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Pavement Maintenance Guidelines for General Aviation Airport Management (2016)

Chapter: Appendix A - Asphalt Distress Types and Descriptions

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Suggested Citation:"Appendix A - Asphalt Distress Types and Descriptions." National Academies of Sciences, Engineering, and Medicine. 2016. Pavement Maintenance Guidelines for General Aviation Airport Management. Washington, DC: The National Academies Press. doi: 10.17226/23649.
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Suggested Citation:"Appendix A - Asphalt Distress Types and Descriptions." National Academies of Sciences, Engineering, and Medicine. 2016. Pavement Maintenance Guidelines for General Aviation Airport Management. Washington, DC: The National Academies Press. doi: 10.17226/23649.
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Suggested Citation:"Appendix A - Asphalt Distress Types and Descriptions." National Academies of Sciences, Engineering, and Medicine. 2016. Pavement Maintenance Guidelines for General Aviation Airport Management. Washington, DC: The National Academies Press. doi: 10.17226/23649.
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Suggested Citation:"Appendix A - Asphalt Distress Types and Descriptions." National Academies of Sciences, Engineering, and Medicine. 2016. Pavement Maintenance Guidelines for General Aviation Airport Management. Washington, DC: The National Academies Press. doi: 10.17226/23649.
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Suggested Citation:"Appendix A - Asphalt Distress Types and Descriptions." National Academies of Sciences, Engineering, and Medicine. 2016. Pavement Maintenance Guidelines for General Aviation Airport Management. Washington, DC: The National Academies Press. doi: 10.17226/23649.
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Suggested Citation:"Appendix A - Asphalt Distress Types and Descriptions." National Academies of Sciences, Engineering, and Medicine. 2016. Pavement Maintenance Guidelines for General Aviation Airport Management. Washington, DC: The National Academies Press. doi: 10.17226/23649.
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Suggested Citation:"Appendix A - Asphalt Distress Types and Descriptions." National Academies of Sciences, Engineering, and Medicine. 2016. Pavement Maintenance Guidelines for General Aviation Airport Management. Washington, DC: The National Academies Press. doi: 10.17226/23649.
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Suggested Citation:"Appendix A - Asphalt Distress Types and Descriptions." National Academies of Sciences, Engineering, and Medicine. 2016. Pavement Maintenance Guidelines for General Aviation Airport Management. Washington, DC: The National Academies Press. doi: 10.17226/23649.
×
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Suggested Citation:"Appendix A - Asphalt Distress Types and Descriptions." National Academies of Sciences, Engineering, and Medicine. 2016. Pavement Maintenance Guidelines for General Aviation Airport Management. Washington, DC: The National Academies Press. doi: 10.17226/23649.
×
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Suggested Citation:"Appendix A - Asphalt Distress Types and Descriptions." National Academies of Sciences, Engineering, and Medicine. 2016. Pavement Maintenance Guidelines for General Aviation Airport Management. Washington, DC: The National Academies Press. doi: 10.17226/23649.
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Suggested Citation:"Appendix A - Asphalt Distress Types and Descriptions." National Academies of Sciences, Engineering, and Medicine. 2016. Pavement Maintenance Guidelines for General Aviation Airport Management. Washington, DC: The National Academies Press. doi: 10.17226/23649.
×
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Suggested Citation:"Appendix A - Asphalt Distress Types and Descriptions." National Academies of Sciences, Engineering, and Medicine. 2016. Pavement Maintenance Guidelines for General Aviation Airport Management. Washington, DC: The National Academies Press. doi: 10.17226/23649.
×
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Suggested Citation:"Appendix A - Asphalt Distress Types and Descriptions." National Academies of Sciences, Engineering, and Medicine. 2016. Pavement Maintenance Guidelines for General Aviation Airport Management. Washington, DC: The National Academies Press. doi: 10.17226/23649.
×
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Suggested Citation:"Appendix A - Asphalt Distress Types and Descriptions." National Academies of Sciences, Engineering, and Medicine. 2016. Pavement Maintenance Guidelines for General Aviation Airport Management. Washington, DC: The National Academies Press. doi: 10.17226/23649.
×
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Suggested Citation:"Appendix A - Asphalt Distress Types and Descriptions." National Academies of Sciences, Engineering, and Medicine. 2016. Pavement Maintenance Guidelines for General Aviation Airport Management. Washington, DC: The National Academies Press. doi: 10.17226/23649.
×
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Suggested Citation:"Appendix A - Asphalt Distress Types and Descriptions." National Academies of Sciences, Engineering, and Medicine. 2016. Pavement Maintenance Guidelines for General Aviation Airport Management. Washington, DC: The National Academies Press. doi: 10.17226/23649.
×
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Suggested Citation:"Appendix A - Asphalt Distress Types and Descriptions." National Academies of Sciences, Engineering, and Medicine. 2016. Pavement Maintenance Guidelines for General Aviation Airport Management. Washington, DC: The National Academies Press. doi: 10.17226/23649.
×
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Suggested Citation:"Appendix A - Asphalt Distress Types and Descriptions." National Academies of Sciences, Engineering, and Medicine. 2016. Pavement Maintenance Guidelines for General Aviation Airport Management. Washington, DC: The National Academies Press. doi: 10.17226/23649.
×
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Suggested Citation:"Appendix A - Asphalt Distress Types and Descriptions." National Academies of Sciences, Engineering, and Medicine. 2016. Pavement Maintenance Guidelines for General Aviation Airport Management. Washington, DC: The National Academies Press. doi: 10.17226/23649.
×
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Suggested Citation:"Appendix A - Asphalt Distress Types and Descriptions." National Academies of Sciences, Engineering, and Medicine. 2016. Pavement Maintenance Guidelines for General Aviation Airport Management. Washington, DC: The National Academies Press. doi: 10.17226/23649.
×
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Suggested Citation:"Appendix A - Asphalt Distress Types and Descriptions." National Academies of Sciences, Engineering, and Medicine. 2016. Pavement Maintenance Guidelines for General Aviation Airport Management. Washington, DC: The National Academies Press. doi: 10.17226/23649.
×
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Suggested Citation:"Appendix A - Asphalt Distress Types and Descriptions." National Academies of Sciences, Engineering, and Medicine. 2016. Pavement Maintenance Guidelines for General Aviation Airport Management. Washington, DC: The National Academies Press. doi: 10.17226/23649.
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31 A P P E N D I X A The following information comes from Asphalt Surfaced Airfields: PAVER™ Distress Manual (U.S. Army Corps of Engineers 2009). Contents Distress Type Page Longitudinal (Non-PCC Joint Reflective) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Transverse Cracking (Non-PCC Joint Reflective). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Edge Cracking (Non-PCC Joint Reflective). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Joint Reflection Cracking from PCC (Longitudinal and Transverse) . . . . . . . . . . . . . . . . . . . . 39 Block Cracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Alligator or Fatigue Cracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Weathering (Surface Wear)—Dense Mix Asphalt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Raveling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Patching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Roughness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Asphalt Distress Types and Descriptions

