Nominal Mix Concrete M20 – Recommended water per 50 kg bag of cement (for normal workability with standard aggregate size)

Introduction / Context:
Water content governs workability and, through the water–cement ratio, strongly influences strength and durability. For nominal mixes like M20 (1:1.5:3 by volume, typical), guidance tables relate target workability to water per 50 kg of cement for standard maximum aggregate size. This question asks for that recommended value used in field batching.

Given Data / Assumptions:

• Nominal mix concrete M20.
• Standard maximum aggregate size (e.g., 20 mm) and normal workability.
• Good compaction and curing are assumed.

Concept / Approach:

Typical guidance indicates about 30 litres of water per 50 kg bag for normal workability with 20 mm aggregate. Final adjustments are made for measured aggregate moisture/surface water and for specific workability requirements (slump). Keeping water low while satisfying placement needs maintains a reasonable w/c ratio for M20 strength levels.

Step-by-Step Solution:

Verification / Alternative check:

Many mix-design examples show that 28–32 L is typical for 20 mm aggregate; 30 L sits at the centre of this band and is widely adopted in nominal work.

Why Other Options Are Wrong:

60 L would produce extremely high w/c; 45 L and 34 L are excessive for M20 with standard aggregate; 30 L aligns with accepted practice.

Common Pitfalls:

Ignoring moisture corrections, using water to solve placement issues instead of improving compaction or using plasticizers, or skipping curing.

Final Answer:

30 litres