Concrete self-repairing method based on topological optimization conduit structure

Abstract

The invention discloses a concrete self-repairing method based on a topological optimization conduit structure, which comprises the following steps: step 1, carrying out topological optimization design on a concrete beam structure under the action of a load, extracting a main tensile stress nephogram of the optimized structure, and carrying out bionic conduit arrangement on a tensile area of the structure; 2, a bionic catheter structure is prepared based on the 3D printing technology; 3, concrete is poured, urease and a nutrient solution are adopted as repairing agents, calcium carbonate precipitates are formed through the urease induced mineralization effect, and accurate repairing of concrete cracks is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of concrete structures, and in particular relates to a concrete self-repairing method based on a topologically optimized conduit structure. Background Art

[0002] Concrete has been widely used in the field of construction engineering due to its high compressive strength and low cost. It is currently the largest and most widely used building material. Since concrete is a typical porous and brittle material, cracks will inevitably appear during use, providing channels for moisture and harmful chemical components to enter the interior of the concrete, which will accelerate the cracking and erosion of the internal steel bars, greatly reducing the functionality and service life of the concrete structure and increasing maintenance costs. Therefore, how to repair cracks in various types of concrete buildings in a timely and efficient manner is the main problem facing us today.

[0003] Existing self-repairing technology solutions generally use microcapsules, microorganisms, hollow fiber tubes, etc. as carriers of repair agents. The microcapsule self-repair method is to inject the repair agent into the hollow microcapsules, and mix the microcapsules containing the repair agent into the concrete material. When cracks occur in the concrete structure, the microcapsules rupture and the repair agent flows out for repair. The microbial self-repair method is to fill bacteria into porous particles. When the concrete cracks, the bacteria are exposed to the external environment, causing microorganisms to induce calcium precipitation to repair the cracks. The hollow fiber tube self-repair method is to wax-seal the hollow fiber tube containing adhesive and pre-embed it in the concrete. When the concrete cracks, the concrete is heated to cause the wax seal layer to melt, and the adhesive flows out and solidifies to fill the cracks.

[0004] First, compared with the microcapsule self-repair method, the 3D printed bionic catheter self-repair method directly places the bionic catheter in the tensile zone of the concrete structure, and bears the force together with the concrete. When cracks appear in the concrete, the bionic catheter will crack accordingly, allowing the repair agent to flow into the matrix for repair. It is more accurate than the microcapsule self-repair method in positioning and has a higher efficiency in targeted repair. In addition, the patent comparisons and differences with other similar devices are as follows:

[0005] 1. CN113185230A A microbial positioning self-repairing concrete material suitable for structural tension zones and its preparation method

[0006] Difference: This method adsorbs the microbial repair liquid on the mesh cloth, fixes the mesh cloth on the edge of the concrete tensile surface mold, pours the concrete and removes the mold to obtain microbial positioning self-repairing concrete.

[0007] Advantages: The 3D printing method adopted in this patent considers the structural stress conditions, designs the conduit structure by the size of the principal tensile stress inside the structure, and arranges it at the principal tensile stress position where cracks may form, including the tension and oblique shear area at the bottom of the beam structure, with more accurate positioning and more reasonable distribution. Direct extraction of urease to induce calcium carbonate precipitation eliminates the process of microbial urease generation, making repair faster and more efficient, and the generated calcium carbonate precipitation more stable.

[0008] 2. CN217461588U A 3D printed internal tube for concrete self-repair

[0009] Difference: In this method, the layout position of the 3D printed built-in tube is set in the tension zone, and the form of the built-in tube is artificially selected.

[0010] Advantages: This patent takes into account that cracks in concrete structures are caused by excessive tensile stress. Through topological optimization results and combined with the main tensile stress, the conduit structure is arranged, and the design is more reasonable.

