Facts & Figures Book - KPI-JCI

The ideal gradation is seldom, if ever, met in naturallyoccurring deposits. Yet the quality and control of thesegradations is absolutely essential to the workability anddurability of the end use. Gradation, however, is a characteristicwhich can be changed or improved with simpleprocesses and is the usual objective of aggregate preparationplants.Crushing, screening and blending are methods used toaffect the gradations of aggregates. However, even followingthese processes, the material may still requirewashing to meet specification as to cleanliness. Also,screening is impractical smaller than No. 8 mesh andhence, hydraulic separation, or classifying, becomes animportant operation.Washing and classifying of aggregates can be consideredin two parts, depending on the size range of material.Coarse material - generally above 3/8” (sometimes splitat 1/4” or 4 mesh). In the washing process, it usually isdesired to remove foreign, objectionable material, includingthe finer particles.Fine aggregates - from 3/8” down. In this case, it generallyis necessary to remove dirt and silt while retainingsand down to 100 mesh, or even 200 mesh.Washin g/Classifyin g93