Sand and gravel industries
The sand and gravel industries play a crucial role in construction and various industrial applications, being the most widely distributed construction aggregates globally. These materials are primarily extracted from glacial deposits, stream sediments, and beach deposits. Sand particles range in size from 0.05 to 4.76 millimeters, while gravel particles are larger, measuring up to 90 millimeters. The main use of sand and gravel is in construction, where they serve as fill material or as aggregates in concrete, with the U.S. producing over 1 billion metric tons of construction sand and gravel annually.
In addition to construction, industrial sands have specialized applications, including glassmaking and foundry use. The overall quality of sand and gravel deposits is influenced by factors like particle composition, shape, and chemical reactivity, which determine their utility in construction. Market dynamics are closely tied to population density and economic conditions, with demand for these materials fluctuating based on construction activity.
Environmental concerns associated with sand and gravel mining, such as land use conflicts and silica dust exposure, are increasingly significant. The industry must balance resource extraction with sustainable practices to mitigate impacts on local ecosystems and communities.
Sand and gravel industries
Where Found
Sands and gravels are widely distributed on the Earth’s surface; all fifty of the United States have producing deposits. Sand and gravel deposits are not spatially ubiquitous, however. Sand and gravel are heavy or dense, high in bulk, and low in value, and they cannot be shipped economically for long distances. Most sand and gravel in the United States and Canada come from glacial deposits, stream terraces and channels, including alluvial fans, or from beach deposits of either current or relict shorelines. Some specialty or industrial sands are derived from bedrock when more rigid control over the character of the sand is required.
Primary Uses
By far the greatest use of sand and gravel is in construction, where they may be employed as fill material or as the in concrete. Industrial sands are more specialized, and their uses demand higher quality. Most industrial sand is used to make glass or as molding sand in foundries. The United States produces more than 1 billion metric tons of construction sand and gravel and between 25 and 30 million metric tons of industrial sands.
Technical Definition
Sand particles are 0.05 millimeter to 4.76 millimeters in diameter. Gravel particles are larger, 4.76 to 80 or 90 millimeters in diameter. Sand fragments are composed almost entirely of single minerals, chiefly quartz, with significant fractions of feldspars and smaller proportions of mica, chert, and heavy minerals. Gravels, on the other hand, are usually fragments of rocks that are composed of several minerals. Gravels reflect the of the stream basin in which they are located, because this is the source of the gravel deposit. Most gravels are resistant, but if the source stream basin is underlain largely by soft sediments, the gravels are less valuable as a resource. Impurities in sand and gravel deposits consist of silts, clays, or excessive proportions of micas, soft sediments, or fragments that have an undesirable chemistry.
Description, Distribution, and Forms
Sand and gravel are the most widely distributed of the construction aggregates, are the easiest to recover or mine, and require only simple beneficiation, usually washing and screening. Historically, in the United States, they have dominated the market for aggregates. However, for many purposes, even in rough construction, they are not as suitable as their closest competitor—crushed or rock—because sharp-edged broken stones interlock, unlike gravels, which are rounded by stream transport.
Both the quality of a sand or gravel deposit and its location with respect to the market determine the resource value of that deposit. Quality concerns include the lithology of the particles (their chemical and physical character), the size and shape of the particles, their resistance to and cracking, the potential for chemical reactivity, and the freedom of the deposit from organic matter, silt, and (in other words, the deposit’s cleanness). Fortunately, most sand deposits are dominated by quartz particles, which are both resistant and inert.
Gravels can pose a greater problem because of the variety of rocks in different drainage basins. Soft rocks or those that relatively rapidly (shales, friable sandstones, some limestones, and certain rocks, especially schists and slate) do not make valuable gravels. A variety of rocks react with the alkalies in portland cement and must be avoided for that particular use. Iron impurities rust, and certain other minerals weather or decompose rapidly. These conditions lead to weakened construction and are avoided. Thus, all gravel deposits are not equally valuable as resources, even if they are favorably located with respect to markets. Just as high-quartz sands are more valuable, so are gravels with high proportions of resistant rocks of the proper chemical composition.
Market, in the case of construction sand and gravel, is defined by population and appropriate construction, such as highways. Thus, a sparsely populated region serves as a significant market while interstate highway construction is under way but becomes a small market when the highway is completed. The fortunes of construction sand and gravel suppliers wax and wane with the general economy; boom times of expanded residential or office building construction provide an excellent market. Recessions with little construction activity result in a shrinkage in production.
The low-value, high-bulk character of sand and gravel dictates that only surface mining is economical (the exception is some higher-value industrial sands, which may be mined underground). Moreover, the mining must be close to metropolitan centers, where most new construction occurs. Inevitably, the urban centers grow and encounter the sand and gravel mining. Zoning may then displace the mining to more remote locations because of complaints about dust, noise, truck traffic, or the unsightliness of gravel pits. Restrictions on the use of wetlands are increasing, particularly in cases in which endangered species may be involved. There is also an increasing concern with silica dust, which may affect specialty industrial sands.
