Aggregate quarry located near Raleigh, NC
Photo courtesy Wake Stone Corp.
In the foreground 50-ton-capacity haul trucks are loaded by hydraulic shovels. A drill is positioned on a 40-foot high bench. The drill is preparing holes to hold explosives which will break the rock into pieces that can be loaded into the trucks and taken to the primary crusher. The drill utilizes a compressed air powered "hammer" in the bottom of the hole. This down-hole type drill helps minimize noise to the surrounding area.
Rock that is too large for the primary crushed is being broken by the crawler-mounted hydraulic machine (upper left). A water truck sprays water on rock that was recently broken by the explosives. The water spray helps reduce dust.The conveyer assembly (upper right) carries rock to the sizing plant located on the surface just out of view. Large rocks are crushed to 12 inches in diameter or less by the primary jaw crusher. The material is further reduced in size by the secondary cone crusher.
Crushed stone is used to make concrete and asphalt roads, concrete for homes and office buildings, and in a wide variety of erosion control projects.
Mines are permitted before production begins. A comprehensive reclamation plan is part of the permitting.
Aggregates are construction materials of crushed stone, sand and gravel. About 10 tons of aggregates are required annually for each North Carolina citizen. A typical residential subdivision requires about 300 tons of aggregate per home.
The single largest market for aggregates is road and street construction, including base and asphalt paving for highways, parking lots and other pavements. One mile of typical 2-lane asphalt road with aggregate base requires about 25,000 tons. Other large markets are portland cement concrete for bridges, pavements and building structures, riprap and erosion control stone, and railroad ballast. Approximately 50 percent of all aggregate is used for publicly funded construction projects such as highways, water and sewer systems, public buildings and airports.
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.
Permitting and Environment
The North Carolina Mining Act, passed in 1971, and its regulations require any aggregate mining operation of one acre or more to apply for and receive North Carolina mining permit. The permit is issued for 10 years, but can be withdrawn if all requirements of the permit are not complied with. Many other local and state permits and environmental regulations control the operation of aggregate plants. All sites must be reclaimed before the reclamation bond will be released at the conclusion of mining.
Once reclaimed, crushed stone quarries are desirable as water reservoirs or recreational lakes, often with residential subdivisions nearby. Sand and gravel sites, also, are useful as wildlife habitat, agricultural fields or as lakes for a variety of uses, including groundwater recharge. Wetlands are often created as a result of mining. The industry is very sensitive and responsive to its need to be a good steward of the environment and a good neighbor in the community.