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 & Project Location Design & Construction Pavement Instrumentation & Performance Maintenance Repairs Pros, Cons & Further Work Future Applications 2
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. 3
INTRODUCTION 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
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
BACKGROUND Site Location: Bloor St W & Aukland Road 6
BACKGROUND Pre-Existing Conditions Arterial Roads Major transit connection High volume of bus & truck traffic Aged and heavily distressed composite pavement 2003 Aerial
BACKGROUND April 24, 2003 8
PAVEMENT DESIGN Bloor Street West Bloor Street Section 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 New Pavement Existing Pavement 150 mm PCC 80 mm HMA 25 mm HMA (High stability HL3) 200 mm PCC 200 mm PCC 150 mm Granular Base 150 mm Granular Base 9
PAVEMENT DESIGN Aukland Road Section 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 Existing Pavement New Pavement 225 mm PCC 190 mm HMA 150 mm Granular Base (new) 260 mm Granular Base 110 mm Granular Base (old) 10
CONSTRUCTION Staging Construction took about 1 month Concrete pavement placed in 3 stages over 2 weekend closures Construction staging minimized traffic delays 11
CONSTRUCTION Bloor Street Section 12
CONSTRUCTION Bloor Street Section 13
CONSTRUCTION End Product Bloor St. (Eastbound) Bloor St. (Westbound) 14
SENSOR INSTALLATION Sensor Layout Bloor Street West Depth (mm) Sensor Street Traffic Below PCC Name Direction 1 & 2 WBD Surface 3 1 WBD 50 WBP 2 WBD 150 3 WBD 50 Bloor EBP 4 Street EBD 50 4 EBD West 5 5 EBD 50 6 & 7 6 EBD 50 7 EBD 150 8 SBL 50 8 & 9 10 11 12 N 9 SBL 225 Aukland 10 SBL 50 Road 11 NBT 50 12 NBD 50 SBL NBT NBD Sensor Data Logger Aukland Road Trench Ga Ga au au ug ug ge ge e e B B Bo Bo od od dy dy y y G G (e (e ( ( el el le le ec ec ct ct tr tr ro ro om om ma ma ag ag gn gn ne ne et et t t c c co co oi oi il il l) l) ) ) F Fl la an ng ge e F F Fl Fl la la an an ng ng ge ge e e To To o o D D Da Da at at ta ta a- a- -l -l lo lo og og gg gg ge ge er er r r T T 15
PAVEMENT PERFORMANCE Sensor Data Clear daily cycles in strain are observed coinciding with daily temperature cycles Measured strains remain fairly low (i.e., well below cracking thresholds) 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
PAVEMENT PERFORMANCE Falling Weight Deflectometer Data Structural Evaluation Falling Weight Deflectometer (FWD) testing was performed to evaluate the existing structural capacity, November 2013 Deflections / Elastic Modulus Values Bloor St – 115 microns / 3516 MPa Aukland Rd – 182 microns / 1921 MPa Load Transfer Bloor St – excellent (87%) Aukland Rd – good-excellent (80%) 17
PAVEMENT PERFORMANCE Typical Distresses Typical pavement condition 18
PAVEMENT PERFORMANCE Field Observations Looking westbound on Bloor St. WB on Bloor at Aukland Looking SB on Aukland August 2011 19
PAVEMENT PERFORMANCE Field Comparative Locations WB on Bloor at Ashbourne, August 2011
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 August 2011, WB on Bloor at Ashbourne
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 23
PROS, CONS AND FURTHER WORK Cost-effectiveness / life-extension to be determined: (2003 Construction Costs, Unit Cost) Unbonded Concrete Overlay: $230,000. , $150./m 2 Jointed Plain Concrete Pavement: $140,000. , $200./m 2 Standard Composite Pavement Rehabilitation $75./m 2 Future Maintenance & Rehabilitation considerations: Consider crack and joint sealant program Develop a crack & spall repair program when needed Double dowelling for utility cut repairs? 24
PROS, CONS AND FURTHER WORK For further research: Climate change adaptation – albedo, heat island effect Greenhouse gas emissions – reduced material and construction demands 25
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 26
THANK YOU QUESTIONS? 27
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