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54 APPENDIX B Catalog of Airport Pavement Preservation Treatments 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

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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). TABLE B1 AIRPORT PAVEMENT PRESERVATION TREATMENTS INCLUDED IN THE CATALOG Both Pavement Types Asphalt Concrete Portland Cement Concrete 3 treatments 12 treatments 9 treatments 1) Texturization using shot 4) Sealing and filling of cracks (with 16) Joint and crack sealing (with blasting hot or cold applied sealants) bituminous, silicone, or compression sealants) 2) Diamond grinding 5) Small area patching (using hot mix, cold mix, or proprietary 17) Partial depth repairs (using AC, 3) Microsurfacing material) PCC, and proprietary materials 6) Spray patching (manual chip seal 18) Full-depth repairs (using AC, and mechanized spray patching) PCC, and proprietary materials 7) Machine patching with AC 19) Machine patching using hot material mix 8) Rejuvenators and seals 20) Slab stabilization and slab- jacking 9) Texturization using fine milling 21) Load transfer 10) Surface treatment (chip seal, chip seal coat) 22) Crack and joint stitching 11) Slurry seal 23) Hot-mix overlays 12) Hot-mix overlay (includes milling 24) Bonded PCC overlay of AC pavements) 13) Hot in-place recycling 14) Cold in-place recycling 15) Ultra-thin whitetopping

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56 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.

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57 Fact Sheet 1--Texturization Using Shot Blasting Abrasive storage Debris storage Vacuum Blast wheel separator 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. 4652. 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.

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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.

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59 Land area: 1/10 inch typical for hard aggregate 1/8 inch typical for soft aggregate Depth of saw cut Width of saw cut (1/17 to 1/13 inch) (1/10 to 1/7 inch) FIGURE B1 Profile of diamond-grooved surface. Improved pavement surface friction is provided by the land area created by the broken- off ridges. 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.

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60 Fact Sheet 3--Microsurfacing Portland cement Aggregate Optional Emulsion tack coat application Pug mill Spreader box Water spray Application unit Feeder & propulsion unit Asphalt distributor 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/RC2009-18, 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%

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61 FIGURE B2 Microsurfacing texture one year after construction; diameter of the coin is 1 in. 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.

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62 Fact Sheet 4--Sealing and Filling Cracks in AC Pavement Locate Rout Clean Seal 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/RC2009-18, 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 freezethaw cycles and pavement loads, FIGURE B3 Water from melting snow readily enters pavement structure through a transverse crack.

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63 FIGURE B4 Transverse crack heaving caused by water that saturated pavement structure and froze. 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.

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64 Fact Sheet 5--Small-Area Patching Add Select Clean Apply a patching Compact and trim tack coat material 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. FIGURE B5 Untreated pothole collects water and accelerates pavement deterioration.

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93 Wedge milling 1 inch minimum 2 to 4 feet Finished overlay FIGURE B13 Wedge milling to key-in a 2-in.-thick AC patch. 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.

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94 Fact Sheet 20--Slab Stabilization and Slabjacking Drill Inject Plug holes grout holes 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.

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95 Approach Slab Leave Slab Injection hole Predominant direction of Observation hole aircraft 6 feet 1 foot 1.5 feet 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. 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.

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96 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.

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97 Cross sectional view 2 inches (min) 4 inches (max) Longitudinal view Mill or saw cut As required 15 2 0 inches Full depth T/2 joint insert T Expansion dowel bar cap 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. 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.

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98 Fact Sheet 22--Crack and Joint Stitching Identify Drill Insert Grout cracks holes tie bar holes 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. 4652. 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.

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

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100 Fact Sheet 23--AC Overlays of PCC Pavements 1. Optional vibratory drum rollers 2. Rubber tired rollers Optional load 3. Static dual steel drum rollers transfer vehicle Hot mix truck Pre-overlay Asphalt distributor repairs Paver Tack coat application 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.

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101 Hot mix overlay Old JPCP Crack arresting Pavement interlayer Base Subgrade Soil FIGURE B17 Crack arresting granular interlayer. 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.

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102 Fact Sheet 24--Bonded PCC Overlay of PCC Pavements Matching joints PCC overly Bonding agent Original PCC pavement 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.

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103 Saw cut reservoir for sealant Bonded overlay Saw cut joint Bonding agent Old JPCP Dowel bar pavement Base Subgrade soil FIGURE B18 Cross section of bonded overlay of jointed plain concrete pavement 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.