A Study on the Evolution of Ballast Particle Surface Damage

Abstract

The role of railway ballast is to spread traffic loads to the underlying ground. The contact area between ballast particles is often very small, leading to high contact stresses and surface abrasion, which is considered to degrade ballast quality and eventually necessitating ballast replacement. It is desirable to recycle and reuse as much of this “life-expired” ballast as possible, in whole or in certain particle sizes, as it would lead to a more sustainable engineering practice. However, research on the effect that particle surface damage has on the mechanics of ballast is required to understand the differences in behavior between recycled and fresh ballast, with a view to improving performance and increasing the length of maintenance cycles. This paper presents a study of ballast particle surface damage in terms of surface roughness using variable focus microscopy. Nanometer-scale surface scans of fresh and recycled ballast particles were acquired at predetermined resolutions and preselected areas. Methods of evaluating surface roughness for railway ballast are proposed, which indicate significant differences in roughness between fresh and recycled ballast. Laboratory tests with a Micro-Deval apparatus were used to quantify damage and the corresponding link to surface roughness.