Nominal mix equivalence: the older designation M10 concrete (≈ 10 MPa characteristic strength) corresponds approximately to which classic nominal mix proportion by volume?

Introduction / Context:
Before widespread use of design mixes, many public works used nominal (arbitrary) mixes. Mapping strength classes to nominal proportions is useful for rough estimates and non-structural works, while remembering that actual strength depends on water–cement ratio, materials, and curing.

Given Data / Assumptions:

• M10 ≈ 10 MPa characteristic cube strength at 28 days.
• Nominal mixes are volumetric ratios of cement : sand : coarse aggregate.
• Ordinary materials and proper compaction/curing are assumed.

Concept / Approach:
Conventional equivalences: 1:3:6 ≈ M10; 1:2:4 ≈ M15; 1:1.5:3 ≈ M20; 1:1:2 ≈ M25. Hence M10 aligns with 1 : 3 : 6.

Step-by-Step Solution:
Identify M10 target → 10 MPa.Recall standard mapping → M10 ↔ 1:3:6.Choose 1 : 3 : 6.

Verification / Alternative check:
Departmental schedule of rates and many handbooks list 1:3:6 for lean concrete layers, blinding, and non-critical members consistent with M10.

Why Other Options Are Wrong:

• 1:2:4 → richer ≈ M15.
• 1:1.5:3 → richer ≈ M20.
• 1:1:2 → richer ≈ M25.

Common Pitfalls:
Treating nominal proportion as a guarantee of strength regardless of w/c and curing; overlooking local aggregate quality.

Final Answer:
1 : 3 : 6