CN114970093A - Construction and application of concrete material strength and fracture toughness compatibility regulation and control model - Google Patents
Construction and application of concrete material strength and fracture toughness compatibility regulation and control model Download PDFInfo
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Abstract
The invention discloses construction and application of a concrete material strength and fracture toughness compatibility regulation model, and aims to solve the technical problem that concrete strength and fracture toughness cannot be considered in the existing concrete mix proportion design. The invention determines the peak load of a test piece cast by aggregates based on different aggregate screening curvesP max And then calculating the nominal intensityσ N Constructed to obtain fracture toughnessK IC，i Representative particle size of sieving curve with aggregated a,i The quantitative relation curve equation of (2); given the expected achievable or controlled fracture toughness of concreteK IC，P Specific value, determining corresponding by quantitative relation curved a,p Based on thed a,p To adjust the aggregate gradationAnd (4) a curve is formed, so that the fracture characteristic of the concrete under the condition of constant strength is adjusted. The test piece used in the method is not limited, the pouring and testing work of the test piece can be met in a common laboratory, the cost is low, and the method is easy to implement.
Description
Technical Field
The invention relates to the technical field of concrete, in particular to construction and application of a concrete material strength and fracture toughness compatibility regulation and control model.
Background
In the actual concrete structure engineering construction process, under the condition that the strength meets the requirement, the damage caused by the condition that the fracture toughness does not meet the structural requirement is also considered. Especially for large-volume concrete structures such as dams and the like, cracks of different degrees appear in the dam body after years of operation, and even some cracks are formed in the construction stage. These cracks tend to start from the surface of the dam, which places higher demands on the safety of the concrete dam. Therefore, the fracture toughness needs to be adjusted to resist cracks in the construction stage, thereby meeting the structural stability requirement.
However, for the current design of concrete mix proportion, the evaluation index of the concrete mix proportion still meets the standard of concrete strength value and is qualified standard, and the related provisions that the concrete toughness meets the standard are not involved in the existing concrete structure design specifications of various industries. Therefore, a double-control technology for simultaneously controlling the strength index and the crack resistance index in the design process of the concrete mix proportion is a scientific difficult problem to be solved urgently, and the deep research on the problem is not reported yet.
The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is known to a person skilled in the art.
Disclosure of Invention
The invention aims to provide construction and application of a concrete material strength and fracture toughness compatibility regulation and control model, and aims to solve the technical problem that concrete strength and fracture toughness cannot be considered in the existing concrete mix proportion design.
In order to solve the technical problems, the invention adopts the following technical scheme:
a concrete material strength and fracture toughness compatibility regulation and control model is constructed, and the method comprises the following steps:
(1) selecting cement with corresponding labels and aggregates with at least more than three aggregate screening curves based on a given concrete mixing proportion w/c, and pouring to form a certain number of concrete test pieces with the same size;
(2) determination of the Peak load P of the concrete samples max When peak load P max When the relative error is larger than 15%, the test result of the group is invalid, and the concrete test piece is poured again until the relative error is smaller than 15%; when the relative error is less than 15%, carrying out the next step;
by controlling the structural failure load P max The strength of the prepared concrete material is basically unchanged;
(3) from the peak load P of each concrete specimen max Calculating its nominal intensity sigma N So as to achieve the nominal strength sigma of the concrete material N A substantially constant purpose;
(4) maximum aggregate particle size d for various aggregate screening curves max,i From Fuller&Calculating the representative particle diameter d by Thompson formula a,i ；
(5) D is calculated according to the following formula a,i Fracture toughness K of each corresponding concrete sample IC,i ；
For a three-point bending test piece,
in the case of a wedge-type split,
wherein W is the height of the test piece; w 1 ＝W-a 0 -Δa fic ；W 2 ＝W+a 0 +Δa fic (ii) a Alpha is the seam height ratio; a is 0 Is the initial fracture length; p is max The actual measurement peak load of each concrete sample is obtained; a is e Is a geometric parameter; Δ a fic Is the virtual crack propagation of the test piece, Δ a fic ＝d a,i 。
(6) (d) obtained in steps (4) and (5) a,i ,K IC,i ) I is more than or equal to 3, and y is established as ax 3 +bx 2 Fracture toughness K of + cx + d IC,i Representative particle size d from the sieving curve of aggregate a,i The quantitative relation curve equation of (2); wherein a, b, c and d are regression coefficients, x represents the representative particle size of an aggregate sieving curve, and y represents fracture toughness.
