National Academies Press: OpenBook

Common Airport Pavement Maintenance Practices (2011)

Chapter: Appendix B - Catalog of Airport Pavement Preservation Treatments

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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Suggested Citation:"Appendix B - Catalog of Airport Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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54 CONTENTS Introduction 55 AC AND PCC PAVEMENTS FACT SHEET 1—TEXTURIZATION USING SHOT BLASTING 57 FACT SHEET 2—DIAMOND GRINDING 58 FACT SHEET 3—MICROSURFACING 60 AC PAVEMENTS FACT SHEET 4—SEALING AND FILLING CRACKS IN AC PAVEMENT 62 FACT SHEET 5—SMALL AREA PATCHING 64 FACT SHEET 6—SPRAY PATCHING (MANUAL CHIP SEAL AND MECHANIZED SPRAY PATCHING) 66 FACT SHEET 7—MACHINE PATCHING OF AC PAVEMENT USING BITUMINOUS MATERIALS 68 FACT SHEET 8—RESTORATIVE SEALS 70 FACT SHEET 9—TEXTURIZATION USING FINE MILLING 72 FACT SHEET 10—SURFACE TREATMENT (CHIP SEAL, CHIP SEAL COAT) 74 FACT SHEET 11—SLURRY SEAL 76 FACT SHEET 12—HOT-MIX OVERLAY OF AC PAVEMENT 78 FACT SHEET 13—HOT IN-PLACE RECYCLING OF AC PAVEMENT 80 FACT SHEET 14—COLD IN-PLACE RECYCLING OF AC PAVEMENT 82 FACT SHEET 15—ULTRA-THIN WHITETOPPING OF AC PAVEMENT 84 PCC PAVEMENTS FACT SHEET 16—JOINT/CRACK SEALING OF PCC PAVEMENT 86 FACT SHEET 17—PARTIAL-DEPTH (PATCH) REPAIRS OF PCC PAVEMENT 88 FACT SHEET 18—FULL-DEPTH (PATCH) REPAIRS OF PCC PAVEMENTS 90 FACT SHEET 19—MACHINE PATCHING OF PCC PAVEMENT WITH AC MATERIAL 92 FACT SHEET 20—SLAB STABILIZATION AND SLABJACKING 94 FACT SHEET 21—LOAD TRANSFER RESTORATION 96 FACT SHEET 22—CRACK AND JOINT STITCHING 98 FACT SHEET 23—AC OVERLAYS OF PCC PAVEMENTS 100 FACT SHEET 24—BONDED PCC OVERLAY OF PCC PAVEMENTS 102 APPENDIX B Catalog of Airport Pavement Preservation Treatments

55 INTRODUCTION The objective of the Catalog of Airport Pavement Preservation Treatments is to describe common airport pavement preservation treatments for both asphalt concrete (AC) and portland cement concrete (PCC) airfield pavements, and to include materials, methods, and applications. The information is organized in the form of Fact Sheets. Each pavement preservation treatment is described on a separate Fact Sheet using a set format. Selection of Treatments Included in the Catalog This appendix includes 24 Fact Sheets, each describing pavement preservation treatments as listed in Table B1. These 24 treatments were compiled from responses to the questionnaire sent to airport managers and engineers that identified 38 separate treatments as part of this synthesis project. Additional information was obtained from the 35 referenced documents listed in the Resource sections of this appendix. The survey is described in chapter one, the survey questionnaire in Appendix A, the key survey results are described throughout the report, and additional survey results are summarized in Appendix A. Briefly, 50 survey responses were obtained from a geographically diverse set of airports ranging in size from one to approximately 3,000 daily aircraft operations. Thirty-eight pavement preservation treatments were included on the survey form for respondents to review; these encompassed commonly used pavement preservation treatments for AC and PCC pavements. The 24 treatments included in the catalog were taken from the 50 responses and each of these has been used routinely by at least one of the airports sur- veyed, or they have been tried by at least 10% of the airports. All treatments included in the survey satisfied these inclusion criteria with the exception of microsurfacing used for PCC pavements. The 38 treatments included in the survey were reduced to 24 treatments included in the catalog by combining treatments that differed primarily by the material used or by the pavement type to which the treatment is applied. An example of combining treat- ments that differ only by the material used is the combination of two types of crack sealing of AC pavements (using hot-poured sealant or using cold-applied sealant) into one treatment (sealing and filling of cracks of AC pavement). An example of combin- ing treatments that differ primarily by the pavement type is microsurfacing of AC pavements and microsurfacing of PCC pave- ments, which became one treatment—microsurfacing. As a result, the Catalog includes 3 pavement preservation treatments applicable to both AC and PCC pavements, 12 treatments applicable to AC pavements, and 9 treatments applicable to PCC pave- ments (see Table B1). Both Pavement Types 3 treatments Asphalt Concrete 12 treatments Portland Cement Concrete 9 treatments 1) Texturization using shot blasting 2) Diamond grinding 3) Microsurfacing 4) Sealing and filling of cracks (with hot or cold applied sealants) 5) Small area patching (using hot mix, cold mix, or proprietary material) 6) Spray patching (manual chip seal and mechanized spray patching) 7) Machine patching with AC material 8) Rejuvenators and seals 9) Texturization using fine milling 10) Surface treatment (chip seal, chip seal coat) 11) Slurry seal 12) Hot-mix overlay (includes milling of AC pavements) 13) Hot in-place recycling 14) Cold in-place recycling 15) Ultra-thin whitetopping 16) Joint and crack sealing (with bituminous, silicone, or compression sealants) 17) Partial depth repairs (using AC, PCC, and proprietary materials 18) Full-depth repairs (using AC, PCC, and proprietary materials 19) Machine patching using hot mix 20) Slab stabilization and slab- jacking 21) Load transfer 22) Crack and joint stitching 23) Hot-mix overlays 24) Bonded PCC overlay TABLE B1 AIRPORT PAVEMENT PRESERVATION TREATMENTS INCLUDED IN THE CATALOG

Sources of Information Information sources used for the preparation of the catalog were similar to those used for the report and are described in the Method- ology section in chapter one of the synthesis report. In addition, each Fact Sheet contains a section titled “Resources,” which typi- cally contains two or three source references and additional information. The main purpose of these references is to direct the reader to key publications containing general and specific information on the treatment. The number of references listed on the Fact Sheets was restricted for brevity. References used in development of the fact sheets included: California Department of Transportation, Maintenance Technical Advisory Guide, 2nd ed., Office of Pavement Preservation, Division of Maintenance, Sacramento, 2008. Michigan Department of Transportation, Capital Preventive Maintenance, 2003 ed., Construction and Technology Division, Lansing, Apr. 2010. Ohio Department of Transportation, Pavement Preventive Maintenance Guidelines, Office of Pavement Engineering, Columbus, May 2001. Minnesota Department of Transportation, Preventive Maintenance Best Management Practices of Hot Mix Asphalt Pavements, Report MN/RC-2009-18, Office of Materials and Road Research, Maplewood, May 2009. Hicks, R.G., S.B. Seeds, and D.G. Peshkin, Selecting a Preventive Maintenance Treatment for Flexible Pavements, Publication FHWA-IF-00-027, Federal Highway Administration, U.S. Department of Transportation, Washington, D.C., 2000. Wu, Z., J.L. Groeger, A.L. Simpson, and G.R. Hicks, Performance Evaluation of Various Rehabilitation and Preservation Treat- ments, Office of Asset Management, Federal Highway Administration, Washington, D.C., Jan. 2010. Organization of the Catalog The Catalog consists of 24 Fact Sheets, each describing a separate pavement preservation treatment. Although the pavement preser- vation treatments are described separately, several treatments can be used on the same pavement section at the same time, or at dif- ferent times, as part of a single pavement rehabilitation project or strategy. For example, a single PCC pavement rehabilitation proj- ect may include four maintenance and rehabilitation (M&R) treatments: shallow patch repair, full-depth repair, diamond grinding, and joint/crack resealing. The order in which the M&R treatments are described in the Catalog was set up according to the following rules: 1. Treatments that can be applied to both AC and PCC pavements without any substantial modification are described first, followed by the description of treatments applicable to AC pavements and PCC pavements. 2. For each pavement type, the treatments are arranged in an approximate order of their increasing contribution to restoring pave- ment serviceability. The Fact Sheets describe treatments using a uniform format. Each Fact Sheet starts with a sketch showing a sequence of operations, and a short definition of the treatment. Service lives and unit costs of the pavement preservation treatments given in the Fact Sheets provide relative information that can be used for orientation and comparison purposes only. The service lives and costs are based on a literature review and apply to typical situations only. The synthesis survey included questions on the usage and performance of pavement preservation treatments, but not on their life spans and costs. 56

57 Fact Sheet 1—Texturization Using Shot Blasting Schematic of Shot Blasting Operation Shot blasting is a texturization technique that uses a self-propelled machine that blasts abrasive particles onto the pavement surface as shown in the above schematic. The objective is to remove contaminants, such as rubber deposits and excess asphalt cement (AC), and to abrade deteriorated surface material to restore both micro- and macrotexture. Surface retexturing with shot blasting can be used for both AC and PCC (portland cement concrete) pavements to improve pavement friction. Sources of Information and Additional Resources The source document and additional general information is from Gransberg, “Life-Cycle Cost Analysis of Surface Retexturing with Shotblasting as an Asphalt Pavement Preservation Tool,” Transportation Research Record: Journal of the Transportation Research Board, No. 2108, Transportation Research Board of the National Academies, Washington, D.C., 2009, pp. 46–52. Purpose and Selection Criteria Unlike fine milling and diamond grinding, shot blasting does not improve pavement smoothness. It can be used to improve pavement friction by removing materials from the pavement surface, to clean pavement surface before the application of sealants, and to remove traffic control lines and signs. The best improvement in pavement surface friction by shot blasting is achieved when abrasion-resisting aggregate particles are embedded in a mortar that can be abraded by shot blasting. Typical Service Life and Costs When used to restore pavement friction by removing softer or deteriorated material, the treatment effectiveness may last 1 to 6 years. When used to remove rubber deposits on runways, the effectiveness depends on the formation of new rubber deposits. The cost is typi- cally lower than for diamond grinding and is in the range of approximately $2 to $10 per square yd. Materials and Construction There are several types of proprietary equipment that can produce a pattern width ranging from approximately 6 in. to 6 ft. The equip- ment includes a system that propels abrasive particles, such as small round steel pellets, onto the pavement surface, vacuums up the resulting pavement material debris and abrasive particles, separates the abrasive particles from debris for re-use, and stores the debris for disposal. The technique is commonly applied to PCC pavements, but has also been successfully used on both AC and surface- treated surfaces. Airport Experience Just over 20% of airports surveyed reported that they have tried using shot blasting for PCC or for AC pavements. None of the air- ports reported routine use of shot blasting for either pavement type. Typically, the performance of shot blasting was reported as good. Vacuum separatorBlast wheel Debris storageAbrasive storage

58 Fact Sheet 2—Diamond Grinding Schematic of Diamond Grinding Operation Diamond grinding is a rehabilitation technique that removes a shallow depth of pavement surface material by saw cutting closely spaced grooves into the pavement surface using diamond-tipped blades. The above illustration shows a self-propelled diamond grinding machine. Sources of Information and Additional Resources California Department of Transportation, Maintenance Technical Advisory Guide, 2nd ed., Office of Pavement Preservation, Division of Maintenance, Sacramento, 2008. Michigan Department of Transportation, Capital Preventive Maintenance, 2003 ed., Construction and Technology Division, Lansing, Apr. 2010. Ohio Department of Transportation, Pavement Preventive Maintenance Guidelines, Office of Pavement Engineering, Columbus, May 2001. Additional resources include a comprehensive manual of practice; the Concrete Pavement Repair Manual was issued by American Con- crete Pavement Association (ACPA) in 2003 and is available from www.pavement.com. American Concrete Pavement Association, Diamond Grinding and Concrete Pavement Restoration, Report TB008P, Skokie, Ill., 2000. Purpose and Selection Criteria The purpose of diamond grinding is to improve pavement smoothness and/or improve pavement surface friction. When used to improve pavement smoothness, diamond grinding is applied only to selected areas of the pavement. For example, to remove slab step- ping (faulting), grinding can be applied to selected transverse joints. When used to improve pavement surface friction, diamond grind- ing is typically used over the entire pavement area. Diamond grinding can remove up to 3⁄4 in. from the pavement surface and can remove surface defects and irregularities such as polished or scaling surface and faulting, and improve pavement surface smoothness. When used to correct faulting, the faulting is expected to be relatively stable in terms of progression and typically does not exceed approximately 1⁄4 in. Diamond grinding is often used as the penultimate treatment in a PCC rehabilitation project, done after load transfer restoration, and partial and full-depth repairs. The last treatment is for joint and crack resealing. Diamond grinding will not address the underlying cause of pavement structural problems and is inappropriate for surfaces with material problems such as durability (D)-cracking or alkali-reactive aggregate. Typical Service Life and Costs The restoration of pavement surface friction by diamond grinding may last 5 to 12 years. Grinding to improve pavement smoothness on faulted slabs may last only a few years, particularly if the original faulting was progressing and the underlying reasons for the fault- ing were not addressed. Typical cost of diamond grinding is in the range of $4 to $12 per square yard, depending on quantities and the hardness of the aggregate. Materials and Construction Diamond grinding employs a large drum, equipped with closely spaced diamond-tipped teeth, mounted on a moving heavy-set frame- work. The best results are achieved with continuous operation employing wide grinding drums. When several grinding passes are required to cover one traffic lane, the passes typically overlap by less than 2 in. The diamond grinding operation is carried out in the longitudinal direction, and preferably against the predominant direction of aircraft operations. The spacing between the diamond-tipped saw blades is such that the ridges (or fins) left between the blades break readily, approx- imately 2 or 3 mm, depending on the strength of the concrete (Figure B1). If the ridges do not break off readily, the spacing between the blades can be reduced. Diamond grinding results in a characteristic corduroy texture with high pavement surface friction produced by the combination of smoothly cut channels and rough surface where the ridges have broken off.

