How to Expand a Prefabricated Slab House

The expansion of a prefabricated slab house must strictly adhere to structural safety principles, achieving safe expansion through professional assessment, reinforcement treatment, and standardized construction. The specific steps are as follows:

I. Construction Preparation Phase

1. Technical Preparation

   • Structural Safety Assessment: Commission a third-party agency to conduct a D-grade dilapidated building assessment, focusing on detecting wall cracks (≤0.3mm), foundation settlement (≤5mm/year), and concrete carbonation depth. Use PKPM software to simulate the impact of additional loads on the original foundation, ensuring a load-bearing capacity surplus coefficient ≥1.2.
   • Detailed Design: Specify the prefabricated slab model (e.g., YKB3351 type, span 3.3m, load 1.5kN/m²), and draw detailed diagrams of the connection nodes between new and old structures (e.g., implanting Φ12mm steel bars with a depth ≥10d, using C40 grout) and slab joint treatment nodes (20mm foam board + micro-expansion concrete).
   • Surveying and Setting Out: Establish a control network using a total station, with axis deviations ≤3mm and elevation reference point allowable deviations ±5mm.

2. Material Preparation

   • Prefabricated Slab Inspection: Check the concrete strength report above C30, geometric dimension deviations (length ±5mm, width ±3mm, thickness ±2mm), and conduct a 1.5-times design load test on three slabs from each batch.
   • Reinforcement Materials: Select HRB400E grade steel bars (tensile strength ≥540MPa), CGM-4 type grout (28d compressive strength ≥40MPa), and 3mm thick SBS waterproof membrane (heat resistance ≥90℃).
   • Stacking Management: Stack prefabricated slabs with two-point support, height ≤6 layers, with square timbers between layers; steel bars should be stored off the ground, elevated 30cm, and protected from rain.

II. Original Structure Reinforcement Construction

1. Wall Reinforcement

   • Double-Sided Steel Mesh: Chisel the original wall (depth ≥6mm), implant φ8mm@300mm tie bars, bind φ6mm@200×200mm steel mesh, and spray C25 fine aggregate concrete (thickness 50mm).
   • Constructional Column Addition: Set up 240mm×240mm constructional columns at the four corners of the expansion area and at the intersections of vertical and horizontal walls.

2. Load-Bearing Structure Reinforcement

   • For prefabricated slabs with hidden dangers, adopt carbon fiber cloth, steel plate bonding reinforcement, or add support beams. The plan must be designed by a professional engineer and executed by a qualified team.

III. Expansion Construction Precautions

1. Avoid Slotting: Route wires along slab joints or install them openly as much as possible to minimize damage to the steel bar protective layer.
2. Waterproofing Treatment: Apply a penetrating crystalline waterproofing slurry, followed by 2-3 coats of polyurethane coating (thickness ≥1.5mm). The use of membranes is prohibited; conduct a 72-hour closed water test after construction.
3. Pipeline Pressure Testing: Conduct a water flow test for drainage pipes and a pressure test for tap water pipes ≥0.6MPa, ensuring no leakage before closing the pipe trenches.
4. Filling Materials: Prioritize lightweight materials such as perlite and ceramsite to avoid deformation of the prefabricated slabs caused by sand and gravel.

IV. Construction Specifications and Acceptance

1. Construction Sequence: Follow the sequence of 'structural reinforcement → waterproofing → piping → filling → decoration' to avoid cross-damage.
2. Hidden Project Acceptance: Document the water and electricity lines and waterproof layers with images, and have them jointly signed by the owner and supervisor.
3. Long-Term Monitoring: Regularly inspect the prefabricated slabs for cracks or deformation within 1-2 years after renovation to ensure safety.