10 BLOCK CRACKING Block cracking is a type of asphalt pavement damage that appears as a network of large, rectangular or square-shaped cracks. Block cracking is caused by shrinkage of the asphalt and its inability to resist thermal expansion and contraction without cracking. It may be related to: • Loss of volatile compounds in the binder over time. • The binder grade used in the asphalt mix design may not have been appropriate for temperature variations in the environment. • An error in design or batching the asphalt may have resulted in not having enough binder for the aggregate used. To prevent block cracking, you can: • Follow design and construction best practices. • Maintain a surface treatment on the asphalt to preserve its flexibility. Tips on responding to block cracking: • If the cracks are working cracks (defined by thermal expansion/contraction of more than 0.1”), consider routing the cracks before sealing them to allow for better adhesion of the sealer material. • Fill cracks soon after they appear to prevent the intrusion of water under the asphalt. • Milling the upper portion of the asphalt (which will have lost much of its volatile binder compounds) prior to placement of a new HMA layer can improve performance.
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