Concrete Overlays and Applications

Pennsylvania Concrete Conference, January 27,

2009Dale S. Harrington P.E., Representing - National Concrete Pavement Technology Center

Concrete Overlay Guide second edition

Second Edition September 2008

Contents1. Overview of Overlay

Families2. Overlay types and uses3. Evaluations & Selections4. Six Overlay Summaries

(11”x17 “sheets)5. Design Section 6. Miscellaneous Design

Details7. Overlay Materials Section8. Work Zones under Traffic9. Key Points for Overlay

Construction10. Accelerated Construction11. Specification

Considerations12. Repairs of Overlays

Overlay Committee (17 Members)• Andy Bennett, Michigan Department of Transportation• Jim Cable, P.E., Iowa State University• Dan DeGraaf, Michigan Concrete Paving Association• Jim Duit, Duit Construction Co., Inc., Oklahoma• Todd Hanson, Iowa Department of Transportation• Randell Riley, Illinois Chapter ACPA• Matt Ross, Missouri/Kansas Chapter ACPA• Jim Shea, New York State Chapter ACPA• Gordon Smith, Iowa Concrete Paving Association• Sam Tyson, Federal Highway Administration• Leif Wathne, American Concrete Pavement Association• Jim Grove, CP Tech Center• Matt Zeller, Concrete Paving Association of Minnesota• Jeff Uhlmeyer, Washington State DOT• Kevin Maillard, OHM Advisors• Robert Rodden, American Concrete Paving Association• Shannon Sweitzer, North Carolina Turnpike Authority

System of Concrete Overlays

Concrete Overlays

Bonded Concrete

Overlay of Concrete

Pavements

Bonded Concrete

Overlay of Asphalt

Pavements

Bonded Concrete

Overlay of Composite Pavements

Bonded Overlay System

Unbonded Concrete

Overlay of Concrete

Pavements

Unbonded Concrete

Overlay of Asphalt

Pavements

Unbonded Concrete

Overlay of Composite Pavements

Unbonded Overlay System

Thinner Thicker

Bond is integral to design Old pavement is base

Page 1

Why Concrete Overlays?

• Consistently provide cost-effective solutions• Constructed quickly and conveniently• Few preoverlay repairs are necessary• Placed using normal concrete pavement

construction practices• Can be opened to traffic within a short time

using standard mixes• Easy to repair• Cost-effective maintenance tool and

valuable rehabilitation tool• Can serve as complete preventive

maintenance or rehabilitation solutions or can be used in conjunction with spot repairs of isolated distresses

Page 2

Versatile and Sustainable Solutions

• As long as the original pavement is stable and uniform for a concrete overlay to be placed, it can be replaced or recycled as needed for maintenance and/or rehabilitation cycles.

• The concrete overlay system can be sustained for 100 years or longer.

• The original pavement will provide a continuing return on the owner-agency’s investment.

• The owner is maintaining and building equity in the pavement system.

Page 2

Pavement Preservation and Rehabilitation

• Involves investing in a carefully planned system of regular routine maintenance, preventive maintenance and minor rehabilitative actives

• Extend the life of existing pavements

• Highway agencies are increasingly relying on a proactive approached called pavement preservation

Major Rehabilitation

Page 3

Preventive MaintenanceExtends the service life by applying cost-effective treatments to the surface of structurally sound pavements such as partial and full depth repairs, dowel bar retrofit, diamond grinding and/or thin bonded overlays.

Page 3

Minor Rehabilitation

Is used when some structural capacity needs to be restored or added to a pavement but major rehabilitation is not required. Typical application could include some spot elements of pavement preservation in conjunction with either a bonded overlay or a thinner (4” to 5”) unbonded overlays

Page 3

Major Rehabilitation

Involves structural enhancements that extend the service life of an existing pavement and improves its load-carrying capability. Pavement preservation techniques are typically used in conjunctions with a new unbonded concrete overlay of 5-in. or greater. However, thicker bonded overlays have been used.

