CN110967237A - Concrete test piece with three-dimensional built-in cracks and manufacturing method thereof - Google Patents
Concrete test piece with three-dimensional built-in cracks and manufacturing method thereof Download PDFInfo
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
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- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
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- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0058—Kind of property studied
- G01N2203/006—Crack, flaws, fracture or rupture
- G01N2203/0062—Crack or flaws
- G01N2203/0066—Propagation of crack
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
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Abstract
The invention relates to a concrete test piece with a three-dimensional built-in crack and a manufacturing method thereof, wherein the method comprises the following steps: raw material and tool preparation; making holes on the side edge of the concrete mould; fixing the volatile matter in the concrete mould through the holes; fully mixing and stirring standard sand, water and reference cement to obtain a mixed material; after a release agent is coated on the inner side wall of the concrete mold, adding the mixed material into the concrete mold, vibrating, and leveling the surface after the concrete is vibrated compactly and the internal bubbles are basically emitted to obtain an initial concrete test piece; standing the initial concrete test piece, and immediately placing the initial concrete test piece into a standard curing room with the temperature of 20 +/-2 ℃ for curing after the initial concrete test piece is demoulded and numbered; and putting the initial concrete sample into an oven to volatilize the N camphor balls, thus obtaining the concrete sample with the three-dimensional built-in cracks. The obtained concrete test piece can simulate a rock test to the maximum extent, and helps people to know the failure mechanism of the rock more deeply.
Description
Technical Field
The invention relates to the technical field of research on a crack expansion rule in a rock, in particular to a concrete test piece with a three-dimensional built-in crack and a manufacturing method thereof.
Background
Our country is a mountainous country, and the area of mountainous areas accounts for about 70% of the total territory. We are again a developing large country. A large amount of resources and energy development (hydropower, mines, petroleum, natural gas and nuclear power) and transportation facilities (railways and roads) are required to be communicated with rocks. That is to say facing a lot of rock excavation and support works. In developed countries such as Europe and America, rock engineering is almost the rest, and is the sunset engineering. They may also be involved in rock engineering in a few fields, such as oil, shale gas, natural gas, nuclear power, and the utilization of a few tunnels and underground spaces. So most of the current large-scale projects (perhaps 70% to 80%) of rock engineering are performed in china worldwide. The most important rock engineering includes underground engineering, slope engineering, oil and gas well engineering, etc. With the need for national economic development and technological advances, rock engineering continues to march into deeper and more complex formations. In coal mine systems in China, mining with the burial depth of more than 800-1000 m is quite common. In water conservancy projects, diversion tunnels buried more than 2000 meters deep have been built (brocade screen secondary diversion tunnels). Undersea tunnels and undersea oil repositories, which have been built and under construction or in planning, are also increasing. Such as the planned johnson channel, the bohai bay channel, etc. (the latter will be the longest submarine tunnel in the world, and may be the deepest). Therefore, our country faces ever-emerging new research hotspots, difficulties and challenges for rock mechanics and rock engineering.
Geotechnical engineering is an important follow-up engineering project in China, is also a fulcrum of civil engineering in China, represents the development direction of civil engineering projects in China, and is a foundation stone in the building industry to guarantee the development direction of the building industry. Currently, many large rock mass projects in China, such as national defense, traffic, hydropower and mining projects, are being planned or constructed. The design, construction, operation and later maintenance of these projects are closely related to the mechanical properties such as the strength of the rock mass to which the projects are attached. In the construction movement of the rock mass, a large number of weak interlayers, structural planes and micro cracks are inoculated in the rock mass, and the rock mass is defined as a jointed rock mass. Many cases prove that instability damage of the rock mass engineering is not generated right from the beginning, but is generated along with the change of internal load of the jointed rock mass and the redistribution of a stress field in the process of excavating the rock mass engineering, so that the weak part in the jointed rock mass is cracked and expanded, cracks are communicated with each other, and finally a macroscopic damage surface is formed. The strength of the rock mass is reduced, and the stability of the rock mass engineering is seriously influenced. Whether the accident of the collapse of the Marpag dam with the dam height of 66 m in 1959 in France or the large landslide of the Wayion reservoir with the dam height of 262 m in 1963 in Italy is closely related to the crack initiation, expansion, penetration and damage of the crack under the action of the ground stress-crack water coupling.
