Concrete Mix Proportioning – Volumetric batching for a 1:3:6 mix per 50 kg bag of cement For a concrete mix specified by volume as 1 : 3 : 6 (cement : sand : coarse aggregates), if batching is done by volume using one 50 kg bag of cement as the cement measure, what volumes of sand and coarse aggregates are required per bag (take one 50 kg cement bag ≈ 35 litres in volume)?

Introduction / Context:
Volumetric batching is widely used on small to medium construction sites, where ingredients for nominal mixes are measured in boxes, pans, or by using one cement bag as a unit volume. For a 1:3:6 concrete (cement : sand : coarse aggregates), it is essential to convert the single cement bag into an equivalent volume so that the corresponding volumes of sand and aggregates can be set out quickly and consistently.

Given Data / Assumptions:

• Nominal mix ratio by volume = 1 (cement) : 3 (sand) : 6 (coarse aggregates).
• One 50 kg cement bag is assumed to occupy ≈ 35 litres (0.035 m^3).
• Volumetric batching boxes or gauges are used.

Concept / Approach:

In volumetric batching, each part in the ratio corresponds to an equal volume unit. If “1 part cement” is taken as the volume of one 50 kg bag (≈ 35 litres), then the sand and aggregate volumes follow directly from the ratio. This method ensures quick field control, provided that moisture corrections for sand and bulking are also considered during actual batching and mixing.

Step-by-Step Solution:

Verification / Alternative check:

Using density approach: bulk density of cement ≈ 1440 kg/m^3 gives volume of 50 kg ≈ 50/1440 m^3 ≈ 0.0347 m^3 ≈ 34.7 litres, commonly rounded to 35 litres for site practice. Multiplying by the ratio yields the same volumes within normal field tolerances.

Why Other Options Are Wrong:

Options with 70 litres or 140 litres do not align with the 1:3:6 proportionality when the cement volume is 35 litres. Using kilograms for sand (option B) mixes mass and volume measures, which is inconsistent with volumetric batching.

Common Pitfalls:

Ignoring bulking of sand (add volume corrections for moist sand), not accounting for water content changes, and confusing mass-based with volume-based batching. Always keep gauges clean and consistent.

Final Answer:

105 litres of sand and 210 litres of aggregates