CreteFoamer Blog

Flowable fill, as it is often called, more formally known as Controlled Low Strength Material (CLSM), has an important place in infrastructure construction. It typically has a small percentage of cement (which may include fly ash), aggregate (usually fine), sometimes local soil, and lots of water.  The water provides the flowability, but must be drained away at the deposit site, which can be a problem.  Foam can be used in place of water to provide flowability and does not have to be dealt with at the deposit site.  Furthermore, use of foam can create a lower density fill which put less load on the substrate below the fill. You may have to slightly increase the cement percentage to get required strengths, or just allow the foam to collapse at the deposit site and then be sure you have completely filled the deposit site. This will result in a "full density" fill.  If you choose the latter approach, you need to use a "flash foam," which is different from our standard CreteFoam concentrate.  Want to know more?  Call 800-553-2404 and talk to Tony, Marty, or Rich.

Lying within the City of Bath World Heritage site, the picture-postcard village of Combe Down is
home to what is thought to be the world's largest single use of foamed
concrete, with the estimated final volume approaching 600,000 cubic meters
and due for completion by December 2009.  {785,000 cubic yards]

Click on this link to learn more about this multi-year project in southwest England.

CLICK HERE



The concern is that the supports which were left during mining of the limestone were too small and too far apart to safely support the ceiling of the mine.

Last Friday, October 16, these two skidmount Cretefoamers were "posed" and photographed before crating for shipment. The one on the left is a CFVT-8C-SM and the one on the right is a CFVT-20C-SM. Skidmount units include water tanks and gas engine powered air compressors (diesel available) to make a complete stand-alone package, ready to go to work. The "8C" has a foam output rate of 8 CFM and has a 100 gallon water tank. The "20C" has a foam output rate of 20 CFM, with a 300 gallon tank. Both can run continuously -- there is no pre-mixing and no guessing required. Rugged, reliable, and simple are three of the many words which describe Richway CreteFoamers. Unfortunately, these are both powder coated black and thus don't show up very well.

Here's a response to some emailed questions we got this morning from a prospective customer in Europe. The questions are not included, but you can figure them out. Go to the "contact us" section of the main website www.CreteFoamer.com if you want any further information.



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Your mix can include Portland cement and sand and aggregate as well, depending on dry density desired. We will be glad to provide a suggested mix design based on your desired density and strength. You will have to adjust this based on the materials you have available. Your production rate is one that we can meet with at least one model of our CreteFoamers.

We have two different foaming agents. Both of them will cost about $10 per cubic meter of foam produced. If you wish to make panels of 1/2 normal density, you will use about one cubic meter of foam per cu meter of concrete slurry in the mixer. Cellular concrete tends to set up more slowly than standard density concrete. You can add accelerator admixture to speed up the set-up time. Silica fume also speeds set-up, if you have it available.

You will mix a batch of material and then add the foam to it directly from the CreteFoamer as it is produced. The amount of foam you will need depends on the batch size of your mixer and the desired density. I am not sure what type of "normal concrete mixer" that you think will cause foam to be lost, but I do not think this will be a major problem. We have used a number of small lab mixers, as well as drum truck mixers and volumetric truck mixers. Ribbon and paddle mixers are also used. None of them seem to have a big effect on the foam.

Concrete density is determined by the amount of foam you put in each batch. You control this by the amount of time you run the foamer for a batch. The density of the foam itself is determined by the machine design, the foaming agent used, and the amount of foaming agent used. Our production sized machines have the ability to change the ratio of foam concentrate used, as well as the foam output rate. The density usually falls in the 3 to 4 lb/cubic foot range. (4 lbs/cu ft = 64 gms/liter) In our experience, it is important to have constant flow rate of foam and constant density, but if the density is in the 2.5 to 4 lb/cu ft range, the exact density is not critical. Using too little foaming agent may produce a foam which has the desired density, but not enough bubble strength and life to produce a good finished product. As the density of the concrete is reduced, it tends to shrink when too little foaming agent is used.

I know of no problems with steel reinforcement and cellular concrete. It is possible that the foaming agent could cause corrosion of the steel, but the amount of foaming agent per cubic meter of concrete is very low. I have not read or heard of any problems. The foaming agent is very similar to air entrainment admixtures. Air entrained concrete is commonly used with steel reinforcement.


We recently shipped a machine to Viet Nam which I think is going to be used in a plant similar to yours, but I do not believe the plant is completely set up yet.

I hope this has answered all your questions. Please email me with any more that you have or if I was not clear in my answers.
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Insulating Concrete Forms (ICFs) continue to gain traction in concrete construction.  We get asked about cellular concrete for use in ICF's with increasing frequency.  "Will it work?" is the essence of the question.  Short answer, yes.  

With 110 to 120 pcf cellular concrete and the proper mix design, it is possible to get compressive strengths in the 3000 to 4000 psi range, which is more than sufficient for above ground residential construction. See earlier posts to the blog.  Note too that the mix design does not have to be exotic, but primarily a low water and higher than normal amount of cement.  Exact strength, as we have noted before, is dependent on local materials, batching techniques and mixing in addition to the mix design itself.  It is the responsibility of the user to do testing of a chosen mix design. 

At a recent demo day, we filled a section of ICF and later stripped away part of the form to view the fill we had achieved.  As you can see, it was pretty good, especially considering that we did not vibrate and did only a minimum amount of tapping on the forms. Considering the flowability that foam adds to concrete, these results are not surprising.  You'll add some (not a lot) of insulative value to the wall at this density. An R-value of .25 to .33 per inch would be typical at density of 110-120 pcf.

Conclusion.  You can provide a good quality job and save money too with cellular concrete!

Stripped away section is in bottom photo..

