Facts & Figures Book - KPI-JCI

Washin g/Classifyin gWASHINGINTRODUCTIONClean aggregates are important to the constructionindustry. Yet producers of aggregates frequently arehard-pressed to meet all requirements for “cleanliness.”Materials engineers constantly strive to improve concreteand bituminous mixes and road bases. While hydraulicmethods are the most satisfactory for cleaning aggregatesto achieve the desired result, they are not always perfect.It is still necessary to accept materials on the basis ofsome allowable percent of deleterious matter.In the broadest terms, construction aggregates arewashed to make them meet specifications. Specifically,however, there is more to the function of water in processingaggregates than mere washing. Among thesefunctions are:1. Removal of clay and silt2. Removal of shale, coal, soft stone, roots, twigsand other trash3. Sizing4. Classifying or separating5. DewateringBecause no washing method can be relied upon to beperfect, and because some materials may require toomuch time, equipment and water to make them conformto specifications, it is not always economically practicalto use such materials. It is important, therefore, to testthe source thoroughly beforehand to ensure the desiredfinished aggregates can be produced at reasonable cost.The project materials engineer can be of immeasurablehelp in determining the economic suitability of thematerial, and generally must approve the source beforeproduction begins, anyway. Further, many manufacturersof washing equipment will examine and test samples todetermine whether their equipment can do the job satisfactorily.No reputable equipment manufacturer wants torecommend his equipment where he has a reasonabledoubt about its satisfactory performance on the job.92