--- title: "Concrete as a structural material" subject: "Concrete Technology and Masonry Structure" chapter: 1 key: "semester_5/concrete_technology_and_masonry_structure:concrete-structural-material" source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/concrete-structural-material site: BCT Engineering --- # Concrete as a structural material Concrete Technology and Masonry Structure · Chapter 1: Introduction to concrete and concrete materials - Asked in: 2079 Baisakh, 4 marks; 2076 Chaitra, 4 marks; 2067 Ashadh (old course), 5 marks (asked 3 times) - Video: [What is Concrete?](https://www.youtube.com/watch?v=UOHURuAf5iY) — Practical Engineering - 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/concrete-structural-material - Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-1 ## Question Explain the use of concrete as a structural material (its advantages, also in comparison with steel). ## Short answer Concrete offers high compressive strength, moldability, durability, fire resistance, and uses local materials. Compared to steel, it is cheaper, fire-resistant, and easily shaped but has lower tensile strength and higher self-weight; it is commonly used with reinforcement for tension. ## Answer Concrete is a composite of cement, fine and coarse aggregates and water that hardens into a stone-like mass. It is the most widely used structural material in the world, and with steel reinforcement (RCC) or prestressing it carries tension as well as compression. #### Advantages as a structural material - **High compressive strength** (20-60 MPa and more) at low cost per unit strength. - Can be **moulded to any shape** (beams, shells, arches, slabs) and cast in place. - Uses **local materials**: cement, sand and aggregate are widely available. - **Durable** and needs little maintenance; it gains strength with age. - Good **fire resistance**, because concrete is a poor conductor of heat and does not burn. - Provides **mass** for stability (dams, foundations) and good sound and thermal insulation. - The alkaline cover (pH about 12.5) protects the steel from corrosion. - Monolithic action in RCC gives rigid frames. - Can use waste products (fly ash, slag). #### Disadvantages Low tensile strength (about 10 per cent of the compressive strength), large self-weight, cracking, shrinkage and creep, long curing time, and difficulty in repair or modification. #### Concrete compared with steel | Point | Concrete (RCC) | Steel | |---|---|---| | Strength per weight | Low; heavy sections | Very high; light sections | | Cost | Cheaper, local materials | Costlier, usually imported | | Fire resistance | Good | Poor; loses strength above 400-500 °C | | Corrosion / maintenance | Little maintenance | Needs painting and protection | | Shape | Easily moulded | Fabricated sections only | | Construction speed | Slower (curing, formwork) | Faster erection | | Ductility / tension | Needs rebar | Ductile in both tension and compression | | Recycling | Limited | 100% recyclable | Hence concrete is preferred for foundations, slabs, dams and low- to medium-rise buildings, and steel for long spans and tall towers. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Concrete's main strength advantage is: A. High tensile strength B. Light weight C. Ductility in tension D. High compressive strength at low cost Answer: D. Concrete is strong in compression and cheap. (Key point: Strength) 2. Why does concrete protect embedded steel? A. Its alkaline cover (pH about 12.5) B. Its acidity C. Its high porosity D. Its low density Answer: A. The alkaline environment passivates steel. (Key point: Corrosion protection) 3. Compared with steel, concrete is: A. Faster to erect B. Better in fire resistance and cheaper, but slower to construct C. Stronger per unit weight D. 100% recyclable Answer: B. Steel loses strength above 400-500 °C and is costlier, but is faster and lighter. 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