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Section 2: Visual Pavement Condition Surveys

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Overview

This section will review condition categories currently evaluated in visual condition surveys by pavement type. For consistent and reliable survey results, it is important to decrease subjectivity and variability in the identification of distresses typically found on flexible and rigid pavements, and provide instructions in recording these observations in an “orderly and consistent manner.” To this end, certification training for visual (human) raters is conducted annually in regional sessions.

The designer/planner is interested in the type, extent, and severity of visible distress or corrective action taken on previous distress (such as number of patches or length of sealed cracks). Depending upon the type of distress, occurrences are recorded in terms of percent area, linear feet per 100-ft. station, number per station, or number per section.

  • For network level evaluation, these statistics are typically captured for each 0.1 mi. section and further summarized by 0.5 mi. section when entered into the Pavement Management Information System (PMIS) database.
  • For project level evaluation, condition statistics may be summarized over the length of the project or in any other fashion amenable to the district planner/designer. Project level surveys are often conducted on foot in order to map the type and extent of distresses in detail. The root causes of these distresses must be addressed in any comprehensive rehabilitation strategy.

For more information on identification and cataloging of visual distress, refer to the PMIS Rater’s Manual or contact the Research & Technology Implementation Office (RTI) at (512) 465-7555 for a copy of the pavement rehabilitation CDs which discuss typical pavement distresses, their causes, and actions required to remedy.

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Flexible Pavement Visual Survey Condition Categories

Rutting (Shallow, Deep, and Severe)

Rutting is a surface depression in a wheel path and is a load-associated distress. Contributing factors to the rutting can range from:

  • insufficient structure for the traffic loading (compressive shear failure in the subgrade or unbound base)
  • unstable mixes due to uncontrolled asphalt cement content that may cause shoving and displacement of hot mix asphaltic concrete (HMAC)
  • moisture sensitive materials (including stripped HMAC in non-surface mixes)
  • post-construction consolidation of HMAC under traffic loads (air void content too high) or
  • temperature-sensitive HMAC mixtures and inappropriate HMAC mix selection for the nature of the traffic loading.

Rutting is rated by area and severity, with the area measured as a percent of the section’s total wheel path area. The severity categories are:

  • Shallow, 0.25-0.49 in.
  • Deep, 0.50-0.99 in.
  • Severe, 1.00-1.99 in.

Rutting 2.0 in. or greater is counted as a failure. At the network or project level, rutting is generally measured using an automated rut bar. It can also be measured manually using a 6.0-ft. straight edge and a steel ruler. If the length of the straight edge is such that the entire width of the rut is not spanned, the resulting depth measurement will not represent the maximum rut depth.

Strategies to correct rutting must account for the origin of the rutting, with special attention to the pavement structure. For example, a thin overlay on top of a rut-susceptible or stripped mix would not be a suitable remedy because rutting would likely return in a relatively short period of time.

Patching

Patches are repairs made to previous distress, indicating prior maintenance activity. If done properly, patches can improve the long-term performance of the structure.

Proper patching should always involve saw-cut edges parallel or perpendicular to the direction of traffic, with excavation to the full depth of the weak material. Replacement material must be properly compacted with tacking of all cut HMAC surfaces to improve impermeability. Provided the patch addressed the full depth of the previous distress/weakness, the life of the patch and the surrounding patch/pavement interface will be extended by placing a full lane width seal or overlay. At the network level, this condition is evaluated in terms of feet of full lane-width patching. Improper patching can introduce a degree of roughness, further deterioration at the edges of the patch, or even failure of the patch itself if the underlying problem was not addressed.

Failures

Failures are localized areas of severe distress including erosion of the surface, cracking where blocks of surface material move about freely, or depressions. The pothole is the classic example, but failures can cover much larger areas than the typical pothole. One example of this is edge failure, where the surface has disintegrated perhaps due to heavy wheel loads encroaching on the paved edge where there is a lack of lateral support deeper in the structure. These distresses may pose a safety hazard and are at increased priority for at least temporary repair measures until a long-term fix can be completed.

Failures are typically a load-associated distress, but are often related to poor construction or moisture-susceptible materials (poor in-place HMAC density, surface HMAC lift not bonded to underlying HMAC, moisture-susceptible base). Even for a light rehabilitation strategy, these distresses must be patched prior to resurfacing. At the network level, this condition is evaluated in terms of number per 0.5-mi. section.

