Block Cracking

Block cracks are interconnected cracks that divide the pavement into approximately rectangular pieces. The blocks may range in size from approximately 1 by 1 ft (0.3 by 0.3 m) to 10 by 10 ft (3 by 3 m). Block cracking is mainly caused by shrinkage of the asphalt concrete and daily temperature cycling, and it is not load associated. The occurrence of block cracking usually indicates that the asphalt has hardened significantly. Block cracking normally occurs over a large portion of pavement area.

Severity Distress Example Description
Low Overview photo of a runway showing block cracking over a large area of the runway surface.            The block cracking is noticeable on the pavement as a pattern of rectangular pieces of pavement where the visible longitudinal and transverse cracks have defined the borders of the           pavement rectangles.  The majority of the cracks in the photo have been sealed. Blocks are defined by cracks that are non-spalled (sides of the crack are vertical) or lightly spalled, causing no foreign object damage (FOD) potential. Non-filled cracks have a 1/4 in (6 mm) or less mean width, and filled cracks have filler in satisfactory condition.
Medium Overview photo showing a pattern of unsealed block cracking.            In the photo, some individual cracks in the block cracking pattern are noticeably spalled. The blocks are defined by one of the following: (1) filled or non-filled cracks that are moderately spalled (some FOD potential); (2) non-filled cracks that are not spalled or have only minor spalling (some FOD potential), but have a mean width greater than 1/4 in (6 mm); (3) filled cracks with a mean width greater than 1/4 in (6 mm) that are not spalled or have only minor spalling (some FOD potential), but have filler in unsatisfactory condition.
High Photo showing a close-up of a wide and severely spalled crack in the asphalt surface. Blocks are well defined by cracks that are severely spalled, causing a definite FOD potential.