Red Seal Ironworker (Reinforcing) Practice Exam

What is the primary principle behind pre-stressing concrete?

1. To increase tensile strength

2. To retain moisture in the concrete

3. To place the concrete in compression

4. To decrease weight for handling

The correct answer is: To place the concrete in compression

The primary principle behind pre-stressing concrete is to place the concrete in compression. This is achieved by introducing pre-compressive forces in the concrete before it is subjected to service loads. The main goal of pre-stressing is to counteract the tensile forces that the concrete will experience under load, as concrete is naturally strong in compression but weak in tension. By inducing compressive stresses within the concrete, it effectively enhances its overall performance, allowing it to handle larger loads and span longer distances without cracking or failure. This method is particularly useful in applications such as bridges and large structural elements where tensile stresses can lead to significant structural issues. The other choices, while related to properties of concrete and structural considerations, do not represent the main principle of pre-stressing. Increasing tensile strength pertains more to different material enhancements rather than the fundamental aspect of pre-stressing. Retaining moisture is important for curing concrete but is not a direct goal of pre-stressing. Decreasing weight may be a consideration in structural design but is not the core intention of pre-stressing techniques.