Concrete Materials – Permissible compressive strength for Grade M150 (legacy designation) In traditional building materials nomenclature used in some older Indian texts, the concrete grade “M150” corresponds to a characteristic compressive strength of 150 kg/cm² at 28 days. What is the permissible (nominal) compressive strength associated with M150?

Introduction / Context:
The designation of concrete by “M” followed by a number historically indicated a compressive strength value. In many legacy references, strengths were expressed in kg/cm² instead of MPa. Understanding older designations such as M150 helps interpret existing drawings, BOQs, and specifications when working on retrofits or reading classic examination problems.

Given Data / Assumptions:

• M150 is a legacy grade label.
• Strength unit requested is kg/cm² at 28 days.
• We assume ordinary Portland cement concrete under standard curing.

Concept / Approach:
The number after “M” historically equaled the characteristic (nominal) compressive strength. In older Indian practice, M150 aligns with approximately 150 kg/cm², which is numerically close to 15 MPa (since 1 MPa ≈ 10.2 kg/cm²). While modern codes prefer MPa (e.g., M15), many academic questions still test the kg/cm² equivalence for clarity.

Step-by-Step Solution:
Identify the legacy mapping: M150 → about 150 kg/cm² at 28 days.Cross-check with the modern MPa scale: M15 ≈ 15 MPa → 15 * 10.2 ≈ 153 kg/cm².Choose the closest listed permissible strength: 150 kg/cm².

Verification / Alternative check:
Many textbooks list M15 in MPa and M150 in kg/cm² interchangeably when discussing nominal mix grades like 1:2:4 for general RCC. These align with the target characteristic strength at 28 days under standard testing.

Why Other Options Are Wrong:

• 100 kg/cm²: corresponds roughly to 10 MPa (M10), which is lower than M150.
• 200 or 250 or 300 kg/cm²: these represent higher grades (about M20, M25, M30 respectively), not M150.

Common Pitfalls:
Confusing MPa and kg/cm²; always convert carefully. Do not mix the notion of characteristic strength with permissible (or working) stress design concepts, which belong to different design philosophies.

Final Answer:
150 kg/cm²