Page 3

Overlay Solutions for Rehabilitation and Maintenance

Page 3

Uses and Advantages- Bonded Overlay of Concrete

• Use when existing pavement is in good structural condition with some surface distress.

• Use to eliminate any surface defects; increase structural capacity; and improve surface friction, noise, and rideability.

• Where vertical clearance issue.

2”–5” thickness

• Typically used directly over concrete without additional repairs except for spot-repairing of severely deteriorated areas.

Pages 4, 12-13

Where any of the above distress are present, their severity and extent should be considered to determine if a bonded overlay is appropriate.

Working cracks to be repaired or sawed since they will reflect through.

Bonded Concrete Overlay over Concrete

Page 12

Bonded on ConcreteKeys to Success

• Bond is important for good performance as a monolithic pavement.

• Concrete aggregate used should have thermal properties similar to that of existing pavement to minimize shear stress in bond.

• Matching joints with underlying pavement allows structure to move monolithically.

• Existing joints must be in fair condition or be repaired

• Timing of joint sawing is important.

• Cut transverse joints full depth +1/2” and longitudinal joints at T/2.

• Curing should be timely and adequate, especially near the edge, due to the surface-to-volume ratio and the risk of early-age cracks.

• Width of transverse joint of overlay to be equal to or greater than underlying crack width of the existing pavement.

Pages 4, 12-13

Page 12

Surface Preparation for Bonded Overlay Bonding is Critical

• Milling

• Shotblasting

Cleaning the Surface to Prepare for Bonding

• Sweeping surface followed by compressed air cleaning in front of the paver.

• Air blasting or water blasting is only necessary to remove material that cannot removed any other way.

• Water or moisture should not be on the surface prior to paving or de-bonding can occur.

Page 13

Shear Test

Pull Off Test (bridges)

• Bonding is Important:

• Overlay opening strength (compressive or flexural) can be a good surrogate criteria for bond strength.

• Maturity methods for strengths can be helpful for early opening conditions.

• Some states are relying on actual bond measurements to increase confidence in quality of the bond.

• Accuracy of the test results are sensitive to the how the test is run.

Page 53

Uses and Advantages- Bonded Overlay of Asphalt or Composite Pavements

• Use when existing pavement is in fair or better structural condition with surface distress.

• Use to eliminate any surface defects; increase structural capacity; and improve surface friction, noise, and ride.

• Where increased traffic requires more structural capacity.

• Where vertical clearances are needed.

2”–5” thickness

Pages 4, 14-17

CONCRETE RESURFACING OF ASPHALT PAVEMENTS

• Spots of distress that aren’t visible can be determined through evaluation such as the stiffness of the asphalt pavement and subgrade support conditions.

• Localized areas of weakness can be strengthen through patching. Milling can remove a number of asphalt surface distresses.

Bonded Concrete Overlay of Asphalt Pavements

Page 14

CONCRETE RESURFACING OF ASPHALT PAVEMENTS

• Asphalt is a good reflector of underlining concrete pavement condition.

• A review of the existing profile grade line should be conducted and areas of significant deviation investigated through analysis of core samples in the laboratory.

Bonded Concrete Resurfacing of Composite Pavements

Page 16

Bonded over Asphalt/CompositeKeys to Success

Bonding is criticalSmall square panels reduce curling,

warping, & shear stresses in bond (1.5 times thickness).

Mill if necessary to correct crown, remove surface distresses, improve bonding. Be sure to leave 3” of HMA after milling.

HMA surface temperature below 120 F before paving.

Transverse joints must be sawed T/3Joints in the overlay should not be placed in

wheel paths, if possibleApplication of curing compound or curing

methods must be timely and thorough

Pages 4, 14-17

Milling: Bonded Overlayof Asphalt or Composite Pavements

The three main objectives of milling:

1. to remove significant surface distortions that contain soft asphalt material;

2. to reduce high spots to help ensure minimum resurfacing depth and reduce the quantity of concrete needed to fill low spots;

3. to roughen a portion of the surface to enhance bond development between the new concrete overlay and the existing asphalt. (don’t leave a thin lift)

Page 15

Milling: Bonded Resurfacingof Asphalt or Composite Pavements

• Direct placement without milling is recommended when rutting in the existing asphalt pavement does not exceed 2”.