History
A measure of the overall relationship between population numbers and construction may be seen in the history of sand and gravel production in the United States. During the Depression of the 1930s annual production was about 180 million metric tons. In 1946, before widespread construction began in the postwar era, production was about 230 million metric tons. By 1960, construction had expanded significantly, and production stood at 641 million metric tons. In 1970, residential construction and the interstate highway program were active; production was about 856 million metric tons. By 1994, although population had grown, highway and commercial construction had declined, and total sand and gravel production was just more than 918 million metric tons, of which about 27 million metric tons were industrial sands. By 2008, US production of sand and gravel for construction was about 1 million metric tons; for industrial use, about 30 million metric tons. By 2023, 698 million tons of construction sand and gravel were produced in the United States, while 120,000 metric tons of industrial sand and gravel were produced.
Throughout the post-World War II period, metropolitan population concentrations were far more important as markets for construction sand and gravel than were rural regions, which generally failed to generate construction in proportion to their population numbers. The major exception to this generalization is the interstate highway construction program, which generated temporary markets for sand and gravel in even the most sparsely settled portions of the country.
Obtaining Sand and Gravel
Nearly all gravel deposits, and most sand deposits, are found in stream sediments. Present-day stream deposits include channels, low terraces, and active portions of alluvial fans. Under these circumstances, sands and gravels removed by dredging or may be renewed by recurrent flooding or high streamflows. Relict stream deposits are those created by glaciation, including outwash fans and valley train deposits (the latter extending to the oceans from the glacial source), as well as relatively minor sources such as eskers, kames, and moraines deposited close to the ice margin. Most alluvial fans in western North America are also relict or inactive in that they were formed during the Pleistocene era and are not renewed by current geologic processes. In either case, virtually all sand and gravel are found in surficial deposits, which are frequently wetlands. This fact has advantages in terms of mining costs, but it also results in environmental problems and land-use conflicts.
Uses of Sand and Gravel
The overwhelming use of sand and gravel is in construction. Use of these materials for fill, base, or subgrade of highways is the least demanding of quality requirements, and sand and gravel may not even be washed or screened for these uses. Usage in concrete, however, is far more demanding, both in terms of size-of-particle requirements (sorting, screening, or crushing may be used to produce the desired size) and in terms of quality (avoiding easily weathered or alkali-reactant rocks). Substitutes for sand and gravel in construction are crushed stone or rock and lightweight aggregates. Lightweight aggregates, largely volcanic rocks, are increasingly employed in specialty concretes and building blocks. Crushed rock is utilized where more rigid specifications for concrete exist or in regions where sand and gravel are scarce (this high-bulk, low-value commodity is shipped largely by truck, and rarely for distances greater than 30 meters).
Industrial sand and gravel encompass a variety of uses, each with its own specifications as to desirable characteristics in the product and its own market—hence the resultant location of mining activities. Glassmaking and foundry or molding sands lead the list of uses by tonnage; the former requires more rigid specifications and is located where construction is active, and the latter is located where metalworking is significant. The industry uses significant quantities for hydraulic fracturing of oil and gas wells. Abrasives, especially for blast sands, also rank high. Each use or type of sand has competition from substitutes that may reduce the resource value of deposits or the profitability of an industry. Glass, for example, has largely been replaced by aluminum and plastics as the material for containers in the food and beverage industry. Abrasives have come under fire for reasons of health, such as the breathing of dust by workers.
Bibliography
Bell, Fred J., and Laurance J. Donnelly. “Gravel, Sand, and Clay Pits.” In Mining and Its Impact on the Environment. New York: Taylor & Francis, 2006.
Evans, Anthony M. An Introduction to Economic Geology and Its Environmental Impact. Malden, Mass.: Blackwell Science, 1997.
Gyr, Albert, and Klaus Hoyer. Sediment Transport: A Geophysical Phenomenon. Dordrecht, the Netherlands: Springer, 2006.
Hamilton, W. N., and W. A. D. Edwards. “Industrial Minerals in Western Canada Sedimentary Basin.” In Industrial Minerals and Extractive Industry Geology: Based on Papers Presented at the Combined 36th Forum on the Geology of Industrial Minerals and 11th Extractive Industry Geology Conference, Bath, England, 7th-12th May, 2000, edited by Peter W. Scott and Colin M. Bristow. London: Geological Society, 2002.
Harben, Peter W., and Robert L. Bates. Geology of the Nonmetallics. New York: Metals Bulletin, 1984.
Kogel, Jessica Elzea, et al., eds. “Industrial Sand and Sandstone.” In Industrial Minerals and Rocks: Commodities, Markets, and Uses. 7th ed. Littleton, Colo.: Society for Mining, Metallurgy, and Exploration, 2006.
Smith, M. R., and L. Collis, eds. Aggregates: Sand, Gravel, and Crushed Rock Aggregates for Construction Purposes. 3d ed. Revised by P. G. Fookes et al. London: Geological Society, 2001.
Yanik, Kevin. "USGS: Aggregate Production Dipped Slightly in 2023." Pit & Quarry, 11 Mar. 2024, www.pitandquarry.com/usgs-aggregate-production-dipped-slightly-in-2023/. Accessed 6 Jan. 2024.