---
title: "Aggregate shape and texture: strength, workability"
subject: "Concrete Technology and Masonry Structure"
chapter: 1
key: "semester_5/concrete_technology_and_masonry_structure:aggregate-shape-texture-strength"
source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/aggregate-shape-texture-strength
site: BCT Engineering
---

# Aggregate shape and texture: strength, workability

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

- Asked in: 2070 Chaitra, 2 marks; 2068 Baisakh (old course), 2.5 marks (asked 2 times)
- 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/aggregate-shape-texture-strength
- Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-1

## Question

What are the effects of the shape and texture of aggregates on the strength, workability and economy of concrete?

## Short answer

Smooth rounded aggregates improve workability and reduce water demand but give lower strength due to poor bond. Rough angular aggregates increase bond and strength (10–20% higher) but reduce workability and raise cement requirement. Flaky and elongated particles harm strength and durability; IS 383 limits combined flakiness and elongation index to 40%.

## Answer

**Shape**: particle shapes are classified as rounded, irregular, angular, flaky and elongated (IS 383).

**Texture**: the surface may be glassy, smooth, granular, rough, crystalline or honeycombed.

| Property | Smooth, rounded aggregate | Rough, angular aggregate |
|---|---|---|
| Workability | Higher (less friction, less surface area) | Lower; needs more water/paste |
| Bond with paste | Weaker (little mechanical interlock) | Stronger bond (interlocking) |
| Compressive strength | Lower, especially at low w/c | Higher (10-20% more in high-strength concrete) |
| Flexural strength | Lower | Higher (strength depends strongly on bond) |
| Water and cement demand | Less | More for the same slump |
| Economy | Cheaper to place, but gravel may cost more in hilly areas | Crushed stone is costlier to produce, needs more cement and more compaction effort |

**Flaky and elongated particles** reduce workability, strength and durability, since they lie in planes and hold bleed water under them. IS 383:2016 limits the combined flakiness and elongation index to 40 per cent (tested as per IS 2386 Part 1).

**Economy**: rounded aggregates reduce the paste requirement, but angular crushed aggregates give higher strength through better bond; the designer balances the extra cement against this benefit.

## Check yourself

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

1. Rough angular aggregate compared with smooth rounded gives:
   A. Stronger bond and higher strength but lower workability
   B. Weaker bond
   C. Better workability
   D. Lower cement need
   Answer: A. Interlock improves bond, strength. (Key point: Rough angular)

2. Flaky and elongated particles are undesirable because:
   A. They improve packing
   B. They reduce workability and strength and hold bleed water
   C. They reduce water demand
   D. They increase bond
   Answer: B. They lie in planes and trap water beneath them. (Key point: Flaky particles)

3. Economy trade-off with angular aggregate:
   A. Cheaper and needs less cement
   B. No difference
   C. Higher strength but more cement/paste needed
   D. Needs less compaction
   Answer: C. The designer balances extra cement against the strength benefit. (Key point: Economy)

## Related in Concrete Technology and Masonry Structure

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