A method for evaluating the self-repairing properties of cement-based materials under load

Abstract

The present invention relates to a method for evaluating the self-repairing performance of cement-based materials under load, belonging to the field of building construction technology, and comprising the following steps: S1: sample preparation; S2: prefabricating cracks; S3: applying loads; S4: repair and curing; S5: three-point flexural test of notched specimens; S6: three-point flexural test of unnotched specimens; S7: calculating strength recovery rate. The present invention can effectively test the self-repairing performance of cement-based materials under sustained bending loads, overcoming the shortcomings of previous test methods that did not consider the self-repairing performance of cement-based materials under sustained three-point bending loads. The strength recovery rate test and characterization method provided by the present invention eliminates the influence of strength growth caused by the sustained hydration of cement-based materials. At the same time, the present invention can effectively test the self-repairing performance of cement-based materials under sustained bending loads, providing strong guarantee and support for better application of cement-based material self-repairing technology in engineering practice.

Description

Technical Field

[0001] The present invention relates to a method for evaluating the self-repairing performance of cement-based materials under load, and in particular to a method for evaluating the self-repairing performance of cement-based materials under continuous bending load, and belongs to the technical field of building construction. Background Art

[0002] As an innovative technology that can autonomously repair structural cracks, cement-based material self-healing technology has become a research hotspot in recent years due to its advantages such as timely repair and high degree of intelligence. How to effectively test and evaluate the self-healing performance of cement-based material cracks is a necessary link and important guarantee for better application of cement-based material self-healing technology in engineering practice.

[0003] Currently, most research on self-healing properties is conducted under no-load conditions. However, in actual engineering applications, most structures are subjected to continuous loads during their service life, which may lead to the inconsistency between existing research results on the self-healing properties of cement-based materials and engineering practice.

[0004] A Chinese invention patent with publication number CN109374870A discloses a method and device for evaluating the repair performance of cement-based self-healing materials, including the following steps: applying pressure to a sample of the cement-based self-healing material and simultaneously dynamically monitoring changes in crack width until the resulting crack reaches a set width, maintaining a constant loading pressure; then curing the test sample of the cement-based self-healing material and simultaneously dynamically monitoring changes in crack width until the self-repair healing of the crack reaches a stable state; and finally analyzing and evaluating the data obtained from the dynamic monitoring.

[0005] The above reference example is an evaluation of the self-healing performance of cement-based materials under continuous compressive loads, but lacks an evaluation of the self-healing performance of cement-based materials under continuous bending loads. In addition, there are problems such as complex operation and inaccurate evaluation indicators. Therefore, there is still a situation where the research results on the self-healing performance of cement-based materials are inconsistent with the actual engineering practice, and therefore improvement is urgently needed. Summary of the Invention

[0006] In order to overcome the existing shortcomings of the lack of evaluation of the self-healing performance of cement-based materials under continuous bending loads, the present invention designs a method for evaluating the self-healing performance of cement-based materials under load, which can effectively test the self-healing performance of cement-based materials under continuous bending loads, and provide strong guarantee and support for better application of cement-based material self-healing technology in engineering practice.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for evaluating the self-repairing performance of cement-based materials under load comprises the following steps:

[0009] S1: Sample preparation: Prepare and mix concrete according to the test raw materials and mix ratio, then form and cure the concrete in sequence to obtain several test pieces;

[0010] S2: Prefabricating cracks: Divide the specimens obtained in step S1 into two groups, one of which is an experimental group and the other is a control group. A notch is cut at the middle position of the lower end of some specimens in the experimental group and at the middle position of the lower end of some specimens in the control group, and the size and shape of each notch are the same;

[0011] S3: Load application: The specimens in the experimental group were mounted one by one on multiple bending load continuous application devices, while the specimens in the control group were not subjected to any treatment;

[0012] S4: Repair and curing: Place the test pieces of the experimental group and the control group in step S3 in a curing room for curing;

[0013] S5: Three-point flexural strength test of notched specimens: The specimens of the experimental group that have reached the repair and curing age and are provided with notches in step S4 are taken out from the bending load continuous application device, and then subjected to a three-point flexural strength test to obtain the average repair flexural strength P of each notched specimen. healed ;

