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Mechanical abrasion tests are an important basis for evaluating the suitability of rock for use as railroad ballast. This paper considers three such tests: Los Angeles abrasion, the test primarily used by North American railroads; Deval abrasion, the test primarily used by British Rail; and mill abrasion, a relatively new test being proposed for use in North America. The mill abrasion test is similar to the Deval test. Previous evaluations of the Deval and mill abrasion tests are summarized. Then test data generated by the authors are presented to show the effect of factors influencing the mill abrasion test results. Finally, mill and Los Angeles abrasion results obtained on a wide range of rock type are compared and evaluated using petrographic analysis.
Ranking of rock type by the mill test is different than by the Los Angeles test. The products of abrasion are quite different, too—the mill test primarily produces particles smaller than the No. 200 sieve, while the Los Angeles test primarily produces particles larger than the No. 200 sieve. Thus these two tests appear to be influenced by different rock structural characteristics. In the mill and Deval tests, the amount of abrasion increases with increasing particle size. Also, the amount of abrasion is significantly greater for freshly crushed particles than for worn particles. In the mill test the abrasion is significantly greater when the test is conducted wet than when conducted dry. The petrographic analysis was useful in explaining the differences in results for the various rock type.
Professor of civil engineering, University of Massachusetts, Amherst, MA
Engineer, Parsons, Brinckerhoff, Quade and Douglass, Inc., Boston, MA
Stock #: GTJ10173J