United States Department of Transportation
i
Balanced Asphalt Concrete Mix Performance in Utah, Phase III: Evaluation of Field Materials Using BBR and SCB-IFIT Tests
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2019-05-01
[PDF-1.36 MB]
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Edition:Final Report May 2017 to March 2019
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Abstract:A study was conducted to evaluate the applicability of two cracking tests for low- and intermediate temperature performance for the purpose of creating a balanced hot-mix asphalt mix. For the low-temperature performance, the Bending Beam Rheometer (BBR) test on mixtures based on AASHTO TP-125-16 protocols was studied. For intermediate-temperature performance, the Flexibility Index (FI) of hot-mix asphalt as determined using the Semi-circular bend (SCB) configuration based on AASHTO TP-124-16 was studied. Seven asphalt mixtures were collected across the State of Utah at two locations: at the plant and at laydown from the windrow. For the low-temperature performance, it was determined that the specification proposed as part of a previous study is adequate and will allow evaluation of the low-temperature performance of asphalt mixtures at specific environments. For the intermediate-temperature test, it was found that the variability in the results (FI) continues to be a problem. At least 8 samples should be tested to obtain an average that represents the actual value within 20%. This requires compaction of 2 gyratory pucks. Regarding the Flexibility Index, asphalt mixtures sampled at the plant can be expected to have an FI generally between 3.0 and 20.0. The material sampled at laydown can be expected to have an FI somewhere between 2.1 and 18.5. A small improvement in the differences between labs was seen when testing was done at a loading rate of 15 mm/min but there was no clear benefit regarding the coefficient of variation. Different loading rates resulted in different performance ranking of the mixtures; however, without any performance information available from the field, it is not known if one loading rate is preferred over the other.
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