Method for quantitatively evaluating concrete surface characteristics based on multi-fractal

Abstract

The invention relates to the technical field of building materials, and particularly discloses a method for quantitatively evaluating concrete surface characteristics, which comprises the following steps: (1) carrying out three-dimensional scanning on the concrete surface to obtain a three-dimensional dot matrix coordinate measurement space; (2) dividing the measurement space obtained in the step (1) into a plurality of subunits, namely a box with the side length of r, r being a real number, and obtaining the distribution probability of the height of the concrete surface profile in each subunit; (3) establishing an evaluation formula of concrete surface characteristics; and (4) obtaining the following analysis parameters: delta f (q, r) and delta alpha (q, r) which are used for describing the surface characteristics of the concrete. According to the method, the roughness, uniformity and complexity of the concrete surface can be accurately described, and the method can be used for guiding improvement of the bonding performance of the concrete interface in a combined component or maintenance and reinforcement scene.

Description

Technical Field

[0001] The present application relates to the technical field of building materials, and in particular to a method for quantitatively evaluating concrete surface characteristics. Background Art

[0002] Ultra-high performance concrete (UHPC) can not only be used alone in new building components due to its excellent mechanical properties, such as the combined structure of UHPC and ordinary concrete, wet joints, etc., but can also be used as a patching material to repair and reinforce existing structures, such as bridge deck repair, bridge pier reinforcement, etc. In fact, whether it is a composite structure or repair and reinforcement, good interface bonding performance is an important prerequisite for ensuring the safe service of UHPC composite components. However, the actual situation is that the interface between UHPC and the base concrete is the weakest. Among them, there are many factors that affect the interfacial bonding performance of composite components, but the surface characteristics of the base concrete have the most significant impact on it. A large number of literatures show that suitable base concrete surface characteristics can greatly enhance the overall performance of UHPC components, and even make its interface strength better than that of the base material. Therefore, reasonable and accurate evaluation of the surface characteristics of the base concrete is an important prerequisite for achieving excellent interfacial bonding performance between UHPC and other concrete composite components.

[0003] At present, the evaluation method for the characteristic performance of concrete surface mainly adopts the roughness index. For example, patent CN114813269 proposes a corresponding roughness measurement method for the bonding performance of ordinary concrete and ECC. However, the concrete surface is extremely complex and irregular, and the roughness value cannot fully reflect the surface characteristics of concrete. This makes it so that sometimes, although the surface roughness value of the base concrete is consistent, the interfacial bonding performance varies greatly, resulting in a wide variety of existing roughness formulas and a large number of empirical parameters for different application scenarios. Patent CN 114152221A proposes a method for determining the roughness of the contact surface of a composite material based on fractal theory, which has a certain universality compared to the roughness index. However, the patent uses a simple fractal theory, which can only describe the overall characteristics of the concrete surface, and cannot further describe the detailed concrete surface characteristic information, which limits its scope of application. Summary of the invention

[0004] In order to solve the problem that it is difficult to comprehensively, accurately and quantitatively characterize the surface characteristics of concrete, this application provides a method for quantitatively evaluating the surface characteristics of concrete, which can achieve an accurate description of the roughness, uniformity and complexity of the concrete surface, and can be used to guide the improvement of the concrete interface bonding performance in composite components or maintenance and reinforcement scenarios.

[0005] The present application provides a method for quantitatively evaluating the surface characteristics of concrete, using the following technical solution:

[0006] A method for quantitatively evaluating concrete surface characteristics comprises the following steps:

[0007] (1) Perform three-dimensional scanning on the concrete surface to obtain a three-dimensional point coordinate measurement space;

[0008] (2) Divide the measurement space obtained in step (1) into a number of sub-units, i.e., boxes with a side length of r, where r is a real number, and obtain the distribution probability of the concrete surface contour height in each sub-unit;

[0009] (3) Establish an evaluation formula for concrete surface characteristics, as follows:

[0010] Introduce functions f(q, r) and α(q, r), where f(q, r) and α(q, r) are determined by different orders q, and the order q is any number in the range of -∞ to +∞, that is:

[0011]

[0012] Where N(r) = 2 k , the power value k is selected as [0, 9];

[0013] P ij (r) is the distribution probability of the concrete surface contour height in the box of the i-th row and j-th column;

[0014]

[0015] (4) Obtain the following analysis parameters: Δf(q, r), Δα(q, r), which are used to describe the surface characteristics of concrete, wherein Δα(q, r) refers to the difference between the maximum and minimum values ​​of α(q, r), and Δf(q, r) refers to the difference between the maximum and minimum values ​​of f(q, r);

