CN114577564B - Method for prefabricating cracks of mortar test piece by three-point bending loading - Google Patents
Method for prefabricating cracks of mortar test piece by three-point bending loading Download PDFInfo
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Abstract
The invention belongs to the technical field of hydraulic concrete material tests, and particularly relates to a method for pre-forming cracks of a mortar test piece by utilizing three-point bending loading. The method comprises the following steps of placing one of the mortar test pieces on a three-point bending test device, applying a preset load to the mortar test piece through the three-point bending test device, obtaining a load-displacement curve, analyzing the damage form and the load-displacement curve characteristics of the prefabricated mortar test piece, obtaining the crack widths of the surfaces of the mortar test pieces at different damage stages, determining the damage load adopted when an irregular crack with the preset width can be prefabricated, and implementing the determined damage load on the other mortar test pieces, so that the mortar test piece meeting the width requirement of the prefabricated crack can be obtained, the problems of singleness and fixity of the crack shape of the self-healing test piece prepared by the existing concrete mortar, particularly the crack prefabrication of the self-healing concrete mortar, and the influence of carbonization reaction on the concrete self-healing process in the curing process can be effectively avoided.
Description
Technical Field
The invention belongs to the technical field of hydraulic concrete material tests, and particularly relates to a method for pre-forming cracks of a mortar test piece by utilizing three-point bending loading.
Background
Concrete materials used for hydraulic structures are often exposed to service environments such as pressurized water, dry-wet cycle coupling effect, corrosion scouring coupling and the like, the mechanical property and the durability of the concrete materials are greatly reduced under the complex environments, and quality defects such as concrete cracking, corrosion, erosion and the like caused by the complex environments are often difficult to repair. Therefore, how to improve the durability of the hydraulic concrete material is the key to solve the problem. The self-healing concrete has the functions of self-diagnosing cracks and self-repairing cracks, when the base concrete generates damaged cracks, the repairing system embedded in the self-healing concrete releases a repairing agent under the condition of force, heat or chemical damage, and bonds and blocks the cracks, so that the repairing purpose is achieved. The concrete crack resistance improving agent can provide a new research approach for improving the crack resistance of concrete or reducing existing cracks of concrete, can also provide a guarantee measure for improving the performance of concrete materials, further prolongs the service life of concrete buildings, and has great application prospects in the engineering fields of concrete structure reinforcement and repair, disaster prevention and reduction and the like. Therefore, when the self-healing concrete is tested and researched for healing performance, a cement-bonded sand strip comparison sample with cracks needs to be manufactured, in order to simulate actual cracks in and on the surface of hydraulic concrete, the cracks of the cement-bonded sand strip need to be irregular cracks of 0.2-0.4 mm, and then the self-healing condition of the cement-bonded sand test piece with the cracks under different curing conditions is observed through tests.
At present, crack manufacturing devices, such as pre-buried steel sheets or special pre-crack molds, are adopted for manufacturing methods and tools for concrete pre-cracks, and regular cracks are pre-manufactured in the concrete sample preparation process. But the crack is prefabricated by the method and the device, so that the crack is smooth and flat, and the depth and the width of the crack are the same. However, in actual engineering, the crack cracking angles generated inside and on the surface of the concrete member are different, the development trend is unpredictable, and the development difference between the prefabricated crack and the actual crack is large. In addition, regular cracks are prefabricated during preparation of concrete samples, carbonization reaction is easy to occur in the curing process, the accuracy of research on mechanical property indexes of concrete is influenced to a certain extent, and the experimental research on the later self-healing of the cracks is influenced.
Disclosure of Invention
The invention provides a method for prefabricating cracks of a mortar test piece by three-point bending loading, which aims to solve the problems of single shape and fixity of cracks of the existing concrete mortar prepared test piece with cracks, and particularly aims at prefabricating the cracks of self-healing concrete mortar, so that the influence of carbonization reaction in the curing process on the self-healing process of concrete is effectively avoided.
