P&Q University Lesson 1: Industry Overview

By |  August 1, 2019

America’s crushed stone, sand and gravel producers – the construction aggregate industry – provide materials so essential to the nation’s quality of life that, without them, virtually nothing could be built. Unfortunately, the public knows relatively little about the aggregate industry, including the fact that it supplies about 2 billion metric tons of vital basic materials each year that are used in every sector of the built environment: residential and commercial construction, surface transportation, civil works, and environmental protection.

The total value of construction aggregate produced in 2013 was about $17.7 billion, contributing $40 billion to the U.S. gross domestic product. The aggregate industry workforce in 2013 was comprised of about 81,500 men and women working at about 10,000 operations around the United States. Still, tens of thousands more jobs in industries that provide machinery, equipment and services are dependent on aggregate production.

In fact, according to a study commissioned by the National Stone, Sand and Gravel Association (NSSGA), every $1 million in aggregate sales creates 19.5 jobs, and every dollar of industry output returns $1.58 to the economy.

Photo by Zach Mentz

Photo by Zach Mentz


U.S. aggregate production and growth increased steadily from the 1950s onward, principally because of higher demand created by post-World War II suburbanization and construction of the Interstate Highway System. Also, more than 95 percent of asphalt pavement and more than 80 percent of concrete sidewalk is made up of aggregate.

Historically, about 40 percent of the construction aggregate market was in road and other transportation-related projects. The remaining 60 percent was equally divided among residential construction, commercial construction and other public works aside from transportation. Those proportions changed somewhat during the Great Recession that began in 2007 and whose effects linger today. The transportation market contracted by about 10 percent, and the other markets rose proportionately.

The 1960s, 1970s and 1980s brought more demand for aggregate due to the requirement to maintain and upgrade the federal highway system and meet the surface transportation needs of a growing population. Much of the 1990s and the early 2000s saw internal industry growth, as larger companies acquired and merged with smaller producers and multinational ownership appeared.

Aggregate production hit an all-time high in 2006 at 3.09 billion metric tons of crushed stone, sand and gravel worth an estimated $21 billion. The workforce at that time was made up of about 121,000 direct employees.

Then, in 2007-08, with the advent of the Great Recession, aggregate producers were adversely affected and production fell off sharply as all sectors of the construction industry came, in many areas of the country, to a virtual halt.

Generally, producers were able to keep their heads above water through a lean period between 2007 and 2011. Some producers survived by seeking and finding alternative uses for their products and by downsizing or reducing production cycles.

Further complicating a recovery from the recession was the inability of Congress to come to grips with reauthorizing a long-term surface transportation program that included a fully funded federal highway system.

The years 2009, 2010 and 2011 were flat for the industry, but in 2012 production began inching up again as a slow recovery from the recession began to manifest itself. Most projections show incremental increases of production through the end of the 2010s, but levels are unlikely to rise to those of 2006 in the foreseeable future.


This photo is one of many from Pit & Quarry magazine’s extensive archives. Photo courtesy of the Construction Machinery Division of Clark Equipment Co.

This photo is one of many from Pit & Quarry magazine’s
extensive archives. Photo courtesy of the Construction Machinery Division of Clark Equipment Co.

There are about 4,000 surface quarry operations across the U.S. and about 90 underground mines. These operations range in size from small operations, ones reporting production of less than 50,000 tpy, to those with annual production of more than 10 million tons. The only state without a crushed stone operation is Delaware, but the state produces construction sand and gravel, and crushed stone is readily available from nearby Maryland and Pennsylvania.

From among the rocks in quarries throughout the U.S., it is possible to assemble a collection of all the major rock types in the earth’s crust: old rocks and young rocks; hard rocks and soft rocks; rocks formed under molten pressure and rocks consolidated from the scrapings of glaciers; rocks consisting of compacted volcanic ash and rocks laid down on the floors of seas; rocks enfolding skeletal remains of microscopic marine organisms and rocks imprinted with tracks left by dinosaurs. All of these can be found in quarries.

Geologists recognize three basic types of rock: igneous, sedimentary and metamorphic. These differ in their origin. Crushed stone can be made up of igneous, sedimentary or metamorphic rock, although it must be hard and durable enough to meet demanding specifications required of construction materials. In a crushed stone operation, controlled blasts produce a predetermined quantity of rock.

