The approximate composition of CaO in Portland cement is in the range of :
- A60% – 65%Correct
- B50% – 55%
- C65% – 70%
- D55% – 60%
Solution
Concept
Oxide composition of OPC
Step-by-step solution
1. Typical OPC: CaO 60–67%, SiO₂ 17–25%, Al₂O₃ 3–8%, Fe₂O₃ 0.5–6%, MgO 0.1–4%. 2. The nearest listed range is 60–65%.
Explanation
Lime is the major oxide of Portland cement, about 60–67 percent. Among the choices, 60%–65% is the closest.
Why the other options are wrong
50–55% and 55–60% are too low, and 65–70% is above the usual maximum of about 67%.
Shortcut
CaO ≈ 63% (60–67%) is the largest oxide in OPC.
Common mistake
Choosing 65–70%.
Correct answer: A) 60% – 65%