59 Slurry resulting from the grinding operation (water is used to cool diamond-tipped blades and suppress dust) is continuously vac- uumed and collected. Diamond grinding done only to improve pavement surface friction on relatively new pavements may not require resealing of joints. Grinding done to correct faulting on older pavements is typically followed up by joint resealing. Airport Use About 8% of airports surveyed use diamond grinding routinely, and approximately 46% of airports surveyed have tried using it. All airports that routinely use or have tried using diamond grinding rated its performance as very good or good. Width of saw cut (1/10 to 1/7 inch) Land area: 1/10 inch typical for hard aggregate 1/8 inch typical for soft aggregate Depth of saw cut (1/17 to 1/13 inch) FIGURE B1 Profile of diamond-grooved surface. Improved pavement surface friction is provided by the land area created by the broken- off ridges.

60 Fact Sheet 3—Microsurfacing Schematic of Microsurfacing Operation Microsurfacing is an unheated mixture of polymer-modified asphalt emulsion, high-quality frictional aggregate, mineral filler, water, and other additives, mixed and spread over the pavement surface as a slurry. The construction of microsurfacing using a self-propelled truck-mounted continuous-feed mixing machine is illustrated by the schematic above. The aggregate skeleton used for microsurfacing consists of high-quality interlocking crushed aggregate particles. Consequently, it is possible to place microsurfacing in layers thicker than the largest aggregate size, or in multiple layers, without the risk of perma- nent deformation. Sources of Information and Additional Resources California Department of Transportation, Maintenance Technical Advisory Guide, 2nd ed., Office of Pavement Preservation, Divi- sion of Maintenance, Sacramento, 2008. Michigan Department of Transportation, Capital Preventive Maintenance, 2003 ed., Construction and Technology Division, Lansing, Apr. 2010. Ohio Department of Transportation, Pavement Preventive Maintenance Guidelines, Office of Pavement Engineering, Columbus, May 2001. Minnesota Department of Transportation, Preventive Maintenance Best Management Practices of Hot Mix Asphalt Pavements, Report MN/RC–2009-18, Office of Materials and Road Research, Maplewood, May 2009. Hicks, R.G., S.B. Seeds, and D.G. Peshkin, Selecting a Preventive Maintenance Treatment for Flexible Pavements, Publication FHWA-IF-00-027, Federal Highway Administration, U.S. Department of Transportation, Washington, D.C., 2000. The International Slurry Surfacing Association (ISSA) maintains a website at www.slurry.org, which contains recommended specifications and useful guidance for microsurfacing (Recommended Performance Guidelines for Micro-Surfacing, A143). Purpose and Selection Criteria Microsurfacing is used to correct surficial distresses such as slight block cracking, raveling and segregation, flushing, and loss of pavement friction. Because microsurfacing contains high-quality crushed aggregate it is also used to fill in ruts and surface deforma- tion to the depth of up to 13⁄4 in. Microsurfacing can also be used to extend the service life of the pavement until a more permanent restoration can be completed. As a preventive maintenance treatment it can be used to seal the surface of the pavement, protecting the pavement from water infil- tration and greatly reducing the rate at which the existing AC surface oxidizes. Microsurfacing is also used on PCC pavements to improve or maintain frictional resistance and smoothness. Typical Service Life and Costs When used to protect the existing pavement structure as a preventive maintenance treatment, microsurfacing can prolong pavement life span by 4 to 6 years. When used to restore or improve pavement surface; for example, to restore pavement friction or to repair wheel track rutting, microsurfacing can last 5 to 8 years. The cost of one application of microsurfacing is approximately $3 to $6 per square yard, typically approximately 75% of the cost of a single hot-mix overlay. Materials and Construction Microsurfacing mix is always designed by a contractor or an emulsion supplier. Figure B2 shows a finished product a year after con- struction. The ISSA recommends two types of gradations, Type II and Type III. The Type II gradation is finer, with 90% to 100% Optional tack coat application Spreader box Pug mill Portland cement Emulsion Aggregate Feeder & propulsion unitApplication unit Asphalt distributor Water spray

61 passing a 4.75 mm sieve. The Type III gradation is coarser with 70% to 90% of aggregate passing the No. 4 sieve size, and can be used on runways. A minimum thickness of microsurfacing mix using Type III gradation is 0.4 in. for a single course. The surface on which microsurfacing is applied is expected to have uniform pavement condition. Areas that exhibit significantly more severe defects than the remainder of the section (e.g., raveling, cracking, or rutting) are repaired. The repairs can by made using an additional course of microsurfacing or by other means depending on the type, extent, and severity of the defects. On high traffic volume facilities, and/or when the surface of the pavement has minor distortions and/or has ruts exceeding approximately 1⁄4 in., two courses of microsurfacing are used. The first (scratch) course is intended to improve the profile of the pavement and the second course provides the wearing surface. Ruts exceeding 1⁄2 in. are typically filled with microsurfacing material using a rut-filling spreader box. After the microsurfacing application, traffic can use the pavement without restrictions in about 45 to 120 minutes, depending on setting time of the asphalt emulsion, weather, and traffic conditions. Microsurfacing is typically carried out only during the warmer, dryer months. Cooler temperatures and wetter conditions can result in longer curing times during which the microsurfacing can be damaged by traffic. Airport Experience Microsurfacing can be used for both AC and PCC pavements. For AC pavements, only one airport surveyed used microsurfacing rou- tinely, and two airports surveyed have tried using it. For PCC pavements, only one of the surveyed airports indicated use of micro- surfacing. FIGURE B2 Microsurfacing texture one year after construction; diameter of the coin is 1 in.

62 Fact Sheet 4—Sealing and Filling Cracks in AC Pavement Illustration of Crack Routing, Cleaning, and Sealing Crack sealing is a maintenance technique that cleans cracks and seals them with a rubberized bituminous compound. The crack seal- ing typically includes routing of the crack to create a reservoir for the sealant at the top of the crack, as shown in the illustration above. Crack sealing without routing is called crack filling. Crack filling is not as cost-effective as crack sealing and is easily damaged by snow plows. For this reason, this Fact Sheet concentrates only on crack sealing. Sources of Information and Additional Resources California Department of Transportation, Maintenance Technical Advisory Guide, 2nd ed., Office of Pavement Preservation, Divi- sion of Maintenance, Sacramento, 2008. Michigan Department of Transportation, Capital Preventive Maintenance, 2003 ed., Construction and Technology Division, Lansing, April 2010. Ohio Department of Transportation, Pavement Preventive Maintenance Guidelines, Office of Pavement Engineering, Columbus, May 2001. Minnesota Department of Transportation, Preventive Maintenance Best Management Practices of Hot Mix Asphalt Pavements, Report MN/RC–2009-18, Office of Materials and Road Research, Maplewood, May 2009. Hicks, R.G., S.B. Seeds, and D.G. Peshkin, Selecting a Preventive Maintenance Treatment for Flexible Pavements, Publication FHWA-IF-00-027, Federal Highway Administration, U.S. Department of Transportation, Washington, D.C., 2000. Additional resources include: Michigan Department of Transportation produced a manual, Sealing and Filling of Cracks for Bituminous Concrete Pavements, Selection and Installation Procedures, which is available on CD and distributed by Foundation for Pavement Preservation, Austin, Tex. [Online]. Available: www.fp2.org. A useful summary of information is available from Crack Seal Application, Pavement Preservation Checklist Series, Publication FHWA-IF-02-005, produced by the Foundation for Pavement Preservation, Austin, Tex. [Online]. Available: www.fp2.org. UFC 3-250-08FA, Standard Practice for Sealing Joints and Cracks in Rigid and Flexible Pavements. Purpose and Selection Criteria The purpose of crack sealing is to prevent water from entering the pavement structure and damaging it. Crack sealing is most effec- tive in a wet-freeze environment. It is applied to “working or active” cracks. These cracks change in width during the year because of temperature changes, and include both transverse cracks and longitudinal cracks. Figure B3 shows how water from melting snow enters the pavement through unsealed cracks. Infiltrated water, together with the effect of freeze–thaw cycles and pavement loads, Locate Rout Clean Seal FIGURE B3 Water from melting snow readily enters pavement structure through a transverse crack.

63 leads to heaving of the cracks (Figure B4) and to the deterioration of the pavement structure beneath the crack. The additional bene- fit of sealing is the prevention of spalling and raveling of unsealed crack edges. Crack sealing is typically done soon after transverse and longitudinal cracks develop, often when the pavement is 2 to 5 years old. At that time, the crack pattern would be well-developed and the crack would reach the width of 0.1 to 0.4 in. at moderate tempera- tures. The initial crack sealing is typically followed by a second sealing carried out when new cracks appear or when the original sealant no longer works, often after another 3 to 5 years. Crack sealing is most cost-effective for thick AC pavements. It is typically not cost-effective for thin AC pavements with the total thickness of the AC layer less than 3 in. Thin pavements tend to develop many secondary cracks that cannot be effectively sealed or filled. Typical Service Life and Costs The expected life of crack sealing is about 2 to 7 years. The crack sealing performance depends on the crack and pavement condition, sealant material, rout configuration, and construction procedures. Typical cost of rout-and-seal treatment is approximately $2 to $3 per linear yard. Materials and Construction There are many AC sealants on the market and their performance can differ significantly. Hot-poured rubberized bituminous sealants are most often used. Some agencies are not satisfied with the existing specifications for sealants (e.g., ASTM D6690 or AASHTO T187-60) and have modified them. The reservoir for the sealant at the top of the crack is created by a router. The opinions regarding the size and shape of the most effective reservoir differ. It is generally agreed that routs with greater width than depth and a rectangular shape are preferable. The routed crack is typically cleaned before sealing. The sealant is heated in a double-jacketed kettle to avoid exposure of the sealant to direct heat. It is important to avoid overheat- ing or re-heating the sealant, and dispersing the sealant into the crack by a device (a pump wand) that maintains the sealant at a desired temperature. Because the sealant shrinks after the installation and cooling, the hot sealant is installed “proud” of the surface. Until the sealant hardens and there is no danger that it will be picked up by passing tires, it is covered by a bond-breaking material such as sawdust or flour. The use of cement or mineral dust is typically avoided. Occasionally, it is necessary to seal cracks wider than 30 mm. These cracks can be temporarily repaired by fine aggregate hot mix or liquefied patching materials similar to a slurry material. Airport Use Based on the survey, a majority of all airports routinely perform crack sealing using a hot-poured bituminous sealant. The majority of the airports surveyed reported good performance of crack sealing. Only a small minority of airports surveyed use cold-applied sealants routinely. The majority of airports surveyed rout cracks prior to sealing. FIGURE B4 Transverse crack heaving caused by water that saturated pavement structure and froze.

64 Fact Sheet 5—Small-Area Patching The Sequence of Operations for Small Patching Repairs Small-area patching is a maintenance treatment that includes placing and spreading of bituminous mixtures, hot or cold, to repair pot- holes and other pavement distresses without the use of mechanical pavers or graders. The illustration shows the sequence of opera- tions. The patching with hot mix or cold mix can be used for both bituminous pavements and PCC pavements; however, permanent repairs of PCC pavements are typically done using PCC material. If pavers or graders are used, the treatment is called machine patch- ing and is described on a separate Fact Sheet. Sources of Information and Additional Resources California Department of Transportation, Maintenance Technical Advisory Guide, 2nd ed., Office of Pavement Preservation, Division of Maintenance, Sacramento, 2008. Additional resources include: A useful manual of practice was issued by the Federal Highway Administration as Report FHWA-RD-99-168, Materials and Pro- cedures for Repair of Potholes in Asphalt-Surfaced Pavements: Manual of Practice, and is available at www.tfhc.gov/pavement/ ltpp/pdf/99168.pdf. Several highway agencies have developed manuals for patching of AC pavements. One of the most comprehensive has been pub- lished by the Minnesota Technology Transfer Center, Best Practices Handbook on Asphalt Pavement Maintenance, Manual No. 2000-04, Minneapolis, 2000. Purpose and Selection Criteria Small-area patching is used to repair localized defects such as potholes, distortion resulting from utility cuts, and small areas with severe ravelling and/or alligator cracking. The repair of potholes such as the one shown in Figure B5 reduces pavement roughness and the rate of pavement deterioration by improving drainage and reducing dynamic traffic loads. The repairs may be permanent, semi-permanent, or temporary. Permanent repairs—Permanent repairs are used on pavements that are in good condition to bring the life span of the repaired area in line with that of the rest of the pavement. Permanent repairs require the use of appropriate patching materials and techniques, with the goal of addressing the underlying cause of the defects being repaired. Unless the original cause for the pavement defects is corrected, the repairs are susceptible to early failure. Semi-permanent repairs—Semi-permanent repairs have a typical life expectancy of one or two years. Usually, the area is not saw cut and may be repaired with cold mix. Temporary repair—Temporary repairs are used to hold the pavement until it can be resurfaced or permanently repaired. They are also used as emergency repairs when the pavement condition may pose a hazard to airplane operations. Clean and trim Apply a tack coat Add patching material Compact Select FIGURE B5 Untreated pothole collects water and accelerates pavement deterioration.

