Sampling, reconstituting, and gradation testing of railroad ballast

Ballast characterization is important for predicting ballast performance and serviceability in track. This paper investigates ballast sampling methods and sizes, reconstitution, splitting, and gradation testing for appropriate characterization of in-track ballast. This paper will review various ASTM test methods and determine how these procedures should be applied to railroad ballast sampling and testing. For example, ASTM D75/75M, Standard Practice for Sampling Aggregates, and ASTM C136/136M, Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates, require sampling ballast with a maximum particle diameter of 75 mm (3 in.) and about 16 to 17 three-quarters full 5-gal buckets to meet the requirements. These methods are important because of the difficulty of obtaining representative in-field ballast samples. Undisturbed ballast samples are not feasible because of the nature of unbonded granular particles, so sampling emphasis must be placed on best methods to collect and reconstitute field ballast conditions in the laboratory. Another aspect that will be discussed is how to deal with local variations in ballast fouling and degradation that can result in significant differences in ballast characteristics. For example, the ballast underneath the tie (i.e., the ballast of interest) will likely be more degraded and fouled than shoulder or crib ballast, but this is also the most difficult location to obtain without track disturbance.