A method for testing the pore structure strength of foamed concrete and its application

Abstract

The present invention discloses a method for testing the pore structure strength of foamed concrete and its application. The testing method comprises the following steps: S1. Obtain the average pore diameter d and the average pore wall thickness h on the top surface of the sample block through an optical microscope; S2. Select n testing areas on the top surface of the sample block, and measure the pore structure failure pressure F i for each testing area, where i = 1, 2, 3…, n; S3. Calculate the pore structure strength δ i of each testing area; S4. Take the average value of all the pore structure strengths δ i to obtain the average pore structure strength δ of the sample block. The present invention applies the testing method to the local defect analysis or macroscopic strength prediction of the foamed concrete product to be tested, can quickly and accurately determine whether the pore structure defect here meets the requirements, and realizes the detection and evaluation of the pore structure at the local position; it can also quickly obtain the predicted macroscopic strength, avoiding the destructive damage caused by large-volume sampling to the foamed concrete component.

Description

Technical Field

[0001] The present invention relates to the strength detection of foamed concrete, and specifically refers to a method for testing the pore structure strength of foamed concrete and its application. Background Art

[0002] Foamed concrete is a new type of lightweight thermal insulation material containing a large number of closed pores formed by mechanically foaming a foaming agent, uniformly mixing the foam with cement slurry, and then performing in-situ construction or mold forming through the pumping system of a foaming machine and undergoing natural curing.

[0003] As a porous material, the pore diameter of foamed concrete is generally 0.1 - 3 mm. At present, its strength is mostly characterized by macroscopic strength. For example, the core drilling method: a concrete sample in the shape of a cube with a side length of 100 mm is intercepted from a concrete component, and the compressive strength is measured under a concrete compression testing machine. This method has the following disadvantages: (1) It directly and extensively damages the concrete structural component, and requires subsequent reinforcement and strengthening treatment; (2) Due to the need to avoid damaging important parts of the concrete component, sampling has certain limitations.

[0004] The compressive strength measured by the above method only represents the overall performance of foamed concrete and cannot determine its local strength. According to the structural characteristics of porous materials, their macroscopic strength is composed of the strength of the pore walls of overlapping pores. Due to the forming characteristics of porous materials, the internal pore wall structure is not completely homogeneous, and there are more or less defects in the pore structure, and the degree of defects in different regions may vary greatly. At present, the analysis of the relationship between the pore structure and pore strength of porous materials mostly starts from parameters such as porosity, pore diameter, and roundness, but the influence of these parameters on the strength of the material can only be analyzed qualitatively or semi-quantitatively, and a direct numerical relationship cannot be established.

[0005] Therefore, it is necessary to develop a method for testing the pore structure strength of foamed concrete that is simple to operate and does not cause overall damage, and apply this testing method to the local defect analysis or macroscopic strength prediction of foamed concrete products. Summary of the Invention

[0006] The purpose of the present invention is to solve the deficiencies of the above background art, provide a method for testing the pore structure strength of foamed concrete that is simple to operate and does not cause overall damage, and apply this testing method to the local defect analysis or macroscopic strength prediction of foamed concrete products.

[0007] The technical solution of the present invention is as follows:

[0008] One of the purposes of the present invention is to provide a method for testing the pore structure strength of foamed concrete, which is characterized by including the following steps:

[0009] S1. Take a cube sample with a side length L satisfying 0.5 cm ≤ L ≤ 1.5 cm. Obtain the average pore diameter d and the average pore wall thickness h on the top surface of the sample through an optical microscope;

[0010] S2. Select n test areas on the top surface of the sample, where n is a positive integer ≥ 4. Select an indenter with a diameter D satisfying d < D < 2d to measure the pore structure failure pressure F i for each test area, i = 1, 2, 3…, n. The specific measurement includes: Align the indenter with each test area and press down until the pore structure is damaged. Monitor the pressure received during the indenter pressing process, and take the maximum value of the received pressure as the pore structure failure pressure F i ;

[0011] S3. Calculate the pore structure strength δ i ,

[0012]

[0013] where, δ i = pore structure strength, unit is MPa;

[0014] F i = pore structure failure pressure, unit is N;

[0015] S = damage contact area, unit is mm 2 ;

[0016] h = average pore wall thickness, unit is mm;

[0017] d = average pore diameter, unit is mm;

[0018] D = indenter diameter, unit is mm;

[0019] S4. Take the average value of all pore structure strengths δ i , i = 1, 2, 3…, n, to obtain the average pore structure strength δ of the sample.

