Evaluation model and evaluation method for crack resistance of secondary distribution panel concrete

Abstract

The invention relates to the technical field of concrete performance evaluation, and discloses a secondary matching panel concrete crack resistance evaluation model which is divided into three layers, namely a target layer for storing the optimal crack resistance concrete mix proportion and a criterion layer for judging index factors influencing the concrete crack resistance. And the scheme layer is used for storing different index factor mixing ratios. According to the method, the crack resistance of the concrete is comprehensively evaluated by utilizing an analytic hierarchy process, and an analytic hierarchy model is constructed by taking test conditions such as a mix proportion as a scheme layer, taking index factors of the crack resistance of the concrete as a criterion layer and taking the optimal crack resistance of the concrete as a target layer. Based on the analytic hierarchy model, the anti-cracking performance of the concrete material can be digitalized, and transverse comparison between different types of concrete can be realized.

Description

Technical Field

[0001] The invention relates to the technical field of concrete performance evaluation, and in particular to an evaluation model and an evaluation method for the anti-cracking performance of secondary distribution panel concrete. Background Art

[0002] At present, the main test methods for evaluating the crack resistance of concrete are the flat plate method and the ring method. Both methods use the cracking time and crack area of ​​concrete specimens as the main evaluation indicators. Among them, the flat plate method is simple and easy to operate, and can quickly and effectively study the plastic shrinkage performance of concrete and mortar; for the ring method, because it can provide sufficient constraints for concrete, it is convenient to compare different concretes by measuring the cracking time. However, the flat plate method and the ring method are not applicable to the test of large-sized specimens of secondary concrete. In addition, there are no clear regulations in the current specifications for the tests that can be directly used to evaluate the crack resistance of secondary concrete.

[0003] The evaluation of early concrete crack resistance is mostly based on various performance parameters of concrete after hardening. There are many factors that affect the crack resistance of concrete, including the early shrinkage and deformation of concrete, the ultimate tensile value, axial tensile strength, elastic modulus, linear expansion coefficient, hydration temperature rise, creep, etc. The above factors are not independent of each other, but are interrelated and influence each other. In addition, many evaluation indicators are proposed based on the different structural uses of concrete, each with different emphases, making it difficult to objectively evaluate the crack resistance of concrete, and even more unfavorable for standardization and mutual comparison.

[0004] The analytic hierarchy process (AHP) is a decision-making method that combines qualitative and quantitative analysis proposed by Saaty and other famous American operations researchers. The analytic hierarchy process decomposes the elements related to decision-making into multiple levels such as goals, criteria, and plans, and conducts qualitative and quantitative analysis on this basis. It is a systematic, simple, flexible and effective decision-making method. The core of the analytic hierarchy process is to hierarchical and digitize the influencing factors. It decomposes an abstract phenomenon or problem from difficult to easy, making it easy to intuitively judge complex problems and make decisions. The analytic hierarchy process has the advantages of simplifying complex problems and simple calculations, and is widely used.

[0005] Therefore, an evaluation model and method for the anti-cracking performance of secondary slab concrete were proposed. Summary of the invention

[0006] In order to solve the technical problems raised in the background technology, the present invention provides an evaluation model for the anti-cracking performance of secondary distribution panel concrete.

[0007] The present invention is implemented by the following technical scheme: an evaluation model for the anti-cracking performance of secondary distribution panel concrete, the model is divided into three layers, namely a target layer for storing the best anti-cracking performance concrete mix ratio, a criterion layer for judging various index factors affecting the anti-cracking performance of concrete, and a scheme layer for storing different mix ratios of various index factors.

[0008] The present invention also proposes a method for evaluating the anti-cracking performance of secondary distribution panel concrete, comprising the following steps:

[0009] Step 1: Establish the evaluation model of the anti-cracking performance of the above-mentioned secondary distribution panel concrete, and clarify the index factors of the model criterion layer that affect the anti-cracking performance of the secondary distribution panel concrete;

[0010] Step 2: Compare the importance of each factor in the criterion layer with respect to the target layer, construct a judgment matrix with reference to the scale table, calculate and obtain the weight vector and perform consistency test;

[0011] Step 3: Based on the various index factors of the crack resistance of the criterion layer, concrete specimens with different mix ratios in the scheme layer are prepared according to the specifications, and corresponding tests are carried out on the concrete specimens after curing them to the specified age, and the test data of the concrete specimens at different ages are recorded;

[0012] Step 4: Standardize the test data of different ages and calculate the crack resistance of specimens with different mix ratios by weighted summation; and the crack resistance of each specimen is calculated according to the following formula:

[0013] M=∑W i ×A i

[0014] Where W i is the weight of the factor, A i It is the dimensionless test data after the range of the factors is standardized, and the larger the M value is, the better the crack resistance is.

