Method for measuring interface roughness of 3d printed concrete for interface bonding

Abstract

The application provides a 3D printing concrete interface roughness measurement method for interface bonding, and belongs to the technical field of interface processing of 3D printing concrete, and comprises the following steps: constructing an original point cloud and performing pretreatment, and constructing a roughness field according to the pretreated point cloud; based on the roughness field, a roughness index system and the calculation method of each index are defined; based on the roughness index system, a roughness-bonding semi-empirical model for multiple working conditions is constructed, the roughness contribution is decomposed into an effective contact factor and a mechanical engagement factor, and a fillable penalty and a time penalty are introduced, which are used to uniformly represent the non-monotonic effect caused by insufficient fillability in the interface between new and old concrete and the interface between 3D printing layers and the re-fusion attenuation caused by the time interval between layers; and the effective roughness is calculated based on the constructed model. The scheme can quantitatively reflect the influence of the concrete interface roughness on the bonding performance, and provides a calculable variable for inferring the process parameters of the best bonding performance.

Description

Technical Field

[0001] This application relates to the field of interface treatment technology in the manufacturing process of concrete products, and in particular to a method for measuring the roughness of 3D printed concrete interfaces oriented towards interfacial bonding. Background Technology

[0002] 3D-printed concrete, as a new generation of automated construction technology, has attracted widespread attention in the field of civil engineering due to its advantages such as eliminating the need for formwork and high material utilization. However, because printed components are formed by layered extrusion and stacking, the interfaces between layers lack sufficient fusion, and weak interfacial bonding has become a key issue restricting the performance of 3D-printed concrete structures. Insufficient interfacial bond strength can make the interlayer interfaces weak points in the structure, potentially leading to cracking, delamination, and other damage, significantly weakening the overall mechanical properties of the component. Therefore, improving the interfacial bonding quality between 3D-printed concrete layers and between 3D-printed concrete and the substrate has become an urgent technical challenge to be solved.

[0003] Numerous studies have shown that surface roughness at the concrete interface is a crucial factor affecting bond performance. Researchers Fan et al. (Fan, J.; Wu, L.; Zhang, B. Influence of Old Concrete Age, Interface Roughness and Freeze-Thawing Attack on New-to-Old Concrete Structure. Materials 2021, 14, 1057.) compared the splitting bond strength of new and old concrete under different ages and surface roughnesses. The results showed that increased roughness contributed more to bond strength than the age of the old concrete, indicating that surface roughness is a key factor determining bond performance when treating the interface of old concrete. Generally, a rough substrate surface provides stronger mechanical interlocking and a larger effective contact area, which is beneficial for improving the bond strength between freshly poured concrete and the substrate. However, in the case of 3D printed concrete, the relationship is not simply linear. Scholars Tao Y, Lesage K, Van Tittelboom K, Yuan Y, De Schutter G. Influence of substrate surface roughness and moisture content on tensile adhesion performance of 3D printable concrete[J]. Cement and Concrete Composites, 2022, 126:104350. found that when the surface roughness of the substrate increases to a high level, due to the limited printing extrusion pressure, the material cannot fully fill the deep concave texture of the rough interface, and the effective contact area of ​​the interface decreases, resulting in a decrease in bond strength. This phenomenon indicates that an excessively rough interface may be detrimental to the interlayer bonding of 3D printed concrete. It is necessary to seek an optimal balance between roughness and bonding performance, and more roughness indices adapted to concrete interface bonding are needed to better quantify the influence of surface roughness on bonding performance.

[0004] Commonly used methods for measuring interface roughness include the sand cone method, contact profilometer, laser profilometry, and stereo vision measurement. The sand cone method involves spreading a certain volume of sand onto a concrete surface, forming a disc, and then calculating the mean roughness depth (MTD) based on the disc's diameter. Its advantages are simplicity, speed, and low equipment requirements; however, it cannot be used for vertical or inclined surfaces. The contact profilometer, also known as a single-point stylus profilometer, records height variations by moving a probe along a single profile of the surface. It can obtain a two-dimensional profile and parameters. and While high-precision methods exist, they are limited to a few sampling lines, resulting in poor representativeness and time-consuming measurements, making it difficult to cover the entire interface. Laser profilometry, a non-contact method based on laser triangulation, can acquire high-density point cloud data of the interface and calculate three-dimensional roughness parameters. It offers even higher precision and can detect macroscopic textures and microscopic pores. However, its disadvantages include expensive and bulky equipment, and stringent environmental requirements (vibration damping, dust protection, etc.). Stereoscopic vision measurement utilizes cameras and light projection to acquire the three-dimensional morphology of surfaces, including multi-view photogrammetry and structured light scanning. Recent developments in camera-based measurement systems use ordinary industrial cameras to acquire multi-angle photographs, reconstructing a three-dimensional interface model to achieve large-area, non-contact roughness measurement. The camera-based measurement system developed by scholars Özcan et al. (Özcan B, Blankenbach J. Quality assessment of a novel camera-based measurement system for roughness determination of concrete surfaces—Accuracy evaluation and validation[J]. Sensors, 2022, 22(11):4211.) showed a high correlation (correlation coefficient > 0.99) in roughness parameters compared with the sand cone method and laser method, with the highest correlation to the laser scanning results. Furthermore, this method is low-cost and portable. However, current research on the influence of surface roughness on the bonding performance of concrete interfaces is mostly qualitative. Existing roughness parameters are also insufficient to quantitatively reflect the influence of surface roughness on bonding performance, making it difficult to achieve an optimal balance between roughness and bonding performance, and thus failing to effectively guide technological practice.