• Any ruts in the existing pavement are filled with concrete, resulting in a thicker concrete overlay above the ruts.

• A minimum of 3"–4" of asphalt should be left after milling because of the reliance on the asphalt pavement to carry a portion of the load.

Page 15

Unbonded Overlay System• Thicker overlays- real pavement• Over concrete, asphalt, or composite• Not considered monolithic • Existing pavement is considered base • Bonding is good!

Unbonded Concrete

Overlay of Concrete

Pavements

Unbonded Concrete

Overlay of Asphalt

Pavements

Unbonded Concrete

Overlay of Composite Pavements

Unbonded Overlay System

Uses and Advantages - Unbonded Overlay of Concrete Pavements

• Use when existing pavement is in poor condition or better.

• Use to restore structural capacity of the existing pavement and increase pavement life equivalent to full-depth pavement.

• Results in improved surface friction, noise and ride.

• Overlays 6” or greater have been used successfully on ASR when underlying pavement and subbase are stable.

• Overlays on “D” crack pavements have had mixed results depending on the amount of localized distress.

4” - 11” thickness

Pages 5, 18-19

• Can the existing concrete and its subbbase provide a uniform strength platform and, if not, what actions are necessary to obtain that uniformity.

Unbonded on Concrete

Page 18

Unbonded Overlay of Concrete PavementsKeys to Success • Full-depth repairs are required only where

structural integrity is lost at isolated spots.

• Separator layer (normally 1” asphalt) is important to isolate unbonded overlay from underlying pavement and minimize reflective cracking.

• With heavy truck traffic, adequate drainage design may be important to reduce pore pressure in asphalt separation layer.

• Some states are experimenting with geotextile materials for separation layer.• Faulting of 3/8 in. or less in the existing concrete pavement is not a

concern when asphalt separation layer is 1 in. or more.

• Shorter joint spacing helps minimize curling and warping stresses. Transverse joints at 1.5 times thickness for <5” and 2 times thickness 5” or greater up to 15’.

• No need to match joints with those of the underlying concrete pavement. Pages 5, 18-

19

Asphalt Separation Layer

Page 18-19

Innovations for Unbonded Overlays -Geotextile

Interlayer-

5 mm-17 yrs

Page 35

Uses and Advantages - Unbonded Concrete Overlay of Asphalt or Composite Pavements

• Restores or enhance pavement structural capacity, resulting in improved friction, reliability, and noise reduction

• Eliminates deteriorated pavement condition

– severe rutting,

– potholes,

– cracking,

– shoving, and pumping

– when composites indicate past D-cracking and ASR,

4” - 11” thickness

• Used when underlying pavements and subbase are stable and uniform except for isolated areas that can be repaired.

Pages 5, 20-23

• Tented panels with significant movement can be repaired to relieve the pressure and provide uniform support before construction of an overlay.

• Faulted panels that do not exhibit continuing movement have proven to provide adequate support for concrete overlays.

• Edge drains have also been successfully used to reduce the progression of faulting.

Unbonded on Composite Pavements

Pages 5, 22

Unbonded Over Asphalt/CompositeKeys to Success

• Milling may be required to eliminate surface distortions of 2 in. (5.1 cm) or more

• Complete repairs at isolated spots where structural integrity needs restoring

• Concrete patches in the existing pavement should be separated from the overlay

– with a thin layer of fabric or other bond breaker;

– or joints should be sawed in the overlay around the concrete patch perimeter

• Surface temperature of existing asphalt pavement should be maintained below 120ºF (48.9ºC) when placing overlay

• Partial bonding between the overlay and the existing asphalt pavement is acceptable and may even improve load-carrying capacity

Pages 5, 20-23