[0011] 3. CN117140723A Preparation of experimental components of self-repairing concrete based on fiber glue tube

[0012] Difference: This patent adopts a multi-section structure design inside the fiber glue tube, which can prevent the repair agent from flowing back or overflowing and wasting when the fiber glue tube is damaged by tension, making the concrete self-repair efficiency higher.

[0013] Advantages: The patented 3D printed catheter has a more reasonable structural layout, and the separate chamber makes it easier to store urease solution and nutrient solution. It can more effectively self-repair cracks at a lower cost.

[0014] However, the existing catheter technology treatment measures have low material utilization rates, and the catheter selection is mostly artificially set, the structural setting lacks rationality, and the repair effect is average. Summary of the invention

[0015] The technical problem to be solved by the present invention is to provide a concrete self-repair method based on a topologically optimized conduit structure. Based on an improved topological optimization algorithm, the main tensile stress area of ​​the optimized structure is considered, and the 3D printed bionic conduit is arranged in the main tensile stress area to achieve precise repair of cracks.

[0016] To achieve the above object, the present invention adopts the following technical solution:

[0017] A concrete self-repair method based on topological optimization conduit structure extracts the main tensile stress area of ​​the concrete structure based on the topological optimization algorithm, arranges the 3D printed bionic conduit in the main tensile stress area, and realizes precise repair of cracks.

[0018] The present invention also provides a concrete self-repairing method based on a topologically optimized conduit structure, comprising:

[0019] Step 1: Arrange the bionic conduit in the tension zone of the structure according to the distribution of the principal tensile stress of the concrete beam structure under load;

[0020] Step 2: preparing a bionic catheter structure based on 3D printing technology;

[0021] Step 3: pour concrete, use urease and nutrient solution as repair agents, and form calcium carbonate precipitation through urease-induced mineralization to achieve precise repair of concrete cracks.

[0022] Preferably, in step 1, the concrete structure is optimized by topological optimization, and the conduit structure is arranged according to the main tensile stress area of ​​the optimized structure.

[0023] Preferably, in step 2, polylactic acid material is used to print the catheter structure.

[0024] Preferably, in step 3, urea in the nutrient solution is hydrolyzed by urease solution and reacted with calcium ions to form calcium carbonate precipitate, and the specimen is placed at room temperature for 24 hours to completely solidify it, thereby achieving precise repair of concrete cracks.

[0025] Preferably, the urease solution is prepared as follows: select soybeans with full grains and put them into a drying oven for 24 hours; put the dried soybeans into a high-speed grinder and grind them into powder, then mix the soybean powder with 30% ethanol to make a 100 g / L solution, and after fully mixing, put the solution into a centrifuge and centrifuge it at a speed of 3000 r / min for 10 minutes; then filter the supernatant with a semipermeable membrane to remove impurities; the solution obtained after the above operations is completed is the urease solution.

[0026] Preferably, the formula of the nutrient solution is: the ratio of calcium chloride to urea is 1:1, and the concentration of calcium chloride to urea is 0.5-1.0 mol / L.

[0027] Preferably, the cross-section of the conduit structure is provided with a variable-section outer wall and a "V"-shaped notch, so that under tension, the cracking direction of the conduit structure occurs radially, the two chambers can crack synchronously, urease and nutrient solution flow out, and react to generate calcium carbonate to repair concrete.

[0028] Preferably, the printing direction is to print layer by layer along the length direction of the catheter; for the oblique catheter structure, Tuozhu PLA-SUPPORT material is used as the tree-like support structure.

