---
title: "Flaky and elongated aggregate"
subject: "Concrete Technology and Masonry Structure"
chapter: 1
key: "semester_5/concrete_technology_and_masonry_structure:flaky-elongated-aggregate"
source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/flaky-elongated-aggregate
site: BCT Engineering
---

# Flaky and elongated aggregate

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

- Asked in: 2064 Jestha (old course)
- Video: [Flakiness and Elongation Test of Aggregate | Shape test](https://www.youtube.com/watch?v=V_KpeEem0kM) — Civil Site visit
- 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/flaky-elongated-aggregate
- Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-1

## Question

Define flaky and elongated aggregate. How do these aggregates affect the strength, workability and durability of concrete? Explain.

## Short answer

Flaky: thickness <0.6 mean dimension; elongated: length >1.8 mean dimension. They reduce strength (weak planes), workability (more water needed) and durability (trapped bleed water, porous interface), and increase cement demand.

## Answer

**Flaky aggregate**: a particle whose least dimension (thickness) is less than 0.6 times its mean dimension (the mean of the sieve sizes between which it falls) (IS 2386 Part 1). The flakiness index is found using the thickness gauge.

**Elongated aggregate**: a particle whose greatest dimension (length) is more than 1.8 times its mean dimension; the elongation index is found with a length gauge.

Flaky and elongated particles are together called poorly shaped particles. Aggregate should preferably be cubical, and IS 383:2016 limits the combined flakiness and elongation index to 40 per cent.

#### Effect on concrete
| Property | Effect of flaky / elongated particles |
|---|---|
| Strength | Reduced; they tend to break under load and create weak planes; poor bond and interlock |
| Workability | Poor: higher surface area, so more water and paste are needed for the same slump; harsh mix, difficult compaction |
| Durability | Lower: water gathers under flat particles (bleed pockets), giving a porous interface zone and higher permeability; flaky pieces orient horizontally |
| Economy | More cement is needed to make a workable mix |
| Other | Tendency to segregate; difficulty in pumping |

Therefore, flaky and elongated aggregate is limited, and cubical, well-shaped crushed stone is preferred.

## Check yourself

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

1. A particle is flaky if its thickness is less than:
   A. 1.8 times its mean dimension
   B. 0.6 times its mean dimension
   C. 0.3 times mean dimension
   D. Equal to mean dimension
   Answer: B. Flaky: least dimension below 0.6 of the mean dimension. (Key point: Flaky definition)

2. A particle is elongated if its length is greater than:
   A. 0.6 times mean dimension
   B. 1.0 times mean dimension
   C. 2.5 times mean dimension
   D. 1.8 times its mean dimension
   Answer: D. Elongated: greatest dimension over 1.8 times the mean dimension. (Key point: Elongated definition)

3. Flaky/elongated particles affect workability by:
   A. Improving it
   B. Giving higher surface area, needing more water and paste, and harsh mix
   C. Reducing water demand
   D. No effect
   Answer: B. Higher surface area raises water and paste demand and makes compaction difficult. (Key point: Effect on workability)

4. Why is durability lowered?
   A. They are chemically reactive
   B. Water gathers under flat particles, giving a porous interface and higher permeability
   C. They reduce cement content
   D. They increase density
   Answer: B. Bleed pockets under flat pieces give porous interface zones. (Key point: Effect on durability)

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