Which component is primarily responsible for improving concrete's ductility and tensile strength?

• A. Aggregate.
• B. Reinforcing steel.
• C. Water.
• D. Portland cement.

Answer: (B)

Concrete handles compression well but is weak in tension and tends to crack in a brittle way. The element that makes concrete ductile and able to carry tensile forces is reinforcing steel. When steel bars are embedded in concrete, they take on tensile stresses once cracking occurs, and their ductility allows the member to deform and absorb energy rather than fail suddenly. The steel and concrete work together as a composite: concrete carries compression while steel carries tension, and a good bond between them transfers forces effectively. Aggregates mainly influence stiffness and compressive strength, not ductility; water and Portland cement are involved in making and binding the mix but don’t provide the necessary tensile reinforcement.