Natural Aggregate - A Primer What Is Aggregate?
The United States produces over 2 billion tons of aggregate per year, which represents half the national non-fuel mining volume. Yet natural aggregate is one of the nation's poorly understood resources.
Natural aggregate consists of material composed of rock fragments that may be used in their natural state or used after mechanical processing such as crushing, washing and sizing.
Gravel and Crushed Stone
Natural aggregate consists of both sand and gravel, and crushed stone.
Gravel generally is considered to be material whose particles are 3/16 to 3 inches in diameter. Its edges tend to be smooth and rounded.
Crushed stone is artificially crushed rock, boulders, or large cobbles. Most or all of the surfaces are produced by crushing, and the edges of crushed stone tend to be sharp and angular.
Mining Aggregate
Sand and gravel commonly is mined with conventional earth moving equipment such as bulldozers, front-end loaders, tractor scrapers, and draglines.
Crushed stone commonly is quarried by drilling and blasting rock, and then extracting the material with power shovels or bulldozers.
Processing Aggregate
After sand and gravel or crushed stone has been mined, most aggregate producers process the material by screening it into various size categories. The individual sizes are then blended back together according to specifications required by the final use.
How Is Aggregate Used?
Major Construction Projects
Construction of the Denver International Airport required about 10 million tons of aggregate. About 1 million tons of the aggregate used in the airport construction was imported from Wyoming.
Houses
One new home, and each home's proportional share of the associated schools, libraries, shopping centers, recreational facilities, and so forth, requires over 325 tons of aggregate.
An Example: The +100 Ton Aggregate-Rich House**
Let's take a very small house - just 800 square feet (that's less than half the size of the average new house). Now, take the seven most aggregate-rich components around that 800 square foot house and, conservatively, estimate the number of tons of aggregate that goes into each component.
- Foundation
2 x 8' high walls, 20' long @ .75' thick plus
2 x 8' high walls, 40' long @ .75' thick
= 36 tons - Drain around foundation.
= 20 tons - Basement Floor
20' x 40' x 1/2' thick
= 20 tons - Garage/Carport Floor
20' x 20' x 1/2' thick
= 10 tons - Driveway
10' x 50' x .75' thick
= 19 tons - Septic System/Drain Field (if necessary)
= 50 - 150 tons - The street directly in front of the house.
= 150-250 tons
That very small house, figured conservatively, will use between 100-400 tons of aggregate.
In addition to the seven large aggregate-rich components, here's seven more that many of us tend to forget.
- Asphalt shingles - the aggregate surface and filler.
- Cultured marble and linoleum surfaces.
- Glass - limestone is a key element.
- Paint, caulk and sealants - aggregate fillers.
- Carpet backing/asphalt tiles.
- PVC plumbing pipe - aggregate fillers.
- Electrical wiring - aggregate filler for insulation.
Demand for Aggregate
You use more stone than you might think. If you live in Colorado, for example, aggregate use exceeds 12 tons per person, per year.
During 1994, aggregate production in Colorado was over 40 million tons , or over 12 tons per person per year. During 1994 aggregate production in Wyoming was over 8 million tons, or about 18.5 tons per person per year.On a per capita rate, the production of aggregate in both Colorado and Wyoming exceed the United States average rate of 9.5 tons.
To interpret that figure another way, imagine stopping by the local home supply center and picking up a 50lb bag of landscaping rock for yourself, and for every person in your family. Now, do that every day this year and you will have an idea how much aggregate you use each year!
Availability of Aggregate
Aggregate occurs where Mother Nature put it, not necessarily where we need it.
Even though aggregate resources are widely distributed throughout North America, large parts of the country are devoid of sand and gravel, and potential sources of crushed stone may be lacking or covered with overburden too thick to allow economic mining.
Areas of the United States where aggregates occur in abundance include the western part of the country (esp. Colorado and Wyoming), upper New England through Maine, New Hampshire and Vermont and Northern Michigan, Minnesota and Wisconsin.
Areas where aggregates are scarce include the Gulf coast regions from Texas to Florida and the Southeastern and Mid-Atlantic shorelines.
Although nature dictates the location of natural aggregates, other factors influence the development of the resources. Prime aggregate sources are lost if parking lots, houses, or other buildings are constructed over the resources. Zoning and permits may restrict other sources. Yet, for economic reasons, aggregate operations must be within reasonable distances of the market area.
Cooperative planning by producers, government, and citizens is the key to successful protection and utilization of aggregate resources.
Aggregate Quality
Even if aggregate is available, it may not meet the quality requirements for certain uses. Suitable aggregate consists of clean, uncoated particles of proper size, shape, and gradation. It must be strong and resist breakdown during handling, mixing, and in use. It must be able to resist the actions of wetting and drying, and freezing and thawing. It must not react with cement when used in concrete.
Reclamation
Reclamation of a mined-out area is highly important to communities near aggregate operations because residents do not want a scarred landscape near their property.
The primary goal of reclamation is to return the land to a beneficial use. Reclaimed pits or quarries have been converted to residential sites, commercial properties, office parks, golf courses, parks and recreation areas, as well as to the natural conditions of the area.
