Discussion on causes and prevention of concrete cracks in Bridges（2）
Crack prevention measures
1. Design anti-crack control measures: avoid the occurrence of load cracks, and try to avoid sudden changes in mechanism or section;If the sudden change of structure is inevitable, the details should be well handled, such as the corner to make a round corner, the sudden change to make a gradual transition, at the same time to strengthen the reinforcement of the structure, in order to improve the crack resistance of concrete.In order to prevent the cracks caused by steel corrosion, the width of cracks should be controlled strictly according to the requirements of the code, and enough protective layer and anti-corrosion concrete should be used in the design.
2. Construction crack control measures:①.Rebar in the processing plant after centralized refueling molding transported to the site for installation, installation strictly grasp the spacing of rebar.The specification, model, quantity, spacing, geometric size, connection position and quality of the reinforcement shall meet the requirements of the design drawing and construction specifications.Concrete blocks shall be arranged between the outer layer of reinforcement and the formwork.
②. For the installation and removal of formwork, the capacity, stiffness and stability of formwork and its support should be checked according to specific projects, and the old use should not be blindly copied according to experience and similar projects.When the formwork is installed, the structure should be compact, no leakage of slurry, no seepage of water, and the shape should be regular to ensure the uniformity of concrete.The removal sequence of the formwork and its support shall be in accordance with the construction technical plan.
③. For concrete pouring, the formwork and support, steel reinforcement and its protective layer thickness, embedded parts, reserved holes, etc. shall be checked before pouring, and the pouring shall be carried out after confirmation of correctness.The mixing and transportation of concrete must meet the requirements of continuous casting.The movement and deformation of steel bar, formwork, positioning bar, cushion block and embedded pipe should be prevented in pouring.
④. The vibration should be compacted to ensure that the concrete can be filled into all corners, while avoiding plastic cracks and dry shrinkage cracks caused by excessive vibration.
⑤. Other measures: the influence of construction sequence on internal force is considered in the design of bridge structure. The construction shall be carried out in strict accordance with the formulated plan, and the construction sequence shall not be changed at will, so as to avoid causing unnecessary additional stress and causing structural cracking.
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