Identification of parameters related to moisture conditioning that cause variability in modified Lottman test

The modified Lottman (AASHTO T283) test method is frequently used for the evaluation of moisture susceptibility of asphalt concrete mixtures. Unfortunately, the test is known to be extremely variable, and it sometimes provides erroneous results. In NCHRP 9-26A, precision estimates of various AASHTO tests, including AASHTO T283, are being investigated. In this paper, the numerous variables introduced in the T283 test method due to the moisture-conditioning procedure are investigated via microscale finite element analyses. For the finite element meshes, X-ray tomography scans are made of two gyratory- and Marshall-compacted mixtures. These mixtures are computationally analyzed for their outside and inside pore-space distribution; the moisture infiltration is simulated via finite element analyses; and the resulting moisture fronts are discussed. The paper focuses on the importance of knowing the actual moisture concentrations inside the material and the relevance of the time frame over which moisture damage may occur in the field. The results of the project are intended to give a fundamental explanation as to why the AASHTO T283 test may give erroneous conclusions and will define the boundaries under which the test could be used. This research shows that the two different compactions and geometries can result in entirely different moisture concentrations inside the specimen. This observation can have a significant impact on the variability of the test results.