United States Department of Transportation
i
Using the bending beam rheometer for low temperature testing of asphalt mixtures : final report.
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2016-07-01
[PDF-5.10 MB]
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Edition:Final report
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Abstract:This work showed that the bending beam rheometer is a viable test to determine the low temperature performance of
asphalt mixtures; it balances the rigor required of any mechanical test and the relation to field performance with the
practicality of a procedure that can be easily adopted. The protocols developed parallel existing asphalt binder
protocols thus allowing for easy implementation since they are based on robust and commercially available
equipment that requires no modification.
It was shown that the size of the beams used for this test are a representative volume element. Mixtures with
nominal maximum aggregate size of ½” or even larger can be tested without large aggregates introducing any
further variability. The size of the beams also allows for multiple specimens obtained from either gyratory
compacted samples or field cores; agencies and contractors can test mixtures and compared results as the difference
between two labs was determined to be less than 10 percent for the modulus and about 20 percent for the m-value.
Finally, based on field performance measurements, it was determined that both creep modulus and m-value are
needed to determine the low temperature performance of asphalt pavements. These values can be visually presented
in a Black Space diagram. Mixtures with high modulus and low m-values are expected to show poor performance
but mixtures with high modulus AND high m-value should have better performance, perhaps allowing for better
performing asphalt mixtures at both low and high temperatures.
The benefits found from using the BBR to test small beams of asphalt mixtures indicate that this is an ideal test to
evaluate the low temperature performance of asphalt mixtures.
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