You can often buy rice hulls already carbonized or burned to ash, or you can make your own using this simple system to save money. In either case, you want low carbon rice hull ash for geopolymer, which is distinctly different than most CRH used in agriculture. In other words, use the basic process shown in the video except totally burn the hulls to ash. This point is verified by Rice Husk Ash of Thailand:
“Nowaday, there are a big demand for low carbon rice husk [hull] ash… The color for this type of product is gray and sometime it is white. The special characteristics of zero carbon rice husk ash is it has very high in silica and very low almost none in carbon. It mainly use in steel and cement industry as a conventional raw material or as a binder. Our company now can produce high and low carbon rice husk ash.”
Grinding rice hull ash to fine powder would improve geopolymer strength and other properties as documented in this previous blog post: Ultra Fine Ash. Especially due to this extra grinding step, I’d be inclined to just buy the ash already processed from local companies. I don’t want to invest in unnecessary machinery, spend extra time and labor, or try to compete against large businesses that have efficient economies of scale. Plus, I’d rather be building houses than burning hulls and choking on smoke.
Cost for one pallet of low carbon rice hull ash not including delivery: $100 for 450 kg.
Complete information on CRH, including different uses (agriculture, fuel briquettes, etc.), how to make the burner and burn the hulls: Carbonized Rice Hull