Preparation Method of Embedded Piece for Concrete / Mortar Specimen Experiment and Controllable Crack

Abstract

The present invention discloses a concrete / mortar test block experimental embedded piece and a preparation method for controllable cracks, belonging to the technical field of concrete. The technical solution is as follows: Heat and melt the alcohol-soluble resin, add ceramic powder and mix evenly, cool, and press into a prefabricated piece 1 by rolling, and cut the prefabricated piece 1 to obtain an embedded piece 1; Dissolve the alcohol-soluble resin in a polar or semi-polar solvent, add inorganic fine powder, stir and mix evenly and place it in a flat shallow dish, and obtain a prefabricated piece 2 after the solvent volatilizes, and cut the prefabricated piece 2 to obtain an embedded piece 2. During the preparation process of the experimental concrete or mortar test block, insert the experimental embedded piece into the appropriate position of the concrete or mortar, cure it under standard conditions to the required age, dissolve the embedded piece, and finally obtain controllable cracks with uniform gaps. The operation method of the present invention is convenient, the prepared crack structure interface is similar to that of concrete / mortar, and the crack specifications are controllable and the uniformity is good, and the relevant experimental results are accurate.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete, and particularly relates to a concrete / mortar test block experimental embedded piece and a preparation method for controllable cracks. Background Art

[0002] During the long-term use of concrete, various cracks will inevitably occur due to factors such as temperature changes, structural stress, and foundation settlement. These cracks will weaken or even invalidate the protective effect of the concrete structure of the building against seawater, rainwater, surface water, and groundwater, thereby affecting the structural safety of the building. Especially in the port and coastal engineering in coastal areas, due to factors such as self-shrinkage cracking and poor impermeability of concrete, the durability of marine concrete is seriously affected. Therefore, the research on the durability of concrete, as well as the control and repair of concrete cracks, has always been the focus of domestic and foreign research. In the experimental research related to the control and self-repair performance of concrete cracks, in order to evaluate the harm of concrete cracks and their self-repair ability, most of them use the pre-pressure splitting method to prefabricate cracks, that is, artificially split a certain width of cracks through a press, and then observe the repair situation of the cracks under certain curing conditions, including the time to complete repair, to test the self-repair ability of the test materials for cracks. Specifically, a splitting method with a middle round bar as the support and pressurization on both sides above is adopted. The width of the cracks generated in this way is often uncontrollable and mostly wedge-shaped; even after splitting more test blocks and selecting samples, due to the internal microscopic factors of concrete, its splitting structure is neither uniform nor unique. One or several cracks appearing on the surface, and cracks generated inside the concrete but not yet appearing outside also objectively exist, which affects the test of the repair effect and the accuracy of the calculation of the repair performance. At the same time, the pre-pressure method also has the disadvantages of long curing time of concrete test blocks. Once the test piece fails to operate, the test piece must be remade, which takes a long time. In recent years, some researchers have used advanced graphic tools and software to calculate the repair area through algorithms. However, in the case of uncontrollable cracks, even if the algorithm is optimized, the consistency of the cracks is still poor.

[0003] In addition, in other similar scientific research experiments, there are also the embedding method, that is, using cement steel nails to insert into microcracks and pressurize to expand the cracks; the plastic shrinkage method, that is, before the concrete sets and hardens, blowing air to promote the rapid evaporation of water to obtain plastic shrinkage cracks; the splitting and compounding method, that is, breaking the concrete test block into two sections, and then bundling and compounding the broken cross-sections with a certain gap; or during the production of concrete test blocks, inserting steel sheets or plastic sheets to create cracks. The deficiencies of these commonly used scientific research methods such as the embedding method, the plastic shrinkage method, and the splitting and compounding method are similar to those of the pre-pressure method. The crack gaps, the internal shapes of the cracks, and the directions are all very different. For the steel sheet insertion method, the crack interface is too smooth, which is quite different from the actual surface conditions of concrete cracks. The above deficiencies will inevitably affect the accuracy and reliability of theoretical research and practical applications. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: to overcome the deficiencies of the prior art and provide a pre-embedded sheet for concrete / mortar test block experiments and a method for preparing controllable cracks using the same, which are mainly used for making controllable cracks during the testing of the self-healing performance, chloride ion resistance, etc. of concrete / mortar.

