Prestressed concrete is achieved by:

• A. Using high-tensile steel strands only after the concrete has hardened
• B. Using conventional reinforcement in tension before curing
• C. Casting with no reinforcement
• D. Introducing precompression by prestressing steel strands before loading

Answer: (D)

Prestressed concrete works by putting the concrete under compression before any external loads are applied. This is achieved by using steel strands or tendons that are stressed so they press the concrete together. In pretensioning, the steel is tensioned before the concrete is poured and locked in as it cures, while in post-tensioning the tendons are tensioned after curing and then anchored, creating compression inside the member. The essential idea is introducing precompression in the concrete so that when service loads cause tension, the material remains cracked-resistant and stronger. The described approach—introducing precompression by prestressing steel strands before loading—captures this fundamental mechanism.