32 Pavement Maintenance Guidelines for General Aviation Airport Management Cracking Problems Longitudinal (Non-PCC Joint Reflective) Description Parallel to the pavement’s center line or laydown direction. They may be caused by: (1) a poorly constructed paving lane joint, (2) shrinkage of the AC surface due to low temperatures or hardening of the asphalt, or (3) a reflective crack caused by cracks beneath the surface course, including cracks in Portland cement concrete (PCC) slabs (but not at PCC joints). Transverse cracks extend across the pavement at approximately right angles to the pavement’s center line or direction of laydown. They may be caused by items (2) or (3) above. These types of cracks are not usually load associated. If the pavement is fragmented along a crack, the crack is said to be spalled. How to Measure Measured in linear feet (m) The length and severity of each crack should be identified and recorded. If the crack does not have the same severity level along its entire length, each portion of the crack having a different severity level should be recorded separately. For an example see “Joint Reflection Cracking.” If block cracking is recorded, longitudinal and transverse cracking is not recorded in the same area. Low Medium High Severity Levels Cracks have only light spalling (little or no FOD potential) or no spalling, and can be filled or non-filled. If non-filled, the cracks have a mean width of ¼ in. (6 mm) or less; filled cracks are of any width, but their filler material is in satisfactory condition. One of the following conditions exists: (1) cracks are moderately spalled (some FOD potential) and can be either filled or non- filled of any width; (2) filled cracks are not spalled or are lightly spalled, but filler is in unsatisfactory condition; (3) non- filled cracks are not spalled or are only lightly spalled, but the mean crack width is greater than ¼ in. (6 mm); or (4) light random cracking exists near the crack or at the corners of intersecting cracks. Cracks are severely spalled and pieces are loose or missing causing definite FOD potential. Cracks can be either filled or non-filled of any width.

