To make aerated concrete, add a foam-forming agent and stir in a significant amount of air. This serves to make the concrete significantly lighter, better insulating, and more resilient to fire. Making it can however be a bit of an issue, often requiring ingredients that aren’t purchased at the average DIY store. This is where [NightHawkInLight]’s method seems rather promising, requiring effectively only xanthan gum and dishwashing detergent.
For the small-scale demonstration, 15 grams of the thickening agent xanthan gum is mixed with enough alcohol to create a slurry. To this 60 mL of the detergent and 1 liter of water is added and mixed until the xanthan gum has absorbed all the moisture, which takes about 5-10 minutes. This mixture is then added to Portland cement with two parts cement to one part xanthan gum/detergent mixture and mixed for a while.
Of importance here is that this mixture will keep expanding in volume while mixing, so you have to have to keep an eye on the amount of air relative to concrete, as this will determine the strength and other properties of the final aerated concrete. If you continue past a certain point you will even create open-celled aerated concrete that’s completely porous, so you have to know what kind of concrete you want before you start mixing up a big batch.
The basic physics behind this approach seem fairly straightforward, with the air captured in soap bubbles by the detergent, reinforced by the xanthan gum to make them significantly more resilient. A normal concrete mixer seems to work fine, but a mixing rod or kitchen mixer seem to do a much better job at getting a predictable result.
After pouring the aerated cement mixture into a mold, it should be kept moist while it cures, as it is more fragile than typical concrete, but if done properly you can produce for example cinderblocks that are quite insulating, as well as something akin to AAC blocks, conceivably with even better performance.
FYI he had a follow up post about adding sand to the mixture that worked well also.
this guy is awesome. when i get my farm i plan to reproduce this and many of his other experiments for the build out
The process seems a bit laborious though, even with the cement mixer. I wonder how it scales up.
It doesn’t, otherwise it would have been common practice in roman times
Roman times were not the apex of human technology. Just because they didnt do something with concrete doesnt mean it doesnt scale. Look at shotcrete. Romans didnt have that either but it scales perfectly fine,.
People love Roman ‘crete.
Until you tell them it didn’t flow, had to be hand applied and shaped.
Similar to roller compacted ‘crete now.
My buddy has a small trailer built commercial concrete foam mixer plant that puts out ~10 m3./hr. The company makes much larger machines as well. Lightweight Cellular Cement is used extensively in bridge fills and wing walls. While this DIY tech might not be so efficient, the tech itself scales just fine.
I’m not so worried about the tech itself, but whether you have to mix and pour this version in small batches simply because the foam might collapse. After all, it’s just dish soap and xanthan gum, which is not really an emulsifier or a glue, or a foaming agent, but a thickening agent.
The xanthan gum makes a shear-thinning liquid much like ketchup is, so the air bubbles and particles stay in suspension when it’s still. If you put a force on it or you shake it, it’ll flow and the particles and bubbles may separate. That’s why, if you pour too much at a time, the weight of the foam itself may cause the mixture to separate before the concrete sets, or you never get it to foam up properly if you mix too much at a time. It may come out like a bad souffle.
If you have to make it one half-bucket at a time, you can’t really do anything other than play around with it.
UK public buildings containing RAAC concrete are closing because of water damage to the metal reinforcement inside the blocks. Aerated might not be the way to go.
I was wondering about trapped moisture and all the various problems it causes
Reported to UK police for ‘wrong speech’.
I don’t think he was advocating its use for weather-facing structural components, and don’t see how anyone with two sense would think it’s a good idea,* but imagine a typical CMU wall for load bearing, faced with aerated blocks for fire-proof insulation.
Or indeed any structural component except maybe the floor deck in a mid-rise?
Like many building materials, weather facing applications require a surface coating sealant.
Only a problem if you actually need the steel reinforcement in your aerated bits or don’t do something to prevent that steel from rusting easily. Which as a rule I’d suggest isn’t true – lots of structures don’t need it or use a steel frame that isn’t cast into the concrete with concrete blocks, timber, etc used to fill in the walls. Though no doubt the buzz of ‘cheap’ and ‘better’ RAAC buildings have got all over the place before it became clear how much its lifespan drops for getting a bit damp…
For instance something lots of us might want to build one day if we don’t already have it is a workshop garage/shed – usually going to be single story, probably fairly small and to get S.O or planning permission type stuff its going to be rendered or clad in something ‘pretty’ that will protect the structure from the weather…
So while I’d probably be using solid concrete blocks in a column under the roof frames to make sure it can take the potential snow load etc (as crazy as snow would be around here) aerated for the bulk of the walls aught to be fine, and would help the structure stay warm/cool inside. Though I’m not sure I’d use DIY versions though – actually testing your blocks/concrete pour and getting a reliable enough results is probably too costly to be worth it for an even slightly structural wall on such a small scale build.