Here it is, direct from ACI, a discussion of 7 and 28 day strength. See our strength test discussion a couple of posts down.

>>> Start of ACI post

"Technical Questions - ACI Concrete Knowledge Center


Q. We test concrete cylinders for compressive strength. Most specifications that we see require a compressive strength of 3000 psi (20.7 MPa) and testing at 7 and 28 days. What ACI standard stipulates the percent of the specified compressive strength that the cylinder must meet in order to pass the compressive strength test at both the 7- and 28-day ages?

A. ACI 318-02, "Building Code Requirements for Structural Concrete," and ACI 301-99, "Specifications for Structural Concrete," contain standards information related to this question.

Section 5.6.2.4 of ACI 318-02 requires a strength test to be the average of the strengths of two cylinders made from the same sample of concrete and tested at 28 days or at the test age designated for determination of the specified compressive strength.

ACI 318-02 doesn't state a percentage of the specified compressive strength that must be reached at 28 days. In accordance with Section 5.6.3.3 of ACI 318-02, the strength level of an individual class of concrete is considered to be satisfactory if every arithmetic average of any three consecutive strength tests equals or exceeds the specified compressive strength and no individual strength test (average of two cylinders) falls below the specified compressive strength by more than 500 psi (3.45 MPa) when the specified compressive strength is 5000 psi (34.5 MPa) or less.

Results from the 7-day tests mentioned are usually not used for acceptance purposes, and thus there isn't a percent of the specified compressive strength that the cylinder must meet in order to pass the compressive strength test. Section 1.6.4.2.e of ACI 301-99, for instance, requires molding and curing three cylinders from each concrete sample and testing one specimen at 7 days for information and two specimens at 28 days for acceptance, unless otherwise specified.

The 7-day test result is used to monitor early strength gain and is often estimated to be about 75% of the 28-day strength (Kosmatka, Kerkhoff, and Panarese, “Design and Control of Concrete Mixtures,” PCA, 2002). Neville (Properties of Concrete, 4th Ed.,” Prentice Hall, 1995), however, suggests that if the 28-day strength is to be estimated at 7 days, a relationship between the 28-day and 7-day strengths has to be established experimentally for the given concrete. For this reason, he states that various expressions for the ratio of the two strengths (expressions that were discussed in the previous edition of his book) are no longer thought to be reliable.

Regardless of the reliability of the estimate for 28-day strength, 7-day strength test results are useful to the contractor and concrete producer as an early warning signal. With today's fast-track concrete-placement schedules, it's essential for the contractor and concrete producer to know when 7-day test results are low. Then suitable steps can be taken promptly to adjust batch quantities, improve quality control procedures at the job site, and ensure that sampling, molding, and testing of the cylinders are being done in accordance with ASTM applicable standards.

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To purchase PCA documents referenced above, visit the bookstore at:
http://www.cement.org/bookstore/

To purchase the book by Neville, visit websites such as http://www.amazon.com


Posted 2/13/06.

Disclaimer: Questions in this column were asked by users of ACI documents and have been answered by ACI staff or by a member or members of ACI technical committees. The answers do not represent the official position of an ACI committee. Only a published committee document represents the formal consensus of the committee and the Institute. " >>> end of ACI post

These are micro photos of foam in our R&D lab. These are illuminated with an LED light source, with different magnifications. We do studies of both bubble size and pore size in the cured concrete because of the importance of pore size in influencing strength of cellular concrete.

Continuing with the Demo Day project discussed below, we did 7 day breaks on three 4x8 cylinders this week.  All three ranged between 2600 and 2800 psi.  Using the commonly accepted "7 day strength is 75% of 28 day strength" rule of thumb, this suggests 28 day strength of 3600 psi.  This more than adequate for many uses.  

Two items of note:  (1) The "75%" rule of thumb is only an approximation and will vary with mix design.  (2) This mix design used fly ash for 30% of the cementitious material.  Fly ash mix designs typically show lower 7 day strengths than Portland-only mixes, but higher 28 day strengths.

Here's the mix design:  Portland 724 lbs,  fly ash 310 lbs,  sand 2200 lbs,  water 430 lbs with mid range water reducer.  When we publish a mix design, it is with the understanding that it is only guideline and carries no assurances that you will get the same results.  Local materials, batching techniques, and mixing can and will affect final results.  As an example, fly ash varies from one generation plant to another.  This used no coarse aggregate, though most of our recent mix designs in this category have included coarse aggregate.  It was also somewhat "cement rich" even after the addition of foam, but money was still saved.

BOTTOM LINE:  Cellular Concrete Saves Money

and Solves Problems

Another Demo Day project was completed yesterday. This was a garage addition with a simple 42" deep trench foundation using a cement & sand mix with foam added to reduce density to 117 pcf. We have been getting 7 day breaks of about 2400 psi with this mix as a lab mix, so we were confident of being able to provide a quality footing/foundation.

We also wanted to test our old Mayco C30 trailer pump and the density gain we'd get with Cretefoam. Our pump performed flawlessly (it was probably the new $70 tires we put on earlier in the day.)  This mix pumped nicely, though slowly, as we obviously need some rebuilding of the pump.  Pumping through 100 feet of 2 inch hose, we had a density change of only 2 pcf.  We pumped about 5 1/2 yards of material. 

Manatt's, the local producer with whom we work on our Demo Days projects, had a really busy day, so we did not see our truck until 5:00, when Russ, one of our old "friends" pulled up.

Russ knows the routine for dosing the truck, so we got rolling pretty quickly. Everything worked as planned and when completed, the owner brought out a cold beverage for everyone.

This was not a big project, but did save 15% in materials by using cellular concrete and made a good demo project.