[0005] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0006] The purpose of this application is to propose a roughness measurement method for 3D printed concrete interfaces oriented towards interfacial bonding. By acquiring interface point clouds through multi-view imaging and 3D reconstruction, a roughness index system with height, normal / slope, area, and multiple scales is constructed. A unified roughness-bond semi-empirical model oriented towards multiple working conditions is built to reflect the contribution of the interface to mechanical interlocking and bonding area, and the effective roughness is calculated. This guides engineering practice to balance roughness to obtain the best bonding performance.

[0007] To achieve the above objectives, this application provides the following technical solution:

[0008] This application provides a method for measuring the surface roughness of 3D printed concrete interfaces oriented towards interfacial bonding, including:

[0009] S1. Take multi-angle photos of the 3D printed concrete interface to be tested, construct the original point cloud using a multi-view stereo algorithm, preprocess the original point cloud, and construct a roughness field based on the preprocessed point cloud.

[0010] S2, Based on the roughness field, define a roughness index system and the calculation method of each index, wherein the roughness index system includes interface undulation height index, interface tilt angle index, interface area index and interface multi-scale index.

[0011] S3. Based on the roughness index system, a roughness-bond semi-empirical model for multiple working conditions is constructed. The roughness contribution is decomposed into effective contact factor and mechanical interlocking factor. Fillable penalty and time penalty are introduced to uniformly characterize the non-monotonic effect caused by insufficient fillable in the interface between new and old concrete and the interface between 3D printed layers, as well as the re-fusion attenuation caused by the interlayer time interval.

[0012] S4. Calculate the effective roughness based on the roughness-bond semi-empirical model. The effective roughness is used to quantitatively characterize the influence of the surface roughness of the concrete interface on the bonding performance.

[0013] Preferably, the expression for the effective contact factor is as follows:

[0014] ,

[0015] In the formula, Indicates interface roughness; Indicates the magnification factor of the interface area; This indicates that a penalty item can be filled. This indicates a time interval penalty.

[0016] Preferably, the formula for calculating the fillable penalty term is as follows:

[0017] ,

[0018] In the formula, The characteristic peak and valley heights are determined by the fillability. It represents the height range and belongs to the category of interface undulation height indicators.

[0019] Preferably, the calculation formula for the time interval penalty term is as follows:

[0020] ,

[0021] In the formula, For printing time intervals, This is the characteristic time constant.

[0022] Preferably, the expression for the mechanical occlusion factor is as follows:

[0023] ,

[0024] In the formula, The root mean square height; , which is the surface area ratio, used to characterize the magnification factor of the interface area; This indicates the mechanical occlusion factor.

[0025] Preferably, the effective roughness is calculated using the following formula:

[0026] ,

[0027] In the formula, Indicates the effective roughness. This represents the arithmetic mean height.

[0028] Preferably, in step S1, constructing a roughness field based on the preprocessed point cloud includes:

[0029] For each measurement point in the point cloud, a fast neighborhood search is performed using a KD-tree to obtain a spherical neighborhood. ;

[0030] Based on the spherical neighborhood The local reference plane for each point is fitted using the least squares method;

[0031] Based on the local reference plane, the normal height deviation of each point is defined as:

[0032] ,

[0033] Global reference direction Based on this, the local normal tilt angle is defined as:

[0034] ,

[0035] In the formula, For point Normal height deviation, For the spherical neighborhood The center of mass, The normal vector of the local reference plane. For point The local normal angle at that location.

[0036] Preferably, in step S2, the interface undulation height index includes: arithmetic mean height. Root mean square height Height range And height quantile index.

