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(a) <br />(b) <br />Figure 1. (a) Surface and (b) underside of chip seal that has "flaked" with stripped material from underlying <br />asphalt pavement <br />Surveys conducted in a Minnesota Local Road Research Board (LRRB) and Minnesota Department of <br />Transportation (MnDOT) study found that 40 of 66 local Minnesota agency engineers observed stripping <br />under chip seals (Wood & Cole, 2013). This concern is particularly important in terms of asphalt <br />pavements constructed in the mid- to late-1990s, which have been found to experience premature <br />aging and thus given to stripping. Given Minnesota's experience with stripping and chip seals, the <br />MnDOT study of chip seals attempted to identify causes of stripping in chip -sealed pavements (Wood & <br />Cole, 2013). The primary hypothesis of this study was that low density (i.e., high air voids) makes asphalt <br />paving mixes more prone to stripping. <br />Wood and Cole (2013) conducted a study of three locations in Minnesota, from which they collected <br />specimens for air void and permeability analysis in the laboratory. In addition to laboratory testing of 16 <br />field specimens, the authors conducted a laboratory trial of SuperPave mixes common to Minnesota <br />with three levels of air voids (7%, 10%, and 14%). The laboratory trials found that there "was no test that <br />explicitly showed asphalt stripping away from mixtures with higher air voids" (p. B-5). However, on the <br />basis of the 16 field specimens, the authors concluded that less dense areas, or high air voids, were the <br />main cause of stripping in Minnesota chip -sealed pavements. <br />1.2 RESEARCH SCOPE AND OBJECTIVES <br />This research project originated from a MnDOT research needs statement that used Wood and Cole <br />(2013) as a starting point for additional investigation of an important issue for local pavement <br />maintenance practices. Thus, the main research objective for this project was to investigate stripping in <br />chip -sealed pavements using testing and analysis of local Minnesota roads. <br />The research team was provided access to eight municipalities, which provided a total of 18 locations for <br />study. The project scope included the use of these locations for field observation and pavement samples <br />for laboratory examination. The first phase of the project work utilized field surveys, specimen <br />collection, laboratory testing, and analysis to: <br />2 <br />