Block Cracking

Block cracking is a climate/materials related distress, where shrinkage of the bituminous surface or underlying stabilized base causes interconnected cracks that divide the surface into irregular pieces. The cracking pattern is much larger than alligator cracking, with blocks ranging from 1 ft. to 10 ft. on edge, and is not limited to the wheel paths. Rating is generally in terms of a percentage of the lane’s total surface area. This distress is not a structural problem until the effects of traffic and the environment further weaken the pavement by allowing moisture infiltration and raveling/spalling of the crack edges.

Addressing this distress as part of a rehabilitation strategy may be as simple as sealing the cracks prior to placing a surface treatment. Additional considerations will be necessary where the extent of the cracking is severe or where cracks continue to be active during cyclic seasonal temperature changes.

Alligator Cracking

This distress is also known as fatigue cracking and is a traffic loading related distress that is initiated in the wheel paths. Alligator cracking consists of interconnected cracks that form small irregularly-shaped blocks (less than 1 ft. on edge) resembling patterns found on an alligator’s skin. Where the appearance of this distress occurs relatively early in the pavement’s performance period, its occurrence can also be linked to inadequate structural thickness (including thin HMAC surfacings), surface layer delaminations, construction practices and/or weak materials. Rating is expressed as a percentage of the total wheel path area for the rated lane.

A minimal rehabilitation strategy should include removal of the affected material and proper patching before placing a new surface. Attempting to seal or place an overlay over these cracks without proper patching will result in rapid reappearance of the distress.

Longitudinal Cracking

These cracks or discontinuities may appear anywhere along a shoulder or driving lane and run roughly parallel to the pavement centerline. For purposes of rating, the cracks must be at least 1/8-in. wide, show evidence of spalling or pumping, or have been previously sealed. Measurement is in terms of linear feet per 100-ft. station. Depending on the relative transverse placement in the lane, this distress may be either load associated (a precursor of alligator cracking in the wheel path) or environmentally associated.

Environmentally-induced longitudinal cracking may be the result of desiccated subgrade soils (edge drying) that causes cracks that reflect up through the pavement structure, widening Portland cement concrete ( PCC) pavement joints reflecting to the surface, or poorly constructed longitudinal mat joints (with high permeability). How active these cracks are and their origin must be considered in any rehabilitation strategy. Crack activity can be observed by selecting a few representative cracked locations, and measuring the crack width during different seasons. The range of crack width can also be found by taking measurements following known wet and dry periods.

Transverse Cracking

These cracks or discontinuities travel at right angles to the pavement centerline. Minimum eligibility for rating criteria are as defined for longitudinal cracking. Measurement is in terms of number of transverse cracks per 100-ft. station, where cracks that do not extend across the full lane width are counted as a fractional (partial) crack.

Transverse cracking is almost always an environmental associated distress that can deteriorate further under traffic effects and surface moisture infiltration. This cracking generally results from natural shrinkage of chemically stabilized base and subbase materials, thermal cycling of the bituminous/HMAC surfaces, or reflection cracking from underlying PCC joints and active cracks. Material properties can also be a contributing factor, including asphalt concrete (AC) binder aging, stiffness of the HMAC, or percent stabilization used in the lower layers. The activity of the cracks and their origin must be considered in choosing a rehabilitation strategy.

Raveling

Raveling is the progressive loss of surface aggregates caused by weathering, traffic, or a combination of the two. In Texas, raveling is mainly associated with seal coats; however, it can occur in HMAC as well. Measurement is in terms of percent of the total lane area, and by degree of severity (low, medium, high). Contributing causes can be linked to excessive AC binder oxidation, low AC binder content, stripping of the binder, and HMAC segregation/high air voids. Corrective action can include applying a fog seal (short term), seal coat, hot-in-place recycling or conventional thin overlay.

Flushing

This distress is also known as bleeding and is described as the presence of excess asphalt on the surface of the pavement. The condition is generally more prevalent in the wheel paths and can be present in both HMAC and seal coat surfaces. Flushing can reduce surface friction and may contribute to a traffic safety hazard. Measurement is in terms of percent of the lane’s total wheel path affected and by degree of severity (low, medium, high). Underlying causes can include high asphalt cement content, excessive densification (low air voids) of the surface mix, temperature susceptibility of the AC binder, soft AC binder, excessive tack, or even migration of AC binder from mixes in lower layers that are moisture susceptible. Corrective actions can include application of microsurfacing, a conventional seal coat (using stringent field control to monitor the asphalt application rate), cold milling with subsequent seal or thin overlay, a permeable friction course, or a conventional thin overlay.

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Rigid Pavement Visual Survey Condition Categories

Spalled Cracks

This distress is the loss of material at the edges of cracks in concrete pavement. In the TxDOT PMIS database, this term is applied to continuously reinforced concrete pavement (CRCP). When occurring in jointed concrete pavement (concrete pavement, contraction design [CPCD]), this distress is known as failed joints and cracks since it may occur at either an intentional joint or shrinkage crack (includes asphalt-patched spalls).

