Method for evaluating crack resistance of cement-based material for reinforcing concrete column

Abstract

Provided is a method for evaluating crack resistance of a cement-based material for reinforcing a concrete column, related to the technical field of concrete. The method for evaluating crack resistance of a cement-based material for reinforcing a concrete column comprises: determining a material parameter and a size parameter of a ring restraint test apparatus; performing a ring restraint test, and monitoring circumferential strain development of an inner surface of a steel ring until a crack occurs in a concrete ring or the test continues to a duration of 28 days; and determining crack resistance of a reinforcing cement-based material. The method for evaluating crack resistance of a cement-based material for reinforcing a concrete column on the basis of a ring restraint test provides a quantitative calculation method for a degree of restraint and an equivalent method for evaluating a stress state of reinforced concrete under the restraint of a steel ring, and under the restraint of an existing concrete column, solving the problem that the tested restraint degree of crack resistance of a cement-based material for reinforcing an existing concrete column does not match an actual restraint degree; the method is simple, and accurate and effective in operation.

Description

Evaluation method for crack resistance of cement-based materials for reinforced concrete columns Technical Field

[0001] This disclosure relates to the field of concrete technology, and more specifically to a method for evaluating the crack resistance of cement-based materials for reinforcing concrete columns based on ring-constrained tests. Background Technology

[0002] Early cracking tests of concrete mainly include flat plate restricted shrinkage cracking test, prism restricted shrinkage cracking test and ring restricted shrinkage cracking test.

[0003] The stress state of the confined concrete in the flat plate type and prism type restricted shrinkage cracking test is far different from the actual stress state of the concrete in column reinforcement. The test results can only qualitatively evaluate the crack resistance of the concrete and cannot accurately predict the confined cracking of the reinforced concrete, thus failing to effectively guide the adjustment of concrete performance.

[0004] The stress state of concrete in the ring-type restricted shrinkage cracking test is consistent with the actual stress state of concrete when it is reinforced. Compared with other tests, it is the most direct way to reflect the shrinkage cracking performance of concrete under reinforcement constraints.

[0005] The conventional ring-confined test is a common ring-restrained shrinkage cracking test. It qualitatively assesses the crack resistance of different concrete types by measuring the cracking time under steel ring confinement. However, due to the relatively fixed size of the apparatus used in the conventional ring-confined test, it cannot reflect the confinement cracking of reinforced concrete columns with different diameters, thus having significant limitations.

[0006] Therefore, it is necessary to propose an equivalent method that can accurately reflect the actual constraint situation of concrete column reinforcement materials and a more scientific and reasonable method for quantitatively evaluating the cracking performance of concrete column reinforcement materials.

[0007] Summary of the Invention

[0008] In view of this, this disclosure provides a method for evaluating the crack resistance of cement-based materials for reinforcing concrete columns based on ring-constrained tests, in order to solve the problem that the test constraint degree of existing cement-based materials for reinforcing concrete columns does not match the actual constraint degree.

[0009] To achieve the above objectives, this disclosure provides a method for evaluating the crack resistance of cement-based materials used in the reinforcement of concrete columns, comprising: determining the material and dimensional parameters of the ring-constrained test apparatus; conducting a ring-constrained test, monitoring the development of circumferential strain on the inner surface of the steel ring until cracks appear in the concrete ring or the test is completed at 28 days; and determining the crack resistance of the reinforced cement-based material.

[0010] In the above scheme, determining the material parameters and dimensional parameters of the ring constraint test device includes:

[0011] S1: Based on the reinforcement scheme for the existing concrete column, obtain the material properties of the existing concrete column and the reinforcing cement-based material, including the radius r0, elastic modulus E3, and Poisson's ratio μ3 of the existing concrete column; the thickness h0, elastic modulus E1, Poisson's ratio μ1, shrinkage value ε0 (28d) corresponding to the age of the reinforcing cement-based material, and tensile strength f. t ;

[0012] S2: Determine the material parameters of the ring restraint test device, which includes a steel ring and a concrete ring. The steel ring is made of Q345 or higher grade steel, and the concrete ring is made of the cement-based reinforcing material described in the reinforcement scheme.

[0013] S3: Determine the dimensional parameters of the ring constraint test device, including the inner and outer surface radii and height of the steel ring and the concrete ring. The inner surface radius r1 and outer surface radius r2 of the steel ring are determined through constraint equivalence analysis. The inner surface radius of the concrete ring is the same as the outer surface radius r2 of the steel ring, and the thickness is the same as the thickness h0 of the reinforcing cement-based material in the reinforcement scheme. That is, the inner surface radius of the concrete ring is r2, and the outer surface radius is r2+h0.

[0014] In the above scheme, the inner surface radius r1 and outer surface radius r2 of the steel ring in step S3 are determined through constraint equivalence analysis, including:

[0015] S301: Initial determination of the inner surface radius r of the steel ring 1i and outer surface radius r 2j ;

[0016] S302: Calculate the circumferential stress σ of the reinforcing cement material in the reinforcement scheme for existing concrete columns. 0,θ (r,28d) and the average circumferential stress along the radial direction

[0017] S303: Calculate the circumferential stress σ of the concrete ring in the ring-constrained test. 1,θ (r,28d) and the average circumferential stress along the radial direction

[0018] S304: Calculate whether the relative error between the circumferential stress of the reinforcing cement material and the circumferential stress of the concrete ring in the ring restraint test in the existing concrete column reinforcement scheme is less than 5%. If so, determine the inner surface radius r of the steel ring in step S301. 1i and outer surface radius r 2jGiven the inner surface radius r1 and outer surface radius r2 of the steel ring in the ring-constrained test device, it is assumed that under this condition, the degree of constraint of the concrete ring in the ring-constrained test is the same as the degree of constraint of the cement material used to reinforce the existing concrete column. The constraint equivalence analysis is completed. If it is not satisfied, repeat steps S301-S304 until it is satisfied.

