Anyone have experience with cellular concrete (AirCrete)?

Question

I am in the process of building an AirCrete foaming gun and molds, with the intent of making insulating blocks of light weight, low density, low-to-medium strength concrete. I am curious if anyone has experience with cellular concrete in any capacity; e.g. residential construction, parking pads, concrete floors, insulated walls/floors, geodesic domes, ADUs, etc.

My main interests are for low cost insulators for non-residential applications, but if I can integrate micro rebar or other enhancements and achieve a code compliant (by PSI compression test) formula, then it's a matter of finding a PE to sign off on a floor, foundation or wall application. I think the cost savings could be significant, but the main hurdle seems to be getting through local inspections. I see no mention of cellular concrete in any local or state code inspection other than 'you can't do that' (note 402.2d)  in non-weathered applications. Weather protected, the 2500 PSI seems to be the metric in NC. For me, in residential applications, it's a matter of figuring out the density formula, assuming a PE would sign off. For non-residential applications (like north side green houses) the thermal benefits could be significant and I'd be exempt from permits.

So, a quick rough estimate of my expected usage: portland cement to water ratio is 2:1 with no aggregate added, foam to slurry ratio roughly 4:1. I plan to run compression tests, with at least two tests, including nothing added and with micro rebar added at different ratios of foam to cement slurry, to see what makes sense.

I'm not sure what I'll discover, but if anyone in NC (specifically central NC) is interested please respond and I will keep you updated.

Russell W. · Answer

I have experience with cellular concrete in a commercial application as mass-backfill (15,000 cubic yards) for a newly constructed building where existing soil bearing pressures were poor. True cellular concrete does not have nearly the compressive strength you are looking to achieve, with 28 day breaks closer to 300-400 psi, rather than the 2,500 that you're looking for. As you noted, cellular concrete is essentially just cement, water and the foaming agent. To achieve higher psi's you'd need to introduce course and fine aggregates. At that point you're getting into what would be considered "lean concrete", which of course becomes heavier. Cellular concrete, while extremely light, is rather brittle (for lack of a better term) and breaks apart like chalk.

Chris Martin · Answer

10-4, thanks for the post. My main interests are for low cost insulators, in potentially hot and humid environments. For structural parts, if I use any, my plan is to use less foam and more Glass Fiber Reinforcement (GFRC) along with galvanized mesh reinforcement. I'm new at this and experimenting. The 2500 PSI is roughly 17.5 MPa, and it looks like adding GFR can increase compressive strength on the order of 25%, up to 40 MPa for 'regular' concrete. I'll add air to approximate 17.5 MPa target and see how it goes.