Abstract
The current method of determining the moisture susceptibility of asphalt concrete mixtures is American Association of State Highway and Transportation Officials (AASHTO) T283. AASHTO T283 is based on the Marshall mix design method, however the current state of the practice for an asphalt concrete mixture design is the Superpave mix design method. There has not been a transition in test procedure from Marshall mix design to Superpave mix design in that Superpave adopted AASHTO T283 to evaluate the moisture susceptibility of asphalt concrete mixtures even though it was based on Marshall mix design. The procedures in AASHTO T283 and National Cooperative Highway Research Program (NCHRP) Report 444 consider the loss of strength due to freeze/thaw cycling and the effects of moisture existing in specimens compared to unconditioned specimens. Current research (NCHRP Project 9-34) is considering the use of a modified environmental conditioning system (ECS) with dynamic complex modulus testing. However, mixtures do not experience such a pure phenomenon. Pavements undergo cycling of environmental conditions, but when moisture is present, there is repeated hydraulic loading with development of pore pressure in mixtures. Thus, AASHTO T283 and NCHRP Report 444 do not consider the effect of pore pressure, but rather consider a single load effect on environmentally conditioned specimens. The test procedure proposed in this paper uses a retained dynamic modulus of 60% of conditioned specimens to unconditioned specimens. This initial criterion was derived as it is the same percentage of mixtures that fail the AASHTO T283 criteria (80%) of the 21 field mixes that were sampled. Comparison of mixtures performance ranked via AASHTO T283 and the proposed retained dynamic modulus criteria results in considerably different rankings. Pavements undergo cycling of environmental conditions, but when moisture is present, there is repeated hydraulic loading with the development of pore pressure in mixtures. Thus, the results of this testing can be input into the AASHTO Mechanistic-Empirical Pavement Design Guide to consider the effects of unconditioned versus conditioned dynamic modulus values and their respective impacts in pavement performance in terms of predicting pavement distresses.
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