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PAVEMENT CONDITION INDEX 2010
PAVEMENT CONDITION INDEX (PCI) METHOD
The Pavement Condition Index (PCI) is an example of an engineeringapproach applied to existing 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 transportationcivil engineering. It
is a statistical measure and requires manual survey of the 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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A surface treatment is placed on a crushed stone base to provide a
roadway with the least expensive permanent type ofbituminous 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
enriches an existing dry or ravelled surface arrests the deterioration of a surface showing signs of distress
provides a skid-resistant surface
provides the desired surface texture
improves light-reflecting characteristics where these are required
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 thesub
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
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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 demonstratingflushing orbleeding 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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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, sharp-
angled 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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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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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
Adequate drainage
Preventive maintenance treatments as the pavement begins to age
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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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
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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 arepair 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 pavements 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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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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Is there anyone who doesnt 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
Adequate drainage
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 thebituminous surface or underlying stabilized base causes interconnected cracks
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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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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
Sandwich Seal
Mill and Fill
Full Depth Reclamation
Prevention
Proper Design
Adequate Drainage
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