Nominal Mixes for RCC – commonly used proportion for slabs, beams, columns and walls (historical practice) For general reinforced concrete work such as slabs, beams, columns, and walls (where nominal mixes were historically specified), which proportion is commonly cited?

Introduction / Context:
Before widespread adoption of design mixes for specific strength grades, many specifications used nominal volumetric mixes. For ordinary RCC elements, a widely cited nominal mix is 1 : 2 : 4 (cement : sand : coarse aggregate), roughly corresponding to lower-middle strength grades with proper water–cement ratio and curing.

Given Data / Assumptions:

• Volumetric batching context with standard aggregates.
• Workability adjusted by water and, if allowed, admixtures.
• Modern practice increasingly prefers design mixes by target mean strength; the question asks historical/common nominal proportion.

Concept / Approach:

Among listed options, 1 : 2 : 4 is the standard nominal mix for RCC, whereas 1 : 3 : 6 and 1 : 4 : 8 are lean mixes used for blinding or mass concrete of lower strength. Proportion 1 : 1 : 2 is a rich mix suited to special cases, not general RCC economy.

Step-by-Step Solution:

Verification / Alternative check:

Traditional schedules and handbooks list 1 : 2 : 4 for RCC where design mixing is not mandated, with cube strength acceptance at 28 days.

Why Other Options Are Wrong:

1 : 3 : 6 and 1 : 4 : 8 are insufficient for most RCC structural demands; 1 : 1 : 2 is unnecessarily rich and uneconomical for general use.

Common Pitfalls:

Using nominal mixes without controlling water–cement ratio; ignoring durability requirements; not switching to design mixes when project demands specific strengths.

Final Answer:

1 : 2 : 4