Igneous rocks once existed in a molten state at very high temperatures. They form as molten minerals cool and harden, just as water freezes to become ice. Grains of pure minerals interlock to form the rock. The size of the grains indicates how quickly the rock cooled from a liquid state.

There are two types of igneous rocks: intrusive and extrusive. Intrusive igneous rocks formed slowly within the body of the earth. The most familiar intrusive igneous rock is granite. Extrusive igneous rocks formed quickly on the earth’s surface. Molten rock on the surface is called lava. The mineral grains in this type of rock are generally too small to distinguish with the naked eye.

Sedimentary rocks are formed in a less dramatic way by the weathering and the subsequent layering of minerals. Sands and muds accumulate in great thicknesses, and eventually pressure and chemical cementation turn them into sandstones and mudstones. Sedimentary rocks are not limited erosional material only. Limestone is made from carbonate muds from seawater and carbonate remains of marine organisms.

Metamorphic rocks are formed by any kind of rock (igneous, sedimentary or metamorphic) altered by high temperature and pressure without re-melting. Metamorphism does not change the rock’s bulk chemical composition but does produce new minerals and textures. Marble is a common metamorphic rock that is formed from limestone.

Crushed stone products tend to be extraordinarily heavy and transporting them to market can be costly. That’s why, on average, crushed stone operations ship no more than 20 to 25 miles from where the product originated. Quarries, as well as sand-and-gravel operations, often are located near the centers of development they supply.


Estimates are that between 70 and 85 percent of crushed stone material is used in the construction of roads, buildings and community infrastructure, with the remaining materials used in agriculture, by the chemical and metallurgical industries and for a wide variety of specialty applications.

These raw resources are indispensable to the maintenance and development of rural and urban environments. The construction of a new house, for example, requires an average of 400 tons of aggregate. Foundations, concrete blocks, bricks, mortar, roofing shingles and wallboard all require aggregate as a basic ingredient. Also, more than 30,000 tons of crushed stone are needed for the construction of one mile of a four-lane highway.

Photo by Zach Mentz

Photo by Zach Mentz

Minerals provide the basic resources for homes, appliances, cars, electricity, communications and even modern medical care. Without minerals from crushed stone, there wouldn’t be the modern necessities that make lives safe, comfortable and productive.

In fact, minerals from crushed stone are so important in everyday life that demand has grown dramatically as society has become more complex. Americans use an average of 38,212 lbs. (including more than 15,200 lbs. of crushed stone, sand and gravel) of new minerals each year, according to the Minerals Education Coalition. Although most people know where to buy the things they want, they seldom know or even consider the source.

Each year, the nation mines and produces minerals to manufacture cosmetics, medicines, cat litter, soaps, plastics, fertilizer, bricks and building materials, magazines, automobile tires, wallpaper, glue, ceramics and many other essentials.

Increasingly, crushed stone is becoming a critical tool used to protect the environment. Erosion-control programs require stone to prevent sediments from clogging waterways. Water and sewer facilities use stone and sand for filtration systems. Utility power plants use crushed limestone to reduce the harmful sulfur dioxide that produces acid rain.

With this economic pull toward the marketplace, mining of aggregate resources can be defined as an urban land use. Typically, this means mining activities exist within the urban fringe, where competition for undeveloped land is high and where there is considerable development activity.
Here are some examples of minerals Americans use every day:

■ Bauxite – A naturally occurring mixture of aluminum hydroxides and mineral impurities. Its uses are important to the manufacture of refractories, ceramics, cements and flame-retardants.

■ Feldspar – The most abundant mineral derived from igneous rocks occurs in numerous forms and mixtures. Feldspar is used in the production of ceramics, pottery, insulators, glass and latex fillers.

■ Granite – Massive quantities of stone products will continue to be required for airports, road systems and key building projects. Granite is used in the building of roads, schools, hospitals, churches, houses and other modern construction.

■ Kaolin – Also known as “china clay,” kaolin is a white aluminosilicate widely used in paints, refractories, plastics, sanitary wares, fiberglass, adhesives, ceramics and rubber products.