65 Typical Service Life and Costs Temporary patching repairs may last one year or less; permanent repairs may last 10 years or more. The cost of small-area patching is highly dependent on the extent of the repairs and on the selection of patching material. A typical unit cost for small-area patching is $20 to $40 per square yard. Materials and Construction The main types of patching materials include hot mix, local or agency-specified cold mix, and proprietary cold mix. A tack coat, if used, is typically an emulsion diluted with additional water. Hot-mix AC patching material provides the most durable treatment. Some suppliers of proprietary cold patching mixes suggest that their products can achieve similar performance and that their products can be successfully applied to potholes containing water. Cold mixes with single-size aggregate may not perform well in relatively large repairs. The single-size aggregate mix has low stability and is susceptible to rutting and ravelling. Typically, small-area permanent patching repair includes the following steps: • Removal of broken pavement material in the patch area by jack hammering, cold milling, and/or pavement sawing. • Cleaning out loose material from the patch area by blowing or brushing. • Applying a tack coat to provide a bond between the existing pavement and the patching material. • Placing the bituminous mix into the patch area. If the patch area is deeper than 2 in., the mix is placed and compacted in lifts until the level of the surrounding pavement is reached. • Compacting the mix with a steel or rubber-tire roller, a vibratory plate compactor, or a hand tamper. Depending on the size and depth of the repair, and the material used, the finished repair will have crown of 0.1 to 0.4 in. • Sealing the joint between the patch and the original pavement with hot-poured crack sealant. Sealing is typically done for larger and deeper repair areas. Airport Experience Patching is one of the most common pavement maintenance treatments. According to survey respondents, the majority of airports (that have AC pavements) routinely use small-area patching using hot mix and a minority of airports routinely use cold mix. None of the agencies surveyed reported poor performance of repairs using hot mix, whereas approximately 20% of agencies surveyed reported poor results using cold mix. A small minority of agencies surveyed routinely used a proprietary mix.

Fact Sheet 6—Spray Patching (Manual Chip Seal and Mechanized Spray Patching) Schematic of Chip Seal Operation Spray patching is a maintenance treatment that includes the application of bituminous material followed by spreading of cover aggre- gate. The technological sequence is shown in the above schematic. Spray patching can be done manually or by specialized self-propelled equipment that sprays an emulsion, applies the cover aggregate, and provides the initial compaction—all in one pass. Mechanized spray patching applied on the full-width of a facility, such as a taxiway, and that is longer than 100 ft, is called surface treatment. The Catalog contains a separate Fact Sheet for surface treatments. Sources of Information and Additional Resources Hicks, R.G., S.B. Seeds, and D.G. Peshkin, Selecting a Preventive Maintenance Treatment for Flexible Pavements, Publication FHWA-IF-00-027, Federal Highway Administration, U.S. Department of Transportation, Washington, D.C., 2000. Asphalt Recycling and Reclaiming Association, Basic Asphalt Recycling Manual, Annapolis, Md., 2001. Additional information includes: U.S. Department of Transportation, Pavement Preservation Compendium II, Publication FHWA-IF-06-049, Sep. 2006. InfraGuide 2005: Preservation of Bituminous Pavement Using Thin Surface Restoration Techniques, 2005 [Online]. Available: http://gmf.fcm.ca/Infraguide/Roads_and_Sidewalks.asp. Purpose and Selection Criteria Spray patching is used to slow down pavement deterioration of vulnerable localized areas or to repair localized pavement distresses such as ravelling, flushing, and block cracking. A properly applied spray patching produces an all-weather surface that seals the pave- ment surface, prevents or retards propagation of surficial distresses, and can provide improved surface friction. The use of spray patching to repair or slow down the progression of transverse or longitudinal cracks is not considered to be cost-effective. Manual spray patching is suitable for localized repairs. Machine patching is typically used to repair large areas that do not require full-width coverage. Typical Service Life and Costs The typical life span of spray patching is 2 to 5 years. A typical cost of spray patching is in the range of $3 to $8 per square yard, depending primarily on the quantity of work. Materials and Construction Manual spray patching employs a variety of bituminous products (applied hot or cold) and aggregates (chips, graded aggregate, or sand). Typically, bituminous products used for spray patching are emulsions heated to less than 185°F. Aggregate used for mechanized spray patching is typically open-graded (chips). Aggregate used for manual patching can be dense or open-graded with a typical maximum aggregate size of approximately 1⁄2 in. Sand is also used. Manual application of emulsion is done with a hand wand or a spray bar. Cover aggregate is applied immediately after spraying emulsion. Compaction with truck tires or rubber-tired rollers follows. Generally, after compaction, 75% of the height of the aggre- gate particles is imbedded in the emulsion. The procedure for manual spray patching typically consists of the following steps: • Removal of all loose material and debris. • Spraying of an emulsion in a uniform manner. • Application of aggregate to obtain even coverage. Asphalt emulsion distributor Self-propelled aggregate spreader Power broom or sweeper Rubber-tired roller 66

67 • Compaction; wheels of the truck used to supply the cover aggregate can be used for compaction. • Sweeping off loose aggregate around and over the patch. Spray patching is generally carried out only during the warmer, dryer months. Cooler temperatures and wetter conditions prolong set- ting (hardening) of the emulsion and the time the repairs are susceptible to damage by traffic. Airport Experience Spray patching used to be one of the key maintenance treatments for AC pavements. However, the usage of manual spray patching has been declining. Only a few airports surveyed routinely use spray patching or have tried it.

Fact Sheet 7—Machine Patching of AC Pavement Using Bituminous Materials Schematic of Machine Patching Operation Machine patching of AC pavements is a maintenance technique that involves placing and spreading of premixed bituminous materi- als (hot or cold mix) using a mechanical paver or a grader on parts of a pavement section. As shown in the illustration, machine patch- ing includes the application of tack coat, placement of the patching material, and compaction. Sources of Information and Additional Resources California Department of Transportation, Maintenance Technical Advisory Guide, 2nd ed., Office of Pavement Preservation, Divi- sion of Maintenance, Sacramento, 2008. Additional resources includes: SHRP H 348: Asphalt Pavement Repair Manuals of Practice, Materials, and Procedures for the Repair of Potholes in Asphalt- Surfaced Pavements, Strategic Highway Research Program, Transportation Research Board, National Research Council, Washington, D.C., 1993. Purpose and Selection Criteria Typical applications of machine patching include repairs of localized areas of ravelling and segregation, alligator cracking, pothol- ing, rutting, frost heaving, and subgrade settlement. The areas selected for patching are expected to be well-defined and separated by areas that are in good condition. If the areas requiring patching are closely spaced, it may be more cost-effective to resurface the entire section. Machine patching repairs can be divided into permanent and semi-permanent repairs: Permanent repairs—Permanent patching repairs can be used on pavements that are in good condition to bring the life span of the repaired area in line with that of the rest of the pavement. For example, if it is expected that the pavement being repaired will require resurfacing in 8 years, the patching repair could be done to also last approximately 8 years. Semi-permanent repairs—Semi-permanent repairs have a limited life expectancy and are used typically when it is anticipated that the entire pavement will be resurfaced within a few years. To save costs, the extent of patching is limited and the patched area may not receive a tack coat. Typical Service Life and Costs Permanent repairs may last 5 to 12 years or more; semi-permanent repairs may last approximately 5 years or less. A typical cost of machine patching is $10 to $25 per square yard. Materials and Construction For permanent repairs, the same type of hot mix may be used for patching as that used for the surface of the existing asphalt pave- ment. Typically, permanent machine patching includes the following steps: • Structural repairs—If the patch is over an area exhibiting structural weakness (e.g., alligator cracking, rutting, or depression and settlement) it may be necessary to remove some or all of the underlying base and subbase material. The granular base is restored and re-compacted. The additional pavement strength, if required, is achieved by replacing some part of the granular material with AC to avoid increasing the overall thickness of the pavement structure. • Removal of the deteriorated AC layer by milling—Milling may be required to maintain pavement elevation or to provide a smooth transition between the original pavement and the patch. Figure B6 shows a construction detail for the start of a long patch. Paver Hot mix truck Asphalt distributor 1. Rubber tired rollers 2. Static dual steel drum rollers Optional tack coatOptional built-in tack coat application 68

69 • Application of a tack coat at the sides of the patch and over the entire patched area to improve the bond between the original pavement and the patch, and to minimize water infiltration. • Placing of the mix. The placement is done by a paver. The material is placed in layers not exceeding 3 in. The minimum thick- ness of a permanent machine-placed patch is typically 11⁄4 in. • Compaction of the patch area using rollers. • Application of a sealant at the joint of the patch and the existing pavement. Resealing the joint if it opens in a few years. Airport Experience About one-half of all survey respondents routinely use or have tried using machine patching. A large majority of respondents reported very good or good performance. 2 to 4 feet 1¼ inch minimumWedge milling Finished overlay FIGURE B6 Wedge milling to key in a 11⁄4-in.-thick AC patch.

70 Fact Sheet 8—Restorative Seals Schematic of Restorative Sealing Operation Restorative seals consist of an application of a bituminous or coal-tar material, typically emulsion-based, to the surface of AC pave- ment as illustrated by the schematic. Restorative seals are also called rejuvenators or fog seals. Some agencies or suppliers recom- mend light sanding of fog seals (approximately 1 lb of sand per square yard). Sources of Information and Additional Resources California Department of Transportation, Maintenance Technical Advisory Guide, 2nd ed., Office of Pavement Preservation, Divi- sion of Maintenance, Sacramento, 2008. Minnesota Department of Transportation, Preventive Maintenance Best Management Practices of Hot Mix Asphalt Pavements, Report MN/RC-2009-18, Office of Materials and Road Research, Maplewood, May 2009. Hicks, R.G., S.B. Seeds, and D.G. Peshkin, Selecting a Preventive Maintenance Treatment for Flexible Pavements, Publication FHWA-IF-00-027, Federal Highway Administration, U.S. Department of Transportation, Washington, D.C., 2000. Additional resources include: Shoenberger, J.E., “Skid Resistance of Rejuvenated Airfield Pavements,” Proceedings of the 27th International Air Transportation Conference, Advancing Airfield Pavements, American Society of Civil Engineers, Reston, Va., 2007. Engineering Technical Letter 03-8, Rejuvenation of Hot-Mix Asphalt (HMA) Pavements, Dec. 2003. Boyer, R. and D.I. Hanson, Non-Coal-Tar Fuel Resistant Sealers and HMA Systems: State-of-the-Practice, prepared for Airfield Asphalt Technology Program Project 05-02, May 2008. Purpose and Selection Criteria Restorative seals can serve one or more of following three purposes: To seal the surface—Restorative seals can reduce penetration of water by sealing small cracks and porous pavement surfaces. Restorative seals can slow the progression of raveling and coarse aggregate loss, and have been used shortly after paving to seal areas with low to moderate segregation. The sealing can also slow down oxidation and hardening of AC. To rejuvenate oxidized and hardened asphalt binder—Restorative seals used primarily to revitalize the surface of the AC pave- ment are called rejuvenators. Rejuvenators are intended to penetrate the surface of the AC pavement and reverse the oxidation and hardening process in the AC. The depth of penetration is usually only 0.1 to 0.2 in. Rejuvenators do not leave much resid- ual material on the surface and can be re-applied. To provide protection against fuel spills and oil leak—Aircraft fuels and lubricants are chemically compatible with AC, can dis- solve it, and degrade the surface of AC pavements. Restorative seals that are not compatible with AC can provide protection from the damaging effects of fuel spills and oil leaks. Typical Service Life and Costs A restorative seal is a temporary fix generally lasting 1 to 3 years. The cost can range from $0.5 to $2 per square yard. Materials and Constructions Restorative seals designed to seal the pavement surface use slow or medium setting asphalt emulsion further diluted with water. Aggregate, if applied to provide better pavement friction, is typically medium to fine sand with the particle size of less than 0.05 in. Restorative seals designed to function as rejuvenators or as rejuvenators/sealers contain proprietary materials that may contain sol- vents. Restorative seals for the protection against fuel spills and oil leaks are typically coal-tar sealers—an emulsion of coal tar sta- bilized with clay. Acrylic-modified bituminous emulsions can also increase protection against fuel spills. Restorative seals are sprayed on the pavement surface by distributors. Asphalt emulsion is typically heated to about 175°F before the application to pavement that is in good condition and has been broomed before the restorative seals are applied. With Optional light sanding Emulsion distributor

71 correct application rates, and in some instances the use of sand, restorative seals can generally provide satisfactory levels of pave- ment friction. Airport Experience About one-half of the airports surveyed routinely use or have used restorative seals, and a large majority of the users reported very good or good performance.

