Preventive Maintenance at General Aviation Airports Volume 2: Guidebook (2015)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

112 This appendix provides an introduction to treatments that can be used as preventive mainte- nance of both asphalt- and concrete-surfaced general aviation pavements. Keep in mind, how- ever, that it is not the treatment itself that determines a preventive maintenance application, but rather the condition of the pavement when the treatment is applied. At the time of publication of this guidebook, a broader ACRP guidebook (from ACRP Proj- ect 09-11) about pavement maintenance was in development. Airport officials may also wish to review that document for information about pavement treatments and preventive maintenance when it is published. For each treatment included in this appendix, a summary table provides the following information: • Treatment description; • Applicable FAA specifications and other guidance (abbreviated as “specs”); • Applications/uses; • Construction considerations; and • Miscellaneous considerations such as costs, treatment life and pavement life extension, safety issues, risk considerations, and climate or environmental limitations. There are many more treatments available than are described in this appendix. Some are not included because they are unlikely to be considered as preventive maintenance at general avia- tion airports. These include various recycling treatments, slab replacement of concrete pave- ments, and concrete overlays. Others are not included because they are variations of a treatment that is included (such as a double chip seal or double application of microsurfacing, or a cape seal) or because they are proprietary products. The exclusion of any product is not meant to suggest that it might not be cost-effective as a preventive maintenance treatment at a general aviation airport; the airport staff or the airport’s consultant is encouraged to identify appropriate treatments both from among those discussed here and using input from other knowledgeable sources. The types of treatment discussed in this appendix are: Flexible Pavements Rigid Pavements Crack sealing and filling Joint resealing and crack sealing Chip seal Diamond grinding Fog seal/rejuvenator Partial-depth repair Sand seal Load transfer restoration Slurry seal Microsurfacing Thin overlay A P P E N D I X D Pavement Treatments

Pavement Treatments 113 CRACK SEALING/FILLING Tr ea tm en t D es cr ip tio n Crack sealing and crack filling consist of the placement of an adhesive material into and/or over cracks at the pavement surface. These treatments are primarily intended to prevent moisture from entering into the pavement structure through existing cracks, thereby reducing further crack deterioration, roughness, and rutting. Crack filling is for cracks that undergo little movement and is characterized by minimal crack preparation and lower-quality materials. Fillers are often found on longitudinal cracks. Crack sealing addresses working cracks (i.e., those that open and close with temperature changes). Sealing operations typically require good crack preparation and high-quality materials [i.e., thermosetting or thermoplastic (bituminous) materials that soften upon heating and harden upon cooling]. Sp ec Guidance AC 150/5380-6B, Guidelines and Procedures for Maintenance of Airport Pavements ACRP Synthesis 22: Common Airport Pavement Maintenance Practices Specifications ASTM D6690 (sealants) ASTM D5078 (fillers) ISSA A175 A pp lic at io ns /U se s Conditions Addressed Longitudinal cracking Transverse cracking Reflection cracking Block cracking (low extent) Alligator cracking (low severity) Conditions Not Addressed: Crack sealing may be applied to structural (i.e., fatigue or reflection) cracks early in their development. While sealing provides no structural benefit, keeping moisture out of the pavement structure may slow down the progression of load-related cracking. Limitations: Overband applications may increase pavement roughness. Cracks greater than about 0.75-in. wide are better addressed by a repair rather than a crack seal. C on st ru ct io n C on sid er at io ns Material selection requirements to consider: adhesion, softening resistance, flexibility, pot life, weather resistance, and cure time. In deciding between hot- and cold-applied crack fillers, consider the size and types of cracks: hot-applied crack fillers are better suited to 0.5-in. wide or larger expanding cracks (large longitudinal, transverse, and reflective cracks), while cold crack fillers work better in smaller cracks that are less than 0.5-in. wide. Cracks should be clean and dry; prior to sealing, cleaning is essential to a good bond and maximum performance. A variety of placement configurations are used, based on local experience, materials used, snowplow use, and anticipated subsequent treatments. Sealants and fillers should be allowed to set before being subjected to traffic. Sealants and fillers require curing before another treatment is applied to the surface, especially if a HMA overlay is to follow. Emulsions usually require several days to cure; hot-applied crack fillers 3 to 4 months. M isc el la ne ou s C on sid er at io ns Cost ($ to $$$$): Crack fill: $ ($0.10–$1.20/ft) Crack seal: $ ($0.75–$1.50/ft) Treatment Life (years): Crack fill: 2 to 4 Crack seal: 3 to 8 Pavement Life Extension (years): Crack seal: 2 to 4 Safety: Extensive crack sealing may require blotting to maintain the pavement’s skid resistance. Risk: Improper installation can cause sealant or filler material to fail. Overband applications may be susceptible to snowplow damage. Sealant that fails to bond and is pulled out of the crack will be a source of FOD. Climate: Placement should be during moderate temperatures when the pavement is dry; while the manufacturer’s guidelines should be followed, a good range of ambient temperatures is 45°F to 65°F. O th er R em ar ks Tracking of seal or fill material by tire action may obscure pavement markings. Applying a blotter coat of sand can reduce such tracking. There are also commercial products and means available to reduce surface tackiness. There is a point at which excessive cracking is better addressed by a blanket solution, such as a surface treatment or milling. Surface bumps may occur at cracks during warm months when sealant or filler material is compressed and bulges out of the crack.

