Determining Time to Uncontrolled Trafficking After Chip Seal Construction

Predicting the strength of the emulsion residue in a chip seal is directly related to when the chip seal can be opened to traffic after construction. This strength is usually judged subjectively during construction by experienced personnel. Unfortunately, this experience is often gained through the empirical process that often leads to vehicle damage when residues that have not gained sufficient strength release chips under traffic loads. This research was conducted to help eliminate the subjectivity involved in determining when a chip seal can be safely opened to traffic without undue chip loss. The study began with the hypothesis that the moisture content of the emulsion-aggregate system was directly related to residue strength. To test this theory a revised version of ASTM D7000 was developed to measure chip loss for four different aggregate sources and five asphalt emulsions using a full-factorial experiment design. Results indicate the amount of water remaining in the emulsion is directly related to residue strength, as expected. Therefore, by establishing the relationship between water content and chip loss in the revised sweep test the time required in the field before traffic is allowed on the fresh chip seal may be estimated in advance. Other results indicate little correlation between emulsion particle charge and aggregate type at the higher moisture loss level tested, but a possible correlation at the lower moisture loss level tested.