72 Fact Sheet 9—Texturization Using Fine Milling Schematic of Milling Operation Texturization techniques using milling include conventional milling, precision milling, and fine milling. Milling is done by a cylin- drical milling drum with closely spaced carbide-tipped tools (teeth). The techniques differ by the spacing of the cutting teeth, as shown on the above illustration, and by the degree of control over the profile of the milled surface. Fine milling, also called micromilling, removes unevenness from the pavement surface or improves its texture, and leaves an abraded surface that can be used as a driving surface. Sources of Information and Additional Resources Hicks, R.G., S.B. Seeds, and D.G. Peshkin, Selecting a Preventive Maintenance Treatment for Flexible Pavements, Publication FHWA-IF-00-027, Federal Highway Administration, U.S. Department of Transportation, Washington, D.C., 2000. Additional resources include: The Basic Asphalt Recycling Manual by the Asphalt Recycling and Reclaiming Association provides guidelines for milling and other texturization techniques. Hall, K.L., J.W. Smith, and P. Littleton, NCHRP Report 634: Texturing of Concrete Pavements, Final Report, Nov. 2008, Transporta- tion Research Board of the National Academies, Washington, D.C., Nov. 2008, 97 pp. Purpose and Selection Criteria Fine milling can improve pavement smoothness and pavement friction. Smoothness is improved by milling of protruding pavement features such as bumps, stepping (faulting) at transverse cracks, and rutting. If the pavement has sufficient structural capacity, the reduction in thickness is not of concern. Figure B7 shows an example of pavement surface where micromilling was used to reduce rutting and roughness. 0.6 to 0.8 inches Self-propelled milling unit 0.2 to 0.5 inches 0.2 inches Conventional MicroPrecision Cutting Teeth Spacing Power broom FIGURE B7 The milled surface has grooves with the peak-to- peak distance of approximately 0.6 in.

73 Typical Service Life and Costs The expected service life of texturization using fine milling is 1 to 7 years. A typical cost is approximately $4 to $12 per square yard. Materials and Construction Milling is a general term used to describe the removal of the surface of AC or PCC materials from pavements by a self-propelled unit having a cutting drum equipped with closely spaced carbide-tipped tools. Micromilling and precision-milling are types of milling that strive to provide a more even platform for an overlay and/or a finished pavement surface. Micromilling and precision-milling oper- ations are also called fine milling. The following definitions of micromilling and precision milling are not universally accepted and are provided for orientation purposes only. Micromilling—Typically, the depth of micromilling is up to 0.6 in. and results in a surface texture depth of about 0.04 in. with the groove-to-groove spacing of 0.2 in. Such surface does not need an overlay. Precision milling—Typically, the depth of precision milling is up to 1 in. and results in a surface texture depth of approximately 0.2 in. A precision-milled surface is usually overlaid. Airport Use A small minority of airports surveyed routinely use or have used fine milling. In addition, one responding airport reported using trans- verse grooving of the AC surface to improve pavement friction.

Fact Sheet 10—Surface Treatment (Chip Seal, Chip Seal Coat) Schematic of Surface Treatment Construction Process Surface treatment (also known as surface seal, seal, and chip seal) is the application of asphalt binder, immediately followed by an application of cover aggregate, to any type of pavement surface. A typical construction process is shown in the schematic. If the aggregate is of uniform size, the treatment is usually called chip seal. Typically, surface treatments are applied on top of a granular base producing surface-treated pavement. Surface treatments can be also applied to AC pavements as a preventive or corrective main- tenance treatment. Sources of Information and Additional Resources California Department of Transportation, Maintenance Technical Advisory Guide, 2nd ed., Office of Pavement Preservation, Division of Maintenance, Sacramento, 2008. Michigan Department of Transportation, Capital Preventive Maintenance, 2003 ed., Construction and Technology Division, Lansing, Apr. 2010. Ohio Department of Transportation, Pavement Preventive Maintenance Guidelines, Office of Pavement Engineering, Columbus, May 2001. Minnesota Department of Transportation, Preventive Maintenance Best Management Practices of Hot Mix Asphalt Pavements, Report MN/RC-2009-18, Office of Materials and Road Research, Maplewood, May 2009. Hicks, R.G., S.B. Seeds, and D.G. Peshkin, Selecting a Preventive Maintenance Treatment for Flexible Pavements, Publication FHWA-IF-00-027, Federal Highway Administration, U.S. Department of Transportation, Washington, D.C., 2000. Additional resources include: Several agencies have published guidelines for the design and construction of surface treatments including the Minnesota Department of Transportation (Janish, D.W. and F.S. Gaillard, Minnesota Seal Coat Handbook, Office of Research Services, St. Paul, 1998). A recent NCHRP Synthesis of Highway Practice provides practical guidelines for the construction of surface treatments (Gransberg, D. and D.M.B. James, NCHRP Synthesis of Highway Practice 342: Chip Seal Best Practices, Transportation Research Board of the National Academies, Washington, D.C., 2005). Purpose and Selection Criteria Surface treatments applied on top of AC pavements can be used as preventive or corrective treatments. As a preventive measure, sur- face treatment is primarily used to seal the surface showing non-traffic-load associated cracks and ravelling. As a corrective measure, surface treatment is used to restore frictional resistance and to maintain wearing surface on AC pavements. Surface treatments using polymer-modified emulsions have been used as crack relief layers between the existing AC surface and an AC overlay, or as stress relief layers between the existing PCC surface and an overlay. Typical Service Life and Costs When used to protect the existing pavement structure as a preventive maintenance treatment, surface treatment can prolong pavement life span by 4 to 6 years. When used to restore or improve pavement surface; for example, to restore pavement friction, surface treat- ment can last 5 to 8 years. The cost of a single surface treatment is approximately $2 to $4 per square yard. Materials and Construction The surface on which surface treatment is applied is expected to have a uniform capacity to absorb emulsion. Active cracks, such as transverse and longitudinal cracks, can be sealed prior to application of the surface treatment. Typically, the asphalt binder used for surface treatment is asphalt emulsion applied at an elevated temperature (120°F to 180°F) using an asphalt distributor. The cover aggregate can be either chips (open-graded aggregate) or dense-graded as shown in Figure B8. tlahpsAetagerggarevoC distributor Self-propelled aggregate spreader Power broom or sweeper Rubber-tired rollers May be one unit 74

75 About 70% of the aggregate is typically imbedded or surrounded by the binder. The need for accurate application of the binder and aggregate cover is facilitated by modern asphalt distributors, which can automatically maintain selected application rates regardless of the distributor speed. Newly constructed surface treatments need to be protected from traffic for several hours after construction. Emulsion application rates for seal coats typically range from 0.2 to 0.4 gallon per square yard depending on the existing surface (granular, seal coat, or AC) and aircraft operations, and are further adjusted during construction according to weather conditions and other factors. Airport Use A small number of the surveyed airports indicated routine use of surface treatments, or have tried them. However, the majority of responding airports that routinely use or have used surface treatment rated its performance as good. Some of the reasons reported for low usage of surface treatments by airports are probably concerns about loose aggregate, dust, and rougher surface texture. FIGURE B8 Surface of a newly constructed surface treatment using 5/8-in.-dense-graded aggregate and high-float emulsion.

Fact Sheet 11—Slurry Seal Schematic of Slurry Seal Construction Slurry seal is an unheated mixture of asphalt emulsion, graded fine aggregate, mineral filler, water, and other additives, mixed and uniformly spread over the pavement surface as slurry. The construction of slurry seal using a self-propelled truck-mounted mixing machine is illustrated by the above schematic. Slurry seal systems are formulated with the objective of creating a bitumen-rich mor- tar. They are similar to microsurfacing, but the mineral skeleton is typically not very strong and has limited interlocking of the aggre- gate particles. Consequently, slurry seals are applied in thin lifts to avoid permanent deformation by traffic. Sources of Information and Additional Resources California Department of Transportation, Maintenance Technical Advisory Guide, 2nd ed., Office of Pavement Preservation, Division of Maintenance, Sacramento, 2008. Hicks, R.G., S.B. Seeds, and D.G. Peshkin, Selecting a Preventive Maintenance Treatment for Flexible Pavements, Publication No. FHWA-IF-00-027, Federal Highway Administration, U.S. Department of Transportation, Washington, D.C., 2000. Additional resources include: The ISSA maintains a website, www.slurry.org, that contains recommended specifications for slurry seal [International Slurry Sur- facing Association, Recommended Performance Guidelines for Microsurfacing, Document ISSA A143 (revised), 2005]. Engineering Brief No. 35A, SEP 27 1994, Thermoplastic Coal-Tar Emulsion Slurry Seal, Amended Interim Specification, Federal Aviation Administration, Washington, D.C. Purpose and Selection Criteria Slurry seals are used to correct surficial distresses such as raveling and coarse aggregate loss, seal slight cracking, and improve pave- ment friction. They are also used as a preventive maintenance treatment to seal pavement surfaces from intrusion of water and slow surface oxidation and ravelling. Slurry seals are best placed on structurally sound pavements that are in good condition with little or no cracking or rutting. Slurry seals perform best on surfaces with uniform characteristics. If defects such as moderate or severe ravelling, cracking, or rutting occur frequently, the section is probably not a good candidate for slurry sealing. Working cracks, such as transverse cracks, can be sealed either before or after the slurry seal application. Typical Service Life and Costs When used as a preventive maintenance treatment, slurry seal can prolong pavement life span by 3 to 6 years. When used to restore or improve pavement surface characteristics, for example to restore pavement friction, slurry seals can last 3 to 7 years. The cost of slurry seal is approximately $2 to $4 per square yard, typically less than half of the cost of a hot-mix overlay. Materials and Construction Asphalt emulsion used in slurry seals is typically cationic and contains about 60% to 65% of residual AC. The slurry mix contains 9% to 10% of AC. Coal tar-based emulsions that provide protection against fuel spills and oil leaks are also available in some markets. Aggregate used for slurry seals is crushed high-quality dense-graded aggregate. Its gradation generally follows one of the three gradation types, Type I, II, or III, recommended by the ISSA. Type II gradation can be used for aprons and low-volume taxiways and Type III gradation for runways. Type III gradation has 70% to 90% of aggregate passing No. 4 sieve. Mineral filler, typically portland cement or hydrated lime, is used to control curing time of the mix (break time of the emulsion). The amount of mineral filler is typically less than 1% of the total dry mix weight. The thickness of a slurry seal application is slightly more than the thickness of the largest aggregate particle in the mix, typically approximately 0.4 in. Spreader box Pug mill Portland cement Emulsion Aggregate Water spray 76

77 Some proprietary slurry seal mixes contain crushed aggregate particles and polymer-modified emulsion and may have strength and durability characteristics that are closer to a microsurfacing than to a traditional slurry seal. The slurry seal mixture is supplied using a specialized equipment that carries all of the components of the mixture, accurately mea- sures and mixes them in a pug mill, and spreads the mixture (by means of a spreader box linked to the mixing unit) in a strip 10 to 12 ft wide as a thin, homogeneous coat of slurry mix. Slurry seals are typically carried out only during the warmer, dryer months. After the slurry seal application, traffic can use the pavement without restrictions (except 360 degree turns by aircraft) in approximately 45 to 120 min, depending on setting time of the asphalt emulsion, weather condition, and traffic conditions. Cooler temperatures and wetter conditions can result in long curing times during which the slurry seal can be damaged by traffic. Airport Experience A small number of surveyed airports reported the use of slurry seals routinely, or have tried using them. The majority of responding airports that use slurry seals reported very good or good performance.

