ARRB Research is currently undertaking research to improve knowledge of the effects of axle load and tyre type on pavement deterioration. Two specific objectives of the research were 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. LDEs for deformation and roughness progression developed from the performance data collected under accelerated loading provided further evidence to support on-going use of the 4th power LDE for granular pavements. It was also found that the relative wear (i.e. the number of cycles to achieve a permanent deformation of 20 mm) 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 caused the same pavement wear (vertical surface deformation) as an 8.2 tonne Standard Axle fitted with dual 11 R22.5 tyres was found to be 5.4 tonne, which is in good agreement with the recommendations contained in the Austroads Pavement Design Guide. (a) For the covering entry of this conference, please see ITRD abstract no. E214938.
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