A design method of a carrier for a core-shell type repair agent for concrete crack self-repair

Abstract

The application discloses a design method of a core-shell type repairing agent carrier for concrete crack self-repairing. The method belongs to the technical field of building materials and is based on the strength grade of applied concrete, the crack width, the crack area and the repairing component parameters, and a core-shell carrier with the inner and outer radii, the elastic modulus and the particle strength matched with the matrix concrete is designed based on the loading capacity and the mechanical response principle. The specific design steps are as follows: the inner radius of the core-shell structure carrier is determined based on the loading capacity design; the suitable outer radius of the carrier is determined according to the regional stress field distribution characteristics; the suitable elastic modulus of the carrier is determined according to the material parameters of the matrix concrete; and the particle strength design value of the core-shell carrier is determined according to the above parameters. The carrier designed by the method has reasonable loading capacity, is matched with the parameters of the concrete matrix and has no negative influence on the matrix strength.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology and relates to a design method for a core-shell type cement-based material carrier. Specifically, it relates to a design method for a cement-based carrier for concrete that is compatible with the concrete matrix and has no negative mechanical impact on the matrix, namely, a design method for a carrier of a core-shell type repair agent for self-healing of concrete cracks. Background Technology

[0002] Concrete, as one of the main engineering materials, will remain irreplaceable in the foreseeable future. As a brittle material, concrete is susceptible to cracking due to environmental factors during service. Microbial self-healing technology is an effective solution for self-diagnosis and self-healing of cracks, effectively avoiding the difficulties in detection and the inability to guarantee repair results associated with traditional passive repair methods.

[0003] Concrete has a dense porous structure, and its hydration products have a pH value exceeding 12.5, which is unfavorable for the long-term survival of microorganisms and severely affects their activity. To extend the survival time of microorganisms in concrete, carriers are generally used to load and protect them. Common carriers include porous materials and core-shell hollow particles, among which core-shell carriers have significant advantages in long-term protection. Typically, components with repair capabilities, such as microorganisms, calcium sources, and carbon sources, are embedded in the "core" of core-shell particles, which are then covered with a protective material as the "shell" to protect the microorganisms. Therefore, the "core" of the core-shell carrier must have a certain loading capacity for the repair components. Simultaneously, after being incorporated into concrete, the "shell" should maintain an immediate response capability to cracks, releasing the internal repair components. Furthermore, core-shell repair agents should not negatively impact the mechanical properties of concrete. However, there is currently no reference on how to design a carrier that matches the matrix concrete while ensuring both the loading capacity for the repair components and the efficient response capability to cracks. Summary of the Invention

[0004] To address the lack of design guidelines for core-shell carriers suitable for concrete, this invention provides a design method for a carrier of a core-shell repair agent for self-healing concrete cracks. This method ensures the repair effect while avoiding negative impacts on the substrate, and also provides immediate response to cracks.

[0005] The technical solution of this invention: The present invention provides a design method for a carrier of a core-shell type repair agent for self-healing concrete cracks. Based on the applied concrete strength grade, crack width, crack area, and repair component parameters, and according to the principles of load capacity and mechanical response, a core-shell carrier with matching inner and outer radii, elastic modulus, and particle strength to the matrix concrete is designed. The specific design steps are as follows:

[0006] Step 1: Based on the load-bearing capacity design, determine the inner radius of the core-shell structure carrier;

[0007] Step 2: Determine the appropriate outer radius of the carrier based on the regional stress field distribution characteristics;

[0008] Step 3: Based on the material parameters of the base concrete, design and determine a suitable carrier elastic modulus;

[0009] Step 4: Based on the above parameters, determine the design value of the core-shell carrier particle strength.

[0010] Furthermore, in step one, the specific determination of the inner radius of the core-shell carrier is as follows:

[0011] The selected representative volume element has a side length of L, and the width of the crack to be repaired is w. sc The volume of the product generated by the reaction of the repair components increases by a factor of k. co The degree of crack repair η;

[0012] The specific operation process is as follows:

[0013] First, calculate the crack area according to formula (1):

[0014] S c =L×L (1)

[0015] In the formula, S c The crack area is represented by L; L represents the side length of the representative volume unit, which is usually taken as 100mm.

