Systemic values of enhanced dynamic damping in concrete sleepers – Comments on the paper: Ahn S, Kwon S, Hwang Y-T, Koh H-I, Kim H-S, Park J. Complex structured polymer concrete sleeper for rolling noise reduction of high-speed train system, Composite Structures, 2019, 223:110944 (doi https://doi.org//10.1016/j.compstruct.2019.110944)

Ahn et al [1] proposed an innovative polymer concrete sleeper for reducing rolling noise of high-speed train systems. The internal structure design of high damping concrete sleepers was conducted by installing polymer concrete to cement concrete sleepers. By mixing polymer and cement concrete, the damping performance of the meta-structure of sleepers was improved. However, the authors evaluated the proposed concept by the rolling noise modelling of slab tracks. Such the application was not well justified in the paper since the rolling noise frequency spectra often appear at a relatively low frequency range [2, 3]. Note that the most noise issues related to high speed rail systems tend to associate with high frequency noises such as aerodynamics, curve noise, break noise and so on. The limited justification with respect to cost/benefit by Ahn et al [1] would then discourage the industry’s adoption of material damping improvement. In fact, recent studies have shown more benefits of damping improvement in concrete sleepers [4-10].