A method for compressive strength correction of non-standard specimens of large-size cement-stabilized crushed stone

Abstract

The present invention provides a method for correcting the compressive strength of non-standard specimens of large-size cement-stabilized gravel, which relates to the field of road engineering technology. The method comprises: determining a benchmark specimen and performing a compressive strength test on the benchmark specimen to obtain a compressive strength value of the benchmark specimen; constructing a calibrated three-dimensional discrete element numerical model of the specimen; using the calibrated three-dimensional discrete element numerical model of the specimen to perform a compressive strength numerical simulation of large-size cement-stabilized gravel specimens of different sizes to obtain a set of failure strengths; obtaining a strength-volume expression of failure strength and specimen size; determining a compressive strength correction coefficient of the large-size cement-stabilized gravel specimen using the strength-volume expression; and obtaining the true compressive strength value of the large-size cement-stabilized gravel specimen using the compressive strength correction coefficient and the compressive strength value of the benchmark specimen. The present invention solves the problem in the prior art of inaccurate test results due to inconsistent compressive strengths under specimens of different sizes.

Description

Technical Field

[0001] The invention relates to the technical field of road engineering, in particular to a method for correcting the compressive strength of a non-standard test piece of large-diameter cement-stabilized crushed stone. Background Art

[0002] Traditional cement-stabilized gravel bases are significantly affected by temperature and humidity, making them prone to shrinkage cracking. Under traffic loads, these cracks gradually propagate upward, forming reflective cracks that severely impact the service life of asphalt pavements. Large-size cement-stabilized gravel, with a large primary aggregate forming the framework and cement-stabilized gravel filler filling the voids, derives its strength primarily from the interlocking action of the large-size aggregate. Furthermore, large-size aggregate has a smaller specific surface area, requiring less cement to coat the aggregate. Using a large-size cement-stabilized gravel base effectively prevents reflective cracking in asphalt pavements.

[0003] Compressive strength is a key control parameter in the composition design of large-particle cement-stabilized crushed stone. Due to uneven aggregate distribution within specimens of varying sizes and the random distribution of microscopic defects such as voids and cracks, the compressive strength measured in laboratory tests varies across specimen sizes, impacting the reliability of the test results. Therefore, only by fully understanding how the compressive strength of large-particle cement-stabilized crushed stone varies with specimen size can the mechanical properties of the mixture be better guaranteed.

[0004] At present, for the use of large-size cement-stabilized gravel materials for road bases, domestic research mainly focuses on the mechanical properties and durability of large-size cement-stabilized gravel. The "Technical Specifications for the Construction of Filled Large-size Cement-stabilized Gravel Bases" (T / CECS G:K23-01-2019) stipulates that large-size gravel is a single-specification aggregate with a maximum nominal particle size of 73mm. The specification does not specify the size of the compressive strength test piece of the mixture. Under normal circumstances, the size of the test mold should be more than 4 times the maximum particle size of the aggregate. Taking into account the difficulties of homemade molds and test operations, most researchers have formed Cylindrical specimens have limitations when used to test the compressive strength of large-size cement-stabilized crushed stone, or when used only to experimentally study fillers in large-size cement-stabilized crushed stone. While some researchers have considered specimen size and have adopted custom sizes in their research, the rationality of these custom sizes and the validity of the measured data remain to be further verified. Summary of the Invention

[0005] In order to overcome the shortcomings of the existing technology, the purpose of the present invention is to provide a method for correcting the compressive strength of non-standard specimens of large-particle cement-stabilized gravel. The present invention solves the problem in the existing technology of inaccurate test results caused by inconsistent compressive strength of specimens of different sizes.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] A method for correcting the compressive strength of non-standard specimens of large-size cement-stabilized crushed stone comprises:

[0008] Determining a reference specimen and performing a compressive strength test on the reference specimen to obtain a compressive strength value of the reference specimen;

[0009] Constructing a three-dimensional discrete element numerical model of the specimen and calibrating the three-dimensional discrete element numerical model of the specimen using the compressive strength value of the reference specimen to obtain a calibrated three-dimensional discrete element numerical model of the specimen;

[0010] Using the calibrated three-dimensional discrete element numerical model of the specimen, numerical simulation of the compressive strength of large-size cement-stabilized crushed stone specimens of different sizes is performed to obtain a failure strength set;