[0005] The technical solution of the present invention is as follows:

[0006] First, a preparation method of a pre-embedded sheet for alcohol-soluble resin ceramic powder composite concrete / mortar test block experiments is provided. The pre-embedded sheet for concrete / mortar test block experiments is divided into a pre-embedded sheet one for concrete / mortar test block experiments with a thickness of not less than 0.3 mm and a pre-embedded sheet two for concrete / mortar test block experiments with a thickness less than 0.3 mm;

[0007] The preparation method of the pre-embedded sheet one for concrete / mortar test block experiments is as follows: heat and melt the alcohol-soluble resin, add ceramic powder and mix evenly, cool, and press into a prefabricated sheet one through a roller press, and cut the prefabricated sheet one to obtain the pre-embedded sheet one for concrete / mortar test block experiments;

[0008] The preparation method of the pre-embedded sheet two for concrete / mortar test block experiments is as follows:

[0009] Dissolve the alcohol-soluble resin in a polar or semi-polar solvent, add inorganic fine powder thereto, stir and mix evenly, place it in a flat shallow dish, and obtain a prefabricated sheet two after the solvent volatilizes. Cut the prefabricated sheet two to obtain the pre-embedded sheet two for concrete / mortar test block experiments.

[0010] Preferably, the weight ratio of the alcohol-soluble resin to the inorganic fine powder is (1-9):(9-1).

[0011] Preferably, the polar or semi-polar solvent is one or more of benzene solvents, ester solvents, ketone solvents, and alcohol solvents.

[0012] Preferably, the solvent is one or more of ethanol, methanol, toluene, ethyl acetate and acetone.

[0013] Preferably, the alcohol-soluble resin is one or more of acrylic resin, polyamide resin, shellac resin, dammar resin, rosin-modified alkyd resin, thermoplastic phenolic resin and polyvinyl butyral resin.

[0014] Preferably, the inorganic fine powder is one or a mixture of ceramic powder, red brick powder and concrete fine powder, and the particle size is 0.001mm-0.5mm.

[0015] In the second aspect, a method for preparing controllable cracks using embedded sheet 1 is provided, as follows:

[0016] 1) Mix cement, quartz sand / standard graded aggregate and water in a predetermined proportion to prepare concrete / mortar, and pour it into the mold;

[0017] 2) Insert the concrete / mortar specimen embedded piece 1 into the concrete / mortar in the mold and compact it using a vibration table to obtain a concrete specimen 1;

[0018] 3) Move the concrete specimens into the standard curing room and cure them for 1 day before demoulding. Continue curing under standard curing conditions for 7 days, 28 days or 56 days.

[0019] 4) Immerse a concrete / mortar specimen cured to a specified age in a polar or semi-polar solvent, and repeatedly rinse the expected cracks with the same solvent to obtain a concrete / mortar specimen with controllable cracks.

[0020] In a third aspect, a method for preparing controllable cracks using the embedded sheet 2 is provided, as follows:

[0021] 1) Mix cement, quartz sand / standard graded aggregate and water in a predetermined proportion to prepare mortar / concrete;

[0022] 2) Measure the size of the experimental embedded piece required for the concrete / mortar test block in advance, cut the experimental embedded piece, fix the two ends of the experimental embedded piece in the middle of the test mold, add the mixed concrete into the test mold in two batches, and vibrate the concrete on a vibrating table to obtain concrete test block 2;

[0023] 3) Move the concrete specimen 2 into the standard curing room and cure it for 1 day before demoulding. Continue curing under standard curing conditions for 7 days, 28 days or 56 days.

[0024] 4) The concrete / mortar specimen 2 cured to the specified age is immersed in a polar or semi-polar solvent, and the expected cracks are repeatedly washed with the same solvent to obtain a concrete specimen 2 with controllable cracks.

