Influence of Asphalt Emulsion Formulation Parameters on the Fluidity of Cement Asphalt Mortar for High-Speed Rail Tracks

The objective of the present study is twofold: firstly, to evaluate the influence of asphalt emulsion properties on the fluidity characteristics of cement asphalt mortar (CAM) for high-speed railway (HSR) track systems; and secondly, to propose a testing protocol that effectively differentiates the asphalt emulsions suitable for CAM with respect to fluidity requirement, considering specific requirements for the application. The study involved assessing CAM fluidity under various emulsion formulation variables, including the pH, residual asphalt content, and emulsifier dosage. In addition, three different test methods were evaluated for their suitability as the protocol for asphalt emulsions evaluation for CAM production in HSR applications. The results showed that the pH of the asphalt emulsion significantly affects the fluidity of the CAM, with cationic emulsions demonstrating less stability because of high alkaline conditions of CAM, while anionic/non-ionic emulsions exhibited stable fluidity. Fluidity in CAM is observed when an asphalt emulsion possesses an optimal micelle concentration, which effectively resists coagulation. The findings emphasize the importance of considering both upper and lower limits for residual asphalt content in emulsion specifications for CAM production. Emulsifier dosage also played a role, with high emulsifier dosages leading to high fluidity in CAM. The study introduced a fluidity ratio test as a suitable method for selecting asphalt emulsions for CAM production for HSR track systems.