Polyurethane coating of railroad ballast aggregate for improved performance

This paper presents preliminary findings of a new technology currently being tested in a research project at the University of Illinois. The effectiveness of elastomer polyurethane coating of ballast is evaluated for its ability to reduce aggregate breakage and resulting ballast fouling. Railroad ballast degradation and fouling related to aggregate breakdown under heavy axle loads, poor drainage, mud pumping, and water/ballast pockets are among the most commonly encountered track substructure (ballast, subballast, and subgrade soil) problems. The structural integrity of seriously fouled ballast can be compromised leading to track instability and ultimately, train derailments. Because of this serious consequence, costly ballast maintenance activities, such as undercutting, tamping, and shoulder cleaning, are routinely performed by railroads especially on tracks serving the heavy axle load unit trains. In the research project, clean AREMA No.4 aggregates along with the polyurethane coated particles were subjected to realistic field loading conditions in a large shear box test apparatus used for strength testing of ballast at full gradation. The urethane coated ballast was allowed to set for 1, 3, 7, and 14 days prior to subjecting the samples up to 10 shear passes. Shear and normal stress data were gathered during testing; and the fines generated by all tested samples were collected and analyzed. Early findings show a major increase in the shear strength gained with the polyurethane coating, a decrease in the breakdown of the coated ballast, and a decrease in particle reorientation which could lead to a reduction in ballast settlement.