Legacy grade notation: For concrete graded as M 150, the specified 28-day compressive strength of a standard 15 cm cube is

Introduction / Context:
Older texts often denote concrete grades in kg/cm2 (M-number). Understanding the correspondence between these legacy labels and strength values is necessary for interpreting historic drawings and tender items.

Given Data / Assumptions:

• M 150 grade is referenced.
• Strength is that of a 15 cm cube at 28 days under standard curing.

Concept / Approach:
The M-number in such legacy notation approximates the characteristic compressive strength in kg/cm2. Hence, M 150 indicates about 150 kg/cm2 (≈ 15 MPa). Modern notation commonly uses MPa (e.g., M20 ≈ 20 MPa ≈ 200 kg/cm2).

Step-by-Step Solution:
Identify grade label → M 150.Map M 150 → 150 kg/cm2 nominal characteristic strength.Select 150 kg/cm2.

Verification / Alternative check:
Conversion: 1 MPa ≈ 10.197 kg/cm2; thus 150 kg/cm2 ≈ 14.7 MPa (close to the 15 MPa class).

Why Other Options Are Wrong:
100/200/250/300 kg/cm2 correspond to other grades and do not match M 150.

Common Pitfalls:
Confusing kg/cm2 notation with MPa or cylinder strengths; always check the specimen type and unit.

Final Answer:
150 kg/cm2.