A Compaction Test Method for Soil-Rock Mixtures in which Equipment Size Effects are Minimized
The development of a standard effort compaction test method for determining compaction characteristics of soil-rock mixtures having maximum particle sizes up to 51 or 76 mm (2 or 3 in.) is described. The method is based on results of a testing program to develop testing procedures for 305 and 457-mm (12 and 18-in.)-diameter molds in which equipment size effects are minimized, i.e., procedures where results for materials tested using a conventional 152-mm (6-in.)-diameter mold may be reproduced with the larger equipment required to test materials having maximum particles sizes of 51 and 76 mm (2 and 3 in.). The testing program consisted of a series of standard effort compaction tests performed using 152, 305, and 457-mm (6, 12, and 18-in.)-diameter molds on four test materials having a maximum particle size of 19.1 mm (3/4 in.) and either plastic or nonplastic fines. Hammer weight was isolated as the main testing variable for use in developing the procedure while maintaining as many features of the conventional procedure as possible. It was found that in the case of 305-mm (12-in.)-diameter mold tests, varying hammer weight did not produce significant effects on results and that 152-mm (6-in.)-diameter mold results could be reproduced with any of the hammers used. In the case of the 457-mm (18-in.)-diameter mold, it was found that 152-mm (6-in.)-diameter mold results could be reproduced with the heaviest hammer [59.6 kg (131.4-lbf) used in the 305-mm (12-in.)-diameter mold tests]. The test method resulting from the investigation utilizes a mechanical compactor equipped with 305 and 457-mm (12 and 18-in.)-diameter molds and a 59.6-kg (131.4-lbf) hammer with a 305-mm (12-in.) drop. Additional tests performed using the test method on minus No. 4 (4.76-mm) sieve fractions of the 19.1-mm (3/4-in.) maximum particle size materials produced significant differences in results due to varying equipment sizes, thus indicating it may be impossible to minimize equipment size effects to the same extent for finer gradations.