Thin Unbonded Concrete Overlays of Concrete Pavements · Thin Unbonded Concrete Overlays of...

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



Outline

Background & Introduction

Thin Overlay Projects (MnROAD & TH 53)

Recent Conventional Overlay Projects

Current Status & Future of Thin Overlays



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”)



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



Stress Relief

PCCPCCPASSRC

Stress Distribution from Underlying

Pavement

Interlayer Reduces Stress Concentration



Cushioning

Interlayer Provides Cushion

Interlayer Provides Cushion



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



Candidate Pavements



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)



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



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



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)



Thin Unbonded Overlays

Research Objectives:– Construct Thinner Overlays

– Observe Performance

– Develop Rational Design Method

– Develop Better Life Prediction Models



Minnesota Road Research Project(MnROAD)

I-94 Mainline Test Sections

Low Volume Test Loop



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



MnROAD Existing Condition

Artificial Joint Deterioration “Road Warrior Pavement

Breaker”

“Fan” Pattern4 Drops

4 Passes



MnROAD Overlay Design



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



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



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



TH 53 Existing Condition

Mid-Panel Cracking

Severe JointDeterioration



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)



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



Electronic Sensors

MnROAD

TH 53



Electronic Sensors

• Strains– Dynamic Vehicle Response – Environmental

• Joint Opening

• Temperature– Slab – Base – Subgrade

• Maturity– Early Age Maturity



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



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 - ??



Mid-Panel Cracks on TH 53



Spalling on TH 53



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



Thanks for Your Attention

Questions?



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.



PASSRC Design



PCC Design

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