Load damage exponents for thin surfaced granular pavements

This paper describes recent research undertaken by ARRB Transport Research into the effects of increased axle loads on the performance of thin surfaced unbound granular pavements. The Australian Accelerated Loading Facility (ALF) was used to assess the performance of three unbound granular test pavements at three axle load levels. Each of the test pavements was constructed of a different basecourse material. Two high quality crushed rocks commonly used in highway construction and one lower quality material used for lower trafficked local roads were used. The test pavements were surfaced with a sprayed bituminous chip seal. The results of the accelerated loading were as expected in that the lower quality material showed much higher deformation and roughness progression compared to the high quality materials. The performance data were analysed and models were derived for the prediction of rutting as a function of pavement strength, cycles of load and load level for each of the test pavements. Load Damage Exponents (LDEs) were derived for each test pavement based on load cycles to equal surface deformation.