A Rockwell hardness measurement method, effective hardness and application of cement-based composite materials

Abstract

The present invention discloses a Rockwell hardness measurement method, effective hardness and application of cement-based composite materials, and belongs to the field of civil engineering technology. The Rockwell hardness measurement method of cement-based composite materials comprises the following steps: casting the cement-based composite material into a test block; after polishing multiple side surfaces, selecting a square measurement area away from the edge on the side surface; evenly selecting points in the measurement area to test the Rockwell hardness; taking the average value of the indentation data of multiple effective points. The measured data range is concentrated, the variance is small, and the accuracy is high. The characterization method of effective hardness comprises the following steps: treating concrete as a two-phase material composed of a coarse aggregate phase and a mortar matrix phase, and calculating the volume of coarse aggregate and the effective length of mortar matrix respectively; experimentally measuring the Rockwell hardness of coarse aggregate and the Rockwell hardness of mortar matrix; and weighting to obtain the effective hardness of concrete. This method improves the defect that the existing hardness testing methods at this stage cannot comprehensively characterize the mechanical properties of materials.

Description

Technical Field

[0001] The invention belongs to the technical field of civil engineering, and in particular relates to a Rockwell hardness measurement method, effective hardness and application of a cement-based composite material. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Hardness refers to the ability of a material's surface to resist plastic deformation caused by the indentation of a harder object. It is an important indicator for measuring the hardness or softness of a material. Common hardness testing methods include Rockwell hardness, Brinell hardness, Vickers hardness, and microhardness. The Rockwell hardness test requires low specimen preparation, and the hardness value read has the same dimension as the indentation data. It has the advantages of a short test cycle and minimal damage to the sample, and is widely used in actual production. The testing principle of Rockwell hardness is to determine the hardness value by measuring the pressure applied by the indenter on the material surface and the indentation depth. By using different indenters, Rockwell hardness can be applied to materials with different hardness ranges. Currently, Rockwell hardness is mainly applied to homogeneous materials such as metals.

[0004] Cement-based composites are the most widely used and consumed artificial materials in the world. These include cement paste, cement mortar, concrete, high-ductility fiber-reinforced cement-based composites, and ultra-high-performance concrete. Rockwell hardness values are susceptible to numerous factors, including test force, indenter shape and size, and specimen surface condition. Therefore, Rockwell hardness testing requires adherence to strict testing conditions and operating procedures to ensure accurate and reliable results. However, due to the complex composition of cement-based composites, a simple, reproducible Rockwell hardness measurement method and its effectiveness are currently unavailable.

[0005] Concrete is a typical heterogeneous material, primarily composed of coarse aggregate, fine aggregate, cementitious materials, and water. Concrete can be considered a two-phase material with coarse aggregate uniformly distributed within a mortar matrix. The Rockwell hardness test only measures the surface hardness of the specimen, i.e., the hardness of the concrete matrix, and is unable to characterize the concrete's overall performance. Summary of the Invention

[0006] In order to address the deficiencies of the prior art, the present invention aims to provide a Rockwell hardness measurement method, effective hardness and application of cement-based composite materials, which not only improves the accuracy of the Rockwell hardness measurement results of cement-based composite materials, but also uses the effective hardness combined with the Rockwell hardness to comprehensively characterize the homogeneity of the cement-based composite materials, providing guidance for material performance optimization.

[0007] In order to achieve the above object, the technical solution of the present invention is:

[0008] In a first aspect, a method for measuring the Rockwell hardness of a cement-based composite material comprises the following steps:

[0009] S1. Casting the cement-based composite material into a test block, wherein the test block has a plurality of side surfaces adjacent to a casting surface;

[0010] S2. After polishing multiple sides flat, select a square measurement area on the side away from the edge;

[0011] S3. Evenly select points in the measurement area, test the Rockwell hardness, and read the indentation data of multiple valid points;

[0012] S4. Taking the average value of the indentation data of multiple valid points as the Rockwell hardness of the cement-based composite material;

[0013] The method for judging effective points is: the distance between the indentation centers of adjacent effective points is not less than 4 times the diameter of the spherical indenter selected during the Rockwell hardness measurement, and the distance between the indentation center and the edge of the specimen is not less than 2.5 times the diameter of the selected spherical indenter.