[0014] At the same time, the three-point flexural strength test was carried out on each specimen with a notch in the control group, and the average repair bending strength P of each specimen with a notch in the control group was obtained. healed1 ;

[0015] S6: Three-point flexural strength test of unnotched specimens: The specimens of the experimental group that have reached the repair and curing age and are not notched in step S4 are taken out from the bending load continuous application device, and then subjected to a three-point flexural strength test to obtain the average initial flexural strength P of each unnotched specimen. ref Then, the three-point flexural strength test was immediately performed on each unnotched specimen to obtain the average residual flexural strength P of each unnotched specimen. unhealed ;

[0016] At the same time, the three-point flexural strength test was repeated for each specimen with a notch in the control group, and the average initial flexural strength P of each specimen without a notch in the control group was obtained. ref1 and the average residual bending strength P unhealed1 ;

[0017] S7: Calculate the strength recovery rate: Calculate the strength recovery rate according to the strength recovery rate formula. The strength recovery rate is shown in the following formula:

[0018]

[0019] Furthermore, step S1 also includes adding an appropriate amount of fiber during the mixing of the concrete.

[0020] Furthermore, a detection device for measuring the displacement of crack opening was installed at the bottom of each specimen in the experimental group.

[0021] Furthermore, the three-point flexural strength test in step S5 and step S6 specifically includes placing the specimen on a three-point flexural testing machine and pressing it to a limit load, and obtaining the bending strength after the three-point flexural testing machine is automatically unloaded.

[0022] Furthermore, the bending load continuous application device includes a base, a pair of bases are symmetrically arranged on the top of the base, the base is arranged in a rectangular frame structure, the specimen is clamped between the two bases, and pads fixed to the bases are provided at the bottom of both ends of the specimen. A top plate located at the upper end of the specimen is also connected between the two bases, and a loading assembly for pressing the specimen is fixed on the top plate.

[0023] Furthermore, the base includes a set of upper and lower parallel and spaced apart kits and a pair of sliding limit plates symmetrically slidably connected on both sides of the two kits. The kit located at the lower end is fixedly connected to the base, and the two ends of the sliding limit plate are respectively slidably connected to the ends of the upper and lower kits. The sliding limit plate is driven to move by the adjusting device and clamps the specimen.

[0024] Furthermore, the adjusting device includes a first bevel gear, a second bevel gear, an adjusting screw and a mounting seat, the inner ring of the first bevel gear is fixedly sleeved with an adjusting rod, the free end of the adjusting rod rotates through the base and then extends outward, the second bevel gears are symmetrically provided with two and are both meshed with the first bevel gear, the adjusting screws are provided with two and are respectively fixedly sleeved with the inner rings of the two second bevel gears, the mounting seat is provided with two and are respectively rotatably connected to the free ends of the two adjusting screws, the top ends of the two adjusting screws are provided with a sliding groove that penetrates the upper surface of the base and is parallel to the adjusting screw, and a sliding rod is slidably engaged in each sliding groove, and the top end of the sliding rod is fixedly connected to the sliding limit plate after extending out of the sliding groove, and the bottom end of the sliding rod is threadedly sleeved with the adjusting screw.

[0025] Furthermore, the loading assembly includes a screw assembly, a loading head and a force rod fixed at the bottom end of the loading head. The screw assembly includes a force screw, which is vertically arranged and has a bottom thread that passes through the top plate and is rotatably connected to the loading head. The loading head and the force rod are arranged in the same direction.

[0026] Furthermore, the screw assembly also includes at least two limiting screws, and the bottom ends of the limiting screws are threaded through the top plate and are rotatably connected to the loading head.

[0027] Furthermore, the top end of the limiting screw extends out of the top plate and is threadedly connected to a first nut, the rod of the limiting screw located at the bottom end of the top plate is threadedly connected to a second nut, and the second nut is arranged in contact with the bottom end of the top plate.

[0028] Compared with the prior art, the present invention has the following characteristics and beneficial effects:

[0029] 1. The present invention provides an intuitive and accurate result on the self-healing performance of cement-based materials under load by setting up steps such as prefabricating cracks, applying loads, repairing and curing, and three-point flexural strength. It accurately reflects the recovery of the self-healing performance of cement-based materials when subjected to loads in actual engineering applications, provides a precise theoretical basis for practical applications, and provides strong guarantees and support for better application of cement-based material self-healing technology in engineering practice. In addition, by setting up a control group, the specific comparison of the strength recovery rates of the experimental group and the control group can be intuitively seen, further improving the applicability of the present invention.