[0025] Preferably, the solvent is one or more of solvents such as ethanol, methanol, toluene, ethyl acetate, acetone, etc.; the alcohol-soluble resin is one or more of resins such as acrylic resin, polyamide resin, shellac resin, dammar resin, rosin-modified alkyd resin, thermoplastic phenolic resin, and polyvinyl butyral.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The operation method of the present invention is convenient. The method for manufacturing the experimental embedded piece does not require special process operations such as high temperature and high pressure, and is safe, stable, and reliable; 2. The surface properties of the prepared controllable crack structure end face are similar to those of concrete / mortar, and the inorganic micropowder of the preferred specification has certain activity, which is more conducive to the stability of the detection of the concrete repair effect; 3. The width of the concrete crack prepared is completely controllable, with good repeatability and consistency; 4. The width, length, and even the volume of the concrete crack can be known in advance by measuring the experimental embedded piece, which is helpful for the detection and quantitative research of the repair performance; 5. The thickness of the experimental embedded piece material is adjustable. The thickness of the first experimental embedded piece can be increased upward, and the second experimental embedded piece can more easily achieve cracks with a width of 0.05 mm and above commonly used in meso-mechanics (although theoretically its thickness can infinitely approach 0 mm), which is helpful for more meso-scale and even micro-scale research; 6. The hardness of the experimental embedded piece is adjustable. This is helpful for manufacturing controllable cracks with various shapes and orientations such as planar and curved surfaces, and is helpful for better simulating the actual situation of concrete cracks for in-depth research. Specific embodiments

[0028] Example 1

[0029] This example provides a method for preparing the first experimental embedded piece for a concrete test block with a thickness of 0.30 mm, which is as follows: Heat 100 g of polyamide alcohol-soluble resin until it melts, add 100 g of ceramic powder and mix evenly, cool, and roll and press it into a 0.30 mm prefabricated piece 1, and cut the prefabricated piece 1 to obtain the first experimental embedded piece for a concrete / mortar test block;

[0030] Use the first experimental embedded piece for the concrete / mortar test block to prepare a controllable concrete crack, which is as follows. Taking C30 concrete as an example:

[0031] 1) Mix and stir according to the ratio of cement:sand:stone:water = 360:650:1200:190 to prepare concrete. Use a triple mold of 150 mm×150 mm×150 mm, and put the concrete into the mold (refer to the "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" (GB / T 50081-2016)) to obtain a concrete test block;

[0032] 2) Insert the first experimental embedded piece for the concrete test block into the concrete, and vibrate it on a vibrating table to obtain the first concrete test block;

[0033] 3) Transfer the first concrete test block to a standard curing room at a temperature of (20 ± 2) °C and a relative humidity greater than 95%. After curing for 1 day, demold it and continue to cure for 7 days under standard curing conditions.

[0034] 4) Immerse the first concrete test block at the age of 7 days of curing in absolute ethanol, and repeatedly rinse the area of the embedded piece to obtain the first concrete test block with controllable cracks.

[0035] Example 2

[0036] This example provides a preparation method for the first experimental embedded piece for concrete test blocks with a thickness of 0.30 mm, which is as follows: Heat 20 g of polyamide alcohol-soluble resin until it melts, add 80 g of ceramic powder and mix evenly. After cooling, press it into a 0.30-mm prefabricated piece No. 1 through roller pressing. Cut the prefabricated piece No. 1 to obtain the first experimental embedded piece for concrete / mortar test blocks;

[0037] Use the first experimental embedded piece for concrete / mortar test blocks to prepare controllable cracks in concrete, which is as follows. Taking C30 concrete as an example:

[0038] 1) Mix and stir to prepare concrete according to the ratio of cement:sand:stone:water = 360:650:1200:190. Use a triple mold of 150 mm × 150 mm × 150 mm, and put the concrete into the mold (refer to "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" (GB / T 50081-2016));

[0039] 2) Insert the first experimental embedded piece for concrete / mortar test blocks into the concrete, and compact it with a vibrating table to obtain the first concrete test block;

[0040] 3) Transfer the first concrete test block to a standard curing room at a temperature of (20 ± 2) °C and a relative humidity greater than 95%. After curing for 1 day, demold it and continue to cure for 7 days under standard curing conditions.

[0041] 4) Immerse the first concrete test block at the age of 7 days of curing in absolute ethanol, and repeatedly rinse the area of the embedded piece to obtain the first concrete test block with controllable cracks.