Asphalt Distress Types and Descriptions 33 Longitudinal Cracking (Non-PCC Joint Reflective) Severity Levels Low Few Cracks Many Cracks

34 Pavement Maintenance Guidelines for General Aviation Airport Management Longitudinal Cracking (Non-PCC Joint Reflective) Severity Levels Medium High

Asphalt Distress Types and Descriptions 35 Transverse Cracking (Non-PCC Joint Reflective) Description Extend across the pavement at approximately right angles to the pavement’s center line or direction of laydown. They may be caused by: (1) shrinkage of the AC surface due to low temperatures or hardening of the asphalt, or (2) a reflective crack caused by cracks beneath the surface course, including cracks in PCC slabs (but not at PCC joints). These types of cracks are not usually load associated. If the pavement is fragmented along a crack, the crack is said to be spalled. How to Measure Measured in linear feet (m) The length and severity of each crack should be identified and recorded. If the crack does not have the same severity level along its entire length, each portion of the crack having a different severity level should be recorded separately. For an example see “Joint Reflection Cracking.” If block cracking is recorded, longitudinal and transverse cracking are not recorded in the same area. Low Medium High Severity Levels Cracks have only light spalling (little or no FOD potential) or no spalling, and can be filled or non-filled. If non-filled, the cracks have a mean width of ¼ in. (6 mm) or less; filled cracks are of any width, but their filler material is in satisfactory condition. One of the following conditions exists: (1) cracks are moderately spalled (some FOD potential) and can be either filled or non- filled of any width; (2) filled cracks are not spalled or are lightly spalled, but filler is in unsatisfactory condition; (3) non- filled cracks are not spalled or are only lightly spalled, but the mean crack width is greater than ¼ in. (6 mm); or (4) light random cracking exists near the crack or at the corners of intersecting cracks. Cracks are severely spalled and pieces are loose or missing causing definite FOD potential. Cracks can be either filled or non-filled of any width.

36 Pavement Maintenance Guidelines for General Aviation Airport Management Transverse Cracking (Non-PCC Joint Reflective) Severity Levels (20 or 50 ft) Low Medium High

Asphalt Distress Types and Descriptions 37 Edge Cracking (Non-PCC Joint Reflective) Description Occur within 4 ft of the edge. They may be caused by: (1) a poorly constructed paving lane joint, (2) shrinkage of the AC surface due to low temperatures or hardening of the asphalt, or (3) a reflective crack caused by cracks beneath the surface course, including cracks in PCC slabs (but not at PCC joints). These types of cracks are not usually load associated. If the pavement is fragmented along a crack, the crack is said to be spalled. How to Measure Measured in linear feet (m) The length and severity of each crack should be identified and recorded. If the crack does not have the same severity level along its entire length, each portion of the crack having a different severity level should be recorded separately. For an example see “Joint Reflection Cracking.” Edge cracks are often treated differently than cracks in the middle of the pavement and are listed separately for this reason. Low Medium High Severity Levels Cracks have only light spalling (little or no FOD potential) or no spalling, and can be filled or non-filled. If non-filled, the cracks have a mean width of ¼ in. (6 mm) or less; filled cracks are of any width, but their filler material is in satisfactory condition. One of the following conditions exists: (1) cracks are moderately spalled (some FOD potential) and can be either filled or non- filled of any width; (2) filled cracks are not spalled or are lightly spalled, but filler is in unsatisfactory condition; (3) non- filled cracks are not spalled or are only lightly spalled, but the mean crack width is greater than ¼ in. (6 mm); or (4) light random cracking exists near the crack or at the corners of intersecting cracks. Cracks are severely spalled and pieces are loose or missing causing definite FOD potential. Cracks can be either filled or non-filled of any width.