In order to achieve the purpose, the invention adopts the technical scheme that:
a method for loading cracks of a prefabricated mortar test piece by three-point bending comprises the following steps
The method comprises the following steps: placing a mortar test piece on a three-point bending test device
Placing one of a plurality of prepared mortar test pieces on a three-point bending test device;
step two: applying a preset load to the mortar test piece through a three-point bending test device and obtaining a load-displacement curve;
step three: analyzing the damage form and the load-displacement curve characteristics of the prefabricated mortar test piece, and acquiring the crack widths of the surface of the mortar test piece in different damage stages;
step four: determining a damage load adopted when an irregular crack with a preset width can be prefabricated;
step five: and (5) applying the damage load determined in the fourth step to the rest mortar test pieces to obtain the mortar test pieces according with the width of the prefabricated cracks.
The three-point bending test device adopted in the first step is a microcomputer-controlled compression-resistant and bending-resistant integrated machine, and the microcomputer-controlled compression-resistant and bending-resistant integrated machine at least comprises a loading cylinder, two supporting cylinders, a force loading part and a computer; the force loading part is used for applying a load force to the mortar test piece; the computer is connected with the force loading part through an electric signal; the two supporting cylinders are fixed on a hydraulic platform of the microcomputer-controlled compression-resistant and bending-resistant integrated machine; the upper part of the loading cylinder is fixedly connected with the force loading part and is positioned above the middle of the two supporting cylinders.
The two supporting cylinders are fixed on the hydraulic platform in parallel, the loading cylinder is parallel to the two supporting cylinders, and the axial directions of the supporting cylinders and the loading cylinder are perpendicular to the long axis direction of the mortar test piece.
The distance between the shaft centers of the supporting cylinders positioned at the two sides of the lower part of the mortar test piece to be tested is 100mm; the diameter of the supporting cylinder and the diameter of the loading cylinder are both 10mm.
One side of the hydraulic platform is fixedly connected with a baffle used for positioning the mortar test piece, and the baffle is arranged in parallel with the supporting cylinder.
The specific method for applying the preset load to the mortar test piece in the step two is as follows: and uniformly loading the load on the mortar test piece at a loading rate of 30-60N/s.
The destruction stage in the third step comprises five stages which are sequentially from front to back: a compaction stage, a linear elasticity stage, an initial crack stage, a crack development stage and a destabilization damage stage.
The compaction stage is a period from the contact of the three-point bending test device with the mortar test piece to the beginning of the stress of the mortar test piece; the linear elastic stage is the period from the moment the mortar test piece is stressed to the moment before cracks appear on the mortar test piece; the initial cracking stage is a period from the occurrence of a crack on the surface of the mortar test piece to the slow expansion; the crack development stage is a period that the cracks on the surface of the mortar test piece are stably expanded, the crack width is increased, and the load is slowly reduced along with the increase of the displacement; the instability damage stage is a period that the cracks of the mortar test piece are subjected to instability expansion, and the load is suddenly reduced along with the increase of displacement.
The breaking load determined in the fourth step is the breaking load when the irregular crack with the width of 0.2 mm-0.4 mm is prefabricated; this load acts as an end point of loading.
The size of the mortar test piece in the first step is 40mm multiplied by 160mm.
Has the beneficial effects that:
(1) The method comprises the five steps of placing one of the mortar test pieces on a three-point bending test device, applying preset load to the mortar test piece through the three-point bending test device, obtaining a load-displacement curve, analyzing the damage form and the load-displacement curve characteristics of the prefabricated mortar test piece, obtaining the crack widths of the surfaces of the mortar test pieces in different damage stages, determining the damage load adopted when irregular cracks with preset widths can be prefabricated, and implementing the damage load determined in the fourth step on the other mortar test pieces, so that the mortar test pieces meeting the crack widths are obtained, the problem that the existing concrete mortar prepared test pieces with cracks have single crack shapes and are fixed is solved, the mortar test pieces are particularly self-healing for the cracks of self-healing concrete mortar, and the influence of carbonization reaction on the concrete healing process in the curing process is effectively avoided.
(2) The three-point bending test device adopted by the invention is a microcomputer-controlled compression-resistant and bending-resistant integrated machine, the equipment is common equipment for concrete mortar experiments, and a mortar test piece with cracks meeting the experiment requirements can be obtained without additionally customizing a mould or an embedded part by adopting the three-point bending test device, so that the purposes of one machine with multiple purposes, cost saving and simple and convenient operation are realized.