[0016] Furthermore, the relationship between the amount of carrier particles added and the inner radius of the core-shell carrier is determined according to equations (2) and (3), respectively:

[0017]

[0018] In the formula, n represents the amount of carrier added to the concrete; r i Indicates the inner radius of the carrier; η represents the degree of crack repair, which is generally taken as 0.2;

[0019] Finally, based on the relationship between the dosage and the inner radius determined by equations (2) and (3), the inner radius of the carrier can be determined by specifying the dosage.

[0020] When the inner radius determined according to formula (3) is negative, the inner radius determined according to formula (2) shall be taken as the final value. When the inner radius determined according to formula (3) is positive, the inner radius shall be taken as the final value.

[0021] Furthermore, in step one, when there is no actual data on the area of ​​the crack to be repaired in the concrete, the splitting crack of the most commonly used 100mm×100mm×100mm cube specimen in concrete is used as the design basis.

[0022] Therefore, the representative volume unit selected has a side length of 100mm.

[0023] Furthermore, in step one, the inner radius of the carrier used for design is ≤5.0mm.

[0024] Furthermore, in step two, determining the outer radius of the core-shell carrier specifically involves:

[0025] Based on the inner radius of the carrier determined in step one, the maximum stress concentration factor of the carrier is calculated according to equation (4), and the maximum stress concentration factor of the concrete matrix is ​​calculated according to equation (5):

[0026]

[0027] In the formula, K i K represents the maximum stress concentration factor of the carrier. o Indicates the maximum stress concentration factor of the concrete matrix; α2, α 22 and α 24 For the parameter terms, calculate according to equations (6), (7), and (8) respectively:

[0028]

[0029] In the formula, E i E represents the elastic modulus of the carrier material. o ν represents the elastic modulus of the matrix material; ν represents the fluctuation ratio, which is generally taken as 0.2; Ω is calculated according to formula (9);

[0030] For cement-based material carriers applied in concrete, if no measured data is available, the elastic modulus is taken as 24 GPa for C30 concrete, 25 GPa for C40 concrete, 27 GPa for C50 concrete, 29 GPa for C60 concrete, and 31 GPa for C70 concrete, with the carrier calculated at 20 GPa. The specific formula is as follows:

[0031]

[0032] Substitute different carrier outer radii into equation (5) to calculate the maximum stress concentration factor of the matrix. When the maximum stress concentration factor of the matrix is ​​not greater than 1.4, the carrier outer radius at this time is taken as the final value.

[0033] Furthermore, given the determined inner and outer radii of the carrier, the maximum stress concentration factor of the carrier is calculated according to formula (4), and the maximum stress concentration factor of the matrix is ​​calculated according to formula (5). The ratio of the maximum stress concentration factor of the carrier to the maximum stress concentration factor of the matrix is ​​the ratio of their tensile strengths. When the tensile strength of the matrix is ​​known, the design tensile strength of the carrier material can be determined.

[0034] Furthermore, in step two, the outer radius design method is applicable to concrete with strength grades of C30-C70.

[0035] Furthermore, in step three: the calculation to determine the carrier's elastic modulus specifically involves:

[0036] Based on the determined inner and outer radii of the carrier and the known concrete strength grade C, the elastic modulus that the carrier should possess at different ages is calculated according to formula (10):

[0037]

[0038] In the formula, C represents the concrete strength grade; t represents the age; β1, β2, β3 and β4 are parameter terms, which are calculated and determined according to formulas (11), (12), (13) and (14) respectively:

[0039]

[0040] In the formula, λ represents the ratio of the tensile strength of the carrier material to the tensile strength of the matrix material;

[0041] The maximum stress concentration factor of the matrix is ​​verified by substituting the calculated elastic modulus of the carrier into equation (5).

[0042] If the maximum stress concentration factor exceeds 1.4, appropriately increase the outer radius of the shell to reduce the maximum stress concentration factor of the matrix; finally, determine the shell thickness.

