---
title: "Why hydration of cement takes place"
subject: "Civil Engineering Materials"
chapter: 5
key: "semester_3/civil_engineering_materials:hydration-of-cement-why"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/hydration-of-cement-why
site: BCT Engineering
---

# Why hydration of cement takes place

Civil Engineering Materials · Chapter 5: Cement

- Asked in: 2078 Bhadra, 1 marks
- Video: [Heat of Hydration of Cement || Hydration of Cement #2 ||](https://www.youtube.com/watch?v=k02fOFB2-iQ) — Anime_Edu - Civil Engineering Videos
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/hydration-of-cement-why
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-5

## Question

Why does hydration of cement take place?

## Short answer

Hydration takes place because anhydrous cement compounds (C3S, C2S, C3A, C4AF) are chemically unstable in water. They react to form stable, insoluble calcium silicate hydrate gel and calcium hydroxide, which set and harden, providing binding strength.

## Answer

Hydration takes place because the anhydrous compounds of cement (C3S, C2S, C3A, C4AF) are chemically unstable in the presence of water. They react with water to form stable, insoluble hydrated products (mainly calcium silicate hydrate, C-S-H gel, and calcium hydroxide), which set and harden and give cement its binding strength. The reaction is exothermic and continues as long as water and unhydrated cement are available.

## Check yourself

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

1. Hydration occurs because anhydrous cement compounds are:
   A. Chemically unstable in water
   B. Stable in water
   C. Inert
   D. Soluble
   Answer: A. They form stable hydrates. (Key point: Cause)

2. Main hydration products are:
   A. Gypsum and clinker
   B. C-S-H gel and calcium hydroxide
   C. CO2
   D. Sand
   Answer: B. These give binding strength. (Key point: Products)

3. Hydration reaction is:
   A. Endothermic
   B. Instantaneous only
   C. Exothermic and continues while water and unhydrated cement remain
   D. Stops at set
   Answer: C. It gives out heat. (Key point: Nature)

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