[0037] Preferably, in step S2, the interface tilt angle index includes: average slope. Root mean square slope Slope dispersion Among them, slope dispersion The calculation formula is as follows:

[0038] ,

[0039] In the formula, This represents the total number of interface measurement points. This is the local normal angle.

[0040] Preferably, the interface area index is specifically the surface area ratio. The calculation formula is as follows:

[0041] ,

[0042] In the formula, This represents the actual three-dimensional surface area of ​​the concrete interface. for The projection onto the local reference plane;

[0043] The interface multi-scale index is characterized by a multi-scale roughness curve, which is obtained as follows: [The text abruptly shifts to a different topic] ...within multiple window radii... Repeatedly construct local neighborhoods and calculate the arithmetic mean height of the entire field. The function curve of interface roughness as a function of sampling scale is obtained.

[0044] The technical solution of this application has the following beneficial effects: It obtains the original point cloud through multi-angle photography and 3D reconstruction, and constructs a roughness field, overcoming the limitations of traditional two-dimensional contour methods or contact measurement methods, which suffer from incomplete information and difficulty in reflecting the true morphology of three-dimensional space. The defined roughness index system integrates undulation height, inclination angle, area, and multi-scale features, and can comprehensively and meticulously describe the complex geometric features of the interface morphology from multiple dimensions. A roughness-bond semi-empirical model is constructed, decomposing the contribution mechanism of roughness into effective contact factor and mechanical interlocking factor for the first time, giving the model a clear physical connotation. This model can be uniformly applied to various working conditions such as the interface between new and old concrete and the interlayer interface of 3D printing, significantly improving the applicability and predictive reliability of the model. By introducing infillable penalty and time penalty mechanisms, it can effectively characterize the non-monotonic change effect of bond strength caused by insufficient filling of post-cast material due to excessively deep or narrow interface grooves (insufficient infill), as well as the interface re-fusion and bond performance decay phenomenon caused by interlayer time intervals in 3D printing, making the method provided in this application closer to actual construction conditions. Attached Figure Description

[0045] Figure 1 These are point cloud diagrams of two typical interface regions, with the left image representing interface 1 and the right image representing interface 2.

[0046] Figure 2 for Figure 1 A comparison chart of two typical interface regions' height-based roughness indices.

[0047] Figure 3 for Figure 1 A comparison chart of two typical interface regions with tilt angle-type roughness indices.

[0048] Figure 4 for Figure 1 A comparison of the surface area ratios of two typical interface regions.

[0049] Figure 5 for Figure 1 Curves for two typical interface regions under different neighborhood radii.

[0050] Figure 6 The bond strength is given by different roughnesses at T=0min and T=30min.

[0051] Figure 7 This represents the relationship between bond strength and effective roughness. Detailed Implementation

[0052] The terms "first," "second," "third," and "fourth," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0053] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0054] "Multiple" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0055] The embodiments of this application will now be described with reference to the accompanying drawings.

[0056] This application provides a method for measuring the surface roughness of 3D-printed concrete interfaces oriented towards interfacial bonding, including:

[0057] S1. Take multi-angle photos of the 3D printed concrete interface to be tested, construct the original point cloud using a multi-view stereo algorithm, preprocess the original point cloud, and construct a roughness field based on the preprocessed point cloud.

[0058] Step S1 starts from the camera image, sequentially obtains the three-dimensional point cloud coordinates of the substrate-newly poured concrete interface, and constructs the roughness field in a unified coordinate system. The process of constructing point clouds and roughness fields from images includes the following sub-steps:

[0059] S11, Camera Imaging Model and Multi-View Stereo Reconstruction.

[0060] The surface roughness measurement system uses a standard digital camera or an industrial camera as the core sensor. The camera can be mounted on a tripod, guide rail, or end effector of a robotic arm to achieve multi-view imaging of the interface under test. During shooting, ensure that adjacent images have sufficient overlap (not less than 60% to 70%), and that the line of sight covers both the interface normal and a certain degree of tilt angle to enhance the accuracy of elevation resolution.

[0061] In the ideal pinhole imaging model, spatial points Image points on the imaging plane The relationship can be written as:

[0062] (1)

[0063] In the formula: As a scale factor, The coordinates of the image point on the imaging plane; This is the camera intrinsic parameter matrix (focal length, principal point coordinates, and distortion parameters). , These are the rotation matrix and translation vector of the rigid body in space, respectively.

[0064] By extracting and matching feature points from multiple images, a dense point cloud covering the entire interface can be obtained through the multi-view stereo (MVS) algorithm for dense reconstruction.

[0065] S12, Point cloud preprocessing and bonding interface region extraction.

