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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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Fatigue Model

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Heavy Vehicle Simulator (HVS)

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HVS Tests in South Africa-1993

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ALF Experiment

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Accelerated Pavement Testing Facility (ALF)

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Asphalt Rubber Interlayers-Description

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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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Thank You

Questions?