Evaluation method for damage degree of ultra-high performance concrete after high temperature
Through the multi-fractal theory and high-resolution camera shooting method, the problem of large workload, high risk coefficient and insufficient accuracy of the evaluation of concrete damage after fire is solved, and the degree of ultra-high performance concrete damage after high temperature is provided quickly and accurately Evaluation and guidance on building restoration or demolition have filled the technical gap.
Patent Information
- Application Number
- CN202411039794.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-07-31
- Publication Date
- 2024-12-13
AI Technical Summary
The prior art methods for evaluating the degree of concrete damage after fire have problems such as large workload, high risk coefficient and insufficient accuracy, especially lack of effective evaluation methods for evaluating the degree of ultra-high performance concrete after high temperatures.
Using multiple fractal theory, the surface photos of ultra-high performance concrete after high temperature are binarized, and the statistical crack information is traversed by square boxes, and the functions Dq~q are introduced to evaluate the degree of damage and predict the compressive strength value, which avoids a large number of The core extraction step is to obtain crack information using a high-resolution camera or drone shooting.
It realizes the evaluation of the damage degree of ultra-high performance concrete after high temperatures, provides important guidance for building repair or demolition, makes up for the gap in the existing technology, and improves the changes in the surface characteristics of concrete Sensitivity.
Smart Images
Figure CN119131454A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of ultra-high performance concrete, and more specifically, to a method for evaluating the degree of damage of ultra-high performance concrete after high temperature. Background Art
[0002] Fire is one of the biggest hidden dangers affecting the safety of concrete buildings. At the same time, since concrete is non-combustible, it will suffer different degrees of fire damage. At present, many scholars are committed to improving the high temperature resistance of concrete, but ignore the evaluation of the residual performance of existing concrete buildings after fire, which is actually of great guiding significance for the subsequent repair or demolition of concrete buildings.
[0003] At present, the "Standard for the Assessment of Building Structures after Fire" is the most widely used method for assessing the extent of damage to concrete buildings after fire. However, this standard mainly focuses on evaluating the color changes of concrete after a fire to infer the extent of damage. The accuracy of the assessment is affected by human subjective judgment and is therefore poor. Therefore, some scholars have also proposed some applicable evaluation methods. For example, patent CN 109946356 uses electrochemical impedance spectroscopy technology to detect the changes in the internal pore structure of concrete to analyze the degree of concrete damage after high temperature and fire, which has certain feasibility. However, for non-homogeneous materials such as concrete, it usually requires a large number of cores to ensure the credibility of the test results. In addition, for post-disaster concrete components, they are usually heated unevenly, which will greatly increase the number of on-site sampling. On the one hand, it increases the difficulty of detection. On the other hand, a large number of cores may cause the bearing capacity of post-disaster concrete buildings to be unstable, which is dangerous. Patent CN108334686 publishes a method for quickly evaluating the bearing capacity of post-fire concrete components based on fire dynamics simulation software, finite element heat transfer and hierarchical model, which solves the problem that the existing detection and evaluation methods cannot quantitatively give the degree of decline in the bearing capacity of concrete components after fire. However, a large number of empirical parameters are used in its model, and its evaluation accuracy needs to be improved. In short, there are few studies on the identification methods of the degree of concrete damage after fire. The existing research methods have the defects of large workload, high risk factor and insufficient accuracy. In particular, there is no report on the evaluation method of the degree of damage of ultra-high performance concrete after high temperature.
[0004] In view of the above shortcomings, this invention aims to provide a convenient, fast, accurate and safe method for evaluating the degree of damage of ultra-high performance concrete after high temperature. Summary of the invention
[0005] In order to solve the problems of large workload, high risk factor and insufficient accuracy in the current methods for evaluating the degree of damage of concrete after fire, especially the lack of methods for evaluating the degree of damage of ultra-high performance concrete after high temperature, the present application provides a method for evaluating the degree of damage of ultra-high performance concrete after high temperature.
