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

The main reasons for renovating prefabricated slab houses to cast-in-place structures are to address issues such as poor integrity, insufficient load-bearing capacity, poor user experience, and weak seismic resistance of the prefabricated slabs. The renovation requires structural inspection, load verification, and plan evaluation, with common methods including adding a composite layer while retaining the prefabricated slabs, and caution is advised for complete demolition.

Reasons for Renovation

Prefabricated slab houses have significant defects due to construction process limitations:

1. Poor Integrity: Prefabricated slabs are installed in sections and connected by concrete grouting between the slabs. Over time, temperature changes and foundation settlement can cause cracks in the slab joints, affecting the overall structural integrity.
2. Insufficient Load-Bearing Capacity: Early prefabricated slabs were designed with lower load standards, making it difficult to meet the load requirements of modern household equipment (such as large furniture and appliances) or functional changes (such as adding mezzanines).
3. Poor User Experience: Water leakage through slab joints is a common issue, especially in wet areas like bathrooms and kitchens. Sound insulation is poor, with floor impact noise easily transmitted to lower floors. The thin thickness of prefabricated slabs results in weak thermal insulation performance.
4. Weak Seismic Resistance: The connection between prefabricated slabs and walls relies on end anchoring. If the overlap length is insufficient (standard requirement ≥80mm) or the steel bars are corroded, the slabs are prone to detachment or complete collapse during earthquakes.

Key Steps Before Renovation

1. Structural Inspection and Evaluation:
   • Inspect the concrete strength, steel bar positions, and corrosion conditions, with a focus on checking whether the end overlap length of the prefabricated slabs meets the standards.
   • Evaluate the condition of the slab joints. If there are severe cracks or exposed steel bars, priority should be given to repair or reinforcement.
2. Load Verification and Plan Evaluation:
   • Recalculate the dead load (such as the weight of renovation materials) and live load (such as human activity and equipment load) of the floor based on the post-renovation usage function (such as residential to commercial conversion).
   • Verify the load-bearing capacity of the existing walls, columns, and foundations. If insufficient, simultaneous reinforcement (such as adding structural columns or expanding foundations) is required.

Mainstream Renovation Methods

1. Adding a Composite Layer While Retaining the Prefabricated Slabs:
   • Bind a steel bar mesh on the surface of the prefabricated slabs and pour 40-60mm thick fine aggregate concrete to form a composite floor. This method causes minimal damage and has a short construction period, but it is necessary to ensure a firm bond between the composite layer and the prefabricated slabs.
2. Complete Demolition of Prefabricated Slabs and Replacement with Cast-in-Place Structures:
   • Temporary supports must be added first, and the prefabricated slabs are removed one by one before binding steel bars and pouring concrete with formwork. This method is costly, and the limited space and complex load transfer in old houses pose high construction risks (such as the use of this method in the renovation of old houses from the 1990s in Shaanxi and two-story self-built houses in Hubei to frame structures).

Renovation Challenges

Renovating old houses is different from new construction, requiring应对 (addressing) issues such as limited space and significant construction interference. Moreover, complete demolition of prefabricated slabs may trigger structural instability and must be carried out by professional teams.