Concrete strength drilling sampling method is a micro-damage detection method, which directly drills core samples from components to test compressive strength. Because the value measured by core drilling method is the compressive strength of cylindrical core sample, there is no need to convert some physical quantities to be measured between it and the compressive strength of standard cubic test block, which is generally considered by experts at home and abroad as a reliable method to evaluate the strength of existing structural concrete and visually inspect the internal situation.
1 Selection conditions of core drilling methods
Generally speaking, the core drilling method is not the first choice to test the strength of concrete, and it is only used when the rebound method is not applicable or there is doubt about other nondestructive testing data. With the development of science and technology, people have higher and higher requirements for the quality and detection accuracy of construction projects. At this time, it is more appropriate to choose the way of core drilling. And now high-strength concrete has been more and more widely used in construction projects, which makes the position of core drilling method more prominent. At present, core drilling method has become an important method to evaluate the strength of concrete. When choosing to use the core drilling method to detect the strength of concrete, there is a certain scope of application. When the following situations occur, it is generally reasonable to choose the core drilling method: First, when the test results of the compressive strength of the test block are abnormal, or the test results are in doubt, or the data obtained from other nondestructive strength tests are in doubt, the core drilling method is adopted; Secondly, if the tested building has been used for many years and has a certain history, then if the strength of concrete in the structure needs to be tested, the core drilling method is adopted; Thirdly, when the concrete is not stored under normal climatic conditions, but suffers from fire, frostbite, chemical erosion or other damage, the core drilling method is adopted; Fourthly, quality problems caused by some related factors, such as improper materials, construction or maintenance, can also be detected by core drilling method.
Core drilling method is not omnipotent, it has its own limitations. In the process of using drilling core method, the selection of drilling core position and the determination of the number will be limited to varying degrees. In the process of operation, concrete members will be damaged to a certain extent, the operation is complicated and the cost will increase. Therefore, it is generally unnecessary, and this method will not be widely used in engineering testing.
2. Selection of site drilling position
The selection of drilling core position is very important, because concrete members are the supporting structure of the whole building project. If the core reaches the key position, it will affect the whole concrete member, and the consequences will be unimaginable. Therefore, as professional technicians of engineering inspection and appraisal, they need to have enough professional knowledge and have a basic understanding of the basic principles of structural design and construction of building engineering. When selecting the position of drilling core, it is also based on a full understanding of concrete members.
First, in practical engineering, there are many types of concrete structures or frames, and the positions of drilling and coring are also different. If it is the same type of structure or component with the same grade, concrete strength grade and pouring date, when selecting core drilling parts, some parts with non-main bearing capacity or some components with less stress should be selected as core drilling samples. For example, some members with small span or height are more suitable as core samples.
Secondly, each concrete member has a concrete beam. Anyone who knows something about mechanics knows that the stress mode of a beam is cosine wave. Through the stress analysis of the middle section of the beam, we can know that the upper part of the section is compressed and the lower part is tensile. After analyzing the shear force of the beam, it will be found that in the span range of 13- 14, the shear force at both ends of the beam is large, and the upper part of the beam is compressed, and there are often shear-bent steel bars in this part. When selecting the drilling core position, it should be at both ends of the beam and the span position of 13- 14 in the middle and lower part of the beam.
Thirdly, when selecting the drilling core position on the concrete column, the drilling core position can be selected on the concrete column, regardless of axial force or eccentric force. Columns, that is, vertical and horizontal intersections, are poured from bottom to top during concrete construction. When the vibration is completed, more stones will be piled up in the lower part of the column and less stones will be piled up in the upper part of the column due to the action of gravity. So the strength of the lower part of the column will be higher than that of the upper part. Some concrete columns are eccentrically compressed columns. For these columns, we can know that the minimum bending moment is roughly in the middle of the column by calculation. Therefore, when selecting the core drilling part on the concrete column, the middle part of the column is often selected, which has scientific basis. As the core drilling point, the middle part of the column can not only represent the actual quality of the column concrete, but also minimize the damage of the column.
3 Problems and solutions in drilling core detection
The core drilling method will be the mainstream method to detect the strength of concrete in future construction projects. Therefore, it is particularly necessary to solve the problems encountered in core drilling test now, which will lay the foundation for better application of core drilling method in the future. In the actual detection process, the drill pipe is running at high speed, which will cause strong friction and jitter of concrete. The result is that the core drilling rig becomes loose slowly, and the faster the friction jitter becomes, the faster it becomes loose. Gradually, the drilling barrel is not perpendicular to the structural plane. There are many problems in the core samples produced by this core drilling machine, such as cracks, missing corners, missing edges, dislocation, inclination, bell mouth deformation, and the verticality between the end face and the axis is more than 2 degrees. These defects are all possible. Sometimes even the Kouga of the drill bit is broken.
These problems all exist in the core drilling method. Defective core samples also greatly affect the test results, resulting in a large deviation between the test strength and the actual strength of concrete. After such test results come out, it will inevitably affect the inspectors' correct evaluation of the construction project, and sometimes even misjudge it, leading to very serious consequences. So in order to avoid these problems as much as possible. The core drilling rig must be fixed when working, and the suitable environment should be selected for core drilling. The specific environment around the construction site needs to match the core drilling work, and the strength range of the selected concrete needs to be appropriate. Generally speaking, it is not advisable to drill core on concrete with strength lower than 10MPa, because when the strength is lower than this value, the core drilling machine is difficult to fix, which affects the core drilling quality. Only when the rotation axis of the spindle of the core drilling machine is perpendicular to the concrete surface of the core sample to be drilled can the core drilling work be started.
4 Some problems that can't be ignored
(1) When drilling floor and other components, the obvious pouring surface should be removed after core sampling, and the pouring surface strength is different from that of concrete components; Absolutely avoid drilling core samples at concrete construction joints, that is, the joints where secondary concrete is poured and poured, where concrete is not representative; When drilling the core, the distance between the drilling cylinder wall and the steel bar should be greater than the diameter of the steel bar, so as not to affect the bonding force between the steel bar and concrete or cut off the steel bar; Avoid the location of main reinforcement, embedded parts and pipelines, and try to avoid other steel bars.
(2) Before the test, the geometric dimensions of the core sample must be measured as follows: average diameter, core sample height, verticality, flatness, etc. This is the most easily overlooked in the actual testing process.
(3) The holes left on the structure or component after core drilling shall be repaired in time. Many people think that this will not affect the safety and beauty of the structure, and there is no need to repair it. If it is not repaired, the protective layer of steel bars around the hole is not enough and it is easy to rust.
5 abstract
In actual construction projects, there are many methods to detect the strength of concrete, and the core drilling method is only one of them. However, with the development trend of construction engineering, the requirements for the construction engineering itself are getting higher and higher, and the requirements for the strength of concrete are also getting higher and higher. Under this trend, the application of core drilling method in future construction projects will be more and more. This paper puts forward its own views on the selection conditions of core drilling methods, the selection of core drilling locations, the problems that will occur during core drilling and the solutions. The purpose is to attract more people of insight to participate in the discussion and make the concrete strength detection technology more advanced and scientific.
For more information about project/service/procurement bidding, and to improve the winning rate, please click on the bottom of official website Customer Service for free consultation:/#/? source=bdzd