What is a Deduct Value?

Deduct Value (PCI)

Definition

A deduct value (DV) is the number that an ASTM D5340 curve gives for one distress at one severity and density.

The Pavement Condition Index (PCI) rates a pavement from 0 to 100. The deduct values are the inputs to that rating. The standard turns them into a corrected deduct value (CDV), and the PCI is 100 minus the maximum CDV. The PCI page covers the whole index, the survey and the rating scale. This page covers the deduct value and how the standard uses it.

Where a deduct value comes from

The inspector records the type, severity and quantity of each distress in a sample unit. The standard then gives these steps (ASTM D5340, 9.1 to 9.3):

1. Add up the quantity of each distress type at each severity level. The unit is area, length or number of occurrences, depending on the type.
2. Divide each quantity by the area of the sample unit and multiply by 100. This is the percent density.
3. Read the deduct value on the deduct curve for that distress type and severity.

For concrete, the density is the percent of slabs in the sample unit that have the distress (10.1 and 10.2).

The deduct curves

Each distress type has its own curves. The asphalt curves are in Appendix X3, and the concrete curves are in Appendix X4. A curve plots the deduct value from 0 to 100 against the distress density in percent, on a logarithmic scale from 0.1 to 100. The curves for alligator cracking, block cracking and corrugation (Figures X3.1, X3.3 and X3.4) have one line for each severity level: low, medium and high. The bleeding curve (Figure X3.2) has one line.

On those four curves, a higher density gives a higher deduct value. At the same density, a higher severity gives a higher deduct value.

From deduct values to the PCI

The standard first checks how many deduct values are greater than 5.

• None or one above 5. Use the total deduct value as the maximum CDV.
• Two or more above 5. Find the maximum CDV with the iterative procedure below.

The iterative procedure (9.5 and 10.3) works like this:

1. Find HDV, the highest deduct value, and calculate m = 1 + (9 / 95) x (100 - HDV). The value of m is at most 10.
2. Keep the m largest deduct values. Multiply the last one by the fractional part of m.
3. Sum the deduct values, and count q, the number of values greater than 5.
4. Read the CDV from the correction curve for q and the sum.
5. Reduce the smallest deduct value that is greater than 5 to 5. Repeat steps 3 to 5 until q is 1.
6. The maximum CDV is the largest CDV from all the passes.

Then PCI = 100 - maximum CDV. The correction curves are Figure X3.19 for asphalt and Figure X4.16 for concrete.

A worked example for jointed concrete

The PCI page works an asphalt example. This one uses the concrete sample unit of ASTM D5340 Figures 7 and 8.

The highest deduct value is 32.0, so m = 1 + (9 / 95) x (100 - 32.0) = 7.44. The standard keeps the seven largest values and 0.44 of the eighth. The sheet lists 32.0, 12.0, 11.0, 10.0, 9.0, 8.0 and 6.0, and 1.3 for the last. The passes give these results:

The sum falls by the amount of each reduction, for example 89.3 - 1.0 = 88.3. The CDV does not fall with it. It drops to 57.0 at q = 3 and then rises to 63.3. The largest value is the maximum CDV, so the PCI of the sample unit is 100 - 63.3 = 36.7.

Deduct value, CDV and PCI

• Deduct value. One number for one distress type and severity at its density.
• Total deduct value. The sum of the deduct values that the procedure keeps.
• Corrected deduct value. The value that the correction curve gives for a total and a q.
• Maximum CDV. The largest CDV of all the passes. The PCI is 100 minus this value.

What a deduct value does not show

A deduct value comes from distress that the inspector sees on the surface. It does not come from a measurement of structure. This page follows the 1998 edition of ASTM D5340. The current edition is D5340-24, and its text was not read. Use the edition that the survey contract names.

Drones

A drone can capture the images from which an inspector records distress. TarmacView’s pavement condition assessment captures the pavement photos. Crack detection and the ASTM D5340 rating are in development, and it does not compute a PCI yet. The service is offered as early access.