Materials for Prefabricated Slab Houses
The main materials used in prefabricated slab houses are concrete and steel bars, with specific compositions and functions as follows:
Concrete: The Basic Material for Prefabricated Slabs
Concrete is the core component of prefabricated slabs, mixed from cement, gravel (such as rice-sized stones), and sand in specific proportions. Its function is to provide structural strength and durability to the prefabricated slabs. During production, concrete is poured into pre-nailed hollow molds, filling the gaps around the steel bars to form a solid structure. Depending on the intended use, the concrete mix can be adjusted; for example, increasing the proportion of cement can enhance strength, but a balance must be struck between cost and performance.
Key Components of Concrete:
- Cement: As a cementitious material, it hardens after reacting with water, binding the gravel and sand together.
- Gravel (Rice-sized Stones): Provides skeletal support, enhancing compressive strength, with a typically small particle size to accommodate the thickness of the prefabricated slabs.
- Sand: Fills the gaps between gravel particles, reducing porosity and improving density and surface smoothness.
Steel Bars: Enhancing Structural Tensile Strength
Steel bars serve as the skeleton of prefabricated slabs, bearing tensile forces within the concrete to compensate for the concrete's insufficient tensile strength. Common types of steel bars used in prefabricated slabs include:
- Coiled Bars (Cold-drawn Wires): Small-diameter steel bars with increased strength after cold-drawing treatment, suitable for non-primary load-bearing parts or distribution bars.
- Main Bars: Large-diameter deformed steel bars or round steel bars arranged along the length of the prefabricated slabs, bearing the main bending moments and shear forces.
Principles for Arranging Steel Bars:
Steel bars must be arranged according to design requirements in terms of spacing and number of layers, typically with one layer on the top and bottom surfaces of the prefabricated slabs, and additional support bars may be added in the middle depending on the span. In hollow prefabricated slabs, the steel bars bypass the hollow holes to ensure structural continuity.
Differences in Materials for Different Types of Prefabricated Slabs
Prefabricated slabs come in two types: solid and hollow, with material selection varying based on structural requirements:
- Solid Prefabricated Slabs: Filled entirely with concrete, using a large amount of material but offering good overall integrity, suitable for scenarios with small spans or high load requirements.
- Hollow Prefabricated Slabs: Reduce the amount of non-load-bearing concrete by pre-forming circular or square holes, achieving lightweight construction. The hollow part typically accounts for 30%-50% of the cross-section, with material reduction compensated by increased steel bar density or slab thickness to ensure strength.
Impact of Production Process on Materials
The production process of prefabricated slabs directly affects material performance:
- Mold Preparation: Hollow molds are nailed together from wooden planks to ensure dimensional accuracy and surface smoothness.
- Steel Bar Installation: Steel bars are fixed in position according to design drawings to prevent displacement during pouring.
- Concrete Pouring: Concrete is poured in layers and vibrated densely to expel air bubbles and prevent honeycombing.
- Curing and Demolding: Natural or steam curing ensures the development of concrete strength, and surface defects are inspected and repaired after demolding.
By reasonably selecting concrete mix proportions, steel bar specifications, and production processes, prefabricated slabs can achieve a balance between efficient construction and long-term durability.