In engineering analysis, although rocks are often treated as linear elastic, homogeneous and isotropic media, this is only an assumption made for the purpose of simplification, and this assumption has a certain limit for understanding the authenticity of internal stresses and strains of rocks and rocks. Rock is an extremely complex material formed through multiple geologic structure movements, and the interior of the rock contains a plurality of discontinuous structural surfaces such as joints, fractures, bedding, faults and the like. Therefore, rock properties should be analyzed from multiple orientations and angles. Rock is a brittle material, so most hard rocks exhibit brittle failure under load and under certain conditions, i.e., the rocks fail suddenly under load without significant deformation. The cause of such damage may be the type of load, the structure of the material and internal fractures, where the propagation of rock internal fractures under load is the most significant cause of rock damage. Therefore, it is necessary to research the propagation law of the internal fracture of the rock. Initially, rock mechanics problems were often reduced to two-dimensional problems in order to simplify the problem or avoid mathematical complexities. In practice, two-dimensional models are of limited use, except that few rock mechanics problems can be handled as a simplification to plane stress or plane strain problems. However, the three-dimensional fracture is studied later due to the complicated expansion condition of the three-dimensional fracture. In fact, both natural surface fractures and built-in fractures are three-dimensional in nature. Therefore, the method has more practical significance for the research of the three-dimensional fracture. At present, translucent resin materials are generally adopted for replacing the indoor test research on the built-in crack propagation of rock materials, but the propagation condition of cracks is only observed, and the internal reflection of the actual rock is not accurate. Little people are involved in the research field of the built-in crack propagation rule of the real rock material, in 2005, Liyanchun, Lishui and the like cooperate with technical personnel in a ceramic factory to firstly manufacture a ceramic test piece with built-in coin-shaped cracks, but the experimental result is not ideal due to the reasons of the manufacturing precision, the CT precision and the like of the test piece at that time.
The research on the three-dimensional built-in fracture propagation mechanism of the rock is always the primary task of geotechnical workers, and the research not only can enable people to know the damage form of the rock more clearly, but also can enable people to take precautionary measures in advance for various geotechnical engineering accidents. The materials used in the three-dimensional crack propagation research currently are homogeneous materials such as organic and inorganic glass. However, natural rocks have many defects such as holes, cracks, joints and the like, and the properties of the natural rocks are greatly different from those of the materials. Therefore, the expansion research of the three-dimensional fracture in the rock or rock-like material becomes an important link for the research of rock mechanics. Because the rock is a brittle material, and the concrete is brittle and heterogeneous as the rock, the concrete is processed and formed by a certain technical means by selecting cement and standard sand as main raw materials after mixing, and main physical and mechanical parameters (such as elastic modulus, Poisson's ratio, compressive strength, tensile strength, volume weight and the like) of a formed concrete test piece are close to those of a real rock, and the test shows the stress deformation characteristic similar to that of the rock. And the prepared concrete material has better workability, is convenient for manufacturing and forming a test piece, presets a three-dimensional crack in the test piece and is easier for demoulding, so the crack extension rule research is carried out by manufacturing the three-dimensional crack in the concrete test piece.
An effective solution to the problems in the related art has not been proposed yet.
Disclosure of Invention
In view of the above problems in the prior art, the first technical problem to be solved by the present invention is: the method for manufacturing the three-dimensional built-in crack in the concrete test piece can be used for effectively simulating a rock test and well explaining the mechanical phenomenon and the constitutive relation of a complex structure in the rock.
The second technical problem to be solved is: the concrete test piece can effectively simulate the rock crack expansion activity.
