Cracks in Prefabricated House Slabs

When cracks appear in the prefabricated slabs of a house, it is necessary to determine their nature and degree of hazard based on their characteristics and take targeted treatment measures, as detailed below:

I. Types of Cracks and Safety Assessment

1. Unidirectional Parallel Cracks If the cracks are unidirectional and parallel to one side of the wall, they are usually caused by asynchronous deformation of adjacent prefabricated slabs. If there is no significant deflection in the floor slab (i.e., no sagging or deformation), such cracks generally pose no structural safety risks, but may lead to water leakage through the cracks, so attention should be paid to waterproofing.

2. Stress-Induced Cracks If the cracks are wide (e.g., exceeding 0.7mm), the floor slab shows obvious deflection or deformation, or the cracks penrate the entire thickness of the slab, there may be structural safety issues. Such cracks require immediate inspection and assessment by a professional agency to determine if reinforcement or repair is needed.

3. Other Types of Cracks

   • Concrete Shrinkage Cracks: These are commonly found at the corners of floor slabs and are caused by water evaporation and shrinkage during the concrete hardening process. When the width is small, they generally do not affect structural safety, but durability should be monitored.
   • Rebar Corrosion Cracks: These run along the direction of the rebar and are caused by concrete cracking due to rebar corrosion and expansion. It is necessary to check the thickness of the rebar's protective layer and the degree of corrosion to assess the impact on the structure.

II. Treatment Measures

1. Surface Treatment For cracks that pose no safety risks (e.g., unidirectional parallel cracks, shrinkage cracks), mesh fabric can be applied to enhance the surface's crack resistance, or epoxy resin and other materials can be used to fill and seal the cracks to prevent water intrusion and rebar corrosion.

2. Reinforcement and Repair If the cracks continue to expand or there are structural issues (e.g., stress-induced cracks), a professional agency should be contacted for inspection and assessment, and reinforcement measures should be taken based on the results. Common methods include increasing slab thickness, adding double-layer bidirectional rebar, and applying carbon fiber sheets to enhance the load-bearing capacity of the floor slab.

3. Waterproofing Treatment For cracks that may cause water leakage (e.g., unidirectional parallel cracks), waterproofing treatment should be carried out simultaneously. Waterproof coatings can be applied to the cracks, or waterproof membranes can be laid to prevent leakage from damaging interior finishes or further deteriorating the structure.

III. Preventive Measures

1. During the renovation or decoration of old houses, design drawings should be strictly reviewed to avoid critical designs (e.g., loads close to the design values).
2. The quality of concrete raw materials should be controlled, and unauthorized changes to the water-cement ratio should be prevented to ensure that the concrete strength meets the requirements.
3. The support system should be stable, and premature removal of formwork should be avoided to prevent cracks in the floor slab due to insufficient support.
4. Rebar positioning and protection should be strengthened to prevent rebar from sinking due to construction trampling, which affects structural loading.
5. Anti-crack mesh should be installed at the intersections of pipelines to reduce stress concentration caused by pipeline layout.
6. Proper concrete curing should be carried out, and premature loading (e.g., stacking heavy objects in advance) should be avoided to prevent early shrinkage cracks in the concrete.

If cracks develop rapidly or are accompanied by obvious deformation, it is recommended to immediately contact a professional agency for inspection and assessment to ensure living safety.