Infrastructure and Construction Materials Guide — Aggregates

Aggregates are sand, gravel and crushed stone. Other materials like slag and recycled concrete can be considered aggregates as well. Aggregates can be put in place as washed stone, mixed with cement for pouring concrete for paving or with asphalt for paving.

Commodity Description

Aggregates are a broad category of construction materials. In terms of tonnage and number of quarries and mines world-wide, aggregates represent the largest mineral production tonnage excluding energy minerals.

Range of grain/rock sizes
Concrete sand and asphalt sand have a grain size of 4.75 mm (0.18 inch) to 0.075mm (0.003 inch). These types of sand are either recovered from alluvial (river) deposits or from stone crushed into fine particles.

Concrete and asphalt sand

 

Crushed stone for road base is typically 3/4 inch.

Typical road base crushed stone – ¾ inch

Rip-rap is a generic term for aggregate as large block and boulders used for erosion control, shore levees and hillside stabilization. It can range in sizes from 2 inches to 72 inches or larger.

Rip-rap

Geology and Mineralogy of Aggregates

The kinds of rock in aggregates includes: any rock that is sound and durable, i.e. will maintain its particle size through freeze-thaw cycles, wide temperature ranges, and wear from water and ice may be used. Here are a few examples:
• Sand and gravel from granite, limestone, basalt, gneiss, and sandstone
• Alluvial and crushed rock from granite, limestone, and sandstone
• Crushed stone from granite, limestone, and marble

Production and Prices

Worldwide aggregate statistics are difficult if not impossible to obtain, because of the size of the total world production or unreliable data from individual countries. A useful guide for a country-by-country aggregate size is total exports by country. The United States exports very little and imports are often required to meet U.S. demand.

For U.S. production statistics and sale prices, and World Mine Production and Reserves, for: “Sand and Gravel (Construction)” go to p.152-153 and for “Stone (crushed)” go to p. 166-167 of the USGS Commodity Summaries 2024.

For top gravel exporters by country, go to World’s Top Exports by Daniel Workman.

Major Producers in the United States

Martin Marietta
Vulcan Material
Cemex
Eagle Material
Summit Materials
Aggregate Industries (LaFarge)

Uses

Concrete construction – commercial, residential, government
Concrete roadways
Concrete bridges and protection structures
Asphalt roadways
Roadway bases
Erosion and remediation “rip-rap”
Decorative stone, building facing, and cemetery and other monuments
Landscaping
Lightweight aggregates for construction materials as fillers, insulation and concrete mixes

Aggregates have a large number of uses and there are no obvious substitutes. Delivered costs and product quality tend to create substitutes from some other aggregate sources such as from granite, limestone and sandstone deposits.

Mining

Aggregate mining is similar to other “hard rock” surface mining methods with a few exceptions.

Drilling and blasting are the first step in surface mines for granite, limestone and sandstone. Underground aggregate mining is also common near metropolitan areas such as Chicago and underground limestone mines in the eastern United States coastal area.

Broken rock is sized through a series of screens. Rock above 12 inches in diameter is set aside for further sizing. Reduction of even larger rocks is accomplished by a hydraulic shovel or backhoe with an attached hammer (“stinger”). The sized rocks are loaded into trucks or moved to storage using a shovel with a bucket and holding thumb.

Aggregate plant

 

The eastern United States has some underground aggregate operations, primarily in limestone deposits.

Underground mine jumbo drill

 

Underground wheel loader

 

Loading sand into freight cars at a quarry

 

Mineral Processing

Large aggregates quarries have similar processes for rock reduction and sizing. These are the primary processing equipment in a sand and gravel quarry operation:

https://www.911metallurgist.com/blog/static-grizzly-screen

  • Grizzly – coarse 15 cm (+6 inch) 
  • Primary crusher types – jaw, gyratory, impact
  • Screens – 2-deck, 3-deck, 4-deck, small to large rock sizing
  • Secondary crusher types – cone, horizontal shaft, impact, roll types
  • The wash plant uses water to remove clay and other fines to meet specifications for concrete and asphalt products.

Light-weight Aggregates Production

There are four general types of light-weight aggregates.

• Natural lightweight aggregate prepared by crushing and sizing with screens, including pumice, scoria, tuff, breccia and volcanic cinders.

• Manufactured structural aggregates prepared by high temperature expansion. Kilns or traveling grate high-temperature sintering machines expand shale, clay or slate. Weight bearing uses include concrete masonry with sizes of 4.0 mm (0.15 inch) to 12.5 mm (0.49 inch).