[0016] The larger the Δα(q, r) value is, the larger the height fluctuation range of the concrete surface is, and the more uneven its surface characteristics are; on the contrary, the smaller the value is, the smaller the height fluctuation range of the concrete surface is, and the more uniform its surface characteristics are;

[0017] The larger the Δf(q, r) value is, the more rough parts there are on the concrete surface and the less smooth the concrete surface is. On the contrary, the smaller the Δf(q, r) value is, the fewer rough parts there are on the concrete surface and the smoother the concrete surface features are.

[0018] Furthermore, P ij (r) = S ij (r) / S T (r),S ij It refers to the sum of the heights of the concrete surface contours in the boxes in the i-th row and j-th column, S T Refers to the sum of the concrete surface profile heights in all boxes.

[0019] Furthermore, after the measurement space is divided into boxes with a side length of r, the total number of boxes is N(r)*N(r).

[0020] Furthermore, the order q is [-20, 20].

[0021] In summary, this application has the following beneficial effects:

[0022] The concrete surface feature evaluation method of the present application is similar to the fractal features found by observing the concrete surface with a magnifying glass of different magnifications, thereby improving the sensitivity to changes in concrete surface features, including uniformity and roughness, etc., breaking through the limitation that traditional methods are difficult to comprehensively summarize concrete surface features, and by avoiding the use of empirical parameters to expand its application scenarios, it achieves a detailed characterization of concrete surface features, which has important guiding significance for improving the interface bonding performance of application scenarios such as concrete composite components or concrete repair and reinforcement. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the cross-sectional morphology of the concrete of Examples 1 to 3 of the present application.

[0024] Figure 2 It is a function diagram of f(α)-α of the concrete cross-sectional morphology of Examples 1 to 3 of the present application.

[0025] Figure 3 This is a test photo of the oblique shear test used in this application to evaluate the interfacial bonding performance of two types of concrete.

[0026] Figure 4 This is the cross-sectional morphology of the concrete of Examples 4 to 7 of the present application.

[0027] Figure 5 It is the f(α)-α function diagram of the concrete cross-sectional morphology of Examples 4 to 7 of the present application. DETAILED DESCRIPTION

[0028] The present application is further described in detail below with reference to the accompanying drawings and embodiments.

[0029] Example

[0030] The present application embodiment provides a method for quantitatively evaluating concrete surface characteristics, comprising the following steps:

[0031] (1) Perform three-dimensional scanning on the concrete surface to obtain a three-dimensional point coordinate measurement space;

[0032] (2) Divide the measurement space obtained in step (1) into several sub-units, i.e., boxes with a side length of r, where r is a real number, and obtain the distribution probability of the concrete surface contour height in each sub-unit; the size of the test space in the embodiment of the present application is 80*80 cm.

[0033] (3) Establish an evaluation formula for concrete surface characteristics, as follows:

[0034] Functions f(q, r) and α(q, r) are introduced, where f(q, r) and α(q, r) are determined by different orders q. The order q is any number in the range of -∞ to +∞. Furthermore, the order q in each embodiment of the present application is [-20, 20], that is:

[0035]

[0036] Where N(r) = 2 k , the power value k is selected as [0, 9];

[0037] P ij (r) is the distribution probability of the concrete surface contour height in the box of the i-th row and j-th column;

[0038]

[0039] The software used may be Matlab, Python, etc., and in this embodiment, Python is used.

[0040] (4) The following analysis parameters are obtained: Δf(q, r) and Δα(q, r), which are used to describe the surface characteristics of concrete. Δα(q, r) refers to the difference between the maximum and minimum values ​​of α(q, r), and Δf(q, r) refers to the difference between the maximum and minimum values ​​of f(q, r).

[0041] Furthermore, P ij (r) = S ij (r) / S T (r),S ij It refers to the sum of the heights of the concrete surface contours in the boxes in the i-th row and j-th column, S T Refers to the sum of the concrete surface profile heights in all boxes.

[0042] Furthermore, the larger the Δα(q, r) value is, the larger the height fluctuation range of the concrete surface is, and the more uneven its surface characteristics are; on the contrary, the smaller the value is, the smaller the height fluctuation range of the concrete surface is, and the more uniform its surface characteristics are.

