Forensic Analysis of Premature Surface Cracking in Full-Depth Asphalt Pavements on Plastic Clays

Premature cracking in new asphalt pavements before the pavements are opened to public traffic, before the development of the sites is completed, and before surrounding buildings are occupied is the focus of this paper. Previous studies have been conducted at individual sites to determine the cause of this phenomenon and have resulted in a variety of probable, but not conclusive, causes. This paper describes a forensic analysis that used interviews with principals experienced with this form of distress and the results of field and laboratory tests intended to expose commonality by soil type, pavement materials properties, construction sequence, and pavement design among several sites where cracking occurred and where cracking was not present. Six factors that were common at each site with cracking were detected: all cracks began at the surface of the pavement and propagated downward; the moisture contents of the subgrade soils beneath the cracks were higher than optimum, as measured by AASHTO T99; the densities of the subgrade soils beneath the cracks were lower than optimum, as measured by AASHTO T99; subgrade soils were classified as AASHTO A7; all pavements were full-depth asphalt placed directly on the subgrade; and all pavements were constructed in private developments with typical curb and gutter sections. In addition, similar pavements constructed on crushed stone bases in the vicinity of the full-depth pavements with the same construction and materials characteristics did not display this cracking. The results warrant a reduction in compaction moisture levels so that compaction densities can be increased when full-depth asphalt is used to pave over plastic clays.