[0043] Furthermore, in step four: the calculation to determine the strength of the carrier particles is:

[0044] Based on the calculated inner diameter, shell thickness, and elastic modulus of the core-shell carrier, the strength of the carrier particles matching the matrix is ​​calculated according to formula (15).

[0045]

[0046] In the formula, F STR Indicates particle strength; D f This represents the shell deflection, twice the amount of carrier deformation; t shell Indicates the shell thickness, and the difference between the outer and inner radii; ν shell This represents the Poisson's ratio of the shell; for cement-based materials, it is generally taken as 0.2.

[0047] According to formula (15), the particle strength that the carrier should have at different ages to match concrete of a specific strength grade can be determined, and it can be used to guide the preparation of the carrier.

[0048] The beneficial effects of this invention are as follows: Features of this invention: 1. It proposes a design method for core-shell carriers, which can provide guidance for the preparation of carriers applied to different types of concrete; 2. By reverse-engineering the carrier size through load capacity, the crack repair effect is guaranteed; 3. The carrier based on mechanical response design can accurately respond to cracks, while greatly reducing the negative impact on the matrix. Attached Figure Description

[0049] Figure 1 This is a flowchart of the design method of the present invention. Detailed Implementation

[0050] To more clearly illustrate the technical solution of the present invention, the technical solution of the present invention will be further described in detail below with reference to the accompanying drawings:

[0051] The present invention discloses a design method for a carrier of a core-shell repair agent for self-healing concrete cracks. Based on the applied concrete strength grade, crack width, crack area, and repair component parameters, and according to the principles of load-bearing capacity and mechanical response, a core-shell carrier with matching inner and outer radii, elastic modulus, and particle strength to the matrix concrete is designed. The specific design steps are as follows:

[0052] Step 1: Based on the load-bearing capacity design, determine the inner radius of the core-shell structure carrier;

[0053] Step 2: Determine the appropriate outer radius of the carrier based on the regional stress field distribution characteristics;

[0054] Step 3: Based on the material parameters of the base concrete, design and determine a suitable carrier elastic modulus;

[0055] Step 4: Based on the above parameters, determine the design value of the core-shell carrier particle strength;

[0056] (Another form of its expression) is:

[0057] 1. Based on the characteristics of the repair components used and the parameters of the concrete matrix, design the load-bearing capacity of the carrier and the inner radius of the carrier;

[0058] 2. Calculate the stress concentration factors of the carrier and the substrate to ensure that the maximum stress concentration factor of the substrate is within the range of 1.0-1.4, and obtain a suitable shell thickness;

[0059] 3. Based on the calculated inner diameter and shell thickness of the core-shell carrier, calculate the elastic modulus of the carrier and verify the maximum stress concentration factor of the matrix.

[0060] Furthermore, in step one, the specific determination of the inner radius of the core-shell carrier is as follows:

[0061] The selected representative volume element has a side length of L, and the width of the crack to be repaired is w.sc The volume of the product generated by the reaction of the repair components increases by a factor of k. co The degree of crack repair η;

[0062] The specific operation process is as follows:

[0063] First, calculate the crack area according to formula (1):

[0064] S c =L×L (1)

[0065] In the formula, S c The crack area is represented by L; L represents the side length of the representative volume unit, which is usually taken as 100mm.

[0066] Furthermore, the relationship between the amount of carrier particles added and the inner radius of the core-shell carrier is determined according to equations (2) and (3), respectively:

[0067]

[0068] In the formula, n represents the amount of carrier added to the concrete; r i Indicates the inner radius of the carrier; η represents the degree of crack repair, which is generally taken as 0.2;

[0069] Finally, based on the relationship between the dosage and the inner radius determined by equations (2) and (3), the inner radius of the carrier can be determined by specifying the dosage.

[0070] When the inner radius determined according to formula (3) is negative, the inner radius determined according to formula (2) shall be taken as the final value. When the inner radius determined according to formula (3) is positive, the inner radius shall be taken as the final value.

[0071] Furthermore, in step one, when there is no actual data on the area of ​​the crack to be repaired in the concrete, the splitting crack of the most commonly used 100mm×100mm×100mm cube specimen in concrete is used as the design basis.

[0072] Therefore, the representative volume unit selected has a side length of 100mm.