[0043] Furthermore, the larger the Δf(q, r) value is, the more rough parts there are on the concrete surface and the less smooth the concrete surface is; on the contrary, the smaller the value is, the fewer rough parts there are on the concrete surface and the smoother the concrete surface features are.

[0044] It should also be noted that the raw materials of C30 ordinary concrete in the embodiment include 205 parts of cement, 51 parts of fly ash, 95 parts of mineral powder, 808 parts of river sand, 1030 parts of 5-15 mm basalt stone, 165 parts of water, and 6 parts of polycarboxylate water reducer;

[0045] The raw materials of the all-light concrete in the embodiment include 300 parts of cement, 50 parts of mineral powder, 65 parts of fly ash, 385 parts of pottery sand (particle size <4.75mm, shale pottery sand), 450 parts of ceramsite (5-10mm, shale ceramsite), 180 parts of water, and 8 parts of polycarboxylic acid water reducer; water reducer model

[0046] The ultra-high performance concrete in the embodiment is composed of 2200 parts of admixture, 200 parts of water, and 15 parts of water reducer, wherein the ultra-high performance concrete admixture is provided by Subot New Materials Co., Ltd., and the model is

[0047]

[0048] The surface roughness of concrete is tested by sand spreading method, the operation is as follows:

[0049] 1. Take 0.15-0.3mm dry and clean river sand for use;

[0050] 2. Clean the concrete section to be tested, with an area of ​​100*100mm;

[0051] 3. Spread river sand on the concrete section, fill the gaps on the uneven concrete surface with sand, and do not allow any floating sand to remain on the concrete surface;

[0052] 4. Calculate the surface roughness of concrete by the ratio of the volume of sand spread to the cross-sectional area of ​​concrete;

[0053] 5. To ensure the accuracy of the test, the test results were repeated three times and the average value was taken.

[0054] The following is an explanation through specific examples.

[0055] Examples 1 to 3

[0056] Three different types of sections of C30 ordinary concrete were randomly selected to simulate the application scenarios of UHPC for repair and reinforcement of ordinary concrete, such as Figure 1Next, the concrete surface roughness test was performed and the surface characteristic parameters of the concrete were obtained based on the evaluation method of the embodiment of the present application. The f(α)-α function solution results of embodiments 1 to 3 are shown as follows: Figure 2 When pouring, ensure that the concrete section is clean and free of visible water, then pour the UHPC, and test its interface bonding performance after 28 days. The bonding performance test is carried out as follows Figure 3 The oblique shear test shown was evaluated.

[0057] The roughness test results of Examples 1 to 3, the concrete surface characteristic parameters and the interface oblique shear strength of the two concretes after UHPC reinforcement can be seen in Table 1.

[0058] Table 1 Surface characteristic parameters of each embodiment and interface oblique shear strength of two concretes after UHPC reinforcement

[0059]

[0060] It can be found from Table 1 that Examples 1-3 have different surface roughness values ​​and interface bonding strengths, but the two are not proportional. It can be seen that it is not accurate to use the traditional concrete surface roughness value to evaluate the concrete surface characteristics. However, the Δf(q, r) and Δα(q, r) analysis parameters given by the concrete surface characteristics evaluation method described in this application can better describe this relationship.

[0061] Specifically, from Example 1 to Example 3, the Δα(q, r) value is getting larger, indicating that the greater the height fluctuation range of the concrete surface, the more uneven its surface characteristics are; in addition, Δf(q, r) is also getting larger, indicating that there are more rough parts on the concrete surface, that is, the less smooth the concrete surface is, and this value is in a very obvious positive proportional relationship with the interface bonding strength of the two concretes. Therefore, it is shown that the relevant parameters of this application can be used to evaluate the surface characteristics of concrete, and then compare the interface bonding strength of the two concretes, which can be used to guide the field of concrete repair and reinforcement.

[0062] Embodiments 4 to 7

[0063] Furthermore, in order to better demonstrate the superiority of the concrete surface characteristics evaluation method of the present application, another type of concrete (all-light concrete) was reinforced with UHPC to simulate the application scenario of concrete composite components. When pouring all-light concrete, different artificial surface treatments were performed before it hardened, and then UHPC was poured after 24 hours, and its interface bonding performance was tested after 28 days. The bonding performance test was carried out as follows: Figure 3 The oblique shear test shown was evaluated.

