n IMIESA - Compaction effects of HMA : roads and bridges




A general concern exists regarding the ability of the South African Hot-Mix Asphalt (HMA) design method to accurately predict the rutting performance of HMA designs through laboratory evaluation. Since 2000, various studies have focused on this issue, and several HMA mixes from construction projects and laboratory-prepared slabs were tested using a range of laboratory wheel-tracking tests to assess the rutting potential of the mixes. The data from these tests were compared with field performance of the HMA. Although some of the tests appeared to be well correlated with rutting in the field, there are at present no generally-accepted and quantified relationships to link laboratory test results to rutting in the field under variable traffic loading and environmental conditions. Other tests that are available for the assessment of rutting, such as the Axial Loading Slab (ALS), are essentially axial tests and do not simulate a rolling wheel load. These tests mainly evaluate the resistance of asphalt to volume change, and not shear response. Shear deformation is known to be the dominant mode of deformation causing rutting in pavements. It is also more sensitive to temperature and rate of loading than volume change.

In a current study on the development of rutting in a standard HMA mix under varying traffic and environmental conditions, the focus is on the evaluation of the effects of different compaction methods on the data obtained from a range of laboratory tests. The aim of this work is to provide input for the selection of appropriate and validated laboratory tests for the evaluation of rut resistance of HMA mixes.
In the paper, the background to the study is firstly provided, followed by a brief discussion on the parameters evaluated. Next, the data obtained from a range of laboratory tests on samples compacted using field and a range of laboratory compaction methods are evaluated and compared, and conclusions are drawn regarding the effect of compaction method on the data obtained from the various laboratory tests. This paper forms part of the research for an M.Tech degree at the Tshwane University of Technology (TUT).


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