[0019] In the above scheme, the circumferential stress σ mentioned in step S302 0,θ (r,28d) includes the circumferential stress σ on the inner surface. 0,θ (r0,28d), circumferential stress σ on the outer surface 0,θ (r0+h0,28d), internal circumferential stress σ 0,θ (r0+h0 / 4,28d), σ 0,θ (r0+h0 / 2,28d)σ 0,θ (r0+h0×3 / 4,28d),

[0020] Step S302 involves calculating the circumferential stress σ of the reinforcing cement material in the existing concrete column reinforcement scheme. 0,θ (r, 28d), the calculation formula used is:

[0021] In Equation 1, E1 is the elastic modulus of the reinforced cement-based material, r is the radius of the calculation point, and σ is the circumferential stress on the inner surface. 0,θ In (r0,28d), r is taken as r0, and the circumferential stress on the outer surface is σ. 0,θ In (r0+h0,28d), r is taken as r0+h0, and the internal circumferential stress σ 0,θ In (r0+h0 / 4,28d), r takes the value of r0+h0 / 4 and σ takes the value of σ. 0,θ In (r0+h0 / 2,28d), r takes the value of r0+h0 / 2 and σ takes the value of σ. 0,θ In (r0+h0×3 / 4,28d), r is taken as r0+h0×3 / 4, and q0 is the radially distributed force on the inner surface of the reinforced cement material caused by shrinkage under the constraint of the existing concrete column. The calculation formula is as follows:

[0022] In Equation 1-1, E1 is the elastic modulus of the reinforced cement-based material, μ1 is the Poisson's ratio of the reinforced cement-based material, E3 is the elastic modulus of the existing concrete column, and μ3 is the Poisson's ratio of the existing concrete column.

[0023] Step S302 involves calculating the average radial circumferential stress of the reinforcing cement material in the existing concrete column reinforcement scheme.

[0024] The average circumferential stress along the radial direction of the reinforcing cement material in the existing concrete column reinforcement scheme. The calculation formula used is:

[0025] In the above scheme, the circumferential stress σ mentioned in step S303 1,θ (r,28d) Circumferential stress σ on the inner surface 1,θ (r 2j ,28d), circumferential stress σ on the outer surface 1,θ (r 2j +h0,28d), internal circumferential stress σ 1,θ (r 2j +h0 / 4,28d), σ 1,θ (r 2j +h0 / 2,28d), σ 1,θ (r 2j +h0×3 / 4,28d);

[0026] In step S303, the circumferential stress σ of the concrete ring in the ring-constrained test is calculated. 1,θ (r, 28d), the calculation formula used is:

[0027] In Equation 3, E1 is the elastic modulus of the concrete ring, r is the radius of the calculation point, and σ is the circumferential stress on the inner surface. 1,θ (r 2j In ,28d), r is taken as r 2j Circumferential stress σ on the outer surface 1,θ (r 2j In +h0,28d), r is taken as r 2j +h0, internal circumferential stress σ 1,θ (r 2j In +h0 / 4,28d), r is taken as r 2j +h0 / 4、σ 1,θ (r 2j In +h0 / 2,28d), r is taken as r 2j +h0 / 2、σ 1,θ (r 2j In +h0×3 / 4,28d), r is taken as r 2j +h0×3 / 4, q1 represents the radially distributed force on the inner surface of the reinforced cement material caused by shrinkage under the constraint of the steel ring. The calculation formula is:

[0028] In Equation 3-1, E1 is the elastic modulus of the concrete ring, μ1 is the Poisson's ratio of the concrete ring, E2 is the elastic modulus of the steel ring, and μ2 is the Poisson's ratio of the steel ring.

[0029] The calculation of the average radial circumferential stress of the concrete ring in the ring-restrained test described in step S303 The calculation formula used is:

[0030] In the above scheme, whether the relative error between the circumferential stress of the reinforcing cement material in the calculation of the existing concrete column reinforcement scheme and the circumferential stress of the concrete ring in the ring restraint test is less than 5% specifically includes:

[0031] In the above scheme, the height of the steel ring and concrete ring in step S3 is 8 to 10 cm, the inner radius r1 of the steel ring is (150, 215) mm, and the outer radius r2 is (175, 225) mm.

[0032] In the above scheme, the step of conducting a ring-constraint test and monitoring the circumferential strain development on the inner surface of the steel ring until cracks appear in the concrete ring or the test is completed at 28 days of age includes:

[0033] S401: The steel ring is placed on a flat steel plate. Within the radius r2 of the steel plate, the steel plate is milled concave to a depth of 2-3mm to form a concave circular groove, which effectively restricts the overall horizontal displacement of the steel ring without affecting the compressive deformation of the steel ring. The outer radius r3 of the steel plate is the same as the outer radius of the concrete ring, r3=r2+h0. At the outer radius of the steel plate, a detachable circular steel template with an inner diameter r3 and a thickness of 2-3mm is set as the outer template during the pouring of the concrete ring.

[0034] S402: Spray lubricating oil on the outer surface of the steel ring so that the concrete adheres tightly to the outer surface of the steel ring but does not stick; spray lubricating oil on the top surface of the steel plate so that the concrete, steel ring and steel plate adhere tightly but do not stick.

[0035] S403: Strain gauges are horizontally arranged at 1 / 2 the height of the steel ring, along the inner surface of the steel ring at four equal points in the circumferential direction. The direction of the strain being measured is the circumferential strain on the inner surface of the steel ring.

[0036] S404: Use a strain gauge to collect the circumferential strain ε on the inner surface of the steel ring. s,0 (t) until cracks appear in the concrete ring or the test is completed at 28 days. The strain acquisition instrument has an acquisition accuracy of not less than ±1με and a frequency of not less than 1 time / min.

[0037] In the above scheme, determining the crack resistance of the reinforced cement-based material includes: determining whether cracks appear in the concrete ring during the test; if cracks appear in the concrete ring during the test, the age corresponding to the cracking is used for characterization, and the crack resistance of the reinforced cement-based material with cracks is inferior to that of the reinforced cement-based material without cracks; if no cracks appear in the concrete ring during the test, the circumferential strain ε on the inner surface of the steel ring within 28 days is first determined. s,0(28d) Calculate the actual maximum circumferential tensile stress σ' of the concrete ring. 1,θ (r2,28d), and then using the actual maximum circumferential tensile stress σ' of the concrete ring. 1,θ (r2,28d) and tensile strength f t The ratio determines the crack resistance of reinforced cement-based materials; the smaller the ratio, the better the crack resistance of the reinforced cement-based materials.