[0030] 2. The present invention effectively eliminates the influence of the specimen's own strength increase due to hydration reaction on the evaluation of self-repair performance by setting the strength test of the specimen after the specimen reaches the end of the repair and maintenance age, further improving the accuracy of subsequent results, while simplifying the testing steps, reducing operating costs, and avoiding the problem that when the strength test of the specimen is set before the specimen reaches the end of the repair and maintenance age, the strength recovery obtained cannot be determined whether the strength increase with age is due to the specimen itself due to hydration reaction or due to the self-repair effect.

[0031] 3. The present invention can continuously apply bending load to the specimen through the setting of the bending load continuous application device, ensure the smooth progress of subsequent steps, improve the overall method steps, play a supporting role through the base, ensure the balance of the specimen, the two bases are convenient for clamping the specimen, and ensure that the specimen 3 receives a good load. The contact area between the pad rod and the force rod and the specimen is small, which can effectively make the two ends of the specimen bear force, and cooperate with the tightening axial force of the force screw and the limit screw, so that the specimen can better bear the bending load, ensuring the accuracy of subsequent test results, and through the setting of the adjustment device, the base can be suitable for specimens of different sizes, thereby improving the applicability of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a flow chart of the method of the present invention;

[0033] Figure 2 This is a schematic structural diagram of the bending load continuous application device of the present invention.

[0034] Figure 3 is a side view of the bending load continuous application device of the present invention;

[0035] Figure 4 It is a schematic structural diagram of the regulating device of the present invention;

[0036] Figure 5 This is a comparison chart of the strength recovery rate of Example 1 of the present invention.

[0037] The figures are marked as follows: 1. base; 101. slide groove; 201. sliding limit plate; 2011. slide rod; 202. base; 2021. kit; 3. top plate; 4. screw assembly; 401. force screw; 402. limit screw; 403. loading head; 404. force rod; 5. test piece; 6. adjusting rod; 601. handle; 7. adjusting device; 701. first bevel gear; 702. second bevel gear; 703. adjusting screw; 704. mounting seat; 8. pad. DETAILED DESCRIPTION

[0038] The present invention will be described in more detail below with reference to the embodiments.

[0039] Example 1

[0040] A method for evaluating the self-repairing performance of cement-based materials under load comprises the following steps:

[0041] S1: Sample preparation: Prepare and mix the concrete according to the test raw materials and mix ratio, and then pass the sample through the size of 40×40×160mm 3 The concrete was molded into twelve specimens 5, and then each specimen 5 was demoulded after being cured for 24 hours. The demoulded specimens 5 were then placed in a standard curing room for curing. After curing for 28 days, the next step was performed.

[0042] The raw materials include: cement (PI 42.5 cement produced by China United Cement Co., Ltd., which complies with GB8076-2008); aggregate (medium sand with a fineness modulus of 2.75); a high-performance polycarboxylic acid water-reducing agent with a solids content of 33.1% and a water reduction rate of 32%; and a superabsorbent resin (sodium polyacrylate) with a water absorption rate (deionized water) of 450 g / g and a density of 0.7 g / ml.

[0043] S2: Prefabricated cracks: The specimens 5 obtained in step S1 were divided into two groups, an experimental group and a control group, each of which included six specimens 5. A notch of the same size and shape was cut in the middle of the lower end of three specimens 5 in the experimental group. At the same time, a notch of the same size and shape was cut in the middle of the lower end of three specimens 5 in the control group. The notch served as the cracking starting point of the three specimens 5 in the experimental group.

