm Conventional HMA over ARAMI.
Strategy III: 60 mm AR Overlay. Strategy IV: 30 mm AR Overlay over
ARAMI.
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LCCA Analysis
FHWA RealCost Software and user’s manual:– http://www.fhwa.dot.gov/infrastructure/asstm
gmt/lccasoft.cfm
Caltrans Life-Cycle Cost Analysis Procedures Manual:– http://www.dot.ca.gov/hq/maint/Pavement/O
ffices/Pavement_Engineering/PDF/LCCA_Manual_MASTERFinal.pdf
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LCCA Approach
Integrate all agency and user costs for initial and discounted future costs to account for all investments over the required service life.
Identify the lowest and/or the best value for the investment outlays.
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Costs
Agency support costs: 31% Rehab and 19% CAPM of total project cost.
User Costs: User delay, vehicle operation and crash costs. Per Caltrans Cal-B/C Model 2004:– $10.46 per hour for passenger cars.– $27.83 per hour for single unit trucks.– $27.83 per hour for combination trucks.
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LCCA Analysis Net Present Value (NPV) Discount Rate (i): 4.0%
IC=Initial Cost, FC: Future Cost
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Maintenance & Rehabilitation Sequence
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Incorporating User and Agency Costs in All Activities
36LCCA Results
- Net Present Value (NPV)
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37Asphalt Rubber Usage Guide
www.dot.ca.gov/hq/esc/Translab/ope/Asphalt-Rubber-Usage-Guide.pdf
CA Pavement Preservation Center
http://www.cp2info.org/
38Maintenance Technical Advisory Guide (MTAG)
http://www.dot.ca.gov/hq/maint/MTA_GuideVolume1Flexible.html
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Final Remarks
Strategies that use a combination of AR overlays and AR interlayers are the most cost-effective.
Strategies that Use AR interlayers are more cost-effective than those without.
Equivalencies of 30 mm to 45 mm for ARAMI seem to be conservative.
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Final Remarks
AR is a proven paving strategy and with a long history of successful performance.
Composite layering systems have shown to provide superior performance over conventional strategies.
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