[0042] Example 3

[0043] This example provides a preparation method for the first experimental embedded piece for concrete test blocks with a thickness of 0.20 mm, which is as follows:

[0044] Dissolve 50 g of alcohol-soluble polyamide resin in 100 g of ethanol, add 50 g of ceramic powder to it, stir and mix evenly, place it in a shallow flat pan, and obtain prefabricated piece No. 2 after the ethanol volatilizes. Cut the prefabricated piece No. 2 to obtain the second experimental embedded piece for concrete / mortar test blocks.

[0045] Use the embedded piece 1 in the concrete / mortar test block experiment to prepare controllable mortar cracks as follows:

[0046] 1) Mix and stir according to the ratio of cement: medium sand: water = 320:1450:300 (unit: kg / m³) to prepare mortar;

[0047] 2) Pre-measure and cut the size of the embedded piece 2 for the mortar test block experiment. Vertically fix both ends of the experimental embedded piece 2 in the middle of the test mold with epoxy adhesive (the mold uses a 40mm×40mm×160mm triple mold, "Test Method for Strength of Cement Mortar" (GB / T 17671-1999)). Then add the mixed mortar into the test mold. The mortar is added in two times and vibrated solid with a vibrating table to obtain the concrete test block 2;

[0048] 3) Move the concrete test block 2 into a standard curing room at a temperature of (20±2)°C and a relative humidity greater than 95% for 1 day, then demold it and continue to cure for 28 days under standard curing conditions.

[0049] 4) Immerse the concrete test block 2 cured to 28 days in anhydrous ethanol, and repeatedly rinse the area of the experimental embedded piece 2 with a washing liquid bottle to obtain the concrete test block 2 with controllable cracks.

[0050] Comparative Example 1

[0051] According to the method in step 1) of Example 1, prepare a group of concrete test blocks without embedded pieces. Randomly take 1 / 4 for the ultimate compressive strength P0, and use P0 as the reference value. Load the remaining test blocks to 80% of the reference value, unload after stabilizing for 20 s to obtain pre-compressed specimens, and select the test blocks with a crack width of about 0.3 mm, which are the test block group B for the pre-pressure splitting method.

[0052] Use the concrete test block group A (concrete test block 1) with 0.3 mm controllable cracks prepared by the method of Example 1 and the test block group B prepared in Comparative Example 1 to explore the impermeability performance of concrete after multiple self-repairs as follows:

[0053] Immerse the concrete test block groups A and B in water, with the immersion depth not exceeding 1 / 5 of the test block height, and keep the water level relatively stable. Under standard curing conditions, cure for 28 days. Conduct the test according to the step-by-step pressure method in the water impermeability test method in "Standard Test Method for Long-Term Performance and Durability of Ordinary Concrete" (GB / T 50082—2009), and carry out the water impermeability test on the test blocks until all of them leak. Then continue to cure the test blocks under standard conditions until 56 d, and conduct the second water impermeability pressure test. Three test blocks are used for parallel tests in the two groups of experiments, and the results are shown in Table 1 and Table 2 respectively.

[0054] Table 1

[0055] 1# Specimen Seepage Pressure / MPa 2# Specimen Seepage Pressure / MPa 3# Specimen Seepage Pressure / MPa 0.3 0.4 0.3 0.3 0.3 0.4 0.4 0.5 0.5 0.4 0.5 0.4 0.4 0.6 0.5 0.5 0.5 0.4 0.5 0.5 0.6 0.4 0.5 0.5

[0056] Table 2:

[0057] 1# Specimen Seepage Pressure / Mpa 2# Specimen Seepage Pressure / MPa 3# Specimen Seepage Pressure / MPa 0.3 0.2 0.4 0.2 0.2 0.3 0.3 0.3 0.4 0.5 0.4 0.5 0.3 0.2 0.4 0.4 0.4 0.8 0.4 0.5 0.5 0.5 0.4 0.4

[0058] Comparing the data in Table 1 and Table 2, the analysis of variance is shown in Tables 3 and 4.

