Renovation of Prefabricated Slab Houses to Cast-in-Place Slab Houses

The core purpose of renovating prefabricated slab houses to cast-in-place slab houses is to address issues such as poor overall integrity, insufficient load-bearing capacity, poor user experience, and weak seismic resistance of prefabricated slabs. The renovation requires structural inspection, load verification, and the selection of a reasonable plan.

Necessary Inspection and Assessment Before Renovation

Before renovation, structural inspection and assessment must be carried out, focusing on the following aspects:

1. Inspection of Prefabricated Slab Condition: Check the concrete strength, steel bar positions, and rust conditions, paying special attention to whether the lap length of the prefabricated slab ends on the wall (beam) is ≥80mm (as required by regulations). If the lap is insufficient or there are severe cracks or exposed steel bars at the bottom of the slab, priority should be given to addressing these issues.
2. Load-Bearing Capacity Verification: Verify the load based on the post-renovation usage function (such as adding floors or changing the purpose) and assess the load-bearing capacity of the original walls, columns, and foundations. The self-weight of cast-in-place slabs is slightly heavier than that of prefabricated slabs (usually with a thickness of 120-150mm). If the original structure's load-bearing capacity is insufficient, the walls or foundations need to be reinforced simultaneously to avoid structural instability due to increased loads.

Three Mainstream Renovation Plans

1. Retain Prefabricated Slabs + Add Cast-in-Place Composite Layer

   • Applicable Scenarios: Houses with minor damage to prefabricated slabs and low requirements for overall integrity.
   • Key Operation Points: Pour a layer of cast-in-place concrete (usually with a thickness of 50-80mm) directly on the surface of the prefabricated slabs to form a composite structure. This plan causes minimal damage and has a short construction period, but it is necessary to ensure that the composite layer adheres firmly to the prefabricated slabs to avoid hollowing.

2. Remove Prefabricated Slabs + Recast Cast-in-Place Slabs

   • Applicable Scenarios: Houses with severe damage to prefabricated slabs or those requiring a thorough improvement in structural performance.
   • Key Operation Points:
     • After removing the prefabricated slabs, clear the floor surface and install flat formwork as support;
     • Install steel bars according to design requirements, ensuring that all steel bars are inserted and welded into the walls and columns to ensure structural integrity;
     • Pour cement and cure it, and remove the formwork after it is completely dry. This plan involves complex construction and high costs, but it can thoroughly address the defects of prefabricated slabs.

3. Composite Structure of Prefabricated and Cast-in-Place Slabs for Rural Self-Built Houses

   • Applicable Scenarios: Rural self-built houses with columns, beams, and cantilevered beams.
   • Key Operation Points:
     • Use an electric pick to chisel a 12 cm wide and 10 cm high wall above the prefabricated slabs and chisel a circle around it to embed the steel bars and concrete into the wall, enhancing the connection;
     • In addition to using tied steel bars for the floor slab, arrange radial steel bars (radiating from the center of the slab to the surroundings) to improve crack resistance. This plan requires strict control over the depth of wall chiseling and the arrangement of steel bars to avoid damaging the original structure.