[0038] In the above scheme, the step of testing the circumferential strain ε on the inner surface of the steel ring within 28 days is... s,0 (28d) Calculate the actual maximum circumferential tensile stress σ' of the concrete ring. 1,θ (r 2j The formula for calculating 28d is:

[0039] In Equation 6, ε e (28d) represents the effective shrinkage strain of the concrete ring after considering the effect of creep, and q' represents the radially distributed force on the inner surface of the reinforced cement material caused by the effective shrinkage of the reinforced cement material under the constraint of the steel ring. The calculation formula is as follows:

[0040] ε e (28d) can be obtained by combining equations 6-1 and 6-2.

[0041] In the formula, E1 is the elastic modulus of the concrete ring, μ1 is the Poisson's ratio of the concrete ring, E2 is the elastic modulus of the steel ring, and μ2 is the Poisson's ratio of the steel ring.

[0042] As can be seen from the above technical solution, the method for evaluating the crack resistance of cement-based materials for reinforcing concrete columns based on ring-constrained tests provided in this disclosure has at least the following beneficial effects:

[0043] 1. The method for evaluating the crack resistance of cement-based materials for reinforcing concrete columns based on ring-constraint tests provided in this disclosure gives a quantitative calculation method for the degree of constraint and an equivalent method for evaluating the stress state of reinforced concrete under steel ring constraint and existing concrete column constraint, thus solving the problem that the test constraint degree of the crack resistance of cement-based materials for reinforcing existing concrete columns does not match the actual constraint degree.

[0044] 2. The method for evaluating the crack resistance of cement-based materials for reinforcing concrete columns based on ring-constraint tests provided in this disclosure gives a method for calculating the stress of the reinforcing concrete and the concrete ring in the ring-constraint test during the reinforcement of the concrete column. Taking the stress state of the reinforcing concrete during the reinforcement of the concrete column as a reference, different degrees of constraint of the steel ring on the concrete ring are achieved by adjusting the size of the steel ring, ensuring that the stress at key points and the average stress of the concrete ring section in the ring-constraint test are consistent with the reference state, and realizing the ability to simulate the real constraint state of the reinforcing concrete when reinforcing concrete columns of different diameters.

[0045] 3. The method for evaluating the crack resistance of cement-based materials for reinforcing concrete columns based on ring-constrained tests provided in this disclosure, compared with the traditional plane-constrained cracking test, uses a test device that ensures that the reinforced concrete is under the same stress state as it is under actual engineering application, both being under ring-constrained conditions. The test results can more realistically and accurately reflect the state under actual application.

[0046] 4. The method for evaluating the crack resistance of cement-based materials for reinforcing concrete columns based on ring-constrained testing provided in this disclosure uses a hollow ring as the ring-constrained testing device, which enables real-time monitoring of the circumferential strain on the inner surface of the steel ring. It is not affected by the moisture in the concrete after early pouring and can monitor the stress development of the reinforcing concrete under real constraints throughout the entire process after the concrete is poured.

[0047] 5. The method for evaluating the crack resistance of cement-based materials for reinforcing concrete columns based on ring-constrained tests provided in this disclosure has a simple test device that can be reused, avoiding the large workload and cost of making full-scale concrete columns for testing, which is very beneficial for laboratory application. Attached Figure Description

[0048] The foregoing contents, as well as other objects, features, and advantages of this disclosure, will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0049] Figure 1 is a flowchart of a method for evaluating the crack resistance of cement-based materials for reinforcing concrete columns based on a ring-constrained test, according to an embodiment of the present disclosure.

[0050] Figure 2 is a schematic diagram of a ring constraint test apparatus according to an embodiment of the present disclosure.

[0051] Figure 3 is a schematic diagram of the strain gauge positions in a ring-constrained testing apparatus according to an embodiment of the present disclosure. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0053] The embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the present disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.

[0054] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0055] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0056] To address the discrepancy between the experimental and actual constraint conditions of existing cement-based materials used for crack resistance strengthening of concrete columns, as shown in Figure 1, this disclosure provides a method for evaluating the crack resistance of cement-based materials used for strengthening concrete columns based on ring-constrained tests. This method includes the following steps:

[0057] Step A: Determine the material and dimensional parameters of the ring constraint test apparatus;

[0058] Step B: Conduct a ring restraint test and monitor the development of circumferential strain on the inner surface of the steel ring until cracks appear in the concrete ring or the test is completed at 28 days.

[0059] Step C: Determine the crack resistance of the reinforced cement-based material.

[0060] In this embodiment of the disclosure, determining the material parameters and dimensional parameters of the ring constraint testing device in step A includes:

[0061] S1: Based on the reinforcement scheme for the existing concrete column, obtain the material properties of the existing concrete column and the reinforcing cement-based material, including the radius r0, elastic modulus E3, and Poisson's ratio μ3 of the existing concrete column; the thickness h0, elastic modulus E1, Poisson's ratio μ1, shrinkage value ε0 (28d) corresponding to the age of the reinforcing cement-based material, and tensile strength f. t ;

[0062] S2: Determine the material parameters of the ring restraint test device, which includes a steel ring and a concrete ring. The steel ring is made of Q345 or higher grade steel, and the concrete ring is made of the cement-based reinforcing material described in the reinforcement scheme.