Preferably, in the step (1), the concrete sample has a height W and an initial crack length a 0 The height W of the three-point bending test piece with the test piece thickness B and the test piece span S is 50-400 mm, and the seam height ratio alpha is 0.1-0.6; or height W, initial crack length a 0 And the wedge split test piece with the test piece thickness B has the height W of 200-2250 mm and the seam height ratio alpha of 0.1-0.7.
Preferably, in said step (3), the nominal intensity σ N Calculated from formula (c) or (d):
for a three point bend test piece:
for wedge split test pieces:
wherein, P max Actually measuring the peak load of each concrete sample; w is the height of the test piece; b is the thickness of the test piece; and S is the test piece span.
Preferably, in the step (5), the geometric parameter a in formula (r) e The following formula is used to calculate,
wherein alpha is a seam height ratio; a is 0 Is the initial fracture length; y (α) is a geometric influence parameter, and:
when S/W is 2.5
When S/W is 4
When S/W is 8, Y (alpha) is 1.106-1.552 alpha +7.71 alpha 2 -13.53α 3 +14.23α 4 ；
If Y (alpha) is calculated by interpolation method when S/W is 2.5-4 or S/W is 4-8, for example, S/W is 2.5-4, then
If S/W < 2.5 or S/W > 8, Y (α) is calculated by extrapolation, e.g. if S/W is 9 > 8, then
Preferably, in the step (5), the geometric parameter a in the formula (c) is e Calculated from the following formula,
wherein alpha is the seam height ratio of each test piece; a is 0 Is the initial fracture length; y (α) is a geometric influence parameter, and
a method for regulating and controlling the compatibility of the strength and the fracture toughness of a concrete material comprises the following steps:
(1) k for concrete given the need to anticipate achieving or setting control IC，P A specific value;
(2) fracture toughness K as established by claim 1 IC,i Representative particle size d from the sieving curve of aggregate a,i Is the quantitative relation curve y ═ ax 3 +bx 2 + cx + d determining the corresponding d a,p ；
(3) Based on corresponding d a,p The aggregate grading curve is adjusted, so that the fracture characteristic of the concrete under the condition of constant strength is adjusted.
Compared with the prior art, the invention has the main beneficial technical effects that:
1. the invention finds out the representative particle diameter d a,i Fracture toughness K of concrete IC,i The relationship is influenced quantitatively.
2. The invention is based on a test specimen and a test method, i.e. the determination or prediction of the concrete material properties from the strength and fracture dual control, or on the corresponding d a,p The aggregate grading curve is adjusted, so that the adjustment of the fracture characteristic under the condition of unchanged concrete strength is realized, and the problem that the related requirements of actual concrete engineering are difficult to meet due to the fact that only the concrete strength is inspected and the regulation and control of the concrete toughness are neglected in the design process of the existing concrete mixing proportion is solved.
3. The test piece used in the method is not limited, the pouring and testing work of the test piece can be met in a common laboratory, the cost is low, and the method is easy to implement.
Drawings
FIG. 1 is a flow chart of a quantitative method for regulating and controlling a model by compatibility of concrete material strength and fracture toughness according to the present invention.
FIG. 2 is a diagram illustrating a quantitative relationship curve and an aggregate gradation adjustment chart established in accordance with an embodiment of the present invention; wherein (a) is fracture toughness K IC,i And a representative particle diameter d a,i The (b) and (c) are respectively the curves for achieving different fracture toughness K IC,i The aggregate gradation adjustment diagram of (1).
FIG. 3 is a quantitative relationship curve and an aggregate gradation adjustment chart established in the second embodiment of the present invention; wherein (a) is fracture toughness K IC,i And represents the particle diameter d a,i The (b) and (c) are respectively the curves for achieving different fracture toughness K IC,i The aggregate gradation adjustment diagram of (1).