• By-product lightweight aggregates prepared by crushing, then sized by screens using granulated slag, organic cinders and coke from steel mill waste.

• Manufactured insulating ultra-lightweight aggregates prepared by thermal expansion from perlite or fine vermiculite.

Transportation Logistics

Transportation logistics are an integral part of aggregates quarry operations and marketing. Aggregate operators are successful with small profit margins, typically from $0.50 to $2 per ton. In their press release of June 2022, Martin Marietta reported a 13.49% net profit margin June 30, 2022; at the 2021 average aggregate price of US$ 9.90 per ton, net profit of $1.35/ton net margin. To remain profitable and competitive, operators, must optimize all transportation modes and delivery destinations from each quarry. Direct company sales and independent vendors make up a quarry’s customer base. The operating company may also have on-site and field asphalt plants, ready mix plants and aggregates storage. The aggregates storage is usually adjacent to rail service and sells to customers in more remote areas for highway construction.

Storage and loadout

A typical quarry operation stores smaller screen sizes on the ground and in storage loadout bins. The sizes can be loaded onto conveyor belts or moved by front-end loaders to loadout points for truck, rail and barge transportation loadout facilities (conveyer and storage bin).

Front-end loader with 4-yard bucket. Wilson private photo library

 

Typical quarry products are in these sizes:
¾” aggregate road base (Colorado Class 6), majority of this size is now crushed from recycled concrete
1 ½” X 1”
1” X ¾”
¾” X ½”
½” X 3/8”
3/8” X 3/16”
3/16” X smaller dimensions

Typical sizes for base and sub-base aggregate below.

Larger crushed stone is stored in the quarry work area or adjacent to the grizzly and primary crusher. Finished product comes in various sizes ranging from 2 inches to 72 inches or larger.

Aggregate Transportation Modes

Truck
Truck is the most commonly used mode for aggregate shipping. An industry rule of thumb is that trucking is economical up to 50 miles from the quarry. Distances beyond 50 miles favor rail and barges.

Rail
Rail mode is a special method for intermediate haul of aggregates. The United States has a large number of aggregate quarries that produce from 500,000 to 1,000,000 tons per year. These quarries have a market area up to approximately 200 miles to customers. Beyond 200 miles competitive quarries serve their local customers with lower delivery costs by truck. Rail isn’t the preferred mode for these competitive quarries.

Rail rates for 2020 were Class I Rail $1.60/ton mile (per bts.gov) so the rail advantage of $1.20 per ton mile over the truck mode has minimal effect on market share among quarries in the larger areas.

Barge
River and canal barges are used extensively on the Ohio and Mississippi Rivers in the United States. These barges serve customers along the rivers. Major Gulf Coast States include Louisiana, Texas, Mississippi, Alabama, Georgia and Florida. These states have significant aggregates shortages, in part, because of the increased use of aggregates to repair and remediate hurricane damage and the growth of aggregate requirements for commercial and residential construction in a growth sector of the country. Another cause of aggregates shortage is the depleted reserves in rip-rap, road base and sand in certain customer areas of high construction activity such as southern California. There are also aggregate imports by ocean-going vessels from several Caribbean counties to the Gulf states.

Barge with cargo on Mississippi River

 

Barge rates for 2020 were $1.60/ton (per bts.gov). However, customers using river barges negotiate directly with barge operator and rates vary significantly from shipment to shipment. Aggregates shipment costs include the tug and crew plus the shipment containers, the days’ loading, time on the river and the days’ unloading. The rates are essentially a 24-hours-a-day cost while the tug and containers are in use. Aggregate shipment costs tend to be the lowest of the river barge cargo costs because:
• the shipment containers do not require covers
• there are typically ten 1500-ton containers equaling a 15,000 ton load
• easy to load by a wharf conveyor
• unloaded with a clamshell or a small reclaimer device.
Barge rates for aggregates can be as much as 30% lower than the $1.60/ton rate noted above. Quoted rates take into account available tugs and containers, available crews and fuel. During the year rates can vary due to water levels and ice on the rivers.

Environmental Factors

The major issue associated with aggregates operation is dust in the quarry area, on the quarry haul roads and around over-the road trucks entering and exiting the quarry area. Local and state regulatory agencies require water truck dust suppression and area cleanup of road dust in proximity to the quarry area. Concurrent site reclamation (see Closure, Reclamation and Post-mining use below) during mining operations and at closure of mine and plant operations reduces larger areas of open ground that can create dust and rock material from surrounding quarrying operations. A major challenge for future aggregate production is the objection of the general public in allowing aggregate quarries to be developed in populated areas.

