Consider the following statements regarding the design requirements of concrete mix : 1. Grade of concrete : M20, M25 connotes the characteristic strength of 30 N/mm² to 35 N/mm². 2. Type of cement : The grade of OPC such as of 33, 43 or 53 grade. 3. Type of mixing and curing water : Whether fresh potable water, seawater, ground water is to be used. Which of the above statements are correct ?
- A1, 2 and 3
- B2 and 3 onlyCorrect
- C1 and 2 only
- D1 and 3 only
Solution
Concept
Design inputs for a concrete mix
Step-by-step solution
1. M20 and M25 denote characteristic strengths of 20 and 25 N/mm², not 30–35 (statement 1 false). 2. OPC is available in 33, 43 and 53 grades (statement 2 true). 3. The quality of mixing and curing water must be specified (statement 3 true).
Explanation
The grade number itself is the characteristic cube strength in N/mm².
Why the other options are wrong
Statement 1 misquotes the grade, so options containing it are wrong.
Shortcut
M25 = 25 N/mm².
Common mistake
Accepting the wrong strength range.
Correct answer: B) 2 and 3 only