Pavement Management
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Flexible Pavement Distress

An introduction to common forms of distress in flexible pavements.

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De-Bonding of HMA Pavements/Layer Bonding

Major Themes From Past Tack Coat Studies This section attempts to identify some of the emerging themes associated with tack coats based on a qualitative meta-analysis of past research. Ideas that are corroborated amongst multiple studies are briefly discussed under individual headings while ideas emerging from single studies that have yet to be corroborated by … Read more »

BST bleeding in the wheelpaths

Bleeding

Description A film of asphalt binder on the pavement surface. It usually creates a shiny, glass-like reflecting surface (as in the first photo) that can become quite sticky. Sometimes referred to as “flushing”. Problem Loss of skid resistance when wet Possible Causes Bleeding occurs when asphalt binder fills the aggregate voids during hot weather and then expands … Read more »

Polished PCC aggregate after 40 years of wear.

Polished Aggregate

Description Areas of pavement (either PCC or HMA) where the portion of aggregate extending above the asphalt binder (in the case of HMA) or cement paste (in the case of PCC) is either very small or there are no rough or angular aggregate particles. Problem Decreased skid resistance Possible Causes Repeated traffic applications. Generally, as … Read more »

Block cracking on a low volume pavement

Block Cracking

Description Interconnected cracks that divide the pavement up into rectangular pieces. Blocks range in size from approximately 0.1 m2 (1 ft2) to 9 m2 (100 ft2). Larger blocks are generally classified as longitudinal and transverse cracking. Block cracking normally occurs over a large portion of pavement area but sometimes will occur only in non-traffic areas. … Read more »

Raveling due to low density.

Raveling

Description The progressive disintegration of an HMA layer from the surface downward as a result of the dislodgement of aggregate particles.   Problem Loose debris on the pavement, roughness, water collecting in the raveled locations resulting in vehicle hydroplaning, loss of skid resistance Possible Causes Several including: Loss of bond between aggregate particles and the … Read more »

Depression in a parking lot.

Depression

Description Localized pavement surface areas with slightly lower elevations than the surrounding pavement. Depressions are very noticeable after a rain when they fill with water. Problem Roughness, depressions filled with substantial water can cause vehicle hydroplaning Possible Causes Frost heave or subgrade settlement resulting from inadequate compaction during construction. Repair By definition, depressions are small … Read more »

Severely fatigued cracked pavement

Fatigue Cracking

Description Series of interconnected cracks caused by fatigue failure of the HMA surface (or stabilized base) under repeated traffic loading. In thin pavements, cracking initiates at the bottom of the HMA layer where the tensile stress is the highest then propagates to the surface as one or more longitudinal cracks. This is commonly referred to … Read more »

Open texture visible after rain

Non-Uniform Texture

Description Differences in appearance within the mat surface. Extreme differences in mat surface appearance often take on the look of tearing or streaking and should be investigated as such. Typically, mat areas that look rougher and more coarse than other areas are of the greatest concern. HMA mixtures with larger nominal maximum aggregate sizes will … Read more »

Mat-wide streaks

Mat Tearing

Description Mat tearing, or streaks in the mat, can be caused by different phenomena: Parts of the mat surface are dragged along by the screed. Under normal operation, the screed passes cleanly over the mat, however, if the screed is applying excess downward force or the mat is too thin for the given nominal maximum … Read more »

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Mat Shoving

Description Displacement of the HMA mixture in a longitudinal direction while compacting. Shoving under traffic loading is covered in a seperate article. Problem Mats that shove under compaction loading are generally unstable and are likely to continue to deform under traffic loading leading to roughness problems. If a mat is not adequately compacted because it … Read more »

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