38 Pavement Maintenance Guidelines for General Aviation Airport Management Edge Cracking (Non-PCC Joint Reflective) Severity Levels Low Medium High

Asphalt Distress Types and Descriptions 39 Joint Reflection Cracking from PCC (Longitudinal and Transverse) Description Occurs only on pavements having an asphalt or tar surface over a PCC slab. This category does not include reflection cracking from any other type of base (that is, cement stabilized, lime stabilized). Such cracks are listed as longitudinal and transverse cracks. Caused mainly by movement of the PCC slab beneath the AC surface because of thermal and moisture changes; it is not load related. Traffic loading may cause a breakdown of the AC near the crack, resulting in spalling and FOD potential. If the pavement is fragmented along a crack, the crack is said to be spalled. Knowledge of slab dimensions beneath the AC surface will help to identify these cracks. How to Measure Measured in linear feet (m). The length and severity level of each crack should be identified and recorded. If the crack does not have the same severity level along its entire length, each portion should be recorded separately. For example, a crack that is 50 ft (15 m) long may have 10 ft (3 m) of a high severity, 20 ft (6 m) of a medium severity, and 20 ft (6 m) of a light severity. These would all be recorded separately. If the different levels of severity in a portion of a crack cannot be easily divided, that portion should be rated at the highest severity present. Low Medium High Severity Levels Cracks have only light spalling (little or no FOD potential) or no spalling, and can be filled or non-filled. If non-filled, the cracks have a mean width of ¼ in. (6 mm) or less; filled cracks are of any width, but their filler material is in satisfactory condition. One of the following conditions exists: cracks are moderately spalled (some FOD potential) and can be either filled or non-filled of any width; filled cracks are not spalled or are lightly spalled, but filler is in unsatisfactory condition; non- filled cracks are not spalled or are only lightly spalled, but the mean crack width is greater than ¼ in. (6 mm); or light random cracking exists near the crack or at the corners of intersecting cracks. Cracks are severely spalled with pieces loose or missing causing definite FOD potential. Cracks can be either filled or non-filled of any width.

40 Pavement Maintenance Guidelines for General Aviation Airport Management Joint Reflection Cracking from PCC (Longitudinal and Transverse) Severity Levels Low Medium High