(3) The invention breaks through the limitation that the pre-buried steel sheet or the special pre-crack die can only pre-crack regular cracks with smooth and flat cracks and the same depth and width of the cracks.
(4) The invention can prefabricate the damage cracks with different widths by determining the loading termination point, thereby meeting the research requirements of different materials or components.
(5) The method can prefabricate the crack at any maintenance period, makes up the defect that the traditional method for prefabricating the crack can only prefabricate the crack during sample preparation, and improves the influence of carbonization reaction at the prefabricated crack.
The foregoing is merely an overview of the technical solutions of the present invention, and in order to make the technical solutions of the present invention more clearly understood and to be implemented in accordance with the content of the description, the following is a detailed description of preferred embodiments of the present invention.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
FIG. 1 is a flow chart of the present invention;
FIG. 2 is a schematic diagram of the arrangement of a mortar test piece according to the present invention;
FIG. 3 is a schematic view of the loading destruction stage of the mortar test piece of the present invention.
In the figure: 1-a mortar test piece; 2-a support cylinder; 3-a baffle plate; 4-a hydraulic platform; 5-loading a cylinder; i, compacting; II, a linear elasticity stage; III, initial cracking stage; IV-crack development stage; v-destabilization destruction stage.
The foregoing is only an overview of the technical solutions of the present invention, and in order to make the technical solutions of the present invention more clear and clear, and to implement them in accordance with the content of the description, the following is a detailed description of preferred embodiments of the present invention.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The first embodiment is as follows:
referring to fig. 1 and 2, the method for loading the cracks of the pre-manufactured mortar test piece by using three-point bending comprises the following steps
The method comprises the following steps: placing a mortar test piece 1 on a three-point bending test device;
placing one of a plurality of prepared mortar test pieces 1 on a three-point bending test device;
step two: applying a preset load to the mortar test piece 1 through a three-point bending test device and obtaining a load-displacement curve;
step three: analyzing the damage form and the load-displacement curve characteristics of the prefabricated mortar test piece 1 to obtain the crack widths of the surface of the mortar test piece 1 in different damage stages;
step four: determining a damage load adopted when the irregular crack with the preset width can be prefabricated;
step five: and (5) applying the damage load determined in the fourth step to the rest mortar test pieces to obtain a mortar test piece 1 according with the width of the prefabricated crack.
In actual use, one of the prepared mortar test pieces 1 is placed on a three-point bending test device, the three-point bending test device is started, a preset load is input into a computer in the three-point bending test device, the three-point bending test device carries out the preset load on the mortar test piece 1, the computer synchronously obtains a load-displacement curve, the fracture widths of the surfaces of the mortar test pieces at different damage stages are obtained through analysis of the damage forms and the load-displacement curve characteristics of the prefabricated mortar test pieces 1, the damage load adopted when irregular fractures with preset widths can be prefabricated is obtained, and then determined damage loads are carried out on the other mortar test pieces one by one to obtain the mortar test pieces with the irregular fractures conforming to the preset widths, so that the mortar test pieces are convenient to use in subsequent tests.
The mortar test pieces in this example were prepared in accordance with the standard of GB 17671.
The mortar test piece is made of hydraulic self-healing mortar and has a self-healing function. The formula of the hydraulic self-healing mortar is as follows: comprises a rubber material, aggregate, an additive, a repairing agent, fiber and water; the adhesive material, the aggregate, the admixture, the repairing agent and the water are respectively mixed according to the following parts by weight: 270 to 290 parts of rubber material, 700 to 750 parts of aggregate, 4 to 4.5 parts of additive, 1.5 to 9 parts of repairing agent and 100 to 110 parts of water. Wherein the fibers are mixed according to the volume, and the volume accounts for 0.5 to 1.2 percent of the total volume; the glue material is prepared from cement and fly ash according to the weight ratio of (8-9): (1-2) by mass; the cement is P.O 42.5 portland cement, and the fly ash is above grade III; the aggregate is natural sand or machine-made sand in the area 2; the admixture is formed by mixing a water reducing agent and an air entraining agent, wherein the using amount of the water reducing agent is 4-4.4 parts by weight, and the using amount of the air entraining agent is 0-0.1 part by weight; the water reducing agent is a polycarboxylic acid water reducing agent; the repairing agent is a cement-based permeable crystallization material; the fiber is short discontinuous fiber, and the short discontinuous fiber is one of steel fiber, polypropylene fiber, basalt fiber or carbon fiber.
