Compaction requirements for concrete

Layering during concrete pouring process. Appropriate changes can be made based on the weather conditions at that time, generally not exceeding 30cm.

When using an immersion vibrator to vibrate concrete, the movement distance should not exceed 3.75 times its vibration radius, that is, the movement distance of 75 vibrators should not exceed 3.75 times x 7.5=28cm, and the movement distance of 50 vibrators should not exceed 3.75 times x 5.0=18cm; When vibrating concrete near the side formwork, the distance between the vibrator and the side formwork should be controlled between 5 cm-10cm (not more than 10cm).

The vibration depth of a plug-in vibrator generally does not exceed 2/3 to 3/4 times the length of the vibrator. For the space between two floors, the lower layer of concrete should be inserted between 5cm-10cm. At the same time, the vibrator shall not collide with the formwork, tie rods, steel bars, or embedded parts during the vibration operation. After each vibration is completed, the vibrator should be slowly removed during vibration.

The vibration time of the plug-in vibrator at each vibration position should not be too short or too long. Concrete that is too short will not be compacted by vibration, while concrete that is too long will segregate. The general vibration time is 20-30 seconds, with a minimum of 10 seconds. Each vibration part must be vibrated until the concrete in that part is compacted.

The sign of compactness is that the concrete stops sinking, no more bubbles appear, the surface is flat, and there is a lack of grout. Since the vibration time of each steel bar varies according to the slump of the concrete, the vibration time of each steel bar is not used as a standard to evaluate whether the vibration is dense.

The slump of the pile foundation concrete is 7-9 cm. Due to the addition of water reducing agents, the mixing time is 2.5 minutes. Due to the use of mixing trucks to transport concrete, the mixing time can be appropriately shortened by 1.5-2 minutes. Admixtures should be mixed into an appropriate solution before addition.

When concrete tilts from a height into the formwork, in order to prevent concrete segregation, methods such as string pipes, sliding pipes, and chutes should be used to fall, and the free fall height should not exceed 2 meters; When the inclination exceeds 10m, a deceleration device should be installed.

What are the hazards of not compacting concrete?

If not compacted, the interior of the concrete will not be dense and the density will be too low, which will affect the strength of the concrete.

2. There may be surface cracks and poor adhesion between the slurry and aggregates.

3. Secondary vibration method with honeycomb pits on the surface

(1) Choosing the appropriate secondary vibration time is the key to achieving the expected results of concrete secondary vibration. The key is to determine a reasonable vibration time. If the time interval from the first vibration is too short, the effect is not significant; If the time interval is too long, especially after the initial setting of concrete, exceeding the reshaping time range, it will damage the concrete structure and affect the quality of concrete.

Practice has shown that the secondary vibration time of concrete should be around 1-4 hours before the initial setting of concrete, especially 1 hour before the initial setting of concrete. When determining the initial setting time of concrete, considering that it is not possible to install a concrete penetration resistance meter on general construction sites, the laboratory can be required to measure the slump of the concrete while measuring the setting time of the concrete. The initial setting time of the concrete can be indirectly determined through the slump value.

(2) Choose different vibration modes based on different structures.

1) For T-shaped and I-shaped precast beams, internal vibrators can be used at a spacing of 20cm between web plates, and attached planar vibrators can be used for wing plates.

2) Prefabricated panels with a thickness less than 20 centimeters can be vibrated using attached vibrators, while those with a thickness greater than 20 centimeters can be vibrated using inserted vibrators.

3) When pouring beams and slabs integrated with columns and walls, stop for 1 hour after pouring the columns and walls to achieve initial settlement, and then continue pouring. The second vibration is carried out using an insertion type vibrator at the top of the column and the top of the wall. The beam and slab parts are respectively vibrated using an insertion type vibrator and an attachment type vibrator.

Concrete vibration compaction treatment plan

1. Treatment of concrete compaction failure: Remove loose concrete and weak mortar around the hole, rinse with pressure water, support the formwork with support box, sprinkle water thoroughly to moisten, and then pour and compact with C35 fine stone concrete with 8% expansion agent.

2. Concrete surface treatment: Remove floating stones and check whether the chiseled concrete surface is dense and whether there are obvious gaps. If there are gaps, chisel them out, rinse them with water, and then apply a layer of cement slurry at the interface between the new and old concrete to better strengthen the bonding between the new and old concrete surfaces.

3. Template support: It depends on the depth of the steel bar surface. When the depth of the steel bar surface is less than 5 cm and the shape of the steel bar surface is larger on the outside and smaller on the inside, or only the surface outside the main reinforcement has a rough surface, template support is not required. When the depth of the steel reinforcement exceeds 5cm and the inner and outer widths are the same, it is difficult to ensure its compactness without a template. Therefore, it is necessary to support the template and open a hole at the top with a width of no less than 5cm to ensure smooth concrete flow and facilitate the insertion of the vibrator.

4. Concrete pouring: The 4-axis cross B-axis frame columns and 6-axis cross B-axis frame columns of the dry cabin have a designed strength of C30 according to the drawings, and are reinforced with C35 micro expansion. The concrete is compacted by vibration. When the depth is less than 5cm, C35 fine aggregate concrete mixed with 8% expansion agent is used for reinforcement; When the depth is greater than 5cm, C35 fine aggregate concrete mixed with 8% expansion agent is used for reinforcement; When the surface is only pitted and there is no exposed reinforcement, cement mortar with a ratio of 1:2.5 and 8% expansion agent is used for reinforcement. Due to the depth of the above parts not less than 5cm, C35 fine aggregate concrete mixed with 8% expansion agent was used for reinforcement. In some cases, due to premature demoulding, 1:2.5 cement mortar mixed with 8% expansion agent was used for reinforcement.

5. Curing: After the surface strength reaches 12 hours, spray water on the area for at least 5 days of curing