从历史上看，种族隔离是在主观的基础上进行衡量的，国家检查员仅根据视觉信息进行判断。这是很困难的，因为，特别是在表面混合料上，离析问题可能在几个月内不会出现。目视观察只能识别表面偏析，而未检测到表面以下的偏析。本报告由美国国家公路与运输协会（AASHTO）和美国国家沥青路面协会（National沥青路面协会）联合出版，阐述了离析以及如何消除离析，以确保生产高质量的路面混合料。

Historically, segregation has been measured on a subjective basis with state inspectors¿ determination based on visual information only. This is difficult because, particularly on surface mix, problems due to segregation may not appear for several months. Visual observation can identify only surface segregation, leaving that below the surface undetected. This report, jointly published by AASHTO and the National Asphalt Pavement Association, addresses segregation and how it can be eliminated to ensure the production of high-quality paving mixtures.