Cellular Concrete Basics
If you are just getting started with cellular concrete or if you have basic questions about cellular concrete, here is a great place to get started. We will explain what cellular concrete is, what applications it is used for, and frequently asked questions. If you still have questions after reading this page, give us a call to discuss your questions or check out our other resource pages to learn more about cellular concrete.
What is Cellular Concrete?
Low density cellular concrete, as defined by ACI chapter 523.1, is concrete made with hydraulic cement, water, and preformed foam to form a hardened material having an oven-dry density of 50 pounds per cubic foot (PCF) or less.
Although the ACI definition specifies low density cellular concrete with a density lower than 50 PCF, cellular concrete can range in density from 20 PCF to 120 PCF.
In a broader sense, any cementitious slurry, or cementitious material that uses an externally generated foam to increase air content above 10%, could be considered cellular concrete. Cellular concrete may go by other names including foam cement, foamed concrete, or lightweight flowable fill.
Although there are a number of lightweight cementitious materials, the key differentiating factor between cellular concrete and other lightweight cementitious materials is the use of externally generated foam to reduce the density. Probably the closest material to cellular concrete is aerated autoclaved concrete (AAC).
The primary differences are the processes used to create the air within the material and the required equipment. AAC uses a chemical reaction within the slurry itself to generate air voids for density reduction. However, producing cellular concrete with externally generated foam provides a more versatile material at a fraction of the capital costs required for equipment.
Uses and Advantages of Cellular Concrete
Cellular concrete has many uses and does not have one singular advantage. Depending on the application, it may be chosen for its thermal and acoustical insulative properties, pumpability and flowability, ease of handling due to its light weight, or as a cost saving alternative to fill materials. Throughout the world, cellular concrete is used in building and construction applications such as roof decks and floor decks, and geotechnical applications such as annular space filling in slip lining and void fill abandonment. Cellular concrete can also be found in architectural and precast applications. Below are many of the more common applications for cellular concrete; however, it’s not an exhaustive list.
Void Filling: Sinkholes, wells, tunnels, cisterns, abandoned utility pipes, annular grouting. Flows easily and provides reduced weight on soil.
Soil Remediation: When poor subsoil conditions exist, cellular concrete can be used to create a strong base while reducing burden on subsoils.
Utility Trench Fill: Protects and supports utility lines and reduces or eliminates need for compaction.
Flowable Fill/Geofoam Alternative: Any applications where flowable fill or geofoam blocks are being used, cellular concrete is an excellent alternative, and in many cases the preferred material choice.
Culvert Trench Fill: Prevents later soil settlement and subsequent dips in road.
Bridge/Overpass Abutment Fill: Eliminates post-construction settling. Because cellular concrete does not need compaction, it won’t compress over time, creating a “dip” in a bridge or overpass approach. Additionally, lateral loads against the existing abutment are essentially eliminated.
Retaining Wall/MSE Wall Backfill: The lateral load reduction is the primary advantage. Cellular concrete can also greatly reduce potential damage to the geogrid during the backfill process.
Fence Panels Along Highways: For sound control and visual blocking. Cost savings potential due to weight savings.
Crash Barriers/Energy Absorption: Pre-cast variable density cubes or pour on location.
Floor Decks: Reduces structural weight while maintaining quality of concrete floor. Used for leveling and replacement of gypsum-based mixes.
Roof Decks: Reduces weight and provides thermal and sound insulation. Moderate slopes are possible.
Precast Specialties: Reduces weight and cost. Reduces transport costs/allows more pieces per truckload. Easier installation.
Thermal Backfill and Sub-slab Fill: Provides thermal insulation and water resistance, and reduces hydrostatic lateral load on foundation.
Interior Walls: Cast on site tilt-up or panel assemblies. Reduces weight and cost below full density concrete wall. More soundproof and fire resistant than stud wall.
Retaining Wall Base: Proper mix design will be self-leveling and can greatly speed base construction and improve load capacity.
Sidewalks, Patios, and Porch Decks: Reduces weight and cost.
Carved Concrete Sculptures: Cellular concrete in the 40-60 PCF range can be carved and shaped with chain saws, hand tools, and other methods to create artwork from a unique medium.
Cellular Concrete FAQs
Note: The following answers 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.
What is the process for making cellular concrete?
There are two methods for producing cellular concrete. The first is the batch production method in which externally generated foam is injected into the drum of a mixer for a calculated amount of time. The second is the continuous production method in which foam is injected in-line, on the discharge side of a pump. Richway offers equipment for both production methods.
What is the strength of cellular concrete?
As density is decreased, the compressive strength also decreases. See the strength tables and charts for more details, but as an example, 60 pcf density will have a strength ranging from 600 to 1000 psi.
When using the batch method, is truck cleanout 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 typically a little longer compared to “normal” concrete, due to the surfactants used in producing the foam. However, like anything produced with Portland cement, there is a finite time for production and placement. Generally, we recommend that the working time be limited to about four hours once the Portland is mixed with water, or about three hours after the foam is added. After this much time, the material should be left alone to continue the set process. Continuing to pump or move the material can result in collapsing and failure of the material. However, the set time can vary depending on the application, jobsite conditions, and the use of either retarders or accelerators.
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 doesn’t suggest a rigid petroleum-based foam or something that is made a long time before it’s 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?
If a neat cement slurry is used with a .50 w/c ratio, the base slurry per yard will have approximately 2060 lbs of cement and 1030 lbs of water, with a density of 115 PCF. If foam is then added until the density is 30 PCF, we’d have 3.65 yards of 30 PCF material, with approximately 565 lbs of cement per yard. We have a mix design calculator available on our website that calculates mix design batch weights, foam dose times, and cost scenario analysis.
Can fly ash or other pozzolans be used in cellular concrete?
Yes. Just as in standard density concrete, the final material attributes will be affected, generally in much the same way alternative pozzolans will affect "normal" concrete. Regarding fly ash, it should be noted that high carbon content ashes may tend to break down the foam, and therefore should be avoided..
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. Some super plasticizers may break down the foam, so thorough testing is essential. Air entrainment admixtures are usually not used in production of the slurry for making cellular concrete because the foam is the air that is added to the mix.
What about placement and finishing?
Cellular concrete is easily pumped. With high water content and low density, it may be virtually self-leveling, but will always be more easily moved than standard density concrete. It is usually easy to finish, but at some densities, it is sticky and hard to trowel. Generally no finishing is needed for geotechnical applications.
Are there any problems with pumping?
Cellular concrete pumps and flows extremely well.