quarryollogy.doc

Industry Overview The process is simple Make big rocks into little rocks. The aggregates industry in the United States is in a state of growth as funding legislation for roadbuilding continues to spark a growing demand for aggregate, and new technologies have increased production capacities.Industry consolidation is on the rise as large producers like Vulcan Materials and Martin Marietta Materials gobble up smaller operations. This trend, coupled with the new influx of cash, means that the aggregate industry is now under the watchful eye of bullish investors. In Washington, the industry is overseen by one major association, which resulted from the merger of the The National Aggregates Association and National Stone Association in 2000. The industry is policed by the Mine Safety and Health Administration MSHA. Natural aggregate Crushed stone and sand and gravel are the main types of natural aggregate used in the United States. Aggregate is used in nearly all residential, commercial, and 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. The widespread use of aggregate results not only from its general availability but also from economic considerations. Aggregate of good quality commonly is available near the site of use at relatively low cost. This aggregate can essentially be obtained and used with a minimum of processing. However, even though crushable stone and sand and gravel resources are widely distributed throughout the United States, availability is not universal. Some areas are devoid of sand and gravel, and some potential sources of crushed stone may be lacking or covered by overburden that is too thick to allow economical surface mining. In some areas, moreover, aggregate does not meet the physical-property requirements for certain uses, or it contains mineral constituents that react adversely when used in cement concrete. Furthermore, citizens commonly prefer that crushed stone and sand and gravel not be mined nearby. Many citizens do not support mining, in part because they do not recognize the dependence of society on aggregate. Direct personal use is very little, if any, and individuals may not recognize aggregate mining as a necessary land use, even though the need for the commodity is constant. Thus, zoning, regulations, and competing land uses may restrict or preclude aggregate mining. Now, and in the future, the rebuilding of deteriorated roads, highways, bridges, airports, seaports, waste disposal and treatment facilities, water and sewer systems, and private and public buildings require that enormous quantities of aggregate be mined or quarried. Long-range planning is necessary to help ensure adequate economical supplies of high-quality aggregate while simultaneously protecting the public from unwanted effects of mining. This report provides an overview of the aggregate industry and of the availability of natural aggregate as an aid to those involved in protecting, conserving, and developing the nations resources. Production and uses of aggregate Sand and gravel are produced commercially in every state in the United States, and crushed stone is produced in 48 of the 50 states. Aggregate production accounts for about half of the nonfuel-mining volume in the United States. There are more than 9,000 quarry operations located in the United States. Individual crushed-stone quarries range in size from small operations reporting production of less than 50,000 short tons annually to those with production of more than 10 million tons. For a variety of reasons, including the large investment in capital equipment, crushed-stone operations tend to be very large. It is estimated that the top 10 producers of aggregate account for more than 20 percent of total aggregate production. As industry consolidation continues, this percentage will grow. Individual sand and gravel operations range in size from those reporting production of less than 25,000 short tons annually to those with production of more than 2.5 million tons. In contrast to crushed stone operations, many sand and gravel operations are relatively small. Production of crushed stone and sand and gravel is necessary to many industries in the United States. Sand and gravel or sand alone is used for sand casting in foundry operations, glass manufacturing, abrasives, and filtration beds of water-treatment facilities. Crushed stone is used as a source of calcium for fertilizers, in metallurgy, and as the major component in the manufacture of cement and lime. Crushed stone may also be used in filtration systems and in the manufacture of glass. Crushed stone and sand and gravel are primarily used for aggregate in the construction industry, especially in cement concrete for residential and commercial buildings, bridges and airports, and as cement concrete or bituminous mixes asphalt for highway construction. A large percentage of aggregate is used without a binder as road base, for road surfacing, and as railroad ballast. Aggregate is also used to provide drainage around house foundations, for septic-system leach fields, for snow and ice control, and as fill in wet or swampy land. Construction of one mile of four-lane interstate highway requires 85,000 tons of aggregate. And few homeowners realize that construction of an average six-room house requires 90 tons of aggregate or that construction of one average-size hospital or school requires 15,000 tons. Basic concepts and terminology Natural aggregate consists of rock fragments that are used in their natural state or after mechanical processing such as crushing, washing and sizing. Quarry stone is crushed and processed to produce aggregate. In this report, the term natural aggregate or aggregate includes mined or quarried stone that has been crushed, washed and sized, as well as sand and gravel. Gravel generally is considered to be material whose particles are 3/16 in. to 3 in. in diameter and tend to be rounded with smooth edges. Sand and gravel aggregate is a mixture aggregation of sand and gravel in which gravel constitutes about 25 percent or more of the mixture. Gravel may be the predominant material in a natural deposit, but typically it occurs in layers or lenses with sand. Crushed stone, as its name implies, is artificially crushed rock, boulders, or large cobbles. Crushed stone tends to be angular with sharp edges. Most or all of the surfaces on the clasts or particles are produced by the crushing operation. Most crushed stone is quarried from bedrock that is blasted, mined, crushed and processed into aggregate. Selection of the bedrock to be used for crushed stone depends primarily on the physical and chemical properties of the rock. Physical and chemical requirements of natural aggregate Most people probably assume that natural aggregate is used chiefly in concrete. Much natural aggregate, however, is unsuitable for such use. We all have seen crumbling driveways and bridges or cracks in sidewalks and patios. Concrete deterioration has many causes, but unsuitable aggregate, containing deleterious ingredients, can be a primary or secondary cause of the problem. Natural aggregate varies widely in quality, depending on the source. To ensure that aggregate is suited for particular uses, testing laboratories compare aggregate properties with predetermined standards. The most generally used national guidelines