---
title: "Comment on cements from oxide composition"
subject: "Concrete Technology and Masonry Structure"
chapter: 1
key: "semester_5/concrete_technology_and_masonry_structure:cement-composition-comment"
source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/cement-composition-comment
site: BCT Engineering
---

# Comment on cements from oxide composition

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

- Asked in: 2064 Jestha (old course)
- Video: [Manufacturing of Portland Cement](https://www.youtube.com/watch?v=aNrNiOQk5ZE) — ETHZ - Physical Chemistry of Building Materials
- 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/cement-composition-comment
- Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-1

## Question

Comment on the properties of cements based on the oxide and compound composition given below:

| Cement | SiO$_2$ | CaO | Fe$_2$O$_3$ | Al$_2$O$_3$ | SO$_3$ | C$_3$S | C$_2$S | C$_3$A | C$_4$AF | Free Lime |
|---|---|---|---|---|---|---|---|---|---|---|
| Cement-A | 22.4 | 68.2 | 0.3 | 4.6 | 2.4 | 69.2 | 12.0 | 11.7 | 0.9 | 3.3 |
| Cement-B | 25.0 | 61.0 | 3.0 | 4.0 | 2.5 | 20.0 | 56.6 | 5.7 | 9.1 | 1.0 |

## Short answer

C ement-A has high C3S and C3A, giving rapid hardening, high heat, poor sulphate resistance, and high free lime risking unsoundness. C ement-B has high C2S, low C3A, low heat, slow strength gain, and moderate sulphate resistance, suitable for mass concrete.

## Answer

The compounds are given by Bogue's calculation, so the comparison is made on C$_3$S, C$_2$S, C$_3$A, C$_4$AF and free lime.

| Item | Cement-A | Cement-B |
|---|---|---|
| C$_3$S | 69.2% (very high) | 20.0% (low) |
| C$_2$S | 12.0% (low) | 56.6% (high) |
| C$_3$A | 11.7% (high) | 5.7% (low) |
| C$_4$AF | 0.9% | 9.1% |
| CaO | 68.2% (high; lime saturation near the upper limit) | 61.0% (low) |
| Free lime | 3.3% (high) | 1.0% (acceptable) |

#### Cement-A
- Very high C$_3$S: **rapid-hardening, high early strength**; quick strength gain at 3 and 7 days, useful for early formwork removal and cold weather.
- High C$_3$A (11.7%) and C$_3$S: very **high heat of hydration** and quick setting (needs gypsum; SO$_3$ is 2.4%), more shrinkage and thermal cracking, and **poor sulphate resistance**.
- Free lime of 3.3% is high: excess free lime causes unsoundness, with expansion and cracking later. The high CaO suggests an over-limed cement, which is risky for soundness (IS 269 controls this through the lime saturation factor and the soundness tests).
- Very low C$_4$AF (Fe$_2$O$_3$ only 0.3%), so it is lighter in colour.
- Use: precast work, repairs and emergency works; not for mass concrete or sulphate-bearing soils.

#### Cement-B
- High C$_2$S (56.6%) and low C$_3$S: **slow strength gain**, but high long-term strength (after 28 days). This composition is typical of a **low-heat cement** (e.g. ASTM Type IV, which requires C$_3$S at most 35% and C$_2$S at least 40%).
- Low C$_3$A (5.7%): lower heat, less shrinkage and **moderate sulphate resistance**. It is just above the 5% limit for a true sulphate-resisting cement (IS 12330), so it is not fully sulphate-resisting. C$_4$AF is moderate (9.1%).
- Low free lime (1.0%): sound cement with a low risk of expansion.
- Use: mass concrete (dams, rafts), hot weather, and moderate sulphate exposure, where thermal cracking must be limited.

**Conclusion**: Cement-A is a high-early-strength, high-heat cement with a soundness risk; Cement-B is a low-heat, durable, slow-gaining cement with moderate sulphate resistance.

## Check yourself

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

1. Cement-A (C3S 69.2%) is:
   A. Low heat
   B. Slow, sulphate resistant
   C. Rapid-hardening, high heat
   D. Slow gaining
   Answer: C. High C3S and C3A give early strength and heat. (Key point: Cement-A)

2. Cement-B is suitable for:
   A. Emergency repair
   B. Early formwork removal
   C. Cold-weather precast
   D. Mass concrete and sulphate-bearing environments
   Answer: D. High C2S, low C3A: low heat and sulphate resistant. (Key point: Cement-B)

3. Free lime of 3.3% in Cement-A risks:
   A. Unsoundness, expansion and cracking
   B. Faster setting only
   C. Lower strength only
   D. Nothing
   Answer: A. Excess free lime expands later. (Key point: Free lime)

## Related in Concrete Technology and Masonry Structure

- [Grade of cement; Bogue's compounds](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Agrade-of-cement-bogue) — Concrete Technology and Masonry Structure, chapter 1
- [3 m wall under wind: free top, fixed bottom](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Awind-wall-3m-free-top) — Concrete Technology and Masonry Structure, chapter 9, asked 2×
- [Physical properties of OPC and concrete behaviour](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Acement-physical-properties) — Concrete Technology and Masonry Structure, chapter 1

## Related in other subjects

- [Fat lime composition, properties, uses](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Afat-lime-composition-properties-uses) — Civil Engineering Materials, chapter 4
- [Projectile at 30°, 61 m/s to target below](https://www.bctengineer.com/question.md?key=semester_1%2Fapplied_mechanics%3Aprojectile-30deg-61ms-target-h-below) — Applied Mechanics, chapter 8, asked 2×
- [Cement mortar versus lime mortar](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Acement-vs-lime-mortar) — Civil Engineering Materials, chapter 6
- [Types of lime, properties and uses](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Atypes-of-lime-uses) — Civil Engineering Materials, chapter 4, asked 3×