Effect of moisture content and broken kernels on the bulk density and packing of corn

Shelled yellow dent corn samples were conditioned to three moisture content levels (12%, 15%, and 18% w.b.) and mixed with a prescribed amount of broken corn particles of known size (geometric mean diameter of 1.0, 1.4, 2.0, 2.8, and 4.0 mm) and concentration (2.5%, 5.0%, and 7.5% by weight) levels. The initial bulk density and grain compaction under simulated overburden pressure tests were determined for each sample. Uniaxial compression tests were performed for seven vertical pressure levels (3.4, 6.9, 14, 28, 55, 110, and 165 kPa) with a minimum of three replications each. Tests were performed at two locations with identical apparatus, which was fully described by Thompson and Ross (1983). These devices used compressed air injected beneath a rubber diaphragm to apply vertical pressure uniaxially to a volume of granular material. Deflections of the grain mass were measured with a dial gauge and were used to calculate changes in bulk density and grain packing. Statistical models were tested for the initial bulk density and packing factor as a function of moisture content, broken corn particle size, and broken corn concentration level and their interactions. For clean corn, the initial bulk density was inversely affected by grain moisture while packing increased slightly with grain moisture. For corn mixed with fines, the initial bulk density decreased with grain moisture and the interaction of broken corn particle size and concentration but increased with the interaction of grain moisture and concentration of fines. Packing of corn mixed with fines increased slightly with grain moisture and broken corn concentration. For a given pressure, the predicted bulk density from the developed model was within 4% of the observed value, which was within the variation among test replications and may in fact represent observed differences in bulk density caused by bin loading methods that have been reported by other engineers. The results can improve predictions by WPACKING, the ASAE standard for estimating capacities of cylindrical grain storage structures.