---
title: "Segregation: forms and control"
subject: "Concrete Technology and Masonry Structure"
chapter: 3
key: "semester_5/concrete_technology_and_masonry_structure:segregation-forms-control"
source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/segregation-forms-control
site: BCT Engineering
---

# Segregation: forms and control

Concrete Technology and Masonry Structure · Chapter 3: Mix design of concrete and property of green concrete

- Asked in: 2082 Bhadra, 2 marks; 2081 Bhadra, 2 marks; 2080 Baisakh, 4 marks; 2066 Bhadra (old course), 2+3 marks (asked 4 times)
- Video: [2.8  Segregation of Concrete](https://www.youtube.com/watch?v=mTHLeQMLzlE) — Interesting Engineering
- 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/segregation-forms-control
- Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-3

## Question

Define segregation and its forms. How can segregation be controlled (and avoided) during discharge from hopper and during placing of fresh concrete?

## Short answer

Segregation is separation of concrete constituents causing non-uniformity; forms include coarse aggregate separating, paste separating, and water bleeding. Control during hopper discharge: limit free fall to 1–1.5 m, open gate fully, discharge centrally. During placing: place near final position, limit drop height, use chutes or tremie, avoid over-vibration.

## Answer

**Segregation** is the separation of the constituents of fresh concrete so that it is no longer uniform: coarse aggregate separates from the mortar, or water separates from the mix. It causes honeycombing, weak and non-uniform concrete, poor durability and surface defects.

#### Forms of segregation
1. **Coarse aggregate separating out**: heavy coarse particles settle or roll away from the mortar (common in dry, harsh and gap-graded mixes).
2. **Paste (grout) separating** from the coarse aggregate: in wet, high-slump mixes, the cement paste flows away from the aggregate.
3. **Water separating** (bleeding): water rises to the surface of a wet mix.

#### Causes
Poor grading, a too-wet or too-dry mix, excess vibration, dropping from a height, long chutes, rough handling, and differences in the density of the materials.

#### Control during discharge from a hopper
- Keep the discharge gate close to the receiving surface (free fall not more than 1-1.5 m), with a funnel or baffle.
- Open the gate fully and discharge centrally, so the concrete falls vertically into the middle of the receiving vehicle, not against its side.
- Use a hopper with a bottom sloping at about 60 degrees and a central outlet.

#### Control during placing
- Place concrete as close as possible to its final position, in layers 300-450 mm thick; do not move it with a vibrator.
- Limit free fall to 1.5 m; use chutes (with baffles), a tremie or drop pipes (elephant trunk) for deeper sections.
- Use well-graded aggregates, a suitable w/c ratio and fines content, or admixtures (air entrainment, viscosity modifier).
- Avoid over-vibration; use the right vibrators; use clean, tight formwork.
- Keep chutes at a suitable slope (about 1 vertical to 2-3 horizontal) so that the concrete neither stops nor shoots; avoid long transport over rough roads, and re-mix if segregation has already occurred.

## Check yourself

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

1. Segregation is...
   A. Separation of constituents so concrete is no longer uniform
   B. Cracking by shrinkage
   C. Hardening
   D. Air entrainment
   Answer: A. It causes honeycombing and weakness. (Key point: Definition)

2. Free fall of concrete should not exceed about...
   A. 1.5 m
   B. 5 m
   C. 10 m
   D. No limit
   Answer: A. Use chutes, tremie or drop pipes for greater depth. (Key point: Free fall)

3. Concrete should be placed...
   A. Far away and moved with a vibrator
   B. Close to final position in layers 300-450 mm
   C. In one tall lift
   D. From any height
   Answer: B. Do not move concrete laterally with a vibrator. (Key point: Placing)

4. Which is a form of segregation?
   A. Coarse aggregate separating from mortar
   B. Steel yielding
   C. Hydration
   D. Curing
   Answer: A. Also paste separating and water bleeding. (Key point: Forms)

## Related in Concrete Technology and Masonry Structure

- [Segregation and bleeding; control during placing](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Asegregation-bleeding-control) — Concrete Technology and Masonry Structure, chapter 3