Concrete hole phenomenon
Cause analysis of 1
Holes are easy to appear near the dense parts of steel bars and embedded parts. Due to the blockage of the coagulation inlet and outlet channels, the holes cannot be filled in time. Concrete segregation, mortar separation and slurry leakage lead to holes; Concrete blanking is too thick, vibrating is not in place, forming holes; Impurities in concrete hinder concrete pouring and form holes.
2 control measures
Where the reinforcement is dense and the structure is complex, fine stone concrete should be used and watered in layers; Reserved holes, bilateral blanking, and open the watering door at the side, vibrating in time; Clean up the sawdust in concrete in time. For the holes that have appeared, the loose concrete and slurry film should be chiseled away, and the fine stone concrete should be repaired after the pressure water is wetted.
Phenomenon of concrete missing edges and falling corners
Cause analysis of 1
The template is not wet enough, resulting in dehydration and shedding; Water absorption expansion crack angle of template; Stick off the edges and corners when removing the form; Dismantling bearing formwork prematurely in low temperature construction; Corners are hit by external heavy objects; Failure to brush the formwork with isolation agent in time or missing brush may lead to the lack of edges and corners in concrete.
2 treatment measures
Fully wet the template and water it in time for maintenance; When the concrete strength reaches above 1.2n/mm2, dismantle the non-bearing formwork; Avoid contact and collision with edges and corners during lifting and formwork removal; When dismantling the formwork, the external corners can be wrapped in straw bags to avoid damage. For missing edges and corners, after chipping loose particles, fully wet them with water, and trim them with cement mortar of 1: 2 or 1: 2.5 according to the damage degree.
Uneven concrete surface
Cause analysis of 1
The shovel simply leveled the surface without leveling and calendering with a trowel; The formwork support foundation is too soft, the support surface is insufficient, the support is loose, and the formwork sinks unevenly when pouring; If concrete does not reach the required strength, people will transport materials or handle it.
2 treatment measures
After concrete pouring, leveling and calendering with trowel, water conservation after final setting; All exposed formwork shall be made of steel formwork with a thickness greater than 5mm, and the thickness of pier formwork panel shall be greater than or equal to 8 mm.. 16m. The internal formwork of T-beam wing plate and precast hollow slab shall be made of integral steel formwork. Support the formwork on the basis of sufficient rigidity, strength, stability and supporting area to prevent it from sinking during pouring; After pouring concrete, check it in time to ensure the specified strength, and then walk, operate and transport materials.
The strength of concrete is not enough and the uniformity is poor.
Cause analysis of 1
Cement is out of date, wet, and its activity is reduced; The gradation of sand and gravel is unreasonable, including impurities, etc. Improper or inaccurate use and dosage of additives will affect the strength of concrete; Improper mixing ratio and random water addition lead to excessive water-cement ratio and reduce concrete strength; Reversing the feeding order, too short mixing time and uneven mixing all affect the strength of concrete; Winter construction, premature freezing or premature formwork removal, insufficient vibration of test blocks and inadequate curing conditions will all affect the strength and uniformity of concrete.
2 treatment measures
Ensure that the cement used is qualified before leaving the factory without caking, and the expired cement will never be used; Ensure the specification requirements such as gravel particle size and gradation, scientifically control the mixture ratio, achieve accurate measurement and calculation, and carry out mixing according to the operating procedures to ensure sufficient mixing time and uniform mixing. Prestressed beams and slabs shall be cured by formwork steam 12 hours or more, with steam curing lasting for 3 days, and then cured by moisture for at least 3 days. If the concrete strength is low, nondestructive methods such as ultrasonic wave and receiver are used to measure the actual strength. If it does not meet the requirements, after checking the structural safety according to the actual strength, the treatment scheme and measures shall be formulated to remedy it.
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