[0063] S3: Determine the dimensional parameters of the ring-constrained testing device, including the inner and outer surface radii and height of the steel ring and the concrete ring. The inner surface radius r1 and outer surface radius r2 of the steel ring are determined through constraint equivalence analysis. The inner surface radius of the concrete ring is the same as the outer surface radius r2 of the steel ring, and the thickness is the same as the thickness h0 of the reinforcing cement-based material in the reinforcement scheme. That is, the inner surface radius of the concrete ring is r2, and the outer surface radius is r2+h0. As shown in Figures 2 and 3, Figure 2 is a schematic diagram of the ring-constrained testing device according to an embodiment of the present disclosure, and Figure 3 is a schematic diagram of the strain gauge position in the ring-constrained testing device according to an embodiment of the present disclosure. In the figure, reference numeral 1 is the steel ring, reference numeral 2 is the concrete ring, and reference numeral 3 is the strain gauge.

[0064] Further, the inner surface radius r1 and outer surface radius r2 of the steel ring in step S3 are determined through constraint equivalence analysis, including:

[0065] S301: Initial determination of the inner surface radius r of the steel ring 1i and outer surface radius r 2j ;

[0066] S302: Calculate the circumferential stress σ of the reinforcing cement material in the reinforcement scheme for existing concrete columns. 0θ (r,28d) and the average circumferential stress along the radial direction

[0067] Among them, the circumferential stress σ in step S302 0,θ (r,28d) includes the circumferential stress σ on the inner surface. 0,θ (r0,28d), circumferential stress σ on the outer surface 0,θ (r0+h0,28d), internal circumferential stress σ 0,θ (r0+h0 / 4,28d), σ 0,θ (r0+h0 / 2,28d)σ 0,θ (r0+h0×3 / 4,28d),

[0068] Step S302 involves calculating the circumferential stress σ of the reinforcing cement material in the existing concrete column reinforcement scheme. 0,θ (r, 28d), the calculation formula used is:

[0069] In Equation 1, E1 is the elastic modulus of the reinforced cement-based material, r is the radius of the calculation point, and σ is the circumferential stress on the inner surface. 0,θIn (r0,28d), r is taken as r0, and the circumferential stress on the outer surface is σ. 0,θ In (r0+h0,28d), r is taken as r0+h0, and the internal circumferential stress σ 0,θ In (r0+h0 / 4,28d), r takes the value of r0+h0 / 4 and σ takes the value of σ. 0,θ In (r0+h0 / 2,28d), r takes the value of r0+h0 / 2 and σ takes the value of σ. 0,θ In (r0+h0×3 / 4,28d), r is taken as r0+h0×3 / 4, and q0 is the radially distributed force on the inner surface of the reinforced cement material caused by shrinkage under the constraint of the existing concrete column. The calculation formula is as follows:

[0070] In Equation 1-1, E1 is the elastic modulus of the reinforced cement-based material, μ1 is the Poisson's ratio of the reinforced cement-based material, E3 is the elastic modulus of the existing concrete column, and μ3 is the Poisson's ratio of the existing concrete column.

[0071] Step S302 involves calculating the average radial circumferential stress of the reinforcing cement material in the existing concrete column reinforcement scheme.

[0072] The average circumferential stress along the radial direction of the reinforcing cement material in the existing concrete column reinforcement scheme. The calculation formula used is:

[0073] S303: Calculate the circumferential stress σ of the concrete ring in the ring-constrained test. 1,θ (r,28d) and the average circumferential stress along the radial direction

[0074] Among them, the circumferential stress σ in step S303 1,θ (r,28d) Circumferential stress σ on the inner surface 1,θ (r 2j ,28d), circumferential stress σ on the outer surface 1,θ (r 2j +h0,28d), internal circumferential stress σ 1,θ (r 2j +h0 / 4,28d), σ 1,θ (r 2j +h0 / 2,28d), σ 1,θ (r 2j +h0×3 / 4,28d);

[0075] In step S303, the circumferential stress σ of the concrete ring in the ring-constrained test is calculated. 1,θ (r, 28d), the calculation formula used is:

[0076] In Equation 3, E1 is the elastic modulus of the concrete ring, r is the radius of the calculation point, and σ is the circumferential stress on the inner surface. 1,θ (r 2j In ,28d), r is taken as r 2j Circumferential stress σ on the outer surface 1,θ (r 2j In +h0,28d), r is taken as r 2j +h0, internal circumferential stress σ 1,θ (r 2j In +h0 / 4,28d), r is taken as r 2j +h0 / 4、σ 1,θ (r 2j In +h0 / 2,28d), r is taken as r 2j +h0 / 2、σ 1,θ (r 2j In +h0×3 / 4,28d), r is taken as r 2j +h0×3 / 4, q1 represents the radially distributed force on the inner surface of the reinforced cement material caused by shrinkage under the constraint of the steel ring. The calculation formula is:

[0077] In Equation 3-1, E1 is the elastic modulus of the concrete ring, μ1 is the Poisson's ratio of the concrete ring, E2 is the elastic modulus of the steel ring, and μ2 is the Poisson's ratio of the steel ring.

[0078] The calculation of the average radial circumferential stress of the concrete ring in the ring-restrained test described in step S303 The calculation formula used is:

[0079] S304: Calculate whether the relative error between the circumferential stress of the reinforcing cement material and the circumferential stress of the concrete ring in the ring restraint test in the existing concrete column reinforcement scheme is less than 5%. If so, determine the inner surface radius r of the steel ring in step S301. 1i and outer surface radius r 2j Given the inner surface radius r1 and outer surface radius r2 of the steel ring in the ring-constrained test device, it is assumed that under this condition, the degree of constraint of the concrete ring in the ring-constrained test is the same as the degree of constraint of the cement material used to reinforce the existing concrete column. The constraint equivalence analysis is completed. If it is not satisfied, repeat steps S301-S304 until it is satisfied.

[0080] Specifically, step S304, which calculates whether the relative error between the circumferential stress of the reinforcing cement material in the existing concrete column reinforcement scheme and the circumferential stress of the concrete ring in the ring restraint test is less than 5%, includes:

[0081] Optionally, in step S3, the height of the steel ring and the concrete ring ranges from 8 to 10 cm, the inner radius r1 of the steel ring ranges from (150, 215) mm, and the outer radius r2 ranges from (175, 225) mm.