78 Fact Sheet 12—Hot-mix Overlay of AC Pavement Schematic of Hot-Mix Overlay Construction Process Hot-mix overlay of AC pavement consists of placing a layer or layers of hot mix over the existing AC surface. The above illustration shows the construction of an overlay including milling of the pavement surface, application of a tack coat, and the use of a material transfer vehicle. Conventional AC overlays are usually constructed with a minimum thickness of 11⁄2 in. Overlays that are less than 11⁄2 in. thick are called thin overlays and typically require special construction provisions. Sources of Information and Additional Resources California Department of Transportation, Maintenance Technical Advisory Guide, 2nd ed., Office of Pavement Preservation, Division of Maintenance, Sacramento, 2008. Michigan Department of Transportation, Capital Preventive Maintenance, 2003 ed., Construction and Technology Division, Lansing, Apr. 2010. Ohio Department of Transportation, Pavement Preventive Maintenance Guidelines, Office of Pavement Engineering, May 2001. Minnesota Department of Transportation, Preventive Maintenance Best Management Practices of Hot Mix Asphalt Pavements, Report MN/RC-2009-18, Office of Materials and Road Research, Maplewood, May 2009. Hicks, R.G., S.B. Seeds, and D.G. Peshkin, Selecting a Preventive Maintenance Treatment for Flexible Pavements, Publication No. FHWA-IF-00-027, Federal Highway Administration, U.S. Department of Transportation, Washington, D.C., 2000. Another useful manual on the construction of asphalt overlays is from the Asphalt Institute (Asphalt Overlays for Highway and Street Rehabilitation, Manual Series No. 17, Lexington, Ky., 1998). Purpose and Selection Criteria Overlays are used to restore pavement serviceability by improving ride quality and providing a new waterproof surface that covers crack- ing, ravelling, rutting, polished pavement surface, and other pavement defects. Overlays are also used as a preventive maintenance treat- ment to seal pavement surfaces from intrusion of water, slow surface ravelling, seal small cracks, and improve surface friction. Overlays can be used to strengthen the pavement structure to accommodate increased pavement loads. In this case, overlay thick- ness is determined by appropriate pavement design procedures. Single overlays are typically constructed over structurally sound pavements. Areas that exhibit weakness (e.g., settlement, alliga- tor cracking, and rutting) can be strengthened by patching or even by full-depth repairs. Some agencies rout and seal cracks in the existing AC pavement before placing an overlay, and carry out full-depth repairs of deteriorated transverse cracks. Typical Service Life and Costs Hot-mix overlays have an expected service life of 7 to 12 years depending on overlay thickness, traffic loads, existing pavement con- dition, environment, and material and construction quality. A typical cost of constructing an AC overlay is in the range of $60 to $90 per ton of material placed. For a 2-in.-thick single overlay, the corresponding cost is approximately $6 to $9 per square yard. Materials and Construction There are many variations in the material of hot mix. Some of the common variations are outlined in the following. Dense-graded and open-graded mixes—The two main types of hot mix used for overlays are dense-graded and open-graded mixes. Dense-graded mixes have aggregate particles that are fairly uniformly distributed. Open-graded mixes contain a large percentage of one-size coarse aggregate resulting in a mix with interconnected voids and high permeability. Open-graded mixes provide good pavement friction and reduce the potential for hydroplaning (Figure B9). Paver Optional material transfer vehicle Hot mix truck Asphalt distributor Power broom Milling machine 1. Optional vibratory dual steel drum rollers 2. Rubber tired rollers 3. Static dual steel drum rollers Tack coat applicationOptional built-in tack coat application

79 Virgin or recycled mixes—The use of recycled material in hot mix is common, particularly for a binder course. For surface courses on runways, the use of virgin materials is usually specified. Superpave—Introduced in 1992 to the highway industry, the Superpave system represented a new system for designing AC mixes. The Superpave system includes the use of performance-graded asphalt binder specifications and Superpave mix design proce- dures. Fuel resistant mixes—There are currently two proprietary hot mixes on the U.S. market that are designed to resist degradation caused by aircraft fuel spills and leaks of lubricants and hydraulic oils. In general, lower air voids and stiffer AC increase the fuel resistance of the mix. The existence of distresses such as ravelling, segregation, and cracking may dictate partial-depth removal (cold milling) of the AC prior to resurfacing. Partial-depth removal is normally accomplished using cold milling equipment. Grade-controlled precision milling may also be used to restore longitudinal and cross-sectional pavement profile and to improve smoothness of the subsequent overlay. The reclaimed asphalt pavement material may be reused as hot or cold mix or mixed with granular material. A tack coat is typically used before placing an overlay. A tack coat is a typically slow or medium setting asphalt emulsion diluted with water. Airport Experience A majority of surveyed airports routinely use or have tried using hot-mix overlays with or without prior milling, and nearly all sur- veyed airports reported very good or good performance. No responding airports reported using thin overlay (with thickness of less than 11⁄2 in.). FIGURE B9 (Left) Thin open-graded hot-mix overlay surface; (Right) Dense-graded overlay surface. Diameter of the coins is 0.7 in.

Fact Sheet 13—Hot In-Place Recycling of AC Pavement Schematic of Hot In-Place Recycling Process Hot in-place recycling (HIR) is a pavement rehabilitation method that involves reprocessing of the existing AC material in-place at temperatures normally associated with hot-mix AC paving. The illustration above shows the construction of HIR with an integral overlay using a reformer. Sources of Information and Additional Resources California Department of Transportation, Maintenance Technical Advisory Guide, 2nd ed., Office of Pavement Preservation, Divi- sion of Maintenance, Sacramento, 2008. Hicks, R.G., S.B. Seeds, and D.G. Peshkin, Selecting a Preventive Maintenance Treatment for Flexible Pavements, Publication FHWA-IF-00-027, Federal Highway Administration, U.S. Department of Transportation, Washington, D.C., 2000. Additional resources include: The 1997 FHWA publication Pavement Recycling Guidelines for State and Local Governments (Report FHWA-SA-98-042, National Technical Information Service, Springfield, Va.) describes all aspects of recycling of asphalt pavement materials to produce new pavement materials. Button, J.W., D.N. Little, and C.K. Estakhri, Synthesis of Highway Practice 193: Hot In-Place Recycling of Asphalt Concrete, Trans- portation Research Board, National Research Council, Washington, D.C., 1994. Taylor, M. and E. Dillman, “Airport Saves with Hot-in-place Recycling,” Public Works, Vol. 19, No. 10, 1999. Purpose and Selection Criteria HIR is suitable for structurally sound pavements with surface defects, such as raveling and segregation, cracking, and rutting that affect mainly the top pavement surface layer. An additional requirement is that the AC surface layer is suitable for recycling, has a uniform composition (aggregate gradation, asphalt content, and thickness), and materials of good quality (aggregate and asphalt binder). Material properties of pavements considered for HIR are thoroughly evaluated. Because of the size of a recycling train, HIR is suitable for large projects with room to maneuver. Typical Service Life and Costs The success of HIR depends on the properties of the existing materials, quality and quantity of new materials added, quality of con- struction, and the thickness and type of the surface layer placed on top of the HIR mix. Consequently, the expected service life can range from about 5 to 12 years. Overall, HIR pavements can perform comparably to conventional asphalt surfaces. A typical cost of a hot-in-place recycling layer is in the range of $5 to $10 per square yard. Materials and Construction There are other types of HIR processes and equipment in addition to the process illustrated above. Typical HIR construction consists of the following steps: • Heating of the existing AC surface—Several methods are available including infrared heating panels, flame burners, and microwave heating. • Pavement scarification—The depth of scarification is usually limited (by the capacity of the heaters) to the top 21⁄4 in. of the AC surface. 1. Vibratory dual steel drum rollers 2. Rubber-tired rollers 3. Static dual steel drum rollers Re-former MixingLeveling and profiling Scarifying Hot mix for integral overly Optional addition of aggregate and/or beneficiating hot mix Infrared heaters Second screed Adding rejuvenator 80

81 • Adding new materials and mixing—Depending on the properties of the existing AC material, the added new materials may include a combination of rejuvenating agents and (hot) aggregate, or the addition of a beneficiating hot mix. The objective is to compensate for deficiencies in the asphalt material to be recycled. • Levelling and reprofiling of the recycled mix—Some improvement can be made to the pavement profile. Addition of new AC overlay is necessary to make significant corrections to profile. • Placement of a thin hot-mix layer (optional)—Some HIR recycling equipment can add new hot-mix material on top of the recy- cled mix as an integral overlay. The thickness of the integral overlay is typically 11⁄4 in. The total thickness of the recycled and new mix is typically up to 3 in. • Compaction—Standard compaction procedures utilizing vibratory steel drum rollers, rubber tired rollers, and static steel drum rollers are employed. The resulting recycled layer can be used as a wearing surface or can be protected by a slurry seal, surface treatment, or a hot-mix over- lay. If an integral overlay is used, the overlay serves as the wearing surface. HIR is typically carried out only during the warmer, dryer months. Cooler temperatures and wetter conditions can result in longer heating times leading to the overheating and burning of the pavement surface, and creating smoke and vapors. Cooler ambient tem- peratures can also result in lower mix temperatures leading to an insufficient depth of scarification, fracturing aggregate during scar- ification, and poor compaction of the mix. Airport Experience None of the airports surveyed used hot-in-place recycling. However, hot-in-place recycling has been used for the rehabilitation of runways.

Fact Sheet 14—Cold In-Place Recycling of AC Pavement Schematic of Cold Recycling Process Cold in-place recycling (CIR) is a pavement rehabilitation method that involves reprocessing of an existing hot-mix asphalt pave- ment at ambient temperatures, either in-place or in an off-site processing plant, and laying it back down. The illustration above shows the construction of CIR. The recycled AC layer is typically covered by a hot-mix overlay. Sources of Information and Additional Resources California Department of Transportation, Maintenance Technical Advisory Guide, 2nd ed., Office of Pavement Preservation, Division of Maintenance, Sacramento, 2008. Hicks, R.G., S.B. Seeds, and D.G. Peshkin, Selecting a Preventive Maintenance Treatment for Flexible Pavements, Publication FHWA-IF-00-027, Federal Highway Administration, U.S. Department of Transportation, Washington, D.C., 2000. Additional resources include: The 1997 FHWA publication Pavement Recycling Guidelines for State and Local Governments (Report FHWA-SA-98-042, National Technical Information Service, Springfield, Va.) describes all aspects of recycling of asphalt pavement materials. The FHWA also maintains a web page on “Cold In-place Recycling State of Practice Review” at: http://www.fhwa.dot.gov/Pavement/ recycling/cir/. Purpose and Selection Criteria CIR is a suitable pavement rehabilitation treatment for thick AC pavements in poor condition exhibiting extensive severe cracking, rutting, or other distresses. CIR mix helps to retard reflection cracking. CIR can also be used for pavements that require increased structural strength. In this case, the additional strength is achieved primarily by an overlay atop the CIR layer. Candidate pavements for cold-in place recycling are thoroughly evaluated and the properties of the existing AC determined. Because of the size of a recycling train, CIR is suitable for large projects with room to maneuver. Typical Service Life and Costs CIR with an appropriate hot-mix overlay provides a service life of 10 years or more. In situations where the surface layer atop the CIR mix is a surface treatment, the expected service life is lower. A typical cost of a 4-in.-thick cold recycled AC pavement is about $9 to $16 per square yard. Materials and Construction Cold recycling can be classified by the location where the recycling takes place as: • Cold in-place recycling (CIR)—All asphalt pavement material processing is completed in situ. CIR is faster and environmen- tally preferable because of the reduced need to transport materials. • Cold central plant recycling (CCPR)—Reclaimed asphalt pavement is hauled to a plant site and stockpiled. Subsequently, it is processed (crushed, screened, and mixed with additives), transported to the job site, and placed and compacted. CIR can also be classified by the type of the asphalt added to the recycled mix: • Addition of emulsified asphalt—Traditionally, asphalt emulsion is used to bind the mix. Polymer-modified asphalt emulsions or polymer-modified high-float emulsions are also used. The total amount of emulsion and water is approximately 4%, the emul- sion alone being approximately 1.5%. Because of the added water, the resulting mix requires a minimum 14 days of curing before the mix can be sealed (overlaid). During this time, the exposed CIR mix can be damaged by traffic. CIR using emulsi- Paver Mixing unit Milling machine 1. Rubber tired rollers 2. Static dual steel drum rollers 82

83 fied asphalt is typically carried out only during the warmer, dryer months. Cooler temperatures and wetter conditions can result in long curing time during which the cold mix is susceptible to moisture intrusion and abrasion by traffic. • Addition of expanded (foamed) asphalt—Although the addition of expanded asphalt can be done in-place or off-site, it is typi- cally done in-place. The resulting material is called cold in-place recycled expanded asphalt mix (CIREAM). CIREAM allows a hot-mix surface course to be placed after only two days of curing. Expanded asphalt mix is less susceptible to environmental conditions than emulsion mix. Airport Experience Only one surveyed airport reported a routine use of cold-in-place recycling. However, the use of CIR is relatively frequent for the rehabilitation of runways and taxiways on small airports.