One crucial step to apply concrete is to use a concrete vibrator tool to remove air bubbles and reduce oxidation of the internal metallic structures. Putting air inside concrete probably will increment that kind of degradation. Unless we are talking about other uses, with small life spans, like roof top covers, slabs or something similar. No such thing as bad materials only bad materials applications.
Adding to the conversation – this type of material (cellular concrete) is often used as flowable fill for a bunch of handy applications where you want something strong-ish but less dense (ie cheaper and lighter) than normal or lightweight concrete. Stabilizing soils with expansive clays, prepping subgrade for laying slabs or fittings, filling in ditches or covering pipes/conduits with something that can be removed with hand tools, filling large cavities economically (pools, voids under slabs, etc), and it can be pumped much farther than normal concrete without performance loss.
I’m excited to try this out. However I question the R value test method he used. I think it would be more accurate to expose both the aerocrete and foam board to a constant temperature environment (no foam board on top), then compare the temperatures of each. And I believe the higher (brighter) thermal camera readings would indicate the less insulting material, with a lower R value, not higher, as he thought.
What density does this aerated type give you (in kg/cm^3 or equivalent)? And what would the density be for a solid lump of the same sort of concrete? Would be nice to have an idea of the difference without having to check through a whole video for the two numbers… Also, I wonder, if this stuff is much lighter than normal concrete, might it work well as a lower density alternative to epoxy granite for damping vibrations in moving parts of machinery where you want to absorb vibrations but also keep the parts light in weight.
This is so timely. I’ve been scratching my head wondering how to insulate a 150 gallon stainless steel water tank, which I’m hoping to use as thermal storage for a thermosyphon hot water system. Easy enough to insulate the walls of the tank, but how to insulate the bottom, and bear the load of the full tank of water… Aerocrete might be just the ticket.
Use aerogel blanket. It’s made for this task, and it’s well studied and tested, unlike this stuff that’ll likely break as the gum is rotting inside the concrete. I think you don’t want to dismantle your installation in 2 years because of a “teasing” chemical trick from a random dude on youtube.
The xanthum gum is not a structural component. Its only purpose is to toughen the foams bubbles so they do not pop before the concrete hardens. Commercial foaming agents are generally a blend of hydrogen peroxide and plant surfactants, the latter of which are just as degradable, and inconsequential to the longevity of the resulting form as this guys xanthum gum.
It ends up as a structural component whether you like it or not, because it’s mixed in.
Like sugar. Different amounts make concrete set faster, slower, tough or brittle… there’s no telling what the xanthan gum really does, and in what amounts, until you test it, age it, expose it to moisture or dry it up completely, and then test again.
The structural strength comes from the concrete. The xanthum, and soap are just the structure of the foam. The speed of setting is a question of temperature, humidity, and the overall hydration of your mix. The foam does not significantly impact the setting speed beyond its contribution to the overal hydration. The main attribute beyond density that the foam influences is how frangible the resulting blocks are.
Which is mixed with a bunch of soap and gum. You don’t think those have any effect on what the concrete does, how it solidifies, distributes itself, or changes in chemical composition or crystal structure whatsoever?
It’s just “concrete is concrete is concrete”, right? Exactly the same as the commercial mixes.
Picture a bubble inside a block of concrete. The bubble is coated with xantham. The concrete dries and the bubble bursts. Is the xantham on the surface of the void structural….nope its not carrying any load. Air entrainment in concrete is not new at all, been around for years with various ways of enhancing the bubbles.
Sure, except at $40 per square foot for 3.5mm thickness it’s probably the most expensive option available.
Is there any alternative to Xanthan gum used, as it is not so easy to find in some countries. Would gelatin powder work instead, or maybe egg white?
At least based on my experiments with thickeners in ice cream – gelatin behaves EXTREMELY differently (and IMO generally inferior to) xanthan gum – especially when you want something to “fluff up” with entrapped air. The only reason I’d ever bother with gelatin in my applications again is because (as this video hints very strongly) – xanthan won’t thicken in a high-alcohol environment but gelatin will.
A mix of xanthan and guar gums often performs significantly better than either alone (I discovered the trick from a white paper about using 25% xanthan 75% guar as an ice cream additive), but IMO guar without xanthan performs very poorly.
This and Starlite goop foundation under aerogel and those thin Mylar sheets. All of the above.
The best part is every part.