Cellular Concrete Technical Information
The lower the density of concrete, the lower the strength. Replacing solid material (aggregate or sand) in the cured concrete with air will reduce strength. Compressive strength drops rather markedly as
density decreases. Flexural strength of cellular concrete is generally 1/3 to 1/2 that of compressive strength. Conversely, thermal and acoustic insulative properties increase as density is reduced.
In general terms, a “normal” concrete mix will have a compressive strength of 3000 to 5000 psi and a
density of 145 pounds per cubic foot (pcf). Strength can, of course, be varied considerably by
cement-sand aggregate ratios, choice of aggregate, admixes, and a number of other factors. A cellular concrete of 80 pcf density with a 1:4 cement/sand mix and no aggregate will have a compressive strength in the range of 500 psi. A cement only (neat cement) cellular concrete of 40 pcf will have an approximate strength of 400 psi. Thus cellular concrete mixes with densities below 90 pcf have limited structural strength, but still offer
considerable advantages over standard concrete in some situations.
The production of cellular concrete is conceptually very simple. A cement/sand slurry is first produced using conventional mixing equipment. Then the amount of foam required to reach a chosen density is added and mixed into the slurry. It is important that the base slurry have sufficient water, as too little water will cause the foam to partially collapse as it gives up water to fully hydrate the cement.
It has been said that “the devil is in the details” and it is these details that make the leap from concept to consistently good field results sometimes difficult. To obtain consistent mechanical properties of the cured concrete, it is vitally important to have a consistent slurry and foam mixture. Most information about cellular concrete discusses only foam density
(expansion ratio), leaving the impression that the operator need only turn on the machine and make foam. From our years of designing and manufacturing foam
generating equipment and foaming agents, we know that consistently producing a good quality foam is not that simple!
For example, hard water requires more foaming agent than soft water and cold water generally does not make as much foam as warmer water. Hot air
temperature will cause foam to break down more quickly and with some foaming agents, the use of an overly high ratio of concentrate will result in a lower foam output. Another variable seldom touched upon is the importance of having a
consistent and small bubble size, similar in appearance to shaving cream. Bubbles which are too large will tend to compress at the
bottom of the pour and be too large at the top for accept-able strength properties.
Use of well designed and reliable foam generation equipment which allows control of the variables and which makes a consistent foam is the single most
important factor in quality cellular concrete production.
At Richway, our expertise is in the design and
manufacture of foam machines to reliably produce the consistent foam required in creating cellular concrete. Our core business, for 34 years, has been the design and production of foam marking systems to mark the path of
agricultural field chemical sprayers. Using surfactant based foaming agents, very similar to that of cellular concrete foam, foam balls are generated and dropped off the end of the sprayer boom to create a path of foam. This allows the operator to know where he has been and prevent application overlaps and gaps, which can greatly reduce crop yield.
Richway manufactures “private label” foam marking
systems for the three largest farm equipment manufacturers in the world, in addition to a large number of other sprayer manufacturers. Equipment
reliability and easy serviceability are essential, because missing the application time “window” for some chemicals can result in considerable crop yield loss. We have also worked with the pest control and greenhouse industries and have produced foam equipment for a variety of cleaning applications.
Cu. Ft. / Cu.
Yd. Cured Concrete
R rating per
(fl. Oz. per Cured Cu.
yard) (see note 2)
|30 to 900
||12 to 25
||.75 to 1.85
||11 to 24
cement & water)
|400 to 1500
||6 to 10
||.25 to .30
||6 to 10
||Sand Mix (Portland
type cement &
|1500 to 2000
||3 to 6
||.1 to .2
||3 to 6
||Sand Mix or Light
|2500 to 5000
||1 to 3
||1 to 3
||Typical Structural Mix
(Foam added to enhance
flow characteristics of
lower slump mixes)
Note (1): All values above are averages and suggested starting points to achieve desired cellular concrete mix designs. Values will vary based on sand and aggregate, if any, selected, as well as water quality.
Note (2): Foam concentrate usage based on 2.5 lb. Per cubic ft. foam mixed at nominal 40:1 water/concentrate ratio. Actual consumption will vary based upon foam concentrate manufacturer and water quality.