[0082] In this embodiment of the disclosure, step B, which involves conducting a ring-constraint test and monitoring the circumferential strain development on the inner surface of the steel ring until cracks appear in the concrete ring or the test is completed at 28 days, includes:

[0083] S401: The steel ring is placed on a flat steel plate. Within the radius r2 of the steel plate, the steel plate is milled concave to a depth of 2-3mm to form a concave circular groove, which effectively restricts the overall horizontal displacement of the steel ring without affecting the compressive deformation of the steel ring. The outer radius r3 of the steel plate is the same as the outer radius of the concrete ring, r3=r2+h0. At the outer radius of the steel plate, a detachable circular steel template with an inner diameter r3 and a thickness of 2-3mm is set as the outer template during the pouring of the concrete ring.

[0084] S402: Spray lubricating oil on the outer surface of the steel ring so that the concrete adheres tightly to the outer surface of the steel ring but does not stick; spray lubricating oil on the top surface of the steel plate so that the concrete, steel ring and steel plate adhere tightly but do not stick.

[0085] S403: Strain gauges are horizontally arranged at 1 / 2 the height of the steel ring, along the inner surface of the steel ring at four equal points in the circumferential direction. The direction of the strain being measured is the circumferential strain on the inner surface of the steel ring.

[0086] S404: Use a strain gauge to collect the circumferential strain ε on the inner surface of the steel ring. s,0 (t) until cracks appear in the concrete ring or the test is completed at 28 days. The strain acquisition instrument has an acquisition accuracy of not less than ±1με and a frequency of not less than 1 time / min.

[0087] In this embodiment of the disclosure, step C, determining the crack resistance of the reinforced cementitious material, includes: determining whether cracks appear in the concrete ring during the test; if cracks appear in the concrete ring during the test, the age corresponding to the cracking is used for characterization, and the crack resistance of the reinforced cementitious material with cracks is inferior to that of the reinforced cementitious material without cracks; if no cracks appear in the concrete ring during the test, the circumferential strain ε on the inner surface of the steel ring within 28 days is first determined. s,0 (28d) Calculate the actual maximum circumferential tensile stress σ' of the concrete ring. 1,θ (r2,28d), and then using the actual maximum circumferential tensile stress σ' of the concrete ring. 1,θ (r2,28d) and tensile strength f t The ratio determines the crack resistance of reinforced cement-based materials; the smaller the ratio, the better the crack resistance of the reinforced cement-based materials.

[0088] Among them, the circumferential strain ε on the inner surface of the steel ring during the test of 28 days is used as a basis. s,0 (28d) Calculate the actual maximum circumferential tensile stress σ' of the concrete ring. 1,θ (r 2j The formula for calculating 28d is:

[0089] In Equation 6, ε e (28d) represents the effective shrinkage strain of the concrete ring after considering the effect of creep, and q' represents the radially distributed force on the inner surface of the reinforced cement material caused by the effective shrinkage of the reinforced cement material under the constraint of the steel ring. The calculation formula is as follows:

[0090] ε e (28d) can be obtained by combining equations 6-1 and 6-2.

[0091] In the formula, E1 is the elastic modulus of the concrete ring, μ1 is the Poisson's ratio of the concrete ring, E2 is the elastic modulus of the steel ring, and μ2 is the Poisson's ratio of the steel ring.

[0092] Based on the method for evaluating the crack resistance of cement-based materials for reinforcing concrete columns based on ring-constrained tests as shown in Figure 1 above, the following detailed description of the method for evaluating the crack resistance of cement-based materials for reinforcing concrete columns based on ring-constrained tests provided in this disclosure is provided in conjunction with Examples 1-2.

[0093] Example 1: A method for evaluating the crack resistance of cement-based materials used in the reinforcement of concrete columns based on ring-constrained tests, including:

[0094] S1: According to the reinforcement scheme of the existing concrete column, the existing concrete column adopts C50 ordinary concrete, and the reinforcement cement-based material adopts ultra-high toughness cement-based material ECC-50. The material property parameters of the existing concrete column and the reinforcement cement-based material are obtained as shown in Table 1.

[0095] Table 1 Material properties of existing concrete columns and reinforced cement-based materials

[0096] S2: Determine the material parameters of the ring constraint test device, which includes a steel ring and a concrete ring. The steel ring is made of Q345 steel, that is, the elastic modulus E2 of the steel ring is 210GPa and the Poisson's ratio μ2 of the steel ring is 0.25. The concrete ring is made of the reinforcing cement-based material mentioned in the reinforcement scheme, that is, ultra-high toughness cement-based material ECC-50.

[0097] S3: Determine the dimensional parameters of the ring-constrained test apparatus, including the inner and outer surface radii and heights of the steel ring 1 and the concrete ring 2. The inner surface radius r1 and outer surface radius r2 of the steel ring 1 are determined through constraint degree equivalence analysis. The specific steps are as follows:

[0098] S301: Initial determination of the inner surface radius r of the steel ring 1i =0.35m and outer surface radius r 2j =0.4m;

[0099] S302: Calculate the circumferential stress σ of the reinforcing cement material in the existing concrete column reinforcement scheme according to Equations 1 and 2. 0,θ (r,28d) and the average circumferential stress along the radial direction

[0100] S303: Calculate the circumferential stress σ of the concrete ring in the ring-constrained test according to Equations 3 and 4. 1,θ (r,28d) and the average circumferential stress along the radial direction

[0101] S304: According to Equation 5, calculate whether the relative error between the circumferential stress of the reinforcing cement material and the circumferential stress of the concrete ring in the ring restraint test in the existing concrete column reinforcement scheme is less than 5%.

[0102] The specific calculation results for S302-S304 are shown in Table 2.

[0103] Table 2 Calculation results of circumferential stress and average circumferential stress for reinforced cement materials and concrete rings.

[0104] According to the calculation results, the relative error between the circumferential stress of the reinforcing cement material and the circumferential stress of the concrete ring in the ring constraint test is less than 5% in the existing concrete column reinforcement scheme. Therefore, the inner surface radius r1 = 0.35m and the outer surface radius r2 = 0.4m of the steel ring are selected.

