This report presents the findings from a field and laboratory experimental program that is designed to develop guidelines regarding the maximum amount of traffic that modified chip seals can support using improved construction procedures. For the laboratory tests, the evaporation test, bitumen bond strength (BBS) test, and Vialit test are used to investigate the curing and adhesive behavior of unmodified and polymer-modified emulsions. In addition, the third-scale model mobile load simulator (MMLS3) was employed to test for aggregate retention, bleeding, and rutting performance. In order to evaluate the actual chip seal performance in the field, a total of 12 field test sections were constructed on three different traffic volume roads using different materials and seal types. Some of the field samples were extracted from the field test sections and moved to the laboratory for the MMLS3 performance testing. Also, the field sections were monitored to compare the field performance with the laboratory performance.
The main findings from this study are: (1) the laboratory test results indicate that the use of PMEs improves the chip seal performance in all areas, i.e., curing and adhesive behavior, aggregate retention, bleeding, and rutting; (2) strong correlations are found between the bitumen bond strength and the aggregate loss found from the Vialit test; (3) the field observations indicate that SBS-modified emulsion performs the best of all the emulsions, regardless of seal type and traffic volume; (4) the single seal with CRS-2P emulsion (fog seal application can be considered) is recommended for roads with less than 5,000 ADT or roads in good condition or newly constructed roads, and the double seal with CRS-2P emulsion (fog seal application can be considered) is recommended for roads with more than 5,000 ADT or for heavily cracked areas on low-volume roads; and (5) the maximum allowable traffic volume can be estimated for multiple seals using Mean Profile Depth analysis. Finally, different chip seal types and application rates may lead to different maximum allowable traffic volumes. Therefore, further study is recommended to suggest more accurate maximum allowable traffic volumes for chip seals.