114 Preventive Maintenance at General Aviation Airports CHIP SEAL Tr ea tm en t D es cr ip tio n A chip seal is a spray application of asphalt (commonly an emulsion, although heated asphalt cement and cutbacks may be used) directly to the pavement surface (0.35 to 0.50 gal/yd2), followed by application of aggregate chips (15 to 50 lb/yd2), which are then immediately rolled to achieve 50% to 70% embedment. The treatment is used to seal the pavement surface against weathering, raveling, or oxidation; slow down moisture infiltration into the pavement structure; correct minor roughness or bleeding; and improve friction. Chip seals can be applied in multiple layers (e.g., double chip seal) and in combination with other treatments, such as microsurfacing, which is called a cape seal and reduces concerns associated with loose chips and a rough surface. Sp ec Guidance AC 150/5370-10G, Standards for Specifying Construction of Airports AC 150/5380-6B, Guidelines and Procedures for Maintenance of Airport Pavements ACRP Synthesis 22: Common Airport Pavement Maintenance Practices Specifications ISSA A165 FAA Item P-609 A pp lic at io ns /U se s Conditions Addressed Longitudinal cracking Transverse cracking Block cracking Friction loss Bleeding Roughness Moisture infiltration Conditions Not Addressed: Adds no structural benefit. Because of its flexibility, a chip seal is more effective at sealing low- to medium-severity fatigue cracks in comparison with other treatments. Limitations: Should not be used where loose chips or FOD are a concern. Steps can be taken to reduce loose chips. C on st ru ct io n C on sid er at io ns Application rates depend on aggregate gradation and maximum size, as well as absorption of existing pavement surface. Pavement surface must be dry and swept clean of dirt, sand, gravel, and other surface contaminants. Chip spreader should follow immediately behind asphalt distributor, and rollers close behind spreader. Traffic may be kept off surface until after curing (typically 2 hours, but depends on ambient conditions). Avoid prematurely applying pavement markings. Brooming is often required to remove loose chips; however, brooming before the emulsion has set hard may strip away properly seated aggregate. M isc el la ne ou s C on sid er at io ns Cost ($ to $$$$): $$ ($1.50–$2.00/yd2 single course conventional) $$$ ($2.00–$4.00/yd2 single course polymer-modified) Treatment Life (years): Single course: 3 to 7 Double course: 5 to 10 Pavement Life Extension (years): Single course: 5 to 6 Double course: 8 to 10 Safety: Loose aggregates on the pavement surface may increase stopping distance and are a potential source of FOD. Risk: Primary risk is due to damage from loose aggregate. Steps should be taken to remove loose aggregate before putting traffic back on pavement. Climate: Performs well in all climatic environments. Placement should occur when temperature in the shade is above 55°F and rising. Avoid placement during cold or wet weather conditions. O th er R em ar ks Enhanced performance is obtained from use of a rapid-set emulsion or polymer- or rubber-modified binder in the mix design, application of a smaller-sized “choke” aggregate to lock in larger chips, limiting excess chips to 5% to 10%, or applying a cape seal (slurry or microsurfacing seal) over the chip seal. FOG SEAL/REJUVENATOR SEAL Tr ea tm en t D es cr ip tio n Fog Seal—A very light application of a diluted asphalt emulsion to the pavement surface with no aggregate. The application seals the surface, although very lightly. Rejuvenator Seal—A specialized emulsion that is sprayed on an existing asphalt surface with the intent of softening the existing binder, enriching the weathered pavement, and thereby inhibiting raveling. The specialized emulsion is typically a mixture of asphalt, polymer latex, and other additives. While it is most commonly used in a fog-seal–type application, it can also be used in a sand seal or scrub seal. Sp ec Guidance AC 150/5380-6B, Guidelines and Procedures for Maintenance of Airport Pavements ACRP Synthesis 22: Common Airport Pavement Maintenance Practices Specifications FAA P-608 (fog seals) FAA P-632 (rejuvenators)

