Which of the following types of cement gives 1-day strength that is equal to the 3-day strength of OPC with the same water content?
- AOrdinary Portland cement
- BPortland pozzolana cement
- CRapid hardening Portland cementCorrect
- DPortland slag cement
Solution
Concept
Rapid hardening cement gains strength fast, so its 1-day strength equals the 3-day strength of OPC.
Step-by-step solution
1. The question asks which cement gains strength very fast in the early days. 2. Rapid hardening cement (RHC) has more C3S and is ground finer. 3. Finer particles and more C3S give faster hydration and early strength. 4. So the 1-day strength of RHC ≈ the 3-day strength of OPC. 5. Answer is (C).
Explanation
Rapid hardening cement is ground finer and has more C3S than OPC. Because of this, it gains strength very quickly. Its 1-day strength is about equal to the 3-day strength of OPC at the same water content.
Why the other options are wrong
(A) OPC is the reference cement, so it cannot be faster than itself. (B) PPC gains strength slowly in the early days because the pozzolana reacts late. (D) PSC also gains early strength slowly because slag hydrates slowly.
Shortcut
Remember: RHC 1 day = OPC 3 days. RHC 3 days = OPC 7 days.
Common mistake
Thinking RHC sets faster. RHC only gains strength faster. Its setting time is similar to OPC.
Correct answer: C) Rapid hardening Portland cement