In order to solve the first technical problem, the invention adopts the following technical scheme: a manufacturing method of a concrete test piece with three-dimensional built-in cracks comprises the following steps:
s100: raw material and tool preparation: preparing a required concrete mold, a release agent, volatile matters for generating cracks, standard sand, water, reference cement and a concrete constant-temperature constant-humidity standard curing box required for mixing concrete in advance;
s200: making M holes on the side edge of the concrete mould, wherein M is M ═ M1，m2，…mt…mM}；
S300: fixing volatile matters in the concrete mold through the holes, wherein the fixed positions, angles, numbers and intervals of the volatile matters correspond to the positions, angles, numbers and intervals of cracks required in advance one by one;
s400: and fully mixing water and the reference cement and stirring to obtain a mixed material, wherein the water-cement ratio is 0.35-0.6. (ii) a In specific implementation, standard sand can be added into the mixture according to needs to adjust the ductility of the concrete;
smearing a release agent on the inner side wall of the concrete mould, then adding the mixed material into the concrete mould, vibrating the concrete layer by layer on a small vibrating table, and leveling the surface after the concrete is vibrated compactly and the internal bubbles are basically emitted to obtain an initial concrete sample;
s500: standing the initial concrete test piece, and immediately placing the initial concrete test piece into a standard curing room with the temperature of 20 +/-2 ℃ for curing after the initial concrete test piece is subjected to mold removal numbering; after the strength of the concrete is greatly improved, taking out the test piece from the standard curing box, and placing the test piece in an indoor ventilation position to evaporate water in the test piece;
s600: and putting the initial concrete test piece obtained in the step S500 into an oven to volatilize volatile matters in the M holes, so as to obtain the concrete test piece with the three-dimensional built-in cracks.
Because the cracks can not be prefabricated in the natural rock, the cracks are left in the concrete by the method, so that the rock failure mode can be simulated to the maximum extent, and finally the expansion rule of the cracks in the rock is obtained.
Preferably, the volatile for generating fissures in the S100 is camphor balls. The camphor balls with higher hardness and capable of changing shapes at will are adopted, the camphor balls gradually volatilize to become gas in the heating process of the concrete test piece containing the camphor balls, overflow from tiny pores of the concrete and finally disappear completely, so that cracks with a designed angle, shape and certain flatness are left in the concrete, the properties of the prefabricated cracks are quite close to the properties around the cracks of a real rock body, the concrete test piece with the cracks has the performance of simulating the cracked rock, a rock test can be simulated to the greatest extent, and people can be helped to know the failure mechanism of the rock more deeply.
Preferably, in S300, the camphor ball is cut into N pieces, where N ═ N1，n2，…ni…nNGet L rootsFine line, L ═ L1，l2，…lj…lLJ pieces of thin thread l are then gluedjWith the i-th camphor ball n after cuttingiAnd (3) adhering together, wherein after N, L, M and firm adhesion, a thin line passes through the t-th hole which is manufactured in advance, i, j, t and each camphor ball is fixed according to the position, angle, number and interval of the crack which are required in advance. Because the cracks can not be prefabricated in the natural rock, the cracks are left in the concrete by the method, so that the rock failure mode can be simulated to the maximum extent, and finally the expansion rule of the cracks in the rock is obtained.
Preferably, the water cement ratio of the water in S400 to the reference cement is 0.5.
Preferably, the relative humidity in the standard curing chamber in S500 is 95% or more, and the curing time is 28 days.
Preferably, the initial concrete sample in S500 is left to stand in an indoor environment at a temperature of more than 5 ℃ for 24 hours.
Preferably, the heating temperature in the S600 is 95-110 ℃, and the heating time is 30-90 min. The volatilization speed of the camphor balls is accelerated due to the temperature rise in the heating process, the camphor balls can be completely volatilized within 30-90 min, and gas generated by volatilization can overflow from tiny pores of a concrete test piece, so that a three-dimensional built-in crack is formed inside the concrete. The heating temperature can be adjusted according to the volatile matter, and the basic requirement of the temperature selection is that the heating temperature is slightly higher than the vaporization temperature of the volatile matter. The heating time is a test measurement and is usually set slightly longer than the test measurement to ensure complete volatilization of the volatile.
