Prefabricated Concrete Slabs for Roof

Prefabricated concrete slabs for roofs were commonly used factory-prefabricated cement components in early 20th-century architecture. They have gradually been phased out and are now only used as temporary options in specific scenarios.

Definition and Manufacturing Process of Prefabricated Slabs

Prefabricated slabs are cement components prefabricated in factories. During manufacturing, a hollow mold is first made using wooden planks. Reinforcing bars are then placed in the hollow part of the mold, and cement is poured in. After drying, the wooden planks are knocked off to form the slab. There are two types: solid and hollow. The hollow structure achieves lightweighting by reducing the non-load-bearing concrete, lowering material costs and structural self-weight.

Application Scenarios and Existing Issues

Prefabricated slabs were once widely used in scenarios such as ditch covers beside highways and roof insulation layers. However, existing prefabricated slab houses generally have three major defects:

1. Weak Earthquake Resistance: Prefabricated slabs are bonded to walls with mortar and are prone to detaching from the main structure during earthquakes. In contrast, cast-in-place roofs are connected to wall reinforcing bars as a whole and can bear forces together.
2. Poor Sound and Heat Insulation: Prefabricated slabs are assembled from separate pieces, and the joints easily form sound and heat bridges. Cast-in-place roofs, being a single piece of concrete, have significantly better sound and heat insulation performance than prefabricated slabs.
3. Short Service Life: Prefabricated slabs are designed to last about 30-50 years, and the joints are prone to cracking, leading to water leakage. Cast-in-place roofs have no joints, have excellent waterproof performance, and are more durable.

Comparison between Prefabricated Slabs and Cast-in-Place Roofs

In terms of earthquake safety, waterproof performance, and sound insulation, prefabricated slabs have obvious disadvantages:

• Earthquake Safety: Cast-in-place roofs are integrated with wall reinforcing bars and can deform协同 (should be 'deform together' or 'deform in coordination') during earthquakes; prefabricated slabs rely on mortar bonding and are prone to disintegration during major earthquakes.
• Waterproof Performance: Cast-in-place roofs are a single piece of concrete with no risk of joint leakage; the joints of prefabricated slabs are prone to cracking due to settlement or temperature changes.
• Sound Insulation: The density and continuity of the concrete in cast-in-place roofs can effectively block sound transmission, while the joints of prefabricated slabs form sound bridges, resulting in poorer sound insulation.

Applicable Scenarios and Policy Orientation

Prefabricated slabs are only suitable for temporary scenarios in one- or two-story buildings on flat ground where immediate occupancy is required. Earthquake-prone areas, high-rise buildings, or scenarios pursuing safety and durability should prioritize cast-in-place roofs. Since 2022, China has implemented a renovation policy for old buildings, focusing on repairing and renovating prefabricated slab houses and only demolishing buildings that meet the criteria for dangerous buildings. The aim is to extend their service life through reinforcement and waterproofing measures while gradually promoting the upgrading of building structures.