What is the primary cause of block cracking in asphalt pavements?

The primary cause of block cracking in asphalt pavements is the shrinkage of the asphalt surface due to temperature changes and asphalt binder aging. As asphalt ages, it becomes stiffer and less flexible, making it more susceptible to cracking. Temperature fluctuations cause the asphalt to expand and contract, and this repeated expansion and contraction can lead to the development of tensile stresses in the pavement. When these tensile stresses exceed the tensile strength of the asphalt, cracks begin to form. Block cracking is characterized by interconnected cracks that divide the pavement surface into approximately rectangular shapes. The cracks are typically shallow and do not extend through the entire asphalt layer. Block cracking is often associated with pavements that have a high asphalt content, a low void content, or a stiff asphalt binder. These factors can contribute to increased shrinkage and reduced flexibility, making the pavement more prone to block cracking. While block cracking may not always be a structural issue, it can allow water to enter the pavement structure, leading to further deterioration.