9.3 Pavement Evaluation - Surface Distress

3 Surface Distress

	Major Topics on this Page
	3.1	Measurement
	3.2	Measurement Techniques

Surface distress is "Any indication of poor or unfavorable pavement performance or signs of impending failure; any unsatisfactory performance of a pavement short of failure" (Highway Research Board, 1970). Surface distress modes can be broadly classified into the following three groups:

Fracture. This could be in the form of cracking (in flexible and rigid pavements) or spalling resulting from such things as excessive loading, fatigue, thermal changes, moisture damage, slippage or contraction.
Distortion. This is in the form of deformation (e.g., rutting, corrugation and shoving), which can result from such things as excessive loading, creep, densification, consolidation, swelling, or frost action.
Disintegration. This is in the form of stripping. raveling or spalling, which can result from such things as loss of bonding, chemical reactivity, traffic abrasion, aggregate degradation, poor consolidation/compaction or binder aging.

Thus, surface distress will be somewhat related to roughness (the more cracks, distortion and disintegration - the rougher the pavement will be) as well as structural integrity (surface distress can be a sign of impending or current structural problems).

Pavement Distress Photo Gallery

An extensive pavement distress photo gallery can be found in:

These galleries include all the major types of pavement damage/distress. Each distress discussion includes (1) pictures if available, (2) a description of the distress, (3) why the distress is a problem and (4) typical causes of the distress. The gallery is organized alphabetically and the pictures are not included in the Module list of figures.

3.1 Measurement

Measures of distress can be either subjective or objective. A simple example of a subjective measurement may be a rating of high, medium, or low based on a brief visual inspection. Objective measurements, which are generally more expensive to obtain, use different types of automated distress detection equipment.

3.2 Measurement Techniques

Measurement techniques are mostly visual. Older techniques, used teams of individuals who drove across every mile of pavement to be measured. Speeds were usually quite slow (on the order of 16 km/hr (10 mph)) and measurement was done visually. More current methods record pavement surface video images at highway speed using a specially equipped van (see Figures 9.8 and 9.9) that is outfitted with high resolution cameras. Evaluation is either done manually by playing the video back on specially designed workstations (see Figure 9.10) while trained crews rate the recorded road surface (see Figure 9.11) or automatically by computer software (see Figure 9.12). Advantages of these more current methods are (Sivaneswaran and Pierce, 2001):

Safety. Data are collected at highway speed, eliminating the need for driving at slow speeds or on the shoulder.
Accurate and complete distress data. Each distress along with its extent, severity and location is identified and stored in a database. The system is also less prone to rating errors.
More effective quality control. A centralized evaluation location and less subjective data make quality control much better.
More efficient data collection. Surface distress, rut and roughness data are all collected at the same time using the same data collecting vehicle.
Video and digital images are available for other users. They are available to bridge and maintenance personnel and can be made available on the Internet in the future.


Figure 9.8: Washington State DOT Pavement Condition Rating Van	Figure 9.9: Inside a Pavement Condition Rating Van


Figure 9.10: Pavement Condition Rating Video Images	Figure 9.11: Pavement Condition Rating Station

Figure 9.12: Screen Shot from a Computer-Based Automatic Crack Detection System
(Image from Roadware's WiseCrax System)

Integrated analysis units can collect pavement surface distress data in the previously described manner as well as collect data on a variety of other characteristics at highway speeds such as:

Transverse profile/rutting
Grade, cross-slope
Pavement texture
GPS coordinates

Panoramic right-of-way video
Pavement video
Feature location

WSDOT Surface Distress Measurement Method

Visual Method - Old
WSDOT used a visual method from 1969 to 1998 consisting of four 2-person teams that drove at 16 km/hr (10 mph) over the entire State road system (over 8,000 miles) every year and visually rated surface distress (Sivaneswaran and Pierce, 2001).

High-Speed Video Imaging
In 1999, WSDOT purchased a data distress collection van that records pavement profile (ride, faulting, and rutting) and video images of the pavement surface, ahead view, and shoulder view. Now, video images of pavement surface are recorded at highway speed using a specially equipped van that uses two high resolution cameras each covering about 2 m (6 ft.) in road width. Digital images are collected at 2 m (6 ft.) intervals along the road and front and right shoulder views are also recorded. Trained crews then rate these images by playing them back on specially designed workstations.