General
- Crushed stone is any type of natural rock that, in order to be mined, has to be first blasted from its natural state in the ground, and then
processed (crushed and screened). The most common types of stone processed into crushed stone include limestone and dolomite, granite,
and traprock. Smaller amounts of marble, slate, sandstone, quartzite, and volcanic cinder are also used.
Production
- Crushed stone makes up 85 percent of aggregate production; construction sand and gravel, about 15 percent. North Carolina is the eighth
largest crushed stone producing state in the U.S. Aggregate is produced from about 135 crushed
stone quarries and about 500 sand and gravel sites throughout the state. Crushed stone, sand and gravel plants
account for 85 percent of all permitted mining operations. There is
aggregate mining in 80 of North Carolina's 100 counties.
- The average production life of a crushed stone quarry is 40 to 50 years or more. Sand and gravel deposits are typically worked out in much
shorter time. Crushed stone Production operation is used to make concrete and asphalt roads,
concrete for homes and office buildings, and is used in a wide variety of erosion control projects. Aggregate operations are relatively long lived and are vital to the economic health of
communities.
- Crushed stone is produced in almost every state in the U.S. The type of crushed stone mined from any particular state depends on the
general geology and rocks of the state. For instance, crushed limestone and dolomite is typical Indiana,
Illinois and Ohio, marble and granite from Vermont, etc. Even though it is quarried and processed all over the United
States, a small number of states account for more than half of
the total crushed stone production. These states, in decreasing order of amount of stone produced, are Texas, Pennsylvania, Florida, Georgia,
Illinois, Missouri, Ohio, North Carolina, Virginia and Tennessee.
- Major rock types processed by the crushed stone industry include limestone, granite, dolomite, traprock, sandstone, quartz, and quartzite.
Minor types include calcareous marl, marble, shell, and slate. Rock and crushed stone products generally are loosened by drilling and
blasting and then are loaded by power shovel or front-end loader into large haul trucks that transport the material to the processing
operations.
Application & Technology
- The crushed stone sand products can be used in conjunction with concrete aggregates or by themselves to achieve desired finishes on precast
concrete products as well as many other applications where natural stone color is required. Decorative crushed stone chips are available in
many different colors and sizes to use as ground cover around homes, offices, etc, in flower beds and around shrubs.
- Tremendous technological advances in stone crushing have taken place in the post- second world war period to build back the war-torn
countries. Modern mechanized construction and the need for high strength concrete and asphalt mixes have bought in new quality standards
for aggregates with severe conditions.
Market
- Crushed stone is a high-volume, low-value commodity. The industry is highly competitive and is characterized by thousands of operations
serving local or regional markets. Production costs are determined mainly by the cost of labor, equipment, energy, and water, in addition to
the costs of compliance with environmental and safety regulations. These costs vary depending on geographic location, the nature of the
deposit, and the number and type of products produced.
- Despite having one of the lowest average-per- ton values of all mineral commodities, the constant dollar price of crushed stone has changed
relatively little during the past 20 years. As a result of rising costs of labor, energy, and mining and processing equipment, the average unit
price of crushed stone increased from $1.58 per metric ton. Increased productivity achieved through increased use of automation and more
efficient equipment was mainly responsible for maintaining the prices at this level.
- Transportation is a major factor in the delivered price of crushed stone. The cost of moving crushed stone from the plant to the market often
equals or exceeds the sale price of the product at the plant. Because of the high cost of transportation and the large quantities of bulk
material that have to be shipped, crushed stone is usually marketed locally.
- Some industry is at a critical juncture in the push to find new markets for fine materials. The U. S. Geological Survey (USGS) estimates the
amount of crushed stone produced in the next 25 years will total slightly more than the quantity produced during the last century.
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