Pavement Treatments 115 A pp lic at io ns /U se s Conditions Addressed Seal/Waterproof Pavement— Prevent or slow the infiltration of moisture into the pavement surface Rejuvenate Surface/Inhibit Oxidation—Enrich the hardened/oxidized existing surface and inhibit raveling Conditions Not Addressed: This spray-applied treatment does not address cracking; pavements with extensive cracking should be treated in another manner. Similarly, pavements with signs of structural deterioration are best treated in some other manner. Limitations: The skid number of treated pavements will decrease immediately after application unless steps are taken to apply a skid-resistant surface or other techniques (such as shot blasting and rejuvenators combined) are used. The impact of the loss of skid-resistance on safe operations and the duration of the reduction in friction should be considered prior to the application of either a fog or rejuvenator seal. C on st ru ct io n C on sid er at io ns Varying application rates may be appropriate based on the openness of the surface. Very tight surfaces will require less spray application than very porous surfaces. Friction immediately following construction may be improved by broadcasting sand, cinders, or other fine-grained mineral products. M isc el la ne ou s C on sid er at io ns Cost ($ to $$$$): $ ($0.25–$0.50/yd2) Treatment Life (years): 1 to 2 Pavement Life Extension (years): 1 to 2 Safety: Primary risk factors are associated with the short-term loss of friction immediately following construction. Risk: The P-632 specification recommends that rejuvenators not be used on airfield pavements. Climate: These treatments should be applied when ambient temperatures are conducive to the application of sprayed bitumen. O th er R em ar ks Neither of these treatments will provide much performance benefit once the pavement exhibits significant cracking or exhibits high-severity weathering. Note that the repeated application of these treatments does not continue to add life to the pavement. SAND SEAL/SCRUB SEAL Tr ea tm en t D es cr ip tio n Sand Seal—A spray application of a rapid-set emulsion with a light covering of sand or screenings that is rolled following application. A sand seal serves a similar function as does a fog seal but provides better surface friction. A sand seal is typically between 0.125 and 0.25 in. thick. Scrub Seal—Similar to a sand seal but includes the use of brooms to push the emulsion into the surface cracks of the pavement and the fine aggregate into the binder. The seal is also rolled following application. The binder is often polymer modified. The thickness of a scrub seal is typically 0.125 to 0.25 in., but multiple layers are sometimes applied, resulting in thicknesses of between 0.375 and 1.5 in. Sp ec A pp lic at io ns /U se s C on st ru ct io n C on sid er at io n Guidance No formal guidance is available from FAA or ACRP documents. Specifications Covered in part by P-608, Emulsified Asphalt Seal Coat Conditions Addressed Moisture infiltration through fine surface cracking Oxidation or aging of the surface, including raveling Loss of skid resistance through softening Conditions Not Addressed: Cracking greater than hairline width Extensive cracking Limitations: Sand seals and scrub seals will not address high- severity raveling, provide much relief from significant raveling, nor seal extensive surface cracking. Many agencies that apply scrub seals construct their own brooming apparatus. The fine-grained aggregates that are applied as part of these treatments should be placed immediately after the application of the binder.

