Which one of the following is the correct sequence in increasing order for the chemical composition of Portland cement?
- AFe₂O₃, Al₂O₃, SiO₂, CaOCorrect
- BAl₂O₃, Fe₂O₃, SiO₂, CaO
- CFe₂O₃, Al₂O₃, CaO, SiO₂
- DAl₂O₃, SiO₂, Fe₂O₃, CaO
Solution
Concept
Oxide composition of OPC
Step-by-step solution
1. Typical OPC: Fe₂O₃ about 3%, Al₂O₃ about 6%, SiO₂ about 21%, CaO about 63%. 2. Increasing order: Fe₂O₃ < Al₂O₃ < SiO₂ < CaO.
Explanation
Lime is the largest component, followed by silica, alumina and iron oxide.
Why the other options are wrong
The other sequences put alumina before iron oxide, or silica after lime.
Shortcut
CaO 63 > SiO₂ 21 > Al₂O₃ 6 > Fe₂O₃ 3.
Common mistake
Swapping alumina and iron oxide.
Correct answer: A) Fe₂O₃, Al₂O₃, SiO₂, CaO