PAVEMENT CONDITION INDEX 2010
PAVEMENT CONDITION INDEX (PCI) METHOD
The Pavement Condition Index (PCI) is an example of an engineering approach applied to existing e xisting pavements. The Pavement Condition Index method is used to obtain a Pavement Condition Index value for airfield pavements through a visual survey of the pavement. The Pavement Condition Index is a numerical rating of the pavement condition that ranges from 0 to 100, with 0 being the worst possible condition and 100 being the best possible condition. The Pavement Condition Index (PCI) method was developed by the Construction Engineering Research Laboratory of the U.S. Army Corps of Engineers. This method can be used on both asphalt surfaced as well as jointed portland cement concrete (PCC) pavements. It is widely used in transportation civil engineering. engineering. It is a statistical measure and requires manual survey of the pavement pavement.. This method has been adopted by Federal Aviation Administration to determine pavement condition. Determination of PCI Value: The following procedure is followed in the PCI method to obtain the PCI value of the pavement. 1. Divide pavement section into sample units and select sample units for inspection. 2. Identify and record pavement distress in sample units. 3. Compute PCI of sample units based on distress within sample unit. 4. Compute PCI of section.
This condition index can give a good indication of the pavement condition of a network. However, trained personnel are required to complete the complicated survey procedure.
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PAVEMENT CONDITION INDEX 2010
A surface treatment is placed on a crushed stone base to provide a roadway with the least expensive permanent type of bituminous surface. It seals and protects the base and provides strength at the road surface so that the base can resist the abrasive and disruptive forces of traffic. It also provides many of the functions that a seal coat provides. When applied to a bituminous pavement surface, a seal coat provides a durable all-weather surfacing that: •
seals an existing bituminous surface against the intrusion of air and water
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enriches an existing dry or ravelled surface
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arrests the deterioration of a surface showing signs of distress
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provides a skid-resistant surface
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provides the desired surface texture
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improves light-reflecting characteristics where these are required
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paved shoulders or other geometric features to be demarcated by
providing a different texture or colour •
provides a uniform-appearing surface.
The functions of the asphalt binder are to bind the aggregate particles to the underlying surface and to provide a waterproof seal. The functions of the aggregate are to resist traffic abrasion, to transmit wheel loads and to provide skid-resistance and the desired surface texture. A seal coat or surface treatment has little or no structural strength itself but by preventing the ingress of water it enables the inherent strength of the pavement and the sub grade to be preserved. If a pavement shows evidence of traffic load associated cracking alligator, longitudinal, transverse), a seal coat is only a temporary solution. Areas that show load-associated cracking may require base repair prior to a seal coat or overlay. A thick asphalt concrete overlay or reconstruction is normally required to correct these problems. Seal coats applied to pavements showing signs of non-traffic load associated longitudinal and transverse cracks have proved somewhat effective. Seal coats usually bridge these cracks in a 2|Page
PAVEMENT CONDITION INDEX 2010 more satisfactory manner than thin asphalt concrete overlays. Ride quality of a pavement cannot be improved significantly by the application of a seal coat. Overlays of various thickness, spot level-up maintenance patches, or reconstruction are normally required to restore pavement ride quality.
Pavements demonstrating flushing or bleeding are difficult to repair with seal coats. The binder normally migrates through an added seal coat unless the asphalt quantity applied to the roadway can be altered at these spot locations. Seal coats utilizing a large maximum size aggregate are suggested if seal coats are used on flushed surfaces. Seal coats have been used successfully on both low- and high-traffic volume roadways, but tend to be more successful on low-volume roadways, especially low-volume truck traffic. The use of seal coats in urban areas where accelerating/decelerating traffic and turning movements frequently occur should be approached with caution and is addressed more in Chapter 2.