■ Limestone – A sedimentary rock composed mostly of the mineral calcite and comprising about 15 percent of the earth’s sedimentary crust. This mineral is a basic building block of the construction industry and the chief material from which aggregate, cement, lime and building stone are made.

■ Mica – A platy mineral occurring in a variety of complex hydrous aluminosilicate forms with differing chemical compositions and physical properties.  Mica is used in cosmetics and electronic applications, as well as joint cements and sealers and oil well drilling muds.

■ Sand – Ranges in size from 0.02 to 2.0 mm. Sand is one of the principle elements used as aggregate in Portland cement concrete, mortar, plaster and other building materials. It is also used in the manufacture of glass and fiberglass, sand traps, landscaping and as an abrasive for cleaning buildings and structures.

■ Shale  – A fissile rock compound made up of a wide variety of clays and other fine-grained rocks that are used in the manufacture of brick, drain tile, vitrified pipe, quarry tile, flue tile, conduit, pottery, stoneware and roofing tile.

Sand and gravel are common minerals resulting from the erosive forces of water, wind and ice. In fact, silica, the basic constituent of sand, is the second-most occurring element in the earth’s crust after oxygen. Unlike crushed stone, which results from a manmade process, sand and gravel are generally found in river and stream valleys where they have been deposited by water, and in ridges and hills where they were left behind by receding glacial action and subsequently altered by erosive forces.

Photo by Zach Mentz

Photo by Zach Mentz

In their natural state, sand and gravel are usually loose, easily handled and, being composed of a range of grain sizes, are readily compacted while retaining good internal drainage characteristics, making them a preferred material for fills and as a base course for pavements and other structures.

When combined with a Portland cement binder, they become the principal ingredient in an unusually strong and long-lasting construction material – concrete – whether used in its plastic state and placed in forms, or precast as pipe, block and other structural components. When combined with asphalt, sand and gravel become the aggregate forming the major element of asphaltic concrete, which is widely used as a paving material.

While some other materials also may be used as aggregate, sand and gravel are most commonly used for these purposes. In some sections of the country, sand and gravel are the only economically viable sources of aggregate. As a natural deposit material, they are a valuable resource where they are relatively close to locations where aggregate may be needed for a broad range of uses.


Today, quarry operators usually are actively involved in their communities, belonging to neighborhood councils and participating in business and education partnerships. With a long tradition in community commitment and as conscientious land managers, responsible producers understand and respect the laws that regulate the industry. Federal, state and local agencies work with producers to ensure safety and avoid environmental degradation. Often, crushed stone producers must obtain dozens of permits to operate in accordance with the many local, state and federal regulations.

Photo by Zach Mentz

Photo by Zach Mentz

Since the early 1990s, reclamation for an aggregate operation’s next use has become an integral part of the ongoing management plan. Now, in most states producers are required to return the land to a like or better condition than when the operation started. Implementing a reclamation plan commonly begins at startup, with special attention given to programs such as wildlife habitat development and land contouring.

The results of successful reclamation can be seen in wildlife refuges, community parks and lakes, golf courses, housing subdivisions and shopping malls throughout the country.

The crushed stone industry has come of age, using the latest technology available. Mining engineers, geologists, hydrologists and environmental experts work together to develop the best methods for controlling dust and noise and assuring overall regulatory compliance while producing quality construction aggregate.

Modern mining techniques are based upon the latest advancements in technology. Computers are commonly used to design the most efficient methods to extract the minerals necessary to produce high-quality crushed stone. Computer design is also an integral part of quarry blasting to assure minimal noise and vibration. As technology advances, more and more quarry operations are becoming automated and plants can run remotely via a computer.

Crushed stone producers maintain a strong and unwavering commitment to safety and health at workplaces, too. Each company has to comply fully with stringent federal, state and local safety and health regulations. Safety and health training programs help develop a knowledgeable workforce capable of recognizing, analyzing and avoiding inherent hazards of the crushed stone and aggregate work environment.

Producers recognize that the earth’s resources are finite and that environmental stewardship is necessary today to preserve the potential for a quality of life for future generations. To that end, producers not only must meet all established environmental regulatory requirements, but also where possible, they must do better than the law and regulations require.

