This report presents the findings from a field and laboratory experimental program that was designed to assess the amount and nature of any construction variability and the impact of any such variability on the performance of chip seal treatments. The research approach involved the construction of three double-seal test sections in Rowan, Moore, and Caswell Counties, respectively, by two contractors and three different construction crews, and the sampling of chip seal specimens obtained from these test sections. Granite 78M and No. 14 aggregate and CRS-2L emulsion were used in the construction. The aggregate application rate (AAR) and emulsion application rate (EAR) were determined using the ignition oven test, and aggregate loss and bleeding were evaluated using the third-scale model mobile load simulator (MMLS3) test. In addition, the research team evaluated the effects of the quality of the emulsion on chip seal performance by measuring the sprayability and drain-out of the fresh emulsion using the three-step shear test in a rotational viscometer and the high temperature binder performance of the residue using the multiple stress creep and recovery (MSCR) test in a dynamic shear rheometer.
The main findings from this study are: (1) the AARs and EARs that were measured from all three field sections constructed by three different construction crews were significantly lower than the targeted design application rates; (2) although the individual application rates were much lower than the targeted application rates, the constructed chip seals did not exhibit significant performance problems in the field based on the condition survey performed eight months after construction because the lower than targeted EARs and AARs seemed to have canceled out the negative effects of having less than adequate amounts of aggregate and emulsion; (3) the MSCR test results were correlated with the amount of bleeding observed from the MMLS3 testing of the chip seal specimens; and (4) a performance-related specification framework that provides guidance for test procedures that can help identify construction variability issues as well as a chip seal best practices document and quality assurance training programs were developed for the NCDOT's future use