Asphalt Distress Types and Descriptions 41 Block Cracking Description Interconnected cracks that divide the pavement into approximately rectangular pieces. May range in size from approximately 1 ft by 1 ft to 10 ft by 10 ft (0.3 m by 0.3 m to 3 m by 3 m). Caused mainly by shrinkage of the AC and daily temperature cycling (that results in daily stress/strain cycling). Not load associated. The occurrence of block cracking usually indicates that the asphalt has hardened significantly. Normally occurs over a large portion of pavement area, but sometimes will occur only in non-traffic areas. Differs from alligator cracking in that the alligator cracks form smaller, many-sided pieces with sharp angles. Also unlike block cracks, alligator cracks are caused by repeated traffic loadings and are located only in traffic areas (that is, wheel paths). How to Measure Measured in ft2 (m2) of surface area. Usually occurs at one severity level in a given pavement section; however, any areas of the pavement section having distinctly different levels of severity should be measured and recorded separately. For asphalt pavements, not including AC over PCC, if block cracking is recorded, no longitudinal and transverse cracking should be recorded in the same area. For asphalt overlay over concrete, block cracking, joint reflection cracking, and longitudinal and transverse cracking reflected from old concrete should all be recorded separately. Low Medium High Severity Levels Blocks are defined by cracks that are non- spalled (sides of the crack are vertical) or lightly spalled, causing no FOD potential. Non- filled cracks have ¼ in. (6 mm) or less mean width, and filled cracks have filler in satisfactory condition. Blocks are defined by either filled or non-filled cracks that are moderately spalled (some FOD potential); non- filled cracks that are not spalled or have only minor spalling (some FOD potential), but have a mean width greater than approximately ¼ in. (6 mm); or filled cracks greater than ¼ in. that are not spalled or have only minor spalling (some FOD potential), but have filler in unsatisfactory condition. Blocks are well defined by cracks that are severely spalled, causing a definite FOD potential.

42 Pavement Maintenance Guidelines for General Aviation Airport Management Block Cracking Severity Levels Low Medium High

Asphalt Distress Types and Descriptions 43 Alligator or Fatigue Cracking Description A series of interconnecting cracks caused by fatigue failure of the AC surface under repeated traffic loading. The cracking initiates at the bottom of the AC surface (or stabilized base) where tensile stress and strain are highest under a wheel load. The cracks propagate to the surface initially as a series of parallel cracks. After repeated traffic loading, the cracks connect, forming many-sided, sharp-angled pieces that develop a pattern resembling chicken wire or the skin of an alligator. The pieces are less than 2 ft (0.6 m) on the longest side. Occurs only in areas that are subjected to repeated traffic loadings, such as wheel paths. Would not occur over an entire area unless the entire area was subjected to traffic loading. (Pattern-type cracking that occurs over an entire area that is not subjected to loading is rated as block cracking, that is, not a load-associated distress.) Considered a major structural distress. How to Measure Measured in ft2 (m2) of surface area. Many times two or three levels of severity exist within one distressed area. If these portions can be easily distinguished from one another, they should be measured and recorded separately. If the different levels of severity cannot be easily divided, the entire area should be rated at the highest severity level present. If alligator cracking and rutting occur in the same area, each is recorded separately as its respective severity level. Low Medium High Severity Levels Fine, longitudinal hairline cracks running parallel to one another with none or only a few interconnecting cracks. The cracks are not spalled. Further development of light alligator cracking into a pattern or network of cracks that may be lightly spalled. Medium-severity alligator cracking is defined by a well-defined pattern of interconnecting cracks, where all pieces are securely held in place (good aggregate interlock between pieces). Network or pattern cracking has progressed so that the pieces are well defined and spalled at the edges; some of the pieces rock under traffic and may cause FOD potential.

44 Pavement Maintenance Guidelines for General Aviation Airport Management Alligator (Fatigue) Cracking Severity Levels Low Medium High

Asphalt Distress Types and Descriptions 45 Surface Distress Weathering (Surface Wear)—Dense Mix Asphalt Description The wearing away of the asphalt binder and fine aggregate matrix from the pavement surface. How to Measure Measured in ft2 (m2). Surface wear is not recorded if medium or high severity raveling is recorded. Low Medium High Severity Levels Asphalt surface beginning to show signs of aging that may be accelerated by climatic conditions. Loss of the fine aggregate matrix is noticeable and may be accompanied by fading of the asphalt color. Edges of the coarse aggregates are beginning to be exposed (less than 1 mm or 0.05 in.). Pavement may be relatively new (as new as 6 months old). Loss of fine aggregate matrix is noticeable and edges of coarse aggregate have been exposed up to ¼ width (of the longest side) of the coarse aggregate due to the loss of fine aggregate matrix. Edges of coarse aggregate have been exposed greater than ¼ width (of the longest side) of the coarse aggregate. There is considerable loss of fine aggregate matrix leading to potential or some loss of coarse aggregate. Weathering (Surface Wear) Severity Levels Low High

