Laboratory fatigue life of cemented materials in Australia

Abstract

In Australia increasing traffic loadings are placing greater pressure on sprayed seal unbound granular pavements, with some non-standard materials no longer being fit-for-purpose. Unfortunately, in many rural areas, the use of high-quality crushed rock is not a cost-effective treatment to improve the structure of these pavements. Consequently, there is growing interest in pavement-strengthening treatments, such as in situ cement stabilisation, that enhance existing non-standard materials. The required thickness of cement stabilisation is commonly governed by the fatigue characteristics of the treated material. This paper presents the results of an on-going Austroads research project to investigate the laboratory fatigue life of a wide range of cemented materials. Flexural beams were manufactured and tested using newly developed laboratory methods. In addition to the fatigue tests, flexural strength and flexural modulus tests were also conducted. Results showed that the fatigue relationship for cemented materials is significantly dependent on breaking strain and not modulus, which suggests that the current Austroads design criterion can be improved. The ratio of initial strain resulting in a fatigue life of 10⁶ cycles divided by breaking strain is seen as a potentially superior method of incorporating material quality into the cemented materials’ fatigue relationship. Finally, a presumptive laboratory relationship based on strain ratio was developed. The presumptive fatigue relationship is conservatively based on a strain ratio of 0.35 for 10⁶ load cycles. A strain damage exponent of 12 is recommended for pavement design.