Ultrasonic rebound comprehensive method This method is based on the relationship between ultrasonic propagation and rebound value and the compressive strength of concrete. It uses the speed of sound and rebound value to conduct a comprehensive analysis to reflect the compressive strength of concrete. strength. The ultrasonic rebound comprehensive method solves to a certain extent the problem of using only one indicator to determine the insufficient strength of concrete. This method corrects the influence of stones and test surfaces from the test results, and the combination of multiple indicators can reflect more comprehensively. The role of various factors related to concrete strength improves the accuracy of detection.
The core drilling method is very different from the first 3 methods. This method uses a special coring machine to directly intercept a cylindrical concrete core sample from the structure being tested, and infers the compressive strength of the concrete through the compressive test strength of the core sample. It is a more intuitive and reliable detection. Concrete strength method, but because it needs to take samples from the structure, there will be some damage to the original structure, so it is a semi-damage method for on-site testing. Ultrasonic pulse method The ultrasonic pulse method is the most common method for detecting concrete problems and operational applications. When there are certain defects or damage in the concrete of the structure, the ultrasonic pulse will produce diffraction and propagate faster than the same type of material without defects. The speed of concrete is smaller and the sound duration is longer; reflection will occur on the defect interface, so the energy is significantly weakened, the amplitude and frequency are significantly lower, and the waveform of the received signal is gentle or even distorted, so that the defects and damage of the concrete can be judged , which can provide a reliable basis for judgment for structural reinforcement and repair in accident handling, reliability appraisal of built buildings and project acceptance.
Detection of the position of steel bars in concrete structures: reliability diagnosis of existing concrete structures and construction quality appraisal of new concrete structures, reliability diagnosis of existing concrete structures and construction quality appraisal of new concrete structures When detecting the location of steel bars and the corrosion of steel bars, it is required to determine the location of the steel bars and the condition of the steel bars. When using the core drilling method to detect the strength of concrete, avoid the steel bars in the taken parts, and the location of the steel bars is also often detected. Electromagnetic induction method detection is suitable for situations where the reinforcement is sparse and the concrete protective layer is not thick. When the steel bars are located on the same plane or at a relatively large distance in different planes, the measured results will be more satisfactory. Detection of steel bar corrosion: If the working environment is harsh, the concrete quality is poor, or other reasons cause different types of cracks in the structure, the steel bars will corrode. The corrosion of steel bars will cause the concrete protective layer to expand and peel off, and the effective area of ??the steel bars will be weakened, etc., which directly affects the load-bearing capacity and service life of the structure. When identifying and testing the reliability of the built structure, the corrosion of steel bars must be carried out. Check for rust. Use the half-cell method to detect the potential difference between the steel bar surface and the probe to determine the possibility and degree of corrosion of the steel bar.
On-site detection method of masonry structure
(1) Indirect measurement method of masonry strength. The indirect measurement method uses special instruments and methods to measure certain items of bricks and mortar. Strength index or a certain physical parameter related to the strength of a material, and thereby identify the strength of masonry. The impact method is based on the principle that the work consumed when an object is broken is proportional to the newly generated surface area during the breaking process, and the formula between the increment of surface area per unit work and the compressive strength established in advance is used to obtain the strength of the brick or mortar sample. strength. Rebound method: The principle of testing the strength of bricks and mortar is the same as the rebound method of testing the strength of concrete, except that a special mortar rebound tester is used. Because there is a certain correlation between the strength and hardness of bricks, the accuracy of this method is High, simple and applicable. Push-out method: The specific name is the single-brick single-shear method, which is to remove the mortar on the top surface and both sides of a single brick, leaving only the bottom surface, and use a special jack to "pull out" it. Under the limit state, measure the The shear strength of the bond between bricks and mortar is obtained, and the compressive strength is calculated based on the relationship between shear strength and compressive strength.
(2) Sampling testing method for direct measurement of masonry strength: including coring method and cutting method. The cutting method has large specimen size and large disturbance during transportation, resulting in low accuracy of test results, and It consumes a lot of material and financial resources. In-situ detection methods: including flat top method, in-situ axial compression method and in-situ shearing method.
The flat roof method uses a flat hydraulic dynamometer installed into the excavated masonry joints to test the strength of the masonry. It perfectly makes up for the shortcomings of the sampling method, but its equipment is complex and the allowable ultimate strain is relatively small. Determining the ultimate strength of masonry is subject to certain limitations.
The in-situ axial compression method is an improvement on the flat roof method. The principle is consistent with the flat roof method. It measures the ultimate compressive strength of masonry and calculates its standard compressive strength. The disadvantage is that the equipment is heavy and difficult to use. convenient. Dynamic measurement synthesis method: vibration inversion theory. Under the action of excitation modes such as pulsation, vibration of the vibration machine, free release or impact, by detecting parameters such as frequency and vibration shape of the masonry structure, the interlayer stiffness is obtained according to the theory of system identification, thereby deducing each The axial compressive strength of layer masonry. This method starts from the whole house. It can not only obtain the strength of the masonry, but also identify the quality of the house. Therefore, it is relatively simple to detect the safety of the house. With the continuous development of detection instrument technology Upgrading, optimizing algorithms, and improving the accuracy of results are promising. Microstructure method: When sound, waves, rays, etc. propagate in the medium, the determination of the microstructure of the material will be different. From this, the strength of the material can be deduced. The accuracy of the stress wave method when measuring low-strength and high-strength mortar masonry is not very high.
Prospects for structural on-site inspection technology
(1) Testing of new parameters and new performance indicators. With the development of materials science, many projects use new materials. With the continuous improvement of building structure design, it is necessary to continuously study the testing methods of these parameter indicators to serve engineering practice. (2) The introduction of new ideas and the innovation and improvement of mathematical models. In the study of building structure inspection methods, new ideas should be introduced, not only macro mechanics but also micro mechanics should be considered to look at the problem in depth and comprehensively. The empirical formulas used in existing detection methods have certain limitations. When establishing a new mathematical model, more attention should be paid to its boundary conditions, the scope of use should be expanded, and the degree of fitting should be improved. (3) Improvement of measuring instruments. With the development and popularization of computers, it has become inevitable to improve measuring instruments. The miniaturization and intelligence of measuring instruments have continuously improved the testing accuracy to meet the needs of on-site testing. (4) Improvement of operating methods. The operating methods of structural testing instruments should become increasingly simplified, making them more suitable for quality testing of large-area construction projects.
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