Facts & Figures Book - KPI-JCI

PROCESSING OF AGGREGATESMuch of the equipment used in the processing of rawaggregates has been adapted from other mineral processingtechniques and modified to meet the specificrequirements of the crushed stone, sand and gravelindustry. Other types of equipment have been introducedto improve efficiency and final product. The equipment isclassified in four groups.1. Reduction equipment: Jaw, cone, roll, gyratory,impact crushers and mills; these reduce materialsto required sizes or fractions.2. Sizing equipment: Vibratory and grizzly screens toseparate the fractions in varying sizes.3. Dewatering equipment: Sand sorters, log washers,sand and aggregate preparation and fine andcoarse recovery machines.4. Sorting equipment. This can include various kindsof feeder traps and conveyor arrangements totransfer, stockpile or hold processed aggregates.As to method, there are two types of operations at mostsand and gravel pits and quarry operations. They include:1. Dry process: Here, the material is excavated bymachines or blasted loose and is hauled to a processingplant without the use of water.2. Wet process: This may involve pumping (dredgepumps) or excavation (draglines) of the aggregatematerial from a pit filled with water. The materialenters the processing operation with varying quantitiesof water.The ideal gradation is seldom, if ever, met in naturallyoccurring sand or gravel. Yet the quality and control ofthese gradations is absolutely essential to the workabilityand durability of the end use.The aggregate has three principal functions:1. To provide a relatively cheap filler for cementing orasphaltic materials.2. To provide a mass of particles that will resist theaction of applied loads, abrasion, percolation ofmoisture and water.3. To keep to a minimum the volume changes resultingfrom the setting and hardening process andfrom moisture changes.10