[0066] The raw point cloud obtained by multi-view stereo algorithms typically contains noisy points, isolated points, and background points unrelated to the interface. Therefore, the point cloud is first preprocessed in a unified coordinate system:

[0067] 1) Noise and outlier removal: A radius filtering method is used, with the number of neighboring points and the point-to-neighbor distance as indicators, to remove isolated points that are significantly deviated from the main surface;

[0068] 2) Interface area clipping: Based on interactive box selection or automatic boundary detection, select the bonding interface area to be analyzed in the 3D view and remove the surrounding irrelevant point cloud;

[0069] After the above preprocessing, a uniformly distributed clean point cloud (i.e., the preprocessed point cloud) can be obtained, and the bonding interface region can be extracted, laying the foundation for subsequent local plane fitting and roughness calculation.

[0070] S13, Local Neighborhood Construction and Normal Estimation.

[0071] In purifying the point cloud, each measurement point in the point cloud... Using a KD-tree as the center, a fast neighborhood search is performed to obtain a spherical neighborhood. In this embodiment, a fixed radius is used. Constructing a spherical neighborhood:

[0072] (2)

[0073] In the formula, For point The neighborhood, Let be any point within the neighborhood.

[0074] Based on spherical neighborhood The local reference plane is fitted using the least squares method. Specifically, the centroid of the neighborhood point set is first set to:

[0075] (3)

[0076] In the formula, spherical neighborhood The center of mass, The total number of points in the neighborhood point set.

[0077] Then construct the covariance matrix:

[0078] (4)

[0079] right Perform eigenvalue decomposition, take the eigenvector corresponding to the smallest eigenvalue as the local reference plane normal vector, and finally write the local plane equation as:

[0080] (5)

[0081] in, This is the normal vector of the local reference plane.

[0082] S14, roughness field construction.

[0083] Construct a local reference plane in a unified coordinate system. Based on the local reference plane, define the normal height deviation of each point as:

[0084] (6)

[0085] In the formula, For point Normal height deviation, The normal vector of the local reference plane. For point The local normal angle at that location.

[0086] Among them, absolute value It directly represents the amplitude of the fluctuation of the point relative to the local plane.

[0087] On the other hand, the normal to the reference plane is used as the global reference direction. global reference direction Based on this, the local normal tilt angle is defined as:

[0088] (7)

[0089] Will and By assigning values ​​to each point, the height roughness field and normal tilt field of the interface can be constructed, collectively referred to as the roughness field, denoted as . The local reference plane of each point is called the local domain, and the local domains of all points are called the total local field. By constructing local domains point by point, calculating the normal height deviation and normal inclination, and performing statistical analysis on these height roughness fields and normal inclination fields within the interface region, we can further obtain various roughness indices of the total local field, providing a foundation for the subsequent construction of an index system and comparison of typical interfaces.

[0090] S2, based on the roughness field, defines the roughness index system and the calculation method of each index. The roughness index system includes interface undulation height index, interface tilt angle index, interface area index and interface multi-scale index.

[0091] Within a unified point cloud and roughness field framework, this application calculates local area and other geometric quantities point by point, and constructs an interface bonding-oriented roughness index system from aspects such as height undulation, normal / slope distribution, surface area and scale effect, which is used to quantitatively characterize the geometric features of the concrete / rock interface.

[0092] S21, Interface undulation height index (abbreviated as: height index).

[0093] Height-related indicators are based on the normal height deviation at each point. Based on this, the roughness of the interface is described from two aspects: "fluctuation amplitude" and "height distribution pattern".

[0094] (1) Arithmetic mean height and root mean square height :

[0095] (8)

[0096] (9)

[0097] In the formula: This represents the total number of interface measurement points. The arithmetic mean height is used to reflect the average undulation of the overall interface. The larger the value, the rougher the overall interface.

[0098] Compared to the arithmetic mean height Root mean square height It is more sensitive to local pits and protruding teeth, and therefore more suitable for depicting interface geometry features with obvious keyway-like undulations.

[0099] (2) Height range :

[0100] (10)

[0101] Height range It is used to describe the maximum height difference between the highest and lowest points of the interface, and can be used to identify whether there are large-scale grooves or protrusions.

[0102] (3) Height quantile index:

[0103] Based on the overall height deviation, a histogram and cumulative distribution function were constructed, and indicators such as the median (P50), high quantile (P90), and P95 were extracted to form the height quantile index. The median reflects the undulation level of typical areas of the interface, while the high quantile reflects the undulation amplitude and area proportion of extremely rough areas.

[0104] S22, Interface tilt angle index (abbreviated as: tilt angle index).

[0105] Tilt-type indicators use the angle between the local normal and the global reference direction. Based on this, it is used to characterize the directionality and steepness of the interface texture.

