Discussion
Which change would NOT improve the value of rice husk ash?
Answer: D
Correct answer: Burning the husk at 1000 degrees
Burning at 1000 degrees crystallises the silica, and crystalline silica cannot react with the calcium hydroxide released during cement hydration. The ash becomes an inert filler worth very little.
The other three all raise the value: controlled combustion below about 700 degrees keeps the silica amorphous, grinding to a high fineness increases the surface area available for that reaction, and keeping the silica amorphous is the property on which everything else depends.
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