[0011] A strength-volume expression of the destructive strength and the specimen size is obtained according to the volume of the large-size cement-stabilized crushed stone specimens of different sizes, the volume of the benchmark specimen, the compressive strength value of the benchmark specimen, and the destructive strength set, wherein the strength-volume expression includes: an abscissa expression and a ordinate expression of the strength;

[0012] Determine the compressive strength correction factor of large-size cement-stabilized crushed stone specimens using the strength-volume expression;

[0013] The true compressive strength value of the large-size cement-stabilized crushed stone specimen is obtained by using the compressive strength correction coefficient and the compressive strength value of the benchmark specimen.

[0014] Preferably, the benchmark specimen is a large-size cement-stabilized gravel specimen of 200mm×200mm×200mm.

[0015] Preferably, the side surface of the reference specimen is a pressure-bearing surface.

[0016] Preferably, the constructing of the three-dimensional discrete element numerical model of the specimen and calibrating the three-dimensional discrete element numerical model of the specimen using the compressive strength value of the reference specimen to obtain the calibrated three-dimensional discrete element numerical model of the specimen includes:

[0017] Obtaining three-dimensional profile information of the aggregate of the benchmark specimen;

[0018] Based on the three-dimensional contour information, the clump distribute command is used to uniformly generate large-size crushed stones step by step from large to small particle sizes, and the ball distribute command is used to generate coarse aggregate in the filling material, thereby obtaining a three-dimensional discrete element numerical model of the initial specimen;

[0019] The virtual specimen was loaded, the loading speed of the left and right walls was set to 0.05 m / s, and the microscopic parameters were adjusted multiple times to obtain the calibrated three-dimensional discrete element numerical model of the specimen.

[0020] Preferably, the intensity volume expression is:

[0021] y=Aexp(-Bx)+C

[0022]

[0023] Where: R c For any volume V c The compressive strength value of the non-standard (benchmark) specimen is shown in Figure 2. R0 is the compressive strength value of the non-standard (benchmark) specimen (200 mm), V0 is the volume of the non-standard (benchmark) specimen, exp is the exponential fitting formula, and A, B, and C are fitting constants.

[0024] Preferably, the expression of the true compressive strength value is:

[0025] R' c =aR0;

[0026] Among them, R' c is the true compressive strength value of the large-size cement-stabilized gravel specimen, a is the compressive strength correction coefficient of the non-standard specimen of large-size cement-stabilized gravel, and R0 is the compressive strength value of the non-standard (benchmark) specimen (200 mm).

[0027] A specimen forming device, comprising:

[0028] Removable test mold and vibratory compactor;

[0029] The detachable test mold is used to load the reference test piece, and the vibration compactor is used to perform vibration compaction on the reference test piece.

[0030] Preferably, the detachable trial mold comprises:

[0031] Base, front and rear baffles, left and right baffles, long bolt rods, short bolts and nuts;

[0032] The front and rear baffles and the left and right baffles are installed at the front, rear, left and right positions of the base. The front and rear baffles are fixed by two groups of long bolt rods and nuts, one group on each side. Each group consists of two long bolt rods and four nuts, and is symmetrically distributed along the central axis of the test mold. There is a protruding short bolt in the middle of the base and it is fixed to the long bolt rod by a nut.

[0033] The present invention discloses the following technical effects:

[0034] The present invention provides a method for correcting the compressive strength of non-standard specimens of large-size cement-stabilized gravel. First, the method for correcting the compressive strength of non-standard specimens of large-size cement-stabilized gravel proposed in this patent is applicable to the determination of the compressive strength of large-size cement-stabilized gravel base layers in the field of road engineering, and the method has strong applicability. The test mold structure combination is simple and clever, and it is easy to disassemble, avoiding a large number of time-consuming and labor-intensive indoor tests. The data obtained by simulation is reliable, and the compressive strength values ​​of large-size cement-stabilized gravel under different maximum nominal particle sizes can be accurately obtained; second, through the method for correcting the compressive strength of non-standard specimens of large-size cement-stabilized gravel proposed in this patent, in indoor tests, non-standard cubic specimens with a specimen size of 200 mm can be directly formed, and the true compressive strength value can be corrected by this method, thereby accurately evaluating the mechanical properties of large-size cement-stabilized gravel mixtures. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0036] Figure 1 A flow chart of a method for correcting the compressive strength of a non-standard specimen of large-size cement-stabilized crushed stone provided in an embodiment of the present invention;

[0037] Figure 2 A schematic diagram of a discrete element model of large-size cement-stabilized gravel provided in an embodiment of the present invention;

[0038] Figure 3 A schematic diagram showing the relationship between the strength ratio and volume ratio of samples of different sizes provided in an embodiment of the present invention;

[0039] Figure 4 A schematic diagram of a detachable test mold structure provided in an embodiment of the present invention.

