Premature cracking in new asphalt pavements before the pavements are opened to public traffic, before development of the sites is completed, and before surrounding buildings are occupied is the focus of this paper. Previous studies to determine the cause of this phenomenon have been done at individual sites resulting in a variety of probable, but not conclusive causes. This paper describes a forensic analysis using interviews with principals experienced with this form of distress and field and laboratory test results intended to expose commonality with respect to soils, pavement materials properties, construction sequence and pavement design among several sites where cracking occurred and where cracking was not present. Five factors have evolved that are common at each site: all cracks began at the surface of the pavement and propagated downward; moisture content of the subgrade soils beneath the cracks was higher than optimum measured by AASHTO T99; density of the subgrade soils beneath the cracks was lower than optimum 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 curb and gutter typical 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 do not display this cracking. Results warrant a reduction in compaction moisture levels so that compaction densities can be increased when paving full-depth asphalt over plastic clays.
Samenvatting