What enhances the strength of prestressed concrete structures?

The strength of prestressed concrete structures is significantly enhanced by the tensioning of reinforcing cables before the concrete is subjected to any loads. This process involves the use of high-strength steel cables, which are deliberately stretched and anchored within the concrete. By tensioning these cables prior to concrete curing and loading, compressive forces are introduced into the concrete, offsetting tensile stresses that occur when the structure is in use.

As the loads are applied to the structure, the prestressing forces help keep the concrete in compression, which is essential because concrete is inherently strong in compression but weak in tension. This pre-emptive measure effectively increases the load-bearing capacity of the concrete, reduces the risk of cracking under service loads, and enhances the overall durability and service life of the structure.

The other options do not contribute to the enhanced strength of prestressed concrete in the same manner. Increased moisture content can weaken concrete and affect curing, while using lighter aggregate materials may not provide the necessary structural integrity needed. Similarly, while layering concrete may offer certain benefits, it does not directly address the fundamental principles of prestressing which play a crucial role in increasing strength.