116 Preventive Maintenance at General Aviation Airports M isc el la ne ou s C on sid er at io ns O th er R em ar ks Cost ($ to $$$$): Treatment Life (years): Sand seal: 2 to 3 Scrub seal: 3 to 4 Pavement Life Extension (years): Sand seal: 1 to 2 Scrub seal: 2 to 3 Sand Seal: $$ ($0.65–$0.85/yd2) Scrub Seal $$ ($0.80–$1.10/yd2) Safety: Sand seal may result in loose aggregates on the pavement surface, which may increase stopping distance. Climate: Placement should occur when temperature in the shade is above 55°F and rising. Avoid placement during cold or wet weather conditions. These seals are similar to fog seals and rejuvenators, with the addition of fine-grained aggregate to provide additional skid resistance. Scrub seals are able to seal hairline cracks better than sand seals. SLURRY SEAL Tr ea tm en t D es cr ip tio n A mixture of emulsified asphalt, well-graded aggregate, additives, and water. The mixture is spread over the pavement surface with a spreader box attached to the back of specially equipped mixing trucks. Thickness ranges from approximately 0.25 to 0.375 in., and the material is applied to the pavement surface at a rate between 8 and 16 lb/yd2 . Sp ec Guidance ISSA Publication A-105 AC 150/5380-6B, Guidelines and Procedures for Maintenance of Airport Pavements ACRP Synthesis 22: Common Airport Pavement Maintenance Practices Specifications AC 150/5370-10G, Item P-626, Emulsified Asphalt Slurry Seal Surface Treatment A pp lic at io ns /U se s Conditions Addressed Longitudinal cracking Block cracking Friction loss Weathering and raveling Bleeding Roughness Moisture infiltration Conditions Not Addressed: Provides no structural benefit. Generally not flexible, so if the pavement has extensive cracking, and especially working cracks, these will all reflect through to the surface. Limitations: The FAA suggests that the treatment is limited to airports serving airplanes weighing 12,500 lbs or less, although with FAA approval the engineer may specify this treatment for airports serving airplanes of up to 60,000 lbs. Traffic must be kept off the sealed surface for 4 to 24 hours, depending on ambient conditions. C on st ru ct io n C on sid er at io ns Application rates depend on aggregate gradation and maximum size as well as absorption of existing pavement surface. Pavement surface must be dry and swept clean of dirt, sand, gravel, and other surface contaminants. The slurry seal should not be applied if the pavement or air temperature is below 50°F. Traffic should be kept off the surface for 4 to 24 hours to allow the seal to fully dry. Avoid prematurely applying pavement markings. Cracks greater than 0.25-in. wide should be treated prior to construction. M isc el la ne ou s C on sid er at io ns Cost ($ to $$$$): $$ ($0.75–$1.00/yd2 single course) Treatment Life (years): 3 to 5 Pavement Life Extension (years): 2 to 5 Safety: Primary safety concern is the loss of bond and the generation of FOD. Loss of friction has also been noted. Risk: Early damage can occur if trafficked before the treatment is set. Treatment may not be durable if placed during inclement weather. Climate: The slurry seal must be applied when the temperature of the air and pavement is above 50°F or above 45°F and rising. O th er R em ar ks Similar to microsurfacing, slurry seals can be modified (e.g., aggregate quality, gradation, polymer) to enhance performance. MICROSURFACING Tr ea tm en t D es cr ip tio n A mixture of crushed, well-graded aggregate, mineral filler (Portland cement), and polymer-modified emulsified asphalt spread over the full width of pavement with an augered spreader box attached to a specialty mixing and distribution truck. Microsurfacing is used primarily to inhibit raveling and oxidation. It is also effective at improving surface friction and filling minor irregularities and rutting up to 1.5-in. deep.

Pavement Treatments 117 Sp ec Guidance AC 150/5380-6B, Guidelines and Procedures for Maintenance of Airport Pavements ACRP Synthesis 22: Common Airport Pavement Maintenance Practices Specifications ISSA A143 FAA P-635 A pp lic at io ns /U se s Conditions Addressed Longitudinal cracking Transverse cracking Block cracking Raveling/weathering Oxidation Friction loss Moisture infiltration Bleeding Roughness Rutting Conditions Not Addressed: Microsurfacing does not add structural capacity. Limitations: Pavements undergoing high deflections or HMA pavements susceptible to stripping are not good candidates for microsurfacing. Pavements with extensive cracking may not be good candidates for microsurfacing. C on st ru ct io n C on sid er at io ns Most pavement markings need to be removed prior to microsurfacing. Cracks greater than 0.25-in. wide should be sealed prior to treatment placement. It is strongly recommended to perform needed patching and crack sealing prior to placement. Pavement surface must be dry and swept clean of dirt, sand, gravel, and other surface contaminants. Vegetation should be removed. Aggregates should be clean, angular/cubical, durable, and uniform, as well as chemically compatible with emulsion systems. Industry guidelines and recommendations regarding application temperatures and dry conditions should be followed. Microsurfacing