How to Construct Cement Beams for Prefabricated Houses
The construction of cement beams for prefabricated houses requires a systematic process, covering key stages such as design, material preparation, pouring, curing, and inspection. The specific steps are as follows:
1. Design and Planning
Determine the cross-sectional dimensions (such as width and height), reinforcement scheme (steel bar diameter and spacing), and whether to use prestressed technology based on engineering requirements such as house span and load. For example, beams with larger spans may require increased steel bar quantities or prestressing to enhance flexural capacity. Additionally, select wear-resistant, tightly-jointed steel molds or custom molds to ensure dimensional deviations of the formed beam are ≤2mm, minimizing the risk of concrete leakage.
2. Material Preparation and Processing
- Concrete Mix Proportioning: Strictly control the slump (80-120mm) and initial setting time (2-4 hours), with a mixing time of no less than 15 minutes to ensure uniformity. For instance, high-strength concrete can incorporate water-reducing agents to improve flowability.
- Steel Bar Processing: Cut and bend steel bars according to design requirements, and apply anti-rust treatment (such as painting with anti-rust paint). The steel bar strength must be ≥400MPa to ensure compliance with load-bearing standards.
3. Pouring and Shaping
- Mold Assembly: Ensure the mold is securely installed, with seams treated with sealing strips to prevent concrete leakage.
- Layered Pouring: Pour each layer to a thickness of ≤30cm, using an immersion vibrator (frequency 1200-1500rpm) to compact the concrete and avoid honeycombing and pitting. For example, the bottom of the beam requires enhanced vibration to expel air bubbles.
4. Curing and Mold Removal
- Curing Conditions: For natural curing, cover with a moisture-retaining film to maintain humidity ≥90%; for steam curing, control the temperature at 60-80℃ to accelerate strength development. The curing period is generally 7 days to ensure full concrete hydration.
- Mold Removal Requirements: Remove the mold only after the concrete strength reaches 70% of the design value. After mold removal, inspect the surface flatness, repairing any deviations exceeding 2mm.
5. Quality Inspection and Transportation
- Strength Testing: Verify concrete performance through compressive and permeability tests, ensuring compliance with national standards (such as GB 50204).
- Lifting and Transportation: Secure the beam with specialized clamps to prevent localized stress cracking; maintain humidity during transportation to prevent shrinkage cracks. Calculate the center of gravity during lifting and halt operations if wind speeds exceed 6 levels.
Precautions: Add antifreeze agents during winter construction and avoid pouring during high-temperature periods in summer to reduce cracking risks; for prestressed beams, tension after the concrete strength reaches 80% of the design value and control the tensioning sequence to prevent lateral bending.