[0040] Description of reference numerals:

[0041] 1-base; 2-front and rear baffles; 3-left and right baffles; 4-long bolt rod; 5-short bolt; 6-nut. DETAILED DESCRIPTION

[0042] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0043] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0044] like Figure 1 As shown, the present invention provides a method for correcting the compressive strength of non-standard specimens of large-size cement-stabilized crushed stone, comprising:

[0045] Step 100: determining a reference specimen and performing a compressive strength test on the reference specimen to obtain a compressive strength value of the reference specimen;

[0046] Specifically, large-size cement-stabilized gravel non-standard specimens were formed as benchmark specimens, and the compressive strength tests were performed on the specimens.

[0047] Step 200: constructing a three-dimensional discrete element numerical model of the specimen and calibrating the three-dimensional discrete element numerical model of the specimen using the compressive strength value of the reference specimen to obtain a calibrated three-dimensional discrete element numerical model of the specimen;

[0048] Specifically, with the help of discrete element software PFC3D, a three-dimensional discrete element numerical model of non-standard (benchmark) specimens of large-size cement-stabilized crushed stone was constructed, and the model was calibrated at a microscopic level using the compressive strength test results.

[0049] Step 300: using the calibrated three-dimensional discrete element numerical model of the specimen, numerically simulate the compressive strength of large-size cement-stabilized crushed stone specimens of different sizes to obtain a failure strength set;

[0050] Step 400: Obtaining a strength-volume expression of the destructive strength and the specimen size based on the volumes of the large-size cement-stabilized crushed stone specimens of different sizes, the volume of the benchmark specimen, the compressive strength value of the benchmark specimen, and the destructive strength set, wherein the strength-volume expression includes: a physical examination abscissa expression and a strength ordinate expression;

[0051] Step 500: Determine the compressive strength correction factor of the large-size cement-stabilized crushed stone specimen using the strength-volume expression;

[0052] Step 600: deriving the true compressive strength value of the large-size cement-stabilized crushed stone specimen using the compressive strength correction coefficient and the compressive strength value of the reference specimen.

[0053] Furthermore, the benchmark specimen is a large-size cement-stabilized gravel specimen of 200mm×200mm×200mm. The maximum nominal particle size d of the large-size cement-stabilized gravel mixture max ≥53mm.

[0054] Specifically, the synthetic gradation of large-size cement-stabilized gravel is shown in Table 1. The maximum nominal particle size dmax of large-size cement-stabilized gravel is 63 mm. Table 1 is as follows:

[0055] Table 1 Synthetic gradation of large-size cement-stabilized crushed stone

[0056]

[0057] The large-size cement-stabilized gravel mixture was loaded into a customized detachable test mold in two layers. During the loading process, a layer of filler was first laid, and then a layer of large-size gravel was piled up. The loading and tamping were repeated until the mixture was completely loaded into the non-standard test mold. A vibratory compactor was used to form non-standard (benchmark) specimens of large-size cement-stabilized gravel. To prevent the large-size gravel from breaking during the vibration process, the vibratory compactor was set to an excitation force of 6900N and a vibration frequency of 30Hz. The vibration was carried out in two layers, with each layer vibrating for 30s to form a 200mm×200mm×200mm cubic specimen. After the non-standard (benchmark) specimen was cured for 7 days according to the standard, the compressive strength of the large-size cement-stabilized gravel cubic specimen was tested using a press, with the side of the formed specimen as the compressive surface during the test.

[0058] Furthermore, the side surface of the reference specimen is a pressure-bearing surface.

