When to Broom or Remove Traffic Control Safely on Fresh Emulsified Asphalt Chip Seals

Abstract

The optimal time to allow brooms to sweep a fresh chip seal is usually determined by experienced field personnel. Factors that affect this decision include aggregate type; aggregate moisture content; emulsion type and grade; application rates of emulsion and aggregate; weather conditions at the site, including humidity, air and pavement temperature, and wind; and number of rollers. Given all these factors, and because changes in one factor can have a significant effect on how an emulsion gains strength and how soon it can resist the forces of brooms and traffic, the decision as to when to allow brooms and traffic on fresh chip seals becomes difficult, at best, to predict. The results of this research suggest that moisture content of the chip seal system is related directly to the strength of an asphalt emulsion residue. Laboratory and field testing confirm that the strength of an asphalt emulsion residue as measured by a modification to the ASTM D7000 sweep test can be used to predict the moisture content level at which a chip seal developed enough strength to resist damage by brooms and vehicular traffic. Three full-scale test pavements were constructed in differing climates, and the results of moisture content testing in the field were compared with modified sweep test results in the laboratory. Results indicated that the three field tests were capable of resisting brooming and traffic damage when the moisture content of the chip seal system ranged between 15% and 25%. This finding correlated well with results of laboratory testing with the modified sweep test on the materials from field tests as well as on experimental laboratory materials.

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