[0073] Furthermore, in step one, the inner radius of the carrier used for design is ≤5.0mm.

[0074] Furthermore, in step two, determining the outer radius of the core-shell carrier specifically involves:

[0075] Based on the inner radius of the carrier determined in step one, the maximum stress concentration factor of the carrier is calculated according to equation (4), and the maximum stress concentration factor of the concrete matrix is ​​calculated according to equation (5):

[0076]

[0077]

[0078] In the formula, K i K represents the maximum stress concentration factor of the carrier. o Indicates the maximum stress concentration factor of the concrete matrix; α2, α 22 and α 24 For the parameter terms, calculate according to equations (6), (7), and (8) respectively:

[0079]

[0080] In the formula, E i E represents the elastic modulus of the carrier material. o ν represents the elastic modulus of the matrix material; ν represents the fluctuation ratio, which is generally taken as 0.2; Ω is calculated according to formula (9);

[0081] For cement-based material carriers applied in concrete, if no measured data is available, the elastic modulus is taken as 24 GPa for C30 concrete, 25 GPa for C40 concrete, 27 GPa for C50 concrete, 29 GPa for C60 concrete, and 31 GPa for C70 concrete, with the carrier calculated at 20 GPa. The specific formula is as follows:

[0082]

[0083] Substitute different carrier outer radii into equation (5) to calculate the maximum stress concentration factor of the matrix. When the maximum stress concentration factor of the matrix is ​​not greater than 1.4, the carrier outer radius at this time is taken as the final value.

[0084] Furthermore, given the determined inner and outer radii of the carrier, the maximum stress concentration factor of the carrier is calculated according to formula (4), and the maximum stress concentration factor of the matrix is ​​calculated according to formula (5). The ratio of the maximum stress concentration factor of the carrier to the maximum stress concentration factor of the matrix is ​​the ratio of their tensile strengths. When the tensile strength of the matrix is ​​known, the design tensile strength of the carrier material can be determined.

[0085] Furthermore, in step two, the outer radius design method is applicable to concrete with strength grades of C30-C70.

[0086] Furthermore, in step three: the calculation to determine the carrier's elastic modulus specifically involves:

[0087] Based on the determined inner and outer radii of the carrier and the known concrete strength grade C, the elastic modulus that the carrier should possess at different ages is calculated according to formula (10):

[0088]

[0089] In the formula, C represents the concrete strength grade; t represents the age; β1, β2, β3 and β4 are parameter terms, which are calculated and determined according to formulas (11), (12), (13) and (14) respectively:

[0090]

[0091] In the formula, λ represents the ratio of the tensile strength of the carrier material to the tensile strength of the matrix material;

[0092] The maximum stress concentration factor of the matrix is ​​verified by substituting the calculated elastic modulus of the carrier into equation (6).

[0093] If the maximum stress concentration factor exceeds 1.4, appropriately increase the outer radius of the shell to reduce the maximum stress concentration factor of the matrix; finally, determine the shell thickness.

[0094] Furthermore, in step four: the calculation to determine the strength of the carrier particles is:

[0095] Based on the calculated inner diameter, shell thickness, and elastic modulus of the core-shell carrier, the strength of the carrier particles matching the matrix is ​​calculated according to formula (15).

[0096]

[0097] In the formula, F STR Indicates particle strength; D f This represents the shell deflection, twice the amount of carrier deformation; t shell Indicates the shell thickness, and the difference between the outer and inner radii; ν shell This represents the Poisson's ratio of the shell; for cement-based materials, it is generally taken as 0.2.

[0098] According to formula (15), the particle strength that the carrier should have at different ages to match concrete of a specific strength grade can be determined, and it can be used to guide the preparation of the carrier.

[0099] The working principle of this invention is as follows: The load-bearing capacity design of the carrier is based on the probability distribution characteristics of the carrier on the crack surface and takes into account the 95% confidence requirement. That is, after the carrier with the load-bearing capacity design is added to the concrete, more than 95% of the cracks will be repaired. The outer radius of the carrier and the shell material parameters are designed based on the stress distribution. By designing a reasonable outer radius and elastic modulus, the stress distribution of the carrier and the substrate is controlled, thereby reducing the stress level borne by the substrate and reducing the negative impact on the substrate. At the same time, the cracking sequence of the carrier can be controlled to ensure that the carrier and the substrate crack synchronously.

