ANS:C - is economical for large spans and is adopted now a days

The post-tensioning system, which involves the use of high-strength steel tendons or cables to apply compressive forces to concrete members, has evolved over the years and has been utilized in various construction projects. The statement "Post tensioning system was widely used in earlier days" is inaccurate because post-tensioning became more prevalent in modern construction rather than in earlier days. Regarding the options provided:

1. Post-tensioning system was widely used in earlier days: This statement is generally incorrect. While post-tensioning techniques have been around for several decades, they have become more commonly used in modern construction due to advancements in materials, construction methods, and engineering practices.
2. Post-tensioning system is not economical and hence not generally used: This statement is also incorrect. Post-tensioning systems can be economical for certain types of structures, particularly for large spans such as bridges, long-span roofs, and high-rise buildings. While the initial cost may be higher than conventional reinforcement methods, the benefits of reduced material usage, thinner sections, longer spans, and improved structural performance can often justify the investment.
3. Post-tensioning system is economical for large spans and is adopted nowadays: This statement is generally accurate. Post-tensioning is indeed considered economical for structures with large spans or where specific structural requirements necessitate its use. It has become increasingly adopted in modern construction practices, especially for projects that require efficient use of materials, reduced structural depth, and improved durability.
4. None of these: While some aspects of the previous statements are inaccurate, the statement that post-tensioning systems are economical for large spans and are commonly used nowadays is generally correct.