[0044] S3: Applying load: The test specimens 5 of the experimental group are mounted one by one on a plurality of bending load continuous application devices, while the test specimens 5 of the control group are not subjected to any treatment, and the control group serves only as a control;

[0045] S4: Repair and curing: Place the test pieces 5 of the experimental group and the control group in step S3 in a curing room for curing for a period of 28 days;

[0046] S5: Three-point flexural strength test of notched specimen 5: The three specimens 5 of the experimental group that have reached the repair and curing age and are provided with notches in step S4 are taken out from the bending load continuous application device, and then subjected to a three-point flexural strength test to obtain the average repair flexural strength P of each notched specimen 5. healed =3.1Mpa;

[0047] At the same time, the three specimens 5 with notches in the control group were subjected to a three-point flexural strength test to obtain the average repair bending strength P of the three specimens 5 with notches in the control group. healed1 =4.7Mpa, average repair bending strength P healed1 Serves as a control;

[0048] S6: Three-point flexural strength test of the unnotched specimens 5: The specimens 5 of the experimental group that have reached the repair and curing age and are not provided with notches in step S4 are taken out from the bending load continuous application device, and then subjected to a three-point flexural strength test to obtain the average initial flexural strength P of each unnotched specimen 5. ref =4.0Mpa, and then immediately perform three-point flexural strength test on each unnotched specimen 5 again to obtain the average residual flexural strength P of each unnotched specimen 5 unhealed =2.5Mpa;

[0049] At the same time, the specimens 5 of the control group that have reached the repair and maintenance age and have no notches are taken out from the bending load continuous application device, and then a three-point flexural strength test is performed to obtain the average initial flexural strength P of the three specimens 5 without notches in the control group. ref1 =5.0Mpa, and then immediately perform three-point flexural strength test on each unnotched specimen 5 again to obtain the average residual flexural strength P of each unnotched specimen 5 unhealed1 =3.5Mpa;

[0050] S7: Calculate the strength recovery rate: Calculate the strength recovery rate according to the strength recovery rate formula. The strength recovery rate is shown in the following formula:

[0051]

[0052] The strength recovery rate of the control group is:

[0053]

[0054] When the strength of the notched specimen 5 is fully restored, that is, P healed and P ref Completely equal, the strength recovery rate is 100%;

[0055] Finally, we get the comparison chart of strength recovery rate between the experimental group and the control group, as shown in the figure below: Figure 5 shown.

[0056] Depend on Figure 5 It can be seen that under the action of continuous bending load, the strength recovery rate of specimen 5 in the experimental group is 50% lower than that of specimen 5 in the control group which is not subjected to continuous load. This shows that continuous bending load has an adverse effect on the strength recovery of specimen 5.

[0057] From the above description, it can be seen that the beneficial effect of the present invention is that, by setting up the experimental group and the control group, and by setting up the steps of prefabricated cracks, load application, repair and curing, and three-point flexural strength, the accurate values ​​of the strength recovery rates of the experimental group and the control group can be obtained, thereby forming an accurate comparison, and having an intuitive and accurate result on the self-repairing performance of cement-based materials under load, accurately reflecting the recovery of the self-repairing performance of cement-based materials in actual engineering applications, providing a precise theoretical basis for practical applications, and providing strong guarantees and support for better application of cement-based material self-repairing technology in engineering practice; at the same time, by setting up a bending load continuous application device, a bending load can be continuously applied to the specimen 5, ensuring the smooth progress of subsequent steps and improving the overall method steps; at the same time, the present invention sets the strength test of specimen 5 after the specimen 5 reaches the end of the repair and curing age, eliminating the influence of the strength increase of the specimen 5 itself due to the hydration reaction on the evaluation of the self-repairing performance, further improving the accuracy of subsequent results, while simplifying the test steps and reducing operating costs.

[0058] Furthermore, step S1 also includes adding an appropriate amount of fiber during the mixing of the concrete.

[0059] From the above description, it can be seen that due to the brittleness of cement-based materials themselves, directly prefabricating cracks can easily lead to complete destruction of the specimen 5. Therefore, a certain amount of fiber is added during the mixing process to improve the toughness of the specimen, thereby achieving the purpose of controlling the crack width. In order to control the crack width of the mortar specimen 5, the fiber used in this embodiment is polypropylene fiber (PP), with a fiber length of 18 mm and a specific gravity of 0.91 g / cm 3 , elastic modulus is 8828MPa and tensile strength is 556MPa.

[0060] In this embodiment, the proportions of the raw materials are shown in Table 1 below:

[0061]

[0062] Table 1.