[0029] The present invention uses a topology optimization algorithm, considers the distribution of the principal tensile stress of the concrete beam structure under load, arranges bionic conduits in the tensile zone of the structure, and prepares the bionic conduit structure based on 3D printing technology. At the same time, concrete is poured, and calcium carbonate precipitation is formed through urease-induced mineralization to achieve precise repair of concrete cracks. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0031] Figure 1 It is a flow chart of a concrete self-repairing method based on a topologically optimized conduit structure according to an embodiment of the present invention;

[0032] Figure 2 This is the topology optimization result diagram;

[0033] Figure 3 is a cross-sectional view of the catheter structure;

[0034] Figure 4 Layout diagram for concrete crack repair. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] Embodiment 1:

[0038] like Figure 1 As shown, an embodiment of the present invention provides a concrete self-repairing method based on a topologically optimized conduit structure, comprising:

[0039] Step S1: Extracting the main tensile stress area of ​​the concrete structure based on the topology optimization algorithm

[0040] A concrete geometric model (size 40mm*40mm*160mm) was established; the concrete elastic modulus and Poisson's ratio and other material properties were set; a simply supported displacement boundary condition was set at 10mm from the bottom of the bending beam to the cross section at both ends, and a vertical concentrated force load was applied at 1 / 4 and 3 / 4 of the top of the bending beam along the longitudinal direction; the mesh size of the concrete specimen was 1mm; the topology optimization objective function was set to minimize strain energy, see formulas (1) and (2); the constraint condition was set to optimize the volume to 0.5 of the original volume, and the load area and boundary condition area were frozen so that they were not optimized. The solid isotropic structural material penalty method (SIMP method) was used for topology optimization, see formula (3), the minimum density was set to 0.001 (remove material) to prevent the stiffness matrix from being singular, the maximum density was 1 (fill material), the penalty function coefficient was set to 3, and the number of iterations was 200. Optimization process: Construct the overall stiffness matrix of the structure, see formula (4) and (5); establish the density interpolation and homogenization relationship between adjacent units through the filter radius, see formula (6) and (7); solve the objective function, and use the derivative of the objective function with respect to the unit density as the sensitivity analysis, see formula (8), determine the degree of influence of a certain unit density on the objective function through the numerical value in the sensitivity analysis, and perform unit deletion operations; combine the optimal criterion method to set the circulation space for the structure, update the unit density according to the volume control condition, and homogenize the unit density according to the density filter function to achieve the optimal design. The topology optimization is completed through the above process, and the unit stress is obtained according to the optimized structural stress, see formula (9), and the unit stress cloud map is constructed to determine the axial tensile and compressive stresses in the overall coordinate system, and the bionic catheter structure is arranged in the main tensile stress area, such as Figure 2 shown.

[0041] minimize c=FTU(x) (1)

[0042] F=K(x)U(x) (2)

[0043]

[0044] H ij =R-dist(i,j) (7)

[0045]

[0046] σ=C 0 BU(x) (9)

[0047] Where, in formula (1), c is the objective function, F is the node force vector, and U(x) is the node displacement vector. In formula (2), K(x) is the stiffness matrix of the 8-node hexahedral unit. Formula (3) is the modified SIMP method, E minis the Young's modulus of the unfilled material, which is set to 0.001 to prevent the stiffness matrix from being singular. i is the cell density of the i-th cell, E0 is the Young's modulus of the filled material, which is set to 1; p is the penalty coefficient, which is set to 3, so that the density of the intermediate cells is reduced and the cell density value tends to 0 or 1. In formula (4), the cell stiffness matrix is ​​solved, C 0 is the unit constitutive matrix, B is the unit strain matrix, and x, y, z are the unit coordinate systems. In formula (5), the overall stiffness matrix is ​​assembled from the unit stiffness matrix. In formula (6), is the density filter function, N i is the total number of cells adjacent to the i-th cell within the filter radius R, H ij is the weight coefficient of the i-th unit to the j-th unit, x j is the density of the jth unit, v j is the volume of the jth unit. The density filter function is used to prevent the occurrence of checkerboard or grid dependence. In formula (7), the weight coefficient H is determined ij , R is the filter radius, which is set according to the size of the structure, and dist(i, j) represents the distance between the i-th unit and the j-th unit. In formula (8), the derivative of the objective function with respect to the unit density is used as a sensitivity analysis. In formula (9), the unit stress is solved, C 0 The constitutive matrix, B is the element strain matrix, and U(x) is the node displacement vector.

