Mechanism of cement on the performance of cement stabilized aggregate for high speed railway roadbed

Field frost-thaw deformation tests show that the frost susceptibility of graded aggregate is a major factor contributing to the instability of high speed railway track. This paper is aimed at studying the effect of cement content (0%, 3%, 5%, 7% and 9%) on the mechanical, dry shrinkage behavior and frost heave susceptibility of cement stabilized aggregate (CSA) used for high speed railway roadbed and the strengthening mechanism of cement. An ultrasonic pulse velocity (UPV) technique was employed to continuously and nondestructively monitor the microstructure formation process of CSA. The experimental results show that compressive strength, flexural strength and frost heave resistance property increase with the cement replacement. However, reverse phenomenon is observed in the shrinkage behavior. Based on the UPV development test, the microstructure evolution process of CSA can be clearly identified into three stages. The mechanism of cement can be classified into "filling effect" and "binding effect" and the latter effect is more dominant. The optimum cement content and water to cement ratio (w/c) are estimated to be 5% and 1, respectively. At these value, an efficient compaction, denser structure and reduced frost susceptibility can be simultaneously achieved. In addition, X-ray tomography technology (XCT) was also employed to characterize the microstructure quantitatively. (C) 2017 Published by Elsevier Ltd.