Question

The grade of concrete used for pre-stressed concrete shall not be less than _____.

• A. M20
• B. M25
• C. M35
• D. M60

Hint:

Remember: \[ \boxed{ \begin{aligned} \text{RCC} &\rightarrow \text{Minimum } M20 \text{Prestressed Concrete} &\rightarrow \text{Minimum } M35 \end{aligned} } \] Prestressed concrete always requires higher-strength concrete than RCC.

Answer 1

The Correct Option is C

Concept: Prestressed concrete members require high-strength concrete so that they can safely resist the large compressive stresses introduced by prestressing and minimize creep, shrinkage, and cracking. According to IS 1343:2012, \[ \boxed{\text{The minimum grade of concrete for prestressed concrete is M35 (cast-in-situ).}} \] For precast prestressed members, even higher grades such as M40 or above are commonly used.

Step 1: Understand the requirement of prestressed concrete. Prestressing introduces high compressive forces into the concrete before external loads act. Therefore, concrete should possess:
• High compressive strength.
• Low creep.
• Low shrinkage.
• Good durability.

Step 2: Recall the minimum grade specified by IS code. As per IS 1343, \[ \boxed{\text{Minimum grade}=M35} \] Hence, \[ \boxed{\text{The correct answer is M35}.} \] Therefore, the correct option is \[ \boxed{(C)\;M35.} \]