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Crushed aggregate, also known as rock aggregate, refers to a crushed stone product produced in quarries. In areas where natural sand and gravel aggregate deposits are insufficient to handle local demand, larger stones are processed in an impact crusher to create crushed rock aggregate. The greater costs of production involved in mining and processing the stones to create crushed aggregate mean that the cost of this material is often significantly higher than that of comparable natural products.
All aggregate is divided into two types: fine and coarse. Fine aggregate is broken up into smaller pieces than coarse aggregate. When put through a separator or aggregate washer, coarse crushed aggregate will pass through a 3-inch (7.62-cm) sieve but will not go through a No. 4 sieve. Fine crushed aggregate will pass through a No. 4 sieve but will be stopped by a No. 200 sieve during the aggregate screening process.
The different aggregate sizes and types are appropriate for specific uses in the construction and landscaping industries. For example, although the larger, coarse crushed aggregates are more economical, this type of aggregate can present problems if used in concrete forms for upright structures. By comparison, fine aggregate is suitable for use in concrete, but it would not be a recommended choice for the creation of a roadbed or driveway.
The stone and aggregate industry creates crushed aggregate using a lengthy process. The stone must be mined in a quarry and then transported to the rock crusher, which begins the process of crushing the larger stones into more manageable pieces. As the stones leave the rock crusher, they are sent on to a rock conveyor for transport to the impact crusher, where they will be broken down further.
After being processed in the impact crusher, the aggregate is screened for sizing. This process might be handled in a screen shaker or during the washing process in an aggregate washer. If the aggregate is sufficiently crushed, it is transported to the storage area. If the stone is not crushed to the desired size and type, the process is repeated or the stone is transported to other equipment for further processing.
So much machinery, time and labor is involved in the creation of crushed aggregate that it can become a very expensive product. Despite the cost, aggregate products are the main component of concrete construction. In the majority of cases, crushed aggregate is used locally to prevent further costs being incurred in transporting the material.
@Charred - Crushed stone is certainly very useful. I prefer it as part of a more cohesive product, like concrete, rather than using it in its native form.
But some people like the crushed stone. I saw someone who had a gravel driveway – no concrete, no stone, just pure gravel all the way. It’s great looking if you like gravel, and I suppose you don’t suffer the problems of having a crack in your driveway or needing it smoothed out or paved.
If you have issues you just add more gravel. Some people like the simplicity of gravel but I prefer nice, smooth stone.
I have a friend who is in the “stone” business, as he explained to me when I first met him. When I looked puzzled, he said that meant that he mines stone from quarries and sells it to commercial construction builders. I am sure that some of these stones would include the crushed aggregate mentioned in the article.
Apparently it seems to be a good business model for him. He didn’t say what crushed concrete was selling for, but he found some quarries in our state and was able to locate buyers as far away as two neighboring states.
He has to ship the stone from the quarries to the buyers. That’s included in the purchase price, I’m sure.