The hydraulic self-healing mortar is prepared by the following method: adding water into the stirring device for several minutes, and then completely discharging the water in the stirring device to ensure that the wall of the stirring barrel is completely wetted; then putting the aggregate weighed by mass parts and the fiber prepared by volume ratio into the stirring device treated in the step one for dry stirring for 110-130 s to uniformly distribute the fiber, and then adding the uniformly mixed glue material and the repairing agent by mass parts for mixing and stirring for 50-70 s; then, fully mixing the admixture weighed according to the parts by mass with water, pouring 50% of mixed liquor into a stirring device, and stirring for 55-65 s; and then, adding the 50 percent of mixed solution left after the admixture and the water are fully mixed into the slurry prepared in the third step, forcibly stirring for 110-130 s, and discharging.
The prepared mortar test piece with the self-healing function is loaded with the crack, and the width of the crack is controlled, so that the mortar test piece is used for the subsequent performance research of the cement with the self-healing function.
The self-healing process of concrete cracks can be promoted through the coupling reaction of carbonization and secondary hydration of concrete. If regular cracks are preset, the exposed area of the cracks is large, carbon dioxide in the air permeates into the concrete cracks to generate a carbonization reaction in the curing process, and adverse effects can be generated on the research of the self-healing effect of the cracks in the later period. The invention loads the crack on the mortar test piece with the self-healing function, solves the problems of the single shape and the fixity of the crack of the test piece with the crack prepared by the existing concrete mortar, and thereby effectively avoids the influence of the carbonization reaction on the self-healing process of the concrete in the curing process.
Example two:
referring to the method for loading the cracks of the prefabricated mortar test piece by using three-point bending as shown in fig. 1 and fig. 2, on the basis of the first embodiment, the three-point bending test device adopted in the first step is a microcomputer-controlled compression-resistant and bending-resistant integrated machine, and the microcomputer-controlled compression-resistant and bending-resistant integrated machine at least comprises a loading cylinder 5, two supporting cylinders 2, a force loading part and a computer; the force loading part is used for applying a loading force to the mortar test piece 1; the computer is connected with the force loading part through an electric signal; the two supporting cylinders 2 are fixed on a hydraulic platform 4 of the microcomputer-controlled compression-resistant and bending-resistant integrated machine; the upper part of the loading column 5 is fixedly connected with the force loading part and is positioned above the middle of the two support columns 2.
During the in-service use, at first place mortar test piece 1 on two support columns 2, two support columns 2 are fixed on the hydraulic pressure platform 4 of computer control resistance to compression bending all-in-one, and the central point of mortar test piece 1 aligns with the center between the axle of two support columns 2. Then, the force loading part enables the loading cylinder 5 to be in contact with the center of the upper surface of the mortar test piece 1 through up-and-down movement, and then the loading cylinder 5 applies a loading force to the mortar test piece 1. By adopting the technical scheme, the mortar test piece 1 to be tested is uniformly stressed and is easy to control.
In a specific application, one of the supporting cylinders 2 and the loading cylinder 5 may be slightly inclined, so that the supporting cylinder 2 and the loading cylinder 5 are in complete contact with the mortar sample 1, so that the load can be uniformly distributed along the width direction of the mortar sample 1 without generating any torsional stress.
The microcomputer-controlled compression-resistant and bending-resistant integrated machine adopted in the embodiment is the prior art, and the implementation process is carried out according to the specification in section 4 of GB/T17671.
Example three:
referring to the method for loading the crack of the prefabricated mortar test piece by using three-point bending as shown in fig. 1 and fig. 2, on the basis of the second embodiment, the two supporting cylinders 2 are fixed on the hydraulic platform 4 in parallel, the loading cylinder 5 is parallel to the two supporting cylinders 2, and the axial directions of the supporting cylinders 2 and the loading cylinder 5 are both perpendicular to the long axis direction of the mortar test piece 1.