When the volatile is camphor ball, the heating temperature can be 95 deg.C, 98 deg.C, 100 deg.C, 105 deg.C or 110 deg.C, and the heating time can be 30min, 40min, 50min, 60min, 70min, 80min or 90 min.
In order to solve the second technical problem, the invention adopts the following technical scheme: a concrete test piece with three-dimensional built-in cracks is prepared by the method.
Compared with the prior art, the invention has at least the following advantages:
1. the method has the advantages of simple and easily obtained raw materials and equipment, suitability for teaching or experimental analysis, small operation difficulty and low cost.
1.2. The concrete test piece with the three-dimensional built-in cracks prepared by the method can simulate a rock test to the maximum extent and help people to know the failure mechanism of the rock more deeply.
Drawings
FIG. 1 is a schematic view of a single crack test piece.
FIG. 2 is a schematic diagram of a single crack production process.
FIG. 3 is a cross-sectional view of a flaw location of a single-flaw test piece
FIG. 4 is a longitudinal cross-sectional view of the flaw location of a single-flaw test piece
FIG. 5 is a schematic view of a parallel dual split test piece.
FIG. 6 is a schematic view of a coplanar dual split test piece.
FIG. 7 is a schematic illustration of a method of manufacturing a coplanar dual split test piece.
FIG. 8 is a schematic view of a misaligned dual split trial.
FIG. 9 is a schematic view of a three-split test piece.
FIG. 10 is a flow chart of a method of manufacturing a concrete specimen having a three-dimensional built-in flaw.
In the figure: 1. cracking; 2. a concrete mold; 3. camphor ball; 4. a thin wire; 5. holes and bolts matched with the holes.
Detailed Description
The present invention is described in further detail below.
The invention discloses a method for manufacturing a concrete test piece with a three-dimensional built-in crack, which comprises the following steps: the concrete mould, the release agent, the camphor ball with regular shape, the standard sand, water, the standard cement, the concrete constant temperature and humidity standard curing box, the fine line, the glue and the like required in the test are prepared in advance. And manufacturing corresponding holes on the side edge of the mold according to the parameters of the reserved cracks, such as positions, angles, numbers, intervals and the like. The camphor ball is cut into required size, two thin lines with equal length are taken, then the thin lines and the cut camphor ball are adhered together by glue, when the strength of the glue is high, the thin lines penetrate through holes made in advance, and the camphor ball is fixed according to the required parameters of the position, the angle, the number, the distance and the like of the reserved crack. And then, weighing standard sand, water and reference cement according to a certain mixing ratio, and fully stirring. And taking out the mold, smearing a release agent in the mold, adding the mixed concrete, vibrating the concrete layer by layer on a small vibrating table, and leveling the surface of the test piece after the concrete is vibrated compactly and the internal bubbles are basically emitted. And standing the test piece in an indoor environment, immediately placing the test piece into a constant-temperature constant-humidity standard curing box for curing after the mold is removed and numbered, taking out the test piece from the standard curing box after the strength of concrete is greatly improved, and placing the test piece in an indoor ventilation position to evaporate water in the test piece. And finally, putting the concrete sample containing the camphor balls in the concrete sample into an oven, wherein the volatilization speed of the camphor balls is accelerated due to the temperature rise in the heating process, and the camphor balls are volatilized completely finally, and gas generated by volatilization can overflow from tiny pores of the concrete sample, so that a three-dimensional built-in crack is formed in the concrete.
The first embodiment is as follows: production of concrete test pieces with single fissure:
a single split test piece is shown in figure 1. The test piece is a cylinder with the diameter of 50mm and the height of 100mm, the crack 1 of the test piece is a closed circle and is positioned at the center of the test piece, the diameter of the test piece is 15mm, and the included angle between the crack and the horizontal plane is 45 degrees.
