by Source: Introduction to Xinzao In recent years, with the strong support of the national and industrial competent departments, prefabricated buildings have achieved rapid development.
Through the preliminary design and planning, the prefabricated prefabricated buildings can integrate the secondary structure, heat preservation, doors and windows, and exterior wall decoration into prefabricated components during the prefabricated assembly design, greatly reducing the on-site construction and secondary operations, 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 currently three types of common quality problems in the production of PC components, which should be paid attention to: 1.
Common structural quality problems: these common quality problems may affect structural safety, which are important quality defects; 2.
Common problems of size deviation: such quality problems may not cause structural defects, but may affect building functions and construction efficiency; 3.
Common quality defects of appearance: these common quality defects 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 projects), these problems will become the main problems.
At the same time, the internal quality problems of components implied by the common defects of appearance quality can not be ignored.
I Common structural quality fault 1.
Insufficient concrete strength – A – Problem description: insufficient strength of PC components out of the pool, insufficient transportation strength or insufficient installation strength, or insufficient final structural strength.
The traditional prefabricated components can be cured at one time under the condition of steam curing with formwork.
The test pieces under the same conditions can not leave the pool until they reach the design strength of more than 100%, and meet the requirements of transportation, installation and use.
However, at present, many component factories have low strength of PC components out of the pool, and the later maintenance measures are not in place.
It is easy to cause missing edges and corners during transportation and installation, and even have internal quality defects in 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, which may lead to potential safety hazards- B – Cause analysis The direct reason is that the concrete curing time is short, the measures are not in place, and the process concrete strength monitoring measures are lacking.
The root cause is that the technical management personnel are not familiar with, attach no importance to and not strict with the concrete quality management in the PC component process- C – Preventive measures For the concrete mix proportion used by PC, make the concrete strength growth curve for quality control reference; When formulating the technical scheme, the reasonable concrete discharge, delivery and installation strength shall be determined in combination with the construction needs; For the concrete produced daily, several groups of test pieces shall be cured under the same conditions every day, and pressure test shall be conducted as required; The concrete shall be well cured at each stage after leaving the pool; For PC components whose concrete strength has not reached the design value, special technical measures shall be taken to ensure quality safety- D-Treatment method For the problem of insufficient concrete strength found in the construction process, continue to strengthen the curing, and use the same condition test block, rebound and other methods to detect the strength, and continue the construction only when the requirements are met; If the final strength fails to meet the design requirements, it shall be submitted to the design institute and the supervising engineer according to the final value to discuss whether the standard can be lowered (concession acceptance).
If it is really unable to meet the structural requirements, the components shall be scrapped and the structure shall be reworked.
2.
Excessive size deviation of reinforcement or structural embedded parts – A – Problem description: The location deviation of PC component reinforcement or structural embedded parts (grouting sleeve, embedded iron, connecting bolt, etc.) is too large (see Figure 1-1), which may affect the appearance and component installation, and may affect the structural stress- B – Collision inspection was not conducted during the detailed design of the cause analysis component; Processing quality of semi-finished reinforcement is unqualified; No deformation proof support is provided during hoisting and temporary storage; Reinforcement and embedded parts are not firmly positioned with tooling; Deformation of reinforcement skeleton and displacement of embedded parts during concrete pouring; The exposed reinforcement and embedded parts are not corrected for the second time before the final setting of concrete; The process inspection is not strict and the technical disclosure is not in place.
-C – Preventive measures In the deepening design stage, BIM technology shall be used to check the collision between the reinforcement of members and between the reinforcement and the reserved holes of embedded parts; High precision machinery is used to process semi-finished steel bars; Considering the position relationship between the reserved reinforcement and the reinforcement of the cast-in-place section in combination with the installation process; The reinforcement must be bound or welded firmly, and the measures for fixing the reinforcement skeleton and embedded parts must be reliable and effective; After concrete pouring, workers shall be specially arranged to reset the embedded parts and reinforcement; Strictly implement the inspection procedure- D – Treatment method The deviation of reinforcement and embedded parts found in the construction process should be rectified in time, and the next process cannot be started until the standard requirements are met; For the deviation of the formed reinforcement and embedded parts, the ones that can be reset shall be reset as far as possible, and the ones that cannot be reset shall be measured, and the design and supervision shall be requested to negotiate whether the standard can be lowered for use (concession acceptance).
If it is really unable to meet the structural requirements, the components shall be scrapped, and the structure shall be reworked.
3 The thickness of the protective layer of the reinforcement is unqualified – A – Problem description: the deviation of the protective layer of the reinforcement in the component is large (too small or too large) (see Figure 1-2), which may not be visible from the appearance, but can be detected by the instrument, and this defect will affect the durability or structural performance of the component- B – Cause analysis: the reinforcement framework is qualified but the component size is out of tolerance; Poor forming quality of semi-finished reinforcement or skeleton; The size of formwork does not meet the requirements; The cushion block of protective layer thickness is unqualified (wrong size or soft); During concrete pouring, the reinforcement skeleton is trampled; The technical disclosure is not in place; The quality inspection is not in place..
