Establishing linkages between ballast degradation and imaging based aggregate particle shape, texture and angularity indices

As railroad ballast ages, it is also progressively fouled primarily due to material degradation with particle breakage filling the void spaces. This paper focuses on investigating ballast performance associated with degradation and fouling levels in the field by analyzing both clean and deteriorated ballast particle size distributions and morphological properties. Los Angeles Abrasion (LAA) tests were conducted on limestone and granite type ballast materials to establish particle crushing or degradation trends associated with increased track usage. These degradation trends were successfully linked to before and after test values of aggregate imaging based shape indices, such as the flatness and elongation ratio, angularity index and surface texture index established using the University of Illinois Aggregate Image Analyzer. At around 400 drum turns of the LAA test, original uniform ballast gradations became more "well-graded" according to the Unified Soil Classification System and approximately two thirds of the particle angularity was lost when compared to the full 1000 turns.