Analysis Table of Cracks in Prefabricated Panel Houses

The following is the analysis table of cracks in prefabricated panel houses:

1. Cracks in the floor slabs of old prefabricated panel houses Characterized by unidirectional cracks parallel to one side wall, caused by asynchronous deformation of two prefabricated panels. If there is no significant deflection in the floor slab, there is generally no safety hazard, but leakage may occur. Treatment recommendation: Grout the cracks if they do not develop; reinforcement is required if they continue to expand.

2. Load-bearing cracks in concrete floor slabs Features include cracks at the edges of two-way slab supports due to insufficient reinforcement, steel bar displacement, or insufficient concrete strength, as well as cracks along the edges of beams (walls) at the upper supports of the floor slab and diagonal cracks at the lower part (which may penetrate the floor slab). When the crack width is small, there is no safety issue; when the width is large, there is a safety hazard, which is an engineering problem. Treatment recommendation: Inspection, assessment, and reinforcement repairs are required.

3. Concrete shrinkage cracks Caused by deformation due to concrete shrinkage in the floor slab, internal forces are released at weak points, resulting in cracks that penetrate vertically, commonly found at the corners of the floor slab and where constraints are weaker. When the width is not large, it does not affect structural safety, but there is a durability issue. Treatment recommendation: Handle in conjunction with cracks caused by steel bar corrosion.

4. Cracks caused by steel bar corrosion After steel bars rust, their volume expands, causing the concrete to crack under stress. The cracks are distributed along the direction of the steel bar placement (horizontal and vertical), and rust marks are visible on the surface of the slab. The cracks gradually increase over time until the steel bars rust and break, reducing the load-bearing capacity of the floor slab. Treatment recommendation: Durability repairs are required.

5. Plastic shrinkage cracks Caused by uneven shrinkage due to rapid surface moisture evaporation during the initial setting stage after pouring, these cracks are shallow (width < 0.5mm) and irregularly reticulated. They are non-structural defects and are considered 'normal' within the scope allowed by industry standards. Treatment recommendation: Strengthen curing.

6. Temperature cracks Caused by excessive temperature differences between the interior and surface of the concrete, these may form penetrating cracks (width 1-3mm, deep). They have a significant impact on structural durability and exceed normal limits, requiring focused investigation. Treatment recommendation: Inspection, assessment, and repair are required.

7. Dry shrinkage cracks When the curing period is insufficient or the environment is dry, the internal moisture of the concrete dissipates, causing volume shrinkage. These cracks are mostly distributed along the length of the component, with a fine width but numerous in number. Cracks with a width ≤ 0.3mm and not appearing in critical areas are considered 'normal'; when the width exceeds the standard or is densely distributed, it is a quality issue. Treatment recommendation: Strengthen curing or repair.

8. Load-induced cracks Caused by exceeding the designed load during demolding, lifting, or transportation, these cracks are wide and fixed in position. They directly threaten structural safety and are a serious quality issue. Treatment recommendation: Repairs must be made.

Supplementary judgment methods: For crack width testing, a business card can be inserted into the crack; if it can be easily inserted, the width is large. For crack development monitoring, transparent tape can be applied to both ends of the crack with the date marked; if the tape is torn or new creases appear, the crack is expanding. For tapping inspection, a small iron rod can be used to tap the joints of the prefabricated panels or the center of the floor slab; if a 'bang' hollow sound is emitted, there may be internal hollowing or loosening.

Industry standard allowable range: Non-structural cracks should have a width ≤ 0.3mm and a depth not exceeding the thickness of the protective layer; the number of cracks per meter length should be ≤ 3, with a crack spacing ≥ 200mm; cracks should not appear in the tension zone, around embedded parts, or at structural connection points.