treatments can be applied during nighttime closures (if other temperature requirements are met) because they undergo a chemical set. Microsurfacing typically can carry traffic after approximately 1 hour. Allow a minimum of 7 days before applying permanent pavement markings. M isc el la ne ou s C on sid er at io ns Cost ($ to $$$$): $$ (1.50–3.50 $/yd2 single course) Treatment Life (years): Single course: 3 to 6 Multiple course: 4 to 7 Pavement Life Extension (years): Single course: 2 to 5 Multiple course: 2 to 6 Safety: Primary safety concern is the loss of bond and the generation of FOD. Loss of friction has also been noted. Risk: Early damage can occur if trafficked before the treatment is set. Treatment may not be durable if placed during inclement weather. Climate: Placement should occur when temperature is 50°F and rising, and the forecast for the next 24 hours is above 40°F. Placement should avoid rain and hot or freezing temperatures. May be applied in either single or double applications. Finished thickness is between 0.25 and 0.75 in., depending on the top size of the stone and whether the application is single or double. THIN HOT-MIX ASPHALT OVERLAYS Tr ea tm en t D es cr ip tio n Thin HMA overlays are composed of asphalt binder and aggregate combined in a central mixing plant and placed with a paving machine in thicknesses of between 0.75 and 1.50 in. Conventional thin HMA overlays can be distinguished by their aggregate gradation: Dense-graded—a well-graded, relatively impermeable mix, intended for general use. Open-graded—an open-graded, permeable mix designed using only crushed aggregate and a small percentage of manufactured sand; typically smoother than dense-graded HMA. Stone matrix asphalt (SMA)—a gap-graded mix designed to maximize rut resistance and durability using stone-on-stone contact. Additionally, it is recommended to mill the existing pavement surface when surface distresses (e.g., segregation, raveling, or block cracking) are evident; other benefits include improving surface friction, maintaining clearance of overhead structures, and providing an improved bonding surface. O th er R em ar ks

118 Preventive Maintenance at General Aviation Airports Sp ec Guidance AC 150/5380-6B, Guidelines and Procedures for Maintenance of Airport Pavements ACRP Synthesis 22: Common Airport Pavement Maintenance Practices Specifications FAA Item P-401 A pp lic at io ns /U se s Conditions Addressed Longitudinal cracking Transverse cracking Raveling/weathering Block cracking Friction loss Bleeding Roughness Conditions Not Addressed: While thin HMA overlays should not be used to address structural deficiencies, greater structural benefit in terms of load-carrying capability is possible the thicker the overlay. Rutting can be addressed with a separate rut-fill application before overlay placement. Limitations: Cold milling provides a smoother riding surface by removing vertical deformations. Ruts should not be filled with a thin overlay. C on st ru ct io n C on sid er at io ns The maximum size of aggregate should not be more than one-half the overlay thickness (note that Superpave mix designs have their own requirements). If milling is not done in conjunction with overlay application, special consideration should be given to bump grinding prior to treatment placement. Pavement surface must be dry and swept clean of dirt, sand, gravel, and other surface contaminants; a tack coat applied prior to overlay application is essential to ensure bond to the existing surface. Because thin HMA overlays dissipate heat rapidly, it is important to specify minimum placement temperatures and to obtain timely compaction. Treatment can be opened to traffic after approximately 1 to 2 hours. Recommendations for obtaining a quality milled surface: Perform pavement patching prior to milling. Remove pavement castings and cover holes prior to milling. Use a good working milling machine (12-ft recommended width). Control milling speed to achieve a smooth, uniform surface (≤30 ft/min). Use a 30-ft ski and string-line to control grade and longitudinal guidance. M isc el la ne ou s C on sid er at io ns Cost ($ to $$$$): $$$ ($2.00–$6.00/yd2 with no milling) $$$ ($5.00–$10.00/yd2 with milling) Treatment Life (years): 4 to 12 (with no milling) 5 to 12 (with milling) Pavement Life Extension (years): 3 to 7 Safety: Ensuring that the overlay is well bonded to the existing pavement eliminates the primary safety concerns. Risk: Though not significantly affected by loading volumes or weights, certain combinations of loadings, environmental conditions, and pavement structure can initiate top-down cracking. Performance will vary according to factors affecting pavement weathering/raveling. Furthermore, treatment can be subject to delamination and reflective cracking. A tack coat prior to overlay placement will help improve bond. Thin overlays cool rapidly, so achieving density within the time available for compaction is especially critical. Climate: Performs well in all environments. O th er R em ar ks Properly constructed thin overlays provide a durable wearing surface. As with other thin treatments, however, the overall pavement performance is likely to be controlled by any underlying