A HOUSE MADE OF CEMENT AND SOAP BUBBLES? MAYBE! (Part 3)

Welcome back!  As you can see from parts 1 and 2 of this post, theoretically, cement and soap bubbles as a building material may not be as silly as it sounds.  Cellular concrete is simple and cheap to work with and seems to have serious positive attributes.  Now, it comes down to simple questions of strength and durability.  These questions require some testing and that is what this post is all about.

Proper testing would require some special equipment including high pressure hydraulic presses with precision gauges for testing strength, drying equipment and precise scales for measuring moisture content, and precision devices for testing impact resistance.  Reality being what it is, I neither have nor have access to such equipment.  There is also a matter of time and funds for multiple testing of multiple batches over a long period of time.  With these factors in mind, do not consider my tests as conclusive.

Removing the form the following morning went very well, still soft but plenty firm enough to hold its shape.  As you can see from the first photo, soft means soft enough to cut with a drywall broad knife.  Being able to cut the material into blocks, shapes, etc., was the first test and went as expected from the information available.  Certainly not what would be expected from regular concrete.  The original pour was 6ft by 16in by 3in, with the cut leaving 2ft and 4ft lengths for further testing.  I then cut a 1in strip from the end of one of the blocks in order to have smaller pieces to test.

Patience is a virtue, though not necessarily one of mine, thus my first big mistake with this project.  Though anyone who has worked with concrete knows it is not really solid after 12 hours, my impatience got the better of me and I lifted up the longer section.  I found it to be very light, however, it also flexed as I lifted it.  Realizing my mistake, I quickly lowered it back down, but the damage had been done.  After a week of cure time, the cracks formed by my mistake were painfully obvious as seen in the photo.  Needless to say, after such a blatant error, I didn't touch it again for a full week.  Lesson learned (at least for this time).

Testing compression strength requires equipment that I do not have access to.  However, while I can't test the actual compression strength, I am equipped to make simple comparisons.  Taking a small piece of aircrete and a similar size piece from the side wall of a concrete block for comparison, I placed them in a 20 ton press to see how they compared.  First, the piece of concrete block.  Ten full strokes of the jack handle were required for it to fail.  As you can see from this photo, it broke up nicely (and suddenly, I might add).

Next, the aircrete went through the same process.  Seven full strokes of the jack handle ended in failure of the sample.  This sample compressed slightly, then began to flake before breaking.  It did not shatter like the concrete, but did fail with less pressure.  Looks like the aircrete is not as strong, but there is also the consideration of cure time.  The aircrete had only cured for 1week, while the concrete block has been around for at least 50 years (yes, I know where it came from and remember when it was purchased).

For an impact test, I had nothing for comparison other than personal experience and my own subjective opinion.  Simply put, I beat one of the larger pieces with an 8lb. hammer to see how it held up.  It broke up more easily than I had hoped, and before breaking, it dented.  Yes, dented!  I was not expecting that.  As for breaking easily, I will also note that looking at the break, I found that the aircrete was still moist inside indicating that it is not fully cured.

I also did a couple of other tests.  As previously mentioned, aircrete is light weight.  It is in fact very lightweight, so I pitched a chunk in a bucket of water.  Yes, it does float.

When I mentioned this type of material to my daughter, one of her questions was about flying debris during a tornado.  Having no answer to such a question and not willing to wait for a tornado to test it,  I devised another test for high velocity impact.  After placing a piece in front of a good back stop. I shot it with a couple of calibers of firearms at a range of 15 yards.  The bullets went completely through the 3in. thick sample.  Though I consider this a fail, in all fairness, at least it didn't shatter.  Also, with the thickness of a house wall and more cure time, it might do better.

After testing, some of my skepticism has been eased.  Compression test comparison wasn't bad considering the short curing time.  The same is true for the impact test.  High velocity impact tests are a concern and I certainly wouldn't consider it suitable for a combat zone.  Weight (or lack of it), and ease of free form use are great.  As for floating, not sure how that is necessarily good or bad.  In the event of a major flood, would the house float away?  A thought for laughs at least.

