---
title: "Bulking of sand"
subject: "Concrete Technology and Masonry Structure"
chapter: 1
key: "semester_5/concrete_technology_and_masonry_structure:bulking-of-sand"
source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/bulking-of-sand
site: BCT Engineering
---

# Bulking of sand

Concrete Technology and Masonry Structure · Chapter 1: Introduction to concrete and concrete materials

- Asked in: 2079 Bhadra, 6 marks; 2079 Baisakh, 4 marks; 2076 Ashwin, 2 marks; 2066 Jestha (old course), 2+3 marks (asked 4 times)
- Video: [What is Bulking of Sand?? | How to Determine Bulking of Sand | Sand Test | All About Civil Engineer](https://www.youtube.com/watch?v=bvWY-MSFDZ0) — All About Civil Engineer
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/bulking-of-sand
- Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-1

## Question

What is bulking of sand (aggregate)? Explain its cause, effect and remedial measures, and its role in the concrete manufacturing process.

## Answer

**Bulking** is the increase in the volume of sand (fine aggregate) when it contains a certain amount of surface moisture, compared with the same mass of dry sand.

#### Cause
Moisture forms a thin film around each sand grain. Surface tension of this film pushes the particles apart and keeps them from packing closely, so voids increase and the volume rises. Bulking is about 20-40 per cent at a moisture content of 4-6 per cent for fine sand. When the sand is fully flooded (saturated), the film is broken and the volume falls back to the dry volume. Finer sand bulks more than coarse sand.

```text
Bulking %
  |        _____
  |      /       \
  |    /          \
  |  /              \___ (flooded:
  |/                      bulking = 0)
  +----------------------------> moisture %
     4-6% peak
```

#### Effect
- If the mix is batched by volume, the actual quantity of sand is less than intended, so the mix becomes **lean in fine aggregate**: the concrete is harsh, honeycombed, less workable, lower in strength, and the yield per bag is lower.
- Wrong sand-cement proportion affects economy and quality.

#### Remedial measures
- Batch sand **by weight**, not volume.
- Make a bulking allowance: increase the sand volume by the bulking per cent found by test.
- Dry the sand or flood it fully before batching.

#### Determination (field test)
Fill a measuring cylinder to a height $h_1$ with moist sand, then add water and stir so that the sand is flooded; the height becomes $h_2$.

$$
\text{Bulking}\ \% = \frac{h_1 - h_2}{h_2} \times 100
$$

#### Role in concrete manufacture
Knowing bulking, the sand quantity measured in volume batching is corrected as: required volume of damp sand = volume of dry sand $\times\ (1 + \text{bulking}/100)$. The free moisture carried by the sand is also deducted from mixing water, so the water-cement ratio stays correct.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Why does damp sand bulk?
   A. Water is absorbed into the grains and they swell
   B. Sand reacts chemically with water
   C. Surface tension of the moisture film pushes grains apart, increasing voids
   D. Fine particles are washed out
   Answer: C. The thin water film keeps grains from packing closely. (Key point: Cause)

2. What happens to the volume when sand is fully flooded?
   A. It reaches maximum bulking
   B. It doubles
   C. It stays at the damp volume
   D. It falls back to the dry volume (bulking about zero)
   Answer: D. Flooding breaks the film so bulking disappears. (Key point: Fully flooded sand)

3. If sand is batched by volume without allowance, the mix becomes:
   A. Lean in fine aggregate, harsh and lower in strength
   B. Rich in sand and very workable
   C. Stronger due to less sand
   D. Unchanged
   Answer: A. Actual sand mass is less than intended. (Key point: Effect)

4. How is the volume of damp sand corrected?
   A. Dry volume x (1 - bulking/100)
   B. Dry volume x (1 + bulking/100)
   C. Dry volume / (1 + bulking)
   D. Dry volume + water volume
   Answer: B. The volume is increased by the bulking percent found by test. (Key point: Allowance)

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