FIG. 4 is a quantitative relationship curve and an aggregate gradation adjustment chart established in the third embodiment of the present invention; wherein (a) is fracture toughness K IC,i And represents the particle diameter d a,i The (b) and (c) are respectively the curves for achieving different fracture toughness K IC,i The aggregate gradation adjustment diagram of (1).
FIG. 5 is a quantitative relationship curve and an aggregate gradation adjustment chart established in the fourth embodiment of the present invention; wherein (a) is fracture toughness K IC,i And represents the particle diameter d a,i The (b) and (c) are respectively the curves for achieving different fracture toughness K IC,i The aggregate gradation adjustment diagram of (1).
Detailed Description
The following examples are intended to illustrate the present invention in detail and should not be construed as limiting the scope of the present invention in any way.
Some of the steps or methods involved in the following examples are conventional in the art, unless otherwise specified, and all of the materials involved are commercially available, unless otherwise specified.
The research of the invention finds that (see figure 1), when the w/c and the size of the test piece are fixed values, the peak load P measured by the change of different aggregate grading curves max And the nominal intensity σ calculated N The difference is very small, but the fracture toughness is very different; maximum of screening curves for various aggregatesAggregate particle diameter d max,i From Fuller&Calculating the representative particle diameter d by Thompson formula a,i The corresponding fracture toughness K can be obtained IC,i (ii) a According to d obtained a,i 、K IC,i Establishing y as ax 3 +bx 2 Fracture toughness K of + cx + d IC,i Representative particle size d from the sieving curve of aggregate a,i The quantitative relation curve equation of (1).
The first embodiment is as follows:
the test specimen is three-point bending specimen concrete, the fine aggregate is river sand, the coarse aggregate is formed by crushing limestone, and the cement is 525 # Ordinary portland cement has a water-cement ratio w/c of 0.4. The test pieces are divided into four groups, wherein the maximum particle size of the aggregate is d max,i 5.25, 10.5, 21, 31.5mm, 3 pieces each. All the dimensions of the test piece are that the height W is 100mm, the thickness B is 100mm, the span height ratio S/W is 3, the initial seam height ratio alpha is a 0 and/W is 0.2. All tests were carried out on a 160kN compression tester.
Respectively mixing the aggregate with the maximum particle diameter d max,1 、d max,2 、d max,3 、d max,4 Substituted into Fuller&Thompson formula
Calculating the ratio of particle sizes of different aggregates, and performing weighted average to calculate the representative particle size d a,1 、d a,2 、d a,3 、d a,4 。
Actual measurement peak load P based on each three-point bending test piece max The form and the size of the test piece, and the nominal strength sigma of the corresponding test piece is calculated according to the formula N ：
According to different representative particle diameters d a,i Calculating different fracture toughness K from the following formula IC,i And (3) calculating:
equivalent crack length a in equation (i) e Calculated by the following formula:
when S/W is 2.5
When S/W is 4
When S/W is 8, Y (alpha) is 1.106-1.552 alpha +7.71 alpha 2 -13.53α 3 +14.23α 4 ；
By (d) a,i ,K IC,i ) I is not less than 4, and establish y as ax 3 +bx 2 Fracture toughness K of + cx + d IC，i Representative particle size d from the sieving curve of aggregate a,i The quantitative relationship curve of (1).
Given the expected breaking toughness K of the concrete IC，P Specific value, by quantitative relation curve y ═ ax 3 +bx 2 + cx + d, i.e. determining the corresponding d a,p (ii) a Based on given d a,p The aggregate grading curve is adjusted, so that the fracture characteristic of the concrete under the condition of constant strength can be adjusted randomly. The nominal strength and fracture toughness calculated from the test data are shown in table 1. Fracture toughness K IC，i And represents the particle diameter d a,i See fig. 2 (a); FIG. 2(b) is the fracture toughness K expected to be achieved IC,p ＝0.95MPa·m 1/2 An aggregate grading curve adjusted according to the quantitative relation curve; FIG. 2(c) is a graph of the predicted fracture toughness K achieved IC,p ＝1.15MPa·m 1/2 And adjusting the aggregate grading curve according to the quantitative relation curve.
