10 Year Performance of an Unbonded Concrete Overlay - A Case Study - - PowerPoint PPT Presentation

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10 Year Performance of an Unbonded Concrete Overlay - A Case Study City of Toronto Mark Berkovitz P.Eng., Senior Engineer Transportation Services February 21, 2016 PRESENTATION OUTLINE Introduction & Acknowledgements Background

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SLIDE 1

10 Year Performance of an Unbonded Concrete Overlay

  • A Case Study

City of Toronto Mark Berkovitz P.Eng., Senior Engineer Transportation Services February 21, 2016

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SLIDE 2
  • Introduction & Acknowledgements
  • Background & Project Location
  • Design & Construction
  • Pavement Instrumentation & Performance
  • Maintenance Repairs
  • Pros, Cons & Further Work
  • Future Applications

2

PRESENTATION OUTLINE

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SLIDE 3

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INTRODUCTION

Definition

Unbonded Concrete Overlay is essentially a new concrete pavement constructed over an existing concrete pavement. A flexible interlayer, typically constructed of hot-mix asphalt (HMA), separates the concrete

  • layers. The flexible interlayer acts as a shear zone, allowing the concrete

layers to move independently of each other, and preventing reflective cracking in the concrete overlay. For this reason, the term “unbonded” is used, although the layers do bond in the sense of adhering together.

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SLIDE 4
  • First unbonded concrete overlay built in the City of

Toronto

  • Built on a composite arterial road
  • Constructed in the summer of 2003
  • A three-way research partnership between the City,

the Cement Association of Canada and Centre for Pavement and Transportation Technology (CPATT) at the University of Waterloo

  • Researched via ongoing live monitoring of stress-

strain gauges within the pavement structure and

  • ccasional site visits to perform non-destructive

testing and visual inspections

4

INTRODUCTION

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SLIDE 5

Acknowledgements

Aleks Kivi

Masters Candidate Waterloo Engineering

Susan Tighe, PhD, P.Eng

Sponsor Professor, Canada Research Chair, Norman W. McLeod Chair In Sustainable Pavement Engineering Centre for Pavement and Transportation Technology Department of Civil and Environmental Engineering University of Waterloo

Rico Fung, P.Eng

Sponsor Structural Engineer Cement Association of Canada

Jozef Grajek, P.Eng.

Senior Engineer & Project Manager City of Toronto

5

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6

BACKGROUND

Site Location: Bloor St W & Aukland Road

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SLIDE 7

BACKGROUND

Pre-Existing Conditions

2003 Aerial

  • Arterial Roads
  • Major transit

connection

  • High volume of bus

& truck traffic

  • Aged and heavily

distressed composite pavement

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SLIDE 8

8

BACKGROUND

April 24, 2003

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PAVEMENT DESIGN

Bloor Street Section

150 mm Granular Base 200 mm PCC 80 mm HMA

Existing Pavement

150 mm Granular Base 200 mm PCC 150 mm PCC

25 mm HMA (High stability HL3)

New Pavement

Bloor Street West

  • Grid pattern short joint spacing of 1.5 m maximum; cut ¼ depth
  • Short joint spacing reduces load-related stresses and prevents

corner cracking

  • Load transfer provided by aggregate interlock
  • Dowels and/or tie bars are generally not required, but were

used close to the intersection to provide additional reliability for heavy turning and/or stopped buses

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SLIDE 10

Aukland Road

  • Existing flexible pavement structure
  • Remove existing HMA surface full depth
  • Replace 150 mm granular base course with fresh material and

re-grade to design elevation

  • Place 225 mm conventional Jointed Plain Concrete Pavement

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PAVEMENT DESIGN

Aukland Road Section

260 mm Granular Base 190 mm HMA

Existing Pavement

110 mm Granular Base (old) 150 mm Granular Base (new) 225 mm PCC

New Pavement

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CONSTRUCTION

Staging

  • Construction took about 1 month
  • Concrete pavement placed in 3 stages over 2 weekend closures
  • Construction staging minimized traffic delays
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SLIDE 12

