Prestressing methods — which statement best describes the current use-case and economy of post-tensioning systems in concrete construction?

Introduction / Context:
Prestressed concrete enhances span capacity and serviceability by introducing a pre-compression that counteracts tensile stresses from external loads. There are two principal methods: pre-tensioning (tendons stressed before casting) and post-tensioning (tendons stressed after concrete hardens). Selecting the right method impacts economy and constructability, especially for long spans.

Given Data / Assumptions:

• Modern bridges, parking structures, long-span floors, and segmental construction often exploit post-tensioning.
• Economy is judged across materials, formwork, construction speed, and life-cycle performance.
• Question focuses on broad practical adoption rather than a niche case.

Concept / Approach:

Post-tensioning uses ducts cast into the concrete. After curing, tendons are stressed and anchored, allowing long spans with thinner sections and reduced cracking/deflection. For large spans, savings from reduced self-weight, fewer supports, and faster erection typically outweigh tendon and anchorage costs. Consequently, it is a mainstream solution today for bridges and large floor plates.

Step-by-Step Solution:

Verification / Alternative check (if short method exists):

Industry practice and numerous case studies show cost/weight reductions and performance improvements using post-tensioning for spans beyond conventional reinforced solutions.

Why Other Options Are Wrong:

It is not obsolete (A) nor generally uneconomical (B); option D is inapplicable; option E is factually incorrect.

Common Pitfalls (misconceptions, mistakes):

Assuming prestress is only for bridges; overlooking post-tensioned slabs in buildings and parking structures.

Final Answer:

Post-tensioning is economical for large spans and is widely adopted nowadays.