[0014] Optionally, in S1, the test block is a cube, the casting surface is any one surface of the cube, and the test block has four side surfaces adjacent to the casting surface.

[0015] Optionally, in S1, the test block is demoulded, polished, and cleaned to obtain a test sample; in one or more embodiments, the test sample is 100*100*100mm 3 of cube blocks.

[0016] Optionally, in S2, after the side surface is polished flat, the powder remaining on the surface of the sample is wiped off with an alcohol cotton ball.

[0017] Optionally, in S2, multiple edge vertical lines are drawn on the side surface to divide each side surface into multiple small square areas, and the square area at the center is selected as the measurement area;

[0018] In one or more embodiments, the vertical line of the edge divides the side into multiple 20*20mm 2 In order to avoid the influence of edge effect, the nine central square areas are selected as the pressure measurement point area.

[0019] Optionally, in S3, a point is taken at the center of the small square area.

[0020] Optionally, in S3, the indentation data is the difference between the total test force indentation depth and the initial test force indentation depth of the Rockwell hardness tester.

[0021] Optionally, in S4, at least one valid point is selected from each side.

[0022] Optional, in S4, in 3 sizes all 100*100*100mm 3 At least 100 valid points are selected on the cube test block for degree measurement.

[0023] In a second aspect, a method for characterizing the effective hardness of concrete comprises the following steps:

[0024] (1) Concrete is considered as a two-phase material composed of a coarse aggregate phase and a mortar matrix phase. The sum of the volumes of the coarse aggregate phase is calculated as the coarse aggregate volume, and the sum of the volumes of the mortar matrix phase is calculated as the mortar matrix volume.

[0025] (2) Calculate the effective length of the coarse aggregate phase based on the volume of the coarse aggregate, and calculate the effective length of the mortar matrix phase based on the volume of the mortar matrix;

[0026] (3) The Rockwell hardness of the coarse aggregate is measured experimentally, and the Rockwell hardness of the concrete sample surface is measured using the Rockwell hardness measurement method of the cement-based composite material, which is the Rockwell hardness of the mortar matrix phase;

[0027] (4) The effective hardness of concrete is obtained by weighting the effective length of the coarse aggregate phase, the Rockwell hardness of the coarse aggregate phase, the effective length of the mortar matrix phase, and the Rockwell hardness of the mortar matrix phase.

[0028] Optionally, the mortar matrix phase includes: a uniform mixture of fine aggregate, cementitious material and water, wherein the fine aggregate refers to aggregate with a particle size of 0.1 to 4.75 mm; and the coarse aggregate refers to aggregate with a particle size of 4.75 to 16 mm.

[0029] Optionally, in step (2), the effective length is: the side length of the cube after the volume is equivalent to a cube.

[0030] Optionally, in step (3), the Rockwell hardness of the coarse aggregate and the Rockwell hardness of the mortar matrix are measured using the same method.

[0031] Thirdly, the above-mentioned effective hardness is used to evaluate the compressive strength of concrete, optimize curing methods or optimize component ratios.

[0032] The beneficial effects of the present invention are:

[0033] 1. The Rockwell hardness test method proposed in this invention can accurately measure the Rockwell hardness of various cement-based composite materials, resolving the shortcomings of existing testing methods that cannot quickly and accurately measure material hardness. By selecting valid points in a set area according to the set method, the measured data range is concentrated, the standard deviation is small, and the accuracy is high. It is applicable to cement-based composite materials with a wide range of properties (such as compressive strength ranging from 30MPa to 220MPa).

[0034] 2. This invention proposes a method for measuring effective hardness, which can reflect the impact of different components within cement-based composites on their overall performance. Because hardness is a comprehensive indicator of mechanical properties such as elasticity, plasticity, strength, and toughness, the accuracy of hardness tests for heterogeneous concrete composites is relatively poor. This method overcomes the shortcomings of existing hardness testing methods, which are unable to comprehensively characterize the mechanical properties of materials.

