Blowup (Buckling)

Severe blowup

Severe blowup

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:

• Joint spalling (reduces slab contact area and provides incompressible material to fill the joint/crack)
• D cracking (weakens the slab near the joint/crack area)
• Freeze-thaw damage (weakens the slab near the joint/crack area)

Repair: Full-depth patch.
 

Corner Break

Corner break on a residential street

Corner break on a highway

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.

Repair: Full-depth patch.
 

Durability Cracking ("D" Cracking)

"D" cracking at panel corners

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 full-depth patch or partial-depth patch can repair the affected area, it does not address the root problem and will not, or course, prevent "D" cracking elsewhere.
 

Faulting

Faulting from ground level

Faulting in the truck lane

Up close near a bus stop

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).

Problem: Roughness

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 JPCP 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.
 

Joint Load Transfer System Deterioration

Exposed failure with rusted dowel bars

Patched failure

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:

• Corrosion.  If inadequately protected, dowel bars can corrode over time.  The corrosion products occupy volume, which creates tensile stresses around the dowel bars, and a severely corroded dowel bar is weaker and may fail after repeated loading.
• Misalignment.  Dowel bars inserted crooked or too close to the slab edge may create localized stresses high enough to break the slab.  Misalignment can occur during original construction or during dowel bar retrofits.

Repair: Removal and replacement of the affected joint load transfer system followed by a full-depth patch for affected area.
 

Linear (Panel) Cracking

Large panel crack

Panel cracks on a residential street

Panel cracking in the truck lane

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.

Patching

Patch on a residential street

Large utility patch

Patch with poor edges

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.

Problem: Roughness

Possible Causes:

• Previous localized pavement deterioration that has been removed and patched
• Utility cuts

Repair: Patches are themselves a repair action.  The only way they can be removed is through an overlay or slab replacement.
 

Polished Aggregate

Aggregate after almost 40 years of wear

A closer look

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.

Repair: Diamond grinding or overlay.
 

Popouts

Large popouts

Popout close-up

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:

• Poor aggregate freeze-thaw resistance
• Expansive aggregates
• Alkali-aggregate reactions

Repair: Isolated low severity popouts may not warrant repair.  Larger popouts or a group of popouts can generally be repaired with a partial-depth patch.
 

Pumping

Pumping in action

Pumping evidence during HVS test

Pumping damage

Broken slabs with pumping evidence

Pumping evidence during HVS test

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:

• Move about under the slab.

• Move from underneath one slab to underneath an adjacent slab.  This type of movement leads to faulting.

• Move out from underneath the slab to the pavement surface.  This results in a slow removal of base, subbase and/or subgrade material from underneath the slab resulting in decreased structural support.

Problem: Decreased structural support of the slab, which can lead to linear cracking, corner breaks and faulting.

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 increase load transfer across any significant transverse joints created by the repair.  Third, consideration should be given to stabilizing any slabs adjacent to the pumping area as significant amounts of their underlying base, subbase or subgrade may have been removed by the pumping.  Finally, the source of water or cause of poor drainage should be addressed.
 

Punchout

Severe punchout

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.

Repair: Full-depth patch.
 

Reactive Aggregate Distresses

Severe crazing

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.

Repair: Partial-depth patch for small areas of scaling or slab replacement for large areas of scaling.
 

Shrinkage Cracking

Shrinkage cracks on brand new slabs

Severe shrinkage cracking

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:

• Contraction joints sawed too late.  In JPCP, if contraction joints are sawed too late the PCC may already have cracked in an undesirable location.
• Poor reinforcing steel design.  In CRCP, proper reinforcing steel design should result in shrinkage cracks every 1.2 - 3 m (4 - 10 ft.).
• Improper curing technique.  If the slab surface is allowed to dry too quickly, it will shrink too quickly and crack.
• High early strength PCC.  In an effort to quickly open a newly constructed or rehabilitated section to traffic, high early-strength PCC may be used.  This type of PCC can have a high heat of hydration and shrinks more quickly and to a greater extent than typical PCC made from unmodified Type 1 portland cement.

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 replacement.
 

Spalling

Linear crack spalling

Spalling onset

Spalling from a bad construction joint

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):

• Excessive stresses at the joint/crack caused by infiltration of incompressible materials and subsequent expansion (can also cause blowups).
• Disintegration of the PCC from freeze-thaw action or "D" cracking.
• Weak PCC at a joint caused by inadequate consolidation during construction.  This can sometimes occur at a construction joint if (1) low quality PCC is used to fill in the last bit of slab volume or (2) dowels are improperly inserted. 
• Misalignment or corroded dowel.
• Heavy traffic loading.

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.