[0015] As a further improvement of the above solution, the criterion layer includes the following index factors affecting the anti-cracking performance of concrete: splitting tensile strength, elastic modulus, compression work, autogenous shrinkage and drying shrinkage of concrete.

[0016] As a further improvement of the above scheme, all influencing factors are classified into positive and negative indicators, and then the data of each factor are standardized according to the range standardization conversion to obtain the standardized dimensionless number A i The test data of the criterion layer are standardized by range standardization. The standardization formula is as follows:

[0017] X i is a positive indicator;

[0018] X i is a negative indicator;

[0019] As a further improvement of the above scheme, the model criterion layer factors that clearly affect the crack resistance of the secondary distribution panel concrete include the following operations:

[0020] Conduct splitting tensile strength test and record the splitting tensile strength;

[0021] Conduct uniaxial compression test; first determine the preload standard, then record the stress-strain curve and load-displacement curve, and calculate the elastic modulus and compression work of concrete based on the data;

[0022] Carry out autogenous shrinkage and drying shrinkage tests; measure the autogenous shrinkage and drying shrinkage of concrete specimens.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention uses the hierarchical analysis method to comprehensively evaluate the crack resistance of concrete, taking the test conditions such as mix ratio as the scheme layer, the index factors of concrete crack resistance as the criterion layer, and the optimal crack resistance of concrete as the target layer to construct a hierarchical analysis model. Relying on this hierarchical analysis model, the crack resistance of concrete materials can be digitized, and horizontal comparison between different concretes can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic flow chart of the main steps of the evaluation method proposed in the present invention;

[0026] Figure 2 This is a schematic diagram of an evaluation model for the crack resistance of a two-stage concrete slab proposed in the present invention. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with the accompanying drawings and specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form a new embodiment.

[0028] Embodiment 1:

[0029] This scheme proposes an evaluation model for the crack resistance of secondary slab concrete. The model is divided into three layers, namely a target layer for storing the best concrete mix ratio for crack resistance, a criterion layer for judging the various index factors affecting the concrete crack resistance, and a scheme layer for storing different mix ratios of various index factors.

[0030] The present invention also proposes a method for evaluating the anti-cracking performance of secondary distribution panel concrete, comprising the following steps:

[0031] Step 1: Establish the evaluation model of the anti-cracking performance of the above-mentioned secondary distribution panel concrete, and clarify the index factors of the model criterion layer that affect the anti-cracking performance of the secondary distribution panel concrete;

[0032] Step 2: Compare the importance of each factor in the criterion layer with respect to the target layer, construct a judgment matrix with reference to the scale table, calculate and obtain the weight vector and perform consistency test;

[0033] Step 3: Based on the various index factors of the crack resistance of the criterion layer, concrete specimens with different mix ratios in the scheme layer are prepared according to the specifications, and corresponding tests are carried out on the concrete specimens after curing them to the specified age, and the test data of the concrete specimens at different ages are recorded;

[0034] Step 4: Standardize the test data of different ages and calculate the crack resistance of specimens with different mix ratios by weighted summation; and the crack resistance of each specimen is calculated according to the following formula:

[0035] M=∑W i ×A i

[0036] Where W i is the weight of the factor, A i It is the dimensionless test data after the range of the factors is standardized, and the larger the M value is, the better the crack resistance is.

[0037] As a further improvement of the above solution, the criterion layer includes the following index factors affecting the anti-cracking performance of concrete: splitting tensile strength, elastic modulus, compression work, autogenous shrinkage and drying shrinkage of concrete.