[0006] The present application provides a method for evaluating the degree of damage of ultra-high performance concrete after high temperature using the following technical solution:
[0007] A method for evaluating the degree of damage of ultra-high performance concrete after high temperature, comprising the following steps:
[0008] (1) Use a square box with a side length of δ to traverse and cover the photo of the ultra-high performance concrete after high temperature with a side length of L, and finally obtain N(δ)×N(δ) square boxes with a scale of δ, where: N(δ) = 2 k , k is a real number;
[0009] (2) Calculate the number of pixels containing cracks in the square box of size δ×δ divided in step (1), and then calculate the probability density p of crack information at different scales δ ij (δ);
[0010] (3) Introducing function D q ~q is used to evaluate the surface crack characteristics of ultra-high performance concrete after high temperature, namely:
[0011]
[0012] q=[-10,10] and q≠1
[0013]
[0014] in,
[0015] (4) To determine the degree of damage of ultra-high performance concrete after high temperature, the function D q The range of ~q is defined as the damage value η, as follows:
[0016] When η<0.3, it is judged that the ultra-high performance concrete is not affected by high temperature, and its compressive strength value is predicted to be no less than 100%;
[0017] When 0.3≤η, the ultra-high performance concrete is judged to be damaged.
[0018] Furthermore, when 0.3≤η<0.35, the ultra-high performance concrete is judged to be slightly damaged, and its compressive strength value is predicted to be 85-100%.
[0019] When 0.35≤η<0.4, the ultra-high performance concrete is judged to be moderately damaged after high temperature, and its compressive strength value is predicted to be 70-85%.
[0020] Furthermore, when 0.4≤η<0.45, it is judged that the ultra-high performance concrete is seriously damaged after high temperature, and its compressive strength value is predicted to be 25-70%.
[0021] Furthermore, when 0.45≤η, it is judged that the ultra-high performance concrete is severely damaged after high temperature, and its compressive strength value is predicted to be less than 25%.
[0022] In addition, it should be noted that the compressive strength value refers to the percentage of the strength after high temperature and the strength before high temperature. When the compressive strength value is predicted to be 85-100%, 100% is not included; when the compressive strength value is predicted to be 70-85%, 85% is not included; when the compressive strength value is predicted to be 25-70%, 70% is not included.
[0023] Furthermore, in step (2), the number of grids v containing crack information in the square box at different δ scales is counted. ij , and divide this value by the total number of grids containing crack information at the L scale Where N(δ) is the total number of grids containing crack information at the δ scale, that is, the probability density p ij (δ) is:
[0024] Furthermore, in step (1), k takes the value [0, 10].
[0025] Furthermore, the surface photograph of the ultra-high performance concrete after high temperature obtained in the step (1) is obtained by binarizing the actual photograph.
[0026] Furthermore, the methods for obtaining photos of the surface of ultra-high performance concrete after high temperature include handheld cameras, mobile phones, drone-mounted cameras or mobile phones, and the shooting resolution is not less than 30 million pixels.
[0027] In summary, this application has the following beneficial effects:
[0028] 1. Convenient, fast and highly safe. It avoids the need to conduct a large number of core sampling to determine the degree of damage of ultra-high performance concrete buildings after fire. The degree of damage of ultra-high performance concrete after high temperature can be accurately evaluated by simply taking pictures with a camera to obtain crack information. For high-rise and large-area buildings, drones can also be used for shooting;
[0029] 2. The model is universal and accurate. This evaluation method is based on multi-fractal theory and can describe the surface characteristics of ultra-high performance concrete after high temperature in different levels of detail. Compared with traditional fractal theory, it improves the sensitivity to changes in concrete surface details;
[0030] 3. Filling the gap and providing strong guidance. The evaluation method provided in this application has important guiding significance for the repair or demolition of ultra-high performance concrete buildings after fire, provides a theoretical basis for ensuring the normal service of buildings after fire, and fills the gap in the current evaluation method for the degree of damage of ultra-high performance concrete after high temperature. BRIEF DESCRIPTION OF THE DRAWINGS
[0031] Figure 1 This is a diagram of crack distribution (after binarization) in the embodiment.
[0032] Figure 2 In the embodiment D q ~q function solution graph. DETAILED DESCRIPTION
[0033] The present application is further described in detail below with reference to the accompanying drawings and embodiments.
[0034] Unless otherwise specified, the materials used in the examples of this application can be obtained from commercial sources. The contents of the various components of concrete in the examples are shown in Table 1.
