Aggregate Production: Sourcing and Processing Methods

1. Production of aggregates

2. Where does gravel come from • Mines – rivers, banks, quarries • Rivers – use dragline to mine gravel from river • Banks – veins of gravel run thru a sand pit. Gravel mined by front end loader • Quarries – rock blasted from walls of quarry, loaded on trucks and crushed • Most gravel needs to be crushed

3. Rock Crusher • Reduce gravel to a smaller size • T 7-1 • F 7-1, 7-2 • Limemill – makes lime • Crusher output depends on crusher size and type, crusher settings, feed size, crusher speed, & other operating conditions F 7-3 • T 7-2 – T 7-3 specs • Primary crusher – first crusher in series • Secondary & tertiary crushers

4. Feeders and Screens • Feeders supply gravel to crusher • Apron – hopper box over plate feeder F 7-4 • Reciprocating plate • Vibratory • Belt – uses hopper to feed belt • Grizzly – used over hoppers to remove oversize material – series of bars

5. Feeders and Screens • Screens • Separate aggregate by size for storage, blending, recrushing • Rotating, vibrating (horizontal, inclined) • Usually in a deck of 2 or more screens F7-5 • Scalping screen removes oversized materials • Capacity based on • Screen size, screen opening size, slope of screen, position in deck, amount of oversize and half size material, material conditions, shape, weight. • F 7-6, Ex 7-1

6. Crushing Cycle • F 7-7 • Ex 7-2

7. Washing & Belt conveyor • Need to wash aggregate before and after crushing • Scrubber drums – inclined revolving drum with fins and spray nozzles • Wet screens – screens with spray nozzles overhead • Log washers – revolving auger paddles in a tub of water • Sand Dehydrators – rotating augers in an inclined trough • Clarifying tank – takes water & fines and clarifies water • Belt conveyor – major piece of equip in quarry – carries aggregate from place to place • Radial stacker – conveyor on a pivot to rotate