[0106] (1) Average slope With root mean square slope .remember Let the local normal angle be the inclination angle, then we have:

[0107] (11)

[0108] (12)

[0109] Among them, average slope Used to reflect the overall tilt of the interface, root mean square slope More sensitive to areas with high slopes.

[0110] (2) Slope dispersion .

[0111] (13)

[0112] Slope dispersion Used to describe the dispersion of the interface slope distribution. The larger the value, the more complex the interface texture, and the existence of concave and convex structures with multiple directions and amplitudes.

[0113] S23, interface area index.

[0114] Height and inclination angle primarily reflect interface morphology, while concrete bonding performance is also closely related to the actual contact area. Therefore, this application introduces the surface area ratio... The magnification factor of the effective bonding area of ​​the interface.

[0115] The interface point cloud is triangularly meshed to obtain the actual 3D surface area. Simultaneously calculate its projected area on the reference plane. ,but:

[0116] (14)

[0117] This reflects the proportion of "additional contact area" caused by roughness. For the 3D printed concrete-substrate interface, too small a proportion is considered insignificant. This means insufficient mechanical engagement, while infinitely increasing... It is also limited by the filling capacity of the grout and the construction process.

[0118] S24, Interface Multiscale Indicator.

[0119] Concrete interface roughness includes both fine undulations at the mortar level and macroscopic undulations such as chiseling texture and surface undulations of precast components. Roughness indices at a single scale are insufficient to fully reflect this multi-scale characteristic; therefore, this application introduces multi-scale roughness curves.

[0120] In multiple window radii Repeatedly construct local neighborhoods and calculate the arithmetic mean height of the entire field. The function curve of interface roughness as a function of sampling scale is obtained.

[0121] when When smaller, It mainly reflects the fine surface roughness; with As the surface roughness increases, small-scale undulations are smoothed out, while macroscopic geometry gradually dominates the roughness index.

[0122] The following experiments will analyze typical interfaces to verify the applicability of the proposed roughness index system.

[0123] Based on the defined roughness index system, the sensitivity of different roughness indices in interface identification under different working conditions is analyzed. In this application, two typical concrete substrate interfaces, denoted as Interface 1 and Interface 2, are used to compare and analyze their roughness characteristics. Figure 1 Two typical interface point cloud diagrams are presented. The left image represents interface 1, a rough interface with obvious pits and jagged textures; the right image represents interface 2, a less processed interface with a relatively smooth overall surface. 3D point clouds of both interfaces were obtained using a multi-view stereo vision method, with a point spacing of 1–2 mm.

[0124] A fixed neighborhood search radius is set for each point (e.g., 0.01 m), and the minimum number of neighboring points is set to 20. Points with insufficient neighboring points are automatically removed. The local reference plane is fitted to the set of neighboring points using the least squares method to obtain the local normal direction and geometric information of the reference plane.

[0125] For each measuring point, calculate the normal height deviation relative to the local reference plane, calculate the angle between the local normal and the global reference Z-axis, and obtain the normal inclination angle (local slope) of each point.

[0126] Under the principal scale (i.e., radius 0.01m), the absolute height deviation of all measuring points on interface 1 and interface 2. The inclination angle of the normal line is statistically analyzed, and the calculation is performed according to the calculation method described above to obtain the index results. Figure 2 A comparison chart of height-related roughness indices is provided. Numerically, interface 1... , Furthermore, the high quantiles P90 and P95 are significantly greater than those of interface 2, indicating that the overall fluctuation range and the depth of the extremely rough region of interface 1 are both greater.

[0127] Figure 3 A comparison chart of roughness indices for slope types, including: average slope Root mean square slope Slope standard deviation The results show that the local normals of interface 1 deviate from the overall plane normal at a larger angle, exhibit stronger fluctuations, and have a more pronounced normal distribution, resulting in a steeper texture. In contrast, the slope of interface 2 is generally smaller and more concentrated, indicating that its surface texture is gentler and tends to have slight undulations in a single direction. The tilt angle index supplements the height index in terms of both directionality and steepness.

[0128] Figure 4 Surface area ratio Comparison chart. In the chart, interface 1... It is approximately 10.202%, while interface 2 is 4.990%. Characterizing the amplification of the actual three-dimensional surface area relative to its projected area: This indicates that, under the same projected area, the actual surface of interface 1 has a larger area due to undulations and textures, which is more conducive to interface adhesion from a geometric point of view.

