Perfromance of SDDOT's New Chip Seal Design

South Dakota Department of Transportation (SDDOT) recently investigated chip seals for use on high-volume/high-speed roadways to improve their performance (SD1999-09 High volume/High Speed Asphalt Roadway Preventive Maintenance Surface Treatments). Twelve chip seal test sections were constructed using two aggregate types (quartzite and natural aggregate) and alternate chip seal designs with new gradations and other modifications and enhancements. Limestone aggregate is commonly used for chip seals in the western portion of the state. The SD1999-09 study provided specific recommendations to improve chip seal performance and developed chip seal design and construction guidelines. The study also recommended to construct test sections in the western part of the state using limestone and natural aggregates and to re-evaluate the chip seal performance on SD50 near Yankton, SD. Since quartzite and natural aggregates were tested on the SD1999-09 study, it is necessary to test the new chip seal design and construction guidelines using limestone aggregate. Particle shape is a concern since flat and elongated particles tend to be more susceptible to becoming dislodged causing windshield damage and not being properly embedded in the emulsion. The flakiness index is a measure of the percentage by weight of flat particles. The amount of flat and elongated particles in aggregates currently being used for chip seals in South Dakota is unknown. The Flakiness Index needs to be evaluated for aggregates commonly used for surface treatments in South Dakota. Minnesota Department of Transportation currently places a fog seal on all chip sealed surfaces. The fog seal aids in chip retention, aesthetics, and reduces damage from snowplows. A fog seal was evaluated as part of the SD1999-09 research study and should be tested on the limestone chip seal. The objectives of this research are: 1) To construct and evaluate a chip seal using limestone aggregate to validate the design and construction guidelines developed under research study SD1999-09. 2) To continue evaluation of the chip seal test sections placed on SD50 for the SD1999-09 research study. 3) To determine the Flakiness Index for aggregates and gradations commonly used for surface treatments in South Dakota. Research tasks are as follows: 1) Meet with the Technical Panel to review project scope and work plan. 2) Review and summarize literature pertinent to the design and construction of limestone chip seals. 3) Determine proper emulsion rates for limestone aggregate. 4) Monitor and evaluate the construction of the chip seal placed on SD40 between Keystone and Hayward and document test results obtained during initial construction and periodic on-site evaluations. Testing should include the sand patch test (ASTM E 965), chip retention, embedment, emulsion and chip application rates. 5) Evaluate the performance of the test sections placed on SD50 for the SD1999-09 research study. Testing should include the condition, sand patch test (ASTM E 965) and embedment. 6) Recommend modifications to the new design procedures from the SD1999-09 research study based on test results. 7) Determine Flakiness Index (FLH T 508-96) for aggregates commonly used for surface treatments by performing the test on aggregate submitted from chip seal projects during 2002 construction season in South Dakota. 8) Prepare a technical memorandum describing the construction and testing that occurred during the summer of 2002 by August 9, 2002. 9) Evaluate the SD40 test section during the spring and summer of 2003. 10) Prepare a final report and executive summary of the literature review, research methodology, findings, conclusions, and recommendations. 11) Make an executive presentation to the SDDOT Research Review Board at the conclusion of the project.