[0105] The inner surface radius of the concrete ring 2 is the same as the outer surface radius r2 of the steel ring 1, and the thickness is the same as the thickness h0 of the reinforcing cement-based material in the reinforcement scheme. That is, the inner surface radius of the concrete ring 2 is r2, and the outer surface radius is r2+h0. The dimensional parameters of the ring constraint test device are shown in Table 3.

[0106] Table 3 Dimensional parameters of the ring restraint test apparatus

[0107] S4: Conduct a ring constraint test and monitor the circumferential strain ε on the inner surface of steel ring 1. s,0(t) Development continues until the experiment reaches 28 days of age, during which the circumferential strain ε on the inner surface of steel ring 1 during the 28-day period is measured. s,0 (28d)=10.5με.

[0108] S5: Evaluate the crack resistance of reinforced cementitious materials. Calculate the actual maximum circumferential tensile stress σ' of the concrete ring according to Equation 6. 1,θ (r2,28d)=4.42MPa, the actual circumferential tensile stress σ' of concrete ring 2 1,θ The ratio of (r2,28d) to tensile strength is 4.42 / 4.8 = 0.92.

[0109] Example 2: A method for evaluating the crack resistance of cement-based materials used in the reinforcement of concrete columns based on ring-constrained tests, including:

[0110] S1: According to the reinforcement scheme of the existing concrete column, the existing concrete column adopts C50 ordinary concrete and the reinforcement cement-based material adopts C80 concrete. The material properties of the existing concrete column and the reinforcement cement-based material are obtained as shown in Table 4.

[0111] Table 4 Material properties of existing concrete columns and reinforced cement-based materials

[0112] S2: Determine the material parameters of the ring restraint test device, which includes a steel ring and a concrete ring. The steel ring is made of Q345 steel, i.e., the elastic modulus E2 of the steel ring is 210 GPa and the Poisson's ratio μ2 of the steel ring is 0.25. The concrete ring is made of the cement-based reinforcing material described in the reinforcement scheme, i.e., C80 concrete.

[0113] S3: Determine the dimensional parameters of the ring-constrained test apparatus, including the inner and outer surface radii and heights of the steel ring 1 and the concrete ring 2. The inner surface radius r1 and outer surface radius r2 of the steel ring 1 are determined through constraint degree equivalence analysis. The specific steps are as follows:

[0114] S301: Initial determination of the inner surface radius r of the steel ring 1i =0.35m and outer surface radius r 2j =0.4m;

[0115] S302: Calculate the circumferential stress σ of the reinforcing cement material in the existing concrete column reinforcement scheme according to Equations 1 and 2. 0,θ (r,28d) and the average circumferential stress along the radial direction

[0116] S303: Calculate the circumferential stress σ of the concrete ring in the ring-constrained test according to Equations 3 and 4. 1,θ (r,28d) and the average circumferential stress along the radial direction

[0117] S304: According to Equation 5, calculate whether the relative error between the circumferential stress of the reinforcing cement material and the circumferential stress of the concrete ring in the ring restraint test in the existing concrete column reinforcement scheme is less than 5%.

[0118] The specific calculation results for S302-S304 are shown in Table 5.

[0119] Table 5. Calculation results of circumferential stress and average circumferential stress for reinforced cement materials and concrete rings.

[0120] According to the calculation results, the relative error between the circumferential stress of the reinforcing cement material and the circumferential stress of the concrete ring in the ring constraint test is less than 5% in the existing concrete column reinforcement scheme. Therefore, the inner surface radius r1 = 0.35m and the outer surface radius r2 = 0.4m of the steel ring are selected.

[0121] The inner surface radius of the concrete ring 2 is the same as the outer surface radius r2 of the steel ring 1, and the thickness is the same as the thickness h0 of the reinforcing cement-based material in the reinforcement scheme. That is, the inner surface radius of the concrete ring 2 is r2, and the outer surface radius is r2+h0. The dimensional parameters of the ring constraint test device are shown in Table 6.

[0122] Table 6 Dimensional parameters of the ring restraint test apparatus

[0123] S4: Conduct a ring constraint test and monitor the circumferential strain ε on the inner surface of steel ring 1. s,0 (t) Development continues until the experiment reaches 28 days of age, during which the circumferential strain ε on the inner surface of steel ring 1 during the 28-day period is measured. s,0 (28d)=15.5με.

[0124] S5: Evaluate the crack resistance of the reinforced cementitious material. Calculate the actual maximum circumferential tensile stress σ' of the concrete ring according to Equation 6. 1,θ (r2,28d)=6.39MPa, the actual circumferential tensile stress σ' of concrete ring 2 1,θ The ratio of (r2,28d) to tensile strength is 6.39 / 3.11 = 2.05.

[0125] Comparing the actual circumferential tensile stress σ' of the concrete rings in Example 1 and Example 2 1,θ The ratio of (r2,28d) to tensile strength, and the actual circumferential tensile stress σ' of the concrete ring in Example 1. 1,θ The ratio of (r2,28d) to tensile strength is less than the actual circumferential tensile stress σ' of the concrete ring in Example 2. 1,θThe ratio of (r2,28d) to tensile strength indicates that the crack resistance of the reinforced cement-based material ECC in Example 1, which is an ultra-high toughness cement-based material, is better than that of the reinforced cement-based material ECC in Example 2, which is an ultra-high toughness cement-based material.

[0126] As can be seen from the above embodiments, the present disclosure provides a method for evaluating the crack resistance of cement-based materials for reinforcing concrete columns based on ring-constraint tests. It provides a method for calculating the stress of the reinforcing concrete and the concrete ring in the ring-constraint test during the reinforcement of the concrete column. Taking the stress state of the reinforcing concrete during the reinforcement of the concrete column as a reference, different degrees of constraint of the steel ring on the concrete ring are achieved by adjusting the size of the steel ring. This ensures that the stress at key points and the average stress of the concrete ring section in the ring-constraint test are consistent with the reference state, and realizes the ability to simulate the real constraint state of the reinforcing concrete when reinforcing concrete columns of different diameters.

