TM 5-623
of all its sample units. Inspection by sampling, however,
as follows:
requires a different approach. If all surveyed sample
Density =
number of slabs containing a particular type X 100
units are selected randomly, the PCI of the pavement
distress number of slabs in sample unit
section is determined by averaging the PCI of its sample
units. If any additional sample units are inspected, a
For example, two slabs in the pavement sample unit
weighted average must be used. The weighted average
shown in figure 3-2 contained linear cracking (distress
is computed by using the following equation:
28) at medium severity, so the density is calculated as 2
20X 100, or 10 percent. The deduct values are then
PCIs = (N-A)(PCI1 + A)(PCO1) + A(PCO2)
determined for each distress combination from the
N
(Equation 3-1)
distress deduct value curves given in figures C-21
through C-39. The CDV is determined from figure C-40,
where PCIs = PCI of pavement section, PCI1 = average
and the PCI is calculated as shown in figure 3-2.
PCI of random samples, PCI2 = average PCI of
e. Determination of distress quantities for a
additional samples, N = total number of samples in the
pavement section.
When a pavement has been
section, and A = number of additional samples
inspected by sampling, it is necessary to extrapolate the
inspected.
quantities and densities of distress over the entire
pavement section to determine total quantities for the
d. Example calculation of the PCI for a sample unit.
section.
The field data sheets described in paragraph 3-3 are
(1) If all sample units surveyed were selected
always used when calculating the PCI of a sample unit.
at random, the extrapolated quantity of a given distress
(1) Asphalt pavement inspection sheet (fig 3-
of a given severity level would be determined as
3).
illustrated in the following example for medium-severity
(a) The difference between calculating
alligator cracking:
a PCI for an asphalt sample unit and calculating a PCI
for a concrete sample unit is in the way the distress
Section Information
density is determined.
Surface type: Asphalt concrete
1. Density for distresses measured by
Area: 24,500 square feet
the square foot is calculated as follows:
Total number of sample units in the section: 10
Density =
distress amount in square feet
sample unit area in square feet
X100
Five sample units were surveyed at random, and the
amount of medium-severity alligator cracking was
2. Density for distresses measured by
determined as follows:
the linear foot (bumps, edge cracking, joint reflection
cracking, lane/shoulder drop off, and longitudinal and
Sample
Sample Unit
Medium-Severity Alligator
transverse cracking) is calculated as follows (see
Unit ID
appendix B for distress definitions):
Number
Area, Square Feet
Cracking, Square Feet
02
2500
100
Density =
distress amount in linear feet
04
2500
200
sample unit area in square feet
X100
06
2500
150
08
2500
50
3. Density for distress measured by number (potholes)
10
2000
100
is calculated as follows:
Total
Random
12,000
600
Density =
number of potholes
sample unit area in square feet
X100
The average density for medium-severity alligator
(b) After the distress density for each distress
cracking is, therefore, 600/12,000 = 05.
The
extrapolated quantity is determined by multiplying the
type/severity combination is calculated, the deduct
density by the section area, i.e., .05X24,500=1225
values are determined from the distress deduct value
square feet.
curves in figures C-1 through C-19 of appendix C. The
(2) If additional sample units were included in
corrected deduct value (CDV) is determined from figure
the survey, the extrapolation process would be slightly
C-20 and is calculated as shown in figure 3-3.
(2) Concrete pavement inspection sheet (fig
different. In the example given in (1) above, assume that
sample unit number 01 was surveyed as additional and
3-2). After inspection, calculate the density of distress
that the amount of medium-severity alligator cracking
3-8
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