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MinnesotaDepartment of Transportation
Minnesota Pavement Conference 1
Thin Unbonded Concrete Overlays of Concrete
Pavements
Mark J Watson, M.S.Minnesota Department of Transportation
Office of Materials & Road Research
MinnesotaDepartment of Transportation
Minnesota Pavement Conference 2
Outline
Background & Introduction
Thin Overlay Projects (MnROAD & TH 53)
Recent Conventional Overlay Projects
Current Status & Future of Thin Overlays
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Definition of Unbonded Overlay
Interlayer(Not Present in
Bonded Overlay)
New PCC Pavement
Underlying PCC (Distressed) Pavement
Conventional Unbonded Overlay (7 – 8”)Thin Unbonded Overlay (4 -5”)
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The Interlayer
– Not a Bond Breaker• Friction is necessary for joints to form
– A Stress Relief Layer• Retards or Prevents Reflective Cracking
– Provides Cushioning• A “Soft Landing” for deformed slabs loaded by
heavy vehicles
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Stress Relief
PCCPCCPASSRC
Stress Distribution from Underlying
Pavement
Interlayer Reduces Stress Concentration
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Cushioning
Interlayer Provides Cushion
Interlayer Provides Cushion
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Dense Graded vs Drainable
– Stripping in Early Test Sections
– Permeable Asphalt Stabilized Stress Relief Course (PASSRC)
– NCHRP Synthesis has recommended drainable interlayers
– How do we get the water out?
– Cost of Additional Drainage
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Candidate Pavements
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Pre-Overlay Pavement Condition
Should Fix or Account For – Active Panel Movements– Severely Deteriorated Joints and cracks– Broken/Shattered Slabs– Blowups
Not Necessary to Repair– Faulting (1” Interlayer can Correct)
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Historical Performance
0.0
1.0
2.0
3.0
4.0
0 5 10 15 20
Age, years
Ave
rage
RQ
I UnBonded
Concrete
326 Records of Unbonded Overlay (100%)1986 to 2007
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Historical Performance
0.0
1.0
2.0
3.0
4.0
0 5 10 15 20
Age, years
Ave
rage
SR
UnBonded
Concrete
326 Records of Unbonded Overlay (100%)1986 to 2007
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Advantages & Disadvantages
Advantages– Minimal Surface Preparation– Restores Ride and Structural Capacity– More Cost Effective than Reconstruction
Disadvantages– Clearance Issues (Bridge Jacking, or Transitions)– Can Have a Higher Initial Expense than other
Rehabilitation Methods, i.e. HMA Overlay– Conduct Life Cycle Cost Analysis (LCCA)
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Thin Unbonded Overlays
Research Objectives:– Construct Thinner Overlays
– Observe Performance
– Develop Rational Design Method
– Develop Better Life Prediction Models
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Minnesota Road Research Project(MnROAD)
I-94 Mainline Test Sections
Low Volume Test Loop
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MnROAD Existing Condition
• 7.1” Doweled PCC Constructed in 1992– Panels 13 or 14’ wide by 20’ (2’ skew)
• Load Transfer Efficiency (LTE) not low enough to Justify an Overlay
• Ride and Surface Condition not severe enough to Justify an overlay Treatment
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MnROAD Existing Condition
Artificial Joint Deterioration “Road Warrior Pavement
Breaker”
“Fan” Pattern4 Drops
4 Passes
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MnROAD Overlay Design
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MnROAD Overlay Design
• 2008 on I-94 in Albertville Mn (SP 8680-157) – 2006 ADT = 62,000 (31,000)
• 4-5” Unbonded Overlay– No Dowels– No Longitudinal Ties or Joint Sealant
• 1” Permeable Asphalt Stabilized Stress Relief Course (PASSRC) Interlayer– PG 64-22
