Evaluating Methods for Ball Mill Disaggregation of Slakable Rock and Fine-Grained Soil

ABSTRACT Geotechnical laboratory tests such as grain size analysis, Atterberg limits, and residual strength and swell-consolidation testing on remolded specimens require disaggregating a sample into its constituent particles. Specimen preparation typically involves hand processing samples with a mortar and rubber-tipped pestle until they pass a designated sieve size. Ball milling is an alternative to hand processing and has the potential to expedite the preparation process and result in more complete disaggregation, leading to more accurate test results. For ball milling to become a validated specimen preparation method and gain wide acceptance, it must be standardized. The research presented here seeks to further the efforts toward standardization by evaluating the effects of ball size, ball material, and milling duration on geomaterials including high plasticity clay, elastic silt, shale, claystone, and clayey sandstone. The research also presents the results of ball milling a fine aggregate (concrete sand) to assess the potential for grain pulverization in each milling scenario. Ball mill performance is material dependent, but for all materials evaluated in this study, ball milling induced a higher degree of disaggregation than hand processing in all scenarios. Grain pulverization from metal ball milling scenarios was evident, especially in materials with higher sand contents. Parameters obtained from ball milling were normalized by hand processed results, and the trends suggest that ball mill processing causes a greater increase in liquid limit than plastic limit compared to hand processing.