Crushed stone, or aggregate, 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. Approximately 50 percent of all aggregate is used for publicly funded construction projects - i.e., highways, water and sewer systems, public buildings, airports and other county and municipal public works projects.
It's a BlastThe photo to the upper left is a view of Wake Stone Corp.'s crushed stone quarry near Raleigh, N.C. It is located near an interstate so the crushed stone can easily be trucked to road construction sites and to concrete plants. A drill is positioned on a 40-foot-high bench. The drill is preparing holes to hold explosives that will break the rock into pieces. The drill utilizes a compressed air-powered hammer in the bottom of the hole. This type of drill helps minimize noise to the surrounding area. In the foreground, diesel-powered 50-ton-capacity haul trucks are loaded by diesel-powered hydraulic shovels with 7.5-cubic-yard bucket capacity. Air rotary self-propelled drills bore 6-inch diameter holes to a depth of 44 feet which are filled with just enough explosive to break the rock.
Water's Double DutyWater regularly is sprayed on the broken rock to control dust generated as the rock is being loaded onto the haul trucks. The addition of water at this stage provides moisture that helps control dust throughout the whole production process. Water trucks also keep the haul road wet from the primary crusher to the mining face to reduce dust.
Water in the crushed stone quarry is collected at the lowest elevation in an area called a sump. In this quarry, the water is conserved and recycled to wash the crushed stone in the sizing plant. The submersible pump is powered by a 250-HP electric motor. A motor this powerful is needed because the water has to be lifted almost 250 feet in elevation to the land surface to discharge the water. At the surface of this crushed stone operation is a pond that is used to recycle and conserve product wash water used in the sizing plant.
Future ConcernsA ready supply of crushed stone is necessary to support future economic development. The biggest concern facing the aggregates industry in coming years is obtaining zoning favorable to the extraction of aggregates. Near urban areas where construction materials are critically needed, it is most important to allow appropriate zoning and the necessary permits to assure a continued supply of aggregates.