Workability guide for nominal mix M15 (vibrated): Approximately how much mixing water is required per 50 kg bag of cement to achieve normal workability suitable for vibration in nominal mix M15 concrete?

Introduction / Context:
Estimating water content per 50 kg bag of cement helps achieve the desired workability for nominal mixes, especially when internal or external vibration is used for compaction. Too much water reduces strength and increases permeability; too little water harms placement and compaction.

Given Data / Assumptions:

• Nominal mix concrete of grade M15.
• Concrete will be compacted with vibration (so a moderate slump is adequate).
• Typical guidance values for water per 50 kg bag are used.

Concept / Approach:
Practical handbooks list typical water requirements per bag for standard workability ranges. For vibrated nominal mixes, about 30–34 litres per bag is commonly used, with 32 litres a representative target for normal conditions and aggregates.

Step-by-Step Solution:
Step 1: Select a nominal water content suited for vibration (lower than hand-placed concrete).Step 2: Use tabulated practical values; 32 litres per 50 kg bag is a standard reference for M15 under normal conditions.Step 3: Choose the nearest listed value that matches standard guidance: 32 litres.

Verification / Alternative check:
Trial mixes can fine-tune water content considering aggregate moisture, shape, and grading. However, 32 litres is a widely accepted starting point for vibrated nominal mixes.

Why Other Options Are Wrong:
30 litres/34 litres: Possible in edge conditions, but 32 litres is the typical benchmark for normal workability under vibration.
45 litres: Excessive; risks high w/c ratio and strength loss.
28 litres: Usually too low for normal workability, leading to placement difficulty.

Common Pitfalls:

• Ignoring aggregate moisture corrections which alter free water.
• Assuming higher slump is always better; with vibration, moderate slumps are adequate.

Final Answer:
32 litres