The manufacturing process of the crack is shown in fig. 2, and the specific steps are as follows: the concrete mould 2, the camphor ball 3 with regular shape, the standard sand 950g for mixing the concrete, the standard cement 450g, the water 225g, the fine line 4 and a plurality of materials (demoulding agent and glue) and tools (a small-sized vibration table and a constant temperature and humidity standard curing box) required in the test are prepared in advance. And manufacturing corresponding holes and matched bolts 5 on two corresponding side edges of the die according to the designed included angle of the reserved crack and the horizontal plane being 45 degrees. The camphor ball is cut into required size, two thin lines with equal length are taken, then the thin lines and the cut camphor ball are adhered together by glue, when the strength of the glue is high, the thin lines penetrate through holes made in advance, and the camphor ball is fixed according to the required parameters of the position, the angle, the distance and the like of the reserved crack. And mixing the concrete according to the water cement ratio of 0.5, and fully stirring. And taking out the mold, smearing a release agent in the mold, adding the mixed concrete, vibrating the concrete layer by layer on a small vibrating table, and leveling the surface of the test piece after the concrete is vibrated compactly and the internal bubbles are basically emitted. Standing the test piece in an indoor environment with the temperature of more than 5 ℃ for 24 hours, immediately placing the test piece into a standard curing room with the temperature of 20 +/-2 ℃ and the relative humidity of more than 95% for curing for 28 days after the mold stripping number, taking out the test piece from the standard curing box after the strength of the concrete is greatly improved, and placing the test piece in an indoor ventilation position to evaporate the water in the test piece. And finally, putting the concrete sample containing the camphor balls inside into an oven, and heating for 30-90 min at the temperature of about 100 ℃, wherein the volatilization speed of the camphor balls is accelerated due to the temperature rise in the process, the camphor balls can be completely volatilized within 30-90 min, and gas generated by volatilization can overflow from tiny pores of the concrete sample, so that a three-dimensional built-in crack is formed inside the concrete.
The actual angle and the diameter of the crack inside the test piece are measured by utilizing the CT scanning technology. The angle measuring method comprises three steps: firstly, scanning a whole image of a test piece, and preliminarily positioning the crack position; secondly, scanning the fracture cross-sectional view, as shown in fig. 3, aiming at finding the maximum angle position of the fracture, wherein the judgment standard is that the fracture forms a straight line in the image, and drawing a line on the test piece for positioning; and thirdly, standing the test piece, scanning along the direction vertical to the position where the line is drawn in the second step to obtain a longitudinal section, measuring and recording an angle as a first angle as shown in fig. 4, rotating the test piece by a small angle left and right, measuring and recording the angle as a second angle and a third angle, wherein if the first angle is larger than the second angle and the third angle, the first angle is the actual angle of the crack in the test piece, and otherwise, continuously searching. And after the angle measurement is finished, slice-by-slice scanning is carried out on the vertical horizontal diameter, and the diameter of the crack is searched and measured. Thus, the initial condition of the fracture can be obtained. Through actual measurement, the shape and the flatness of the crack in the test piece are better, and the test requirements can be completely met.
Example two: production of concrete test pieces with parallel double fissures:
a parallel dual split test piece is shown in figure 5. The two closed circular cracks are positioned in the center of the test piece, the diameter of the test piece is 15mm, and the distance between the two closed circular cracks is 10 mm. All the slits included the same 45 degrees from the horizontal.
The concrete steps of the crack manufacturing are as follows: the concrete mould 2, the camphor ball 3 with regular shape, the standard sand 950g for mixing the concrete, the standard cement 450g, the water 225g, the fine line 4 and a plurality of materials (demoulding agent and glue) and tools (a small-sized vibration table and a constant temperature and humidity standard curing box) required in the test are prepared in advance. According to the design, the included angle between the reserved crack and the horizontal plane is 45 degrees, and the reserved crack is parallel double cracks, so two rows of corresponding holes and matched bolts 5 are manufactured on two corresponding side edges of the die. Cutting the camphor ball into required size, taking a plurality of fine lines with equal length, then using glue to stick the fine lines and the cut camphor ball together, and placing aside until the strength of the glue is gradually increased. And (3) mixing the concrete according to the water cement ratio of 0.5, and uniformly stirring. Taking out the mould, smearing a release agent in the mould, fixing two camphor balls which are parallel to each other according to the required parameters such as the position, the angle and the like of the reserved crack, then adding the mixed concrete, vibrating the concrete layer by layer on a small-sized vibrating table, and leveling the surface of the test piece after the concrete is vibrated compactly and the internal bubbles are basically emitted. Standing the test piece in an indoor environment with the temperature of more than 5 ℃ for 24 hours, immediately placing the test piece into a standard curing room with the temperature of 20 +/-2 ℃ and the relative humidity of more than 95% for curing for 28 days after the mold stripping number, taking out the test piece from the standard curing box after the strength of the concrete is greatly improved, and placing the test piece in an indoor ventilation position to evaporate the water in the test piece. And finally, putting the concrete sample containing the camphor balls inside into an oven, and heating for 30-90 min at the temperature of about 100 ℃, wherein the volatilization speed of the camphor balls is accelerated due to the temperature rise in the process, the camphor balls can be completely volatilized within 30-90 min, and gas generated by volatilization can overflow from tiny pores of the concrete sample, so that a three-dimensional built-in crack is formed inside the concrete.
