Reinforced Concrete Prefabricated Roof

The reinforced concrete prefabricated roof is a roof structure formed on the basis of prefabricated reinforced concrete slabs, combined with different processes and structural forms. It has the characteristics of convenient construction and controllable costs, but attention should be paid to structural performance and maintenance issues.

Structural Forms and Processes

1. Reinforced Concrete Slab Tile Roof
   Prefabricated reinforced concrete hollow slabs or cast-in-place flat slabs are used as the base layer, and tiles are covered on the surface to meet fire prevention or styling requirements. The processes are divided into two categories:

   • Felt Waterproof Layer Process: After laying felt on the leveling layer, use wooden wedges to fix the felt pressing strips and tile hanging strips for tile laying, forming a flexible waterproof layer.
   • Waterproof Cement Mortar Process: Directly apply waterproof cement mortar on the roof slab for tile pasting, which is common in antique buildings and complies with GB/T50855-2024 'Calculation Standard for Quantities of Antique Building Engineering' (to be implemented in September 2025).

2. Prefabricated Slab Installation Process
   Prefabricated slabs are prefabricated in the factory and then transported to the site for hoisting. Mortar is filled between the slabs and node connections are made. Its overall rigidity is weaker than that of a fully cast-in-place structure. In the event of an earthquake or uneven foundation settlement, slab joints, nodes, and load-bearing walls are prone to damage. In the 1980s and 1990s, some prefabricated slab residential buildings had problems such as roof leakage, fine wall cracks, and poor sound insulation due to incomplete ring beams and structural columns, and insufficient end anchoring and bearing lengths of the slabs. Long-term water leakage will cause the mortar in the slab joints to fail, and the expansion of steel bar corrosion will further damage the concrete.

Construction Cases and Structural Reinforcement

1. Self-made Cement Slab Roof
   In foreign cases, cement slabs are self-made using hollow bricks and steel bars:

   • Stack three layers of hollow bricks and wet them with water. Insert steel bars into the holes of the hollow bricks at both ends, and pad dry sand at the bottom to make the steel bars protrude.
   • Pour cement mortar and let it solidify to form a cement slab, which is fixed by clamping with steel bar columns. After splicing, arrange steel bars horizontally and vertically and pour concrete, and finally level the surface.

2. Combination Process of Prefabricated Slabs and Cast-in-Place Construction

   • Lay prefabricated cement slabs on wooden beams, fix the spacing of the beams with special bricks, and bind wooden boards at the bottom to enhance the load-bearing capacity.
   • Bind a steel bar grid and fix it with formwork, pour concrete to ensure a dense structure, push a wheelbarrow to fill the gaps and level the surface, forming a flat and sturdy roof.

Performance Characteristics and Maintenance Suggestions

• Advantages: Fast construction speed and relatively low cost, suitable for rapid construction needs.
• Defects: Its integrity is weaker than that of a cast-in-place structure, and it is necessary to strictly set ring beams, structural columns, and end anchoring of slabs according to standards.
• Maintenance: Regularly check the waterproofing of slab joints and repair water leakage problems to prevent steel bar corrosion from causing concrete cracking; antique buildings should follow special standards for quantity calculation and construction.