Prefabricated Floor Slabs for Building Floors

Prefabricated floor slabs were a common type of floor used in early 20th-century buildings. They are concrete prefabricated components that are manufactured in factories and then installed on-site to complete the floor construction.

Production and Types of Prefabricated Slabs

Prefabricated slabs are primarily made of concrete. During production, a hollow mold is first created using wooden planks. Reinforcing bars are then placed inside the mold, and cement is poured. After the cement solidifies, the wooden planks are knocked off to form the finished product. Based on structural differences, prefabricated slabs are divided into two types: solid slabs and hollow slabs:

• Solid slabs: These have no internal voids, offering high overall strength but are relatively heavy. They are mostly used in areas with high load-bearing requirements.
• Hollow slabs: By creating voids inside, the amount of non-load-bearing concrete is reduced, achieving a lightweight design while maintaining a certain level of strength. They are more commonly used.

Applications and Characteristics of Prefabricated Slab Buildings

Prefabricated slab buildings were widely used in urban residential buildings from the 1970s to the 1990s, especially those with brick-concrete structures. Their core advantages include:

• High construction efficiency: Factory-prefabricated components can be mass-produced, and on-site installation only requires assembly, eliminating the need to wait for the cement to fully solidify (cast-in-place floors require about 15 days, while prefabricated slab floors only need 3 days to complete one floor's construction).
• Lower cost: Reduces on-site construction procedures and labor input, lowering the overall construction cost.

However, prefabricated slab buildings also have significant drawbacks:

• Poor unit layout flexibility: Room sizes must strictly match the specifications of the prefabricated slabs, making it difficult to achieve personalized designs.
• Risk of joint leakage: Cracks can easily form at the joints between slabs due to settlement or aging, leading to water leakage problems.
• Insufficient overall stiffness: They have weak seismic performance and are difficult to renovate (e.g., removing or modifying walls may damage the structural stability).

Replacement in Modern Buildings and Old Building Renovation Policies

With the development of construction technology, frame structures and reinforced concrete structures have gradually replaced the simple use of prefabricated slabs, enhancing the overall structural integrity and safety through cast-in-place processes. Since 2022, China has implemented old building renovation policies, adopting differentiated approaches to prefabricated slab buildings:

• Renovation and upgrading as the main approach: Buildings that do not meet the criteria for dangerous buildings are reinforced, waterproofed, and functionally upgraded.
• Demolition of dangerous buildings: Only prefabricated slab buildings with severe structural damage and safety hazards are demolished and rebuilt.

Prefabricated slab buildings are products of a specific historical period, reflecting the need to balance efficiency and cost at the time. However, modern buildings place greater emphasis on safety, durability, and flexibility, leading to a significant reduction in the use of prefabricated slabs.