[0129] Figure 5 Two typical interface regions under different neighborhood radii Curve. In multiple different neighborhood radii For the following (5 mm, 10 mm, 15 mm, 20 mm, 30 mm) values, repeat the above process of local plane fitting and height deviation calculation. For each radius... Calculate the entire interface ,get Multi-scale curves varying with sampling scale were plotted for interface 1 and interface 2, respectively. – Radius curves. It can be seen that both curves increase with scale, indicating that at larger scales, the geometric undulations traversed within the local sampling window are greater; simultaneously, at all scales, interface 1… Both are higher than interface 2, and the difference increases slightly with increasing radius. This indicates that the overall roughness level of interface 1 is higher than that of interface 2, both at the microscopic (a few millimeters) and relatively macroscopic (a few centimeters) scales, and the scale effect shows a consistent but different trend in magnitude between the two interfaces.

[0130] The above analysis shows that the roughness index system proposed in this embodiment can not only effectively distinguish and quantify the roughness differences of different types of interfaces, but also reveal the specific connotations of the differences from multiple physical dimensions such as height, slope, and surface area. Through the mutual supplementation of multi-dimensional indexes, a comprehensive evaluation of the interface morphology is formed, laying a reliable characterization foundation for subsequent research on the relationship between interface roughness and adhesive mechanical properties.

[0131] S3 is based on a roughness index system to construct a roughness-bond semi-empirical model for multiple working conditions. It decomposes the roughness contribution into an effective contact factor and a mechanical interlocking factor, and introduces fillable penalty and time penalty to uniformly characterize the non-monotonic effect caused by insufficient fillable in the interface between new and old concrete and the interface between 3D printed layers, as well as the re-fusion attenuation caused by the interlayer time interval.

[0132] S4 calculates the effective roughness based on the roughness-bond semi-empirical model. The effective roughness is used to quantitatively characterize the influence of the surface roughness of the concrete interface on the bond performance.

[0133] The purpose of steps S3 and S4 is to apply the roughness index system, that is, to transform the geometric index of roughness into a calculable variable that can be used for interfacial bonding performance analysis and engineering decision-making. In conjunction with current research on the relationship between roughness and bonding performance, a literature dataset is established, parameter calibration and model verification are completed, and finally a theoretical integration and calculable model for interfacial bonding is formed, which is called the roughness-bonding semi-empirical model.

[0134] Step S3 includes the following sub-steps:

[0135] S31, a unified expression and variable mapping for two types of interface problems.

[0136] In this embodiment, the interfacial adhesion of interest can be summarized into two typical operating conditions:

[0137] (1) Interface between new and old concrete (substrate - repair / overlay layer): The substrate is a hardened body, and the bonding process of the interface is mainly controlled by "wetting - penetration - formation of interface transition zone - micro-mechanical interlocking"; roughness affects not only the actual contact area and mechanical interlocking, but also the local stress concentration and failure path through the morphology of pores / grooves. Hoła J, Sadowski Ł, Schabowicz K. Usefulness of 3D surface roughness parameters for nondestructive evaluation of pull-off adhesion of concrete layers[J]. Construction and Building Materials, 2015, 84: 111–120.) conducted 3D scanning and pull-off tests on the surface of a 50×50mm substrate, and gave the "3D roughness parameters - The corresponding data and statistical characteristics of “” can be used as an external verification dataset for the indicator system of this application.

[0138] (2) 3D printing interlayer: The compaction of the upper layer material is limited by nozzle pressure, thixotropic recovery and water loss caused by interlayer time interval, and moisture content and morphology changed by surface treatment. Van Der Putten et al. (Van Der Putten J, Vantyghem G, Van Tittelboom K, et al. Surface modification as a technique to improve inter-layer bonding strength in 3D printed cementitious materials[J]. RILEM Technical Letters, 2019, 4: 32–38.) also gave the moisture content, 2D profile roughness Ra and interlayer bonding strength under different surface modifications, providing a reproducible empirical basis for the joint modeling of "geometric roughness + state factor".

[0139] S32, a unified roughness-bond semi-empirical model for multiple operating conditions.

[0140] To simultaneously adapt to the interlayer interface of 3D printing and the interface between new and old concrete, in this embodiment, the effective load-bearing capacity brought about by roughness is decomposed into two calculable factors: effective contact factor and mechanical interlocking factor.

[0141] (1) The formula for calculating the effective contact factor is as follows:

[0142] (15)

[0143] in, This is the magnification factor for the interface area; For fillable penalty items; This is a time interval penalty term; for the interface between new and old concrete, this penalty term can be taken as... =1 (no effect).

[0144] (2) The formula for calculating the mechanical occlusion factor is as follows:

[0145] (16)

[0146] in, The magnitude of the root mean square height. The magnification factor of the interface area is used to characterize the interlocking potential using both the magnitude and the area.