As stated above, these tests are not precise or conclusive, but simply my attempt to gain enough information to make an informed decision on aircrete as a possible building material.  These tests were done at 1week of cure time and I will be doing follow up and posting updates when it has cured more.

If you have any questions or suggestions for further testing, please let me know in the comments.  I look forward to all response.

Thank You.

A HOUSE MADE OF CEMENT AND SOAP BUBBLES? MAYBE! (Part 2)

In part 1, I briefly laid out some thoughts on a variety of alternative materials, the pros and cons (which certainly do not apply to all circumstances), and how I discovered the concept of aircrete, aka cellular concrete.  Now, I will try to give a clear idea of how it works.

As with any type of construction, there are specific tools required.  In this case, the only equipment needed is a large container to mix the cement in, a means of generating foam and a means of mixing the foam into the cement.  The container can be a 55 gallon barrel (ideal for mixing a full bag of cement), or any large water tight, open container (depending on the size batch).  I used an old feed tub acquired from a local rancher, which works well for mixing a half bag batch.

Equipment for generating foam and mixing can be purchased, or you can make and improvise equipment which will do the same job with less expense.  You will also need an air compressor that will maintain 90 pounds of pressure to generate the foam.  I already had the compressor and chose to make and improvise the foam generator and purchase a mixer attachment for my drill.

The contraption made of PVC pipe and assorted hoses and fittings at the top of the first photo is my home made foam generator.  Assembled mostly from left over and salvaged items, the cost was really cheap.  Operation is simple.  Fill the tank with the dish soap and water mix, hook up the air compressor, open one valve to pressurize the tank then open the other valve to get the foam.  The foam in question is pretty much the consistency of shaving cream.  To make sure the mix and air pressure were correct, I weighed the foam on a kitchen scale.  According to the instructions, the foam should weigh approximately 3 ounces per quart.  Mine weighed just under 3 1/4.  Not bad for the first try.  Time to shut down the foam and mix the cement.

Half of a bag of Portland cement and 3 gallons of water into the tub for a thorough mixing.  My old, slow 1/2 inch power drill worked great, though you can't see the actual mixer in this photo.  The mixer is a standard drywall/grout mixer designed for use with a drill.  It came from the local home improvement store and was not at all expensive.  It took a few minutes for a good mix, which looked pretty thin to me and not much volume.  I actually thought about dumping the rest of the bag in and making a larger batch.  Really glad I resisted that impulse. 

Ready for the soap bubbles.  This was the hard part for me.  Having worked with concrete quite a bit over the years, it felt like a serious waste of perfectly good cement, but I pushed forward.  Adding foam with the mixer running, I saw the volume begin to grow.  Soon the approximate recommended volume was achieved.  After turning off the foam, I mixed a bit more to make sure the foam was completely mixed into the cement, as it tends to want to float on top.

Time to pour the test batch.  The form was something I put together quickly in advance using a couple of 2x4s and some thin scrap plywood.  It was not really very solid but all it had to do was hold the concrete in long enough to cure.  Thinking in terms of a tub almost full of concrete, my mind was thinking heavy.  Sliding the tub closer to the form removed that thought.  The coffee can I had on had to dip from the tub would not be needed.  I simply picked up the tub and dumped the mix into the form.  

Troweling the surface was interesting, and not at all like working with concrete.   The texture and flow was more like, you probably guessed it, shaving cream.  Actually, if you bake and have worked with meringue, it is more like that.  Still trying to wrap my head around working with something that looks like concrete and works like meringue, but I may have to get used to it.  Time to wait for the curing process. 

Your questions and comments are welcome, and I will do my best to explain.  I can hardly wait to show test results.  Thank you for your time and please stay tuned for part 3.

For more information on Aircrete, I have included a website which I found very helpful.  They give recipes and helpful tips as well as options for purchasing equipment, etc. 

 http://www.domegaia.com/how-to-make-aircrete.html