[0038] As a further improvement of the above scheme, all influencing factors are classified into positive and negative indicators, and then the data of each factor are standardized according to the range standardization conversion to obtain the standardized dimensionless number A i The test data of the criterion layer are standardized by range standardization. The standardization formula is as follows:

[0039] X i is a positive indicator;

[0040] X i is a negative indicator;

[0041] As a further improvement of the above scheme, the model criterion layer factors that clearly affect the crack resistance of the secondary distribution panel concrete include the following operations:

[0042] Conduct splitting tensile strength test and record the splitting tensile strength;

[0043] Conduct uniaxial compression test; first determine the preload standard, then record the stress-strain curve and load-displacement curve, and calculate the elastic modulus and compression work of concrete based on the data;

[0044] The elastic modulus E is the secant of the stress from 0.5Mpa to 40% of the failure stress, according to the formula Get the elastic modulus E value, Δσ is the stress increase value from 0.5Mpa to 40% of the failure stress (MPa), Δε is the strain increase value from 0.5Mpa to 40% of the failure stress (mm); compression work W 1.0 It is the area under the load-displacement curve (kN·mm) of axial deformation from 0 to L0×1.0% mm (L0 is 150 mm).

[0045] Carry out autogenous shrinkage and drying shrinkage tests; measure the autogenous shrinkage and drying shrinkage of concrete specimens.

[0046] Embodiment 2:

[0047] For the splitting tensile strength test, uniaxial compression test, autogenous shrinkage and drying shrinkage test in Example 1, the parts were cured and tested according to the relevant procedures in the "Test Procedure for Hydraulic Concrete" (SL / T 352-2020).

[0048] In the evaluation model of the crack resistance of the secondary slab concrete proposed in this scheme, in step 4, the factor a ij Please refer to the following table for scale selection:

[0049] Table 1a ij Scale

[0050] <![CDATA[a ij Scale]]> meaning 1 Indicates that two factors are equally important. 3 Indicates that compared with the two factors, the former is slightly more important than the latter 5 Indicates that compared with the two factors, the former is significantly more important than the latter 7 Indicates that compared with two factors, the former is more important than the latter 9 Indicates that compared with the two factors, the former is extremely more important than the latter 2、4、6、8 Between two important dimensions reciprocal Indicates the importance of comparing the corresponding two factors in the order of swapping

[0051] The evaluation method of the present invention believes that the main factors affecting the crack resistance of concrete are drying shrinkage, elastic modulus and splitting tensile strength. Autogenous shrinkage mostly occurs in the first three days after concrete pouring, which has an impact on the overall shrinkage of concrete but is not the main factor. At the same time, considering the extrusion damage suffered by the panel concrete, compression work is also one of the important indicators of the crack resistance of the panel concrete. Based on the above analysis, the hierarchical analysis model of the present invention has five factors at the criterion level: drying shrinkage, splitting tensile strength, elastic modulus, compression work, and autogenous shrinkage. ij The judgment matrix is ​​constructed by scaling method.

[0052] Table 2 Judgment matrix of concrete crack resistance

[0053]

[0054] After constructing the judgment matrix, it is necessary to calculate the weight of each influencing factor and use the square root method to calculate the weight:

[0055] Step (a), calculate the mth power of the product of each row to obtain an m-dimensional vector, and use formula 4 to calculate:

[0056] In formula 4, a ij For scale;

[0057] The weight of each influencing factor is calculated as follows:

[0058] Drying shrinkage:

[0059] Splitting tensile strength:

[0060] Modulus of elasticity:

[0061] Compression work:

[0062] Autogenous Shrinkage:

[0063] Step (b), normalize the vector to obtain the weight vector, that is, obtain the standardized weight, and calculate it using Formula 5:

[0064]

[0065] In formula 5, is the weight value of each factor.

[0066] The standardized calculation of the weights of each influencing factor is as follows

[0067] Drying shrinkage:

[0068] Splitting tensile strength:

[0069] Modulus of elasticity:

[0070] Compression work:

[0071] Autogenous Shrinkage:

[0072] Get the normalized weight vector:

[0073] w=[0.2308 0.2308 0.2308 0.1794 0.1282]

[0074] After obtaining the standardized weight matrix, it is also necessary to determine whether its consistency is passed. The consistency test is used to check whether the constructed judgment matrix contains logical errors to ensure that there is no situation where A>B, B>C, but C>A.

[0075] Step (c): Find the maximum characteristic root

[0076] Use Equation 6 to calculate:

[0077]

[0078] In Formula 6: n is the dimension, and in the embodiment of the present invention, n=5; Aw is the judgment matrix×standardized weight.

