Currently, foamed concrete is applied in various fields such as foundation pit filling, highway subgrade, treating the phenomenon of bridge abutment jump, tunnel filling, platform ground, ancient building protection and restoration, special structure shaping, and backfilling of mined-out areas. It is favored for its light weight, higher strength compared to common backfill materials, its fluid and plastic nature during construction for ease of application, and its strong self-supporting ability, high durability, sound insulation, vibration reduction, and fast construction speed. Its widespread use in foundation pit filling, highway subgrade, treating bridge abutment jump, and special structure shaping has yielded excellent results, making it one of the primary materials of choice in the backfilling field.

Common Filling Operations:

Pre-job inspection

Prior to pouring foam concrete, proper waterproofing and drainage measures should be taken on the base. After the excavation of the pit is completed, a drainage outlet no wider than 1 meter should be dug at a lower point to prevent water accumulation in the pit.

(2) Clear the construction area's foundation pit of any water and debris, ensuring that there are no obstructions or water during the pouring process. Prepare the subgrade for cleanliness, free from oil stains, float, and residue.

(3) For projects requiring template assistance, all template works must be completed and approved prior to construction.

(4) Ensure proper concealed acceptance procedures at the operational level.

(5) Prior to construction, the ±50cm horizontal control line should be reviewed. During construction, it is not permitted for workers from other trades to interleave and perform work.

(6) Survey and Line Layout: According to the construction drawing, level lines ±50cm should be marked on the perimeter structure, as well as the specified thickness for the design. Measure out the horizontal levels of each layer and mark them on the surrounding perimeter structure. Also, mark the construction area for foam concrete on the subgrade.

2. Foam concrete pouring

The production process of foamed concrete includes foam preparation, foamed concrete mixture preparation, casting and shaping, curing, and inspection.

(2) Foam concrete must be layered and poured at a specific thickness. The upper layer can be filled once the lower layer has reached final setting. The layer thickness is generally controlled between 30-100cm. Too thin a layer hinders the integrity of the single layer of foam concrete, while too thick a layer can cause bubble compression in the lower foam concrete, affecting its density and complicating construction operations. During pouring, attention should be given to the temperature and diurnal temperature variations, and the thickness of each layer should be reasonably arranged to avoid excessive accumulation of hydration heat, which may lead to temperature cracks and impact the performance of foam concrete. It is advisable to pour a layer every 10-14 hours for foam concrete filling, and appropriately control the vertical filling speed.

(3) When the filling area is large and the entire layer cannot be filled before the initial setting of the foam concrete, it must be divided into sections. The size of the section should primarily refer to the location of the settlement joints, and be determined based on the initial setting time of the foam concrete, the equipment's feeding capacity, and the layer thickness (it is advisable to divide longitudinal filling sections into 5-15m, and sections for horizontal pouring wider than 15m should also be divided).

3. Install steel wire mesh. To enhance the overall integrity of foam concrete, it is generally advisable to lay steel wire mesh during the filling process.

Mesh wire sheets with a hole size of (5~10) cm x (5~10) cm, wire diameter not less than 3mm.

Prior to installation, inspect the appearance of the wire mesh. Do not use wire mesh with visible rust.

(3) Adjacent rolls of wire mesh should overlap by 5~10cm, with the overlapping sections connected and secured using wire ties or U-shaped clips. The distance between adjacent mesh sheets should not exceed 10mm in length.

At the expansion joint locations, the steel wire mesh has been disconnected and laid.

After pouring 1 to 2 layers (at 50 to 100 cm above the base) of foam concrete, lay a layer of steel mesh.

(6) A layer of wire mesh is laid at the junctions of foam concrete of different densities, below the ceiling by 80 cm.