Fact Sheet 15—Ultra-thin Whitetopping of AC Pavement Ultra-thin Whitetopping Pavement Rehabilitation Method Ultra-thin whitetopping (UTW) of AC pavements is a rehabilitation method where a thin layer of PCC (2 to 4 in. thick) is bonded to the milled AC pavement to form a composite pavement structure with a new wearing surface. UTW uses short square slabs, typically from 2 and 6 ft, as shown in the above illustration. If the thickness of the PCC overlay is more than 4 and less than 8 in., whitetopping is usually called thin whitetopping; if the thick- ness exceeds 8 in., it is called conventional whitetopping. Sources of Information and Additional Resources California Department of Transportation, Maintenance Technical Advisory Guide, 2nd ed., Office of Pavement Preservation, Division of Maintenance, Sacramento, 2008. Additional resources include: ACPA-issued, comprehensive Construction Specification Guidelines for Ultra-thin Whitetopping (IS120). Rasmussen, R.O. and D.K. Rozycki, NCHRP Synthesis of Highway Practice 338: Thin and Ultra-Thin Whitetopping, Transportation Research Board of the National Academies, Washington, D.C., 2004. Saeed, A., M.I. Hammons, and J.W. Hall, “Design, Construction, and Performance Monitoring of Ultra-Thin Whitetopping at a Gen- eral Aviation Airport,” Proceedings of the 27th International Air Transportation Conference, 2007. Purpose and Selection Criteria UTW can be used to rehabilitate AC runways, taxiways, and aprons. It has also been successfully used to mitigate rutting of AC pave- ments, block cracking, and fuel spill damage, and to increase structural capacity of pavements. The surface of the existing pavement is cold milled to remove the deteriorated AC pavement. The milled surface also enhances the bond between the new PCC overlay and the existing AC pavement. The objective is to provide a sound platform for the PCC slab with a minimum thickness of AC pavement after milling of at least 4 in. A thorough engineering analysis is performed to ensure the suitability of a UTW overlay. Severe distresses (such as frost heaving and subgrade settlement) are repaired full depth prior to the placement of UTW. UTW placed on a thick cracked AC layer may result in reflection cracking of PCC slabs. Typical Service Life and Costs Preliminary results suggest life spans of 10 years or more. The typical cost of a UTW is estimated to be in the range of $12 to $18 per square yard. Materials and Construction PCC mixes used in UTW overlays are typically high early-strength mixes and generally contain fibers such as polyolefin and polypropylene. Fibers are expected to increase tensile strength of the mix and improve its resistance to shrinkage and fatigue cracking. The construction of UTW consists of the following steps: Pre-overlay repair—Localized repairs may be required to obtain uniform support for UTW. Surface preparation—Milling of the existing AC is essential for the good performance of the UTW overlay. Milling removes deteriorated AC and provides a roughened surface that enhances the bond between the remaining AC and the new PCC surface, thereby creating an integrated pavement layer. Milling is followed by cleaning to remove all debris and any slurry resulting from Existing hot mix asphalt pavement 2 to 6 feet 2 to 4 inchesMilled surface Short square slabs Thin slabs 84

85 milling. The typical predominant defect of UTW overlays is corner cracking attributed to the loss of bond between the PCC slab and the underlying hot-mix asphalt. PCC placement—Conventional paving practices are used. Ambient temperatures are considered to ensure that UTW concrete is not placed on an overly hot AC surface. The hot surface could cause the PCC slab to crack when it cools down at night. It could also reduce the available water (for the chemical hardening process) at the interface of the two materials, thereby reducing the strength of the PCC at the interface. The AC surface is moistened before the PCC placement to minimize absorption of water from the PCC mix by AC and to promote bonding. Texturing—Conventional texturing methods, such as tining, are used. Curing—Curing is important for all PCC pavements. It is especially important for UTW overlays because of their small thickness (and large exposure area relative to the volume). Curing compound is placed on all exposed surfaces immediately after textur- ing and at twice the normal rate. Joint sawing and sealing—Joint sawing starts as soon as it can be done without significant chipping of the joint edges. Typical joints are 1 in. deep and 1⁄8 in. wide, and are spaced 2 to 6 ft apart depending on thickness. Joints are not sealed. Airport Experience Only a few surveyed airports reported routine use of whitetopping. The Spirit of Saint Louis Airport in Missouri was the first general aviation airport in the United States to receive an ultra-thin whitetopping in 1995. Since then, whitetopping has been used on both small and large airports, including the George Bush Intercontinental Airport in Huston.

Fact Sheet 16—Joint/Crack Sealing of PCC Pavement Sequence of Sealing Joints and Cracks in PCC Pavements Sealing of joints and cracks in PCC pavements is a maintenance treatment that re-seals joints that have missing or poorly perform- ing sealants, and seals major cracks. The sequence of the operation is shown on the above illustration. Sources of Information and Additional Resources California Department of Transportation, Maintenance Technical Advisory Guide, 2nd ed., Office of Pavement Preservation, Divi- sion of Maintenance, Sacramento, 2008. Michigan Department of Transportation, Capital Preventive Maintenance, 2003 ed., Construction and Technology Division, Lansing, Apr. 2010. Hicks, R.G., S.B. Seeds, and D.G. Peshkin, Selecting a Preventive Maintenance Treatment for Flexible Pavements, Publication FHWA-IF-00-027, Federal Highway Administration, U.S. Department of Transportation, Washington, D.C., 2000. Additional resources include: Evans, L.D., K.L. Smith, and A.R. Romine, Materials and Procedures for the Repair of Joint Seals in Portland Cement Concrete Pavements—Manual of Practice, FHWA-RD-99-146, Federal Highway Administration, McLean, Va., 1999. A comprehensive Concrete Pavement Repair Manual issued by the ACPA in 2003 is available from www.pavement.com. Engineering Technical Letter 02-8, Silicone Joint Sealant Specification for Airfield Pavements, 2002. Purpose and Selection Criteria The purpose of joint and crack sealing is to prevent incompressible materials from getting into joints, and to prevent infiltration of water and de-icing chemicals into the pavement structure. The presence of incompressible material in the joints can cause spalling and raveling when the joints close in the summer months. Excess water in the pavement structure can lead to erosion of the base sup- port, and de-icing chemicals can corrode dowels and tie bars. The objective of resealing is to keep all joints sealed. Typically, only working cracks with the opening (at moderate temperatures) between 1⁄4 and 1⁄2 in. are sealed. Working cracks are typically transverse and longitudinal cracks. Re-sealing operations are carried out as scheduled maintenance when more than 50% of transverse joints start to show adhesion failures. Typically, pavements requiring joint resealing and crack sealing also require other maintenance treatments, such as partial-depth repairs. Typical Service Life and Costs There are three main categories of sealants for PCC pavements on the market: hot-poured bituminous sealants, silicone sealants, and compression seals (preformed or neoprene). Hot-pour sealants have a service life of 8 or more years, silicone sealants 10 years, and compression seals 12 or more years. The performance of sealants can differ significantly depending on the material and workmanship. The typical cost of resealing operation is in the range of $3 to $4 per yard for hot-poured rubberized sealant, $4 to $5 per yard for silicone sealant, and $6 to $7 per yard for compression seals. Materials and Construction Typical joint and crack resealing operation consists of the following steps. Removal of existing sealant—Damaged and underperforming sealant is removed. This may be accomplished by a mechanical device mounted on a garden-type tractor. Preparation of sealant reservoir—Typical as-constructed transverse joints have sufficient reservoir at the top of the joint for hot- poured sealant. If the slab faces at the top of the joint do not have sufficient reservoir, the joint may be refaced by diamond saw cutting. Preformed compression seals require that joint sidewalls are perpendicular and without spalling. In the case of cracks, the reservoir is created by using a saw equipped with a special crack-sawing blade, rather than by using impact or rotary routers (e.g., those used for routing AC pavements) that can chip away at the crack face. Locate Install Backer rod laeSnaelC 86

87 Cleaning—All debris are cleaned by sand blasting or water blasting to remove all loose and weakened material, and to remove slurry residue from saw cutting. If sand blasting is used it is followed by air blasting to clean the joint. Joints must be dry before installing sealant. Insertion of backer rod—Bituminous sealants may require a device that would prevent a liquid sealant from seeping deep inside the joint. One such device is a backer rod (Figure B10). The backer rod keeps the sealant in place near the surface of the pave- ment and prevents bituminous sealant from seeping into the widened crack opening. Sealant application—The application of hot-poured sealant is similar to the application used for sealing AC pavements. Sealing operation with compression seals requires the application of a lubricant/adhesive to the joint sidewalls before the insertion of the seal. Compression seals are typically applied by a specialized machine and primarily used on new pavements. High-modulus silicone sealants are leveled (tooled) to force the sealant into a full contact with the joint sidewalls and to produce the correct shape of the sealant on top. Airport Experience A majority of surveyed airports reported routine use of silicone sealants, half of the responding airports have used bituminous sealants, and a minority of responding airports has used neoprene sealants. The silicone sealants as reported by survey respondents performed best, with all airports reporting very good or good performance. A majority of surveyed airports reported very good or good performance using bituminous sealants or compression sealants. Sealant Backer Rod Crack opening 3 to 6 mm recess Depth of original saw cut FIGURE B10 Resealed transverse contraction joint with bituminous sealant and a backer road.

Fact Sheet 17—Partial-depth (Patch) Repairs of PCC Pavement Construction Steps of Partial-depth Repair of PCC Pavement Partial-depth patch repair of PCC pavements is a maintenance activity that includes removal of damaged material from shallow areas and replacing it with new PCC material or AC material. The key construction steps involved are shown in the above illustration. Sources of Information and Additional Resources California Department of Transportation, Maintenance Technical Advisory Guide, 2nd ed., Office of Pavement Preservation, Division of Maintenance, Sacramento, 2008. Michigan Department of Transportation, Capital Preventive Maintenance, 2003 ed., Construction and Technology Division, Lansing, Apr. 2010. Ohio Department of Transportation, Pavement Preventive Maintenance Guidelines, Office of Pavement Engineering, Columbus, May 2001. Hicks, R.G., S.B. Seeds, and D.G. Peshkin, Selecting a Preventive Maintenance Treatment for Flexible Pavements, Publication FHWA-IF-00-027, Federal Highway Administration, U.S. Department of Transportation, Washington, D.C., 2000. Additional resources include: A comprehensive manual of practice, Concrete Pavement Repair Manual, issued by the ACPA in 2003, is available from www.pavement.com. Fowler, D., D. Zollinger, and D. Whitney, Implementing Best Concrete Pavement Spall Repairs, FHWA/TX-08/5-5110-01-1, National Technical Information Service, Springfield, Va. [Online]. Available: www.ntis.gov. UFC 3-270-03, Concrete Crack and Partial-Depth Spall Repair, U.S. Department of Defense, Washington, D.C., 2006, 68 pp. Purpose and Selection Criteria The purpose of partial-depth repairs is to repair localized shallow areas of damaged pavement, such as joint and corner spalling (joint chipping, cracking, and breaking), and any loss of material caused by weak concrete. The objective is to prevent further deteriora- tion, restore pavement smoothness, remove the potential for loose material coming off the pavement, and facilitate joint resealing. Partial-depth repairs are typically done only for surface distresses that affect up to one-half of the slab thickness. Partial-depth repairs are not suitable for slabs with poor load transfer and areas where reinforcing steel or load transfer devices are exposed. Partial- depth repairs cannot effectively address spalls caused by durability (D) cracking or alkali silica reaction (ASR) damage. If there are several moderate or severe spalls present along one joint, it may be necessary and more economical to repair the joint using a full- depth repair. Partial-depth repairs are often done in combination with full-depth repairs, joint re-sealing and diamond grinding as part of a pave- ment rehabilitation project. Typical Service Life and Costs A partial-depth repair can last as long as the slab itself, typically 10 years or more. A typical cost of a partial-depth repair operation is in the range of $160 to $220 per square yard. Materials and Construction The selection of repair material depends on a number of factors including time constraints, climate, repair size and configuration, experience with local materials, and future maintenance and rehabilitation plans. Ideal repair materials have similar physical proper- ties, such as elastic modulus, strength, and thermal expansion, as the original concrete. PCC repair materials can be general-use hydraulic cement or high early-strength hydraulic cement. There are also rapid-set proprietary patching materials on the market. Bonding agents, if used, are typically sand–cement slurries or epoxy-modified cement slurries. AC material is typically used for tem- porary repairs only. Saw cut and remove material Select repairs Apply bonding agent Place patching material 88

89 The patching procedure using PCC materials consists of the following steps: 1. Marking the boundaries of deteriorated and/or delaminated concrete. 2. Removal of existing concrete by saw cutting and chipping, or by milling, to create vertical surfaces of the sides of the exca- vated area. 3. Cleaning of the excavated area by sand blasting or water blasting. 4. Installation of a joint breaker, if the repairs are adjacent to joints, as shown in Figure B11. 5. Application of bonding agent (if used). 6. Placement of the patch material and its consolidation. 7. Finishing and texturing to match surrounding surface. 8. Application of a curing compound to retain moisture. 9. Joint resealing if the patch is adjacent to a joint. The use of AC material for patching of PCC pavements is considered to be a temporary repair. For this reason, the excavated area is typically not saw cut and a joint breaker is not installed. Airport Experience About one-half of the airports surveyed routinely used or have tried partial-depth repairs with PCC material, a majority of surveyed airports have used AC material, and a large minority of surveyed airports has used proprietary materials. Overall, the performance of PCC materials was reported to be better than the performance of AC or proprietary materials. FIGURE B11 Prepared repair area; the insert, separating the repair area from the joint, extends beyond the saw cut into the existing longitudinal joint.

