This report presents a new performance-related mix design method for chip seal construction. The components of this method include the determination of an optimal aggregate application rate (AAR) using the modified board test and determination of an optimal emulsion application rate (EAR) using the laser profiler. The board test used in the Modified Kearby chip seal mix design method has been modified further to accommodate an optimal board size and a minimum number of board test replicates to yield the least variability and most representative AAR to fill the board tray with a single layer of aggregate. The main concept used in the determination of the optimal EAR is that the initial embedment depth of the aggregate particles should be 50% of the total depth. The 50% embedment concept is validated by the aggregate loss and bleeding test results using the third scale Model Mobile Loading Simulator (MMLS3). This validation study used Granite 78M and lightweight aggregate with CRS-2L emulsion to fabricate the chip seal specimens in the laboratory. Three different gradations with vastly different performance uniformity coefficients (PUCs) were used for each of the two aggregate types. An optimum AAR for each gradation was determined by the modified board test. Chip seal specimens were fabricated using the laboratory scale chip spreader, ChipSS, and EARs were varied from 0.1 to 0.3 gal/yd2 at increments of 0.05 gal/yd2. It was found from the bleeding test that the optimal EARs determined by the NCSU mix design method for the different chip seal specimens were the maximum EARs that did not cause bleeding, thus validating the NCSU mix design concept. The final optimum EAR is determined after accounting for the aggregate absorption and existing pavement surface absorption via the percentage of absorption of the aggregate and the surface texture measurements obtained from the laser profiler. A comparison of the mix design rates with the rates used by the NCDOT Divisions reveals that the mix design AARs and EARs are about 40% and 20% lower than the field rates, respectively. Various factors explain these differences, including wet aggregate and traffic whip-off to explain the AARs, and the absorption of both the aggregate and existing pavement surface to explain the EARs. Finally, further research is suggested to conduct field calibration and validation of the performance-related chip seal mix design method in order to take full advantage of the performance-related mix design method so that the NCDOT can implement the proposed method in routine chip seal construction.