[0035] 3. The effective hardness proposed in this invention reflects the impact of different components within a cementitious composite material on its overall performance. The effective hardness testing method of this invention allows for the assessment of a material's compressive strength without destructive testing. Given the same Rockwell hardness, effective hardness can be used to assess material homogeneity, providing a basis for further optimization of curing methods and component ratios. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0037] Figure 1 Schematic diagram of the Rockwell hardness measurement process in a specific embodiment of the present invention;

[0038] Figure 2 It is a schematic diagram of a method for selecting pressure measurement point areas in a specific embodiment of the present invention.

[0039] Figure 3 It is a distribution diagram of the results of the Rockwell hardness measurement method in a specific embodiment of the present invention.

[0040] Figure 4 It is a schematic diagram of a method for calculating effective length in a specific embodiment of the present invention.

[0041] Figure 5 This is an example of calculating the effective hardness in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0042] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0043] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0044] Example 1

[0045] A method for measuring the Rockwell hardness of a cement-based composite material comprises the following steps:

[0046] S1. Cast the cement-based composite material into three cubic test blocks. Each test block has four sides adjacent to the casting surface. After demoulding, polishing and cleaning, the test blocks are obtained to obtain a test sample size of 100*100*100mm. 3 of the sample.

[0047] S2. After polishing the sides, wipe off the powder remaining on the surface of the sample with an alcohol cotton ball to prevent the powder from affecting the subsequent indentation test. Figure 2 As shown, multiple lines perpendicular to the side edges are drawn on the side to divide each side into 20*20mm square blocks, totaling 25 square blocks; to avoid the influence of edge effects, the middle nine square blocks are selected as the pressure measurement point area.

[0048] S3. Take a point at the center of the small square block in the measurement area, test the Rockwell hardness, and read the indentation data of multiple valid points;

[0049] S4. Take the average value of the indentation data of at least 100 valid points on the three cubic test blocks as the Rockwell hardness of the cement-based composite material, and calculate its standard deviation.

[0050] In S3, the Rockwell hardness measurement methods for a single effective point include:

[0051] Place the sample on the platform of the Rockwell hardness tester and fix it;

[0052] Select a steel ball with a diameter of 1.5875 mm as the indenter, set the initial test force (Preliminary force), preferably 29.42 N, and set the total test force (Total force), preferably 147.1 N;

[0053] Start the instrument, such as Figure 1 As shown, the sample contacts the indenter until the initial experimental force is reached, and the initial experimental force is maintained for 15 seconds. The instrument measures the indentation depth and calculates it as the baseline indentation depth h0;

[0054] The instrument continues to load until the total test force is reached, maintains the total test force for 15 seconds, then unloads to the initial test force and maintains it for 15 seconds. The instrument measures the indentation depth and calculates it as the baseline indentation depth h1;

[0055] Calculate the Rockwell hardness H (mm),

[0056] Using the test parameters of S3, the method for determining the effective point is: the distance between the centers of two adjacent indentations should be at least 4 times the diameter of the spherical indenter (6.35mm) and shall not be less than 2mm; and the distance between the center of any indentation and the edge of the specimen should be at least 2.5 times the diameter of the spherical indenter and shall not be less than 1mm.

[0057] According to the method of this embodiment, the Rockwell hardness of the cement-based composite material with the set components is measured, and the Rockwell hardness is measured on the same material according to the random point method. The measurement results of the method of this embodiment are statistically analyzed. Figure 3 The variance of the method in this embodiment is 2.2, while the variance of the random point method is 4.5. It can be seen that the data of the method in this embodiment is more concentrated, the variance is lower, and it has better accuracy and reliability.

[0058] Example 2

[0059] Method for determining unidirectional homogeneous materials

[0060] In cement-based composite materials, the common matrix is cement mortar.