[0020] Preferably, in the step S1, the specific steps for obtaining the average pore diameter d and the average pore wall thickness h of the sample include:

[0021] Randomly measure the pore diameters and pore wall thicknesses of N pore structures on the top surface of the sample, where N is a positive integer ≥ 3. Take the average value of all measured pore diameters to obtain the average pore diameter d, and take the average value of all measured pore wall thicknesses to obtain the average pore wall thickness h.

[0022] Preferably, the value range of N is 3 - 10.

[0023] Preferably, in the step S1, L = 1 cm.

[0024] Preferably, in step S2, the value range of n is 4 - 16.

[0025] Preferably, in step S2, the pressing rate of the indenter is 5 - 50 mm / min.

[0026] The second object of the present invention is to provide an application of the foam concrete pore structure strength testing method described in any one of the above, which is characterized in that it is used for local defect analysis or macroscopic strength prediction of foam concrete products to be tested.

[0027] Preferably, the local defect analysis includes the following steps:

[0028] a. Select multiple qualified foam concrete products, measure the average pore structure strength of each qualified product, and take the average of the average pore structure strengths of all qualified products to obtain the standard pore structure strength δ0;

[0029] b. Select multiple local positions on the foam concrete product to be tested, and measure the average pore structure strength of each local position to obtain the local average pore structure strength δ';

[0030] c. Compare the magnitudes of δ' and δ0, and determine the pore structure defects of each local position according to the comparison results:

[0031] If δ' ≥ δ0, it is determined that the pore structure defect of the local position meets the standard level;

[0032] If δ' < δ0, it is determined that the structural defect of the local position does not meet the standard level.

[0033] Preferably, the macroscopic strength prediction includes the following steps:

[0034] a. Select multiple qualified foam concrete products, measure the macroscopic strength and average pore structure strength of each qualified product, take the average of the macroscopic strengths of all qualified products to obtain the standard macroscopic strength Φ0, take the average of the average pore structure strengths of all qualified products to obtain the standard pore structure strength δ0, and calculate the standard magnification factor K0 = Φ0 / δ0;

[0035] b. Take a sample on the foam concrete product to be tested to measure the average pore structure strength δ, and calculate the predicted macroscopic strength Φ' = δ × K0.

[0036] The beneficial effects of the present invention are as follows:

[0037] 1. The sampling volume is small, and there is almost no damage to the foam concrete component, which is convenient for sampling at each local position of the foam concrete component.

[0038] 2. An indenter with a diameter d < D < 2d is used to press the sample. The purpose of such a setting is to ensure that the indenter destroys at least one complete pore, and at the same time avoid the error generated when the indenter destroys multiple pores.

[0039] 3. Compare the local average pore structure strength δ’ of the foam concrete product to be tested with the standard pore structure strength δ0, and the pore structure defect here can be quickly and accurately determined whether it meets the requirements, realizing the detection and evaluation of the pore structure at the local position.

[0040] 4. Multiply the average pore structure strength δ obtained by randomly sampling at one place on the concrete product to be tested by the standard magnification factor K0 of the standard concrete product, and the predicted macroscopic strength can be quickly obtained, avoiding the destructive damage caused by large-volume sampling to the foam concrete components. Brief Description of the Drawings

[0041] Figure 1 Schematic diagram of the pore structure under the action of the indenter during the test

[0042] Figure 2 Schematic diagram of the structure of the pore structure strength test device for foam concrete of the present invention

[0043] Figure 3 Schematic diagram of the structure of the digital display controller

[0044] Figure 4 Schematic diagram of the structure of the pressure bar and the indenter parts

[0045] Wherein: 1 - horizontal crossbeam, 2 - sensor, 3 - bracket, 4 - digital display controller, 5 - pressure bar (51 - boss), 6 - indenter (61 - center indenter 611 - first threaded blind hole 62 - matching indenter 621 - mating blind hole 622 - rubber ring), 7 - placement table, 8 - base, a - pore structure, b - indenter action area, c - compressed pore wall. Detailed Embodiments

[0046] The following specific embodiments further illustrate the present invention in detail.

