1 embedded position deviation and displacement
Embedded box deviation
problem description
The embedded box deflects and sinks.
basic requirement
Technical Specification for Assembled Concrete Structures stipulates that the position deviation of embedded pipes and electric boxes in the plane center line of members is 20mm, and the height difference is 0 ~ 10 mm.
cause analysis
1) The box body is not fixed firmly, and the box body shifts when pouring concrete or vibrating.
2) Concrete vibrating box
control point
1) The box bottom embedded in the upper surface of precast members must be supported.
2) When vibrating concrete, it is forbidden to touch the embedded box and conduit.
2. The surface of prefabricated members is covered with small holes.
Surface pore pit
problem description
The outer surface of precast concrete members is characterized by a large number of pores, large apertures and pits.
cause analysis
1) adopts grease release agent, which leads to the formation of air holes in grease parts after concrete pouring.
2) If the formwork is not cleaned and the release agent is painted, the surface of the formwork is easy to form convex parts, and after the concrete is poured and hardened, it is easy to form pores.
3) concrete vibrating is not dense
control point
1) Use water-based release agent or oil-based release agent instead of grease.
2) Before the release agent is painted, the mold platform must be cleaned, and the springboard is used in the process of steel binding and embedding. It is not allowed to walk on the mold platform coated with release agent.
3) Technical disclosure of concrete vibrating shall be made to the workers, and they shall stand by for one week during the vibrating process.
3 Surface cracks of precast members
surface crack
problem description
External surface cracks of precast concrete members
cause analysis
1) Windows and doors, openings, etc. The design drawings are not provided with stiffeners according to the specification requirements.
2) Before the reinforcement is not hoisted and transported according to the design.
control point
1) doors and windows, holes, etc., and stiffeners shall be set according to the specification requirements.
2) Before hoisting and transportation, the components must be reinforced according to the design requirements, and can be hoisted and transported only after passing the inspection.
4. On-site acceptance and stacking of preset components
The pads are not in a vertical line.
Component stacking is short of cushion blocks.
problem description
Precast members are piled up at random on site, and the upper and lower rows of wood blocks are not in a straight line, which is easy to cause cracks.
Treatment measures
When stacking prefabricated members, the stacking site must be relatively flat first. If the site is uneven, it is necessary to adjust the cushion blocks to ensure that the bottom cushion blocks are on the same plane, and the prefabricated members at the bottom are placed flat and evenly stressed. Second, the stacking number of laminated plates should not exceed 6; Third, there should be no shortage of pads between plates, the vertical pads should be in a straight line, and all pads should meet the requirements of the specification.
5. The design of lifting point position is unreasonable.
There are obvious cracks during hoisting.
It is unreasonable to set up lifting points here.
problem description
In the process of field hoisting, obvious cracks appeared and prefabricated components were damaged.
cause analysis
1) The design of prefabricated components is unreasonable.
2) The design of lifting point is unreasonable.
Treatment measures
1) When designing components, analyze and calculate the position of lifting points to ensure the safety of lifting and reasonable lifting points.
2) Parts with missing hanging points or unreasonable hanging point design shall be returned to the factory for processing.
6 Precast wallboard hoisting deviation
The wall deviates too much from the control line.
The two walls are obviously staggered.
problem description
The deviation of precast wall is serious, which seriously affects the engineering quality.
cause analysis
1) The wall installation was not strictly controlled according to the control line, resulting in deviation after the wall fell.
2) There are some quality problems in the component itself, and the thickness is inconsistent.
Treatment measures
1) wall position correction
2) The construction unit should strengthen on-site construction management to avoid similar problems.
3) Supervision units should strengthen on-site inspection and supervision.
7 Precast component pipeline is omitted, which is inconsistent with the site reservation.
Precast components lack embedded pipes.
The embedded pipeline is seriously deviated.
problem description
It is found that some prefabricated pipes are missing and offset, which leads to problems such as gouging of prefabricated components during site installation, which is easy to damage prefabricated components.
cause analysis
1) The embedded pipe fittings are omitted when the components are processed.
2) Pipeline installation is not carried out according to the drawings.
Treatment measures
Strengthen management, the embedded pipeline must be constructed according to the drawing, and no omission is allowed. Strengthen inspection before pouring concrete.
8 Precast member grouting is not dense
Joint filling of external wall
Poor grouting quality in site
cause analysis
1) The grouting material configuration is unreasonable.
2) corrugated pipe drying
3) The grouting pipeline is not smooth and the seal is not dense, resulting in slurry leakage.
4) The operator was careless and did not fill it up.
preventive measure
1) is prepared in strict accordance with the proportion and feeding order in the instruction, and the mixing method and time are controlled according to the instruction.