Therefore, the grading curve of the aggregate is quantitatively adjusted by the representative particle size of the aggregate, and the function that the strength of the concrete is unchanged and the toughness index is randomly changed in the design process of the mix proportion of the concrete can be realized.
TABLE 1 nominal Strength and fracture toughness of three-Point bending test pieces
Example two:
the test specimen is three-point bending specimen concrete, the fine aggregate is natural sand, the coarse aggregate is formed by crushing limestone, and the cement is 525 # Ordinary portland cement has a water-cement ratio w/c of 0.37. The test pieces are divided into four groups, wherein the maximum particle size of the aggregate is d max,i 10, 16, 20, 31.5mm, 3 pieces each. The sizes of the test pieces are all that the height W is 100mm, the thickness B is 100mm, the span height ratio S/W is 4, and the initial seam height ratio alpha is a 0 and/W is 0.5. All tests were performed on an Instron 8501 digital servo hydraulic test system.
Respectively mixing the aggregate with the maximum particle diameter d max,1 、d max,2 、d max,3 、d max,4 Substituting into Fuller&Thompson formula
Calculating the ratio of different aggregate particle sizes, and calculating the representative particle size d by weighted average a,1 、d a,2 、d a,3 、d a,4 。
Based on the actual measurement peak load, the test piece form and the test piece size of each test piece, the nominal strength sigma of the test piece is calculated according to the formula III N 。
According to different representative particle diameters d a,i Calculating different fracture toughness K by formula IC,i 。
Equivalent crack length a in equation (i) e Calculated by formula (v).
By (d) a,i ,K IC,i ) I is more than or equal to 4, and y is established as ax 3 +bx 2 Fracture toughness K of + cx + d IC，i Representative particle size d from the sieving curve of aggregate a,i The quantitative relationship curve of (1).
Given a desired mix to be achieved or controlledFracture toughness K of concrete IC,P Specific value is determined by the quantitative relation curve y ═ ax 3 +bx 2 + cx + d, the corresponding d can be determined a,p (ii) a Based on given d a,p The aggregate grading curve is adjusted, so that the fracture characteristic of the concrete under the condition of constant strength can be adjusted randomly.
The nominal strength and fracture toughness parameters calculated from the test data are shown in table 2. Fracture toughness K IC,i And represents the particle diameter d a,i See fig. 3 (a); FIG. 3(b) is the fracture toughness K expected to be achieved IC,p ＝1.28MPa·m 1/2 An aggregate grading curve adjusted according to the quantitative relation curve; FIG. 3(c) is the predicted fracture toughness K achieved IC,p ＝1.36MPa·m 1/2 And adjusting the aggregate grading curve according to the quantitative relation curve.
Therefore, the grading curve of the aggregate is quantitatively adjusted through the representative particle size of the aggregate, and the function that the strength of the concrete is unchanged and the toughness index is randomly changed in the design process of the mix proportion of the concrete can be realized.
TABLE 2 nominal Strength and fracture toughness of three-Point bending test pieces
Example three:
the test specimen is wedge split test specimen concrete, and the used materials are river sand and gravel produced in Dalian cement plant and 425 produced in Dalian cement plant # Ordinary portland cement has a water-cement ratio w/c of 0.48. The test pieces are divided into four groups, wherein the maximum grain diameter of the aggregate is d max,i 20, 40, 80, 150mm, 4 pieces each. The test pieces all have the height W of 450mm, the thickness B of 450mm and the initial seam height ratio alpha of a 0 and/W is 0.4. All tests were performed on a 5000kN compression tester.
Respectively mixing the aggregate with the maximum particle diameter d max,1 、d max,2 、d max,3 、d max,4 Substituting into Fuller&Thompson formula
Calculating the ratio of different aggregate particle sizes, and calculating the representative particle size d by weighted average a,1 、d a,2 、d a,3 、d a,4 。
Based on the actual measurement peak load, the test piece form and the test piece size of the test piece, the nominal strength sigma of the test piece is calculated according to the following formula N :
According to different representative particle diameters d a,i Calculating different fracture toughness K from the following formula IC,i ：
Equivalent crack length a in formula- e Calculated by the following formula:
by (d) a,i ,K IC,i ) I is more than or equal to 4, and y is established as ax 3 +bx 2 Fracture toughness K of + cx + d IC，i Representative particle size d from aggregate sieving curve a,i The quantitative relationship curve of (1).