[0035] Table 1 Content of each component of concrete in each embodiment
[0036]
[0037] The “cement” in the embodiment is P·Ⅱ52.5 silicate cement; the “silicon fume” in the embodiment is silicon fume with a silicon content of 92% and a surface area of 16.19 m 2 / g; the "fly ash" in the embodiment is first-class fly ash with a median particle size of 17.8μm; the sand in the embodiment is a continuously graded river sand of 0.075-4.75mm; the polypropylene fiber in the embodiment is 6mm in length and 40μm in diameter; the "water reducer" in the embodiment is a polycarboxylic acid admixture with selective adsorption, and the water reducer model is
[0038] When preparing the materials in the above Examples 1-5, cement, silica fume, fly ash and sand were first mixed in a vertical axis planetary forced mixer for 1 minute, and then water and a water reducing agent were added to the obtained mixture. After stirring for 1 minute, polypropylene fiber was added, and steel fiber was added after continuing to stir for 2 minutes. Finally, the ultra-high performance concrete was obtained by stirring for 3 minutes, and then placed in a standard curing environment for curing for 28 days.
[0039] Example
[0040] This embodiment provides a method for evaluating the degree of damage of ultra-high performance concrete after high temperature, comprising the following steps:
[0041] (1) Obtain a surface photo of the ultra-high performance concrete after high temperature, perform binarization processing, obtain the crack distribution state of the surface, and then use a square box with a side length of δ to traverse and cover the photo with a side length of L in step 1. Among them, the method of obtaining the surface photo of the ultra-high performance concrete after high temperature includes a handheld camera, a mobile phone, a camera mounted on a drone or a mobile phone, and its shooting resolution is not less than 30 million pixels. The embodiment of the present application uses a handheld camera with a shooting resolution of 50 million pixels.
[0042] Use a square box with a side length of δ to traverse and cover the photos with a side length of L in step 1, and finally obtain N(δ)×N(δ) square boxes with a scale of δ, where: N(δ)=2 k , k is a real number. In this embodiment, k is [0, 10];
[0043] (2) Count the number of grids v containing crack information in the square box at different δ scales ij , and divide this value by the total number of grids containing crack information at the L scale Where N(δ) is the total number of grids containing crack information at the δ scale, that is, the probability density p ij (δ) is: Where i is the number of rows and j is the number of columns.
[0044] (3) Introducing function D q ~q is used to evaluate the surface crack characteristics of ultra-high performance concrete after high temperature, namely:
[0045]
[0046] q=[-10,10] and q≠1
[0047]
[0048] in,
[0049] The software used may be Matlab, Python, etc., and in this embodiment, Python is used.
[0050] (4) To determine the degree of damage of ultra-high performance concrete after high temperature, the function D q The range of ~q is defined as the damage value η, as follows:
[0051] When η<0.3, it is judged that the ultra-high performance concrete is not affected by high temperature, and its compressive strength value is predicted to be no less than 100%;
[0052] When 0.3≤η, the ultra-high performance concrete is judged to be damaged.
[0053] Furthermore, when 0.3≤η<0.35, the ultra-high performance concrete is judged to be slightly damaged, and its compressive strength value is predicted to be 85-100%.
[0054] Furthermore, when 0.35≤η<0.4, the ultra-high performance concrete is judged to be moderately damaged after high temperature, and its compressive strength value is predicted to be 70-85%.
[0055] Furthermore, when 0.4≤η<0.45, it is judged that the ultra-high performance concrete is seriously damaged after high temperature, and its compressive strength value is predicted to be 25-70%.
[0056] Furthermore, when 0.45≤η, it is judged that the ultra-high performance concrete is severely damaged after high temperature, and its compressive strength value is predicted to be less than 25%.
[0057] The following is an illustration through specific embodiments.
[0058] Examples 1-5
[0059] First, a high temperature test was conducted on the concrete of Examples 1-5. The specific operation was as follows: First, the ultra-high performance concrete specimens that had been cured were dried by natural ventilation, and a high temperature test was conducted when the moisture content no longer changed; then, a high temperature test was conducted in an electrically heated high temperature furnace, with a heating system of 1°C / min and a heat preservation time of 4h. The high temperature treatment times of Examples 1-5 were 200°C, 400°C, 600°C, 800°C, and 1000°C, respectively.