[0147] (3) The fillable penalty term uses a smooth saturation function to characterize insufficient contact when the peak-valley height is too large:

[0148] (17)

[0149] In the formula, The characteristic peak and valley heights are determined by the fillability.

[0150] The above The function form satisfies when hour, , hour, This allows for a non-monotonic effect where excessive roughness leads to a decrease in effective contact.

[0151] (4) The time interval penalty term is only enabled for the interlayer interface of 3D printing, and the exponential decay is used to characterize the decrease in refusion capability caused by the time interval:

[0152] (18)

[0153] in, For printing time intervals, The characteristic time constant reflects the combined effect of early-age structure establishment and surface state evolution of materials. Further analysis using literature data is needed. Perform calibration.

[0154] Based on the above derivation, step S4 yields the following formula for calculating the effective roughness:

[0155] (19)

[0156] This formula represents the expression derived from classical three-dimensional roughness geometric indices. Considering the effective contact area factor and mechanical occlusal factor This allows us to obtain the effective roughness for measuring interfacial adhesion. .

[0157] In the above formula, the effective contact factor The mechanical interlocking factor is influenced by both the fillability penalty (which depends on the filling capacity of the particles) and the time penalty (which depends on the interlayer time interval of the 3D printed concrete). Influenced by the comprehensive form of geometric indices.

[0158] The following section presents examples of parameter calibration and calculation.

[0159] To determine the filling capacity of the particles, further experiments are needed to test different aggregate particle sizes. Parameter calibration. For the mechanical engagement factor... This can be directly calculated using geometric indices. Below, based on literature data, we will analyze the characteristic time constants in the time penalty term. The calibration.

[0160] In the research of scholar Van Der Putten (Van Der Putten J, Vantyghem G, VanTittelboom K, et al. Surface modification as a technique to improve inter-layer bonding strength in 3D printed cementitious materials[J]. RILEM Technical Letters, 2019, 4: 32–38, referred to as Reference 1), a two-dimensional roughness index was used. ( (arithmetic mean height in the direction) and To represent interface roughness ( The arithmetic mean height in the direction is used to obtain the interface roughness and bond strength at T=0min and T=30min for different treatment methods. Combined with the roughness index system provided in this application, the geometric roughness of different treatment methods can be obtained. The results are shown in Table 1, which is as follows:

[0161] (20)

[0162] Table 1. Roughness and bond strength under different treatment methods

[0163]

[0164] draw The scatter plot of the bond stress is shown in the figure. Figure 6 As shown. The average bond strength at T=0min and T=30min in reference 1 (Van Der Putten J, Vantyghem G, Van Tittelboom K, et al. Surface modification as a technique to improve inter-layer bonding strength in 3D printed cementitious materials[J]. RILEM Technical Letters, 2019, 4: 32–38) is denoted as and According to the definition of the time penalty term, we have:

[0165] (twenty one)

[0166] (twenty two)

[0167] Based on the columns “σ / MPa (T=0min)” and “σ / MPa (T=30min)” in Table 1, the following can be calculated: Then, using formula (22) to calculate This characteristic parameter is the characteristic time constant for a given material mix. Therefore, an effective reduction mapping for the time penalty term is obtained, which can be used to reduce the same geometric roughness. In different Downmapping to different The results are shown in Table 1. "Column. Further, plot the effective roughness." A scatter plot of the relationship between the bond strength and the bond strength yields the following results. Figure 7 ,observe Figure 7 It can be observed that after introducing effective roughness, the trend of bond strength change with roughness becomes clearer.

[0168] In summary, based on existing research demonstrating the significant impact of roughness on interfacial adhesion, and considering the various roughness measurement methods available, this application proposes a three-dimensional roughness measurement method based on multi-view stereo vision for 3D printed concrete interfaces. The basic idea is to acquire interface point clouds through multi-view imaging and 3D reconstruction, construct a local reference plane in a unified coordinate system, and calculate geometric quantities such as normal height deviation, normal inclination angle, and local area point by point to form a roughness field. Based on the statistical analysis of the entire field, a multi-scale roughness index system is constructed, including height-based, normal / slope-based, area-based, and multi-scale roughness indices, to reflect the interface's contribution to mechanical interlocking and bonding area. Specific effects include:

[0169] 1) A three-dimensional roughness measurement process of "image-point cloud-roughness field" for 3D printed concrete interface is proposed: Based on multi-view stereo vision to obtain dense point cloud, and with local reference plane as the reference in unified coordinate system, roughness field such as normal height deviation and normal inclination angle is constructed point by point, and subsequent statistical index calculation and full field comparison analysis are supported.