[0063] Furthermore, a detection device for measuring the displacement of crack opening was installed at the bottom of each test piece 5 in the experimental group.

[0064] From the above description, it can be seen that by setting up the detection device, the displacement of the crack opening can be better controlled to ensure that the crack sizes of each test piece 5 are the same, and the variables can be better controlled to ensure the reliability of the final experimental results.

[0065] Furthermore, the three-point flexural strength test in step S5 and step S6 specifically includes placing the specimen 5 on a three-point flexural testing machine and pressing it to the ultimate load. After the three-point flexural testing machine is automatically unloaded, various bending strengths, namely, the average repaired bending strength, the average initial bending strength and the average residual bending strength, are obtained.

[0066] It can be seen from the above description that the above steps can make the results more accurate.

[0067] Example 2

[0068] A method for evaluating the self-repairing performance of cement-based materials under load, based on the above-mentioned embodiment 1, further defines the mechanical structure of the bending load continuous application device as follows:

[0069] like Figures 2 to 4 As shown, the device for continuously applying bending load includes a base 1, a pair of bases 202 are symmetrically arranged on the top of the base 1, the base 202 is arranged in a rectangular frame structure, the specimen 5 is clamped between the two bases 202, and pads 8 fixed to the base 202 are arranged at the bottom of both ends of the specimen 5. A top plate 3 located at the upper end of the specimen 5 is also connected between the two bases 202, and a loading component for pressing the specimen 5 is fixed on the top plate 3.

[0070] From the above description, it can be seen that the base 1 plays a supporting role to ensure the balance of the specimen 5. The two bases 202 are used to clamp the specimen 5. The contact area between the pad 8 and the specimen 5 is small, which can effectively make the two ends of the specimen 5 bear force. The pad 8 cooperates with the loading assembly, so that the specimen 5 can better withstand the bending load, thereby ensuring the accuracy of subsequent test results.

[0071] Furthermore, the base 202 includes a set 2021 that is arranged in parallel and spaced apart above and below, and a pair of sliding limit plates 201 that are symmetrically slidably connected on both sides of the two sets 2021. The set 2021 at the lower end is fixedly connected to the base 1, and the two ends of the sliding limit plate 201 are respectively slidably connected to the ends of the upper and lower sets 2021. The sliding limit plate 201 is driven to move by the adjustment device 7 and clamps the specimen 5.

[0072] As can be seen from the above description, by sliding the sliding limit plate 201 and the setting of the adjustment device 7, the size of the rectangular frame of the base 202 can be adjusted to adapt to test pieces 5 of different sizes, thereby improving the applicability of the device.

[0073] The first gear 701 is fixed with the second gear 702, and the second gear 703 is fixed with the first gear 702. The second gear 703 is fixed with the second gear 703 and the second gear 703 is fixed with the first gear 702.

[0074] As can be seen from the above description, during adjustment, by rotating the adjusting rod 6, the adjusting rod 6 drives the first bevel gear 701 to rotate, and then drives the second bevel gear 702 to rotate through the first bevel gear 701. The rotation of the second bevel gear 702 can drive the adjusting screw rod 703 to rotate. Under the rotation action of the adjusting screw rod 703, the sliding rod 2011 can move along the sliding groove 101, and then drive the sliding limit plate 201 to move and adjust the size of the rectangular frame. The size of the rectangular frame can be adjusted by rotating the adjusting rod 6. The transmission is reliable, the adjustment is convenient, the applicability is strong, and it can effectively clamp the specimen 5 to ensure that the specimen 5 is subjected to force.

[0075] Furthermore, the loading assembly includes a screw assembly 4, a loading head 403 and a force rod 404 fixed at the bottom end of the loading head 403. The screw assembly 4 includes a force screw 401. The force screw 401 is vertically arranged and the bottom end thread passes through the top plate 3 and is rotatably connected to the loading head 403. The loading head 403 and the force rod 404 are arranged in the same direction.

[0076] From the above description, it can be seen that the contact area between the force rod 404 and the specimen 5 is small, which can better transmit pressure, and then cooperate with the pad rod 8 to enable the specimen 5 to better receive the bending load. The setting of the force screw 401 makes it convenient to apply force to the loading head 403, and the force screw 401 is convenient to connect with the torque wrench, which makes it easy to control the axial force of the force screw 401 on the loading head 403, thereby improving the convenience of operation and ensuring the accuracy of the results.