46 Pavement Maintenance Guidelines for General Aviation Airport Management Raveling Description Dislodging of coarse aggregate particles from the pavement surface. How to Measure Measured in ft2 (m2) of surface area. Mechanical damage caused by hook drags, tire rims, or snowplows is counted as areas of high-severity raveling. Dense Mix Severity Levels As used herein, coarse aggregate refers to predominant coarse aggregate sizes of the asphalt mix. Aggregate clusters refer to when more than one adjoining coarse aggregate piece is missing. If in doubt about a severity level, three representative areas of 1 yd2 each (1 m2) should be examined and the number of missing coarse aggregate particles counted. Low Medium High Severity Levels (1) In a yd2 (m2) representative area, the number of coarse aggregate particles missing is between 5 and 20, and/or (2) missing aggregate clusters are less than 2% of the examined yd2 (m2) area. In low-severity raveling, there is little or no FOD potential. (1) In a yd2 (m2) representative area, the number of coarse aggregate particles missing is between 21 and 40, and/or (2) missing aggregate clusters are between 2% and 10% of the examined yd2 (m2) area. In medium-severity raveling, there is some FOD potential. (1) In a yd2 (m2) representative area, the number of coarse aggregate particles missing is over 40, and/or (2) missing aggregate clusters are more than 10% of the examined yd2 (m2) area. In high- severity raveling, there is significant FOD potential. Slurry Seal/Coal Tar over Dense Mix (1) The scaled area is less than 1%. (2) In the case of coal tar where pattern cracking has developed, the surface cracks are less than ¼ in. (6 mm) wide. (1) The scaled area is between 1% and 10%. (2) In the case of coal tar where pattern cracking has developed, the cracks are ¼ in. (6 mm) wide or greater. (1) The scaled area is over 10%. (2) In the case of coal tar, the surface is peeling off.

Asphalt Distress Types and Descriptions 47 Raveling Severity Levels Low High

48 Pavement Maintenance Guidelines for General Aviation Airport Management Patching Description A defect, no matter how well it is performing. How to Measure Measured in ft2 (m2) of surface area. If a single patch has areas of differing severity levels, these areas should be measured and recorded separately. For example, a 25-ft2 (2.5-m2) patch may have 10 ft2 (1 m2) of medium severity and 15 ft2 (1.5 m2) of low severity. These areas should be recorded separately. Any distress found in a patched area will not be recorded; however, its effect on the patch will be considered when determining the patch’s severity level. A very large patch (area > 2500 ft2 [230 m2]), or feathered-edge pavement, may qualify as an additional sample unit or as a separate section. Low Medium High Severity Levels Patch is in good condition and is performing satisfactorily. Patch is somewhat deteriorated and affects ride quality to some extent. Moderate amount of distress is present within the patch or has FOD potential, or both. Patch is badly deteriorated and affects ride quality significantly or has high FOD potential. Patch soon needs replacement.

Asphalt Distress Types and Descriptions 49 Patching Severity Levels Low Medium High

50 Pavement Maintenance Guidelines for General Aviation Airport Management Roughness Roughness, as used in this tool, is a combination of several distress types, which are corrugation, depression, and swell. Regardless of the distress type, select the category that matches the impact of the distress. Corrugation Description A series of closely spaced ridges and valleys (ripples) occurring at fairly regular intervals (usually less than 5 ft) (1.5 m) along the pavement. The ridges are perpendicular to the traffic direction. Traffic action combined with an unstable pavement surface or base usually cause this type of distress. How to Measure Measured in ft2 (m2) of surface area. The mean elevation difference between the ridges and valleys of the corrugations indicates the level of severity. To determine the mean elevation difference, a 10-ft (3 m) straightedge should be placed perpendicular to the corrugations so that the depth of the valleys can be measured in inches or mm. The mean depth is calculated from five such measurements. Severity Runways and High- Speed Taxiways Taxiways and Aprons L <¼ in. (6 mm) <½ in. (13 mm) Corrugations are minor and do not significantly affect ride quality. M ¼ to ½ in. (6 to 13 mm) ½ to 1 in. (13 to 25 mm) H >½ in. (13 mm) >1 in. (25 mm)

