--- title: "Clinker compounds and their functions" subject: "Civil Engineering Materials" chapter: 5 key: "semester_3/civil_engineering_materials:cement-clinker-compounds-functions" source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/cement-clinker-compounds-functions site: BCT Engineering --- # Clinker compounds and their functions Civil Engineering Materials · Chapter 5: Cement - Asked in: 2081 Chaitra (new course), 3 marks; 2076 Chaitra, 3 marks; 2076 Asoj, 3 marks; 2072 Chaitra, 2 marks; 2068 Chaitra, 1 marks; 2068 Baisakh, 4 marks; 2066 Shrawan (old course), 8 marks; 2070 Chaitra (old course), 5 marks; 2065 Shrawan (old course), 8 marks (asked 9 times) - Video: [Bogue's Compounds in Cement | Lec-2 | Building Materials | SSC JE, RRB JE & All State AE/JE 2026-27](https://www.youtube.com/watch?v=ymVZKqu4QtA) — CIVIL ENGINEERING PRO LEARNING - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/cement-clinker-compounds-functions - Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-5 ## Question What are the compounds present in cement clinker? Explain their functions (role in setting and hardening). ## Short answer Clinker compounds: C₃S gives early strength (7 days) and high heat; C₂S provides later strength and low heat; C₃A causes flash set (controlled by gypsum), high heat, poor sulphate resistance; C₄AF acts as flux, gives colour, little strength. C-S-H gel from C₃S and C₂S is the main strength source. ## Answer Cement clinker is made by burning limestone and clay at about 1450 °C. It contains four main compounds (Bogue's compounds). | Compound | Formula | Short | Approx. % | |---|---|---|---| | Tricalcium silicate | 3CaO·SiO₂ | C₃S | 40-50 | | Dicalcium silicate | 2CaO·SiO₂ | C₂S | 25-30 | | Tricalcium aluminate | 3CaO·Al₂O₃ | C₃A | 8-12 | | Tetracalcium alumino-ferrite | 4CaO·Al₂O₃·Fe₂O₃ | C₄AF | 8-12 | #### Functions 1. **C₃S (alite):** hydrates quickly and gives early strength (first 7 days); produces high heat of hydration. More C₃S gives rapid hardening cement. 2. **C₂S (belite):** hydrates slowly and is responsible for the strength after 7 days, up to a year. Gives low heat and good resistance to chemicals. 3. **C₃A:** reacts immediately with water and causes the **initial flash set**, controlled by adding 2 to 3% gypsum. It evolves large heat, adds some early strength, but makes cement weak to sulphate attack. 4. **C₄AF:** acts as a flux that lowers the burning temperature; gives the grey colour, adds little strength and hydrates moderately fast. Hydration of C₃S and C₂S produces calcium silicate hydrate (C-S-H gel), which gives the strength, and Ca(OH)₂. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which clinker compound gives early strength in the first 7 days and also produces high heat of hydration? A. C3S (alite) B. C2S (belite) C. C4AF D. Gypsum Answer: A. C3S hydrates quickly, giving early strength and high heat; more C3S gives rapid hardening cement. (Key point: C3S role) 2. Why is C2S important for a structure that must keep gaining strength for months? A. It hydrates instantly and causes flash set B. It hydrates slowly and gives strength after 7 days up to a year C. It acts as a flux in the kiln D. It gives the grey colour only Answer: B. C2S (belite) hydrates slowly, so it is responsible for later strength, with low heat and good chemical resistance. (Key point: C2S role) 3. What causes the initial flash set of cement and how is it controlled? A. C2S reacts at once; lime controls it B. C4AF reacts at once; silica controls it C. C3A reacts at once with water; 2-3% gypsum controls it D. C3S reacts at once; water controls it Answer: C. C3A reacts immediately with water, so gypsum (2-3%) is added to regulate setting; C3A also weakens sulphate resistance. (Key point: C3A and gypsum) 4. What is the main role of C4AF in cement clinker? A. Main source of early strength B. Main source of long-term strength C. Cause of flash set D. Flux that lowers burning temperature and gives grey colour Answer: D. C4AF acts as a flux, lowers the burning temperature, gives the grey colour and adds little strength. (Key point: C4AF role) ## Related in Civil Engineering Materials - [Clinker compounds strength-time graph](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aclinker-strength-graph) — Civil Engineering Materials, chapter 5 - [Short note: rapid hardening cement](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Arapid-hardening-cement) — Civil Engineering Materials, chapter 5 - [Ingredients of cement and functions](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aingredients-of-cement-functions) — Civil Engineering Materials, chapter 5, asked 7× - [Define initial and final setting time](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Ainitial-final-setting-time-define) — Civil Engineering Materials, chapter 5 - [Setting time significance and test](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Asetting-time-significance-test) — Civil Engineering Materials, chapter 5 ## Related in other subjects - [Setting versus hardening of cement](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Asetting-vs-hardening) — Concrete Technology and Masonry Structure, chapter 1 - [Hydration of cement and role of compounds](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Ahydration-compounds-strength) — Concrete Technology and Masonry Structure, chapter 1, asked 3× - [Bogue's compounds and their role](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Abogue-compounds-role) — Concrete Technology and Masonry Structure, chapter 1, asked 7× - [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