---
title: "Soundness of aggregate and its measurement"
subject: "Concrete Technology and Masonry Structure"
chapter: 1
key: "semester_5/concrete_technology_and_masonry_structure:soundness-of-aggregate"
source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/soundness-of-aggregate
site: BCT Engineering
---

# Soundness of aggregate and its measurement

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

- Asked in: 2082 Bhadra, 3 marks; 2074 Chaitra, 2+3 marks (asked 2 times)
- Video: [Classification and Quality Tests Value of Aggregate. Impact, Abrasion, Soundness Tests Value](https://www.youtube.com/watch?v=edUR2K7lzlI) — Civil Engineering Education
- 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/soundness-of-aggregate
- Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-1

## Question

What is soundness of aggregates? How is it measured in the laboratory?

## Short answer

Soundness is the ability of aggregate to resist disintegration from freezing, thawing, or wetting–drying. It is measured by the sodium sulphate or magnesium sulphate soundness test (IS 2386-5): after 5 cycles of soaking and oven drying, the percentage weight loss should not exceed 12% (sodium sulphate) for coarse aggregate.

## Answer

**Soundness** is the ability of an aggregate to resist excessive changes in volume due to changes in physical conditions such as freezing and thawing, alternate wetting and drying, or temperature changes. Unsound aggregates swell, crack and disintegrate, causing pop-outs and loss of durability of the concrete.

#### Laboratory measurement (IS 2386 Part 5)
Soundness is tested by accelerated attack with **sodium sulphate or magnesium sulphate**.

1. Take washed, oven-dried and sieved fractions of the aggregate (e.g. 10-20 mm for coarse aggregate; 300 micron to 10 mm for fine aggregate), weighing 100 g per fraction (fine) or the specified quantity (coarse).
2. Immerse the sample in a saturated solution of sodium sulphate (or magnesium sulphate) for 16-18 hours at 27 ± 1 °C. Salt crystals form in the pores.
3. Remove it, drain for 15 min, then dry it in the oven at 105-110 °C. This is one cycle.
4. Repeat for 5 cycles. The crystallisation pressure in the pores is similar to that of ice formation.
5. Wash out the salt (until the barium chloride test shows no sulphate), dry, and sieve over the original sieve.
6. Calculate the percentage loss in weight.

$$
\text{Loss}\ \% = \frac{\text{original weight} - \text{final weight retained}}{\text{original weight}} \times 100
$$

#### Limits (IS 383)
After 5 cycles, the weighted average loss should not exceed **12 per cent with sodium sulphate** and **18 per cent with magnesium sulphate** for coarse aggregate, and **10 per cent (sodium sulphate)** and **15 per cent (magnesium sulphate)** for fine aggregate.

## Check yourself

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

1. Soundness is the resistance of aggregate to:
   A. Crushing
   B. Abrasion
   C. Volume change due to freeze-thaw, wet-dry or temperature
   D. Water absorption
   Answer: C. Unsound aggregate swells, cracks and pops out. (Key point: Definition)

2. The laboratory soundness test uses:
   A. Hydrochloric acid
   B. Steel balls in a drum
   C. Hammer blows
   D. Sodium or magnesium sulphate for 5 cycles
   Answer: D. Crystallisation pressure simulates ice formation. (Key point: Test)

3. After 5 cycles loss limit for coarse aggregate with sodium sulphate:
   A. 12%
   B. 30%
   C. 45%
   D. 5%
   Answer: A. Magnesium sulphate limit is 18%. (Key point: Limit)

## Related in Concrete Technology and Masonry Structure

- [Mechanical properties of aggregates](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aaggregate-mechanical-properties) — Concrete Technology and Masonry Structure, chapter 1, asked 2×
- [Requirements of aggregates; need of grading](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aaggregate-requirements-grading) — Concrete Technology and Masonry Structure, chapter 1
- [Flaky and elongated aggregate](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aflaky-elongated-aggregate) — Concrete Technology and Masonry Structure, chapter 1
- [Aggregate properties and their influence on concrete](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aaggregate-properties-influence) — Concrete Technology and Masonry Structure, chapter 1
- [Aggregate crushing value determination](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aaggregate-crushing-value) — Concrete Technology and Masonry Structure, chapter 1
- [Aggregate shape and texture: strength, workability](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aaggregate-shape-texture-strength) — Concrete Technology and Masonry Structure, chapter 1, asked 2×

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