[0059] Furthermore, the constructing of the three-dimensional discrete element numerical model of the specimen and calibrating the three-dimensional discrete element numerical model of the specimen using the compressive strength value of the reference specimen to obtain the calibrated three-dimensional discrete element numerical model of the specimen includes:

[0060] Obtaining three-dimensional profile information of the aggregate of the benchmark specimen;

[0061] Based on the three-dimensional contour information, the clump distribute command is used to uniformly generate large-size crushed stones step by step from large to small particle sizes, and the ball distribute command is used to generate coarse aggregate in the filling material, thereby obtaining a three-dimensional discrete element numerical model of the initial specimen;

[0062] The virtual specimen was loaded, the loading speed of the left and right walls was set to 0.05 m / s, and the microscopic parameters were adjusted multiple times to obtain the calibrated three-dimensional discrete element numerical model of the specimen.

[0063] Specifically, the EinScan SPV2 desktop scanner was used to scan the large-size crushed stone aggregate to obtain its three-dimensional profile information. The clump distribute command was used to uniformly generate large-size crushed stone in descending order of particle size. The ball distribute command was used to generate the coarse aggregate in the filler. The fine aggregate in the filler was uniformly replaced by balls with a radius of 2.5 mm. A numerical model of large-size cement-stabilized crushed stone with the same gradation as the benchmark specimen was constructed. The constructed model is shown in the figure below. Figure 2 As shown in the figure, the contact model between the large-size crushed stone unit, the internal unit of the filler, and the large-size crushed stone and filler unit is set as a parallel bond model, and the contact model between the wall and the aggregate is set as a linear contact model. The linear contact modulus, parallel bond modulus, stiffness ratio, normal strength, and tangential strength in the model are given initial values. The virtual specimen is loaded, and the loading speed of the left and right walls is set to 0.05 m / s. The stress-strain curve of the virtual specimen during the loading and failure process is recorded. The microscopic parameters are adjusted multiple times, and the relative error of the failure stress and Poisson's ratio of the two is calculated to be 2%. The parameter calibration results are shown in Table 2. Table 2 is as follows:

[0064] Table 2 Calibration results of microscopic parameters of large-size cement-stabilized gravel

[0065]

[0066] More specifically, large-size cement-stabilized crushed stone cube virtual specimens were constructed, with side lengths of 2.0dmax, 2.5dmax, 3.0dmax, 3.5dmax, and 4.0dmax, respectively. The compressive strength was numerically simulated, and the failure strength values ​​of the specimens were obtained as shown in Table 3. Table 3 is as follows:

[0067] Table 3 Average compressive strength of specimens of different sizes

[0068]

[0069] Furthermore, the ratio of the destructive strength of virtual specimens of different sizes to the destructive strength of non-standard (reference) specimens is used as the ordinate, and the ratio of the volume of virtual specimens of different sizes to the volume of non-standard (reference) specimens is used as the abscissa. The relationship diagram is shown below. By nonlinear fitting, the mathematical model of the strength ratio and volume ratio is established as follows: Figure 3 .

[0070] Specifically, the intensity volume expression is:

[0071] y=Aexp(-Bx)+C

[0072]

[0073] Where: R c For any volume V c The compressive strength value of the non-standard (benchmark) specimen (200 mm) is given in Figure 2. R0 is the compressive strength value of the non-standard (benchmark) specimen (200 mm), V0 is the volume of the non-standard (benchmark) specimen, and A, B, and C are fitting constants.

[0074] Furthermore, the expression of the true compressive strength value is:

[0075] R' c =aR0;

[0076] Among them, R' c is the true compressive strength value of the large-size cement-stabilized gravel specimen, a is the compressive strength correction coefficient of the non-standard specimen of large-size cement-stabilized gravel, and R0 is the compressive strength value of the non-standard (benchmark) specimen (200 mm).

[0077] More specifically, the established mathematical model is used to calculate that when x approaches infinity, the value of y is 0.95, so the size conversion coefficient a of the compressive strength of the large-size cement-stabilized crushed stone non-standard specimen is 0.95, and the true compressive strength value R' of the large-size cement-stabilized crushed stone specimen is c It is calculated by the following formula.

[0078] R c '=0.95R0=3.47MPa.

[0079] This embodiment further provides a specimen forming device, which includes: a detachable test mold and a vibration compactor; the detachable test mold is used to load a reference specimen, and the vibration compactor is used to vibrate and compact the reference specimen.