Photo by Kevin Yanik

Photo by Kevin Yanik

Companies work with community leaders and citizen groups to develop plans for appropriate uses of the land once mining operations are completed. These plans naturally look out for the community’s best interest because this will result in the highest land values.

Recent advancements in electronic technology have made possible the design of aggregate production facilities capable of assuring compliance with all regulations. More importantly, though, the absolute necessity of community acceptance has been the primary reason aggregate producers have adopted state-of-the-art technology in crushed stone operations.


Aggregate mining is an industrial land use. But rapid urban and suburban expansion made possible by access to construction aggregate resources presents challenges to every operation. Before a company can begin producing aggregate, extensive requirements such as comprehensive land-use plans, zoning ordinances and regulations must be met.

It’s in the interest of the community to have construction aggregate close to the market. This places the mining industry in the midst of increasingly populated areas. As a result, significant strides have been made over the last 30 years in site planning and beautification.

As more and more people surround mine sites, even in rural areas, the industry has become more visible. Consequently, citizen input has had a positive impact on the operations’ land-use decisions because more people are involved in the process.

Progressive communities are finding that prohibition of aggregate mining eliminates neither the demand for construction material nor the conflicts associated with mining. It simply creates a different set of problems due to increased trucking from more remote areas. Longer hauling distances mean more trucks, more fuel consumption, more wear on roads and more conflicts with urban land uses because the market remains within the urban area.

Rather than eliminating mining from urban areas, communities are getting involved in setting operational and reclamation performance standards jointly with aggregate producers. Such partnerships assure compatibility with adjacent land uses, both existing and future.

The industry competes with others to secure specific parcels of land that are capable of producing quality aggregate and supplying the sufficient quantity needed to justify the capital investment required to produce the material. In fact, several states and communities faced with significant shortages of aggregate resources established policies and legislation protecting these resources so they’re available for the needs of future generations.

The industry’s experience securing the ability to produce aggregate has not been an absolute success. This is partially due to an assumption on the part of the public that an aggregate operation is a nuisance during and following the active use of the land.

Photo by Kevin Yanik

Photo by Kevin Yanik

However, current land use and other environmental controls, many of which are initiated by producers, have served to illustrate the industry’s acceptability in the communities where they’re located. The success these producers experience is the result of two important factors:

■ Improved technology in the extraction and processing of the material.

■ The pre-planning of the site for a new and productive use for the property following extraction of the resource.

Still, the industry continues to struggle to secure the right to produce aggregate because of the dual sets of requirements of local zoning ordinances and state acts affecting the industry’s surface mining activities. Such provisions usually involve the necessity of securing permits from two levels of government; are frequently vague in their specific requirements; and, unlike other industrial uses, the permits are frequently restricted to a limited period of time, requiring extensive and expensive renewal procedures on the part of the producer – with no assurance that the permit will be renewed.

Thus, the substantial capital investment required for a modern sand-and-gravel plant becomes a hazardous undertaking for the prospective producer. Still, aggregate producers recognize the legitimate concerns of the public and its demand for effective environmental controls.

Aggregate operations are industrial by nature. They use heavy machinery, involve a processing procedure and use rail and truck lines to ship products. These are areas the aggregate industry has in common with most industrial uses of land.

The aggregate industry is different from others, though: It is self-consuming. The longer producers operate at any one location, the shorter the remaining life of the mine. Thus, unlike most other industrial uses, aggregate operations represent a transitional use of land that makes important contributions to the economy.

The aggregate industry is in a unique situation as far as land development is concerned. The industry uses heavy earth-moving equipment and often has large volumes of earth material that’s unsuitable to market for creating functional landforms. Because it’s necessary to move this material – overburden, clay, silt, fines – to extract the aggregate, it becomes a matter of manipulating that material with the equipment at hand in a manner that will achieve the most desirable land areas for development.

Photo by Kevin Yanik

Photo by Kevin Yanik


The underlying principle of true conservation has been held to mean the wise use of resources. The aggregate industry is in full agreement with that principle and recognizes its responsibility as stewards of the land.