[0061] Using the test method of Example 1, the effective hardness, Rockwell hardness, and tensile strength of cement pastes (CP-1 to CP-5) and cement mortars (CM-1 to CM-7) with different component ratios were tested. Cement paste is a single-phase homogeneous material composed of cement and water, while cement mortar is a cement-based material composed of fine aggregate, cementitious material, and water. In this example, fine aggregate refers to aggregate with a particle size of less than 4.75 mm. Therefore, cement mortar is used as a two-phase material in this example.

[0062] The volume of fine aggregate (V 细骨料 ) is converted into the effective length of fine aggregate phase (l 细骨料 ), the mortar matrix volume (V 水泥净浆 ) is converted into the effective length of cement paste phase (l 水泥净浆 ); among them, Figure 4 As shown, the effective length is: the side length of the cube after the volume is equivalent to the cube, as shown in the following formula:

[0063]

[0064]

[0065] Fine aggregate was used to prepare the specimens and the Rockwell hardness of the fine aggregate was measured. 细骨料 ), the Rockwell hardness (H 水泥净浆 ), the Rockwell hardness of fine aggregate and the Rockwell hardness of cement paste are measured using the same parameters, and the Rockwell hardness of cement paste is measured using the method in Example 1.

[0066] The effective hardness of cement mortar (H) is obtained by weighting the effective length of fine aggregate phase, Rockwell hardness of fine aggregate, effective length of cement paste phase and Rockwell hardness of cement paste. 有效 ), the calculation method of effective hardness is as follows:

[0067]

[0068] Using the test method of Example 1, cement pastes (CP-1 to CP-5) and cement mortars (CM-1 to CM-7) with different component ratios were tested. Different numbers represent different ratios and properties. Cement mortar is a uniform mixture of fine aggregate, cementitious material, and water. The fine aggregate size range is 3 to 4.75 mm, which is the same as the conventional fine aggregate size range in the field. The test results are shown in Table 1.

[0069] Table 1

[0070]

[0071] It can be seen from Table 1 that the effective hardness and Rockwell hardness of the cement paste as a homogeneous material are the same, and the measured effective hardness and Rockwell hardness of the cement mortar are also the same. The effective hardness and Rockwell hardness results of the cement paste and cement mortar are the same, that is, the cement mortar can be used as a single-phase homogeneous material similar to the cement paste in the characterization method of the present invention, and further participate in the evaluation of the effective hardness of cement-based composite materials.

[0072] Example 3

[0073] The method for characterizing the effective hardness of concrete and other cement-based composite materials comprises the following steps:

[0074] (1) Concrete is considered as a two-phase material composed of a coarse aggregate phase and a mortar matrix phase, wherein the mortar matrix phase includes the cement paste or cement mortar in Example 2; the sum of the volumes of the coarse aggregate phase is calculated as the coarse aggregate volume (V 粗骨料 ), and the sum of the volumes of the mortar matrix phase is calculated as the mortar matrix volume (V 基体 ); In this embodiment, the coarse aggregate is a rock particle aggregate with a particle size of 4.75 to 16 mm.

[0075] (2) The volume of coarse aggregate (V 粗骨料 ) is converted into the effective length of the coarse aggregate phase (l 粗骨料 ), the mortar matrix volume (V 基体 ) is converted into the effective length of the mortar matrix phase (l 基体 ); among them, Figure 4 As shown, the effective length is: the side length of the cube after the volume is equivalent to the cube, as shown in the following formula:

[0076]

[0077]

[0078] (3) The coarse aggregate rock was used to prepare the sample, and the Rockwell hardness of the coarse aggregate (H 粗骨料 ); The Rockwell hardness of the concrete sample surface measured in the test is the Rockwell hardness of the mortar matrix (H 基体 ); the Rockwell hardness of the coarse aggregate and the Rockwell hardness of the mortar matrix are measured using the same parameters, and the Rockwell hardness of the mortar matrix is measured using the method in Example 1.

