PAVEMENT CONDITION INDEX (PCI) METHOD
Background:
The Pavement Condition Index (PCI) method is used to obtain a Pavement Condition Index (PCI) value for airfield pavements through a visual survey of the pavement. The Pavement Condition Index (PCI) 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. This method has been adopted by Federal Aviation Administration to determine pavement condition (Advisory Circular No. 150/5380-6, Guidelines and Procedures for Maintenance of Airport Pavements).
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.
A description of each of these steps is presented next.
1. Divide Pavement Section Into Sample Units and Select sample Units for Inspection:
For asphalt surfaced pavements, a sample unit consists of 5000 + 2000 sq. ft. of pavement. The actual area of the sample units to be used is determined based on the geometry of the pavement section. For a PCC pavement, a sample unit consists of 20 + 8 slabs. As for asphalt surfaced pavements, the number of slabs to be included in a sample unit is determined based on the geometry of the pavement section. Once the sample unit size is determined, the pavement section is divided into sample units. Thereafter, the number of sample units for inspection is determined.
The minimum number of sample units for inspection is determined based on the total sample units within the section, as shown in the following table.
Number of sample units for inspection.
|
Total Number of |
Number of |
|
Samples |
Samples for |
|
in Section |
Inspection |
|
1 to 5 |
1 |
|
6 to 10 |
2 |
|
11 to 15 |
3 |
|
16 to 40 |
4 |
|
Over 40 |
10% |
A much higher sampling rate than the minimum sampling rate shown in the above table was used during the inspections that were carried out in 2002. Typically, a minimum sampling rate of 20% was used for all sections, irrespective of the number of total sample units within the section.
Once the number of sample units to be inspected has been determined, the spacing interval of the sample units to be inspected is determined. The spacing interval (i) of the sample units is calculated by the following formula and rounded to the lowest whole number:
i = N/n
where,
N = total number of sample units in the section
n = number of sample units to be inspected
The first sample unit to be inspected is selected at random from sample units 1 through i. The sample units within the section that are successive increments of the interval i after the first randomly selected unit are also inspected. If there are sample units within the section that are not representative of the section, such sample units are inspected in addition to the sample units that are selected at random. Such sample units include very poor or excellent samples that are not typical of the section, such as sample units that contain an unusual distress such as an utility cut.
2. Identify and Record Pavement Distresses in Sample Units:
The type, severity and quantity of pavement distress within each sample unit is determined by visual inspection of the pavement and recorded on data sheets. The procedures described in ASTM Standard D 5340 are used to determine the distress types, identify severity levels, and to measure the quantity of distress. Sixteen types of distresses are identified on asphalt surfaced pavements, while fifteen types of distresses are identified on PCC pavements. The types of distresses identified on asphalt surfaced pavements and PCC pavements are presented in the following tables.
Distress types for airfield pavements.
|
Distress Types on Asphalt Surfaced Pavements |
Distress Types on PCC
Pavements |
|
Alligator Cracking |
Blow Up |
|
Bleeding |
Corner Break |
|
Block Cracking |
Longitudinal, Transverse, Diagonal Cracks |
|
Corrugation |
Durability (D) Cracking |
|
Depression |
Joint Seal Damage |
|
Jet Blast Erosion |
Patching –Small |
|
Joint Reflection Cracking |
Patching Large and Utility Cuts |
|
Longitudinal and Transverse Cracking |
Popouts |
|
Oil Spillage |
Pumping |
|
Patching and Utility Cut Patching |
Scaling, Map Cracking and Crazing |
|
Polished Aggregate |
Settlement or Faulting |
|
Raveling and Weathering |
Shattered Slab/Intersecting Cracks |
|
Rutting |
Shrinkage Cracks |
|
Shoving |
Joint Spalling |
|
Slippage Cracking |
Corner Spalling |
|
Swell |
|
3. Compute PCI of Sample Units Based on Distress Within Sample Unit:
The procedure to compute the Pavement Condition Index (PCI) of a sample unit is described in ASTM standard D 5340. This procedure has been implemented in PAVER to compute the PCI value of each sample unit when the distress data is entered into PAVER. The following steps that are used to compute the PCI of a sample unit.
(a) Determine Distress Quantities: For asphalt concrete surfaced pavements, the total quantity of each distress type at each severity level is added up. For PCC pavements, the total number of slabs that have a particular distress type for a specific severity level are added up.
(b) Determine Distress Density: For asphalt concrete surfaced pavements, the total quantity of each distress type at each severity level is divided by the total area of the sample unit and multiplied by 100 to obtain the percent density of each distress type and severity. For PCC pavements, the total number of slabs for each distress type at each severity level is divided by the number of slabs that are contained within the sample unit and multiplied by 100 to obtain the percent density of each distress type and severity.
(c) Determine Deduct Value: The deduct value for each distress type and each severity level is determined by using the deduct value curve for that particular distress type. These deduct value curves are shown in ASTM Standard D 5340. The following figure shows a deduct value curve for linear cracking in asphalt surfaced pavements.
DeDeduct value curve for linear cracking on asphalt surfaced pavements.
(d) Obtain Correct Deduct Value: If none or only one deduct value is greater than five, the sum of the deduct values is used to obtain the total deduct value for the sample. Otherwise, a value called the corrected deduct value for the sample is computed using the deduct values obtained for the different distress types. This procedure is used because there is an interacting effect between different distress types, and if the deduct values were not corrected an unreasonable deduct value would be computed for the sample. The deduct values obtained for each distress type and each severity levels are combined using the procedure described in ASTM standard D 5340 to obtain the corrected deduct value for the sample.
(e) Obtain PCI of Sample Unit: Subtract the deduct value (or corrected deduct value if applicable) from 100 to obtain the PCI of the sample unit.
4. Compute PCI of Section:
If all surveyed sample units that were surveyed were selected randomly, or if all sample units within the section were surveyed, the PCI of the section is the average of the PCI values that were obtained for the samples within the section. If additional sample units were surveyed within the section, then a weighted averaging method is used to compute the PCI of the section. The details of this method are given in ASTM standard D 5340.