[0127] Compared with the traditional planar confined cracking test, the test device used in this disclosure ensures that the reinforced concrete is under the same stress state as it is under actual engineering application, both being under ring confined state. The test results can more realistically and accurately reflect the state under actual application.

[0128] This disclosure provides a method for evaluating the crack resistance of cement-based materials used for reinforcing concrete columns based on ring-constrained testing. The ring-constrained testing device uses a hollow ring, which enables real-time monitoring of the circumferential strain on the inner surface of the steel ring. It is not affected by the moisture present in the early stages of concrete pouring and can monitor the stress development of the reinforcing concrete under real constraints throughout the entire process after the concrete pouring is completed.

[0129] This disclosure provides a method for evaluating the crack resistance of cement-based materials used in the reinforcement of concrete columns based on ring-constrained tests. The test equipment is simple and reusable, avoiding the large workload and cost associated with fabricating full-scale concrete columns for testing, which is highly beneficial for laboratory application.

[0130] Those skilled in the art will understand that the features described in the various embodiments of this disclosure can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in this disclosure. In particular, the features described in the various embodiments of this disclosure can be combined and / or combined in various ways without departing from the spirit and teachings of this disclosure. All such combinations and / or combinations fall within the scope of this disclosure.

[0131] The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of this disclosure. It should be understood that the above descriptions are merely specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