2) Before hoisting components, carefully check whether the grouting pipe and flat-fell seam are unobstructed, and sprinkle a small amount of water to wet the grouting pipe half an hour before grouting, but there can be no water.
3) When using the pressure grouting machine, the grouting holes in the components should be filled continuously at one time, and the surface of the grouting holes should be compacted and smoothed before the final set of grouting materials.
4) Ensure that the grouting material is used up within 30 minutes after mixing.
5) Strengthen the training and management of operators and improve the construction quality awareness of manual personnel.
Grouting inspection
Closed in time after grouting is completed.
9 Precast member reinforcement deviation
Rebar deviation
cause analysis
1) The vertical reinforcement is not restricted, and it is fixed before the concrete pouring of the floor slab.
2) The concrete pouring and vibrating of the floor slab make the vertical reinforcement deviate.
preventive measure
1) according to the component number, the steel bar positioning frame is used for limiting, and the steel bar frame is properly supported with scissors to ensure the accurate position of the steel bar.
2) After the completion of concrete pouring, check the center position of the steel dowel of the wall column member reserved at the site according to the layout of the steel dowel and the sideline or control line of the on-site member, and the steel dowel with the deviation of the center position exceeding 10mm shall be appropriately revised according to the drawings.
10 reinforcement connection problem
Threaded connection disconnection
Leave a serious bend.
problem description
There are some problems in steel bar connection at cast-in-place joint, such as loose sleeve joint, lap joint and serious bending of steel bar, which bring hidden dangers to structural safety.
cause analysis
1) When connecting the steel casing, the workers did not operate normally.
2) On-site supervision and management is not in place.
Treatment measures
1) When pouring concrete on the platform, strengthen the protection measures for the reinforced sleeve joint to avoid sundries falling on it.
2) When steel bars are connected, workers should take measures such as cleaning and oiling to ensure that the quality of sleeve connection meets the specification requirements.
3) Management personnel need to strengthen site management, strengthen the inspection of each sleeve joint, the supervisor should do a good job of standing by, and the engineering department should carefully recheck and rectify in time when problems are found.
1 1 Too much sealing mortar.
Thick mortar
problem description
There is too much mortar in horizontal joint of external wall of stairwell, which seriously affects grouting quality.
cause analysis
1) No notch is reserved for the prefabricated member at the lower part of this part, and the horizontal clearance is too large.
2) the construction unit management dereliction of duty
Treatment measures
1) Take plugging measures again, and report the treatment plan to the supervisor and the engineering department of Party A for approval before implementation.
2) Require the construction unit to strengthen site management, and it is strictly prohibited to affect the grouting quality due to too dense mortar.
3) Improve the relevant technical specifications of NPC, and clearly specify the thickness and volume ratio of dense mortar, so as to facilitate the on-site inspection and acceptance according to the specifications.
12 The main reinforcement is not in the stirrup.
The main reinforcement is not in the stirrup.
problem description
The main reinforcement of the wall at the joint is not in the stirrup, which brings hidden dangers to the structural safety.
cause analysis
1) deviation of main reinforcement
2) The length of stirrup reserved by the prefabrication plant is insufficient.
Treatment measures
1) Take corresponding remedial measures.
2) Strengthen on-site construction management to avoid steel bar deviation.
3) Feedback the information to the processing plant in time, and redesign the stirrup extension length to avoid similar problems from happening again.
13 laminate cracked.
Laminated plate crack
cause analysis
The curing time of the laminate is not enough, and the laminate has not reached the specified strength.
Treatment measures
1) Require the construction unit to replace the qualified composite slab. Considering the site progress, relevant special repair plans can be issued and submitted to the supervisor and Party A for approval before rectification.
2) The construction unit is required to strengthen site management, and the composite slab can only be dismantled and hoisted when it reaches 100% of its strength.
3) Supervision units should strengthen on-site inspection and supervision.
Other common quality problems
In addition to the above-mentioned common quality defects of 13, there are other problems in the assembly site, such as: the elevation is wrong, and it has not been carefully detected (the elevation problem can be seen from the hole); The hoisting is not standardized, and there are potential safety hazards; The garbage is not cleaned up, which affects the grouting quality; The finished product is damaged, and the finished product protection is not done after the component is installed, and the subsequent construction is polluted and damaged. ...
In a word, to ensure the quality of prefabricated buildings, we must start with strengthening the quality management of precast concrete components, improve the design quality of precast components, strengthen the quality control of component manufacturing, stacking, transportation and site construction hoisting, node connection, finished product protection and other links, distinguish the responsible subjects of each link, improve the quality control level of managers in each link and the quality awareness of front-line workers, and achieve "ingenious construction" to promote the healthy development of prefabricated buildings.
I believe that after the above introduction, everyone has a certain understanding of the common quality problems and treatment measures of 13 prefabricated buildings. Welcome to Zhong Da for more information.
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