Rating is by number of cracks that show spalling at least 1-in. wide covering more than 1 ft. of the crack length. Spalling on CRCP longitudinal cracks is considered a rarity and is not rated. A spalled longitudinal crack on a CPCD slab is rated as one longitudinal crack if it travels from one transverse joint to the next transverse joint or from a transverse joint to an edge joint and measures more than half the slab length.

Crack spalling is due to excessive local pressure at the joint. This pressure may be due to a combination of traffic action, thermal expansion, and/or steel corrosion. The occurrence may be exacerbated by over-finishing/ excessive consolidation, where excessive surface paste exists, or improper curing.

If cracks become wide enough to allow the introduction of incompressible materials, subsequent expansion by the slab in warmer weather will cause stress concentrations where these materials are found, resulting in spalling. Also, in areas subject to freeze-cycles, water entering the crack may saturate the concrete around the crack. Freezing temperatures may result in freezing and thawing damage, such as spalling, around the crack. Excessive deflection at the crack from traffic loading may also result in spalling. Finally, if the slab is faulted at the crack, the spalling may be a result of traffic striking the raised edge of the slab.

As a minimum, corrective action will almost always involve cleaning and sealing cracks/joints, but may also include sawing stress relief joints, slab-jacking, patching using bituminous or polymer patching materials, or a thin bonded Portland cement concrete (PCC) or hot mix asphalt concrete (HMAC) overlay.

Punchouts

A punchout is a full-depth block of pavement, formed at the pavement edge, when one short longitudinal crack forms between two existing transverse cracks. The existing cracks are closely spaced, usually less than 4 ft. apart. The punchout is often rectangular, but some may appear in other shapes. Punchouts are most common in continuously reinforced concrete pavements. Where punchouts occur in CPCD pavements, the distress is recorded as a failure. The boundary of the punchout will be severely spalled or faulted.

Formation is usually related to surface moisture infiltrating into the base through the closely spaced transverse cracks and the adjacent longitudinal joint, followed by erosion/pumping of the base and cantilevering of the small slab. Heavy load applications will connect the transverse cracks with a short longitudinal crack. The punchout progresses with spalling of the cracks, possible rupturing of the reinforcing steel, and eventually settlement of the punchout below the original surface of the pavement. In some cases the punchout may become dislodged and present a traffic hazard.

Incorporating a non-erodible base and tied concrete shoulders has been the preferred preventative design strategy. Full-depth PCC patching is generally the preferred method of repair, although asphalt concrete (AC) patches may be used temporarily to address safety issues. Rating is in terms of number of occurrences per mile.

Asphalt Patches

In rigid pavements, full-depth repairs to localized distress are often made using asphalt concrete as an expeditious, temporary fix. As with patching in a flexible pavement, proper patching should always involve saw-cut edges parallel or perpendicular to the direction of traffic, with excavation to the full depth of the slab. Patches should be maintained until such time that a full-depth PCC patch can be placed. Where base erosion was a contributing cause of the original failure, permanent repair measures must address the viability of support under the patch.

Asphalt patches are rated in terms of total number observed, with patches longer than 10 ft. counting as two patches. In the PMIS system, asphalt patches are a rated category for CRCP pavements only; when these patches occur in a CPCD pavement they are rated as a failure. Proper patch construction is discussed in Chapter 10, “Rigid Pavement Rehabilitation.”.

Concrete Patches

Concrete patches are intended as “permanent” repairs of localized distress and as such should be properly tied in to the existing structure to insure load transfer and longevity. An area sufficiently large enough to include the entire distress-affected area must be removed, leaving clean, square edges prior to patching. Failure to do this will often result in propagation of distress immediately adjacent to the patch.

Current TxDOT standards require patches to be full-depth, full-lane width, and a minimum of 6 ft. in the direction of travel. Patches placed at joints require a minimum of 38 in. on either side of the joint. Concrete patches are evaluated in terms of total number observed. Proper patch construction is discussed in Chapter 10, “Rigid Pavement Rehabilitation.”

Average Crack Spacing

This evaluation is made on CRCP pavements and is used as a method to obtain the percentage of transverse cracks that are spalled, and to determine whether the slab is behaving as designed. Very small crack spacing (<2.0 ft.) may be a precursor to punchouts, whereas large crack spacing (>10.0 ft.) may mean wider crack widths that allow non-compressibles in and may have poor load transfer. A recommended technique to evaluate this condition is to count the total number of transverse cracks in two 200-ft. sections (beginning and end of a typical 0.5-mi. section), and then average the results.

