---
title: "Gradation; function of admixture"
subject: "Concrete Technology and Masonry Structure"
chapter: 1
key: "semester_5/concrete_technology_and_masonry_structure:gradation-admixture-function"
source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/gradation-admixture-function
site: BCT Engineering
---

# Gradation; function of admixture

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

- Asked in: 2081 Baisakh, 4 marks
- Video: [Types Of Admixtures Used In Construction | Type of Concrete Admixtures and their uses | #CivilGuruji](https://www.youtube.com/watch?v=7tHrG98Mmug) — The Institute of Construction Managment 
- 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/gradation-admixture-function
- Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-1

## Question

What do you mean by gradation? What is the function of admixture?

## Short answer

Gradation is the particle size distribution from sieve analysis; good gradation minimises voids, improving workability and economy. Admixtures modify fresh or hardened concrete properties: increase workability, control setting, entrain air, enhance durability, reduce water or bleeding, and save cement.

## Answer

**Gradation (grading)** is the distribution of aggregate particle sizes in a sample, found by sieve analysis (IS 2386 Part 1) and expressed as the percentage passing (or retained) on a series of standard sieves. Good gradation, within IS 383 limits, means a smooth continuous grading curve with minimum voids, giving workable, economical and strong concrete.

**Function of admixture**: An admixture (IS 9103) is a material added in small quantities to concrete during or before mixing, to modify its properties. Its functions include:
- Increase workability or reduce water content (plasticisers, superplasticisers).
- Accelerate setting and early strength (accelerators) or delay setting (retarders) for hot weather and long transport.
- Entrain air to improve frost resistance (air-entraining agents).
- Improve durability, reduce permeability and heat (pozzolans, fly ash, silica fume).
- Reduce bleeding, segregation and shrinkage, and save cement.

## Check yourself

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

1. Gradation of aggregate is:
   A. Its specific gravity
   B. Distribution of particle sizes found by sieve analysis
   C. Its moisture content
   D. Its crushing strength
   Answer: B. Gradation is particle size distribution expressed as percent passing on standard sieves. (Key point: Gradation meaning)

2. Why are retarders used?
   A. To accelerate early strength
   B. To entrain air
   C. To delay setting in hot weather and long transport
   D. To increase shrinkage
   Answer: C. Retarders delay setting, useful for hot weather and long haul. (Key point: Retarder function)

3. Air-entraining admixtures mainly improve:
   A. Frost resistance
   B. Early strength
   C. Cement fineness
   D. Aggregate strength
   Answer: A. Entrained air bubbles improve frost resistance. (Key point: Air entrainment)

4. An admixture is added:
   A. In large quantity at the cement factory
   B. In small quantities during or before mixing to modify properties
   C. Only after hardening
   D. Only to aggregate in the quarry
   Answer: B. IS 9103 admixtures are added in small amounts during or before mixing. (Key point: Admixture dose)

## Related in Concrete Technology and Masonry Structure

- [Setting, setting time, admixture vs additive](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Asetting-time-admixture-additive-diff) — Concrete Technology and Masonry Structure, chapter 1

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