[0079] (4) The effective hardness of concrete (H) is obtained by weighting the effective length of the coarse aggregate phase, the Rockwell hardness of the coarse aggregate, the effective length of the mortar matrix phase, and the Rockwell hardness of the mortar matrix. 有效 ), the calculation method of effective hardness is as follows:

[0080]

[0081] The Rockwell hardness of concrete (CC-1 to CC-7) with different component ratios was tested using the test method of Example 1. The effective hardness was calculated using the effective hardness characterization method of this embodiment, with different numbers representing different ratios and properties. High-ductility cement-based composite materials (ECC-1 to ECC-2) do not contain coarse aggregate, and some even do not contain fine aggregate. In the characterization of effective hardness, they are calculated as single-phase homogeneous materials. Ultra-high performance concrete (UHPC-1 to UHPC-4) does not contain coarse aggregate, but contains fine aggregate. Since the weight of coarse aggregate is zero, it is a single-phase homogeneous material.

[0082] It can be seen from Example 2 that cement mortar is a single-phase homogeneous material, so concrete can be a two-phase material composed of coarse aggregate and mortar matrix.

[0083] The Rockwell hardness of concrete was measured according to the measurement method in Example 1.

[0084] Calculation example Figure 5 The results of all samples are shown in Table 2.

[0085] Table 2

[0086]

[0087]

[0088] It can be seen that the effective hardness of concrete is different from the result of Rockwell hardness, that is, concrete cannot be regarded as a homogeneous material, but can only be regarded as a two-phase heterogeneous material composed of cement mortar (composed of fine aggregate, cementitious material and water) and coarse aggregate; and the numerical distribution of effective hardness and Rockwell hardness has different rules, which can characterize material properties that Rockwell hardness does not involve.

[0089] Example 4

[0090] The compressive strength of concrete is assessed based on its effective hardness.

[0091] Traditional ultra-high performance concrete (UHPC) doesn't contain coarse aggregate, but in practice, adding coarse aggregate to UHPC can improve compressive strength. In this example, 20% by volume of coarse aggregate was added to the cement mortar matrix of an ultra-high performance concrete (UHPC-1). The coarse aggregate was made of calcined bauxite with a Rockwell hardness of 96.7 (HR15T). The volume ratio of the cement mortar matrix was 80%, and the Rockwell hardness was the same as that of the ultra-high performance concrete (UHPC-1). This produced an ultra-high performance concrete (UHPC-1-2) containing coarse aggregate.

[0092] The compressive strength, Rockwell hardness and effective hardness were tested / calculated respectively, and the results are shown in Table 3.

[0093] Table 3

[0094] serial number Compressive strength (MPa) Rockwell hardness (HR15T) Effective hardness (HR15T) UHPC-1 156.3 76.4 76.4 UHPC-1-2 180.3 76.4 84.2

[0095] As can be seen, the Rockwell hardness values measured on the test specimen surfaces are identical due to the identical cement mortar matrix. However, due to the different coarse aggregate additions and their proportions, the specimens exhibited different effective hardnesses. Compressive strength testing reveals that concrete's compressive strength is positively correlated with its effective hardness. Therefore, even with identical Rockwell hardness measurement results, the effective hardness can be used to assess concrete's compressive properties. Higher effective hardness correlates with higher compressive strength.

[0096] This is because the effective hardness characterizes the performance of coarse aggregate in concrete, and the performance of coarse aggregate will affect the compressive strength of concrete. Therefore, the compressive capacity of concrete can be evaluated based on the effective hardness without having to conduct destructive tests on the specimens.

[0097] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for measuring the Rockwell hardness of cement-based composite materials, characterized in that: The following steps are involved: S1. Casting the cement-based composite material into a test block, wherein the test block has a plurality of side surfaces adjacent to a casting surface; S2. After polishing multiple sides flat, select a square measurement area on the side away from the edge; S3. Evenly select points in the measurement area, test the Rockwell hardness, and read the indentation data of multiple valid points; S4. Taking the average value of the indentation data of multiple valid points as the Rockwell hardness of the cement-based composite material; The method for judging effective points is as follows: the distance between the indentation centers of adjacent effective points is not less than 4 times the diameter of the spherical indenter selected during the Rockwell hardness measurement, and the distance between the indentation center and the edge of the specimen is not less than 2.5 times the diameter of the selected spherical indenter; In S2, multiple edge vertical lines are drawn on the side surface to divide each side surface into multiple small square areas, and the square area at the center is selected as the measurement area; and in S3, a point is taken at the center of the small square area.

