ARRB Research is currently undertaking an Austroads technical research project: Influence of vertical loading on the performance of unbound and cemented materials. Two specific objectives are to determine load damage exponents (LDEs) and to assess the relative damaging effects of wide single tyres and steer axle tyres compared to dual tyres for Australasian pavement types. This paper summarises the experimental program, analysis and findings of the assessment of the impacts of axle mass increases and tyre types on road deterioration for sprayed seal surfaced unbound granular pavements, the most common pavement type in Australasia. Performance data collected under accelerated loading provided evidence to support on-going use of the 4th power LDE for granular pavements. It was also found that the relative (deformation) wear was 1.6 times, 3.8 times and 4.7 times for the 445/65R22.5 and 385/65R22.5 wide single tyres and 295/80R22.5 steer axle tyre respectively compared to the conventional dual tyres when all testing was conducted with the 40 kN half-axle ALF load. The reference load on a steer axle with 295/80R22.5 single tyres which was estimated to cause the same pavement wear (vertical surface deformation) as an 8.2 tonne standard axle fitted with dual 11R22.5 tyres was found to be 5.4 tonne, which is in good agreement with the Austroads Pavement Design Guide. (a) For the covering entry of this conference, please see ITRD abstract no. 0612AR242E.
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