12

CONSTRUCTION

Bloor Street Section

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CONSTRUCTION

Bloor Street Section

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CONSTRUCTION

End Product

Bloor St. (Westbound) Bloor St. (Eastbound)

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SLIDE 15

Sensor Street Name Traffic Direction Depth (mm) Below PCC Surface 1 Bloor Street West WBD 50 2 WBD 150 3 WBD 50 4 EBD 50 5 EBD 50 6 EBD 50 7 EBD 150 8 Aukland Road SBL 50 9 SBL 225 10 SBL 50 11 NBT 50 12 NBD 50

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SENSOR INSTALLATION

Sensor Layout

N

Bloor Street West Aukland Road

WBD WBP EBP EBD SBL NBT NBD Sensor

Data Logger

Trench

8 & 9 10 11 12 1 & 2 3 4 5 6 & 7

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SLIDE 16

PAVEMENT PERFORMANCE

Sensor Data

  • Unbonded overlay: overall trend
  • f increasing compression is
  • bserved both at the bottom

and top of the concrete layer

  • Considerable remaining

pavement service life is expected

  • Clear daily cycles in strain are
  • bserved coinciding with daily

temperature cycles

  • Measured strains remain fairly

low (i.e., well below cracking thresholds)

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  • Structural Evaluation
  • Falling Weight Deflectometer (FWD) testing was performed

to evaluate the existing structural capacity, November 2013

PAVEMENT PERFORMANCE

Falling Weight Deflectometer Data

  • Load Transfer

Bloor St – excellent (87%) Aukland Rd – good-excellent (80%)

  • Deflections / Elastic Modulus Values

Bloor St – 115 microns / 3516 MPa Aukland Rd – 182 microns / 1921 MPa

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PAVEMENT PERFORMANCE

Typical Distresses

Typical pavement condition

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PAVEMENT PERFORMANCE

Field Observations

Looking westbound on Bloor St. Looking SB on Aukland WB on Bloor at Aukland August 2011

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SLIDE 20

WB on Bloor at Ashbourne, August 2011 PAVEMENT PERFORMANCE

Field Comparative Locations

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SLIDE 21

August 2011, WB on Bloor at Ashbourne

PAVEMENT MAINTENANCE

2015 Repairs

Cracked and spalled panels and repair (full depth with dowels) Full depth concrete repair in accordance with OPSS Special Provision 399S43

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SLIDE 22

August 2011, WB on Bloor at Ashbourne

PAVEMENT MAINTENANCE

2015 Repairs

Damaged Catchbasin and Repair

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PROS, CONS

AND FURTHER WORK

+ Maintains investment in old pavement + Excellent performance under heavy traffic loads and harsh

Canadian environmental conditions

+ Can be rapidly constructed

  • Concrete surface requires more frequent repainting
  • Utility cut repairs and patching are more costly

? Cost-effectiveness / life-extension to be determined ? Future rehabilitation considerations

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PROS, CONS

AND FURTHER WORK

Cost-effectiveness / life-extension to be determined:

(2003 Construction Costs, Unit Cost)

  • Unbonded Concrete Overlay: $230,000. , $150./m2
  • Jointed Plain Concrete Pavement: $140,000. , $200./m2
  • Standard Composite Pavement Rehabilitation $75./m2

Future Maintenance & Rehabilitation considerations:

  • Consider crack and joint sealant program
  • Develop a crack & spall repair program when needed
  • Double dowelling for utility cut repairs?
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For further research:

  • Climate change adaptation – albedo, heat island effect
  • Greenhouse gas emissions – reduced material and

construction demands PROS, CONS

AND FURTHER WORK

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MUNICIPAL APPLICATIONS

For Consideration

  • Highly distressed areas

characterized by:

  • heavy traffic
  • poor soil conditions
  • Limited underground

utilities

  • Examples:
  • turn lanes
  • bus bays & pads
  • Intersections
  • Industrial roads
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THANK YOU QUESTIONS?