[0047] Embodiment 1

[0048] The present invention provides a method for testing the pore structure strength of foam concrete, including the following steps:

[0049] S1. Take a cube sample block with a side length L = 1 cm, and obtain the average pore diameter d and the average pore wall thickness h on the top surface of the sample block through an optical microscope. The specific measurement steps of d and h include:

[0050] Randomly measure the pore diameter and pore wall thickness of N pore structures on the top surface of the sample block through an optical microscope. N is a positive integer ≥ 3. Take the average value of all measured pore diameters to obtain the average pore diameter d, and take the average value of all measured pore wall thicknesses to obtain the average pore wall thickness h. In this embodiment, the test data of the pore diameter and pore wall thickness are shown in Table 1 below.

[0051] Table 1

[0052]

[0053] In this embodiment, N = 5;

[0054] S2. Select n test areas on the top surface of the sample block, where n is a positive integer ≥ 4. Select an indenter with a diameter D satisfying d < D < 2d to measure the pore structure failure pressure F for each test area, i = 1, 2, 3…, n. The specific measurement includes: Align the indenter with each test area and press down (the indenter pressing rate is 30 mm / min) until the pore structure is damaged. During the pressing process as i shown (the indenter action area b is a circular dot area, and the compressed pore wall c is at the thick black line), monitor the pressure received during the indenter pressing process, and take the maximum value of the received pressure as the pore structure failure pressure F Figure 1 ; i

[0055] S3. Calculate the pore structure strength δ of each test area i ,

[0056]

[0057] where δ i = pore structure strength, unit is MPa;

[0058] F i = pore structure failure pressure, unit is N;

[0059] S = failure contact area, unit is mm 2 ;

[0060] h = average pore wall thickness, unit is mm;

[0061] d = average pore diameter, unit is mm;

[0062] D = indenter diameter, unit is mm;

[0063] S4. Take the average value of all pore structure strengths δ i , i = 1, 2, 3…, n, to obtain the average pore structure strength δ of the sample block.

[0064] The data in steps S2 - S4 are shown in Table 2 below

[0065] Table 2

[0066]

[0067] In this embodiment, n = 6 and D = 2 mm.

[0068] Example 2

[0069] ​Apply the pore structure strength test method of Example 1 to the local defect analysis of the foam concrete product to be tested, including the following steps:

[0070] a. Select multiple qualified foam concrete products, measure the average pore structure strength of each qualified product, and take the average value of the average pore structure strengths of all qualified products to obtain the standard pore structure strength δ0. In this example, δ0 = 0.172 MPa;

[0071] b. Select 5 local positions on the foam concrete product to be tested, and measure the average pore structure strength of each local position to obtain the local average pore structure strength δ';

[0072] c. Compare the magnitudes of δ' and δ0, and determine the pore structure defects of each local position according to the comparison results:

[0073] If δ' ≥ δ0, it is determined that the pore structure defects of the local position meet the standard level;

[0074] If δ' < δ0, it is determined that the structural defects of the local position do not meet the standard level.

[0075] The data and judgment results in step b are shown in Table 3 below.

[0076] Table 3

[0077]

[0078] Example 3

[0079] Apply the pore structure strength test method of Example 1 to the local defect analysis of the foam concrete product to be tested, including the following steps:

[0080] a. Select multiple qualified foam concrete products, measure the macroscopic strength and average pore structure strength of each qualified product, take the average value of the macroscopic strengths of all qualified products to obtain the standard macroscopic strength Φ0, take the average value of the average pore structure strengths of all qualified products to obtain the standard pore structure strength δ0, and calculate the standard magnification factor K0 = Φ0 / δ0. In this example, Φ0 = 0.64 MPa, δ0 = 0.172 MPa, then K0 = Φ0 / δ0 = 3.7;

[0081] b. Take a sample on the foam concrete product to be tested to measure the average pore structure strength δ = 0.156 MPa (measured in Example 1), and calculate the predicted macroscopic strength Φ' = δ × K0 = 0.58 MPa.

