Cracks in the Prefabricated Roof of a House

Cracks in the prefabricated roof of a house are mainly caused by factors such as the characteristics of prefabricated panels, rapid shrinkage, improper steel bar placement, and hidden dangers left during construction.

1. Caused by the characteristics of prefabricated panels: Prefabricated panels are not integral structures but are assembled by placing individual pieces on the roof. There are originally gaps between the prefabricated panels, which are usually filled with mortar or concrete. However, this filling method is difficult to achieve a perfect bond. Over time, cracks or small gaps are prone to appear. This is an inherent characteristic of the prefabricated panel structure, which to a certain extent increases the likelihood of cracks appearing on the roof.
2. Rapid shrinkage: After concrete is poured onto the roof, it goes through a setting period, also known as the shrinkage period. During this stage, if the concrete is not properly cured, especially in hot weather, the rate of water evaporation is very fast. The rapid loss of water in the concrete leads to rapid setting. Since there are many air bubbles in the concrete, when shrinkage occurs too quickly, these air bubbles cannot be smoothly squeezed out and are trapped inside the concrete. As time goes on, when the air bubbles burst, they will have a撑开 (expanding, here it means exerting an expanding force) effect on the concrete, thus forming cracks.
3. Improper steel bar placement: Steel bars play a crucial tensile role in concrete. If improper operations occur during the placement of steel bars, such as randomly adding through-bars on already laid steel bars, it will change the overall tensile force of the entire structure. This change in tensile force will cause inconsistent situations during the shrinkage and setting of the concrete, resulting in cracks. In addition, elements such as the wire boxes for adding lights in the middle of the house may also affect the layout and tensile force of the steel bars, thereby causing cracks.
4. Hidden dangers left during construction: The formation of cracks is not necessarily due to the long-term disrepair of the house. Some cracks may have already existed during the construction of the house. During the construction process, factors such as construction techniques and material quality may cause small cracks to appear on the roof, which just go unnoticed at the time. As time passes, these small cracks gradually become larger and eventually attract people's attention.