Concrete as a structural material

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

Hence concrete is preferred for foundations, slabs, dams and low- to medium-rise buildings, and steel for long spans and tall towers.