structural deficiencies, if present. PCC JOINT RESEALING/CRACK SEALING Tr ea tm en t D es cr ip tio n Joint resealing and crack sealing PCC pavements prevent moisture and incompressible materials from infiltrating concrete pavement structures. They help to slow or minimize the development of moisture-related distresses (such as pumping or faulting) and to prevent the occurrence of spalling, blowups, and other pressure-related distresses that might be caused by incompressible materials collecting in the joints. Joint resealing consists of removing and replacing existing deteriorated joint sealant, whereas crack sealing consists of applying adhesive material into or over surface cracks. Effective sealing operations typically require thorough joint or crack preparation and the use of high-quality sealant materials. Sp ec Guidance AC 150/5380-6B, Guidelines and Procedures for Maintenance of Airport Pavements ACRP Synthesis 22: Common Airport Pavement Maintenance Practices Specifications ASTM D6690 (hot-applied sealants) ASTM D5893 (silicone sealants) ASTM D3406 (elastomeric sealants)

Pavement Treatments 119 A pp lic at io ns /U se s Conditions Addressed Longitudinal cracking* Transverse cracking* *Crack sealing is most effective when cracks do not exhibit faulting or spalling. Conditions Not Addressed: Crack sealing may be applied to structural cracks early in their development. While sealing provides no structural benefit, keeping moisture and incompressible materials out of the pavement structure may retard the rate of deterioration. Limitations: Joints or cracks experiencing vertical movement rather than horizontal movement may not remain sealed. C on st ru ct io n C on sid er at io ns Critical material characteristics to consider when selecting a sealant include adhesiveness, cohesiveness, durability, extensibility, resilience, curing time, and shelf/pot life. Effective cleaning of the joint or crack is essential to achieving a good bond and ultimately to the performance of the sealant. The old sealant material must be removed from each joint/crack face, either by sawing or through mechanical means. After removal of the sealant material, the joint/crack faces should be sandblasted to remove any slurry or laitance. Sealants should be tack free before being subjected to traffic (typically 1 to 2 hours). Sealant on the surface may be tracked by traffic or pulled out during snow removal. M isc el la ne ou s C on sid er at io ns Cost ($ to $$$$): • Joint resealing: $ ($1.00–$2.50/ft) • Crack sealing: $ ($0.75–$2.00/ft) Treatment Life (years): Joint resealing: 2 to 8 Crack sealing: 4 to 7 Pavement Life Extension (years): Joint resealing: 2 to 6 Crack sealing: N/A Risk: Improper installation can cause sealant or filler material to fail. Overband applications should be avoided on heavily trafficked roadways due to high tensile stresses directly above crack edges, resulting in edge separations. Overband applications are also susceptible to snowplow damage. Climate: Performs well in all climatic environments. Sealants perform best in dry, warm environments without large daily temperature cycles. Placement should take place when the pavement is dry and during moderate temperatures (typically 45°F to 65°F, although the manufacturer’s recommendations should be followed). O th er R em ar ks Because resealing concrete joints is not a seasonal maintenance activity, periodic inspections should be scheduled to determine when treatment is necessary. DIAMOND GRINDING/GROOVING Tr ea tm en t D es cr ip tio n Diamond grinding is the removal of a thin layer of concrete (usually between 0.12 and 0.25 in.) from a concrete pavement surface, using special equipment fitted with a series of closely spaced, diamond saw blades. Diamond grinding removes joint faulting and other surface irregularities, thereby restoring a smooth riding surface while also increasing surface friction. Diamond grooving consists of cutting narrow, discrete grooves into the pavement surface in order to improve tire–pavement interaction during wet weather landings. Sp ec Guidance FAA AC 150/5320-12C, Measurement, Construction, and Maintenance of Skid-Resistant Airport Pavement Surfaces AC 150/5380-6B, Guidelines and Procedures for Maintenance of Airport Pavements ACRP Synthesis 22: Common Airport Pavement Maintenance Practices Specifications International Grinding and Grooving Association (IGGA) Guide Specification: Conventional Diamond Grinding for Pavement Preservation A pp lic at io ns /U se s Conditions Addressed Joint faulting (grinding) Slab curling/warping (grinding) Friction loss (grinding/grooving) Worn away grooves (grooving) Conditions Not Addressed: Diamond grinding and diamond grooving do not provide any structural benefit to the existing pavement, nor do they address or correct the mechanisms of the pavement distress. Limitations: Diamond grinding is the most effective means of restoring desirable surface characteristics to existing concrete pavements. The cause of poor surface characteristics should be identified prior to use. Diamond grinding should not be used where there is a materials-related distress (such as D-cracking or alkali-silica reactivity that is damaging the pavement).

