British Columbia Stone, Sand
amp; Gravel Association
FACTS and Frequently Asked Questions about Aggregate ...
Aggregates production accounts for about half of the non-fuel mining volume in the United States.
Q: What is Aggregate?
Basically, Aggregate is sands, gravels and crushed stone - all the products of a pit or quarry.
Q: Is a Pit the same as a Quarry ?
Generally, a pit contains loose sands and gravels that are directly excavated, screened, and transported. A Pit can produce some products that consist of round stones, whereas all products from a quarry are crushed which lead to sharp edges.
A quarry contains bedrock that must be blasted first before it can be crushed into smaller particles.
Q: What is Sand and Gravel used for ?
Sand and Gravel used to build roads, sewers, sidewalks, schools, factories, offices, parking lots, driveways, basements, walls, roofs, gardens, walkways, paths, recreation centers, sports fields, golf courses sand traps, landscape rock, and hiking trails, to name a few. Industrial sands are used in the process of making glass, for grit for roofing paper, and as additives to paint and stucco.
Q: What is the difference between sand & gravel and crushed rock ?
Sand and gravels are naturally occurring, in pits, while crushed rock is a product of blasting and crushing rock, in a quarry.
Q: Where does Sand & Gravel come from ?
Sand and gravel is found in certain geological settings in certain areas around B.C. It is not found everywhere. It used to be bedrock that was ground up by the movement and melting of glaciers during the last ice age which ended tens of thousands of years ago. Deposits are often found in and near river deltas and at widenings in rivers where flow slows and deposits fall out.
Q: How much Aggregate is used in B.C. every year ?
Approximately 50,000,000 metric tons (or tonnes) or about one truckload per man, woman and child in B.C. each year.
Q: What is Rehabilitation?
Rehabilitation means to treat land from which aggregate has been excavated so that the use or condition of the land:
There are hundreds of cases of successful reclamations of aggregate mines and their reuse as another source of development. The Butchart Gardens on Vancouver Island, Queen Elizabeth Park in Vancouver, Lafarge Lake in Coquitlam, and Mary Hill housing development, and many other park spaces are all on lands which were once gravel pits.
- is restored to the former use or condition, or
- is changed to another use desirable by and compatible with the needs of a community.
Q: How do you call different sizes of aggregate ?
The following table outlines names given to rocks of different sizes.
Q: Do you just dig up the sand and gravel and sell it ?
|Boulder: ||More than 10 in. (254mm) in diameter|
|Cobble: ||From 2.5 to 10 in. (64 to 254mm) in diameter|
|Pebble: ||From .16 to 2.5 in. (4 to 64mm) in diameter|
|Granule: ||From .08 to 0.16 in. (2 to 4mm) in diameter|
|Grain: ||From .04 to .08 in. (1 to 2mm) in diameter|
There are many operations applied to the raw product before it is sold to the
end-user. A pile of sand does not have only one grain size but it has a
distribution of sizes - from small sands to 6 inch and higher cobbles.
The first operation is usually a jaw crusher - two plates forced together on a rotating basis - which breaks up large pieces of rock, found in almost all deposits.
Conveyor belts take the product to screening, followed by recirculation to a cone
crusher for larger particles.
Screening and classifying, separates particles of similar
size in one pile. This is accomplished through the use of mechanically vibrated screens, or sieves, stacked one on top of the other.
Larger particles which remain are sent back to the cone crusher, which takes the recirculated product and reduces the size as it falls through an off-centre rotating core to break the rock. The product is then sent back to the screen. This occurs over and over for any larger sizes remaining at the top of the screen. In a rock quarry, there is more recirculation through the cone crusher.
For various industrial applications there are different standards that
say what series of sieves are used and what percentage of sand must be
in each sieve to be a given size (e.g. 1/2" or 1/4"). Product passing through
to the bottom of the screens is conveyed into piles or a surge bin, which then fills trucks for transport.
A washing cycle may also be included depending on the type of product. Washed, or clear, gravel will have any fines (dust, clays, fine grained) removed.
Q: What are the standard sizes used to screen sand and gravels.
Selected Standard Sieve Sizes and Mesh Openings*
US | British | Nominal | Open | Open |
Canadian | | Size mm | in. | mm |
2.5 8.00 0.3150 8.00
3 6.73 0.2650 6.73
3.5 5.60 0.2230 5.66
4 4.75 0.1870 4.76
5 4.00 0.1570 4.00
6 5 3.35 0.1320 3.36
7 6 2.80 0.1110 2.83
8 7 2.36 0.0937 2.38
10 8 2.00 0.0787 2.00
12 10 1.70 0.0661 1.68
14 12 1.40 0.0555 1.41
16 14 1.18 0.0469 1.19
18 16 1.00 0.0394 1.00
* There are some minor variations in the sizes
according to which reference is used.
Q: What is the difference between cement, concrete, and aggregates ?
Cement is an ingredient of, or part of, concrete. Concrete is a mixture of aggregates and paste. The aggregates are sand and gravel or crushed stone; the paste is water and portland cement.