[0048] Step S2: 3D printing the catheter structure

[0049] The 3D printer model used is Tuozhu X1E. The 3D printing parameter settings are: layer height 0.2mm, nozzle temperature 250℃, nozzle size 0.4mm, and printing speed 30mm / s. Figure 3 As shown, a catheter structure 2 is printed using polylactic acid (PLA) material. Combined with the topology optimization results, catheters with different diameters are designed for different sizes of the main tensile stress region. The outer diameter of the large catheter is 6 mm, and a vertical spacer layer 4 (such as Figure 3 As shown), the layer thickness is 0.5mm, the chamber adopts arc surface design, the chord length is 4mm, the starting and ending points of the arc segment are 1mm away from the outer wall, and the midpoint of the arc segment is 1.5mm away from the outer wall; the outer diameter of the small catheter is 3mm, and a vertical spacing layer 4 (as shown) is set Figure 3 As shown), the layer thickness is 0.5mm, the chamber adopts arc surface design, the chord length is 2mm, the arc segment start and end points are 0.5mm away from the outer wall, and the arc segment midpoint is 0.7mm away from the outer wall. A "V"-shaped notch 7 is provided at the bottom of the catheter structure, the notch width is 0.5mm, and the depth is 0.3mm. Figure 3As shown. The design of the variable cross-section outer wall and the "V"-shaped notch is to make the catheter structure crack radially under tension, so that the two chambers can crack synchronously, and the repair agent can flow out and react to avoid the phenomenon that only one side of the chamber cracks and reduces the repair efficiency. The printing direction is to print layer by layer along the length of the catheter to ensure that the normal direction of the interface between the printed layers is consistent with the direction of the main tensile stress, so that the interface between the bionic catheter is easy to crack under tension to improve the repair efficiency. For the inclined catheter structure, due to the inconsistent height of the bottom interface, Tuozhu PLA-SUPPORT material is used as a tree-like support structure to ensure that the normal direction of the interface between the printed layers of the inclined catheter is consistent with the direction of the oblique shear stress. The support can be manually removed directly after printing. The highest branch catheter of the catheter structure along the height direction of the concrete beam structure extends to the top, which is convenient for adding urease and nutrient solution.

[0050] Step S3: preparing urease solution and nutrient solution (i.e., mixed solution of urea and calcium chloride)

[0051] First, prepare the urease solution: select soybeans with full grains and put them into a drying oven for 24 hours. Put the dried soybeans into a high-speed grinder and grind them into powder. Then, mix the soybean powder with 30% ethanol to make a 100g / L solution. After fully mixing, put the solution into a centrifuge and centrifuge it at 3000r / min for 10 minutes. Then filter the supernatant with a semipermeable membrane to remove impurities. The solution obtained after the above operation is completed is the urease solution. After the preparation is completed, it is loaded into the urease solution chamber 6 (such as Figure 3 Next, prepare a nutrient solution, the formula ingredients are calcium chloride (0.5-1.0 mol / L) and urea (0.5-1.0 mol / L), the ratio of calcium chloride to urea is 1:1, and after preparation, put it into the nutrient solution chamber 6 (as shown in Figure 3 shown).

[0052] Step S4: Concrete pouring

[0053] The mix ratio is 550:650:550:395 for cement:fly ash:sand:water. The cement used is Portland cement with a strength of 42.5MPa. The sand particle size range is 0.125-0.25mm, which is first-class sand. Put the cement, fly ash and sand into the mixer and dry mix for 4 minutes. Add water and mix for 4 minutes. First, fix the conduit 2 structure in the mold (the size is 40mm*40mm*160mm). When printing the conduit structure, print 2 support structures 3 with a diameter of 1mm and a height of 4mm at the bottom of the conduit to fix the position of the conduit structure in the concrete matrix 1 to ensure that the conduit structure is accurately positioned during the pouring process, such as Figure 4 Then pour concrete to fill the mold, cover the surface with plastic wrap and sprinkle water, put it in a curing chamber (96% ± 2% RH, 20 ± 2°C) for 28 days and then remove the mold.

