Improper feeding method is likely to cause the cushion block between the reinforcement and the formwork to be out of position.
2.
The function of reinforced concrete protective layer mainly has two points: first, ensure the good bonding between stressed reinforcement and concrete, make the reinforcement and concrete bear the force together, and improve the service performance of reinforced concrete structure; The second is to protect the concrete stressed reinforcement of the protective layer from the corrosion of the external environment, ensure that the service performance of the structure is not damaged and prolong the service life of the structure.
Improper insertion position of vibrating rod is easy, Cause displacement of reinforcement.
Therefore, in the process of concrete pouring, the thickness of zaowei protective layer is unqualified due to the impact or vibration of concrete unloading.
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2.2.1 reasons for reinforcement processing and installation: the thickness of protective layer is reflected as the distance between reinforcement and formwork during construction.
Under the condition that other influencing factors remain unchanged, the larger the die and what size will lead to the greater the thickness of the protective layer, and vice versa.
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Generally, the beam and slab reinforcement is hoisted after being processed on the reinforcement formwork.
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During lifting, the hooks shall be lifted and placed gently to avoid deformation of the reinforcement mesh and affecting the thickness of the protective layer.
When the geometric size of the formwork is certain, the larger the reinforcement size of the pier column skeleton, the smaller the thickness of the corresponding protective layer, and vice versa.
2.2.4 deformation caused by external force and not corrected in time after installation; The reinforcement framework is not firmly fixed as a whole, resulting in displacement during concrete pouring; The fine diameter reinforcement is deformed due to human trampling or equipment collision during installation and concrete pouring.
Pier column reinforcement processing and installation The pier column reinforcement is generally designed to bear vertical force.
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The author found at the reinforcement processing and installation site that for the overall stiffness of the reinforcement cage, the consolidation of the main reinforcement and spiral stirrup is particularly important.
When the main reinforcement is bent, the bending starting point is not well controlled and the bending position is not accurately controlled, resulting in the unqualified size of the main reinforcement skeleton and the small skeleton, then the protective layer is too thick; If the skeleton is too large, the protective layer of main reinforcement is insufficient.
Therefore, the key to control the geometric size of pier column reinforcement cage is to control the geometric size of circumferential skeleton reinforcement.
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During the installation of reinforcement, it can be fixed only when all main reinforcement falls in the ring formed by ink line, and the installation of reinforcement is completed.
The construction process of pier column with deviation during reinforcement installation is relatively simple.
The overall stiffness of the reinforcement skeleton is realized by strengthening the welding of the main reinforcement and the annular skeleton reinforcement and the fixation of the main reinforcement and the external spiral stirrup.
Assuming that the plane position and geometric dimension of the reinforcement are strictly consistent with the design, the maximum geometric dimension error of the formwork shall not exceed 5mm.
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When the bearing platform and tie beam are large, the reinforcement cage is heavy, the influence of personnel and concrete on the reinforcement framework during concrete pouring causes the reinforcement framework to sink or deform, and the strength of ordinary mortar cushion block is insufficient, resulting in the decrease of the protective layer at the bottom of the bearing platform and the decrease of the protective layer at the top.
Most of them are to process and install reinforcement first, use shaped steel formwork to control the geometric size of pier column, pour concrete and vibrate it tightly, and adopt appropriate curing measures according to the environment.
What is the protective layer? There are two types of reinforcement protective layers: protective layer and net protective layer.
Therefore, the geometric size of pier column reinforcement framework directly affects the thickness of protective layer of pier column after forming.
3.
The so-called reinforcement protective layer is the concrete from the outer edge of the stressed reinforcement to the surface of the component in the structural concrete; The concrete between the outer edge of reinforcement framework stirrup, horizontal reinforcement and spiral reinforcement and the component surface.
The main reinforcement is welded and fixed to the circumferential skeleton reinforcement according to a certain spacing, and the spiral stirrup is coiled outside the main reinforcement according to a certain spacing.
2.2.5 concrete pouring the concrete pouring process directly affects the adjusted and reinforced reinforcement and formwork.
During the fabrication of reinforcement framework, the size shall be strictly controlled.
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All binding wire heads for binding reinforcement shall be bent inward to prevent intrusion into the protective layer, so as not to affect the thickness of the protective layer.
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Reasons for unqualified thickness of protective layer 2.1 inaccurate fabrication and installation of reinforcement It is mainly the bearing platform, tie beam, bent cap and other parts.
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Otherwise, the plane position protective layer of the pier column cannot meet the standard requirements at the same time, In this case, the thickness of the protective layer is generally sacrificed to ensure the accuracy of the plane position, which is also a common problem at present.
After the reinforcement mesh formwork, organize personnel to inspect the reinforcement framework and timely adjust the deformed reinforcement framework or adjust the position of mortar cushion block..
2.2.
During the blanking of reinforcement, the bending position shall be accurately controlled.
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It is suggested to adopt spot welding or wire quincunx fixation at the intersection of the main reinforcement and spiral stirrup, that is, at intervals of – intersection points.
Secondly, due to the strict requirements for the plane position of the pier column, jtgf80-2004 standard for quality acceptance and evaluation of highway engineering stipulates that the axis deviation of the pier column is 10mm and the thickness of the pier column protective layer is ± 5mm, which means that the installation position of the pier column reinforcement must be controlled within ± 5mm of the design position.
During lifting, the steel wire rope shall be hung on the lifting frame first, 2-3 hooks shall be set on the lifting frame every 2m, and the hooks shall be hung vertically on the reinforcement mesh.
Protective layer thickness pre control measures 3.1.
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If the reasonable error of the plane position and geometric dimension of the reinforcement is considered, the accuracy required for formwork processing will be higher.
In the construction process, cushion blocks are often placed less or even not placed in order to save trouble or trouble, or the position of binding cushion blocks is inaccurate and the binding is not firm.
High strength mortar cushion block is mainly used for control.
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The position of high-strength mortar cushion block is changed due to collision during hoisting, or the reinforcement mesh is deformed during hoisting and is not corrected in time after installation, resulting in unqualified thickness of protective layer.
The center point shall be determined for the installation and positioning of reinforcement, and marked with ink line on the site according to the design radius of ± 5mm in the drawing.
In the hoisting process, the steel wire rope is directly hung on the reinforcement mesh, which is subject to uneven stress and easy to deform; In order to solve this problem, the project department shall make a special lifting frame for reinforcement with round steel pipe before beam and slab construction.
2.2.2 reasons for shaped steel formwork the geometric dimension of shaped formwork directly determines the geometric dimension of pier column after forming, and the geometric dimension of pier column and the geometric dimension and plane position of reinforcement framework jointly determine the protective layer.
In addition, the spiral stirrup shall be straightened before use, and bent into a similar annular radius on the circular members with similar radius for standby, so as to ensure that the spiral stirrup is closely attached to the main reinforcement.
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The quantity and construction quality of cushion blocks play a decisive role in the formed concrete protective layer.
2.2.3 reasons for cushion block of protective layer reinforcement protection is mixed.
Improper way of vibrating personnel up and down is likely to cause the overall shaking of the reinforcement and lead to position deviation.
