The performance of cemented pavement materials under heavy axle loading

In this thesis, improved approaches to the laboratory characterisation of cemented materials are developed and verified enabling a more informed understanding of the load-carrying capacity of cemented materials used in road pavements. The increasing use of high productivity road freight vehicles and the application of mechanistic-empirical pavement analysis has led to the need for improved knowledge of the performance of pavement materials. In Australia, standard methods are not available for the elastic characterisation of cemented materials. As a result, presumptive values or correlations with parameters such as unconfined compressive strength (UCS) are used. In this study pavement design methods, failure mechanisms and approaches to cemented materials characterisation are investigated. Theoretical modelling and prediction of crack growth in cemented materials under repetitive loading is reviewed. The use of initial modulus and the reduction in modulus under repetitive loading is proposed as a pragmatic indicator of fatigue crack growth. Improved laboratory protocols for the characterisation of strength, breaking strain, modulus and fatigue are developed using a four-point bending, dynamic flexural beam test. The protocols were applied to two typical cemented materials, a hornfels with 3% cement and a siltstone with 4% cement at a range of curing ages. Breaking strain was identified as an indicator of initial micro-cracking. A stress controlled fatigue test was used to establish relationships between initial strain (S) and fatigue life (N) (load cycles to half initial modulus). The verification of the improved laboratory protocols involved a comparison of the labboratory test results with the results of full-scale accelerated pavement testing (APT). For the siltstone, the laboratory and field performance results aligned well. Differences between the laboratory and field materials properties resulted in a lesser alignment of the performance results for the hornfels. The relative performance ranking between the two cemented materials from the improved laboratory protocols matched that from the APT. The ranking from the traditional UCS did not align with the APT results. Further verification was sought using the Australian long term pavement performance study and anecdotal evidence of cemented materials performance to enable consideration of combined environmental and traffic effects over an extended timeframe. In the final stage of the study, the applicability of the improved laboratory protocols to a wide range of cemented materials was confirmed and a limited study into the extent of initial micro-cracking and the fatigue load-damage exponent was undertaken for two cemented materials. It was concluded that the four-point bending flexural beam test developed and verified in the study provided a significantly improved method of assessing the performance of cemented materials compared to the UCS test. The improved laboratory protocols were found to be suitable for testing a wide range of cemented materials. It was also found that, where consistent micro-cracking was present, the load-damage exponent was not dependent on the extent of initial micro-cracking.