Still, it can do so only when it has the opportunity to use the resource deposits naturally occurring at locations convenient to serve community needs. Because of the size of most aggregate operations, quarries present tremendous opportunities for preserving open space and wildlife habitats to benefit both the environment and the community.

Wildlife is certainly not new to aggregate properties. But often, a fully developed, managed wildlife program may represent a tremendous value to the community. Woodlands and meadow restoration, companion crop use for re-vegetating areas and alternative runoff management are just a few examples.

Significant portions of most mining sites sit idle and exist either as dedicated buffer areas or properties held for future development. These unused buffer areas represent opportunities to create and restore habitat critical to wildlife.

While large, contiguous parcels are most beneficial, isolated plots and small greenways devoted to wildlife are valuable ecologically. Employees at crushed stone operations are committed to these programs. Employees and neighbors join in these projects and guard their sites’ wildlife personally and protectively. Special vegetation plantings, food-plot establishment, nest-box placement, and species-specific enhancement are typical at some sites.

In today’s aggregate operations, there are many examples of exceptional site improvements that demonstrate how operations can successfully fit into the community during and after mining. In some instances, site aesthetics and environmental impact mitigation plans can be integrated into pre-mine reclamation planning. Site beautification involving screening, dust and noise control, landscaping, truck routing and special quarry entrance designs are incorporated into existing operational programs.

Many outstanding and varied developments occur as a result of aggregate properties reclamation. They range from local and state parks and wildlife areas to exclusive golf courses, housing projects, office parks and prime agriculture land.  Careful planning for an aggregate property’s next use is in the producer’s best interest for several reasons. Higher property values are obtained if the land is reclaimed for an enhanced purpose.

While mining alters — sometimes dramatically — the shape of the land, it often provides a reconfigured parcel that is of more interest and value than it was in its original state. In addition, few other land uses present opportunities to create new and productive wildlife habitats, marshes and wetlands that exist through mining.

The image of the industry is contorted by the past and by a poor understanding of its potential as a shaper of landscapes. But mining is an essential and integral part of the total land-shaping process. It is often the very characteristics of the quarry that evolve into the most attractive and valuable features of the end use. Irregular topography, vertical stone walls, rock outcroppings and, of course, fresh water lakes are landscape characteristics sought after and valued by the public.

America’s aggregate industry has a continuing commitment to make its operations compatible with the neighborhoods in which they exist. Providing jobs and paying local taxes, aggregate producers contribute to the building of their communities in a variety of ways, from producing the stone to build needed infrastructure to donating time and money to Little Leagues.

Across the country, communities depend on construction aggregate. Likewise, aggregate producers depend on their reputations as environmental stewards, community leaders and as producers of quality construction materials for their success in meeting the communities’ needs today and in the future.


Photo by Joe McCarthy

Photo by Joe McCarthy

Oil and natural gas drilling companies are using a technique called hydraulic fracturing to retrieve otherwise inaccessible product. This has created a new demand for a specific type of aggregate. It works like this: Once all of the gas or oil is extracted from a vertical-shaft well, drilling companies make horizontal shafts and pump them with a water, chemical and sand mixture under high pressure. The sand finds and holds open fissures in the earth, releasing pockets of oil or gas that are then captured at the surface.

McLanahan Corp’s Director of Process Engineering Scott O’Brien says tens of thousands of tons of sand are used in some of these holes. But this is no run-of-the-mill sand. The material, known also as proppants, comes in three basic forms. The ceramic proppant is by far the most expensive and is the least available. It is made from an aluminum ore called bauxite. Most of this material is imported from places like Brazil, Jamaica, China and Australia.

A step down the quality chart from ceramics is resin-coated sand. This material is domestically produced. The resin coating, which gives the material added strength and in-well performance, also draws the ire of environmentalists who charge that the resins will contaminate ground- and drinking-water sources.

The most common proppant is natural sand, which falls into two basic quality categories. Ottawa, or similar, sand is the most sought after and typically found in the upper Midwest region of the United States – and into Canada.. In southwestern states like Texas and Arkansas, you can find the lower-quality Brady sand.

