Pre-stressed Concrete Strength as per IS:1343-2012

Pre-stressed concrete is a structural material where internal stresses are introduced to counteract the stresses caused by external loads. This technique improves the performance and load-carrying capacity of concrete elements. The characteristic strength of concrete used in pre-stressed members is crucial for ensuring the durability and structural integrity of the element.

The Indian Standard code IS:1343-2012 provides guidelines for the design and construction of pre-stressed concrete structures. This standard specifies the minimum characteristic strength requirements for concrete depending on the method of pre-stressing used. There are two main methods: pre-tensioning and post-tensioning.

IS:1343-2012 Minimum Requirements for Concrete Strength

IS:1343-2012 specifies different minimum characteristic strengths for pre-tensioned and post-tensioned structural elements.

• Pre-tensioned concrete: In this method, the tendons are tensioned before the concrete is poured and hardened. Once the concrete gains sufficient strength, the tension is released, transferring the force to the concrete. This method requires a higher concrete strength at an early age to withstand the transfer forces. According to IS:1343-2012, the minimum characteristic strength of concrete for pre-tensioned structural elements is M40.
• Post-tensioned concrete: In this method, ducts are provided in the concrete element, and the tendons are tensioned after the concrete has hardened sufficiently, often close to its full strength. The tension is then anchored at the ends of the element. According to IS:1343-2012, the minimum characteristic strength of concrete for post-tensioned structural elements is M30.

Therefore, the minimum characteristic strength of pre-stressed concrete as per IS:1343-2012 for post-tensioned and pre-tensioned structural elements are M30 and M40, respectively.

Summary of Minimum Concrete Strengths

Comparing with the Options

We are looking for the minimum strengths for post-tensioned and pre-tensioned concrete, in that order. The requirements are M30 for post-tensioned and M40 for pre-tensioned.

• Option 1: M20 for both (Incorrect)
• Option 2: M40 and M30 (Incorrect, order is reversed)
• Option 3: M30 and M40 (Correct)
• Option 4: M15 and M20 (Incorrect)

Based on IS:1343-2012, the correct combination of minimum characteristic strength for post-tensioned and pre-tensioned structural elements is M30 and M40.