United States Department of Transportation
i
Balanced Asphalt Concrete Mix Performance, Phase II: Analysis of BBR and SCB Tests
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2017-12-01
[PDF-2.38 MB]
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Edition:Final Nov 2015 to Dec 2017
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Abstract:An evaluation of the ability of the BBR and the IFIT tests to determine changes in asphalt mixture parameters was conducted as well as the possible implications of adoption these two tests at low and intermediate temperatures. It was found that the FI from the IFIT was a more sensitive parameter than the creep modulus or m-value from the BBR to detect changes in binder content; the reverse was true for air voids. Both tests indicate that RAP is detrimental to the overall expected performance of the mixtures when compared to a mixture with no RAP. However, the BBR appears to be a more sensitive test to capture the effect of aging and RAP on the material. It was found that aging of the loose mixture at 135 ºC prior to compaction shows a more consistent trend that aging the compacted specimen at 80 ºC in both tests. One hour of loose mix aging at 135 ºC results in the same mechanical changes as 47 to 55 hours of compacted mix aging at 80 ºC. Based on the results, it is concluded that adoption of the IFIT as a required test for mixture acceptance would likely result in mixtures with higher binder content being favored during design; no such changes would be expected with the adoption of the BBR as a required test. At the same time, the BBR appears to be a more sensitive test to capture the effect of aging and RAP on the material. Thus, adoption of the BBR as a specification test would likely result in changing the mixture design process to favor mixes with lower RAP content and less sensitivity to aging.
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