Given the expected breaking toughness K of the concrete IC,P Specific value, by quantitative relation curve y ═ ax 3 +bx 2 + cx + d, i.e. determining the corresponding d a,p (ii) a Based on given d a,p The aggregate grading curve is adjusted, so that the fracture characteristic of the concrete under the condition of constant strength can be adjusted randomly.
Nominal strength and fracture toughness parameter calculated from test dataSee table 3. Fracture toughness K IC，i And represents the particle diameter d a,i See fig. 4 (a); FIG. 4(b) is the predicted fracture toughness K achieved IC,p ＝1.06MPa·m 1/2 An aggregate grading curve adjusted according to the quantitative relation curve; FIG. 4(c) is the predicted fracture toughness K achieved IC,p ＝1.16MPa·m 1/2 And adjusting the aggregate grading curve according to the quantitative relation curve.
The grading curve of the aggregate is adjusted quantitatively by representing the particle size of the aggregate, so that the function that the strength of the concrete is unchanged and the toughness index is changed randomly in the design process of the mix proportion of the concrete is realized.
TABLE 3 nominal Strength and fracture toughness of wedge split test pieces
Example four:
the test specimen is wedge split test specimen concrete, and the used materials are natural fine aggregate, coarse aggregate and 425 # Ordinary portland cement has a water-cement ratio w/c of 0.55. The test pieces are divided into four groups, wherein the maximum particle size of the aggregate is d max,i 10, 19, 38, 76mm, 3 pieces each. The test pieces are all 760mm in height W, 410mm in thickness B and a alpha in initial seam height ratio 0 and/W is 0.2. All tests were carried out on a 5000kN compression tester.
Respectively mixing the aggregate with the maximum particle diameter d max,1 、d max,2 、d max,3 、d max,4 Substituting into Fuller&Thompson formula
Calculating the ratio of different aggregate particle sizes, and calculating the representative particle size d by weighted average a,1 、d a,2 、d a,3 、d a,4 。
Based on the actual measurement peak load, the test piece form and the test piece size of the test piece, the nominal strength sigma of the test piece is calculated by the formula (IV) N 。
According to different representative particle diameters d a,i Calculating the different fracture toughness K IC,i Calculated by equation (c).
Equivalent crack length a in formula- e Calculated by equation (v).
By (d) a,i ,K IC,i ) I is not less than 4, and establish y as ax 3 +bx 2 Fracture toughness K of + cx + d IC，i Representative particle size d from the sieving curve of aggregate a,i The quantitative relationship curve of (1).
Given the expected breaking toughness K of the concrete IC,P Specific value, by quantitative relation curve y ═ ax 3 +bx 2 + cx + d, i.e. determining the corresponding d a,p (ii) a Based on given d a,p The aggregate grading curve is adjusted, so that the fracture characteristic of the concrete under the condition of constant strength can be adjusted randomly.
The nominal strength and fracture toughness calculated from the test data of this example are shown in Table 4. Fracture toughness K IC，i And represents the particle diameter d a,i See fig. 5 (a); FIG. 5(b) is the predicted fracture toughness K achieved IC,p ＝0.76MPa·m 1/2 An aggregate grading curve adjusted according to the quantitative relation curve; FIG. 5(c) is the predicted fracture toughness K achieved IC,p ＝0.85MPa·m 1/2 And adjusting the aggregate grading curve according to the quantitative relation curve.
The grading curve of the aggregate is adjusted quantitatively by representing the particle size of the aggregate, so that the function that the strength of the concrete is unchanged and the toughness index is changed randomly in the design process of the mix proportion of the concrete is realized.
TABLE 4 nominal Strength and fracture toughness of wedged Split test pieces
While the invention has been described in detail with reference to the drawings and examples, it will be understood by those skilled in the art that various changes in the form and details may be made therein without departing from the spirit and scope of the invention.
