Conversion of Prefabricated Slabs to Cast-in-Place in Rural Houses

The conversion of prefabricated slabs to cast-in-place in rural houses requires steps such as demolition, formwork installation, steel bar installation, and concrete pouring, with specific operations strictly following norms to ensure safety.

1. Demolition of Prefabricated Slabs

Demolition of prefabricated slabs is the first step in the renovation, but overall demolition carries a high risk. The connections between the prefabricated slabs and walls or beams may have loosened or rusted due to long-term use. During demolition, professional tools (such as electric pickaxes) should be used to gradually break them down, avoiding violent demolition that could cause sudden structural instability. During the demolition process, all debris on the floor should be cleared to ensure an unobstructed work area, and temporary supports should be provided for the surrounding walls to prevent collapse due to local load changes.

2. Installation of Floor Formwork

The formwork serves as the support system for the cast-in-place concrete, and its flatness directly affects the quality of subsequent plastering. Boards that meet the required strength (such as wooden or steel formwork) should be selected, and their surface flatness should be calibrated using a level, with an error controlled within 3mm. The joints between formwork pieces should be treated with sealing strips to prevent concrete leakage during pouring. Support frames (such as steel tube scaffolding) should be installed at the bottom of the formwork, with spacing adjusted according to the floor span, generally not exceeding 1.2 meters, to ensure the formwork does not deform during pouring.

3. Installation of Steel Bars on the Floor

Steel bars are the core load-bearing components of the cast-in-place floor. All steel bars should be inserted and welded into the walls and columns, with the welding length meeting the norm requirements (usually more than 10 times the diameter of the steel bar). If a cast-in-place layer is to be added on top of the prefabricated slabs, columns, beams, and cantilever beams should be set up in advance as support structures. The steel bars should be tied into a mesh, with the diameter of the main bars recommended to be 2-3 grades thicker than those of the original prefabricated slabs (for example, if Φ8 steel bars were originally used, Φ10-Φ12 are recommended for the cast-in-place layer), with the spacing between horizontal and vertical steel bars not exceeding 150mm. The structural strength of the slab reinforcement should be greater than the load-bearing capacity of the original prefabricated slabs, and radiating bars should be added at the corners and mid-span of the slabs to disperse stress and reduce the load on the prefabricated slabs.

4. Concrete Pouring

Before concrete pouring, the formwork should be sprayed with water to prevent water absorption that could affect strength. If a cast-in-place layer is to be added on top of the prefabricated slabs, an electric pickaxe should be used to chisel out a 12-centimeter-wide and 10-centimeter-high groove along the edge of the prefabricated slabs, allowing the steel bars of the cast-in-place layer to be embedded and connected with the walls, enhancing overall integrity. The concrete should be poured in layers (each layer not exceeding 300mm in thickness) and compacted with a vibrating rod to avoid honeycombing and pitting. After pouring, the concrete should be covered with plastic film for moist curing for at least 7 days, and the formwork can only be removed after the concrete strength reaches at least 75% of the design value (usually taking 14-28 days).