[0060] The concrete of Examples 1-5 after high temperature treatment was analyzed as described in this application, and the results are as follows:
[0061] Figure 1 Schematic diagram of crack distribution state after being photographed by camera and binarized in each embodiment, Figure 2 Shows the Figure 1 The processing function (D q ~q) results, Table 2 shows the comparison between the evaluation results of each embodiment and the present application. The compressive strength test standard is T / CECS 864-2021, where the measured compressive strength ratio = compressive strength after high temperature / compressive strength before high temperature.
[0062] Table 2 Comparison of results between various embodiments and the present invention
[0063]
[0064] It can be seen from Table 2 that the evaluation prediction results of each embodiment are consistent with the actual results, which shows that the evaluation method for the damage degree of ultra-high performance concrete after high temperature provided by the present invention has high accuracy and good feasibility.
[0065] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.
Claims
1. A method for evaluating the degree of damage of ultra-high performance concrete after high temperature, characterized in that: The following steps are involved: (1) Use a square box with a side length of δ to traverse and cover the photo of the ultra-high performance concrete after high temperature with a side length of L, and finally obtain N(δ)×N(δ) square boxes with a scale of δ, where: N(δ) = 2 k , k is a real number; (2) Calculate the number of pixels containing cracks in the square box of size δ×δ divided in step (1), and then calculate the probability density p of crack information at different scales δ ij (δ); (3) Introducing function D q ~q is used to evaluate the surface crack characteristics of ultra-high performance concrete after high temperature, namely: q=[-10,10] and q≠1 in, (4) To determine the degree of damage of ultra-high performance concrete after high temperature, the function D q The range of ~q is defined as the damage value η, as follows: When η<0.3, it is judged that the ultra-high performance concrete is not affected by high temperature, and its compressive strength value is predicted to be no less than 100%; When 0.3≤η, the ultra-high performance concrete is judged to be damaged.
2. The method for evaluating the degree of damage of ultra-high performance concrete after high temperature according to claim 1, characterized in that: When 0.3≤η<0.35, the ultra-high performance concrete is judged to be slightly damaged, and its compressive strength value is predicted to be 85-100%.
3. The method for evaluating the degree of damage of ultra-high performance concrete after high temperature according to claim 1, characterized in that: When 0.35≤η<0.4, the ultra-high performance concrete is judged to be moderately damaged after high temperature, and its compressive strength value is predicted to be 70-85%.
4. The method for evaluating the degree of damage of ultra-high performance concrete after high temperature according to claim 1, characterized in that: When 0.4≤η<0.45, it is judged that the ultra-high performance concrete is seriously damaged after high temperature, and its compressive strength value is predicted to be 25-70%.
5. The method for evaluating the degree of damage of ultra-high performance concrete after high temperature according to claim 1, characterized in that: When 0.45≤η, it is judged that the ultra-high performance concrete is severely damaged after high temperature, and its compressive strength value is predicted to be less than 25%.
6. The method for evaluating the degree of damage of ultra-high performance concrete after high temperature according to claim 1, characterized in that: In step (2), the number of grids v containing crack information in the square box at different δ scales is counted. ij , and divide this value by the total number of grids containing crack information at the L scale Where N(δ) is the total number of grids containing crack information at the δ scale, that is, the probability density p ij (δ) is:
7. The method for evaluating the degree of damage of ultra-high performance concrete after high temperature according to claim 1, characterized in that: In step (1), k takes the value [0, 10].
8. The method for evaluating the degree of damage of ultra-high performance concrete after high temperature according to claim 1, characterized in that: The surface photo of the ultra-high performance concrete after high temperature obtained in the step (1) is obtained by binarizing the actual photograph.
9. The method for evaluating the degree of damage of ultra-high performance concrete after high temperature according to claim 8, characterized in that: Methods for obtaining photos of the surface of ultra-high performance concrete after high temperature include handheld cameras, mobile phones, drone-mounted cameras or mobile phones, and the shooting resolution must be no less than 30 million pixels.