This section is a summary of the major flexible pavement distresses. 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. For larger views of the pictures, click on the thumbnails.
|Index of Pavement Distresses Shown on this Page|
Description: A localized upward slab movement and shattering at a joint or crack. Usually occurs in spring or summer and is the result of insufficient room for slab expansion during hot weather.
Problem: Roughness, moisture infiltration, in extreme cases (as in the second photo) can pose a safety hazard
Possible Causes: During cold periods (e.g., winter) PCC slabs contract leaving wider joint openings. If these openings become filled with incompressible material (such as rocks or soil), subsequent PCC slab expansion during hot periods (e.g., spring, summer) may cause high compressive stresses. If these stresses are great enough, the slabs may buckle and shatter to relieve the stresses. Blowup can be accelerated by:
Description: A crack that intersects the PCC slab joints near the corner. "Near the corner" is typically defined as within about 2 m (6 ft) or so. A corner break extends through the entire slab and is caused by high corner stresses.
Problem: Roughness, moisture infiltration, severe corner breaks will fault, spall and disintegrate
Possible Causes: Severe corner stresses caused by load repetitions combined with a loss of support, poor load transfer across the joint, curling stresses and warping stresses.
Description: Series of closely spaced, crescent-shaped cracks near a joint, corner or crack. It is caused by freeze-thaw expansion of the large aggregate within the PCC slab. Durability cracking is a general PCC distress and is not unique to pavement PCC.
Problem: Some roughness, leads to spalling and eventual slab disintegration
Possible Causes: Freeze-thaw susceptible aggregate.
Repair: "D" cracking is indicative of a
general aggregate freeze-thaw problem. Although a
partial-depth patch can repair the affected area, it does not address
the root problem and will not, or course, prevent "D" cracking elsewhere.
Description: A difference in elevation across a joint or crack usually associated with undoweled JPCP. Usually the approach slab is higher than the leave slab due to pumping, the most common faulting mechanism. Faulting is noticeable when the average faulting in the pavement section reaches about 2.5 mm (0.1 inch). When the average faulting reaches 4 mm (0.15 in), diamond grinding or other rehabilitation measures should be considered (Rao et al., 1999).
Possible Causes: Most commonly, faulting is a result of slab pumping. Faulting can also be caused by slab settlement, curling and warping.
Repair: Faulting heights of less than 3
mm (0.125 inch) need not be repaired. Faulting in an undoweled
between 3 mm (0.125 inch) and 12.5 mm (0.5 inch) is a candidate for a dowel
bar retrofit. Faulting in excess of 12.5 mm (0.5 inches) generally
warrants total reconstruction.
Description: Transverse crack or corner break developed as a result of joint dowels.
Problem: Indicator of a failed load transfer system, roughness
Possible Causes: Load transfer dowel bars can fail for two principal reasons:
Repair: Removal and replacement of the
affected joint load transfer system followed by a
patch for affected area.
Description: Linear cracks not associated with corner breaks or blowups that extend across the entire slab. Typically, these cracks divide an individual slab into two to four pieces.
Problem: Roughness, allows moisture infiltration leading to erosion of base/subbase support, cracks will eventually spall and disintegrate if not sealed
Possible Causes: Usually a combination of traffic loading, thermal gradient curling, moisture stresses and loss of support.
Repair: Slabs with a single, narrow linear crack may be repaired by crack sealing. More than one linear crack generally warrants a full-depth patch.
Description: An area of pavement that has been replaced with new material to repair the existing pavement. A patch is considered a defect no matter how well it performs.
Description: Areas of PCC pavement where the portion of aggregate on the surface contains few rough or angular aggregate particles.
Problem: Decreased skid resistance
Possible Causes: Repeated traffic applications. Generally, as a pavement ages the protruding rough, angular particles become polished. This can occur quicker if the aggregate is susceptible to abrasion or subject to excessive studded tire wear.
Description: Small pieces of PCC that break loose from the surface leaving small divots or pock marks. Popouts range from 25 - 100 mm (1 - 4 inches) in diameter and from 25 - 50 mm (1 - 2 inches) deep.
Problem: Roughness, usually an indicator of poor material
Possible Causes: Popouts usually occur as a result of poor aggregate durability. Poor durability can be a result of a number of items such as:
Repair: Isolated low severity popouts may
not warrant repair. Larger popouts or a group of popouts can generally
be repaired with a
Description: Movement of material underneath the slab or ejection of material from underneath the slab as a result of water pressure. Water accumulated underneath a PCC slab will pressurize when the slab deflects under load. This pressurized water can do one of the following:
Possible Causes: Water accumulation underneath the slab. This can be caused by such things as: a high water table, poor drainage, and panel cracks or poor joint seals that allow water to infiltrate the underlying material.
Repair: First, the pumping area should be
repaired with a full depth patch to remove any deteriorated slab areas.
Second, consideration should be given to using
dowel bars to
transfer across any significant
created by the repair. Third, consideration should be given to
stabilizing any slabs adjacent to the pumping area as significant
amounts of their underlying
subgrade may have been
removed by the pumping. Finally, the source of water or cause of poor
drainage should be addressed.
Description: Localized slab portion broken into several pieces. Typically a concern only with CRCP.
Problem: Roughness, allows moisture infiltration leading to erosion of base/subbase support, cracks will spall and disintegrate.
Possible Causes: Can indicate a localized construction defect such as inadequate consolidation. In CRCP, it can be caused by steel corrosion, inadequate amount of steel, excessively wide shrinkage cracks or excessively close shrinkage cracks.
Description: Pattern or map cracking (crazing) on the PCC slab surface caused by reactive aggregates. Reactive aggregates are those that either expand or develop expansive by products when introduced to certain chemical compounds.
Problem: Roughness, an indication of poor aggregate - will eventually lead to PCC slab disintegration.
Possible Causes: This type of distress is indicative of poor aggregate qualities. Most commonly, it is a result of an alkali-aggregate reaction.
Partial-depth patch for small areas of scaling or slab replacement for
large areas of scaling.
Description: Hairline cracks formed during PCC setting and curing that are not located at joints. Usually, they do not extend through the entire depth of the slab. Shrinkage cracks are considered a distress if they occur in an uncontrolled manner (e.g., at locations outside of contraction joints in JPCP or too close together in CRCP).
Problem: Aesthetics, indication of uncontrolled slab shrinkage. In JPCP they will eventually widen and allow moisture infiltration. In CRCP, if they are allowed to get much wider than about 0.5 mm (0.02 inches) they can allow moisture infiltration (CRSI, 1996).
Possible Causes: All PCC will shrink as it sets and cures, therefore shrinkage cracks are expected in rigid pavement and provisions for their control are made. However, uncontrolled shrinkage cracking can indicate:
Repair: In mild to moderate severity
situations, the shrinkage cracks can be sealed and the slab should perform
adequately. In severe situations, the entire slab may need
Description: Cracking, breaking or chipping of joint/crack edges. Usually occurs within about 0.6 m (2 ft.) of joint/crack edge.
Problem: Loose debris on the pavement, roughness, generally an indicator of advanced joint/crack deterioration
Possible Causes: Possible causes are (AASHTO, 1993):
Repair: Spalling less than 75 mm (3 inches) from the crack face can generally be repaired with a partial-depth patch. Spalling greater than about 75 mm (3 inches) from the crack face may indicated possible spalling at the joint bottom and should be repaired with a full-depth patch.