The modified Lottman (AASHTO T 283) test method is frequently used for the evaluation of moisture susceptibility of asphalt concrete mixtures. Unfortunately, the test is known to be very variable and sometimes provides erroneous results. In the NCHRP 9-26A project, precision estimates of various AASHTO tests are being investigated. In this paper the various variableswhich are introduced in the T 283 test procedure due to moisture conditioning procedure are investigated via micro-scale 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. In the paper, focus is placed on the importance of knowledge of 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 intend to give a fundamental explanation of why the AASHTO T 283 test may give erroneous conclusions and will define the boundaries under which the test could be used. From the research presented in this paper it can be seen that the two different compactions and geometries can result in entirely different moisture concentrations inside the specimen. This can have a significant impact on the variability of the test results.
Abstract