Dynamic Modulus Characteristics of Bound Cement-Treated Crushed Rock Base course

Cement-treated base is a conveniently and effectively stabilised pavement material consisting of a mixture of standard base course materials blended with a prescribed amount of Portland cement and water. The cement-treated base material is suitable for use in high-traffic roads and airfield pavements, and usually provides superior engineering properties compared to standard road base material. However, fully bound or stabilised cement-treated base is a relatively stiff pavement base material which is prone to fatigue failure under repeated loading. In pavement design, current fatigue models for cement-treated base material remain empirical, and there exists a lack in scientific linkage between the models themselves and real fatigue perfor-mance. Consequently, a more reliable fatigue deterioration model for cement-treated base is required in order to maximise the usage of such material in pavements. The provision of ‘bottom-up’ constitutive equations is preferable when seeking a deeper understanding of cement-treated base course behaviour under repeated loading. This study focuses on evaluating the dynamic moduli (i.e., the moduli under cyclic loading conditions), of cement-treated base under traffic loads. The same testing basis used for asphalt concrete was adopted in this research. As such, the dynamic moduli were measured under different temperatures and loading frequencies, based on the dynamic modulus testing protocol for asphalt concrete. Test results revealed that cement content and curing time significantly influence the dynamic modulus of bound cement-treated base course. However, the dynamic modulus property was slightly affected by the changes in temperature and loading frequency within a specific range of testing conditions of the test protocol. At the end of this research, a predictive equation for the dynamic modulus was tentatively put forward. This equation was developed from the relationship of the modulus to the unconfined compressive strength. It should be noted that this predictive equation requires further verification due to its development being based on limited number of test samples and results.Cement-treated base is a conveniently and effectively stabilised pavement material consisting of a mixture of standard base course materials blended with a prescribed amount of Portland cement and water. The cement-treated base material is suitable for use in high-traffic roads and airfield pavements, and usually provides superior engineering properties compared to standard road base material. However, fully bound or stabilised cement-treated base is a relatively stiff pavement base material which is prone to fatigue failure under repeated loading. In pavement design, current fatigue models for cement-treated base material remain empirical, and there exists a lack in scientific linkage between the models themselves and real fatigue performance. Consequently, a more reliable fatigue deterioration model for cement-treated base is required in order to maximise the usage of such material in pavements. The provision of ‘bottom-up’ constitutive equations is preferable when seeking a deeper understanding of cement-treated base course behaviour under repeated loading. This study focuses on evaluating the dynamic moduli (i.e., the moduli under cyclic loading conditions), of cement-treated base under traffic loads. The same testing basis used for asphalt concrete was adopted in this research. As such, the dynamic moduli were measured under different temperatures and loading frequencies, based on the dynamic modulus testing protocol for asphalt concrete. Test results revealed that cement content and curing time significantly influence the dynamic modulus of bound cement-treated base course.However, the dynamic modulus property was slightly affected by the changes in temperature and loading frequency within a specific range of testing conditions of the test protocol. At the end of this research, a predictive equation for the dynamic modulus was tentatively put forward. This equation was developed from the relationship of the modulus to the unconfined compressive strength. It should be noted that this predictive equation requires further verification due to its development being based on limited number of test samples and results

Shrinkage Behaviour of Cement-Treated Crushed Rock Base in Western Australia

Shrinkage cracking is a significant problem when using cement stabilised materials in the construction of road pavements. Reflective (upward) cracks travel from the cement stabilised base layer to the top of the asphalt surface can cause water ingress through the underlying pavement layers. This paper examines the shrinkage behaviour of cement-treated crushed rock base as applied to pavement conditions in Western Australia. The testing protocol to examine the shrinkage behaviour of the material was adapted from the cement shrinkage test in Australian Standards, AS 1012.13. The test results showed that the amount of shrinkage in the cement-treated material did not increase with additional amounts of cement. The highest shrinkage values were found for the 2% and 6% cement specimens, where shrinkage was approximately 17% greater than the lowest shrinkage value found for the 4% cement sample. Based on the results of this study, it seems that shrinkage in the samples with relatively higher cement content of 5% and 6% mainly results from loss of water during the hydration reaction process between cement and water. Shrinkage in the low cement content samples of 2% and 3% is governed by the evaporation of excess water after the hydration reaction. The 4% cement content sample demonstrated the optimum cement content when considering the lowest shrinkage values among other cement content samples and an appropriate unconfined compressive strength value