Example three: production of concrete test pieces with coplanar double fissures:
as shown in FIG. 6, the coplanar double-slit test piece has two closed circular slits located at two sides of the center of the test piece, the diameter of the two closed circular slits is 15mm, the distance between the tips of the two closed circular slits is 10mm, and the included angles between all the slits and the horizontal plane are the same and 30 degrees and are located on the same plane. The manufacturing process of the crack is shown in fig. 7, and the specific steps are as follows: the concrete mould 2, the camphor ball 3 with regular shape, the standard sand 950g for mixing the concrete, the standard cement 450g, the water 225g, the fine line 4 and a plurality of materials (demoulding agent and glue) and tools (a small-sized vibration table and a constant temperature and humidity standard curing box) required in the test are prepared in advance. And manufacturing corresponding holes and matched bolts 5 on two corresponding side edges of the die according to the designed included angle of the reserved crack and the horizontal plane of 30 degrees. The camphor ball is cut into required sizes, two thin lines with equal length are taken, due to the coplanar double-slit structure, the thin lines and the two cut camphor balls are required to be adhered together according to the distance of 10mm by glue, the two camphor balls are uniformly distributed on two sides of the center of the thin lines, when the strength of the glue is high, the thin lines penetrate through holes which are manufactured in advance, and the camphor balls are fixed according to required parameters such as the position, the angle and the like of the reserved slit. And mixing the concrete according to the water cement ratio of 0.5, and fully stirring. And taking out the mold, smearing a release agent in the mold, adding the mixed concrete, vibrating the concrete layer by layer on a small vibrating table, and leveling the surface of the test piece after the concrete is vibrated compactly and the internal bubbles are basically emitted. Standing the test piece in an indoor environment with the temperature of more than 5 ℃ for 24 hours, immediately placing the test piece into a standard curing room with the temperature of 20 +/-2 ℃ and the relative humidity of more than 95% for curing for 28 days after the mold stripping number, taking out the test piece from the standard curing box after the strength of the concrete is greatly improved, and placing the test piece in an indoor ventilation position to evaporate the water in the test piece. And finally, putting the concrete sample containing the camphor balls inside into an oven, and heating for 30-90 min at the temperature of about 100 ℃, wherein the volatilization speed of the camphor balls is accelerated due to the temperature rise in the process, the camphor balls can be completely volatilized within 30-90 min, and gas generated by volatilization can overflow from tiny pores of the concrete sample, so that a three-dimensional built-in crack is formed inside the concrete.
Example four: manufacturing a concrete sample with staggered double cracks:
the dislocated dual split trial is shown in figure 8. The two closed circular cracks are positioned at two sides of the center of the test piece, the diameter of each closed circular crack is 15mm, the distance between the tips of the two cracks is 10mm, the crack tips are close to the center, and the included angles between the two cracks and the horizontal plane are both 30 degrees but are not on the same plane.
The fabrication of the fissures is identical to that of the coplanar double fissures described in example three, except that the two camphor balls are placed in different positions.
Example five: production of concrete test pieces with three cracks:
the three-split test piece is shown in FIG. 9. The three closed circular cracks are positioned in the center of the test piece, the distance is 10mm, and the included angles between all the cracks and the horizontal plane are the same and are 45 degrees.
