Nominal mix equivalence: the old designation M 150 concrete (≈ 15 MPa characteristic strength) corresponds approximately to which nominal mix proportion by volume?

Introduction / Context:
Older practice referenced concrete by compressive strength in kg/cm2 (e.g., M 150 ≈ 150 kg/cm2). Modern designations use characteristic cylinder/cube strengths in MPa (e.g., M15 ≈ 15 MPa). Knowing the rough nominal mix that corresponds to these strength classes aids preliminary estimates and small works.

Given Data / Assumptions:

• M 150 ≈ 15 MPa characteristic cube strength.
• Nominal mixes are by volume: cement : fine aggregate : coarse aggregate.
• Workability and w/c ratio are adjusted to achieve the target.

Concept / Approach:
Standard nominal mixes (legacy) map approximately as: 1:3:6 → M10, 1:2:4 → M15, 1:1.5:3 → M20, 1:1:2 → M25 (approximate). Thus M 150 aligns with 1 : 2 : 4. Actual strength depends on water/cement ratio, aggregate, and curing, so these are indicative starting points.

Step-by-Step Solution:
Identify M 150 as ≈ 15 MPa → corresponds to M15.Recall nominal mapping: M15 → 1 : 2 : 4.Therefore select 1 : 2 : 4.

Verification / Alternative check:
Many departmental schedules and handbooks list 1:2:4 as the standard nominal mix for M15 works such as slabs and beams in non-critical applications.

Why Other Options Are Wrong:

• 1:3:6 (leaner) ≈ M10.
• 1:1:2 (richer) ≈ M25.
• 1:1.5:3 (richer) ≈ M20.

Common Pitfalls:
Treating nominal proportions as guarantees of strength without controlling w/c ratio and curing.

Final Answer:
1 : 2 : 4