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The process is simple--Make little rocks from big rocks.
Crushed stone and sand and gravel are the main forms
of natural aggregate used in the United States. Aggregate
is used in nearly all residential, commercial, industrial
building construction and in most public-works projects
such as roads and highways, bridges, railroad beds,
dams, airports, water and sewer systems, and tunnels.
Construction of one mile of four-lane interstate highways
requires 85,000 tons of aggregate. An average six room
house requires 90 tons of aggregate.
Crushed stone or aggregate is crushed rock, boulders,
or large cobbles. It tends to be angular with sharp
edges. Most crushed stone is quarried from bedrock that
is blasted, mined, crushed, and then processed into
aggregate. Because aggregate is a high-bulk, low-cost
commodity, the transportation cost to the construction
site is a significant part of the total cost. Therefore,
it is commonly used within 20 miles of the place of
extraction.
Aggregate is produced from open pits in three major
steps: (1) site preparation, (2) mining or extraction,
and (3) processing. Site preparation consists of preparing
the site and construction of berms, roadways, and processing
equipment. Mining/extraction is removing the material
from the deposit and transporting it to the processing
equipment. Processing involves equipment such as dozers,
loaders, crushers, screens and other equipment to process
the aggregate into a finished product.
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While production is occurring so is the reclamation
of the site. Aggregate mining is generally viewed as
an interim use of the land, not the final use. The primary
goal of reclamation is to return the land to an alternative
beneficial use. Residential developments are a popular
use for reclaimed sites. Reclaimed pits or quarries
have also been converted to industrial and commercial
properties or to office parks, golf courses, parks and
recreation areas, storm-water management, or farmland.
Our society is faced today with a significant problem
relating to our landfills. As space in our landfills
diminishes, it becomes important to preserve the precious
space by diverting any product that can be recycled.
The mining industry provides a recycle service by taking
concrete, asphalt, and other rubble generated in construction
and demolition (C&D) and using it in its processing
to generate a recycled product that is in many circumstances
better than a 100% native product.
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