Bulking of Sand – definition in concrete technology What does the term “bulking of sand” specifically refer to in the context of fresh mortar and concrete proportioning?

Introduction / Context:
Bulking is a practical site phenomenon that directly affects volumetric batching. When moist, sand occupies more volume than in the fully saturated or dry state due to the formation of a water film that pushes particles apart. If not corrected, this leads to under-sanded mixes, poor cohesiveness, and strength loss.

Given Data / Assumptions:

• Natural sand used for mortar or concrete.
• Moisture contents around 2–8% where bulking is prominent.
• Volumetric proportioning by gauge boxes or wheelbarrows.

Concept / Approach:

A thin water film increases interparticle repulsion and arching, creating an apparent volume increase at given mass. Bulking peaks at moderate moisture, then declines toward zero as the voids fill and particles are submerged (saturated). The correct response is to measure bulking and adjust gauged volume of sand accordingly, or to batch by mass instead of volume.

Step-by-Step Solution:

Verification / Alternative check:

Cylinder tests show a typical bulking of 20–35% for fine sands at around 4–6% moisture, returning to the saturated volume when inundated.

Why Other Options Are Wrong:

Options A, B, C, and E describe different processes (grading, lime addition, maximum water, compaction) and are not the definition of bulking.

Common Pitfalls:

Ignoring bulking when using gauge boxes; assuming saturated sand has maximum bulking (it does not).

Final Answer:

Increase in apparent volume (swelling) of sand when it is wetted