Flashing of Floor Slabs in Prefabricated Slab Houses

The main reasons for the 'flashing' (cracks or deformation) of floor slabs in prefabricated slab houses are non-standard construction, material aging or unsuitability, design flaws, and foundation settlement. Depending on the severity, measures such as reinforcement, re-pouring, or structural modification should be taken for treatment.

Cause Analysis

1. Non-standard Construction: If the installation of prefabricated slabs is not carried out strictly according to specifications, such as improper treatment of slab joints, insecure connections, or insufficient support, it can lead to uneven stress distribution on the floor slab, resulting in cracks or deformation after long-term use.
2. Material Issues: The use of inferior or aged prefabricated slabs, insufficient concrete strength, or rusted and broken steel bars can reduce the load-bearing capacity of the floor slab, triggering the 'flashing' phenomenon.
3. Design Flaws: Insufficient floor slab thickness, excessive span, or failure to consider load distribution can lead to concentrated structural stress, exceeding the material's load-bearing capacity.
4. Foundation Settlement: Uneven settlement of the house foundation can cause the floor slab to lose its stress balance, resulting in cracks or deformation, especially in cases of soft soil foundations or uncompacted backfill.

Treatment Methods

1. Minor Flashing:
   • Surface Reinforcement: For floor slabs with crack widths less than 0.2mm, materials such as epoxy resin can be used to fill the cracks, and carbon fiber cloth or glass fiber mesh can be pasted to enhance tensile properties.
   • Adding a Concrete Layer: Pour a 3-5cm thick layer of fine aggregate concrete on the floor slab surface, incorporating a steel bar mesh (e.g., φ4@150mm) to improve overall stiffness.
2. Severe Flashing:
   • Re-pouring Cement: Completely remove the old cement layer to a solid base, clean the dust and keep it dry, apply a bonding agent, and then pour concrete with a strength of C30 or higher, with a thickness not less than the original design value.
   • Steel Bar Reinforcement: Add steel beams or profile steel supports at the bottom of the floor slab, or increase transverse steel bars through the technique of planting steel bars to form a composite structure and enhance load-bearing capacity.
3. Structural Modification:
   • Thickening the Floor Slab: For areas with large spans and heavy loads, disperse stress through composite layers or adding secondary beams.
   • Redesign: If the original design has fundamental flaws, it is necessary to commission a professional institution to recalculate the loads and adjust the floor slab thickness, reinforcement, or support system.

Precautions

Before treatment, it is necessary to commission a structural engineer to assess the safety of the house to avoid secondary damage caused by blind construction. If foundation settlement is the main cause, foundation reinforcement (such as grouting or pile foundation underpinning) should be carried out before treating the floor slab.