120 Preventive Maintenance at General Aviation Airports C on st ru ct io n C on sid er at io ns Aggregate type and hardness influence costs and productivity. Grinding slurry must be collected on site and disposed of in accordance with local regulations. Slab stabilization, full-depth repairs, and spall repairs should be completed prior to grinding. Joint resealing should follow grinding to ensure proper sealant depth. Diamond grooving should be done according to FAA specifications. M isc el la ne ou s C on sid er at io ns Cost ($ to $$$$): Diamond grinding: $$ ($1.75–$5.50/yd2) Diamond grooving: $$ ($1.25–$3.00/yd2) Treatment Life (years): Diamond grinding: 8 to 15 Diamond grooving: 10 to 15 Pavement Life Extension (years): Diamond grinding: N/A Diamond grooving: N/A Safety: Safety is improved by restoring pavement surface texture, providing directional stability and increasing skid resistance, and reducing potential for hydroplaning. Risk: If the cause of the need for grinding is not established and corrected, the condition may recur. More frequent grinding may be necessary to maintain surface friction where polishing of the aggregate is a problem, especially if soft aggregate was used. Climate: No significant climate limitations. O th er R em ar ks Usually PCC pavements can be diamond ground at least three times without significantly affecting fatigue life. Can be accomplished during off-peak hours with short closures. PARTIAL-DEPTH REPAIR (PCC Patching) Tr ea tm en t D es cr ip tio n Partial-depth repairs address small, shallow areas of deteriorated PCC. These deteriorated areas are removed and replaced with an approved repair material, thereby maintaining the serviceability of the pavement. Partial-depth repairs should be used to correct joint spalling and other surficial distresses that are limited to the upper third of the slab. Sp ec Guidance AC 150/5380-6B, Guidelines and Procedures for Maintenance of Airport Pavements, Item 564, Repair of Pavement Distresses in Rigid (PCC) Pavements ACRP Synthesis 22: Common Airport Pavement Maintenance Practices Specifications N/A A pp lic at io ns /U se s Conditions Addressed Joint spalling caused by non- materials–related sources, such as incompressible materials or joint inserts Corner spalling Mechanical damage to pavement surface Conditions Not Addressed: Partial-depth repairs restore the structural integrity of localized areas of deteriorated concrete. Limitations: Partial-depth repairs may result in increased roughness if not finished properly. Diamond grinding may be used to blend the repaired surface with the surrounding pavement. C on st ru ct io n C on sid er at io ns It is important to properly determine repair boundaries; prepare the patch area; and finish, texture, and cure the repair material according to governing specifications. Material selection depends on various factors, such as opening requirements, ambient temperature, cost, and size and depth of patch. Proper and adequate preparation of the area to be patched is critical to ensure treatment success. The patch limits should extend 2 to 6 in. beyond the area of unsound concrete. Minimum spall repair dimensions are 4 by 12 in. (i.e., 12 in. along a transverse joint and 4 in. away from the transverse joint). Vertical faces are necessary when patching with most cementitious repair materials. Certain proprietary repair materials may be capable of successfully patching tapered sections. After concrete removal, the repair area should be prepared by sandblasting or water blasting, and should be air blasted clean immediately prior to the placement of the repair material. When specified, bonding agents (e.g., Portland cement grout or epoxy resin) should be appropriate for the time available before opening and should be compatible with concrete pavement. Inserting a compressible bond breaker prevents intrusion of the patch material into the joint, which could result in premature compressive failure of the repair. If the depth of the repair exceeds 1/3 of the slab thickness, then the placement of a full- depth repair should be considered. Small milling machines (oriented either parallel or perpendicular to the joint) have been effectively used for concrete removal when spalling exists along the entire length of a joint.

