Select the incorrect statement A. The loss of prestress is more in pre-tensioning system than in post-tensioning system. B. Pretensioning system has greater certainty about its durability. C. For heavy loads and large spans in buildings or bridges, post-tensioning system is cheaper than pretensioning system D. none of the above

The correct answer is C.

Pretensioning is a method of prestressing concrete in which the tendons are tensioned before the concrete is placed. Post-tensioning is a method of prestressing concrete in which the tendons are tensioned after the concrete has been placed.

The main advantage of pretensioning is that it results in a more durable concrete structure. This is because the concrete is placed under compression when the tendons are tensioned, which helps to protect it from cracking. The main advantage of post-tensioning is that it is more flexible than pretensioning. This is because the tendons can be tensioned after the concrete has been placed, which allows for more precise control of the prestress force.

For heavy loads and large spans, post-tensioning is usually the preferred method. This is because the tendons can be tensioned to a higher level of stress, which results in a more efficient structure. However, for smaller structures, pretensioning may be the more economical option.

In conclusion, the incorrect statement is C. For heavy loads and large spans in buildings or bridges, post-tensioning system is cheaper than pretensioning system.