Deterioration in Flexible Pavement

15 This manual is prepared to assist user of the Pavement Management System PMS in identifying surface distress in a uniform and repeatable manner. The distresses included in this manual are used to calculate the Pavement Condition Index PCI for pavements surfaced with asphalt concrete and surface treatments. This part contains general descriptions of the major types of distress that may be encountered in both flexible asphalt concrete and rigid pavements. Also noted is a typical description of three distress severity levels associated with each distress. A pavement moisture accelerated distress identification system. These descriptions are provided as a guide to user agencies only and should not be viewed as a standard method for distress type severity identification. This information, along with an estimate of the amount of each distress severity combination, represents an example of the minimum information needs required for a thorough condition distress surveyAASHTO, 1993.

2.3 Pavement Distress

Pavement distresses are those defects visible on the pavement surface. They are symptoms, indicating some problem or phenomenon of pavement deterioration such as cracks, patches and ruts. The type and severity of distress a pavement has can provide great insight into what its future maintenance andor rehabilitation needs will be. The distress is generally described in terms of severity, extent and distress type. However, the distress identification and measurement procedures may slightly vary from agency to agency Luo,2005. Defects in the asphalt pavement can be classified groups on the basis of appearance as follows David, 2006:

2.3.1 Cracks

2.3.1.1 Alligator or Fatigue Cracking a.

Description Alligator cracking is a series of interconnecting cracks caused by fatigue failure of the asphalt concrete surface under repeated traffic loading .cracking begins at the bottom of the asphalt surface or stabilized 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