Closure, Reclamation and Post-mining use

Aggregate quarries, including surrounding storage areas and on-site asphalt plants, ready mix plants and wash plants, are subject to federal and state reclamation regulation operating permits and regulation compliance. Quarries on federal lands are regulated by the Bureau of Land Management of the Department of Interior or the USDA Forest Service of the U.S. Department of Agriculture, depending on location. Quarries on state or private lands are subject to the state regulations for the site location.

A common practice in today’s aggregates industry is a closure plan for quarry and processing facilities created in the early stages of the life of the quarry operations and updated as required. Reclamation sureties are usually required by regulating agencies in the case of an operation not completing the reclamation on a timely basis upon cessation of operations or a bankruptcy for the company owning the quarry.

Reclamation of the quarry area and processing area consists of final slopes grading typically at a 3 to 1 grade. Seeding of natural vegetation and growth enhanced with mulching and other plants. At the time of closure, vegetation practices continue for up to three years as a regulatory stipulation. Post mining use in aggregate quarries is currently using water storage in metropolitan areas and use of mined-out areas for golf courses, residential development and open space recreation areas.

Safety and Hazards

The primary regulatory agency for aggregate quarries and adjacent processing facilities is the Mine, Safety and Health Agency (“MSHA”) of the United States Department of Health. This agency inspects and enforces regulations for safe operation under federal law. MSHA does not “permit” quarries, but inspectors, as part of their inspections, may issue notice of rule violations along with a time and substantial monetary fines that are not deductible from operating costs for the quarry operator.

Auxiliary facilities such as rail loadout, separate asphalt plants and ready-mix plants are regulated by the Occupational and Health Agency (“OSHA”), also an agency of the United States Department of Health. OSHA similarly makes inspections, enforces safety rules and can issue violation notices and enforce fines. However, OSHA also has regulatory authority over all non-mining business.

MSHA regulations govern safe in-pit truck safety procedures for company and contractor drivers. Entry and egress of truck traffic to and from the quarry onto public roads is monitored and traffic signs are placed at potential accident points. All drivers in the quarry area are provided safety training and safety tips. The drivers are prohibited from entering active mining areas and must remain in truck loading areas.

Community Relations and Blasting

Two major ongoing concerns for activity of aggregate quarries operations related to community relations are road dust conditions and aggregate truck traffic. Aggregate companies spend considerable funds and time on controlling dust and providing reasonable safe scheduled truck hours. Frequent road sweeping and water suppression in and around quarries are routine. In-pit truck and public traffic are generally limited to eight-hour workdays.

Another community concern is explosives blasting to facilitate rock breaking in aggregate quarries. The Bureau of Alcohol, Tobacco, Firearms and Explosives (“ATF”), a law enforcement agency in the United States Department of Justice, regulates all mining operations in the Unites States that use explosive for blasting rock. The Bureau also regulates mining supervision and blasting personnel in charge of explosives ensuring or requiring training and the secure storage of explosives. In addition to the ATF, communities have jurisdiction on blasting schedules under county use permits. A typical drill and blast plan includes drilling on weekdays and a one-time blast on Friday of that work week. This schedule allows the surrounding community to anticipate the noise and possible “window rattling” each week on the same day and time. This scheduling also allows the quarry personnel to prepare and assure safe condition for all personnel on a regular day and time of blasting. Most aggregate operations that use blasting techniques to loosen or break rock monitor each blast with seismic equipment to assure that ground motion induced by the blast is well within 10% of permissible limits.

References

Aggregates Handbook, Second Addition, National Stone, Sand and Gravel Association, 1991.

Bureau of Transportation Statistics (bts.gov).

SME Industrial Minerals & Rocks 7th Edition.  SME Books. Editors: Jessica Elzea Kogel, Nikhil C. Trivedi, James M. Barker, Stanley T. Krukowski, 2006.

United States Geological Survey (USGS) Commodity Summaries 2023. https://pubs.usgs.gov/publication/mcs2023. The 2023 summary reports 2022 statistics.

United States Geological Survey (USGS) Commodity Summaries 2024. https://pubs.usgs.gov/publication/mcs2024. The 2024 summary reports 2023 statistics.