By adopting the technical scheme, the mortar test piece 1 meets the relevant regulations in section 4 of GB/T17671, and the mortar test piece 1 meeting the preset crack width is prepared.
Example four:
referring to the method for prefabricating the cracks of the mortar test piece by using three-point bending loading shown in fig. 1 and 2, on the basis of the second embodiment, the distance between the axial centers of the supporting cylinders 2 positioned at the two sides of the lower part of the mortar test piece 1 to be tested is 100mm; the supporting cylinder 2 and the loading cylinder 5 each have a diameter of 10mm.
In practical use, the distance between the two support columns 2 is 100mm, the distance between the support column 2 close to one side of the baffle 3 and the baffle 3 is 30mm, and the loading column 5 is positioned above the middle of the two support columns 2. By adopting the technical scheme, the mortar test piece 1 can be accurately placed at the position vertical to the axes of the supporting cylinder 2 and the loading cylinder 5, the center of the mortar test piece 1 is aligned to the loading cylinder 5, the loading force is conveniently applied, and the mortar test piece 1 is damaged from the middle. The test instrument for loading the prefabricated crack on the mortar test piece meets the requirements of the CB/T17671 fourth section on a cement mortar anti-fracture test instrument.
Example five:
referring to fig. 1 and 2, in a method for prefabricating a mortar test piece crack by using three-point bending loading, on the basis of the second embodiment, a baffle 3 for positioning the mortar test piece 1 is fixedly connected to one side of a hydraulic platform 4, and the baffle 3 is arranged in parallel with a support cylinder 2.
In actual use, when the mortar test piece 1 is placed, one side face of the mortar test piece 1 needs to be in contact with the baffle 3, so that the relative stability of the positions of the mortar test piece 1 and the supporting cylinder 2 is ensured, the middle part of the mortar test piece 1 is aligned to the axis position of the loading cylinder 5, and the damaged position of the mortar test piece 1 is ensured to be the middle part.
Example six:
referring to fig. 1 and 2, a method for prefabricating a mortar test piece crack by using three-point bending loading is shown, and on the basis of the first embodiment, a specific method for applying a preset load to the mortar test piece 1 in the second step is as follows: the loading rate of 30N/s-60N/s is adopted to evenly load the load on the mortar test piece 1.
In actual use, the load is uniformly loaded on the mortar test piece 1 by applying the load to the mortar test piece 1 by 30-60N per second. When the loading rate is less than 30N/s, the loading time of the cracks appearing on the mortar test piece 1 is too long, the working efficiency is not favorable, and the crack prefabricating effect is not more beneficial; when the loading rate is more than 60N/s, the crack of the mortar test piece 1 is developed too fast due to the overlarge loading rate, the prefabricated crack is more than 0.4mm, and even the mortar test piece is directly fractured, so that the mortar test piece 1 can uniformly generate the crack of 0.2mm to 0.4mm within a certain time by selecting the loading rate of 30N/s to 60N/s.
Example seven:
referring to fig. 1-3, in the method for loading cracks of a pre-manufactured mortar test piece by using three-point bending, on the basis of the first embodiment, the failure stage in the third step is divided into five stages, which are sequentially from front to back: a compaction stage I, a linear elasticity stage II, an initial crack stage III, a crack development stage IV and a destabilization damage stage V.
Furthermore, the compaction stage I is a period from the contact of the three-point bending test device with the mortar test piece to the beginning of the stress of the mortar test piece; the linear elasticity stage II is a period from the beginning of the stress of the mortar test piece to the time before the crack of the mortar test piece appears; the initial cracking stage III is a period from the occurrence of a crack on the surface of the mortar test piece to the slow propagation; the crack development stage IV is a period that cracks on the surface of the mortar test piece are stably expanded, the crack width is increased, and the load is slowly reduced along with the increase of the displacement; and the instability destruction stage V is a period of the crack instability propagation of the mortar test piece, and the load is suddenly reduced along with the displacement increase.