2. The Rockwell hardness measurement method of cement-based composite material according to claim 1, characterized in that: In S1, the test block is a cube, the casting surface is any one surface of the cube, and the test block has four side surfaces adjacent to the casting surface.

3. The Rockwell hardness measurement method of cement-based composite material according to claim 2, characterized in that: In S1, the test block is demoulded, polished, and cleaned to obtain a sample to be tested.

4. The method for measuring Rockwell hardness of cement-based composite materials according to claim 3, wherein: The sample to be tested is of cube blocks.

5. The Rockwell hardness measurement method of cement-based composite material according to claim 1, characterized in that: In S2, the side surface was polished and smoothed, and then the powder remaining on the surface of the sample was wiped off with an alcohol cotton ball.

6. The method for measuring Rockwell hardness of cement-based composite materials according to claim 5, wherein: In S2, the vertical line of the edge divides the side into multiple In order to avoid the influence of edge effect, the nine central square areas are selected as the pressure measurement point area.

7. The method for measuring Rockwell hardness of cement-based composite materials according to claim 1, wherein: Pick at least one valid point on each side.

8. The method for measuring Rockwell hardness of cement-based composite materials according to claim 7, wherein: In S4, all three sizes are At least 100 valid points are selected on the cube test block for reading.

9. A method for characterizing the effective hardness of concrete, characterized in that: The following steps are involved: (1) Concrete is considered as a two-phase material consisting of a coarse aggregate phase and a mortar matrix phase. The sum of the volumes of the coarse aggregate phase is calculated as the coarse aggregate volume, and the sum of the volumes of the mortar matrix phase is calculated as the mortar matrix volume. (2) Calculate the effective length of the coarse aggregate phase based on the volume of the coarse aggregate, and calculate the effective length of the mortar matrix phase based on the volume of the mortar matrix; (3) The Rockwell hardness of the coarse aggregate is measured experimentally, and the Rockwell hardness of the surface of the concrete sample is measured experimentally using the Rockwell hardness measurement method for the cement-based composite material according to any one of claims 1 to 8, which is the Rockwell hardness of the mortar matrix phase; (4) The effective hardness of concrete is obtained by weighting the effective length of the coarse aggregate phase, the Rockwell hardness of the coarse aggregate phase, the effective length of the mortar matrix phase, and the Rockwell hardness of the mortar matrix phase; The calculation method of effective hardness is shown in the following formula: ； ； ； H 有效 is the effective hardness of concrete; H 粗骨料 is the Rockwell hardness of coarse aggregate; H 基体 is the Rockwell hardness of the mortar matrix; l 粗骨料 is the effective length of the coarse aggregate phase; l 基体 is the effective length of the mortar matrix phase; V 粗骨料 is the volume of coarse aggregate; V 基体 is the volume of the mortar matrix.

10. The method for characterizing the effective hardness of concrete according to claim 9, wherein: The mortar matrix phase includes a uniform mixture of fine aggregate, cementitious materials and water. Fine aggregate refers to aggregate with a particle size range of 0.1~4.75mm.

11. The method for characterizing the effective hardness of concrete according to claim 9, wherein: Coarse aggregate refers to aggregate with a particle size range of 4.75~16mm.

12. The method for characterizing the effective hardness of concrete according to claim 9, wherein: In step (3), the Rockwell hardness of the coarse aggregate and the Rockwell hardness of the mortar matrix are measured in the same manner.

13. Use of the method for characterizing the effective hardness of concrete according to any one of claims 9 to 12 in evaluating the compressive strength of concrete.

Images