[0077] Furthermore, the screw assembly 4 also includes two limiting screws 402 , which are symmetrically arranged on both sides of the force-applying screw 401 . The bottom ends of the limiting screws 402 are threadedly passed through the top plate 3 and are rotatably connected to the loading head 403 .

[0078] From the above description, it can be seen that through the setting of the limiting screw 402, in cooperation with the force screw 401, the loading head 403 is limited to prevent the loading head 403 from deviating. At the same time, by rotating the force screw 401, the loading head 403 can also be evenly stressed, thereby better applying axial force to the specimen 5.

[0079] Furthermore, the top end of the limiting screw 402 extends out of the top plate 3 and is threadedly connected to a first nut, and the rod of the limiting screw 402 located at the bottom end of the top plate 3 is threadedly connected to a second nut, and the second nut is arranged in contact with the bottom end of the top plate 3.

[0080] It can be seen from the above description that, by setting the first nut and the second nut, it is ensured that the limiting screw 402 can be fixed to the top plate 3 to prevent the limiting screw 402 from moving.

[0081] The working principle of this embodiment is as follows: the specimen 5 is placed between the two bases 202, and the force rod 404 is ensured to be located in the middle of the top of the specimen 5, and the force rod 404 is arranged along the width direction of the specimen 5, and then the adjusting rod 6 is rotated so that the sliding limit plate 201 clamps the specimen 3, thereby fixing the specimen 3, and then a torque is applied to the force screw 401 and the limit screw 402 through a torque wrench, so that the tightening torque of the force screw 401 and the limit screw 402 is converted into axial pressure and this pressure is maintained, thereby achieving the application of a continuous three-point bending load to the specimen 5.

[0082] The present invention can effectively test the self-repairing properties of cement-based materials under continuous bending loads. The experiment selected super absorbent resin as a self-repairing agent, and studied the self-repairing properties of mortar specimens under continuous bending loads by testing strength changes. At the same time, a control group (without continuous load) was set up for comparison. In the description of the present invention, it should be noted that the orientation or position relationship indicated by the terms "inside", "outside", "upper", etc. is based on the orientation or position relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention.

[0083] In the description of the present invention, it should be noted that, unless otherwise specified or limited, the term "connection" should be understood in a broad sense. For example, it can mean a fixed connection, a detachable connection, or an integral connection; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0084] Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

Claims

1. A method for evaluating the self-repairing performance of cement-based materials under load, characterized by: The steps include: S1: Sample preparation: Prepare and mix concrete according to the test raw materials and mix ratio, then form and cure the concrete in sequence to obtain several test pieces (5); S2: Prefabricated cracks: the test pieces (5) obtained in step S1 are divided into two groups, one of which is an experimental group and the other is a control group. A notch is cut at the middle position of the lower end of some test pieces (5) in the experimental group and at the middle position of the lower end of some test pieces (5) in the control group, and the size and shape of each notch are the same; S3: Applying load: The test specimens (5) of the experimental group are mounted one by one on a plurality of bending load continuous application devices, and the test specimens (5) of the control group are not subjected to any treatment; S4: Repair and curing: Place the test pieces (5) of the experimental group and the control group in step S3 in a curing room for curing; S5: Three-point flexural strength test of notched specimens (5): The specimens (5) of the experimental group that have reached the repair and curing age and are provided with notches in step S4 are taken out from the bending load continuous application device, and then subjected to a three-point flexural strength test to obtain the average repair flexural strength P of each notched specimen (5). healed ; At the same time, the three-point flexural strength test was performed on each specimen (5) with a notch in the control group, and the average repair bending strength P of each specimen (5) with a notch in the control group was obtained. healed1 ; S6: Three-point flexural strength test of the specimens without notches (5): The specimens (5) of the experimental group that have reached the repair and curing age and have no notches in step S4 are taken out from the bending load continuous application device, and then subjected to a three-point flexural strength test to obtain the average initial flexural strength P of each specimen without notches (5). ref , and then immediately conduct three-point flexural strength test again on each unnotched specimen (5), and obtain the average residual flexural strength P of each unnotched specimen (5) unhealed ; At the same time, the three-point flexural strength test was repeated for each specimen (5) without a notch in the control group, and the average initial flexural strength P of each specimen (5) without a notch in the control group was obtained. ref1 and the average residual bending strength P unhealed1 ; S7: Calculate the strength recovery rate: Calculate the strength recovery rate according to the strength recovery rate formula. The strength recovery rate is shown in the following formula: or p = *100%; The bending load continuous application device comprises a base (1), a pair of bases (202) are symmetrically arranged at the top of the base (1), the bases (202) are arranged in a rectangular frame structure, the test piece (5) is clamped between the two bases (202), and pads (8) fixed to the bases (202) are arranged at the bottoms of both ends of the test piece (5), and a top plate (3) located at the upper end of the test piece (5) is also connected between the two bases (202), and a loading component for pressing the test piece (5) is fixed on the top plate (3); The base (202) includes upper and lower parallel sets (2021) and a pair of sliding limit plates (201) symmetrically slidably connected on both sides of the two sets (221), the set (2021) at the lower end is fixedly connected to the base (1), and the two ends of the sliding limit plate (201) are respectively slidably connected to the ends of the upper and lower sets (221), and the sliding limit plate (201) is driven to move by the adjustment device (7) and clamps the specimen (5).

