Prefabricated Slabs in Housing Construction

Prefabricated slabs in housing construction were commonly used concrete prefabricated components in the early 20th century. They were prefabricated in factories and installed on-site, and were once widely used in scenarios such as residential floor slabs, thermal insulation layers, and infrastructure coverings. However, due to structural defects, they have gradually been replaced by modern construction techniques.

Definition and Manufacturing Process of Prefabricated Slabs

Prefabricated slabs are concrete components prefabricated in factories or prefabrication yards using molds. The core manufacturing process involves: nailing wooden planks to form a hollow mold, arranging steel bars inside, pouring cement, and knocking off the mold after solidification to form the finished product. Depending on their structure, they can be classified into two types: solid and hollow. The hollow design achieves lightweighting by reducing the non-load-bearing concrete, thereby lowering transportation and installation costs.

Application Scenarios and Historical Background

Prefabricated slabs were widely used in 20th-century construction, with typical scenarios including:

1. Residential Floor Slabs: Before 1985, residential buildings in China mostly used prefabricated slab structures due to their fast construction speed and low cost, which met the needs of large-scale housing construction in the 1970s and 1980s.
2. Infrastructure Coverings: Such as highway ditch cover plates and roof thermal insulation layers, utilizing their standardized dimensions and convenient installation characteristics.
3. Temporary Buildings: Scenarios requiring rapid construction, such as work sheds and warehouses.
   Historical Background: During the period of housing shortage in China, prefabricated slabs were extensively used due to their characteristics of being "cheap and fast", resulting in a large inventory of prefabricated slab buildings nationwide.

Defects and Reasons for the Obsolescence of Prefabricated Slabs

1. Low Structural Safety:
   • Limited Lifespan: The designed lifespan is approximately 30-50 years. After aging, the concrete is prone to powdering and shedding.
   • Poor Earthquake Resistance: The overall integrity is weak, and the joints are prone to cracking and slab disintegration during earthquakes.
   • Waterproofing Issues: The joints between slabs are prone to leakage and require additional waterproofing treatment.
2. Replacement by Modern Construction Techniques: Frame structures and cast-in-place reinforced concrete techniques significantly improve building safety and durability by enhancing overall integrity and ductility, gradually replacing prefabricated slabs.

Renovation Policies and Handling of Existing Buildings

1. Policy Orientation: Since 2022, China has implemented renovation policies that focus on repair and renovation, with only dangerous buildings being demolished, avoiding large-scale demolition and construction.
2. Renovation Grading:
   • Level 1 Renovation: Appearance renovation (such as painting) for structurally safe buildings.
   • Level 2 Reinforcement: Adding steel bars or concrete to buildings with minor damage.
   • Level 3 Reconstruction: Demolishing and rebuilding severely damaged buildings.
   • Level 4 Dangerous Building Handling: Direct demolition.
3. Renovation Results: As of 2024, 26.3% of old prefabricated slab buildings have completed reinforcement and renovation, significantly improving residential safety.

As a product of a specific historical period in construction, the rise and fall of prefabricated slabs reflect the profound impact of technological progress and policy adjustments on the construction industry. Currently, through scientific classification and renovation, both the historical value of buildings is preserved and the safety of residents' lives and property is ensured.