[0059] Table 3

[0060] Analysis of Variance A Source of Variation SS df MS F P - value F crit Between Groups 0.11166667 7 0.0159524 3.828571429 0.012412137 2.657197 Within Groups 0.06666667 16 0.0041667 Total 0.17833333 23

[0061] Table 4

[0062] Analysis of Variance B Source of Variation SS df MS F P - value F crit Between Groups 0.23333333 7 0.03333 2.962962963 0.03410297 2.657197 Within Groups 0.1800000 16 0.01125 Total 0.41333333 23

[0063] It can be seen from Tables 3 and 4 that at the significance level of α = 0.05, P-value (specimen group A) = 0.0124, P-value (specimen group B) = 0.0341. For the test data of specimen group A and specimen group B under the same conditions, 0.05 ≥ P > 0.01, and they are all statistically significant.

[0064] In Tables 1 and 2, MS(A) is less than MS(B), indicating that the random error of the data obtained by the controllable crack method in the experiment of specimen group A is smaller than that of the data obtained by the pre-pressure splitting method, and the experimental accuracy is higher. That is, the experimental results obtained by preparing specimens with controllable cracks by the embedded piece adopted in the present invention are more uniform and stable.

[0065] Comparative Example 2

[0066] Manufacture concrete specimens according to the method in step 1) of Example 2, and manufacture concrete specimens with cracks by the pre-pressure splitting method in the aforementioned Comparative Example 1. Select specimens with a crack width range of about 0.3 mm and label them as specimen group D.

[0067] Use the concrete specimen group C with 0.3 mm controllable cracks prepared in Example 2 and the specimen group D prepared in Comparative Example 2 to explore the impermeability performance after concrete self-repair, as follows:

[0068] Keep the specimen group C and the specimen group D under standard curing conditions and continue to cure them until 28 d. Conduct the test according to the step-by-step pressure method in the water impermeability test method in the Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete (GB / T 50082—2009), and carry out the pressure test on the impermeability specimens until all of them are permeated. Six specimens are used for the parallel test in both groups of experiments, and the results are shown in Table 5.

[0069] Table 5

[0070] Impermeability Pressure / MPa 1# Specimen / MPa 2# Specimen / MPa 3# Specimen / MPa 4# Specimen / MPa 5# Specimen / MPa 6# Specimen / MPa Embedded Piece Method for Specimen Group C 0.3 0.4 0.3 0.3 0.4 0.3 Pre - pressure Splitting Method for Specimen Group D 0.3 0.2 0.3 0.5 0.4 0.5

[0071] For the data in Table 5, an analysis of variance was performed, as shown in Table 6.

[0072] Table 6

[0073] Group Number of Observations Sum Average Variance Row 1 6 2 0.333333 0.002666667 Row 2 6 2.2 0.366667 0.014666667 Source of Variation SS df MS F P - value F crit Between Groups 0.003333 1 0.003333 0.384615385 0.549014 4.964603 Within Groups 0.086667 10 0.008667 Total 0.09 11

[0074] As can be seen from Table 6, the within-group variance of test block group C is 0.00267, and the within-group variance of test block group D is 0.01467. The results of the embedded piece method are more consistent.

[0075] The operation method of the present invention is convenient. The method for manufacturing the experimental embedded pieces does not require special process operations such as high temperature and high pressure, and is safe, stable, and reliable; the surface properties of the prepared controllable crack structure end face are similar to those of concrete, and the ceramic powder of the preferred specification has certain activity, which is more conducive to the stability of the detection of the concrete repair effect; the thickness of the prepared concrete crack is completely controllable, with good repeatability and consistency; the width, length, and even the volume of the concrete crack can be known in advance by measuring the experimental embedded pieces, which is helpful for the detection and quantitative research of the repair performance; the thickness of the experimental embedded piece material is adjustable. The thickness of experimental embedded piece 1 can be increased upward, and experimental embedded piece 2 can relatively easily achieve cracks with a width of 0.05 mm and above commonly used in meso-mechanics (although theoretically its thickness can infinitely approach 0 mm), which is helpful for more meso-scale and even micro-scale research; the hardness of the experimental embedded piece is adjustable, which is helpful for manufacturing controllable cracks with various shapes and orientations such as flat and curved surfaces, and is helpful for better simulating the actual situation of concrete cracks for in-depth research.