[0082] Example 4

[0083] As Figures 2 - 4 shown, this example provides a foam concrete pore structure strength test device for the pore structure failure pressure F in the pore structure strength test iFor the measurement, the test device includes a horizontal crossbeam 1, a sensor 2, a bracket 3, a digital display controller 4, a pressure rod 5, a pressure head 6, a placement table 7, and a base 8.

[0084] The base 8 is fixedly connected to the lower end of the bracket 3, the placement table 7 is fixedly connected to the top surface of the base 8, the horizontal crossbeam 1 is vertically movably connected to the upper end of the bracket 3, the base 8 and the horizontal crossbeam 1 are vertically opposite. The pressure rod 5 is fixedly connected to the crossbeam 1, the pressure head 6 is arranged at the lower end of the pressure rod 5, the sensor 2 is arranged inside the crossbeam 1 to sense the pressure received by the pressure head 6 during the hole structure test, the digital display controller 4 is electrically connected to the sensor 2 to display the pressure value measured by the sensor 2, and the digital display controller 4 is electrically connected to the crossbeam 1 to control the lifting of the crossbeam 1. In this embodiment, the crossbeam 1 can be a hydraulic cylinder with a fixed end fixedly connected to the bracket 3 and a telescopic end moving vertically, as well as any mechanism that can be controlled to achieve the vertical movement of the telescopic end.

[0085] In this embodiment, the digital display controller 4 is provided with an emergency stop button 41, a start button 42, a manual upward button 43, a manual downward button 44, a compression speed reduction button 45, a compression speed increase button 46, and a force value display screen 47. The emergency stop button 41 is used to control the pressure rod 5 to stop moving (mainly to prevent the pressure head from colliding with the placement table 7 during the test and damaging the sensor 2), the start button 42 is used to control the pressure rod 5 to descend uniformly at a set speed, the manual lifting button 43 is used to control the pressure rod 5 to move upward to adjust the position, the manual downward button 44 is used to control the pressure rod 5 to move downward to adjust the position, the compression speed reduction button 45 is used to decrease the speed value when setting the uniform descent rate of the pressure rod 5, the compression speed increase button 46 is used to increase the speed value when setting the uniform descent rate of the pressure rod 5, and the force value display screen 47 is used to display the pressure value of the sensor 2.

[0086] In this embodiment, the pressure head 6 includes a central pressure head 61 and a plurality of matching pressure heads 62. Both the central pressure head 61 and the matching pressure heads 62 are in the shape of a frustum of a cone. The central pressure head 61 is provided with a central threaded blind hole 611 and is threadedly connected to the pressure rod 5 coaxially. All the matching pressure heads 62 are numbered starting from 1 in increasing order of outer diameter. All the matching pressure heads 62 are provided with mating blind holes 621 and rubber rings 622 are circumferentially attached to the mating blind holes 621. Then, the mating blind hole 621 of the first matching pressure head 62 corresponds to the outer diameter of the central pressure head 61 so that it can be directly coaxially pressed on the central pressure head 61. Subsequently, the inner diameter of the mating blind hole 621 of any subsequent matching pressure head 62 corresponds to the outer diameter of the previous numbered matching pressure head 62 so that it can be directly coaxially pressed on the previous matching pressure head 62. Except for the first matching pressure head 62, the depth of the mating blind hole 621 of any subsequent matching pressure head 62 corresponds to the overall height of the previous numbered matching pressure head 62.

[0087] In this embodiment, a boss 51 is coaxially provided at the lower end of the pressure rod 5. The outer diameter of the boss 51 is smaller than that of the pressure rod 5, and the boss 51 is threadedly connected to the first threaded blind hole 611.

[0088] The working process of this device is as follows:

[0089] Install the indenter: Connect the center indenter 61 to the pressure rod 5, and then start pressing in sequence according to the numbers from the first matching indenter 62 until the outer diameter satisfies d < D < 2d in step S1 of Embodiment 1.

