> Foam concrete, also known as Lightweight Cellular Concrete (LCC), Low Density Cellular Concrete (LDCC), and other terms is defined as a cement-based slurry, with a minimum of 20% (per volume) foam entrained into the plastic mortar.[1] As mostly no coarse aggregate is used for production of foam concrete the correct term would be called mortar instead of concrete
https://en.wikipedia.org/wiki/Aircrete
It's pretty crazy stuff. It's light enough that it floats on water, and it's waterproof. It's also fireproof, as well as bug-proof and mold- and mildew-resistant. It's very durable but you can work it with hand tools, saw it, drill it, etc. It takes nails. It's also a great insulator.
There are folks who figured out how to make backyard-scale foamers for ~$100 of parts from any hardware store, and they make these beautiful aircrete dome homes: https://www.domegaia.com/
I've also seen companies that manufacture large aircrete bricks that are assembled onsite like giant LEGO blocks.
You need to have a sufficient range of particle sizes to fill in the gaps between the stones.
An individual stone is strong and has no voids. A pile of stones is weak because it has voids, the stones can roll around each other, and don't have much contact area. In concrete (and asphalt, etc.) the voids between the large stones are filled with sand. The gaps between the sand grains are then filled with cement, which is even finer. You end up with a solid mass of material with minimal voids and all the particles fixed in place.
Concrete is stronger than mortar because a larger portion of it is solid material (the interior of the stones is solid, whereas the "mortar" contains voids between the sand grains).