[0100] Example 1

[0101] The repair agent has an expansion ratio of 2.5, and the required repair ratio for cracks is 20%.

[0102] Step 1: Calculate and determine the inner radius of the core-shell carrier.

[0103] According to Formula 1, for a cubic specimen with dimensions of 100mm × 100mm × 100mm, the crack area is 10000mm². 2 When the crack width is 0.5 mm, the crack volume is 5000 mm². 3 When the repair requirement is 20%, the crack filling volume is 1000 mm². 3 According to Equation 3, the relationship between the amount of particles added and the inner diameter is as follows:

[0104] n×r i =663400 (1)

[0105] When the number of particles is 620,000, the inner diameter of the particles is 1.07 mm.

[0106] Step 2: Calculate and determine the outer radius of the core-shell carrier.

[0107] Substituting the inner diameter of 1.07 mm, the elastic modulus of the carrier of 15 GPa, and the elastic modulus of the matrix of 25 GPa into Equation 5, the maximum stress concentration factor of the matrix is ​​1.35 when the shell thickness is 1.0 mm. Within an acceptable range, the shell thickness is determined to be 1.0 mm, that is, the outer radius of the core-shell carrier is 2.07 mm.

[0108] Step 3: Calculate and determine the elastic modulus of the core-shell carrier.

[0109] Based on the determined inner diameter and shell thickness, when the tensile strength of the carrier shell is twice the tensile strength of the matrix, the ratio of the carrier's elastic modulus to that of the matrix, determined by the ratios in Formulas 4 and 5, is 0.86. For concrete with a strength grade of 35 MPa, the upper limits of the elastic modulus of the carrier shell at 1d-7d, 14d, and 28d are 10.0 GPa, 15.3 GPa, 17.2 GPa, 18.0 GPa, 18.4 GPa, 18.7 GPa, 18.8 GPa, and 19.5 GPa, respectively.

[0110] Step 4: Calculate and determine the strength of core-shell carrier particles

[0111] The upper limits of particle strength calculated according to Equation 15 are 43.7N, 66.8N, 76.3N, 78.8N, 80.5N, 81.6N, 82.3N, 85.5N, and 86.9N, respectively. Furthermore, considering that the particle strength should be at least 70N to prevent excessive breakage during stirring, a particle strength of 76N is ultimately selected.

[0112] Finally, it should be understood that the embodiments described in this invention are only used to illustrate the principles of the embodiments of this invention; other variations may also fall within the scope of this invention; therefore, as examples rather than limitations, alternative configurations of the embodiments of this invention can be regarded as consistent with the teachings of this invention; correspondingly, the embodiments of this invention are not limited to the embodiments explicitly introduced and described in this invention.

