United States Department of Transportation
i
Balanced Asphalt Concrete MIX Performance in Utah, Phase IV: Cracking Indices for Asphalt Mixtures
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2020-09-01
[PDF-1.39 MB]
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Edition:Final Report, Nov. 2018 to Sep. 2020
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Abstract:The Utah Department of Transportation (UDOT) has been seeking a test to balance its asphalt mixes against the stiffness encouraged by the Hamburg Wheel Tracking test and the use of recycled asphalt pavement (RAP). Without this balance, the over-stiffening of mixes has led to premature cracking. Two configurations of cracking tests have been studied previously, and conclusions about them can be found in Phases I, II and III of this series. These reports are available on the UDOT website. In this study, the IDEAL-CT test as described in ASTM D 8225 is investigated compared to the I-FIT cracking index test on the basis of between- and within-lab repeatability and precision. It was found that, even though the IDEAL-CT test is not as fundamentally based as the I-FIT test, in samples built using the same procedures, the repeatability and precision were relatively the same. It was shown that if the samples in the IDEAL-CT test were prepared from larger samples and cut to size, repeatability was generally higher but below a tolerable threshold. If samples were built according to the ASTM procedure (62 mm uncut), the variability increased above tolerable values. If samples were compacted to a height of 75 mm, the repeatability was within tolerance standards. It is recommended that IDEAL-CT be favored over I-FIT to evaluate mixtures for potential intermediate- temperature cracking due to the much simpler sample preparation and equivalent repeatability. It is also recommended that field-produced mixes be studied to determine sample geometry and threshold specification values.
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