Construction Materials: Steel and Reinforced Concrete — CSEC Building Technology
Concrete and steel are combined to make a strong structural material used in foundations, beams, columns and slabs.
Concrete
Concrete is made of cement, water and aggregate (fine sand and coarse stone). It is:
- strong in compression (resisting being squashed), but
- weak in tension (resisting being stretched).
After placing, concrete must be cured (kept moist) so the cement hydrates and develops full strength.
Steel reinforcement
Steel is strong in tension, so steel reinforcing bars (rebar) are placed inside concrete to carry the tensile forces concrete cannot. The result, reinforced concrete, combines:
- the compressive strength of concrete, and
- the tensile strength of steel.
Formwork
Formwork (shuttering) is the temporary mould that holds and shapes wet concrete until it sets. Once cured, the formwork is removed (struck).
Corrosion
If water and oxygen reach the steel (e.g. through cracks or insufficient cover), it rusts and expands, cracking the concrete. Adequate concrete cover protects the steel.
Steel as a structural material
Steel has a high strength-to-weight ratio, can be welded and bolted, and is used for frames, beams and reinforcement.
Exam tips
- Concrete is strong in compression, weak in tension — hence steel reinforcement.
- Steel provides tensile strength; concrete provides compressive strength.
- Formwork moulds wet concrete; curing develops strength.
- Corrosion of reinforcement is caused by water and oxygen.