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What is a Concrete Aggregate?

A man smoothing out a concrete floor.
Sand is a common example of a fine aggregate in concrete.
Wet concrete being poured.
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  • Written By: Mary McMahon
  • Edited By: O. Wallace
  • Last Modified Date: 24 September 2014
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Concrete aggregate is a material which is mixed with cement to create concrete which is hard, strong, and long-lasting. There are a number of different types of concrete aggregate, with contractors selecting their aggregate on the basis of the type of job being performed. If you live in an area with concrete structures, you may be able to see some examples of aggregate in action.

Using aggregate makes concrete much stronger, with the aggregate acting as a type of reinforcement. The aggregate increases the lifetime of the concrete, and makes it more durable. Contractors can choose from fine aggregates, made from small particles of material, and coarse aggregates, which are made with large chunks. Companies which produce concrete aggregate usually grade their products by size, allowing contractors to order from a spectrum of sizes.

In order for aggregate to be effective, it must be strong. Weak aggregate materials will weaken the resulting concrete, which is not desirable. Aggregate must also be hard, so that it keeps its shape without deforming in the concrete. Finally, it must be clean, which in the construction sense means that it is free of chemicals, clays, and various leached materials which could interact with the concrete and interfere with the way it sets.

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The texture of the aggregate is also a consideration. Coarse, porous materials will suck up water during the mixing process, requiring the addition of more water to compensate. This in turn throws off the water to concrete ratio, requiring the contractor to add more concrete to avoid weakening the mixture. Smoother aggregates do not require additional water, and they are less likely to cause cracks when the concrete sets.

Sand is a common example of a fine aggregate. Rocks and crushed glass can be used as large aggregates. Natural aggregate materials are quarried and crushed down to size. Some companies use recycled materials, including metal, with the goal of keeping usable materials out of landfills, although the concrete aggregate may be slightly more expensive because it needs to be thoroughly cleaned before use.

Some contractors like to use exposed concrete aggregate in their projects, making the aggregate visible with a variety of construction techniques. Concrete with exposed aggregate is designed to be pleasant to look at, and it may be made with aggregate which is decorative as well as functional. This technique is often used for walkways and concrete furniture to add more visual interest to what would otherwise be a bland gray expanse.

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lighth0se33
Post 6

@Perdido – I guess that would depend on how dirty your concrete is. Do you have stains, or is it mostly just dirt?

I wash my concrete aggregate driveway with a pressure hose, and I've never had any problems with it coming apart. I think that a dried aggregate surface is pretty tough, so you should be fine to use your hose.

If the hose doesn't shoot all the dirt off, you can try a little bit of dish soap diluted with water. If that doesn't work, there are cleaners out there containing acid made specially for cleaning concrete aggregate.

After you have cleaned your home, you might want to apply a concrete sealer. This will help keep it cleaner in the future.

Perdido
Post 5

How should I go about cleaning my aggregate concrete? The outside of my home is made of this, and it has gotten pretty dirty over the years.

I have high water pressure in my area, and I have been afraid to use the garden hose on my house. I don't want to send any of the stones shooting out of their beds.

Should I just scrub my house down with soapy water and gently rinse it with the hose on a low setting? Is there some special type of cleaner I should use instead?

wavy58
Post 4

There is a house in my neighborhood made of exposed aggregate concrete. The driveway is made of the same material, so the house looks like a vertical continuation of the driveway!

It is a pretty cool visual effect. Both house and driveway have yellow, orange, and pink stones, giving them a warm feel and a brightness that ordinary concrete lacks.

My neighbor was particularly concerned about the amount of tornadoes we have in our state, so he wanted a concrete house that could stand up to extremely high winds. Because of concrete aggregate, he didn't even have to sacrifice appearance for sturdiness.

shell4life
Post 3

My dad has worked in construction for decades, and he and his crew have built several high-rise office buildings from lightweight concrete aggregate. He says that it is a good, sturdy material for structures that have a lot of weight and height.

From the outside, they look attractive, as well. There is one building that is the gray color of concrete, but the incorporation of various colors of stones into the mix makes it visually interesting.

Of course, when building something that is several dozen stories high, the durability of the structure is the main concern. Appearance is secondary.

anon74725
Post 1

It is good for students and engineers. I want more details about a pt slab.

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