Effect of Sand Grading and Proportion on the Performance of Cement Asphalt Mortar for High-Speed Rail Slab Track Systems

Abstract

Sand makes up about 40% of cement asphalt mortar (CAM) used in non-ballast tracks for high-speed rail infrastructure, playing a crucial role on the performance of CAM. This study investigates the influence of sand gradation (quantified using fineness modulus [FM]), and sand-to-cementitious component ratio (S/CC) on key CAM parameters, including flow time, working time, material separation, compressive strength, elastic modulus, and shrinkage. Multiple gradations and S/CC ratios were evaluated to establish combinations that achieve the required flow time (16–28 s), a minimum 30 min working time, minimize material separation, and ensure desired mechanical performance. Results indicate that coarser gradations improve workability but increase material separation, whereas finer gradations reduce separation but prolong flow time. An FM of 1.6, with particles passing 1.18 mm sieve ensure desired flow time and homogeneity of CAM. An S/CC ratio of 2 maintained good workability, reduced shrinkage and deformation, and improved compressive strength and modulus. These findings offer insights for CAM mix design particularly with reference to sand gradation and proportion selection.