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Concrete ingredients; concrete versus steel

Short answer

Concrete contains cement, fine and coarse aggregates, water, and optional admixtures. Compared to steel, concrete is cheaper, fire-resistant, needs little maintenance, can be cast to any shape, has good compressive strength, and bonds well with steel owing to similar thermal expansion coefficients.

Explain concrete ingredients and concrete as a structural material over steel.

Concrete ingredients

  • Cement: the binder (OPC, PPC), which reacts with water.
  • Fine aggregate: sand (below 4.75 mm); fills the voids between the coarse particles.
  • Coarse aggregate: crushed stone or gravel (above 4.75 mm, usually 10-40 mm); forms the bulk and the strength skeleton. Fine and coarse aggregates together make up about 70-75% of the volume of concrete.
  • Water: for hydration and workability (clean, potable; IS 456 cl. 5.4).
  • Admixtures (optional): plasticisers, retarders, air-entraining agents, fly ash, silica fume.

Typical mix: M20 is 1:1.5:3 by volume, with w/c about 0.5.

Concrete as a structural material over steel

  • Cheaper and made from local materials; steel is costlier and often imported.
  • Fire-resistant, whereas steel loses strength rapidly at 400-500 °C.
  • Needs little maintenance and no painting (steel needs repeated corrosion protection).
  • Can be cast to any shape and gives monolithic, rigid structures.
  • Good compressive strength, mass for stability, and good sound and thermal insulation.
  • Works well with steel: concrete resists compression, steel resists tension, and they have nearly equal thermal expansion (≈10−12×10−6\approx 10-12 \times 10^{-6}/°C).

Limitations: heavy self-weight, low tensile strength, slow construction and cracking; steel is better for very long spans and for faster erection.

✓ Answer checked by Claude Opus 5.5 (high effort)

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