Mix Designs FAQs

Q: Is cellular concrete chemically compatible with common admixtures?

Cellular concrete is compatible with common concrete construction admixtures; however, most common admixtures are added to plain concrete to effect a change in the characteristics of the concrete that are not applicable to cellular concrete application performance. As an example, cellular concrete needs no air entrainment or finishing aids; however, color admixtures and strength enhancing admixtures work well if they are applicable to the project.

--------------------------------------------------------------------------------------------------------

Q: What additives are common to cellular concrete?

Fiber reinforcement
Heat-of-hydration reducers (iced water or chemicals)
Compressive strength enhancers
Coloring pigments or color enhancing admixtures

--------------------------------------------------------------------------------------------------------

Q: What is the correct water to cement ratio for the cement water slurry?

Typically, a .5 water to cement ratio slurry consisting of two parts cement to one part water is typically used as a base mixture for cellular concrete. The water cement ratio is varied according to specific project requirements. We should note that cellular concrete obtains it’s natural fluidity from the air bubble structure, not from excess water content.

--------------------------------------------------------------------------------------------------------

Q: Do cellular concrete mix designs contain either fine or course aggregate?

Cellular concrete may also contain normal or lightweight, fine and/or coarse aggregates. The rigid foam air cell system differs from conventional aggregate concrete in the methods of production and in the more extensive range of end uses. Cellular concrete may be either cast-in-place or pre-cast. Cellular concrete mix designs in general are designed to create a product with a low density and resultant relatively lower compressive strength (when compared to plain concrete). The typical density range of neat cement cellular concrete mixes is 20 – 60 lbs/cu. ft. which develops a corresponding compressive strength range of 50 psi – 930 psi. When higher compressive strengths are required, the addition of fine and/or course aggregate will result in a stronger cellular concrete with resultant higher densities.

We should note that most cellular concrete applications call for a lightweight material. When considering the addition of course aggregate, one must consider how appropriate this heavy aggregate will be to a project, which typically calls for lightweight material. The inclusion of aggregate, particularly course aggregate may be counterproductive to the materials intended performance.

--------------------------------------------------------------------------------------------------------

Q: What type of cement is appropriate for cellular concrete?

Cellular concrete may be produced with any type of portland cement or portland cement & fly ash mixture. The performance characteristics of type II, type III and specialty cements carry forward into the performance of the cellular concrete.

--------------------------------------------------------------------------------------------------------

Q: Is it appropriate to add fly ash to the cement and water slurry for cellular concrete?

Fly ash added to the cement does not adversely affect the basic hardened state of cellular concrete. Infusing and supporting the cellular concrete with the air cell system is a mechanical action and is not problematic with fly ash or admixture concrete chemistry. Note that some fly ash mixes may take longer to set than pure portland cement applications. Mixes with large percentages of fly ash may take an very extended time to set up. High carbon content fly ash such as typical “bottom ash” should be generally avoided in most cellular or plain concrete mixes.