Nominal mix identification: The common nominal volumetric mix proportion (cement : sand : coarse aggregate) used for grade M200 (≈ 20 MPa) concrete is

Introduction / Context:
Older nomenclature sometimes denotes “M200” concrete (≈ 200 kg/cm2 characteristic strength), corresponding approximately to modern M20 (≈ 20 MPa). For quick site estimates, nominal mixes are used when design mixes are not specified.

Given Data / Assumptions:

• M200 ≈ M20 concrete grade.
• We are choosing a standard nominal proportion by volume.
• Workability and aggregate grading are within typical limits.

Concept / Approach:
Traditional nominal mixes associate M20 with approximately 1 : 1.5 : 3 (cement : sand : coarse aggregate). M15 is commonly 1 : 2 : 4, and M10 is 1 : 3 : 6. Richer mixes like 1 : 1 : 2 are used for higher strength/repair works, not typical for M20.

Step-by-Step Solution:
Relate M200 (kg/cm2) to M20 (MPa).Recall nominal mix table: M20 → 1 : 1.5 : 3.Select the matching option.

Verification / Alternative check:
Handbooks list 1 : 1.5 : 3 for M20; nonetheless, many codes now recommend designed mixes rather than nominal for structural concrete.

Why Other Options Are Wrong:
1 : 2 : 4 (M15), 1 : 3 : 6 (M10), 4 : 2 : 1 (reversed order), 1 : 1 : 2 (richer than needed).

Common Pitfalls:
Confusing old kg/cm2 grades with MPa grades; using nominal mixes where durability requirements demand designed mixes.

Final Answer:
1 : 1.5 : 3.