[0170] 2) Within the framework of a unified point cloud and roughness field, a bond-oriented roughness index system was established, covering dimensions such as height undulation, tilt angle / slope, surface area magnification, and scale effect. This system can be used to characterize the comprehensive geometric features of an interface. Computational analysis was performed using data from two typical interfaces.

[0171] 3) Regarding the theoretical integration and engineering application of interfacial bonding, this application proposes a unified roughness-bond semi-empirical modeling framework: decomposing the roughness contribution into an effective contact factor and a mechanical interlocking factor, and introducing infillability penalty and time penalty to uniformly characterize the "non-monotonic effect caused by insufficient infillability" and the "re-fusion attenuation caused by interlayer time interval" in the interface between new and old concrete and the interface between 3D printed layers. Based on this, an effective roughness is defined, providing a calculable variable for subsequent strength trend aggregation and process parameter inference across literature data.

[0172] 4) The calculation example based on existing literature data gives the calibration path of the time penalty characteristic constant: using the average bond strength at different times in the literature, the characteristic time constant of the material is calculated in reverse through the exponential decay form, thereby realizing the mapping of "same geometric roughness - different time intervals - different effective roughness", providing a reproducible process for converting discrete test data into unified model parameters.

[0173] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for measuring the surface roughness of 3D-printed concrete interfaces oriented towards interfacial bonding, characterized in that, include: S1. Take multi-angle photos of the 3D printed concrete interface to be tested, construct the original point cloud using a multi-view stereo algorithm, preprocess the original point cloud, and construct a roughness field based on the preprocessed point cloud. S2, Based on the roughness field, define a roughness index system and the calculation method of each index, wherein the roughness index system includes interface undulation height index, interface tilt angle index, interface area index and interface multi-scale index. S3. Based on the roughness index system, a roughness-bond semi-empirical model for multiple working conditions is constructed. The roughness-bond semi-empirical model decomposes the roughness contribution into an effective contact factor and a mechanical interlocking factor, and introduces fillable penalty and time penalty to uniformly characterize the non-monotonic effect caused by insufficient fillable in the interface between new and old concrete and the interface between 3D printed layers, as well as the re-fusion attenuation caused by the interlayer time interval. S4. Calculate the effective roughness based on the roughness-bond semi-empirical model. The effective roughness is used to quantitatively characterize the influence of the surface roughness of the concrete interface on the bond performance. In step S1, a roughness field is constructed based on the preprocessed point cloud, including: For each measurement point in the point cloud, a fast neighborhood search is performed using a KD-tree to obtain a spherical neighborhood. ; Based on the spherical neighborhood The local reference plane for each point is fitted using the least squares method; Based on the local reference plane, the normal height deviation of each point is defined as: ， Global reference direction Based on this, the local normal tilt angle is defined as: ， In the formula, For point Normal height deviation, For the spherical neighborhood The center of mass, The normal vector of the local reference plane. For point The local normal angle at that location; In step S2, the interface undulation height index includes: arithmetic mean height. Root mean square height Height range and height quantile index; The interface tilt angle indexes include: average slope. Root mean square slope Slope dispersion Among them, slope dispersion The calculation formula is as follows: ， In the formula, This represents the total number of interface measurement points. The local normal angle; The interface area index specifically refers to the surface area ratio. The calculation formula is as follows: ， In the formula, This represents the actual three-dimensional surface area of ​​the concrete interface. for The projection onto the local reference plane; The interface multi-scale index is characterized by a multi-scale roughness curve, which is obtained as follows: [The text abruptly shifts to a different topic] ...within multiple window radii... Repeatedly construct local neighborhoods and calculate the arithmetic mean height of the entire field. The function curve of interface roughness as a function of sampling scale is obtained.

2. The method according to claim 1, characterized in that, The expression for the effective contact factor is as follows: ， In the formula, Indicates interface roughness; Indicates the magnification factor of the interface area; This indicates that a penalty item can be filled. This indicates a time interval penalty.

3. The method according to claim 2, characterized in that, The formula for calculating the fillable penalty term is as follows: ， In the formula, The characteristic peak and valley heights are determined by the fillability. This indicates a significant difference in altitude.

4. The method according to claim 2, characterized in that, The formula for calculating the time interval penalty term is as follows: ， In the formula, For printing time intervals, This is the characteristic time constant.

5. The method according to claim 2, characterized in that, The expression for the mechanical occlusion factor is as follows: ， In the formula, The root mean square height; , which is the surface area ratio, used to characterize the magnification factor of the interface area; This indicates the mechanical occlusion factor.

6. The method according to claim 5, characterized in that, The formula for calculating the effective roughness is as follows: ， In the formula, Indicates the effective roughness. This represents the arithmetic mean height.

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