Claims

1. A design method for a carrier of a core-shell type repair agent for self-healing of concrete cracks, characterized in that, The specific design steps are as follows: Step 1: Based on load-bearing capacity design, determine the inner radius of the core-shell structure carrier; specifically: The selected representative volume element has a side length of L, and the width of the crack to be repaired is w. sc The volume of the product generated by the reaction of the repair components increases by a factor of k. co The degree of crack repair η; The operation process is as follows: First, calculate the crack area according to formula (1): S c =L×L (1) In the formula, S c The crack area is represented by L; L represents the side length of the representative volume unit, which is 100 mm. Furthermore, the relationship between the amount of carrier particles added and the inner radius of the core-shell carrier is determined according to equations (2) and (3), respectively: In the formula, n represents the amount of carrier added to the concrete; r i Indicates the inner radius of the carrier; η represents the degree of crack repair, with a value of 0.2; Step 2: Determine the appropriate outer radius of the carrier based on the regional stress field distribution characteristics; specifically: Based on the inner radius of the carrier determined in step one, the maximum stress concentration factor of the carrier is calculated according to equation (4), and the maximum stress concentration factor of the concrete matrix is ​​calculated according to equation (5): In the formula, K i K represents the maximum stress concentration factor of the carrier. o Indicates the maximum stress concentration factor of the concrete matrix; α2, α 22 and α 24 For parameter items; Substitute different carrier outer radii into equation (5) to calculate the maximum stress concentration factor of the matrix. When the maximum stress concentration factor of the matrix is ​​not greater than 1.4, the carrier outer radius at this time is taken as the final value. In addition, given the determined inner and outer radii of the carrier, the maximum stress concentration factor of the carrier is calculated according to formula (4), and the maximum stress concentration factor of the matrix is ​​calculated according to formula (5). The ratio of the maximum stress concentration factor of the carrier to the maximum stress concentration factor of the matrix is ​​the ratio of their tensile strengths. When the tensile strength of the matrix is ​​known, the design tensile strength of the carrier material can be determined. Step 3: Based on the material parameters of the matrix concrete, design and determine a suitable elastic modulus of the carrier; specifically: Based on the determined inner and outer radii of the carrier and the known concrete strength grade C, the elastic modulus that the carrier should possess at different ages is calculated according to formula (6): In the formula, C represents the concrete strength grade; t represents the age; β1, β2, β3 and β4 are parameter terms; The maximum stress concentration factor of the matrix is ​​verified by substituting the calculated elastic modulus of the carrier into equation (5). If the maximum stress concentration factor exceeds 1.4, appropriately increase the outer radius of the shell to reduce the maximum stress concentration factor of the matrix; finally, determine the shell thickness. Step 4: Based on the above parameters, determine the design value of the core-shell carrier particle strength.

2. The design method of the carrier for a core-shell type repair agent for self-healing concrete cracks according to claim 1, characterized in that: In step one, when there is no actual data on the area of ​​the cracks to be repaired in the concrete, the splitting cracks of the 100mm×100mm×100mm cubic specimens used in the concrete are used as the design basis. Therefore, the representative volume unit selected has a side length of 100mm.

3. The design method of the carrier for a core-shell type repair agent for self-healing concrete cracks according to claim 1, characterized in that: In step one, the inner radius of the carrier used for design is ≤5.0mm.

4. The design method of the carrier for a core-shell type repair agent for self-healing concrete cracks according to claim 1, characterized in that, In step two, α2, α 22 and α 24 Calculate according to equations (7), (8), and (9) respectively: In the formula, E i E represents the elastic modulus of the carrier material. o ν represents the elastic modulus of the matrix material; ν represents the fluctuation ratio, which is usually taken as 0.2; Ω is calculated according to formula (10); For cement-based carriers applied in concrete, if no measured data is available, the elastic modulus is taken as 24 GPa for C30 concrete, 25 GPa for C40 concrete, 27 GPa for C50 concrete, 29 GPa for C60 concrete, and 31 GPa for C70 concrete, with the carrier calculated at 20 GPa, as shown in the following formula:

5. The design method of the carrier for a core-shell type repair agent for self-healing concrete cracks according to claim 1, characterized in that, In step two, the outer radius design method is applicable to concrete with strength grades of C30-C70.

6. The design method of the carrier for a core-shell type repair agent for self-healing concrete cracks according to claim 1, characterized in that, In step three: β1, β2, β3 and β4 are calculated and determined according to equations (11), (12), (13) and (14), respectively: In the formula, λ represents the ratio of the tensile strength of the carrier material to the tensile strength of the matrix material.

7. The design method of the carrier for a core-shell type repair agent for self-healing concrete cracks according to claim 1, characterized in that, In step four: the calculation to determine the strength of the carrier particles is: based on the calculated inner diameter, shell thickness and elastic modulus of the core-shell carrier, the strength of the carrier particles that match the matrix is ​​calculated according to formula (15); In the formula, F STR Indicates particle strength; D f This represents the shell deflection, twice the amount of carrier deformation; t shell Indicates the shell thickness, and the difference between the outer and inner radii; ν shell This represents the Poisson's ratio of the shell; for cement-based materials, it is typically taken as 0.

2. According to formula (15), the particle strength that the carrier should have at different ages to match concrete of a specific strength grade can be determined, and it can be used to guide the preparation of the carrier.

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