“Rice husks protect the precious grains from wind and rain, and their high silica content allows them to resist moisture and decay, meaning they naturally boast the same properties as many traditional construction materials. "The whole point of the rice husk is to protect the rice while it grows," Guimond says. "What is it protecting it from? Moisture, pests, rot, those types of things." 

In addition to protecting against moisture, the high silica content means rice husks are surprisingly resilient to fire, according to Fine. Modern Mill's product is designated as Wildland Urban Interface (WUI) compliant, meaning it has passed California's fire safety testing.”

https://www.bbc.com/future/article/20261009-the-houses-made-from-rice-husks

A paper from the Bluesky discussion where I saw the article

https://www.mdpi.com/1996-1944/18/15/3534

Deleted nonsense arising from confusing the bran layer with the husk. Delete at will.

Edited October 15Oct 15 by TheVat

Reading the link, it seems this is about combined ashes from controlled burning of rice husks and wood.

Rice husks apparently contain a lot of silica(!) which is present in the ash as finely divided amorphous silica. Wood ash contributes calcium oxide and other alkalis. The combination allows a "pozzolanic" reaction to take place in the presence of water, forming a hydrated, combined CaO.SiO2 structure which subsequently takes up CO2 from the air as it hardens. The term "pozzolanic" originates from Pozzuoli, near Naples in Italy, where the ancient Romans quarried siliceous volcanic ash which they used in this way for construction materials.

What isn't clear to me is how much building material can be produced from the amount of rice husk and wood ash available. Clearly this can be an elegant way to deal with rice husk waste but is enough generated, I wonder, to support commercial scale production of blocks for building? Or will the idea founder on the need to spend a lot of effort collecting rice husks in enough quantity to feed a viable manufacturing operation?

The effect @exchemist mentions is responsible for the longevity, and 'self healing', of 2 Millenia old Roman concrete.

But apparently coal ash can be used with similar effect as volcanic ( Vesuvius ) ash ... or rice husks.

9 hours ago, exchemist said:

What isn't clear to me is how much building material can be produced from the amount of rice husk and wood ash available.

Coming from a farming family (with a few ministers and teachers mixed in there), I've heard that agricultural chaff is produced in massive quantities. If the world produces 600-800 million metric tons of rice per year I would suspect that's a lot of husk that rice mills would be happy to part with. Maybe the question is how much sawdust and bark and other woody waste is used by timber mills to make composite wood products, and how much they would sell for cheap.

12 minutes ago, TheVat said:

Coming from a farming family (with a few ministers and teachers mixed in there), I've heard that agricultural chaff is produced in massive quantities. If the world produces 600-800 million metric tons of rice per year I would suspect that's a lot of husk that rice mills would be happy to part with. Maybe the question is how much sawdust and bark and other woody waste is used by timber mills to make composite wood products, and how much they would sell for cheap.

Yes I suppose if hulling of rice is chiefly done on an industrial scale in large mills then it would work.

17 hours ago, TheVat said:

If the world produces 600-800 million metric tons of rice per year

I always wondered how rice was a staple for so many ( Billions ) of people, when the areas where it is grown are so limited, as compared to grain.
World production for grain is almost 5 times greater that that of rice, 2.5 Billion metric tons vs 500 Million metric tons ( milled as opposed to @TheVat 's unmilled ) in 2026.
I guess that leaves about 300 Million metric tons of milling byproduct to be used for construction.

23 hours ago, MigL said:

I always wondered how rice was a staple for so many ( Billions ) of people, when the areas where it is grown are so limited, as compared to grain.
World production for grain is almost 5 times greater that that of rice, 2.5 Billion metric tons vs 500 Million metric tons ( milled as opposed to @TheVat 's unmilled ) in 2026.
I guess that leaves about 300 Million metric tons of milling byproduct to be used for construction.

Wild rice harvesting predates millet by centuries, if not milllennia, in E. Asia. It just looks like a case of natural availability in the earliest times.

Edited October 18Oct 18 by StringJunky

23 hours ago, MigL said:

I always wondered how rice was a staple for so many ( Billions ) of people, when the areas where it is grown are so limited, as compared to grain.
World production for grain is almost 5 times greater that that of rice, 2.5 Billion metric tons vs 500 Million metric tons ( milled as opposed to @TheVat 's unmilled ) in 2026.
I guess that leaves about 300 Million metric tons of milling byproduct to be used for construction.

I wonder how much of that rice is fed to livestock? In the US anyway, most corn produced is not consumed directly by people. Worldwide (according to google) half of all grain produced in the world is not used as food for humans but used for livestock and industrial purposes.