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PAVEMENT CONDITION INDEX 2010
TYPES OF DISTRESS
ALLIGATOR CRACKING It is a series of interconnection cracks caused by fatigue failure of asphalt concrete surface under repeated traffic loading. Cracking begins at the bottom on the asphalt surface (base) where tensile stress and strain are highest under a wheel load. The cracks propagate to the surface initially as a series of parallel longitudinal cracks. After repeated traffic loading, the cracks connect, forming many-sided, sharpangled pieces that develop a pattern resembling chicken wire or the skin of an alligator. The pieces are less than 2 ft. (.6m) on the longest side. Alligator cracking occurs only in areas subjected to repeated traffic loading, such as wheel paths. Alligator cracking is considered a major structural distress and is often accompanied by rutting. This type of distress often will have two or three levels of severity often within one distressed area. If these portions can be easily distinguished from each other, they should be measured and recorded separately. Low Severity Alligator
Low: Fine, longitudinal hairline cracks running parallel to each other with one or only a few interconnecting cracks. The cracks are not spalled. This clack is in a wheel path and is oriented in the direction of travel.
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PAVEMENT CONDITION INDEX 2010
Medium Severity Alligator
Medium: Further development of light alligator cracking into a pattern or network of cracks that may be lightly spelled.
High Severity Alligator
High: Network or pattern cracking has progressed so that the pieces are well defined and spalled at the edges. Some pieces may rock under traffic. Potholes of all sizes are recorded as high severity alligator cracking.
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PAVEMENT CONDITION INDEX 2010 Interconnected cracking with a pattern resembling alligator skin. It is a pavement that is fatigued or worn out from heavy traffic. Alligator crack was caused by inadequate structure, accumulated damage, age hardening, and poor drainage. Fatigue cracking indicates a failure of the pavement structure. Full depth reclamation or thick overlays are in order.
Solutions - Prevention •
The use of quality structural design and materials during construction
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Adequate drainage
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Preventive maintenance treatments as the pavement begins to age
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Structural overlays applied at the right time to increase the pavement
strength •
Elastomeric polymer modified binders have been found to be especially
effective
DEPRESSION Depressions are localized pavement surface areas having elevations slightly lower than those of the surrounding pavement. In many instances, light depressions are nit noticeable until after a rain, when ponding water creates a ‘birdbath” area but the depressions can also be located without rain because of strains created by ponding water. Severity Levels Low – Depression can be observed or located. by stained areas, only slightly affects pavement riding quality and may cause hydroplaning potential on runways.
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PAVEMENT CONDITION INDEX 2010
Medium – The depression can be observed moderately affects pavement riding quality and causes hydroplaning potential on runways.
High - The depression can be readily observed, severely affects pavement riding quality, and causes definite hydroplaning potential.
EDGE CRACKING 7|Page
PAVEMENT CONDITION INDEX 2010 Edge cracks are crescent-shaped or fairly continuous cracks, parallel to, and usually within 300mm-600mm of the pavement edge. It usually occurs when paved shoulders do not esist.
Basic construction steps associated with a repair along the edge of the pavement depend upon the severity and depth of the deterioration. If the distress is confined mainly to the HMA surface, the steps associated with a regular patching operation should be employed. If the deterioration extends well below the surface, the steps associated with a dig out are more appropriate. In both cases, the intent is to improve the lateral support along the pavement’s edge. Accordingly, extra precautions should be taken for achieving adequate compaction and maintaining good drainage at that interface with the shoulder.
LONGITUDINAL & TRANSVERSE CRACKING Longitudinal cracking is crack or discontinuity in a pavement that runs generally parallel to the pavement centerline. Longitudinal cracks may occur as a result of poorly constructed paving lane joints, thermal shrinkage, inadequate support, reflection from underlying layers, or as a precursor to fatigue cracking. Longitudinal cracking that occurs in the wheel path is generally indicative of alligator cracking.
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PAVEMENT CONDITION INDEX 2010
Transverse cracking is cracks perpendicular to the pavement's centerline or laydown direction. It is unconnected cracks running transversely.