The manufacturing process of the crack is the same as that of the parallel double cracks described in the second embodiment, and the three cracks are sequentially manufactured by the same method from bottom to top.
In conclusion, by means of the technical scheme, the camphor balls with higher hardness and capable of changing shapes at will are adopted, the camphor balls gradually volatilize to become gas in the heating process of the concrete test piece containing the camphor balls, overflow from tiny pores of the concrete and finally disappear completely, so that cracks with a designed angle, shape and certain flatness are left in the concrete, the properties of the prefabricated cracks are very close to the properties around the real cracks of the rock mass, a rock test can be simulated to the maximum extent, and people can be helped to understand the failure mechanism of the rock more deeply.
Finally, the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all of them should be covered in the claims of the present invention.
Claims (8)
1. A manufacturing method of a concrete test piece with three-dimensional built-in cracks is characterized by comprising the following steps: the method comprises the following steps:
s100: raw material and tool preparation: preparing a required concrete mold, a release agent, volatile matters for generating cracks, water required for mixing concrete, reference cement and a concrete constant-temperature constant-humidity standard curing box in advance;
s200: making M holes on the side edge of the concrete mould, wherein M is M ═ M1，m2，…mt…mM}；
S300: fixing volatile matters in the concrete mold through the holes, wherein the fixed positions, angles, numbers and intervals of the volatile matters correspond to the positions, angles, numbers and intervals of cracks required in advance one by one;
s400: fully mixing water and reference cement and stirring to obtain a mixed material, wherein the water cement ratio is 0.35-0.6;
smearing a release agent on the inner side wall of the concrete mould, then adding the mixed material into the concrete mould, vibrating the concrete layer by layer on a small vibrating table, and leveling the surface after the concrete is vibrated compactly and the internal bubbles are basically emitted to obtain an initial concrete sample;
s500: standing the initial concrete test piece, and immediately placing the initial concrete test piece into a standard curing room with the temperature of 20 +/-2 ℃ for curing after the initial concrete test piece is subjected to mold removal numbering;
s600: and putting the initial concrete test piece obtained in the step S500 into an oven to volatilize volatile matters in the M holes, so as to obtain the concrete test piece with the three-dimensional built-in cracks.
2. The method of manufacturing a concrete specimen having three-dimensional built-in fissures as claimed in claim 1, characterized in that: the volatile matter used for generating the cracks in the S100 is camphor balls.
3. The method of manufacturing a concrete specimen having a three-dimensional built-in flaw according to claim 2, characterized in that: in the step S300, the camphor ball is firstly cut into N pieces, wherein N is { N ═ N1，n2，…ni…nNGet L threads, L ═ L1，l2，…lj…lLJ thin lines l are then gluedjWith the i-th camphor ball n after cuttingiAnd (3) adhering together, wherein after N, L, M and firm adhesion, a thin line passes through the t-th hole which is manufactured in advance, i, j, t and each camphor ball is fixed according to the position, angle, number and interval of the crack which are required in advance.
4. The method of manufacturing a concrete specimen having three-dimensional built-in fissures as claimed in claim 1, characterized in that: and the water-cement ratio of the water in the S400 to the reference cement is 0.5.
5. The method of manufacturing a concrete specimen having three-dimensional built-in fissures as claimed in claim 1, characterized in that: and the relative humidity in the standard curing chamber in the S500 is more than 95%, and the curing time is 28 days.
6. The method of manufacturing a concrete specimen having three-dimensional built-in fissures as claimed in claim 1, characterized in that: and S500, standing the initial concrete sample in an indoor environment with the temperature of more than 5 ℃ for 24 hours.
7. A method of manufacturing a concrete specimen having three-dimensional built-in fissures according to any one of claims 2 to 6, characterized in that: in the step S600, the heating temperature is 95-110 ℃, and the heating time is 30-90 min.
8. The utility model provides a concrete sample with three-dimensional built-in crack which characterized in that: the concrete test piece is prepared by the method in claim 7.
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