[0076] Although the present invention has been described in detail in this specification in a general description and in combination with preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, those of ordinary skill in the art can make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions should all be within the scope covered by the present invention; any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A preparation method of an embedded piece for concrete / mortar specimen experiment, characterized in that: The concrete / mortar test block embedded piece is divided into a concrete / mortar test block embedded piece 1 with a thickness of not less than 0.3 mm and a concrete / mortar test block embedded piece 2 with a thickness of less than 0.3 mm; The preparation method of the concrete / mortar test block embedded sheet 1 is as follows: heating and melting an alcohol-soluble resin, adding inorganic micropowder and mixing, stirring evenly, cooling, pressing the prefabricated sheet 1 by roller pressing, and cutting the prefabricated sheet 1 to obtain the concrete / mortar test block embedded sheet 1; The preparation method of the second embedded piece of concrete / mortar specimen experiment is as follows: Dissolve the alcohol-soluble resin in a polar or semi-polar solvent, add inorganic micropowder, stir and mix evenly, and place in a flat shallow dish. After the solvent evaporates, a prefabricated sheet 2 is obtained. The prefabricated sheet 2 is cut to obtain a concrete / mortar test block embedded sheet 2; The weight ratio of the alcohol-soluble resin to the inorganic micropowder is 1-9:9-1; The alcohol-soluble resin is one or more of acrylic resin, polyamide resin, shellac resin, dammar resin, rosin-modified alkyd resin, thermoplastic phenolic resin and polyvinyl butyral resin; The inorganic fine powder is one or more of ceramic powder, red brick powder and concrete fine powder, and the particle size is 0.001mm-0.5mm.

2. The preparation method of the embedded piece for concrete / mortar specimen experiment according to claim 1, characterized in that: The polar or semi-polar solvent is one or more of a benzene solvent, an ester solvent, and an alcohol solvent.

3. The preparation method of the embedded piece for concrete / mortar specimen experiment according to claim 1, characterized in that: The solvent is one or more of ethanol, methanol, toluene and ethyl acetate.

4. A method for preparing concrete / mortar test blocks with controllable cracks by using the first embedded piece prepared by the method according to claim 1, characterized in that, The details are as follows: 1) Mix cement, quartz sand / standard graded aggregate and water in a predetermined proportion to prepare concrete / mortar, and pour it into the mold; 2) Insert the concrete / mortar specimen embedded piece 1 into the concrete / mortar in the mold and compact it using a vibration table to obtain a concrete / mortar specimen 1; 3) Move the concrete / mortar specimens into a standard curing room and cure them for 1 day before demoulding. Continue curing under standard curing conditions for 7 days, 28 days, or 56 days. 4) Immerse a concrete / mortar specimen cured to a specified age in a polar or semi-polar solvent, and repeatedly rinse the expected cracks with the same solvent to obtain a concrete / mortar specimen with cracks.

5. A method for preparing a controllable crack in a concrete / mortar specimen using the embedded piece two prepared by the method according to claim 1, characterized in that, The details are as follows: 1) Mix cement, quartz sand / standard graded aggregate and water in a predetermined proportion to prepare concrete / mortar; 2) Measure the size of the experimental embedded piece required for the concrete / mortar specimen in advance, cut the experimental embedded piece, fix the two ends of the experimental embedded piece in the middle of the test mold, add the mixed concrete into the test mold in two batches, and vibrate it on a vibrating table to obtain the concrete / mortar specimen No. 2; 3) Move the concrete / mortar specimen 2 into the standard curing room and cure for 1 day before demoulding. Continue curing under standard curing conditions for 7 days, 28 days, or 56 days. 4) The concrete / mortar specimen 2 cured to the specified age is immersed in a polar or semi-polar solvent, and the expected cracks are repeatedly washed with the same solvent to obtain a concrete specimen 2 with controllable cracks.

6. The method according to claim 4 or 5, characterized in that: The solvent is one or more of ethanol, methanol, toluene and ethyl acetate; The alcohol-soluble resin includes one or more of acrylic resin, polyamide resin, shellac resin, dammar resin, rosin-modified alkyd resin, thermoplastic phenolic resin, and polyvinyl butyral resin.