It is a cracking in the direction of flow of traffic, usually at the edge of wheel paths. This type of distress was caused by pavement that is fatigued or worn out from heavy traffic (especially the side walls of high pressure truck tires), an unstable base and poor construction. Solutions - Cures Several options are available, based on severity of the cracking and the condition of the pavement structure. For very minor cracking, the important thing is to prevent moisture from entering the crack and damaging the underlying structure. More severe longitudinal cracking usually indicates a larger problem with pavement structure. Solutions - Prevention •
The use of quality structural design and materials during construction
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Preventive maintenance treatments as the pavement begins to age
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Structural overlays applied at the right time to increase the pavement
strength •
Polymer modified binders meeting the applicable PG grades for heavy
traffic have been found to be especially effective.
PATCHING 9|Page
PAVEMENT CONDITION INDEX 2010 Patches are repairs made to previous distress, indicating prior maintenance activity. If done properly, patches can improve the long-term performance of the structure. A patch is considered a defect no matter how well it performs. The extent and frequency of patching can be useful indicators of the structural adequacy of the pavement. Defects can occur within a patch or the patch can be further defect where it is raised or depressed below the level of the pavement surface.
Proper patching should always involve saw-cut edges parallel or perpendicular to the direction of traffic, with excavation to the full depth of the weak material. Replacement material must be properly compacted with tacking of all cut HMAC surfaces to improve impermeability. Provided the patch addressed the full depth of the previous distress/weakness, the life of the patch and the surrounding patch/pavement interface will be extended by placing a full lane width seal or overlay. At the network level, this condition is evaluated in terms of feet of full lane-width patching. Improper patching can introduce a degree of roughness, further deterioration at the edges of the patch, or even failure of the patch itself if the underlying problem was not addressed where cracks continue to be active during cyclic seasonal temperature changes.
POTHOLES Small, bowl-shaped depressions in the pavement surface that penetrate all the way through the HMA layer down to the base course. They generally have sharp edges and vertical sides near the top of the hole. Potholes are most likely to occur on roads with thin HMA surfaces (1 to 2 inches) and seldom occur on roads with 4 inch or deeper HMA surfaces
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PAVEMENT CONDITION INDEX 2010
Is there anyone who doesn’t know what a pothole is? It be caused by a number of factors, but usually form when water gets into cracks and destroys the underlying structure. They most often appear when the pavement is most subjected to moisture in the early spring. The factors are inadequate structure, accumulated damage, age hardening and poor drainage. Solutions - Cures No matter what cure is chosen, it is important to fix the situation which caused the pothole. Solutions - Prevention •
Quality structural design, materials and construction
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Adequate drainage
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Preventive maintenance treatments
•
Structural overlays applied at the right time to increase the pavement
strength •
Elastomeric polymer modified binders have been found to be especially
effective
BLOCK CRACKS Interconnected cracks that divide the pavement up into rectangular pieces. The cracking pattern is much larger than alligator cracking.
Block
cracking is a climate/materials related distress, where shrinkage of the bituminous surface or underlying stabilized base causes interconnected cracks 11 | P a g e
PAVEMENT CONDITION INDEX 2010 that divide the surface into irregular pieces. Blocks range in size from approximately 1 ft2 to 100 ft2. Larger blocks are generally classified as longitudinal and transverse cracking. Block cracking normally occurs over a large portion of pavement area but sometimes will occur only in non-traffic areas. Addressing this distress as part of a rehabilitation strategy may be as simple as sealing the cracks prior to placing a surface treatment. Additional considerations will be necessary where the extent of the cracking is severe or
BLEEDING Bleeding is the presence of free bitumen binder on the surface resulting from upward migration of the binder, causing low texture depth and inadequate tyre to stone contact. It is most likely to occur in the wheel paths during hot weather.
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PAVEMENT CONDITION INDEX 2010
The result can mean a loss of surface texture on the pavement. It is caused by too high asphalt content and moisture damage. Solutions - Cures Standard Solutions •
Microsurfacing
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Sandwich Seal
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Mill and Fill
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Full Depth Reclamation
Prevention •
Proper Design
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Adequate Drainage
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