Development and Evaluation of Performance Measures To Augment Asphalt Mix Design in Idaho
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2019-08-01
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Edition:Final Report 01/01/2016 - 6/30/2018
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Abstract:The Superpave volumetric mix design should be complemented with performance criteria to evaluate the mix resistance to cracking, rutting and moisture damage. Rutting and cracking are observed in pavements that are designed using the Superpave method. With the use of new materials such as Reclaimed Asphalt Pavement (RAP) and Reclaimed Asphalt Shingles (RAS), asphalt mixes tend to get stiffer and crack prematurely if not properly designed. The main objective of this study was to develop performance thresholds to ensure adequate mix resistance to cracking and rutting in Idaho. Two rutting tests were selected and used in this study: Hamburg Wheel Tracking Test (HWTT) and Asphalt Pavement Analyzer (APA) rut test. The cracking tests included three monotonic tests (Indirect Tension (IDT) test [ASTM D6931], semi-circle bending flexibility index (SCB-FI) test [AASHTO TP 124], and semi-circle bending Jc (SCB-Jc) test [ASTM D8044]), in addition to a newly developed multi-stage semi-circle bending dynamic (MSSD) test that was presented by the research team of this study. A total number of 12 performance indicators calculated from the monotonic tests were evaluated. The Weibull-cracking resistance index (WeibullCRI) index is a new performance indicator that was also proposed by the research team and it is calculated using the IDT test. In addition, two cracking resistance indicators were calculated from the MSSD test. This study proposed performance thresholds to ensure adequate resistance to cracking, rutting, and moisture damage. Two cracking resistance indicators were recommended; WeibullCRI calculated from the IDT test and the slope (z) of the MSSD test. Good cracking resistance was associated with higher WeibullCRI (WeibullCRI > 4.7) and small MSSD slope (Z < 1.9), while poor cracking resistance was associated with lower WeibullCRI (WeibullCRI < 3.57) and higher MSSD slope (Z > 2.9). Thresholds for other performance indicators calculated from the monotonic tests were also proposed. In addition, this study proposed two rutting performance thresholds for the HWTT and APA rut test. A maximum rut depth of 10 mm for HWTT after 15,000 passes and 5 mm for APA rut test after 8,000 cycles are proposed to ensure good rutting resistance. The HWTT test is recommended over the APA since it can be used to evaluate both rutting and moisture damage resistance.
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