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

Introduction & Acknowledgements

Background & Project Location

Design & Construction

Pavement Instrumentation & Performance

Maintenance Repairs

Pros, Cons & Further Work

Future Applications

2

PRESENTATION OUTLINE

3

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.

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 occasional site visits to perform non-destructive testing and visual inspections

4

INTRODUCTION

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

6

BACKGROUND Site Location: Bloor St W & Aukland Road

BACKGROUND Pre-Existing Conditions

2003 Aerial

Arterial Roads

Major transit connection

High volume of bus & truck traffic

Aged and heavily distressed composite pavement

8

BACKGROUND April 24, 2003

9

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

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

10

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

11

CONSTRUCTION Staging

Construction took about 1 month

Concrete pavement placed in 3 stages over 2 weekend closures

Construction staging minimized traffic delays

12

CONSTRUCTION Bloor Street Section

13

CONSTRUCTION Bloor Street Section

14

CONSTRUCTION End Product

Bloor St.

(Westbound)

Bloor St.

(Eastbound)

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

15

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

TToo DDaattaa--llooggggeerr

FFllaannggee

FFllaannggee

GGaauuggee BBooddyy

((eelleeccttrroommaaggnneett ccooiill))

TToo DDaattaa--llooggggeerr

FFllaannggee

GGaauuggee BBooddyy

((eelleeccttrroommaaggnneett ccooiill))

PAVEMENT PERFORMANCE Sensor Data

Unbonded overlay: overall trend of increasing compression is observed both at the bottom and top of the concrete layer

Considerable remaining pavement service life is expected

Clear daily cycles in strain are observed coinciding with daily temperature cycles

Measured strains remain fairly low (i.e., well below cracking thresholds)

17

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

18

PAVEMENT PERFORMANCE Typical Distresses

Typical pavement condition

19

PAVEMENT PERFORMANCE Field Observations

Looking westbound on Bloor St.

Looking SB on Aukland

WB on Bloor at Aukland

August 2011

WB on Bloor at Ashbourne, August 2011

PAVEMENT PERFORMANCE Field Comparative Locations

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

August 2011, WB on Bloor at Ashbourne

PAVEMENT MAINTENANCE 2015 Repairs

Damaged Catchbasin

and Repair

23

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

24

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?

25

For further research:

Climate change adaptation – albedo, heat island effect

Greenhouse gas emissions – reduced material and construction demands

PROS, CONS

AND FURTHER WORK

26

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

27

THANK YOU

QUESTIONS?