Characterizing Ballast Degradation through Los Angeles Abrasion Test and Image Analysis

Abstract

Ballast fouling, often associated with deteriorating railroad track performance, refers to the condition in which the ballast layer changes its composition and develops a much finer grain size distribution. Fouling is commonly caused by degradation or breakage of ballast aggregates under traffic loading, although other fine materials including but not limited to coal dust, fine-grained subgrade soils, and sand can also contaminate a clean and uniformly graded ballast layer. An experimental approach is described to characterize stages of railroad ballast degradation studied through Los Angeles abrasion testing in the laboratory. An aggregate image analysis approach is used to investigate ballast particle abrasion and breakage trends at every stage through detailed quantifications of individual ballast particle size and shape properties. The experimental study indicated that the fouling index (FI) commonly used by practitioners was indeed a good indicator of fouling conditions, especially when all voids created by larger particles were filled by fine materials as FI values approached 40. Image analysis results of ballast particles larger than 9.5 mm (3/8 in.) scanned after a number of turns of the Los Angeles abrasion drum showed good correlations between percentage changes in aggregate shape properties, that is, imaging-based fatness and elongation, angularity and surface texture indexes, and the FI. The establishment of such relationships between in-service track fouling levels and ballast size and shape properties with similar field imaging techniques would help to understand field degradation trends better and as a result improve ballast serviceability and life-cycle performance.

Characterization and prediction of permanent deformation properties of unbound granular materials for Pavement ME Design

“…Among these properties, particle size gradation, dry density and moisture content are considered as basic performance indicators. Wet ball mill value and LA abrasion are used specially to evaluate the durability of coarse aggregates, while Atterberg limits and sand equivalent are applied to fine aggregates [22]. The existing studies focused on the prediction of the permanent deformation properties of UGM using these indicators [9,[15][16].…”

Effects of Ballast Degradation on Permanent Deformation Behavior From Large-Scale Triaxial Tests

“…The outlined procedure was repeated until enough materials were generated for conducting large-scale triaxial tests and all the generated degraded ballast material were evenly mixed before preparing the triaxial test specimens. Further details on generating degraded ballast material through LA abrasion tests have been provided elsewhere [7]. The gradations of clean and degraded ballast specimens (after 1500 turns of LA abrasion test) are shown in Figure 2.…”

“…sieve were hand collected to conduct image analyses using the recently enhanced University of Illinois Aggregate Image Analyzer (E-UIAIA) (see Figure 4) to quantify the shape property changes of ballast particles after degradation. Details of image analyses of aggregate particle shapes before and after the LA abrasion tests can be found elsewhere [7]. These shape indices can also be used in the future as the essential morphological data to generate ballast aggregate particle shapes as 3D discrete elements for a currently developed ballast DEM model.…”

Behavior of Geogrid Reinforced Ballast at Different Levels of Degradation

“…This LA abrasion test procedure was repeated until enough degraded ballast material was generated. More details on the steps followed to generate the degraded ballast through the LA abrasion testing have been provided elsewhere (Qian et al 2014). Fig.…”