[0079] Aw is calculated as shown in Table 3

[0080] Table 3 Aw value

[0081]

[0082]

[0083]

[0084] Step (d), solving the consistency index CI value

[0085] Use equation 7 to solve:

[0086]

[0087] In formula 7, λ max is the largest characteristic root, n is the number of influencing factors

[0088] That is to obtain:

[0089]

[0090] Step (e), solve the test coefficient CR value

[0091] Use equation 8 to solve:

[0092]

[0093] In formula 8, RI is the random consistency index, which can be obtained by looking up Table 4. When n=5, the RI value is 1.12.

[0094] Table 4 R.I. values

[0095]

[0096] In the embodiment of the present invention:

[0097]

[0098] Therefore, the logical requirement is met.

[0099] In this scheme, based on the existing research status, concrete with good crack resistance has higher splitting tensile strength, higher compression work, lower elastic modulus and shrinkage, so splitting tensile strength and compression work are positive indicators, elastic modulus, autogenous shrinkage and drying shrinkage are negative indicators. Then use the range standardization conversion to calculate by formula 2 and formula 3:

[0100]

[0101] In step 6, the crack resistance index M of concrete is calculated by formula 1:

[0102] M=∑W i ×A i Formula 1;

[0103] According to the test data of this embodiment, the concrete crack resistance index is obtained by formula 1, see Table 5

[0104] Table 5 Crack resistance index

[0105]

[0106] Note: In the table, jz is the reference concrete; s represents the volume content of steel fiber, unit %; p represents the content of PVA fiber, unit %.

[0107] It can be seen intuitively from Table 5 that when the volume content of steel fiber is 1.0% and the volume content of PVA fiber is 0.2%, the anti-cracking performance of concrete is the best.

[0108] The above-mentioned embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and substitutions made by technicians in this field on the basis of the present invention shall fall within the scope of protection required by the present invention.

Claims

1. An evaluation model for the crack resistance of secondary slab concrete, characterized in that: The model is divided into three layers, namely, a target layer for storing the best concrete mix ratio for crack resistance, a criterion layer for judging various index factors affecting concrete crack resistance, and a scheme layer for storing different mix ratios of various index factors.

2. A method for evaluating the crack resistance of secondary slab concrete, characterized in that: The following steps are involved: Step 1, establishing the hierarchical structure model as claimed in claim 1, so as to clarify the index factors of the model criterion layer that affect the crack resistance of the secondary distribution panel concrete; Step 2: compare the importance of each factor in the criterion layer relative to the target layer. Specifically, construct a judgment matrix with reference to the scale table, calculate and obtain the weight vector, and perform consistency check; Step 3: Based on the various index factors of the crack resistance of the criterion layer, concrete specimens with different mix ratios in the scheme layer are prepared according to the specifications, and corresponding tests are carried out on the concrete specimens after curing them to the specified age, and the test data of the concrete specimens at different ages are recorded; Step 4: Standardize the test data of different ages and calculate the crack resistance of specimens with different mix ratios by weighted summation; and the crack resistance of each specimen is calculated according to the following formula: M=∑W i ×A i Where W i is the weight of the factor, A i It is the dimensionless test data after the range of the factors is standardized, and the larger the M value is, the better the crack resistance is.

3. The evaluation method for the crack resistance of a two-stage concrete slab according to claim 2, characterized in that: The criterion layer includes the following index factors affecting the anti-cracking performance of concrete: splitting tensile strength, elastic modulus, compression work, autogenous shrinkage and drying shrinkage of concrete.

4. The method for evaluating the crack resistance of a two-stage concrete slab according to claim 2, characterized in that: All index factors are classified into positive and negative indicators, and then the data of each factor is standardized according to the range standardization conversion to obtain the standardized dimensionless number A i The test data of the criterion layer are standardized by range standardization. The standardization formula is as follows: X i is a positive indicator; X i Negative indicator.

5. The method for evaluating the crack resistance of a two-stage concrete slab according to claim 2, characterized in that: The step 1 of clarifying the index factors of the model criterion layer that affect the crack resistance of the secondary distribution panel concrete includes the following operations: Conduct splitting tensile strength test and record the splitting tensile strength; Conduct uniaxial compression test; first determine the preload standard, then record the stress-strain curve and load-displacement curve, and calculate the elastic modulus and compression work of concrete based on the data; Carry out autogenous shrinkage and drying shrinkage tests; measure the autogenous shrinkage and drying shrinkage of concrete specimens.

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