for specifications and testing procedures are those of the American Society for Testing and Materials ASTM. National specifications must be broad, and at best they serve as general guidelines. Local specifications need to reflect specific uses, availability and quality of local aggregates, and local climatic conditions. Suitable aggregate consists of clean, uncoated particles of proper size and gradation, shape, physical soundness, hardness and strength, and chemical properties. The final use of the aggregate determines the specific properties sought. Generally, specifications for aggregate used in cement concrete or bituminous mixes are more stringent than are those for other construction-related uses. Mechanical sieving or screening is used to grade, or sort to size, aggregate. In general, aggregate for cement concrete should be well-graded throughout the sand and gravel range of particle sizes, although gap grading aggregate with specific particle sizes missing may be used and may be necessary for some products. Specifications for bituminous mixes are dependent on the pavement design, and therefore, no general statement can be made regarding the sizes of aggregate used. Particle shape affects both the grading limits of aggregate used in cement concrete and the workability of the concrete. The presence of excessive amounts of angular particles can require addition of a greater percentage of sand to the mixture, which in turn requires more water and cement. In contrast, because intergranular contact provides strength in bituminous mixes, angular particles generally are desirable. Smooth particle surfaces offer little assistance in holding the aggregate in place in bituminous mixes. In both cement concrete and bituminous mixes, too many flat or long particles may be harmful. Physical soundness is the ability of aggregate to resist weathering, particularly freezing-thawing and wetting-drying cycles. Generally, aggregate that contains weak, easily broken, absorptive, or swelling particles is not suitable. Specifications for physical soundness are similar for use in cement concrete and bituminous mixes. Hardness and strength of aggregate affect the ability of the final product to resist mechanical breakdown. The breakdown of soft or weak particles during handling or mixing is deleterious in both cement concrete and bituminous mixes. Such breakdown affects the grading of the aggregate, and it can be aggravated by weathering or traffic. Specifications for hardness and strength of aggregate are similar for use in cement concrete and bituminous mixes. Ideally, the aggregate is an inert filler, and it should not change chemically once in place. However, some aggregate contains minerals that chemically react with or otherwise adversely affect the concrete or bituminous mixes. In cement concrete, these chemical processes are reactions between the aggregate and the cement, solution of soluble materials, or oxidation of constituents. In bituminous mixes, chemical factors may influence oxidation of the asphalt or strip the bituminous film from the aggregate. When aggregate does not meet the required specifications, a number of corrective alternatives exist. These include 1 blending high-quality aggregate with the unsuitable aggregate to achieve an acceptable overall quality; 2 removing deleterious materials from the aggregate by processing techniques; 3 making adjustments during processing, such as recrushing to change particle shape; or 4 adding chemicals or making other adjustments to cement mixtures or bituminous mixes. A new process for roadbuilding, called Superpave, is changing the world of aggregate specifications as they apply to asphalt. What is Superpave The Superpave SUperior PERing Asphalt PAVEments system was developed by the Strategic Highway Research Program SHRP. The asphalt research program had three objectives To investigate why some pavements per well, while others do not. To develop tests and specifications for materials that will outper and outlast the pavements being constructed today. To work with highway agencies and industry to have the new specifications put to use. The Superpave system consists of three interrelated elements Asphalt binder specification. Volumetric mix design and analysis system. Mix analysis tests and a perance prediction system that includes computer software, weather database, and environmental and perance models. After five years of intensive research and testing, SHRP introduced the Superpave system. The Federal Highway Administration FHWA then assumed responsibility for further development and validation of the Superpave specifications and test procedures and initiated a national program to encourage the adoption of the Superpave system. As the Superpave system becomes more widely adopted, more and more highway projects are now required to meet these tighter specifications. Therefore, more of the aggregate produced today must meet tighter specs, as well. Geology Sources of aggregate, such as sand and gravel and rock for crushed stone, were ed by geologic processes. Volcanoes, glaciers, wind, rivers, and seas ed the shape and character of rock materials over millions of years. The gravel used today may have been deposited thousands of years ago - just yesterday geologically. Hard, dense limestone may have been deposited as a limy ooze hundreds of millions of years ago. When an aggregate supply is required, geological investigations can determine the location, distribution, and nature of potential aggregate in an area. Sand and gravel Sand and gravel deposits are products of erosion of bedrock and surficial materials and the subsequent transport, abrasion, and deposition of the particles. The principal geologic agent that affects the distribution of deposits of sand and gravel is water. Consequently, gravel is widely distributed and abundant in glaciated areas, in alluvial basins, and in, adjacent to, or near rivers and streams. Windblown deposits generally are fine grained and rarely used for aggregate. Stream-channel and terrace deposits Sand and gravel deposited by rivers or streams is widely distributed throughout the United States as stream-channel or terrace deposits. In hilly or mountainous areas, bedrock is chemically and physically weathered and is progressively broken into smaller and smaller particles. Chemically less resistant minerals are dissolved or altered into clay minerals; the more resistant minerals remain as rock fragments. Depending on the composition and structure of the bedrock and on the climate, land cover, and topography, the remaining soils may range in thickness from almost nothing to many tens of feet, and may range in composition from nearly all clay, through mixtures of clay, silt, sand, and gravel, to nearly all sand and gravel, to rubble. Gravity and sheetwash move some of this material downslope, where it s a deposit called colluvium. Eventually, the colluvium is moved into valleys of relatively high gradient streams. In the stream channels, rock fragments are subjected to abrasion, rounding, and sorting. The stream-transported material is deposited in channels and on floodplains and consists of sand and gravel in some areas and silt and clay in others. Erosion can alter an already-established floodplain. If the river or stream incises its channel, the older channel