Prefabricated Mezzanine Process for Duplex Houses

If the prefabricated mezzanine in duplex houses adopts the cast-in-place concrete process, the following steps should be followed for standardized construction to ensure structural safety and durability:

1. Formwork Setup and Foundation Treatment
First, mark and position according to the design height, with errors controlled within millimeters. Use bamboo plywood as horizontal formwork and secure it to ensure formwork flatness. Then, remove the wall plaster down to the original concrete layer and thoroughly clean the surface dust. This step directly affects the depth of rebar embedding and the bond strength between rebar and the wall. If there are cracks or loose areas in the wall, repair and reinforce them in advance.

2. Rebar Embedding and Steel Framework Installation

• Drilling: Drill holes in the wall to a depth of 12-15 cm (15 cm for exterior walls), with a hole diameter 2-4 mm larger than the rebar diameter. Clean the dust inside the holes with a high-pressure air gun.
• Adhesive Injection: Use epoxy resin-based adhesive for rebar embedding. Inject enough adhesive to fill more than two-thirds of the hole depth, ensuring full coverage of the rebar after insertion.
• Rebar Layout: Use Φ12 Grade III deformed steel bars as main rebars, woven into a mesh in two layers with a spacing of 15-20 cm. Tie the rebar intersections with stainless steel wire. Secure the perimeter with galvanized angle steel pre-installed on the original wall to enhance overall stability. If the mezzanine area exceeds 20㎡, add 16-18 gauge rebar beams and secure them with rebar loops.

3. Concrete Pouring and Vibration

• Material Mix: Use C30 concrete with a cement grade of 425, with a mix ratio of cement:sand:gravel = 1:2:3, and a water-cement ratio controlled below 0.5.
• Pouring Process: Pour in layers, with each layer not exceeding 30 cm in thickness. Use an immersion vibrator to vibrate until the surface bleeds and no bubbles are emitted. The vibrator should be inserted quickly and withdrawn slowly to avoid touching the rebar framework. After pouring, level the surface with a screed board and finish it smoothly.

4. Curing and Formwork Removal

• Curing Conditions: When the indoor temperature is ≥20℃, water the surface 3-4 times a day to keep it moist; when the temperature is <15℃, water it every two days. The curing period should be no less than 14 days, and it is recommended to extend it to 15 days in spring.
• Formwork Removal Timing: After the curing period, the concrete strength should reach at least 75% of the design value before removing the formwork. After formwork removal, continue to cover and moisturize the surface until 28 days. Scaffolding at large-span load-bearing areas should be retained until 28 days.

Special Case Handling: If the house has a reserved cast-in-place floor structure, connect the newly added rebar with the original reserved rebar through overlapping, tying, or welding, and pour with C25 fine aggregate concrete. If there is no reserved structure, use I-beam or other steel framework beams for load-bearing. The steel structure should be corrosion-resistant and meet load calculation requirements.