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n IMIESA - Deformation behaviour of HMA : roads and bridges
Efficient road transport is dependent upon construction of high-quality roads. It is important that hot-mix asphalt (HMA) surfaced roads resist permanent deformation, or rutting, in order to provide a high level of service to the road user. In order to improve the resistance of HMA layers against permanent deformation, the Gauteng Department of Public Transport, Roads and Works (GDPTRW) has commissioned a multiphase study into the behaviour of different types of HMA under typical traffic and environmental-loading conditions. The study includes laboratory and field evaluation of a standard HMA mix, as well as different HMA mixes that were designed to be rut resistant.
In this paper, the focus is on the comparison between the permanent deformation behaviour of the standard HMA mix and one rut-resistant HMA mix of which the grading differs from that of the standard HMA mix. The permanent deformation has been monitored under traffic loading with the heavy vehicle simulator (HVS), and the temperature, under which the loading was applied, was varied. Other parameters, such as the binder type of the HMA, and load levels of the HVS, were kept constant to focus the attention on the effect of the change in grading of the HMA mix.
The data presented in this paper indicate that the grading of the HMA mix can play a major role in the resistance to the permanent deformation of the mix, even under severe temperature conditions. The potential rut-resistant benefit of coarser grading for HMA mixes have been supported through HVS tests. Further tests are required, both in the laboratory and field, to evaluate the durability and fatigue properties of the coarser HMA mix against the standard reference mix.
This paper forms part of studies towards a masters degree in technology at Tshwane University of Technology (TUT) of the third author. The outcome of the overall research will contribute to road owners and design engineers' better understanding the deformation mechanism and being able to plan, design and construct HMA pavements that are resistant to it. These results will also be incorporated into updated Guidelines for the Design of Hot-Mix Asphalt in South Africa.
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