The five stages are divided according to the internal stress condition and the crack development condition of the test piece, and the mortar test piece in the compaction stage I is unevenly stressed and is in the initial stress stage; the stress of the mortar test piece 1 in the linear elastic stage II is in direct proportion to the deformation, and the loading stop test piece can be restored to the original shape at the moment, namely the inner part of the mortar test piece 1 is not damaged and no inner and surface cracks appear; a crack appears on the surface of the mortar test piece 1 in the initial cracking stage III and slowly expands, if the loading is stopped at the initial cracking stage, an irregular crack appears on the surface of the mortar test piece 1, and the crack width is related to the loading termination point; a stably-expanded crack appears in the middle of the mortar test piece 1 in the crack development stage IV, and the width is large, so that the self-healing process of concrete is not facilitated; and the sand sample 1 at the instability damage stage V can be broken and damaged. The crack development width can be controlled by performing stage division on the damage process of the mortar test piece 1 and analyzing the stress and the cracking condition of the mortar test piece 1 in each stage, so that the anti-fracture crack with a certain width can be prefabricated.
Example eight:
referring to fig. 1-3, in a method for prefabricating a mortar test piece crack by using three-point bending loading, on the basis of the first embodiment, the failure load determined in the fourth step is the failure load when an irregular crack with a width of 0.2 mm-0.4 mm is prefabricated; this load acts as an end point of loading.
Different loading end points are controlled by a microcomputer, the crack width of each group of test pieces is measured after loading is finished, the damage load when the crack width is 0.2-0.4 mm and an irregular crack is selected from the crack width, and the technical scheme can accurately determine the damage load when the mortar test piece 1 reaches the specified prefabricated crack width.
Example nine:
referring to fig. 1 and 2, a method for preparing cracks of a mortar test piece by using three-point bending loading is shown, and on the basis of the first embodiment, the size of the mortar test piece 1 in the first step is 40mm × 40mm × 160mm.
In a specific application, the mortar test piece 1 is prepared according to the relevant regulations in the test method for testing the strength of the cement mortar of GB 17671. Adopt the mortar test piece to adopt 140mm X40 mm X160 mm's unified specification, not only convenient prefabrication has laid good foundation for the uniformity of experimental result moreover.
Example ten:
the embodiment provides a method for loading a prefabricated mortar crack by three-point bending, which comprises the following steps:
s1, placing a flat surface of a mortar test piece 1 on two supporting cylinders 2, and enabling one side surface of the mortar test piece 1 to be in contact with a baffle 3;
s2, uniformly transmitting the load force to the mortar test piece 1 through the loading cylinder 5 at a rate of 40N/S, and obtaining a load-displacement curve on a computer;
s3, analyzing the damage form and the load-displacement curve characteristics of the mortar test piece 1, wherein the load in the compaction stage I is increased in a nonlinear manner along with the displacement; the load in the linear elastic stage II is in a linear increasing rule along with the change of displacement; in the initial cracking stage III, cracks begin to appear on the surface of the mortar test piece 1, the cracks slowly expand, the load reaches the peak value, and the cracks on the surface of the mortar test piece 1 are about 0.05 mm-0.7 mm; in the crack development stage IV, the surface cracks of the mortar test piece 1 are stably expanded, the crack width is increased, the surface cracks of the mortar test piece 1 are about 0.5-3 mm, and the load is slowly reduced along with the increase of the displacement; in the instability damage stage V, the crack is expanded in an instability manner, the load is suddenly reduced along with the increase of displacement, the loading is automatically stopped, and the mortar test piece 1 is broken and damaged;
and S4, performing a prefabricated crack test on the same group of test pieces by respectively adopting 90%, 85% and 80% of peak load for the breaking load, and measuring the width of the breaking crack of the test pieces, wherein the test results are shown in Table 1. It was thus determined that the breaking load employed when irregular cracks of 0.2mm to 0.4mm could be preformed was 90% of the peak load.
In actual use, 90% of peak load can be judged by a microcomputer and controlled automatically, and only the loading stop point can be controlled because the breaking load of each test piece is different.
The test results are shown in table 1.