Failures

This is a CPCD condition category. Failures are localized areas where traffic loads do not appear to be transferred across joints or cracks. Failures are typically areas of surface distortion or disintegration.

Failures are evaluated in terms of total number observed and include the following distresses: corner breaks, punchouts (previously discussed), asphalt patches (previously discussed), concrete patches (previously discussed), severe faulting, D-cracking, spalls (asphalt filled or not – previously discussed), and popouts (>12 in. wide or long, >3 in. deep).

  • A corner break is a crack (which may or may not be spalled or faulted) that travels from a joint to a slab edge. To be rated as a failure, the crack must intersect between 1 ft. and half way across each edge. Concrete patches that are spalled and/or faulted around all edges are rated as failures, not as patches.
  • Failed concrete patches are simply patches where severe distress has reappeared following the patch repair.
  • Faulting means that one edge of the pavement on one side of a crack is at least 1/4-in. higher than on the other side. Severe faulting is defined as an elevation difference greater than 2 in.
  • D-cracking is a series of closely-spaced cracks that curve around a slab corner. They are concave away from the slab corner and concentric toward the center of the slab. The cracking will parallel the transverse joint and curve around to parallel the longitudinal joint. As D-cracking progresses, the cracks radiate outward from the intersection of the joints.

D-cracking is believed to be an environmentally induced distress. As water permeates through the slab, the bottom of the slab tends to be saturated. Freezing and thawing cycles will deteriorate the saturated aggregate near the bottom of the slab. The deterioration starts at the bottom of the slab and eventually progresses to the surface of the pavement.

  • A popout is an aggregate or piece of pavement missing; forming a hole in the surface of concrete pavement. It can be round or oblong in shape. A weakened plane exists at the depth of the popout which may be the result of improper curing. Popouts usually occur with absorptive aggregates subjected to freeze-thaw temperature cycles.

Shattered Slabs

This is a CPCD condition category. Shattered slabs are formed when a series of cracks intersect to divide the slab into four or more pieces. Although the pieces still remain in their original position, they may settle below the original elevation of the pavement. Also, the intersecting cracks can be accompanied by severe spalling. The slab is so badly cracked that it warrants complete replacement. When five or more failures exist on a single slab, or one or more failures encompass more than half the slab’s area, the slab is rated as a shattered slab.

Slab shattering is primarily due to a lack of subgrade support. The base materials may settle, contain voids, or may be susceptible to erosion, resulting in loss of support. Overloading the concrete slab will create excessive bending stresses where the slab has no support. The result is severe cracking, possible spalling, and settlement. Current TxDOT policy requires a non-erodible base beneath all rigid pavements.

Slabs with Longitudinal Cracks

This is a CPCD condition category. Longitudinal cracks are cracks that follow a course approximately parallel to the centerline of the pavement. These cracks are generally straight but they may curve slightly back and forth across the length of the pavement. Slabs with cracks that are over half the slab in length and show severe spalling or are faulted, are counted regardless of the number of such cracks in the slab.

Causes of longitudinal cracking can be related to environmental conditions or improper construction. One possible cause of such cracks is that the joints were not sawed quickly enough during construction (ideally, such joints should be sawed as soon as the concrete can support the sawing equipment). If the slab is too wide or longitudinal joints were not cut deep enough (refer to “Joints” in Chapter 9) plastic shrinkage and lateral thermal contraction can cause a longitudinal crack to appear. Also, swelling soils or loss of foundation support may cause excessive bending stresses in the slab. Finally, warping and curling stresses may be sufficient to initiate longitudinal cracking.

Working cracks (cracks that open and close due to temperature variations and/or traffic loading) are a structural concern – the origin must be addressed to allow for proper remedy.

Apparent Joint Spacing

This is a CPCD condition category. Some transverse cracks may become so wide that they look and act like joints. The crack must be greater than 0.5 in. wide across the complete width of the lane. These ‘apparent’ joints are important to monitor because they do not have load transfer capability outside of frictional contact and potentially become additional traps for incompressible debris that can cause further damage to the slab. At the network level, the minimum value recordable in the PMIS database is 15.0-ft. Rating should be accomplished by evaluating a 200-ft. section at the beginning and end of each 0.5-mi. section and averaging the results.

Apparent joints may form for a number of reasons ranging from excessive loading to poor construction practices to environmental reasons. Construction practice shortcomings can include improperly sawn joints, poor dowel bar alignment, poor paste bond on dirty aggregates, and poor curing practices. Environmental contributors include swelling soils, loss of foundation support, and warping and curling stresses.


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