Fact Sheet 18—Full-depth (Patch) Repairs of PCC Pavements Sequence of Operation of Full-depth Repair of PCC Pavements Full-depth patch repair of PCC pavements is a rehabilitation method that involves the full-depth removal of an entire slab or a sub- stantial portion of the entire slab, the installation of load transfer devices (and other reinforcement if applicable), and the replacement of PCC material. The sequence of the operation is shown on the above illustration. Sources of Information and Additional Resources California Department of Transportation, Maintenance Technical Advisory Guide, 2nd ed., Office of Pavement Preservation, Divi- sion of Maintenance, Sacramento, 2008. Michigan Department of Transportation, Capital Preventive Maintenance, 2003 ed., Construction and Technology Division, Lansing, Apr. 2010. Ohio Department of Transportation, Pavement Preventive Maintenance Guidelines, Office of Pavement Engineering, Columbus, May 2001. Hicks, R.G., S.B. Seeds, and D.G. Peshkin, Selecting a Preventive Maintenance Treatment for Flexible Pavements, Publication FHWA-IF-00-027, Federal Highway Administration, U.S. Department of Transportation, Washington, D.C., 2000. Additional resources include: A comprehensive manual of practice, Concrete Pavement Repair Manual, was issued by the ACPA in 2003 and is available from www.pavement.com. Concrete Pavement Rehabilitation—Guide for Full-depth Repairs, Report FHWA-RC Atlanta 1/10-03, Resource Center, Federal Highway Administration, Atlanta, Ga. Purpose and Selection Criteria The purpose of full-depth repairs is to repair slabs that can no longer be repaired using partial-depth repairs. This includes slabs with deteriorated concrete (particularly near joints), corner breaks, mid-slab cracking, slabs damaged by frost heaving and subgrade set- tlement, slabs with poor load transfer, and slabs where dowels are exposed. The objective of the repair is to restore the smoothness and structural integrity of the pavement, and to arrest further deterioration. Full-depth repairs are often done together with other maintenance treatments, such as partial-depth repairs, load transfer restora- tion, and crack and joint sealing, as part of a pavement rehabilitation project. Full-depth repairs using PCC are also done before over- lays. Typical Service Life and Costs The full-depth repairs are designed to last as long as the adjacent un-repaired slabs, typically 10 years or more. The typical cost of a full-depth repair using PCC material is in the range of $160 to $240 per square yard. Materials and Construction Full-depth repairs can be done using PCC or AC materials. Patching with AC materials is not considered a permanent repair. When using PCC materials, depending on the need to open the area to traffic, PCC repair materials can be a conventional PCC paving con- crete or a “fast-track” high early-strength mix. Cement mixes modified with the addition of accelerating admixtures, polymers, or proprietary cement materials are also used. If timing is critical, the use of pre-cast slabs can be considered. Typical full-depth cast-in-place repair of jointed PCC pavement with dowels consists of the following steps: Selection of repair boundaries—Full-depth repairs are typically done on the full width of the lane and have the minimum length of approximately 6 ft. Detailed engineering investigation is required to properly identify the areas requiring full-depth repairs. Visual examination is not sufficient (Figure B12). Drill holes Identify extent Saw cut Place patching material Insert Dowels Restore base 90

91 Base preparation—After the removal of the deteriorated concrete, the base course, subgrade, and subdrains are restored. Any dis- turbed base material is re-compacted. Dowel and tie bar placement—Load transfer across the transverse repair joints is re-established. The illustration at the beginning of this Fact Sheet shows the sequence of operations for installing dowels. Tie bars may be installed into the side of the PCC repair area using epoxy; these tie bars will hold the patch to the existing concrete. Placement of concrete—Before placing concrete, the exposed portion of the dowel bars is coated with a bond breaker. Tie bars are not coated as it is important for the concrete to bond to the tie bar to prevent separation at the interface between the patch and the existing concrete. Finishing and texturing—Unless a grinding operation or an overlay placement is to follow, the patch is textured to resemble the finish on the rest of the pavement. Curing—Curing compound is placed as soon as the texturing is completed. Joint cutting and sealing—All longitudinal and transverse joints are cut and sealed, or resealed. Pre-Cast Repairs Pre-cast repairs can provide a good alternative to cast-in-place repairs when it is necessary to minimize the duration of repairs. A new pre-fabricated concrete slab is placed into the prepared repair area in one piece. The restoration of the load transfer is accomplished by installing the dowels before or after the slab placement. Airport Experience A majority of surveyed airports routinely used or have tried full-depth repairs using PCC or AC materials. A large minority of sur- veyed airports used proprietary materials. The frequent use of AC materials is surprising and may be the result of the temporary nature of the repairs and to the low priority for restoring load transfer between PCC slabs on aprons and taxiways. Performance of both AC and PCC materials was similar, with the majority of surveyed airports reporting very good or good performance. None of the sur- veyed airports reported using precast panels. Actual deterioration at bottom of slab Visual deterioration seen on the surface Dowel barExisting Joint Width of the repair area, 6 feet minimum Full-depth saw cut FIGURE B12 Cross section of deteriorated transverse joint.

92 Fact Sheet 19—Machine Patching of PCC Pavement with AC Material Schematic of Machine Patching Operation of PCC Pavement Machine patching of PCC pavements is a maintenance technique that involves placing and spreading of AC mix using a paver on parts of a pavement section. Machine patching includes the preparation of the patching area, addition of the patching material, and compaction as shown on the illustration above. Sources of Information and Additional Resources California Department of Transportation, Maintenance Technical Advisory Guide, 2nd ed., Office of Pavement Preservation, Division of Maintenance, Sacramento, 2008. Additional resources include: A comprehensive manual of practice, Concrete Pavement Repair Manual, was issued by the ACPA in 2003 and is available from www.pavement.com. Purpose and Selection Criteria Hot-mix patching of PCC pavements does not substantially improve their structural capacity. Machine patching is most suitable for repairing surface defects such as map cracking, scaling, loss of pavement friction, and durability cracking. The areas selected for patching are expected to be well-defined and separated by areas that are in good condition. If the areas requiring patching are closely spaced, it may be more cost-effective to resurface the entire section. Machine patching repairs can be divided into permanent and semi-permanent repairs: Permanent repairs—Permanent patching repairs are used on pavements that are in good condition to improve surface characteristics and extend the life span. For example, if it is expected that the pavement being repaired will require resurfacing in 6 years, the patching repair lasting approximately 6 years will be appropriate. Semi-permanent repairs—Semi-permanent repairs have a limited life expectancy and are typically used when it is anticipated that the entire pavement will be resurfaced/reconstructed within a few years. Typical Service Life and Costs Permanent repairs may last 6 to 10 years or more; semi-permanent repairs may last about 3 to 5 years. A typical cost of machine patch- ing repairs is in the range of $10 to $30 per square yard. Materials and Construction Typically, permanent machine patching includes the following steps: • Removal of the deteriorated PCC material by milling or chipping. Milling may be required to provide a smooth transition between the original pavement and the patch. Figure B13 shows a construction detail for the start of a long patch applied over a full width of a facility. • Application of a tack coat at the sides of the patch and over the entire patched area to improve the bond between the original pavement and the patch, and to minimize water infiltration. • Placing of the mix. The placement is done by a paver, and typically in layers not exceeding 3 in. The minimum thickness of a permanent machine-placed patch is approximately 2 in. • Compaction of the patch area using rollers. Paver Hot mix truck Asphalt distributor 1. Rubber tired rollers 2. Static dual steel drum rollers Optional tack coatOptional built-in tack coat application

93 Airport Experience A few surveyed airports reported on the use of machine patching of PCC pavements with AC routinely; other surveyed airports reported that they have tried it. Performance data from the survey are incomplete. 2 to 4 feet 1¼ inch minimumWedge milling Finished overlay FIGURE B13 Wedge milling to key-in a 2-in.-thick AC patch.

Fact Sheet 20—Slab Stabilization and Slabjacking Illustration of Slab Stabilization Procedure Slab stabilization is a rehabilitation technique that fills voids underneath PCC slabs with grout, but does not raise slabs. Slab stabi- lization is also called slab subsealing and under-slab grouting. Slabjacking fills voids underneath PCC slabs and raises the grade of the slabs. The construction sequence is shown on the above illustration Sources of Information and Additional Resources Hicks, R.G., S.B. Seeds, and D.G. Peshkin, Selecting a Preventive Maintenance Treatment for Flexible Pavements, Publication FHWA-IF-00-027, Federal Highway Administration, U.S. Department of Transportation, Washington, D.C., 2000. Additional resources include: A comprehensive manual of practice, Concrete Pavement Repair Manual, was issued by the ACPA in 2003 and is available from www.pavement.com. Purpose and Selection Criteria The purpose of slab stabilization is to stabilize a pavement slab by pressurized injection of grout underneath the slab. The objective is to fill existing voids and restore full slab support, particularly at transverse joints and cracks. The main benefit of subsealing is slow- ing down the erosion of base and subgrade materials caused by excessive pavement deflections. Slab stabilization is typically carried out at the first signs of pumping (wetness and discoloration at transverse cracks during wet weather) and before the onset of visible signs of pavement damage such as corner cracks. Slab stabilization is typically done only for joints and working cracks that exhibit loss of support. The purpose of slabjacking is to raise pavement slabs, which have settled over time, back to their original grade by pressurized injection of grout underneath the slab. At the same time, slabjacking will also stabilize the slab. The objective is to improve pave- ment smoothness and to fill voids underneath the pavement. Slabjacking can raise PCC slabs by over 2 in. Slab stabilization and slabjacking are typically carried out concurrently with other rehabilitation techniques such as partial- and full-depth repairs, diamond grinding, and joint resealing. Slab stabilization is also used to achieve uniform foundation for overlays and as part of the installation of precast PCC panels. Typical Service Life and Costs The expected service life of slab stabilization and slabjacking is 5 to 10 years. The typical cost of slab stabilization is in the range of $80 to $180 per square yard. Materials and Construction Grouting materials used for slab stabilization include portland cement, fly ash-cement, polyurethane, and proprietary products. Typ- ical slab stabilization material consists of a mixture of three parts fly ash and one part Type 10 cement, and water. Important proper- ties of the grout material include the ability to flow into small voids, sufficient strength to support the slab and the load, and long-term resistance to erosion and deterioration. Typical slab stabilization operation consists of the following steps: Location of injection and observation holes—The number of holes depends on the size of the slab. Figure B14 shows an example pattern of injection and observation holes for the stabilization of transverse joints of a small slab (approximately 15 ft by 20 ft). Drilling holes—Holes are typically 2 in. in diameter or smaller, and penetrate 2 to 6 in. below the concrete slab. Injection holes are grouted the same day. grout Drill holes Plug holes Inject 94

95 Grout injection—During the grout injection process, vertical movement of the slabs is continuously monitored. The injection process is complete when grout undiluted with water appears in the observation holes, when the slab begins to rise, or when no grout material is injected at the maximum allowable pressure (typically 100 psi). Plugging and cleanup—After injecting one hole, the hole is immediately temporarily plugged. After all holes are injected, the temporary plugs are removed and the holes are filled flush with cement grout. Verification testing—After a minimum of 24 h, slabs are retested for the presence of voids and load transfer efficiency. It is pos- sible to repeat the slab stabilization operation if the first attempt is insufficient. In this case, a new set of injection and obser- vation holes is used. Slabjacking process is similar to the slab stabilization process. However, the injection of grout continues until the slab reaches the desired grade. Airport Experience One surveyed airport reported routine use of slab sub-sealing. A small minority of surveyed airports has tried slab sub-sealing. Per- formance data from the survey are insufficient. Leave SlabApproach Slab 1 foot 1.5 feet 6 feet Predominant direction of aircraft Injection hole Observation hole FIGURE B14 Typical location of injection and observation holes for the stabilization of a transverse joint; altogether there are five injection holes and two observation holes per slab.

Fact Sheet 21—Load Transfer Restoration Slots with Dowel Bars for Load Transfer Restoration Load transfer restoration is a rehabilitation method that restores the ability of the concrete slabs to transfer wheel loads across trans- verse joints. The illustration above shows three slots with dowel bars prior to grouting (Source: Pierce et al. 2009). Sources of Information and Additional Resources California Department of Transportation, Maintenance Technical Advisory Guide, 2nd ed., Office of Pavement Preservation, Division of Maintenance, Sacramento, 2008. Michigan Department of Transportation, Capital Preventive Maintenance, 2003 ed., Construction and Technology Division, Lansing, Apr. 2010. Additional resources include: The FHWA in conjunction with the ACPA has issued a useful publication entitled Guide for Load Transfer Restoration. ACPA also issued as a useful guide Stitching Concrete Pavement Cracks and Joints, Special Report SR903P [Online]. Available: www.pavement.com. Pierce, L.M., J. Weston, and J.S. Uhlmeyer, Dowel Bar Retrofit—Do’s and Don’ts, Report No. WA-RD 576.2, Washington State Depart- ment of Transportation, Olympia, Mar. 2009. Purpose and Selection Criteria Load transfer restoration (also called dowel bar retrofit) is achieved by inserting tie bars across the transverse joints of jointed PCC pavements. The objective is to increase load transfer across joints. Load transfer restoration is suitable for pavements with the load transfer efficiency of 60% or less, early signs of faulting (typically more than 0.1 inch but less than 0.4 inch), and with adequate slab thickness. To ensure proper selection of transverse joints that would benefit from load transfer restoration, evaluation of the load transfer efficiency is typically carried out using Falling Weight Deflec- tometer (FWD) testing. Load transfer restoration is typically done concurrently with other rehabilitation treatments such as full-depth repairs and resealing of joints. It is also used prior to overlays. Typical Service Life and Costs The estimated service life for load transfer restoration is between 5 and 15 years. The typical cost of a load transfer restoration or crack stitching is on the order of $50 to $100 per dowel bar or tie bar. Materials and Construction The procedure of load transfer restoration includes the following steps: Selecting joints—The selection is normally based on FWD testing. Some joints may not require any repairs, and some joints may require full-depth repair rather than load transfer restoration. 96

97 Slot cutting—A diamond-tipped slot cutting saw has become the most common equipment for slot cutting, although modified milling machines have been also used. It is important that the slots are perpendicular to the transverse joint, are large enough to place the dowel at mid-depth of the slab and allow for the backfill material to flow under and around the dowel, and are prop- erly cleaned by sand blasting followed by air blasting. Insertion of dowels—The most common type of load transfer device is a smooth epoxy-coated dowel bar. The size of the dowel bars depends on the slab thickness and anticipated loads. Typically, dowel bars have the diameter of 1 to 3⁄4 in. and a length of 15 to 20 in. (Figure B15). One-half of the dowel bar is coated with a bond-breaking agent. Backfilling the slots—It is important that backfill materials do not exhibit excessive shrinkage. For some installations, emphasis is placed on backfill materials that develop early strength to facilitate timely opening of the pavement to traffic. Polymer con- cretes and high early-strength PCC materials have been used in most installations to date. Airport Experience About one-quarter of surveyed airports report routine use or have tried dowel retrofit. Performance data from the survey are insufficient. Longitudinal view T T/2 Cross sectional view Mill or saw cut Expansion dowel bar cap As required Full depth joint insert 15 – 2 0 inches 2½ inches (min) 4 inches (max) FIGURE B15 Placement of a dowel in the slots. Dowel is placed on a support chair and is approximately 1⁄2 in. above the bottom of the slot.