[0090] Set the indenter descent rate: Use the manual up button 43 and manual down button 44 on the digital display controller 4 to adjust the distance between the indenter 6 and the sample block, and use the compression speed reduction button 45 and compression speed increase button 46 to adjust the test speed (the uniform descent speed of the indenter). After setting, press the start button 42 to start the test. During the test, the digital display controller 4 will display and record the sensed values of the sensor 2. When the hole structure is damaged, the crossbeam 1 stops moving, and take its maximum value as the hole structure damage pressure F i .

[0091] If other areas of the sample block need to be measured, just move the position of the sample block on the placement table 7 and re-measure.

Claims

1. A method for testing the strength of the pore structure of foamed concrete, characterized in that, It includes the following steps: S1. Take a cube sample block with a side length L dimension satisfying L = 1 cm, and obtain the average pore diameter d and the average pore wall thickness h on the top surface of the sample block through an optical microscope; S2. Select n test areas on the top surface of the sample block, where n is a positive integer ≥ 4. Select an indenter with a diameter D satisfying d < D < 2d to measure the pore structure failure pressure F for each test area, i = 1, 2, 3…, n. The specific measurement includes: align the indenter with each test area and press down until the pore structure is damaged. Monitor the pressure on the indenter during the pressing process, and take the maximum value of the pressure as the pore structure failure pressure F i ; i ; S3. Calculate the pore structure strength δ of each test area i , where δ i = the strength of the pore structure, with the unit of MPa; F i = Destruction pressure of pore structure, unit: N; S = Contact area of damage, unit: mm 2 ; h = average pore wall thickness, with the unit of mm; d = average pore diameter, with the unit of mm; D = indenter diameter, with the unit of mm; S4. Take the average value of the strength δ of all pore structures i where i = 1, 2, 3…, n, to obtain the average pore structure strength δ of the sample block; The pore structure strength test method for the foam concrete is used for the local defect analysis of the foam concrete product to be tested, and the local defect analysis includes the following steps: a. Select multiple qualified foam concrete products, measure the average pore structure strength of each qualified product, and take the average value of the average pore structure strengths of all qualified products to obtain the standard pore structure strength δ0; b. Select multiple local positions on the foam concrete product to be tested, and measure the average pore structure strength of each local position to obtain the local average pore structure strength δ'; c. Compare the magnitudes of δ' and δ0, and determine the pore structure defects of each local position according to the comparison results.

2. The method for testing the pore structure strength of foamed concrete according to claim 1, characterized in that, In the step S1, the specific steps for obtaining the average pore diameter d and the average pore wall thickness h of the sample block include: Randomly measure the pore diameters and pore wall thicknesses of N pore structures on the top surface of the sample block, where N is a positive integer ≥ 3. Take the average value of all measured pore diameters to obtain the average pore diameter d, and take the average value of all measured pore wall thicknesses to obtain the average pore wall thickness h.

3. The method for testing the pore structure strength of foamed concrete according to claim 2, characterized in that, The value range of N is 3 - 10.

4. The method for testing the pore structure strength of foamed concrete according to claim 1, wherein, In the step S2, the value range of n is 4 - 16.

5. The method for testing the pore structure strength of foamed concrete according to claim 1, characterized in that, In the step S2, the indenter pressing rate is 5 - 50 mm / min.

6. The method for testing the pore structure strength of foamed concrete according to claim 1, characterized in that, The pore structure strength test method for the foam concrete is also used for the macroscopic strength prediction of the foam concrete product to be tested, and the macroscopic strength prediction includes the following steps: a. Select multiple qualified foam concrete products, measure the macroscopic strength and the average pore structure strength of each qualified product, take the average value of the macroscopic strengths of all qualified products to obtain the standard macroscopic strength Φ0, take the average value of the average pore structure strengths of all qualified products to obtain the standard pore structure strength δ0, and calculate the standard magnification factor K0 = Φ0 / δ0; b. Take a sample on the foam concrete product to be tested to measure the average pore structure strength δ, and calculate the predicted macroscopic strength Φ' = δ × K0.

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