Which statement correctly describes pre-tensioned concrete?

• A. High tensile strength steel strands are tensioned after the concrete cures.
• B. Concrete is poured around the strands without bonding.
• C. High tensile strength of steel is wound inside tubing after pouring.
• D. High tensile strength steel strands are tensioned before pouring, bond to the concrete, and the completed unit is shipped to the job site.

Answer: (D)

Pre-tensioned concrete uses high-strength steel strands that are stretched before the concrete is placed. The strands are anchored at the ends, the concrete is poured around them and cures, and the bond between concrete and steel transfers the prestress to the member. When the cure is complete, the built-in tension remains in the concrete, so the finished unit is shipped to the job site with prestress already in place.

If the strands were tensioned after pouring, that would describe post-tensioning rather than pre-tensioning; pouring around strands without bonding wouldn’t develop prestress; and winding steel inside tubing after pouring isn’t how pretensioned members are made.