by Source: xinyingzao introduction in recent years, with the strong support of the state and industry competent departments, prefabricated buildings have achieved rapid development.
Through the early design and planning of prefabricated buildings, the secondary structure, thermal insulation, doors and windows, exterior wall decoration, etc.
can be integrated into the prefabricated components in the prefabricated assembly design, greatly reducing the on-site construction and secondary operation, and solving many quality problems of cast-in-situ buildings.
At the same time, due to the rapid development of the industry, few skilled workers, immature industrial supporting facilities and other factors, there are three common quality problems in PC component production, which should be paid attention to: 1.
Common structural quality problems: these common quality problems may affect structural safety and belong to important quality defects; 2.
Common problems of dimensional deviation: such quality problems may not necessarily cause structural defects, but may affect building function and construction efficiency; 3.
Common appearance quality problems: these common quality problems usually have no great impact on structures and buildings, and are secondary quality defects, However, in projects with high appearance requirements (such as fair faced concrete project), such problems will become the main problems.
At the same time, the internal quality problems of components implied by common problems of appearance quality can not be ignored.
I.
common problems of structural quality 1.
Insufficient concrete strength – A – description of PC # components with insufficient exit strength, insufficient transportation strength or installation strength, or insufficient final structural strength.
Traditional precast structures Under the condition of steam curing with formwork, the specimens can be cured at one time.
Under the same conditions, the specimens can not leave the pool until they reach more than 100% of the design strength, and meet the requirements of transportation, installation and use.
However, at present, the strength of # components out of the pool in many component factories is low, and the later maintenance measures are not in place.
It is easy to cause missing edges and corners during transportation and installation, and even internal quality defects of the structure.
Sometimes there are safety problems, because all anchors and embedded parts are considered based on the standard value of concrete design, but insufficient concrete strength during production, transportation and installation may lead to insufficient anchoring force, resulting in potential safety hazards- B-cause analysis the direct cause is that the concrete curing time is short, the measures are not in place, and there is a lack of process concrete strength monitoring measures.
The fundamental reason is that the technical management personnel are not familiar with, pay no attention to and strict with the concrete quality management in the process of {PC} components- C – preventive measures: for the concrete mix proportion used, prepare the concrete strength growth curve for quality control reference; When formulating the technical scheme, the reasonable out of tank, delivery and installation strength of concrete shall be determined in combination with the construction needs; For the daily production of concrete, several groups of specimens cured under the same conditions shall be made every day, and the pressure test shall be carried out as required; Do a good job in the curing of each stage after the concrete comes out of the tank; For # components whose concrete strength has not reached the design value, special technical measures shall be taken to ensure quality and safety- D-treatment method: for the problem of insufficient concrete strength found in the construction process, continue to strengthen the maintenance, and test the strength with the same condition test block, rebound and other methods, and continue the construction only after meeting the requirements; If the final strength fails to meet the design requirements, it shall be submitted to the design institute and the supervising engineer for negotiation according to the final value, Whether the standard can be reduced (accepted under concession).
If it really cannot meet the structural requirements, the components shall be scrapped and the structure shall be reworked.
2.
The dimensional deviation of reinforcement or structural embedded parts is too large – a-problem description pc# the position deviation of component reinforcement or structural embedded parts (grouting sleeve, embedded iron, connecting bolt, etc.) is too large (see Figure 1-1).
It may affect the appearance and component installation, or the stress of the structure.
– B – cause analysis: collision inspection is not carried out during the detailed design of components; the processing quality of semi-finished reinforcement is unqualified; anti deformation support is not made during hoisting and temporary storage; reinforcement and embedded parts are not firmly positioned with tooling; reinforcement framework is deformed and embedded parts are displaced during concrete pouring; The exposed reinforcement and embedded parts are not secondary corrected before the final setting of concrete; The process inspection is not strict and the technical disclosure is not in place.
– C – BIM # technology shall be applied in the detailed design stage of preventive measures to check the collision between component reinforcement and reserved holes between reinforcement and embedded parts; Processing semi-finished steel bars with high-precision machinery; Combined with the installation process, the position relationship between the reserved reinforcement and the reinforcement in the cast-in-situ section shall be considered; Reinforcement binding or welding must be firm, and measures for fixing reinforcement framework and embedded parts shall be reliable and effective; After pouring concrete, special workers shall be arranged to reset the embedded parts and reinforcement; Strictly implement the inspection procedures- D-treatment method the deviation of reinforcement and embedded parts found during construction shall be rectified in time, and the next process cannot be carried out if the standard requirements are not met; For the deviation of formed reinforcement and embedded parts, reset as much as possible if it can be reset.
If it cannot be reset, measure the data and submit it to the designer and supervisor for negotiation, Whether the standard use can be reduced (acceptance under concession).
If it really cannot meet the structural requirements, the members shall be scrapped and the structure shall be reworked.
3.
Unqualified thickness of reinforcement protective layer – a-problem description ￠ large deviation of protective layer of member reinforcement (too small or too large) (see Figure 1-2).
It may not be seen from the appearance, but it can be detected by instruments.
This defect will affect the durability or structural performance of the component.
– b-cause analysis – the reinforcement skeleton is qualified but the component size is out of tolerance; the semi-finished reinforcement or skeleton forming quality is poor; the formwork size does not meet the requirements; the thickness cushion block of the protective layer is unqualified (wrong size or soft); reinforcement framework is trampled during concrete pouring; technical disclosure is not in place; quality inspection is not in place..