Pavement Treatments 121 M isc el la ne ou s C on sid er at io ns Cost ($ to $$$$): $$$ ($75–$150/yd2) Treatment Life (years): 5 to 15 Pavement Life Extension (years): N/A Safety: Poorly bonded patches that fail will cause large FOD potential. Risk: Performance failures are often caused by one or more of the following: bond failure, compression failure, variability and improper use of repair material, insufficient consolidation, and differences of the coefficient of thermal expansion between the existing pavement and patch. Climate: PCC patches should not be placed when the air temperature or pavement temperature is below 40°F unless adequately insulated. Furthermore, temperatures below 55°F will usually require a longer cure period. Placement should not proceed if rain is imminent. The use of all proprietary materials should closely follow the manufacturer’s recommendations. O th er R em ar ks Not applicable for spalling caused by dowel-bar misalignment or lockup; cracking caused by improper joint construction; working cracks caused by shrinkage, fatigue, or foundation movement; and spalls caused by materials-related distress (e.g., D-cracking or alkali-silica reactivity). Full-depth repair is necessary if dowel bars or tie bars are exposed in the patch area. Where the amount of patching is extensive, other strategies should be considered. There are many patching materials available, both non-proprietary and proprietary. Selection of the appropriate material should be based on available closure times, operational considerations, desired performance, condition of the pavement, previous experience with materials in the same or similar application, and so on. LOAD TRANSFER RESTORATION (DOWEL-BAR RETROFIT) Tr ea tm en t D es cr ip tio n Sp ec s A pp lic at io ns /U se s C on st ru ct io n C on sid er at io ns Load transfer restoration is the placement of mechanical load transfer devices (typically dowel bars) across joints or cracks in an existing jointed PCC pavement. These devices increase the load transfer capacity of the joint or crack, thereby reducing deflections and decreasing the potential for the development of pumping, faulting, and corner breaks. Poor load transfer at existing joints or cracks may result from an undoweled jointing situation (in which excessive joint or crack openings lead to reduced aggregate interlock), corrosion of existing load transfer devices, and poor pavement drainage resulting in loss of underlying support. Guidance ACRP Synthesis 22: Common Airport Pavement Maintenance Practices Specifications International Grinding and Grooving Association (IGGA) Guide Specification: Dowel Bar Retrofit (DBR) Conditions Addressed Joint faulting Pumping Corner breaks Conditions Not Addressed: The load transfer efficiency of a joint or crack strongly influences the structural performance of a PCC pavement; poor load transfer can result in pumping, faulting, corner breaks, and spalling. Limitations: Unlikely to be effective when placed in a pavement with a materials problem such as D-cracking or alkali-silica reactivity. Careful consideration must be given to selecting patch material and isolating the joint for repair. Special diamond slot cutters capable of creating multiple cuts in a single operation should be employed for highest productivity. Slots created with milling machines typically cause excessive spalling on the surface and do not create uniform slot widths. Dowel-bar slots should be sawed to a depth sufficient to place the center of the dowel bar within 1 in. of the mid-depth of the pavement and should be aligned to avoid existing longitudinal cracks. Additionally, slots should be centered over—allowing equal lengths of the dowel to span—the transverse joint or crack and parallel to the pavement centerline. Transverse joints/cracks should be maintained with a compressible insert. The transverse joint or crack should be caulked sufficiently to prevent any of the patching material from entering the joint/crack. The dowel bar for chairs should be strong enough to allow full support of the dowel bar, as well as allowing ≥1/2-in. clearance between the bottom of the dowel and the bottom of the slot. End caps should allow ≥1/4 in. of movement at each end of the dowel bar. Patching material should be placed in a manner that does not disturb the dowel bar within the slot; thus, patching material should not be dumped into the slots and instead should be placed on the surface adjacent to the slot and shoved into the slot.

122 Preventive Maintenance at General Aviation Airports M isc el la ne ou s C on sid er at io ns O th er R em ar ks Treatment Life (years): 10 to 15 Pavement Life Extension (years): 5 to 15 Safety: The primary safety concerns are associated with failed slot-filling material Cost ($ to $$$$): $$$ ($25–$35/dowel bar) causing risk of FOD. Risk: The alignment of dowel-bar slots must be parallel to the pavement centerline; slots perpendicular to skewed joints will cause joint lockup and lead to cracking. Additionally, slots sawed too deeply will contribute to corner cracks under loading. Climate: The material used to fill the slots should be placed following the appropriate climatic limitations for the material. It is most effective to apply treatment as structural distresses (e.g., pumping or corner breaks) are just beginning to appear. Diamond grinding done in conjunction with load transfer restoration will provide a smooth riding surface.

Abbreviations and acronyms used without definitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S.DOT United States Department of Transportation

TRA N SPO RTATIO N RESEA RCH BO A RD 500 Fifth Street, N W W ashington, D C 20001 A D D RESS SERV ICE REQ U ESTED ISBN 978-0-309-30875-5 9 7 8 0 3 0 9 3 0 8 7 5 5 9 0 0 0 0 N O N -PR O FIT O R G . U .S. PO STA G E PA ID C O LU M B IA , M D PER M IT N O . 88 Preventive M aintenance at G eneral A viation A irports, V olum e 2: G uidebook A CRP Report 138 TRB