[0054] Step S5: Concrete self-repair

[0055] The concrete structure was subjected to a bending test. Cracks appeared at the bottom of the concrete structure. The cracks developed to the point where the conduit was exposed to the environment, and the test was stopped. The urease solution and nutrient solution in the two chambers flowed out. Urease hydrolyzed the urea in the nutrient solution and reacted with calcium ions to form calcium carbonate precipitation. The specimen was placed at room temperature for 24 hours to fully solidify.

[0056] In the embodiment of the present invention, the concrete structure is optimized by topological optimization, and the conduit structure is arranged according to the main tensile stress area of ​​the optimized structure. The conduit distribution range is wider and the accuracy of the possible crack location is higher. The conduit structure is integrally formed by 3D printing equipment, and the structure has good integrity. The PLA printing structure is used, and the cost is lower. The inside of the conduit is divided into two chambers, each containing urease solution and nutrient solution to prevent the reaction of the two from blocking the conduit.

[0057] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A concrete self-repair method based on topological optimization conduit structure, characterized in that: Based on the topology optimization algorithm, the main tensile stress area of ​​the concrete structure is extracted, and the 3D printed bionic catheter is arranged in the main tensile stress area to achieve precise repair of cracks.

2. A concrete self-repair method based on topological optimization conduit structure, characterized in that: include: Step 1: Arrange the bionic conduit in the tension zone of the structure according to the distribution of the principal tensile stress of the concrete beam structure under load; Step 2: preparing a bionic catheter structure based on 3D printing technology; Step 3: pour concrete, use urease and nutrient solution as repair agents, and form calcium carbonate precipitation through urease-induced mineralization to achieve precise repair of concrete cracks.

3. The concrete self-repairing method based on topology optimization conduit structure according to claim 2 is characterized in that: In step 1, the concrete structure is optimized by topological optimization, and the conduit structure is arranged according to the main tensile stress area of ​​the optimized structure.

4. The concrete self-repairing method based on topology optimization conduit structure according to claim 3 is characterized in that: In step 2, the catheter structure is printed using polylactic acid material.

5. The concrete self-repairing method based on topological optimization conduit structure according to claim 4 is characterized in that: In step 3, the urea in the nutrient solution is hydrolyzed by urease solution and reacts with calcium ions to form calcium carbonate precipitate. The specimen is placed at room temperature for 24 hours to completely solidify it, thereby achieving precise repair of concrete cracks.

6. The concrete self-repairing method based on topology optimization conduit structure according to claim 5, characterized in that: The urease solution is prepared as follows: select soybeans with full grains and put them into a drying oven for 24 hours; put the dried soybeans into a high-speed grinder and grind them into powder, then make a 100g / L solution of the soybean powder and 30% ethanol, and after fully mixing, put the solution into a centrifuge and centrifuge it at a speed of 3000r / min for 10 minutes; then filter the supernatant with a semipermeable membrane to remove impurities; the solution obtained after the above operations are completed is the urease solution.

7. The concrete self-repairing method based on topological optimization conduit structure according to claim 6 is characterized in that: The formula of the nutrient solution is: the ratio of calcium chloride to urea is 1:1, and the calcium chloride and urea are 0.5-1.0 mol / L.

8. The concrete self-repairing method based on topological optimization conduit structure according to claim 7, characterized in that: The cross section of the conduit structure is provided with a variable cross-section outer wall and a "V"-shaped notch, so that under the action of tension, the cracking direction of the conduit structure occurs radially, the two chambers can crack synchronously, urease and nutrient solution flow out, and react to generate calcium carbonate to repair concrete.

9. The concrete self-repairing method based on topology optimization conduit structure according to claim 7, characterized in that: The printing direction is to print layer by layer along the length of the catheter; for the oblique catheter structure, Tuozhu PLA-SUPPORT material is used as the tree-like support structure.

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