The reason ceramic proppants have the highest sticker price on the lot is because they work the best inside the well. Their spherical shape and high compression strength get into and keep the fissures open better than any other proppant. They also allow the most oil and gas to pass on the way out, a characteristic called conductivity.

Like ceramic proppants, Ottawa sand is also spherical and strong, just to a lesser degree. It is, however, much more abundant. Wisconsin, Minnesota and Illinois are rife with the stuff. Ottawa sand is also used to make resin-coated proppants. The Brady sand, while abundant and close to the drilling sites, lacks the spherical shape, compressive strength and conductivity of Ottawa sand.

Ceramics and resin-coated proppants aside, the quality of sand for fractured hydraulic drilling is either something you have or don’t have – it is all in the deposit. Shape, strength and conductivity must be laboratory certified.


Once a producer determines that the deposit has the right shape and strength, the real work begins. After the sand is pulled from ground, it is screened once to remove overs and unders. Then comes highly specialized washing, screening and drying.

“It has to be super clean,” says Eagle Iron Works’ Sales Manager Steve Slater. It is very important, he says, that the dirt, iron ore, ferrous oxides and other material are removed to meet the end users’ specifications.

And size, it turns out, really does matter.

Photo courtesy of Bluegrass Materials

Photo courtesy of Bluegrass Materials

“Generally, in the concrete and asphalt business you are dealing with specs that you can drive a bus through,” O’Brien says. “The C-33 spec is a wide, forgiving specification to hit. When you start looking at frac sands … you have to have very narrow size distribution.”

Those sieve sizes required are generally passing a 16 and retained on a 30, passing a 20 and retained on a 40, passing a 30 and retained on a 50, passing a 40 and retained on a 70, and passing a 70 and retained on a 140.

Frac sand requires a special drying process, and material handling is an issue when shipping frac sand by truck or rail. Once it is dry, you have to put it in a pressure-differential or some kind of container truck like you would cement.

“You are going to need a wet-processing plant to make some separations that make the sand more manageable in the drying end of the process,” O’Brien says. “The bigger thing is going to be the drying and the sizing of the material on screens. Frac-sand size distributions are so tight that you really can’t produce them through hydraulic classification. To get to the polishing stage on screens, you need to dry that sand and then put it through a screening plant. And we are not talking about screens normally seen in the aggregate industry. We are talking about screens that are made specifically for making fine, tight separations. That’s a big outlay [of cash] and maybe something that sand producers who are in the aggregate business right now don’t have any sort of handle on.”

O’Brien says that most frac-sand plants can produce between 200 and 500 tph from the wet side. And at one Colorado operation, frac-sand processing is taking place alongside concrete sand processing. That operation uses a hydrosizer to make sharp separations that are later blended for concrete. One of those size separations is dried and screened for frac sand, he says.

Regional processing centers are popping up to offset the difficulty and expense of processing and transporting the final product. Here, the crude sand is mined and initially sized, then shipped in bulk to a washing, screening and drying plant nearer the oil and gas drilling. This type of operation will be especially useful during the winter months when wet processing in the north becomes extremely difficult.

Frac sand is just one specialty product. The entire aggregate industry, with well over 10,000 operations in North America, continues to evolve and grow to serve the market’s needs.

What is frac sand?

Frac sand is generally large-grain sand high in silica content. The material is usually 20/40 mesh, 40/70 mesh or 100 mesh. The smallest of these – 100 mesh – is the most common type used for hydraulic fracturing of Marcellus Shale, which extends throughout much of the Appalachian Basin.



Contributors to this chapter include the following, in alphabetical order:

Gus Edwards
Former President & CEO
National Stone, Sand & Gravel Association

U.S. Geological Survey


Lesson 1 Quiz

1. What are two primary reasons that U.S. aggregate production increased steadily after the 1950s?

2. For every $1 million in aggregate sales, how many jobs are created?

3. How many quarry operations are there in the United States?

4. How many tons per year will a small aggregate operation produce in North America?

5. What are the three basic types of rock?

6. What type of rock is formed by the weathering and layering of minerals over time?

7. What is considered the “basic building block of the construction industry” and key for aggregate and cement?

8. What are the three forms of hydraulic-fracturing proppant?


Click here for the quiz answers.


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