2. The method for evaluating the self-repairing performance of cement-based materials under load according to claim 1, characterized in that: Step S1 also includes adding an appropriate amount of fiber during the mixing of the concrete.

3. The method for evaluating the self-repairing performance of cement-based materials under load according to claim 1, characterized in that: The bottom of each specimen (5) in the experimental group is equipped with a detection device for measuring the displacement of crack opening.

4. The method for evaluating the self-repairing performance of cement-based materials under load according to claim 1, characterized in that: The three-point flexural strength test in step S5 and step S6 specifically includes placing the test piece (5) on a three-point flexural testing machine and pressing it to the ultimate load, and obtaining the flexural strength after the three-point flexural testing machine is automatically unloaded.

5. The method for evaluating the self-repairing performance of cement-based materials under load according to claim 1, characterized in that: The adjusting device (7) comprises a first bevel gear (701), a second bevel gear (702), an adjusting screw (703) and a mounting seat (704); the inner ring of the first bevel gear (701) is fixedly sleeved with an adjusting rod (6); the free end of the adjusting rod (6) rotates through the base (1) and then extends outward; two second bevel gears (702) are symmetrically provided and both mesh with the first bevel gear (701); the adjusting screw (703) is provided with two fixing sleeves respectively with the inner rings of the two second bevel gears (702); The mounting base (704) is provided with two and is rotatably connected to the free ends of the two adjusting screw rods (703) respectively. The top ends of the two adjusting screw rods (703) are provided with a slide groove (101) that passes through the upper surface of the base (1) and is parallel to the adjusting screw rod (703). A slide rod (2011) is slidably engaged in each slide groove (101). The top end of the slide rod (2011) extends out of the slide groove (101) and is fixedly connected to the sliding limit plate (201). The bottom end of the slide rod (2011) is threadedly sleeved with the adjusting screw rod (703).

6. The method for evaluating the self-repairing performance of cement-based materials under load according to claim 1, characterized in that: The loading assembly comprises a screw assembly (4), a loading head (403) and a force rod (404) fixed at the bottom end of the loading head (403). The screw assembly (4) comprises a force screw (401). The force screw (401) is vertically arranged and has a bottom thread passing through the top plate (3) and is rotatably connected to the loading head (403). The loading head (403) and the force rod (404) are arranged in the same direction.

7. The method for evaluating the self-repairing performance of cement-based materials under load according to claim 6, characterized in that: The screw assembly (4) further comprises at least two limiting screws (402), wherein the bottom ends of the limiting screws (402) are threadedly passed through the top plate (3) and are rotatably connected to the loading head (403).

8. The method for evaluating the self-repairing performance of cement-based materials under load according to claim 7, characterized in that: The top end of the limiting screw (402) extends out of the top plate (3) and is threadedly connected to a first nut. The rod of the limiting screw (402) located at the bottom end of the top plate (3) is threadedly connected to a second nut, and the second nut is arranged in contact with the bottom end of the top plate (3).

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