TABLE 1
Example eleven:
the embodiment provides a method for loading a prefabricated mortar crack by three-point bending, which comprises the following steps:
s1, placing a smooth surface of a mortar test piece 1 on two supporting cylinders 2, and enabling the side surface of one side of the mortar test piece 1 to be in contact with a baffle 3;
s2, uniformly transmitting the loading force to the mortar test piece 1 through a loading cylinder 5 at a speed of 50N/S, and obtaining a load-displacement curve on a computer;
s3, analyzing the damage form and the load-displacement curve characteristics of the mortar test piece 1, wherein the load in the compaction stage I increases in a nonlinear manner along with the displacement; the load in the linear elastic stage II is in a linear increasing rule along with the change of displacement; in the initial cracking stage III, cracks begin to appear on the surface of the mortar test piece 1, the cracks slowly expand, the load reaches the peak value, and the cracks on the surface of the mortar test piece 1 are about 0.05 mm-0.7 mm; in the crack development stage IV, the surface cracks of the mortar test piece 1 are stably expanded, the crack width is increased, the surface cracks of the mortar test piece 1 are about 0.5-3 mm, and the load is slowly reduced along with the increase of the displacement; in the instability damage stage V, the crack is expanded in an instability manner, the load is suddenly reduced along with the increase of displacement, the loading is automatically stopped, and the mortar test piece 1 is broken and damaged;
and S4, performing a prefabricated crack test on the same group of test pieces by respectively adopting 90%, 85% and 80% of peak load for the damage load, and measuring the damage crack width of the mortar test piece 1, wherein the test results are shown in Table 2. It was thus determined that the breaking load employed when irregular cracks of 0.2mm to 0.4mm could be preformed was 90% of the peak load.
The test results are shown in Table 2.
TABLE 2
Example twelve:
the embodiment provides a method for prefabricating a mortar crack by utilizing three-point bending loading, which comprises the following steps of:
s1, placing a smooth surface of a mortar test piece 1 on two supporting cylinders 2, and enabling the side surface of one side of the mortar test piece 1 to be in contact with a baffle 3;
s2, uniformly transmitting the loading force to the mortar test piece 1 through the loading cylinder 5 at a rate of 60N/S, and obtaining a load-displacement curve on a computer;
s3, analyzing the damage form and the load-displacement curve characteristics of the mortar test piece 1, wherein the load in the compaction stage I is increased in a nonlinear manner along with the displacement; the load in the linear elastic stage II is in a linear increasing rule along with the change of displacement; in the initial cracking stage III, cracks begin to appear on the surface of the mortar test piece 1, the cracks slowly expand, the load reaches the peak value, and the cracks on the surface of the mortar test piece 1 are about 0.05 mm-0.7 mm; in the crack development stage IV, the surface cracks of the mortar test piece 1 are stably expanded, the crack width is increased, the surface cracks of the mortar test piece 1 are about 0.5-3 mm, and the load is slowly reduced along with the increase of the displacement; in the instability damage stage V, the crack is expanded in an instability manner, the load is suddenly reduced along with the increase of displacement, the loading is automatically stopped, and the mortar test piece 1 is broken and damaged;
and S4, performing a prefabricated crack test on the same group of test pieces by respectively adopting 90%, 85% and 80% of peak load for the damage load, and measuring the damage crack width of the mortar test piece 1, wherein the test results are shown in Table 3. It was thus determined that the breaking load employed when irregular cracks of 0.2mm to 0.4mm could be preformed was 90% of the peak load.
The test results are shown in Table 3
TABLE 3
The results of the experiments of the tenth to twelfth examples can be combined to obtain the following results:
different values of the breaking load have great influence on the width of the prefabricated crack, and when the value of the breaking load is 90% of the peak load, irregular cracks of 0.2 mm-0.4 mm can be prefabricated at the loading rate of 40N/s-60N/s.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
In the case of no conflict, a person skilled in the art may combine the related technical features in the above examples according to actual situations to achieve corresponding technical effects, and details of various combining situations are not described herein.
It should be noted that all directional indicators (such as up, down, left, right, front, back \8230;) in the embodiments of the present invention are only used to explain the relative positional relationship between the components, the motion situation, etc. in a specific posture (as shown in the attached drawings), and if the specific posture is changed, the directional indicator is changed accordingly.