Fact Sheet 22—Crack and Joint Stitching Illustration of Steps in Crack and Joint Stitching Crack stitching is a rehabilitation method that repairs longitudinal and meandering cracks, and nonworking transverse cracks. Joint stitching strengthens longitudinal joints. There are two crack stitching methods: cross stitching and slot stitching. The illustration above shows an operational sequence of cross stitching of a longitudinal crack. Sources of Information and Additional Resources Gransberg, D.D., “Life-Cycle Cost Analysis of Surface Retexturing with Shotblasting as an Asphalt Pavement Preservation Tool,” Transportation Research Record: Journal of the Transportation Research Board, No. 2108, Transportation Research Board of the National Academies, Washington, D.C., 2009, pp. 46–52. Additional resources include: The FHWA in conjunction with the ACPA has issued a useful publication entitled Guide for Load Transfer Restoration. ACPA has also issued Stitching Concrete Pavement Cracks and Joints, Special Report SR903P, which is available at: www.pavement.com. Pierce, L.M., J. Weston, and J.S. Uhlmeyer, Dowel Bar Retrofit—Do’s and Don’ts, Report No. WA-RD 576.2, Washington State Department of Transportation, Olympia, Mar. 2009. Purpose and Selection Criteria Crack and joint stitching is done by inserting tie bars across cracks or joints. This prevents widening of cracks and joints (slab migra- tion). Narrow cracks maintain aggregate interlock, reduce the potential for faulting, and are easier to seal. Good candidates for crack stitching are pavements in good condition where longitudinal cracks and joints show signs of slab migration. If longitudinal cracks and joints perform well simply by sealing them, crack and joint stitching may not be necessary. Typical Service Life and Costs The estimated service life for crack stitching is 5 to 15 years. A pioneering crack stitching application on a highway pavement was still performing well after 15 years. A typical cost of crack stitching is in the order of $60 to $120 per dowel bar or tie bar. Stitching of Cracks and Joints Stitching of cracks using slot stitching is very similar to load transfer restoration with the following main exceptions: • Stitching is done to repair longitudinal and meandering cracks, nonworking transverse cracks, and longitudinal joints. • Deformed tie bars with a smaller diameter are used instead of smooth dowel bars and are placed further apart than dowel bars. • Tie bars are not coated with a bond-breaking agent. Cross stitching includes the following steps: • Drilling holes at a 35° to 45° angle so that they intersect the longitudinal crack or joint at about the slab mid-depth (Figure B16). • Cleaning of holes by air blasting. • Injecting epoxy into the hole in a sufficient amount to fill all the available space after a tie bar is inserted. • Inserting a tie bar into the hole, leaving approximately 1 in. between the pavement surface and the end of the tie bar. • Removing excess epoxy and finishing it flush with the pavement. Airport Experience A small minority of surveyed airports reported routine or trial use of crack and joint stitching. Performance data from the survey are insufficient. Drill holes Grout holes Insert tie bar Identify cracks 98

99 Deformed tie bars inserted and grouted into drilled holes (diameter is typically ¾ inch) Dowel barPCC Slab Base 35º – 45º Longitudinal Crack Cross sectional view Longitudinal Crack Plan view Drill hole @ 24 inches FIGURE B16 Stitched longitudinal crack.

Fact Sheet 23—AC Overlays of PCC Pavements Schematic of Paving Operation for Asphalt Overlay of PCC Pavement AC overlay of PCC pavements is a rehabilitation technique that includes repairs of structural deficiencies in the existing PCC slab, application of a bonding agent (tack coat) and/or a layer intended to mitigate the propagation of reflection cracking, and placement of a hot-mix asphalt overlay. The construction sequence is illustrated above. Sources of Information and Additional Resources California Department of Transportation, Maintenance Technical Advisory Guide, 2nd ed., Office of Pavement Preservation, Division of Maintenance, Sacramento, 2008. Additional resources include: The Asphalt Institute has issued a useful publication entitled Asphalt Overlays for Highway and Street Rehabilitation, Manual Series No. 17, Lexington, Ky., 1998. Purpose and Selection Criteria AC overlays of PCC pavements can be classified as functional overlays and structural overlays. Functional overlays—The purpose of functional overlays is to improve functional deficiencies of the PCC pavement such as low pavement surface friction, inadequate cross-slope, and roughness. However, if roughness is caused primarily by slab stepping (faulting), a functional overlay may not be a cost-effective solution. The thickness of functional overlays ranges from 2 to about 3 in. Functional overlays are suitable for pavements in good structural condition without progressive faulting or for pavements that can be effectively brought to good structural condition by a limited amount of load transfer restoration, slab stabilization, and full-depth patching. Structural overlays—The purpose of structural overlays is not only to improve the functional deficiencies, but also to improve the structural capacity of the entire pavement. The improvement in the structural strength of the pavement may be required because the structural capacity has been inadequate or is expected to be inadequate considering future aircraft operations. Typical Service Life and Costs The typical service life of AC overlays over PCC pavement is 8 to 15 years. Cost can range widely depending on the overlay thick- ness and on the treatment of the existing PCC pavement. Considering that a typical cost of hot mix is $60 to $90 per ton, a 4-in.-thick overlay will cost $12 to $18 per square yard. However, this cost does not include any rehabilitation of the underlying PCC pavement that may be required before placing the overlay. Materials and Construction Materials used for hot-mix overlay of PCC pavements are similar to those used for hot-mix overlay of AC pavements and are described in Fact Sheet 12, Hot Mix Overlay of AC Pavement. The main challenge in constructing hot-mix overlay of jointed PCC pavements is the prevention or reduction of reflection crack- ing and the subsequent deterioration of reflection cracks. Over the years, many methods and materials have been developed and field tested. Some of these methods, arranged in the order of increasing costs, include: Tack coat—Tack coat will not significantly affect reflection cracking, but will improve the bond of hot mix with the PCC surface and thus will reduce the potential for delaminating near the reflection cracks. Paver Optional load transfer vehicle Hot mix truck Asphalt distributor 1. Optional vibratory drum rollers 2. Rubber tired rollers 3. Static dual steel drum rollers Tack coat application Pre-overlay repairs 100

101 Sawing and sealing of joints in the overlay—Sawing is done directly above the joints in the underlying PCC pavement and the saw cuts are sealed with liquid asphalt or joint sealant material. This technique prevents uncontrolled reflective cracking and provides joints that can be maintained. Stress relieving interlayers—A number of products designed to reduce stress in the overlays caused by joint movements have been tested. These products include geotextile fabrics and rubber or polymer-modified tack coats (with or without cover aggregate) and surface treatments used singly or in various combinations. Crack arresting interlayers—Crack arresting interlayers are typically bound and unbound aggregate layers containing large aggregate particles. The thickness of the interlayer is typically more than 4 in., and the layer contains crushed open-graded aggregate with large numbers of voids (see Figure B17). Increased overlay thickness—The increased overlay thickness delays the appearance of reflection cracks on the pavement sur- face. Typically, cracks propagate through the overlay at the rate of approximately 1⁄2 to 3⁄4 in. per year. Pre-overlay repairs—Repairs include slab repairs (slab stabilization, load transfer restoration, full-depth repairs) and improving drainage (retrofit subdrains). Fracturing the PCC slabs—The methods include crack-and-seat and rubblization. Airport Experience Nearly one-half of the surveyed airports reported using AC overlays of PCC pavements routinely or have tried them. All surveyed airports that have used AC overlays rated their performance as very good or good. Crack arresting interlayer Old JPCP Pavement Subgrade Soil Base Hot mix overlay FIGURE B17 Crack arresting granular interlayer.

102 Fact Sheet 24—Bonded PCC Overlay of PCC Pavements Illustration of Bonded PCC Overlay Bonded PCC overlay of PCC pavements is a rehabilitation technique that features the placement of a thin PCC overlay directly on the surface of the existing PCC pavement with the overlay bonded to the existing pavement. Bonded overlays are typically 2 to 5 in. thick and are constructed as jointed plain concrete pavements with transverse and longitudinal joints matching those in the underly- ing pavement as shown in the illustration above. Sources of Information and Additional Resources Hicks, R.G., S.B. Seeds, and D.G. Peshkin, Selecting a Preventive Maintenance Treatment for Flexible Pavements, Publication FHWA-IF-00-027, Federal Highway Administration, U.S. Department of Transportation, Washington, D.C., 2000. Additional resources include: Up-to-date information on design, construction, and performance of PCCP overlays is summarized in Portland Cement Concrete Overlays, State of the Art Technology Synthesis, Publication FHWA-IF-02-045, U.S. Department of Transportation, Federal Highway Administration, Apr. 2002. ACPA document TB-007 P, Guidelines for Bonded Concrete Overlays, provides useful practical guidelines. Saeed, A., M.I. Hammons, and J.W. Hall, “Design, Construction, and Performance Monitoring of Ultra-Thin Whitetopping at a Gen- eral Aviation Airport,” Proceedings of the 27th International Air Transportation Conference, Advancing Airfield Pavements, American Society of Civil Engineers, Reston, Va., 2007. Purpose and Selection Criteria The purpose of the bonded PCC overlay is to improve pavement smoothness and pavement surface friction and to provide increased structural strength of the pavement. Most bonded PCC overlays are placed on jointed plain concrete pavements, and such placement is assumed herein. A bonded overlay is an appropriate rehabilitation method if the structural strength of the pavement needs to be increased, and the existing PCC pavement is in a condition conducive to such a treatment. The need for the overlay is based on an anticipated increase in aircraft loads (more and/or heavier aircraft). If load-associated pavement defects are already visible, a bonded overlay is not an appropriate rehabilitation technique. Even though bonded overlays increase structural capacity of the pavement, they are unable to arrest progression of faulting. A bonded overlay is also inappropriate if durability-related defects are present, such as scaling and D-cracking. These defects limit the ability of the overlay to bond with its base. Typical Service Life and Costs The expected service life of bonded overlays is approximately 10 to 20 years, and their cost is approximately $15 to $25 per square yard for a 4-in.-thick overlay. Materials and Construction Bonded overlays usually use conventional PCCP paving mixes. Bonded overlays may also utilize high early-strength PCCP mixes and mixes containing polypropylene and other fibers. The construction of a bonded overlay consists of the following construction tasks: Pre-overlay repairs—Bonded overlay is placed over pavements in good structural condition. However, some localized repairs may be required such as partial-depth repairs, full-depth patching, and load transfer restoration. All cracks (corner, longitudinal, or transverse) in the underlying pavement are repaired. PCC overly Bonding agent Original PCC pavement Matching joints

103 Surface preparation—It is essential to ensure that the bonded overlay slab and the slab underneath act as one monolithic slab. The existing concrete surface is cleaned and roughened through a mechanical process that removes a thin layer of concrete. The most commonly used procedures are shot blasting or micromilling followed by air blasting. A bonding agent is applied just prior to paving; a commonly used bonding agent is a mixture of cement and water; this slurry is placed immediately in front of the paver. PCC placement, finishing, texturing, and curing—The placement of a bonded overlay and texturing uses conventional procedures. It is very important that the bonding agent not dry out prior to placement of new concrete. Proper curing is also important because of the large surface area of the overlay relative to its thickness. A higher than usual application rate of a curing com- pound is typically used. Joint construction and sealing—It is important to locate the transverse and longitudinal joints of the bonded overlay directly above those in the underlying pavement, with the deviation not exceeding 1 in. Transverse joints are sawn through the entire slab thickness plus additional 1⁄2 in. to ensure a complete slab separation. Longitudinal joints are sawed to one-half of the slab thick- ness. Sawing is done as soon as possible and the joints are sealed. Sealing requires additional saw cutting to create a reservoir on the top of the pavement and filling the reservoir with sealant (Figure B18). Airport Experience A few surveyed airports reported the use of bonded overlays routinely or have tried them. Performance data from the survey are incomplete. Dowel bar Bonding agent Saw cut joint Old JPCP pavement Subgrade soil Base Saw cut reservoir for sealant Bonded overlay FIGURE B18 Cross section of bonded overlay of jointed plain concrete pavement

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TRB’s Airport Cooperative Research Program (ACRP) Synthesis 22: Common Airport Pavement Maintenance Practices explores how airports implement a pavement maintenance management program, including inspecting and tracking pavement condition, scheduling maintenance, identifying necessary funds, and treating distresses in asphalt and concrete pavements.

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