CreteFoamer - Cellular Concrete Frequently Asked Questions

Cellular Concrete FAQ’s

What is the process for making cellular concrete?
For a drum truck or stationary mixer, a cement/water slurry is first made. For heavier finished densities, sand and aggregate may also be added. At the job site, an externally generated foam is then added to the mixer and then mixed for a few minutes. For volumetric mixers, the foam is added into the hopper. The foam is generated using a foam generator, such as the CreteFoamer. The amount of foam required is calculated to provide the desired final density.

What is the strength of cellular concrete?
As density is decreased, the compressive strength is also decreased. See strength tables and charts for more details, but as an example, 60 pcf density will have a strength ranging from 600 to 1000 psi.

Is truck clean-out a problem?
Usually it will be easier, but if there is cement paste without any foam incorporated into it coating the drum, it may be more difficult.

What is the set time for cellular concrete?
The set time for cellular concrete is usually increased over standard density concrete because the surfactant (foaming agent) may act as a retardant. Many retardants are either sugars, starches, or fatty acids. Foaming agents may include fatty acids or derivatives of fatty acids to provide foam stabilization.

I have read a little bit about cellular concrete and the term "pre-formed foam" is used. Why do you use the term "externally generated"?
We think “externally generated” is much more clear terminology and does not suggest a rigid petroleum based foam or something that is made a long time before it is used. The foam has the consistency of rich stiff shampoo lather and is generated “on-the-go” as it is mixed or injected into the mixer. It is externally generated rather than internally generated by the action of the mixer itself, as is the case with an air-entraining agent.

How much cement powder is used in a yard of cellular concrete?
A typical basic cement/water slurry mix may have 2300 pounds of Portland powder and 1050 to 1150 pounds of water. To make it easy, let’s round this to 120 pcf density. If we add foam to make a 60 pcf density cellular concrete, we will have two yards of finished material with 1150 pounds of powder per yard --- more than standard density concrete. If we add enough foam to get to a 40 pcf density, we will have about three yards of finished cellular concrete with about 770 pounds of powder per yard.

Can fly ash or ground slag be used in cellular concrete?
Yes. Just as in standard density concrete, the cure times might be extended. The maximum amount which can be used depends on the application. It is generally recommended that only type F fl y ash be used, rather than the higher carbon type C. High carbon materials may tend to break down the foam. Low density cellular concrete with high amounts of any fl y ash may shrink excessively after placement due to the action of free carbon. Most other cementitious materials may also be used in cellular concrete.

Can I use water reducers and other admixtures?
Yes, water reducers can be used and will help with dispersion and wetting of the cement powder before adding the foam. Most other admixtures can also be used, but in all cases tests should be run before mix design is finalized. Air entrainment admixtures should not be used in production of the slurry for making cellular concrete.

What about placement and finishing?
Depending on application, cellular concrete is often pumped. With high water content and low density, it may be virtually self leveling, but will always be more easily moved that standard density concrete. It is usually easy to finish, but at some densities, it is sticky and hard to trowel to a really smooth finish.

What about placement and fi nishing?
Depending on application, cellular concrete is often pumped. With high water content and low density, it may be virtually self leveling, but will always be more easily moved that standard density concrete. It is usually easy to fi nish, but at some densities, it is sticky and hard to trowel to a really smooth finish.

Note: The FAQs are correct to the best of our knowledge, but may not apply in specific applications or situations. Most of them are designed to provide general information, rather than information for a particular project or application.