# Density of Concrete

The density of concrete usually ranges between 90 and 145 pounds per cubic foot.

However, variance in density is high.

When fully-set and cured, the eventual density of concrete is frequently 150 pounds per cubic foot(CF).

The metric equivalents range from 1,750 kg/m3 to 2,400 kg/m3.

Concrete is made by a process of mixing different aggregates like pebbles or sand with water and cement and letting it harden through the process of hydration.

Hydration is the process of allowing concrete to cure while being kept moist. Hydration causes crystals to form, and these crystals bind together in an interlocking manner.

The process of mixing concrete can be modified to form a higher or lower density of concrete end product.

Digging deeper, the density of concrete is capable of significant variance depending on the specific application and concrete mix design.

For instance, when lead shot is used as an aggregate in nuclear power station applications the concrete density can be up to 8900 kg/m3.

Conversely, when foamed concrete is used it can be as little as 1,000 kg/m3.

Another concrete application that requires concrete of high density is around steel cables that are stretched by hydraulic jacks.

The concrete is permitted to harden and then the jacks are released.

As the cables contract, they compress the concrete.

Compressed concrete is the strongest concrete there is and is used for bridges, roofs, and floors.

On the other hand, concrete with air entrained in it works well in harsh weather and is used in roads and airport runways.

Lightweight concrete uses pumice, a very lightweight mineral, as aggregate.

One way to determine the concrete density is to first determine the density of the materials that go into it.

Cement weighs 830 to 1,650 kilograms per cubic meter, equal to a range of 52 lbs. per cubic foot to 103 lbs. per cubic foot.

The rule of thumb is to consider that a 94 lb. bag of cement will make one cubic foot when it is freshly packed. Cement will naturally compresses when shipped.

Because of the large difference in bulk volume, cement should be measured by mass rather than volume.

As for concrete itself, the density of concrete of normal weight is about 2,400 kg per cubic meter, or 145 lbs. per cubic foot, as I mentioned earlier.

The density of concrete varies depending on the amount and density of the aggregate, how much air is entrapped or purposely entrained, the cement concentration, and the maximum size of aggregate used.

Lightweight concrete has a density of 115 lbs. per square foot.

Perhaps the easiest and most accurate way to calculate the density of concrete is to measure some into a container of known volume and weighing it.

Density is simply a mass to volume ratio.

If you are considering concrete countertops, you might wonder if lightweight concrete should be used to minimize stress on the cabinetry and flooring below.

But with standard counter top thickness of 1.5 inches, standard weight concrete weighs about 18 lbs. per square foot, while lightweight concrete weighs about 14.5 lbs. per square foot.

The 3.5 lb weight savings is not enough to make a significant difference, and concrete of normal density for counter tops is easier to polish.

If you need a lighter density of concrete, some or all normal-weight aggregate can be replaced with lightweight aggregate.

Half a pound of lightweight aggregate takes up as much space as one pound of normal aggregate.

In other words, same volume, but lighter weight.

Please know that there are important considerations to account for if you convert regular concrete to lightweight.

Lightweight aggregate in concrete mix affects the appearance, performance, and workability of concrete.

The lightweight aggregates are usually brown, orange, or dark gray, and because of their porosity, they don't polish well.

Using lightweight aggregates will also affect compressive strength, elasticity, and tensile strength.

Lightweight concrete that uses Vermiculite, Styrofoam, or Perlite as aggregates are not suitable for structural purposes.

However, for use as in insulation or a lightweight filler, lightweight concrete is a good choice.

A final consideration with lightweight concrete is that the aggregates are more porous and therefore hold more moisture.

Lightweight aggregates continue to soak up moisture for weeks after being watered for the curing process.

Therefore, concrete loses mix water to the lightweight aggregates during the curing process.

That water loss can cause variations in color, mottling, and surface cracks.

It's important to keep track of all the mix water added and keep it in the proper range so as not to adversely affect the density of concrete as well as its performance and appearance.

When you plan to build with concrete, always keep the required density in mind. Density is a vital property of concrete to consider when utilizing concrete as a building material.

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