Under properly controlled combustion and temperature, what is the percentage of silica content that can be obtained from rice husk ash?
- A40% - 50%
- B60% - 70%
- C57% - 68%
- D85% - 95%Correct
Solution
Concept
Rice husk burnt under controlled temperature (about 500-700 °C) gives ash with a very high content of amorphous silica, about 85-95%.
Step-by-step solution
1. Rice husk is an agricultural waste. 2. When burnt under controlled conditions, most of the organic matter is removed. 3. The ash left behind is mostly amorphous (reactive) silica. 4. Its silica content is about 85-95%. 5. Answer: (D) 85% - 95%.
Explanation
Rice husk ash (RHA) made by controlled burning is very rich in reactive silica, about 85-95%. Because of this, it acts as a good pozzolana and can partly replace cement in concrete.
Why the other options are wrong
A, B and C: These ranges are too low. Properly burnt RHA has more than 85% silica.
Shortcut
RHA silica = 85-95%, similar to silica fume.
Common mistake
Confusing RHA with fly ash, which has much less silica (about 50-60%).
Correct answer: D) 85% - 95%