by Source: Even though the connection mode of the prefabricated structure has been greatly optimized at present, the quality hazard of the component connection nodes still exists.
The common connection modes are divided into dry connection (weld connection, bolt connection) and wet connection (sleeve grouting connection, grout anchor lap, concrete joint surface connection).
This paper summarizes the quality inspection methods for sleeve grouting connection, grout anchor lap, joint surface connection, internal defects of joints, and 10 questions about the connection quality and inspection technology of prefabricated concrete structures.
Before the introduction, let’s first learn the teaching video of the sleeve grouting connection of the prefabricated concrete structure reinforcement: embedded detection method embedded sensor method – the grouting plumpness detection technology of the sleeve grouting The vibration attenuation principle is used to detect the grouting plumpness of the prefabricated concrete structure reinforcement sleeve.
The characteristics of the medium around the sensor are directly related to its vibration attenuation law.
In three different media, air, fluid grout and solidified grout, the vibration energy attenuation law is different.
Scope of application: 1) Quality control during construction and monitoring of grouting construction process; 2) It is used for quality inspection of node grouting plumpness in the later stage.
Advantages: 1) For the quality control of the construction process, as long as the slurry outlet is seen, it indicates that it has been filled; The instrument can monitor the leakage of grout before setting.
2) In the later stage, the quality of node grouting is suspected, and the sensor must be embedded.
To ensure random sampling, sensors need to be embedded at each slurry outlet.
Drawing method of embedded steel wire – the grouting plumpness principle of sleeve grouting extends the special steel wire horizontally from the grout outlet of the sleeve to the position of the reinforcement surface near the grout outlet side of the sleeve, and the exhaust hole of the special steel wire with rubber plug is directly above after it is in place.
Judgment of test results: take the average value of the three maximum values of the ultimate pullout load at the same batch of test points, 40% of the average value is recorded as a, and 60% of the average value is recorded as b.
If the data at the test point is higher than b, judge that the corresponding sleeve grouting at the test point is full; If the measured point data is between a and b, other methods need to be further used for supplementary detection; If the data of the measuring point is lower than a or 1.0kN, it can be directly judged that the corresponding sleeve grouting of the measuring point is not full.
Non-destructive testing method – X-ray method – portable X-ray testing of internal defects of grouting sleeve joints: paste the film on one side of the wall, the film can completely cover the tested sleeve, place the portable X-ray detector on the other side of the wall, the radiation source is facing the same tested sleeve, and adjust the distance from the radiation source to the film to be the same as the focal length of the X-ray machine.
Observe the grouting quality of the sleeve through the film imaging camera.
Limited scope of application: the thickness should not be greater than 200mm; Prefabricated shear wall with sleeve single row or “quincunx” arrangement.
Usually, the local damage method is also required for verification.
There is radiation during X-ray detection, and personnel should be in the radiation safety area (30m away from the X-ray machine) 。 Ultrasonic – The ultrasonic testing of the grouting plumpness of sleeve grouting is to determine the defects in the grouting material by measuring the acoustic parameters such as the propagation speed of ultrasonic longitudinal wave in the structural grouting material, the acoustic speed and the frequency of the received signal through the low-frequency ultrasonic instrument.
Impact echo – grouting plumpness impact echo method of sleeve grouting has not been able to effectively detect internal defects so far.
Impact echo – principle of bonding surface and grout-anchor lapping quality: impact echo method is to excite low-frequency impact elastic wave on the concrete surface through mechanical impact, spread to the interior of the structure, and be reflected back by the defect surface or the bottom surface of the component.
The shock elastic wave is reflected back and forth between the structural surface, the internal defect surface or the bottom boundary to generate transient resonance, whose resonance frequency can be identified in the amplitude spectrum and used to determine the depth of the internal defect and the thickness of the component.
Analyze the time-history waveform of the measuring point and compare the typical time-history diagram.
When the dynamic time history response time of the shock elastic wave is significantly longer than that of the area without void, void can be judged.
Comprehensive analysis is based on the thickness-distance map, three-dimensional thickness map and amplitude map.
With the increase of defect depth, the difficulty of defect detection will increase again.
Foreign research shows that if the transverse dimension of the defect exceeds 1/3 of its buried depth, the depth of the defect can be detected; If the transverse dimension is more than 1.5 times of the buried depth, the defect is equivalent to an infinite interface, and the defect location and depth can be identified by the plate thickness parameter.
Array ultrasonic – slurry anchor lapping quality can effectively identify pre-set hole defects and form 3D images, so that the test results can be displayed efficiently and intuitively.
Radar instrument – the radar antenna of the pre-cast round hole plate secondary pouring quality radar instrument transmits radar waves from the concrete surface to the inside.
When there are defects (cavities, honeycomb, etc.) in the concrete, it receives different internal reflected waves of the media, and judges the internal defects of the concrete according to the strength of the reflected waves, return time, and the size of the reflection area.
Local damage detection method – core drilling method – the strength of grouting material is drilled on the representative grouting material structure with a special drill, and the compressive strength is measured after necessary sorting and processing.
The internal conditions of local grouting materials can be observed through core samples, such as aggregate distribution, crack size, etc.
Connection quality and inspection technology of prefabricated concrete structures Q 1.
What are the standards for interfaces? What exactly does “interface” mean? If it refers to the grout inlet and outlet of the grouting sleeve, there is no uniform standard requirement at present, which is usually determined by the manufacturer.
If it is the interface of the L-shape plumpness monitor, it can be universal in most cases.
2.
How to detect the sleeve grouting compactness of the elbow? For the sleeve with non-linear duct at the slurry outlet, the hole can be opened on the sleeve barrel wall, the hole diameter should be controlled below 8mm, and staggered with the sleeve slurry outlet position, not in a plane, to avoid the adverse impact caused by the weakening of the sleeve section.
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