Ural Federal University named after the first President of Russia B. N. Yeltsin, Ekaterinburg, Russia:

V. B. Ponomarev, Assistant Professor, Candidate of Engineering Sciences, v.b.ponomarev@urfu.ru

Rock breaking waste (screenings) are widely used in production of various grade concrete. A shortage of screenings is high content of dust fractions, which increases consumption of cement. The process of concentration of screenings means separation of weak varieties and impurities which lower the material quality, and grading the concentrate material based on strength. This operation uses dry or wet approaches. Wet separation plants are mostly inoperative in winter, require considerable expenditures connected with cleaning of flush water in clarification tanks and need recycling water supply. Dry separation of screenings is feasible year round but requires special design separator. The article describes the design of commercial pneumatic classifier featuring a vibrator mounted directly on separating screen, which allows dedusting of screenings at natural moisture content. The classifier was trialed in a ballast quarry, where secondary processing involved chalky rocks from dumps with a view to obtain additional product (large-fraction ballast) and have extra dumpunoccupied land. Rocks were crushed and screenings were fed in the classifier. The trial has shown that dry separation of screenings in such design classifier allows production of small-fraction ballast and mortar sand with dust content not higher than 5% at the initial material moisture content up to 7%. The achieved capacity of the classifier ranged from 40 t/h (moisture content of 7%) to 85 t/h (moisture content of 3%).

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