The foregoing is illustrative of the preferred embodiments of the present invention, and the present invention is not to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. Any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention are within the scope of the technical solution of the present invention.
Claims (7)
1. A method for prefabricating a mortar test piece crack by utilizing three-point bending loading is characterized by comprising the following steps:
the method comprises the following steps: placing a mortar test piece on the three-point bending test device;
placing one of a plurality of prepared mortar test pieces on a three-point bending test device;
step two: applying a preset load to the mortar test piece through a three-point bending test device and obtaining a load-displacement curve;
step three: analyzing the damage form and the load-displacement curve characteristics of the prefabricated mortar test piece, and acquiring the crack widths of the surface of the mortar test piece in different damage stages;
step four: determining a damage load adopted when an irregular crack with a preset width can be prefabricated;
step five: carrying out the damage load determined in the fourth step on the other mortar test pieces to obtain mortar test pieces meeting the width of the prefabricated cracks;
the three-point bending test device adopted in the first step is a microcomputer-controlled compression-resistant and bending-resistant integrated machine, and the microcomputer-controlled compression-resistant and bending-resistant integrated machine at least comprises a loading cylinder, two supporting cylinders, a force loading part and a computer; the force loading part is used for applying a load force to the mortar test piece; the computer is in electrical signal connection with the force loading part; the two supporting cylinders are fixed on a hydraulic platform of the microcomputer-controlled compression-resistant and bending-resistant integrated machine; the upper part of the loading cylinder is fixedly connected to the force loading part and is positioned above the middle of the two supporting cylinders;
the specific method for applying the preset load to the mortar test piece in the step two is as follows: loading the load on the mortar test piece uniformly at a loading rate of 30-60N/s;
the breaking load determined in the fourth step is the breaking load when the irregular crack with the width of 0.2 mm-0.4 mm is prefabricated; this load acts as an end point of loading.
2. The method for loading the cracks of the prefabricated mortar test piece by using three-point bending as claimed in claim 1, wherein the method comprises the following steps: the two supporting cylinders are fixed on the hydraulic platform in parallel, the loading cylinder is parallel to the two supporting cylinders, and the axial directions of the supporting cylinders and the loading cylinder are perpendicular to the long axis direction of the mortar test piece.
3. The method for preparing the cracks of the mortar test piece by utilizing three-point bending loading according to claim 1, which is characterized in that: the distance between the axis centers of the supporting cylinders positioned at the two sides of the lower part of the mortar test piece to be tested is 100mm; the diameter of the supporting cylinder and the diameter of the loading cylinder are both 10mm.
4. The method for loading the cracks of the prefabricated mortar test piece by using three-point bending as claimed in claim 1, wherein the method comprises the following steps: one side of the hydraulic platform is fixedly connected with a baffle used for positioning the mortar test piece, and the baffle is arranged in parallel with the supporting cylinder.
5. The method for preparing the cracks of the mortar test piece by using the three-point bending loading as claimed in claim 1, wherein the failure stage in the third step comprises five stages which are sequentially from front to back: a compaction stage, a linear elasticity stage, an initial crack stage, a crack development stage and a destabilization damage stage.
6. The method for preparing the mortar test piece crack by utilizing three-point bending loading according to claim 5, wherein the compaction stage is a period from the time when the three-point bending test device contacts the mortar test piece to the time when the mortar test piece just begins to bear force; the linear elastic stage is the period from the moment the mortar test piece is stressed to the moment before cracks appear on the mortar test piece; the initial cracking stage is a period from the occurrence of a crack on the surface of the mortar test piece to the slow expansion; the crack development stage is a period that the cracks on the surface of the mortar test piece are stably expanded, the crack width is increased, and the load is slowly reduced along with the increase of the displacement; the instability damage stage is a period that the cracks of the mortar test piece are subjected to instability expansion, and the load is suddenly reduced along with the increase of displacement.
7. The method for loading the cracks of the prefabricated mortar test piece by using three-point bending as claimed in claim 1, wherein the method comprises the following steps: the size of the mortar test piece in the first step is 40mm multiplied by 160mm.
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