Claims (6)
1. A method for constructing a concrete material strength and fracture toughness compatibility regulation and control model is characterized by comprising the following steps:
(1) selecting cement with corresponding labels and aggregates with at least more than three aggregate screening curves based on a given concrete mixing proportion w/c, and pouring and molding a certain number of concrete test pieces with the same size;
(2) determination of the Peak load P of the concrete samples max When peak load P max When the relative error is more than 15%, the test result of the group is invalid, and the concrete sample is poured again until the relative error is less than or equal to 15%, and the next step is carried out;
(3) from the peak load P of each concrete specimen max Calculating its nominal intensity sigma N So as to achieve the nominal strength sigma of the concrete material N A substantially constant purpose;
(4) maximum aggregate particle size d for various aggregate screening curves max,i From Fuller&Calculating the representative particle diameter d by Thompson formula a,i ；
(5) D is calculated according to the following formula a,i Fracture toughness K of each corresponding concrete sample IC,i ；
For a three-point bending test piece,
in the case of a wedge-type split,
wherein W is the height of the test piece; w 1 ＝W-a 0 -Δa fic ；W 2 ＝W+a 0 +Δa fic (ii) a Alpha is the seam height ratio; a is 0 Is the initial fracture length; p max The actual measurement peak load of each concrete sample is obtained; a is e Is a geometric parameterCounting; Δ a fic Is the virtual crack propagation of the test piece, Δ a fic ＝d a,i ；
(6) (d) obtained in steps (4) and (5) a,i ,K IC,i ) I is not less than 3, and establish y as ax 3 +bx 2 Fracture toughness K of + cx + d IC,i Representative particle size d from the sieving curve of aggregate a,i The quantitative relation curve equation of (2); wherein a, b, c and d are regression coefficients, x represents a representative particle size of an aggregate sieving curve, and y represents fracture toughness.
2. The method for constructing the model for regulating compatibility of strength and fracture toughness of concrete material according to claim 1, wherein in the step (1), the concrete sample has a height W and an initial crack length a 0 The height W of the three-point bending test piece with the test piece thickness B and the test piece span S is 50-400 mm, and the seam height ratio alpha is 0.1-0.6; or height W, initial crack length a 0 And the wedge split test piece with the test piece thickness B has the height W of 200-2250 mm and the seam height ratio alpha of 0.1-0.7.
3. The method for constructing the concrete material strength and fracture toughness compatibility regulation model according to claim 1, wherein in the step (3), the nominal strength σ is N Calculated from formula (c) or (d):
for a three point bend test piece:
for a wedged split test piece:
wherein, P max Actually measuring the peak load of each concrete sample; w is the height of the test piece; b is the thickness of the test piece; and S is the test piece span.
4. The concrete material strength and fracture toughness compatibility regulating and controlling mold according to claim 1The method for constructing a template is characterized in that, in the step (5), the geometric parameter a in the formula (r) e Calculated from the following equation:
wherein alpha is a seam height ratio; a is 0 Is the initial fracture length; y (α) is a geometric influence parameter, and:
when S/W is 2.5
When S/W is 4
When S/W is 8, Y (alpha) is 1.106-1.552 alpha +7.71 alpha 2 -13.53α 3 +14.23α 4 ；
If S/W is 2.5-4 or S/W is 4-8, calculating Y (alpha) by adopting an interpolation method;
if S/W is less than 2.5 or S/W is more than 8, an extrapolation method is adopted to calculate Y (alpha).
5. The method for constructing the concrete material strength and fracture toughness compatibility regulation model according to claim 1, wherein in the step (5), the geometric parameter a in the formula (II) is e Calculated from the following formula:
wherein alpha is the seam height ratio of each test piece; a is 0 Is the initial fracture length; y (α) is a geometric influence parameter, and
6. a method for regulating and controlling the compatibility of the strength and the fracture toughness of a concrete material comprises the following steps:
(1) k for concrete given the need to anticipate achieving or setting control IC，P A specific value;
(2) fracture toughness K established by claim 1 IC,i Representative particle size d from aggregate sieving curve a,i Is the quantitative relation curve y ═ ax 3 +bx 2 + cx + d determines the corresponding d a,p ；
(3) Based on corresponding d a,p The aggregate grading curve is adjusted, so that the fracture characteristic of the concrete under the condition of constant strength is adjusted.
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