A method for evaluating the crack resistance of cement-based materials used in the reinforcement of concrete columns, comprising: Determine the material and dimensional parameters of the ring constraint test apparatus; Ring-constrained tests were conducted to monitor the development of circumferential strain on the inner surface of the steel ring until cracks appeared in the concrete ring or the test was completed at 28 days. Determine the crack resistance of reinforced cement-based materials. The method for evaluating the crack resistance of cement-based materials for reinforcing concrete columns according to claim 1, wherein, The determination of the material and dimensional parameters of the ring constraint test apparatus includes: S1: Based on the reinforcement scheme for the existing concrete column, obtain the material properties of the existing concrete column and the reinforcing cement-based material, including the radius r0, elastic modulus E3, and Poisson's ratio μ3 of the existing concrete column; the thickness h0, elastic modulus E1, Poisson's ratio μ1, shrinkage value ε0 (28d) corresponding to the age of the reinforcing cement-based material, and tensile strength f. t ; S2: Determine the material parameters of the ring restraint test device, which includes a steel ring and a concrete ring. The steel ring is made of Q345 or higher grade steel, and the concrete ring is made of the cement-based reinforcing material described in the reinforcement scheme. S3: Determine the dimensional parameters of the ring constraint test device, including the inner and outer surface radii and height of the steel ring and the concrete ring. The inner surface radius r1 and outer surface radius r2 of the steel ring are determined through constraint equivalence analysis. The inner surface radius of the concrete ring is the same as the outer surface radius r2 of the steel ring, and the thickness is the same as the thickness h0 of the reinforcing cement-based material in the reinforcement scheme. That is, the inner surface radius of the concrete ring is r2, and the outer surface radius is r2+h0. The method for evaluating the crack resistance of cement-based materials for reinforcing concrete columns according to claim 2, wherein, The inner surface radius r1 and outer surface radius r2 of the steel ring mentioned in step S3 are determined through constraint equivalence analysis, including: S301: Initial determination of the inner surface radius r of the steel ring 1i and outer surface radius r 2j ; S302: Calculate the circumferential stress σ of the reinforcing cement material in the reinforcement scheme for existing concrete columns. 0,θ (r,28d) and the average circumferential stress along the radial direction S303: Calculate the circumferential stress σ of the concrete ring in the ring-constrained test. 1,θ (r,28d) and the average circumferential stress along the radial direction S304: Calculate whether the relative error between the circumferential stress of the reinforcing cement material and the circumferential stress of the concrete ring in the ring restraint test in the existing concrete column reinforcement scheme is less than 5%. If so, determine the inner surface radius r of the steel ring in step S301. 1i and outer surface radius r 2j Given the inner surface radius r1 and outer surface radius r2 of the steel ring in the ring-constrained test device, it is assumed that under this condition, the degree of constraint of the concrete ring in the ring-constrained test is the same as the degree of constraint of the cement material used to reinforce the existing concrete column. The constraint equivalence analysis is completed. If it is not satisfied, repeat steps S301-S304 until it is satisfied. The method for evaluating the crack resistance of cement-based materials for reinforcing concrete columns according to claim 3, wherein, The circumferential stress σ mentioned in step S302 0,θ (r,28d) includes the circumferential stress σ on the inner surface. 0,θ (r0,28d), circumferential stress σ on the outer surface 0,θ (r0+h0,28d), internal circumferential stress σ 0,θ (r0+h0 / 4,28d), σ 0,θ (r0+h0 / 2,28d)σ 0,θ (r0+h0×3 / 4,28d), Step S302 involves calculating the circumferential stress σ of the reinforcing cement material in the existing concrete column reinforcement scheme. 0,θ (r, 28d), the calculation formula used is: In Equation 1, E1 is the elastic modulus of the reinforced cement-based material, r is the radius of the calculation point, and σ is the circumferential stress on the inner surface. 0,θ In (r0,28d), r is taken as r0, and the circumferential stress on the outer surface is σ. 0,θ In (r0+h0,28d), r is taken as r0+h0, and the internal circumferential stress σ 0,θ In (r0+h0 / 4,28d), r takes the value of r0+h0 / 4 and σ takes the value of σ. 0,θ In (r0+h0 / 2,28d), r takes the value of r0+h0 / 2 and σ takes the value of σ. 0,θ In (r0+h0×3 / 4,28d), r is taken as r0+h0×3 / 4, and q0 is the radially distributed force on the inner surface of the reinforced cement material caused by shrinkage under the constraint of the existing concrete column. The calculation formula is as follows: In Equation 1-1, E1 is the elastic modulus of the reinforced cement-based material, μ1 is the Poisson's ratio of the reinforced cement-based material, E3 is the elastic modulus of the existing concrete column, and μ3 is the Poisson's ratio of the existing concrete column. Step S302 involves calculating the average radial circumferential stress of the reinforcing cement material in the existing concrete column reinforcement scheme. The average circumferential stress along the radial direction of the reinforcing cement material in the existing concrete column reinforcement scheme. The calculation formula used is: The method for evaluating the crack resistance of cement-based materials for reinforcing concrete columns according to claim 4, wherein, The circumferential stress σ mentioned in step S303 1,θ (r,28d) Circumferential stress σ on the inner surface 1,θ (r 2j ,28d), circumferential stress σ on the outer surface 1,θ (r 2j +h0,28d), internal circumferential stress σ 1,θ (r 2j +h0 / 4,28d), σ 1,θ (r 2j +h0 / 2,28d), σ 1,θ (r 2j +h0×3 / 4,28d); In step S303, the circumferential stress σ of the concrete ring in the ring-constrained test is calculated. 1,θ (r, 28d), the calculation formula used is: In Equation 3, E1 is the elastic modulus of the concrete ring, r is the radius of the calculation point, and σ is the circumferential stress on the inner surface. 1,θ (r 2j In ,28d), r is taken as r 2j Circumferential stress σ on the outer surface 1,θ (r 2j In +h0,28d), r is taken as r 2j +h0, internal circumferential stress σ 1,θ (r 2j In +h0 / 4,28d), r is taken as r 2j +h0 / 4、σ 1,θ (r 2j In +h0 / 2,28d), r is taken as r 2j +h0 / 2、σ 1,θ (r 2j In +h0×3 / 4,28d), r is taken as r 2j +h0×3 / 4, q1 represents the radially distributed force on the inner surface of the reinforced cement material caused by shrinkage under the constraint of the steel ring. The calculation formula is: In Equation 3-1, E1 is the elastic modulus of the concrete ring, μ1 is the Poisson's ratio of the concrete ring, E2 is the elastic modulus of the steel ring, and μ2 is the Poisson's ratio of the steel ring. The calculation of the average radial circumferential stress of the concrete ring in the ring-restrained test described in step S303 The calculation formula used is: The method for evaluating the crack resistance of cement-based materials for reinforcing concrete columns according to claim 4, wherein, Step S304, which calculates whether the relative error between the circumferential stress of the reinforcing cement material and the circumferential stress of the concrete ring in the ring restraint test in the existing concrete column reinforcement scheme is less than 5%, specifically includes: The method for evaluating the crack resistance of cement-based materials for reinforcing concrete columns according to claim 2, wherein, In step S3, the height of the steel ring and the concrete ring ranges from 8 to 10 cm, the inner radius r1 of the steel ring ranges from (150, 215) mm, and the outer radius r2 ranges from (175, 225) mm. The method for evaluating the crack resistance of cement-based materials for reinforcing concrete columns according to claim 1, wherein, The ring-constraint test was conducted to monitor the circumferential strain development on the inner surface of the steel ring until cracks appeared in the concrete ring or the test was completed at 28 days. This included: S401: The steel ring is placed on a flat steel plate. Within the radius r2 of the steel plate, the steel plate is milled concave to a depth of 2-3mm to form a concave circular groove, which effectively restricts the overall horizontal displacement of the steel ring without affecting the compressive deformation of the steel ring. The outer radius r3 of the steel plate is the same as the outer radius of the concrete ring, r3=r2+h0. At the outer radius of the steel plate, a detachable circular steel template with an inner diameter r3 and a thickness of 2-3mm is set as the outer template during the pouring of the concrete ring. S402: Spray lubricating oil on the outer surface of the steel ring so that the concrete adheres tightly to the outer surface of the steel ring but does not stick; spray lubricating oil on the top surface of the steel plate so that the concrete, steel ring and steel plate adhere tightly but do not stick. S403: Strain gauges are horizontally arranged at 1 / 2 the height of the steel ring, along the inner surface of the steel ring at four equal points in the circumferential direction. The direction of the strain measurement is the circumferential strain on the inner surface of the steel ring. S404: Circumferential strain ε on the inner surface of the steel ring is collected using a strain gauge. s,0 (t) until cracks appear in the concrete ring or the test is completed at 28 days. The strain acquisition instrument has an acquisition accuracy of not less than ±1με and a frequency of not less than 1 time / min. The method for evaluating the crack resistance of cement-based materials for reinforcing concrete columns according to claim 1, wherein, The determination of the crack resistance of the reinforced cement-based material includes: Determine whether cracks appear in the concrete ring during the test; If cracks appear in the concrete ring during the test, the age corresponding to the cracking time shall be used for characterization. The crack resistance of the reinforced cement-based material that has cracked is inferior to that of the reinforced cement-based material that has not cracked. If no cracks appear in the concrete ring during the test, the circumferential strain ε on the inner surface of the steel ring during the 28-day test period should be used as the initial test result. s,0 (28d) Calculate the actual maximum circumferential tensile stress σ' of the concrete ring. 1,θ (r2,28d), and then using the actual maximum circumferential tensile stress σ' of the concrete ring. 1,θ (r2,28d) and tensile strength f t The ratio determines the crack resistance of reinforced cement-based materials; the smaller the ratio, the better the crack resistance of the reinforced cement-based materials. The method for evaluating the crack resistance of cement-based materials for reinforcing concrete columns according to claim 9, wherein, The circumferential strain ε on the inner surface of the steel ring was tested within 28 days. s,0 (28d) Calculate the actual maximum circumferential tensile stress σ' of the concrete ring. 1,θ (r 2j The formula for calculating 28d is: In Equation 6, ε e (28d) represents the effective shrinkage strain of the concrete ring after considering the effect of creep, and q' represents the radially distributed force on the inner surface of the reinforced cement material caused by the effective shrinkage of the reinforced cement material under the constraint of the steel ring. The calculation formula is as follows: ε e (28d) can be obtained by combining equations 6-1 and 6-2. In the formula, E1 is the elastic modulus of the concrete ring, μ1 is the Poisson's ratio of the concrete ring, E2 is the elastic modulus of the steel ring, and μ2 is the Poisson's ratio of the steel ring.

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