Concrete Overlays. ACPA Pennsylvania Chapter. ACPA Pennsylvania Chapter. Versatile & Sustainable Solutions. Reasons to Consider a Concrete Overlay

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1 Overlays February 22, 2012 ACPA Pennsylvania Chapter Overlays John M. Becker, P.E. ACPA Penn Chapter February 22, 2012 One of 25 state paving associations affiliated with ACPA National Comprised of approximately 60 members (paving and rehabilitation contractors, cement and other material suppliers, equipment manufacturers, ready-mixed producers, and engineering firms. 2 ACPA Pennsylvania Chapter Overlays Supporter of the National Pavement Technology Center (Iowa) Through affiliation with ACPA, also partner with the International Grooving & Grinding Association Pennsylvania Chapter Staff John M. Becker (Eastern Penn) Mark B. Snyder (Western Penn) 3 Reasons to Consider a Overlay A durable, long lasting, deformation free surface. Low maintenance and rehabilitation costs. Well-established construction techniques. Added structural capacity. Cost effective. Quick to construct. Sustainable solution. Many others.. Versatile & 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. District 8 Winter School 1

2 Overlays February 22, 2012 Pavement Rehabilitation (CPR) Strategies Overlay Solutions for Rehabilitation & Maintenance Overlay Guide, 2 nd Ed. Overview of Overlay Families Overlay types and uses Evaluations & Selections Six Overlay Summaries Design Section Miscellaneous Design Details Overlay Materials Section Work Zones Under Traffic Key Points for Construction Accelerated Construction Specification Considerations Repairs of Overlays Second Edition September 2008 National Overlay Database Many examples of successful PCC overlay projects. Consult the National Overlay Explorer App on the ACPA website. Overlays in Pennsylvania System of Overlays Thinner Overlays Thicker Overlay System Overlay System 11 Bond is integral to design Old pavement is base 12 District 8 Winter School 2

3 Overlays February 22, 2012 Overlay over Generally used on aviation projects 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. 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 strengthened through patching. Milling can remove a number of asphalt surface distresses. 14 Examples of Overlays in Pennsylvania US-119 (Constructed 2010) I-83/US-22 (1995, still in service) 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. 15 See ACPA Overlay Explorer for Details on all Overlays and (Gallery) for the US-119 construction details Allen Road (2011, More on this Later) Effects of Joint Spacing 3.0 ft. 3.0 ft. 3.0 ft. 9.0 ft. Short joint spacing allows slabs to deflect instead of bending. This reduces stresses to reasonable values. Construction Steps for Over / Mill and clean surface. Pre-overlay repairs, if required. Set forms for roller screed. Prepare surface. Place concrete. Texture pavement. Apply curing compound. Saw cut joints. Monitor strength gain (maturity). District 8 Winter School 3

4 Overlays February 22, 2012 Surface Preparation Milling asphalt surface. Remove rutting. Restore profile. Enhance bond. Minimum asphalt thickness after milling: 3 to 5 in. Surface broomed to remove loose material. Pre-Overlay Repairs The purpose of pre-overlay repairs is to restore uniform support. These repairs are generally required for potholes and localized areas of severe alligator cracking. The preferred method of repair is with concrete rather than asphalt (due to bond). Cracks can be filled, but generally are not. Placement placement should follow standard placement procedures. Do not allow the concrete to freefall more than a few feet to avoid segregation. Place the concrete as uniformly as possible in front of the screed/paver. Do not overwork the surface. Do not add water in excess of the specified w/c. Finishing & Texturing Use of a 12 to 16 foot straightedge immediately behind the paver or screed can greatly improve ride quality. Do not over-finish and bring excessive paste to the surface! Curing of Curing must be done as soon as possible after placement. The curing should completely encapsulate the slab, top and sides. Because of the large surface area and small volume of concrete, this is even more critical than in normal construction operations. The slab should be uniformly white. Good Bad Sawing Joints for PCC No different than other concrete pavements Important construction step. Timeliness is key: Large surface area of the thin slab, moisture loss and temperature differentials are key issues. If the joints are not sawed efficiently, random cracks will occur. Contractors must consider the mix and the environment when timing saw cuts. District 8 Winter School 4

5 Overlays February 22, 2012 Overlay Design AASHTO 93 Shortcomings Current Methods MEPDG Design Being Developed Colorado DOT Illinois DOT ACPA System of Overlays Thinner Overlay System Overlays Overlay System Thicker See the complete ACPA web apps Bond is integral to design Old pavement is base 26 Overlay Designed as a new pavement Pre-overlay repair is minimal. Existing pavement is the base for the overlay One inch asphalt or geotextile fabric used as bond-breaker if existing pavement is concrete. placed directly on asphalt pavement (milling not needed) Overlay System Thicker overlays- real pavement Over concrete, asphalt, or composite Not considered monolithic Existing pavement is considered base Bonding is good! Overlay System on Uses and Advantages - PCC Can the existing concrete and its sub-base provide a uniform strength platform and, if not, what actions are necessary to obtain that uniformity. 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 thickness Results in improved surface friction, noise and ride. Overlays 6 or greater have been used successfully on Can overlay pavement with ASR when underlying pavement and sub-base are stable. District 8 Winter School 5

6 Overlays February 22, 2012 Keys 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. 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. No need to match joints with those of the underlying concrete pavement. Innovations for Overlays (Geotextile Interlayer) on or 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. Uses and Advantages - / PCC 4 to 11 thickness 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, Used when underlying pavements and subbase are stable and uniform except for isolated areas that can be repaired. Over / Keys 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 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 District 8 Winter School 6

7 Overlays February 22, 2012 Overlays Built in the 1990 s in PA Lessons Learned overlays provided for well performing pavements Performance was typical of a 20-year rigid pavement Construction using the DBI produced a quality pavement The asphalt interlayer remained intact Overlays Built in the 1990 s in PA More The unbonded overlay would have worked better (30 years or more) if poor subsurface drainage was addressed The original pavement condition was not detrimental to the performance of the overlay Efforts to mismatch existing joints (in JRCP and skewed JPCP) was not problematic Innovations in Equipment Minimum or Zero Clearance Pavers Innovations in Equipment -Stringless Pavers GPS Receiver GPS Controller & Laser Height Gages Laser Sensor Notice edge of paver riding next to curb High Resolution Laser Upcoming Training Integrated Materials for Construction Practices & Overlays February 28 at New Stanton (Western Office of Turnpike) April 12 at King of Prussia (District 6 Construction Conference Room) Registration form at John M. Becker, P.E. American Pavement Association Pennsylvania Chapter (717) Jbecker@pavement.com District 8 Winter School 7