Rutting is a longitudinal surface depression in a wheel path and is a load-associated distress. Consolidation or lateral movement of the pavement materials due to traffic loads causes rutting. Contributing factors to the rutting can range from:

Rutting is rated by area and severity, with the area measured as a percent of the section’s total wheel path area. Severity of rutting is described in terms of depth:

At the network level, rutting is evaluated using the automated rut-measuring system on the profiler/rutbar vehicle. Project level surveys can also be conducted using the profiler/rutbar vehicle or manually using a 6.0-ft. straight edge and a steel ruler. Failure rutting (> 2.0 in.) must be measured using a 6.0-ft. straight edge. 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.

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 HMA 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 converted to the percentage of the rated lane's total surface area. 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 are localized areas of severe distress where the surface has been severely eroded, badly cracked (where blocks of surface material move about freely), severely faulted, depressed, or severely shoved. A group (3 or more) of small potholes 4-12 in. in diameter and deeper than 2 in., or a single pothole greater than 12 in. in diameter and deeper than 2 in., are classic examples of a failure, 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 have an 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 HMA density, surface HMA lift not bonded to underlying HMA, 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. Failed areas longer than 40 ft. are considered to be multiple failures.

Block cracking is a climate/materials related distress, where age-hardening of the asphalt coupled with 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 rendered in terms of total feet of full-lane width block cracking converted to 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.

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. Alligator cracks are formed whenever the pavement surface is repeatedly flexed under traffic loads. 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 for the current traffic loads (including thin HMA surfacings), surface layer delaminations, poor construction practices and/or weak materials. Total feet of alligator cracking is converted to 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 consists of cracks or breaks that run approximately parallel to the pavement centerline and may appear anywhere along a shoulder or driving lane. 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. Longitudinal cracking wider than 2.0 in. or faulted greater than 2.0 in. is rated as a failure. 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.

Longitudinal cracks may occur as a result of poorly constructed HMA mat joints, thermal shrinkage, inadequate support, or reflection from underlying layers. Differential movement beneath the surface is the primary cause of longitudinal cracking outside of the wheel path. Environmentally-induced longitudinal cracking may originate in desiccated subgrade soils (edge drying), embankment consolidation/slope failures, widening interfaces or active portland cement concrete (

PCC

) pavement joints reflecting to the surface. 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.

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 frequently associated with environmental surface shrinkage due to temperature cycling, or may result from differential movement beneath the pavement surface. Transverse cracking can deteriorate further under traffic effects and surface moisture infiltration. Movement beneath the pavement surface may be from natural shrinkage of chemically stabilized base and subbase materials, or reflection cracking from underlying PCC joints and active cracks. Material properties can also be a contributing factor, including asphalt cement (AC) binder aging, stiffness of the HMA, 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 is the progressive disintegration of the surface due to dislodgment of aggregate particles caused by weathering, traffic, or a combination of the two. In Texas, raveling is mainly associated with seal coats; however, it can occur in HMA 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 (or low seal shot rate/poor chip embedment), stripping of the binder, and HMA segregation/high air voids. Corrective action can include applying a fog seal (short term), seal coat, hot-in-place recycling, or thin overlay.

This distress is also known as bleeding and is described as the presence of excess asphalt on the pavement surface. The condition is generally more prevalent in the wheel paths and can be present in both HMA 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 length affected and by degree of severity (low, medium, high). Underlying causes can include high AC content (or seal shot rate too high in the wheel path), 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/use of variable transverse asphalt rates), cold milling with subsequent seal or thin overlay, a permeable friction course, or a thin overlay. Hydroblasting the wheel path using a specialized vacuum recovery vehicle has also been used with success for the removal of excess asphalt.