Asphalt Distress Types and Descriptions 51 Depression Description Localized pavement surface areas having elevations slightly lower than those of the surrounding pavement. In many instances, light depressions are not noticeable until after a rain, when ponding water creates birdbath areas, but the depressions can also be located without rain because of stains created by ponding of water. Can be caused by settlement of the foundation soil or can be built during construction. Cause roughness and, when filled with water of sufficient depth, could cause hydroplaning of aircraft. How to Measure Measured in ft2 or m2 of surface area. The maximum depth of the depression determines the level of severity. Measured by placing a 10-ft (3-m) straightedge across the depressed area and measuring the maximum depth in inches or mm. Larger than 10 ft (3 m) across must be measured by using a stringline. Maximum Depth of Depression Runways and High-Speed Taxiways Taxiways and Aprons Severity Levels L ⅛ to ½ in. (3 to 13 mm) ½ to 1 in. (13 to 25 mm) Depression can be observed or located by stained areas, only slightly affects pavement riding quality, and may cause hydroplaning potential on runways (see measurement criteria). M ½ to 1 in. (13 to 25 mm) 1 to 2 in. (25 to 51 mm) The depression can be observed, moderately affects pavement riding quality, and causes hydroplaning potential on runways (see measurement criteria). H >1 in. (>25 mm) >2 in. (>51 mm) The depression can be readily observed, severely affects pavement riding quality, and causes definite hydroplaning potential (see measurement criteria).

52 Pavement Maintenance Guidelines for General Aviation Airport Management Swell Description An upward bulge in the pavement’s surface. May occur sharply over a small area or as a longer, gradual wave. Either type of swell can be accompanied by surface cracking. Usually caused by frost action in the subgrade or by swelling soil, but a small swell can also occur on the surface of an asphalt overlay (over PCC) as a result of a blowup in the PCC slab. How to Measure Measured in ft2 or m2. The severity rating should take into consideration the type of pavement section (that is, runway, taxiway, or apron). For example, a swell of sufficient magnitude to cause considerable roughness on a runway at high speeds would be rated as more severe than the same swell located on an apron or taxiway where the normal aircraft operating speeds are much lower. For short wavelengths, locate the highest point of the swell. Rest a 10-ft (3-m) straightedge on that point so that both ends are equal distance above the pavement. Measure this distance to establish severity rating. The following guidance is provided for runways: Severity Height Differential Severity Levels L <¾ in. (20 mm) Swell is barely visible and has a minor effect on the pavement’s ride quality. (Low-severity swells may not always be observable, but their existence can be confirmed by driving a vehicle over the section. An upward acceleration will occur if the swell is present). M ¾ to 1½ in. (20 to 40 mm) Swell can be observed without difficulty and has a significant effect on the pavement’s ride quality. H >1½ in. (40 mm) Swell can be readily observed, and severely affects the pavement’s ride quality. Rate severity on high-speed taxiways using measurement criteria provided in the previous table. Double the height differential criteria for other taxiways and aprons.

Next: Appendix B - Concrete Distress Types and Descriptions »
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TRB's Airport Cooperative Research Program (ACRP) Report 159: Pavement Maintenance Guidelines for General Aviation Airport Management provides guidance to general aviation airport managers in determining the most cost-efficient and appropriate preventative maintenance solution to common pavement issues. In addition to the guidebook, two additional products were developed.

The Airport Pavement Maintenance Recommendation Tool is an interactive tool that will assist the user in identifying pavement issues. The Field Guide for the Airport Pavement Maintenance Recommendation Tool is intended to assist in identifying the specific pavement issues while in the field.

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