• Horizontal Strip/Wick Drains Installed– Under Cl V and HMA Shoulders– 1” H X 12” W and spaced at 100’ Intervals
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Conventional Unbonded Overlay
• 2008 on I-90 in Dexter, Mn (SP 5080-146) – 2006 ADT 5,650– 8” Unbonded PCC Overlay– 1.25” Epoxy Coated Dowels – Tied Longitudinal Joints– 1.5” PASSRC Interlayer– Subsurface Edge Drain System Installed– Sub-Cut and 9.5” PCC and Paving Transitions under
overpasses to maintain vertical clearance
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TH 53 Existing Condition
• 8” Doweled PCC Constructed in 1972– Panels 12’ wide by 27’ (2’ skewed)
• 2 Concrete Pavement Repair (CPR) 1983, 1992• State Hwy Traffic (2008 ADT = 12,300), Used
by Heavy Logging Trucks• Poor Ride• Low Load Transfer Efficiency (LTE)• A Good Candidate for an Unbonded Overlay
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TH 53 Existing Condition
Mid-Panel Cracking
Severe JointDeterioration
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TH 53 Overlay Design
• 5” Unbonded PCC Overlay in 2008 Under (SP 6916-99)
– Panels 12’ wide by 12’ long (no skew)– No Dowels – Supplemental Panel Reinforcement – Test section with 6’ wide by 6’ long Panels (no skew)
• 1” Dense Graded HMA Interlayer– SPNWB330B (PG 58-28)
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Conventional Unbonded Overlay
• 2007 SP 0301-48 on TH 10 in Hawley, Mn– 2005 Traffic 11,900 ADT– 7” Unbonded PCC Overlay– 1.0” PASSRC Interlayer– 1.25” Epoxy Coated Dowels – Tied Longitudinal Joints– Subsurface Edge Drain System– Sub-Cut and 9.0” PCC and Paving Transitions under
overpasses to maintain vertical clearance
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Electronic Sensors
MnROAD
TH 53
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Electronic Sensors
• Strains– Dynamic Vehicle Response – Environmental
• Joint Opening
• Temperature– Slab – Base – Subgrade
• Maturity– Early Age Maturity
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Thin Unbonded Overlays
• Pavement Testing (Before and After)– Pavement Management Van
• Ride Quality Index (RQI)• Surface Condition (SR)
– Falling Weight Deflectometer (FWD)• Load Transfer Efficiency (LTE)• Deflection Basins
• MnROAD - Early Age Pavement Testing – Warp and Curl– Joint Opening
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Current Status
• TH 53 is currently open to Traffic• Plan to Overlay North Bound in 2009• Short Term Performance?
• Mid-panel Cracks - Joints Sawed Too Late?, Excessive Joint Interval?
• Crack Propagation – No PASSRC Used• Sleever Spalls – Early Joint Sawing?• Corner Breaks - ??
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Mid-Panel Cracks on TH 53
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Spalling on TH 53
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MnROAD Current Status
• MnROAD Opened to Traffic on 2-3-2009• Initial Measurements Still Being Processed• University of MN has a Contract to
Develop a Fracture Mechanics Model of TUBOL
• Further Research to Develop a Rational Design Method
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Thanks for Your Attention
Questions?
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Thanks for Your Attention
AcknowledgementsMn/DOT Office of Materials and Road Research
References1. Engstrom, G. Unbonded Concrete Overlays, Minnesota Experiences. Minnesota
Department of Transportation, Interim Report, January 1993.2. Eres Consultants. Evaluation of Unbonded Portland Cement Concrete Overlays.
Transportation Research Board, National Research Council, NCHRP Report No. 415, Washington, D.C. 1999.
3. Lukanen, E. Unpublished Charts from Mn/DOT Pavement Management System Data. Mn/DOT June 2008.
4. Harrington, D., Degraaf, D., Riley, R. Guide to Concrete Overlay Solutions. National Concrete Pavement Technology Cener (CP Tech Center), Iowa State University, January 2007.
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PASSRC Design
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PCC Design