[0064] Specifically, the surface treatment of all-light concrete includes no surface treatment (WCL, Example 4), surface scratch treatment (HH, Example 5), surface hole poking treatment (CD, Example 6) and surface wire mesh stamping treatment (YY, Example 7). The specific operation process is: when pouring fresh all-light concrete, only pour half the height of the 100*100*100mm concrete mold, and then perform different types of surface treatment before its final setting. Among them, WCL does not take any treatment method; HH uses a 4mm diameter iron round rod to perform a roughening scratch treatment on the concrete surface; CD uses a 15mm diameter iron round rod to perform an evenly spaced poking treatment; YY uses a stainless steel mesh with an inner side length of 15mm for stamping treatment. The photos of the concrete sections after each group of treatment can be seen. Figure 4 The roughness test results of Examples 4 to 7, the concrete surface characteristic parameters and the interface oblique shear strength of the two concretes reinforced with UHPC can be seen in Table 3.

[0065] Table 3 Surface characteristic parameters of each embodiment and interface oblique shear strength of two concretes after UHPC reinforcement

[0066]

[0067] It can be found from Table 2 that Examples 4-7 have different surface roughness values ​​and interface bonding strengths after different surface treatments, but the two are not proportional. It can be seen that it is not accurate to use the traditional concrete surface roughness value to evaluate the concrete surface characteristics. However, there is a good linear relationship between the Δα(q, r) analysis parameter given by the concrete surface characteristics evaluation method described in this application and the interface oblique shear strength, which can better describe this relationship.

[0068] Specifically, from Example 4 to Example 7, the Δα(q, r) value is getting larger and larger, indicating that the larger the height fluctuation range of the concrete surface, the more uneven its surface characteristics, and this value is in a very obvious positive proportional relationship with the interface bonding strength of the two concretes. Therefore, the concrete surface characteristic evaluation method described in this application can not only accurately characterize the concrete surface characteristics, but also has important guiding significance for improving the interface bonding performance of concrete composite component application scenarios.

[0069] Therefore, it can be seen from Examples 1-7 that the two analytical parameters Δα(q, r) and Δf(q, r) obtained in this application can form a good linear relationship with the interfacial bonding strength of the two types of concrete, whether for ordinary concrete or lightweight concrete, whether for the field of concrete repair or the field of composite components, thereby effectively ensuring the interfacial bonding performance of gradient concrete. In addition, the relevant parameters involved in the present invention are simple, easy to obtain, and highly repeatable.

[0070] 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 quantitatively evaluating concrete surface characteristics, characterized in that: The following steps are involved: (1) Perform three-dimensional scanning on the concrete surface to obtain a three-dimensional point coordinate measurement space; (2) Divide the measurement space obtained in step (1) into a number of sub-units, i.e., boxes with a side length of r, where r is a real number, and obtain the distribution probability of the concrete surface contour height in each sub-unit; (3) Establish an evaluation formula for concrete surface characteristics, as follows: Introduce functions f(q, r) and α(q, r), where f(q, r) and α(q, r) are determined by different orders q, and the order q is any number in the range of -∞ to +∞, that is: Where N(r) = 2 k , the power value k is selected as [0, 9]; P ij (r) is the distribution probability of the concrete surface contour height in the box of the i-th row and j-th column; (4) Obtain the following analysis parameters: Δf(q, r), Δα(q, r), which are used to describe the surface characteristics of concrete, wherein Δα(q, r) refers to the difference between the maximum and minimum values ​​of α(q, r), and Δf(q, r) refers to the difference between the maximum and minimum values ​​of f(q, r); The larger the Δα(q, r) value is, the larger the height fluctuation range of the concrete surface is, and the more uneven its surface characteristics are; On the contrary, the smaller the value, the smaller the fluctuation range of the concrete surface and the more uniform its surface characteristics; The larger the Δf(q, r) value is, the more rough parts there are on the concrete surface and the less smooth the concrete surface is. On the contrary, the smaller the Δf(q, r) value is, the fewer rough parts there are on the concrete surface and the smoother the concrete surface features are.

2. A method for quantitatively evaluating concrete surface characteristics according to claim 1, characterized in that: P ij (r) = S ij (r) / S T (r),S ij It refers to the sum of the heights of the concrete surface contours in the boxes in the i-th row and j-th column, S T Refers to the sum of the concrete surface profile heights in all boxes.

3. A method for quantitatively evaluating concrete surface characteristics according to claim 1, characterized in that: After the measurement space is divided into boxes with a side length of r, the total number of boxes is N(r)*N(r).

4. A method for quantitatively evaluating concrete surface characteristics according to claim 1, characterized in that: The order q is [-20, 20].

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