[0080] Specifically, the detachable test mold consists of a base 1, front and rear baffles 2, left and right baffles 3, long bolt rods 4, short bolts 5 and nuts 6. The test mold base 1 is a 280mm×280mm square with a thickness of 15mm. The front and rear baffles 2 of the test mold are a 280mm×250mm rectangle with a thickness of 10mm. The left and right baffles 3 of the test mold are a 200mm×250mm rectangle with a thickness of 10mm. The left and right baffles 3 are 30mm away from the side of the base 1. The front and rear baffles 2 are fixed by two groups of long bolt rods 4 and nuts 6, one group on each side of the left and right. Each group consists of two long bolt rods 4 and four nuts 6, and they are symmetrically distributed along the central axis of the test mold with a fixing spacing of 150mm. There is a protruding short bolt 5 in the middle of the base 1, which is fixed to the long bolt rod 4 by nuts 6. The schematic diagram of the structure of the large-size cement-stabilized gravel test mold is shown as follows: Figure 4 shown.

[0081] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0082] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A method for correcting the compressive strength of non-standard specimens of large-size cement-stabilized crushed stone, characterized in that: include: Determining a reference specimen and performing a compressive strength test on the reference specimen to obtain a compressive strength value of the reference specimen; Constructing a three-dimensional discrete element numerical model of the specimen and calibrating the three-dimensional discrete element numerical model of the specimen using the compressive strength value of the reference specimen to obtain a calibrated three-dimensional discrete element numerical model of the specimen; Using the calibrated three-dimensional discrete element numerical model of the specimen, numerical simulation of the compressive strength of large-size cement-stabilized crushed stone specimens of different sizes is performed to obtain a failure strength set; A strength-volume expression of the destructive strength and the specimen size is obtained according to the volume of the large-size cement-stabilized crushed stone specimens of different sizes, the volume of the benchmark specimen, the compressive strength value of the benchmark specimen, and the destructive strength set, wherein the strength-volume expression includes: a volume abscissa expression and a strength ordinate expression; Determine the compressive strength correction factor of large-size cement-stabilized crushed stone specimens using the strength-volume expression; The true compressive strength value of the large-size cement-stabilized crushed stone specimen is obtained by using the compressive strength correction coefficient and the compressive strength value of the benchmark specimen.

2. The method for correcting the compressive strength of non-standard specimens of large-size cement-stabilized crushed stone according to claim 1, characterized in that: The benchmark specimen is a large-size cement-stabilized gravel specimen of 200mm×200mm×200mm.

3. The method for correcting the compressive strength of non-standard specimens of large-size cement-stabilized crushed stone according to claim 1, characterized in that: The side surface of the reference specimen is a pressure-bearing surface.

4. The method for correcting the compressive strength of non-standard specimens of large-size cement-stabilized crushed stone according to claim 1, characterized in that: The constructing of the three-dimensional discrete element numerical model of the specimen and calibrating the three-dimensional discrete element numerical model of the specimen using the compressive strength value of the reference specimen to obtain the calibrated three-dimensional discrete element numerical model of the specimen includes: Obtaining three-dimensional profile information of the aggregate of the benchmark specimen; Based on the three-dimensional contour information, the clump distribute command is used to uniformly generate large-size crushed stones step by step from large to small particle sizes, and the ball distribute command is used to generate coarse aggregate in the filling material, thereby obtaining a three-dimensional discrete element numerical model of the initial specimen; The virtual specimen was loaded, the loading speed of the left and right walls was set to 0.05 m / s, and the microscopic parameters were adjusted multiple times to obtain the calibrated three-dimensional discrete element numerical model of the specimen.

5. The method for correcting the compressive strength of non-standard specimens of large-size cement-stabilized crushed stone according to claim 1, characterized in that: The intensity volume expression is: ； Where: For any volume The compressive strength value, is the compressive strength value of the non-standard specimen, is the volume of the non-standard specimen, exp is the exponential fitting formula, and A, B and C are fitting constants respectively.

6. The method for correcting the compressive strength of non-standard specimens of large-size cement-stabilized crushed stone according to claim 1, characterized in that: The expression of the true compressive strength value is: ； in, is the true compressive strength value of the large-size cement-stabilized gravel specimen, is the compressive strength correction coefficient of non-standard specimens of large-size cement-stabilized crushed stone, It is the compressive strength value of non-standard specimen.

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