Prefabricated and Cast-in-Place Slabs in Compound Houses

In compound houses, prefabricated slabs and cast-in-place slabs can be closely combined for use, and there are differences in their characteristics and application scenarios.

Cast-in-Place Slabs:
Cast-in-place slabs are formed by on-site formwork erection, steel bar binding, and concrete pouring, offering significant structural advantages. They have strong integrity, excellent seismic performance, high load-bearing capacity, and good thermal and sound insulation. The common thickness ranges from 80 to 160 millimeters, with an allowable error range of -5 millimeters to +8 millimeters, requiring strict quality control during construction. Cast-in-place slabs are suitable for areas with strict waterproofing requirements, such as pitched roofs, flat roofs, and bathrooms, as their self-waterproofing structural characteristics can effectively prevent leakage. In compound houses, if the load-bearing structure for cast-in-place floor slabs is reserved, it is safe to add reinforced concrete floor slabs later, but four conditions must be met:

1. Reasonable load-bearing structure: The original structure must have sufficient load-bearing capacity to avoid overloading due to the addition.
2. Construction convenience: There must be sufficient space on-site for formwork erection and concrete pouring operations.
3. Standardized curing and formwork removal: After concrete pouring, curing must be carried out according to specifications to ensure that the strength meets the standards before formwork removal.
4. Professional design support: The addition plan must be designed by a structural engineer to avoid safety hazards caused by random construction.

Prefabricated Slabs:
Prefabricated slabs are prefabricated in factories and then transported to the site for hoisting and splicing, offering high construction efficiency but with obvious limitations. They have relatively weak integrity, lower seismic performance than cast-in-place slabs, and the slab joints are prone to steel bar corrosion due to mortar aging or rainwater infiltration, which can damage the floor slab structure. However, according to the current national standard "Unified Standard for Reliability Design of Building Structures" (GB 50068-2018), the design service life of prefabricated slab buildings is 50 years, the same as that of cast-in-place slabs. 30 years is not a mandatory scrap year stipulated by the state. Whether a building can continue to be used depends on the safety appraisal report issued by a professional institution. If the appraisal result is safe, measures such as reinforcing slab joints and applying waterproof coatings can be taken to extend the service life.

Suggestions for Combined Use:
In compound houses, cast-in-place slabs and prefabricated slabs can be combined for use. For example, cast-in-place slabs can be used in areas with high waterproofing and seismic requirements, such as bathrooms and stairwells, while prefabricated slabs can be used in spaces like bedrooms and living rooms to reduce costs. However, it should be noted that:

• The joints of prefabricated slabs need to be strengthened with waterproofing treatment to prevent water seepage.
• When adding floors, cast-in-place slabs should be preferred to ensure structural integrity.
• Regular housing safety inspections should be carried out, and aging problems should be repaired in a timely manner.