Concrete crack repairing method without influencing observation of active crack of concrete structure

Abstract

The invention belongs to the technical field of concrete repairing, and discloses a concrete crack repairing method which does not affect observation of active cracks of a concrete structure. According to the repairing method provided by the invention, a double-layer structure of the bottom functional layer and the surface functional layer is designed, the influence on crack identification and observation is small, the influence on regular maintenance and detection work of a bridge is small, a larger crack width change range can be met, the adverse influence of the breath effect of the crack on a direct coating can be reduced, and the repairing efficiency is improved. And a more excellent durable protection effect and a more long-acting repair effect are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of concrete repair, and in particular to a concrete crack repair method which does not affect the observation of active cracks in a concrete structure. Background Art

[0002] There are a large number of concrete bridges in China. By the end of 2022, the number of domestic highway bridges will reach 1.033 million. Among them, concrete bridges account for about 85%. As China gradually enters the "post-construction market", the proportion of critically ill and old concrete bridges is relatively high. Even some bridges are about to reach the end of their service life, and concrete structural damage and durability diseases are obvious. Among them, concrete cracks are one of the main forms of bridge damage.

[0003] According to whether the crack width changes during the operation of the bridge, concrete cracks can be divided into static cracks and active cracks. Active cracks are common in bridge components, showing the characteristics of opening and closing from time to time. The factors affecting crack activity mainly include seasonal temperature difference and load effect. (1) Seasonal temperature difference. The temperature difference caused by environmental changes often cycles from year to year with seasonal changes, and shows obvious periodicity. The width of the temperature cracks caused by this changes with the seasons, mainly showing that the crack width is larger in winter and the crack width is smaller or even closed in summer. Even in some areas with large temperature differences between day and night, this temperature difference between day and night can cause large changes in concrete cracks within 24 hours. (2) Vehicle and other load effects. Vehicle load is the main factor causing cracks in highway concrete bridges. As vehicles frequently pass through the cross-section where the cracks are located, the cracks show a periodic change pattern of "load increase-crack expansion-load reduction-crack contraction or closure".

[0004] From this, we can summarize several main characteristics of active cracks: (1) The width of active cracks cannot remain stable; (2) The width of active cracks is affected by temperature difference and load, and the frequency of change is not fixed; (3) The rate of change of the width of active cracks is not fixed, and the range of change is large.

[0005] According to the current and revised traffic industry specifications, bridge concrete crack repairs use adhesives, mainly including sealants, potting adhesives and caulking adhesives. Among them, sealants are mainly used to seal and fill static cracks; potting adhesives are used to restore the integrity and partial strength of components; caulking adhesives are used to fill active cracks. However, since grooving is required at the concrete cracks during caulking adhesive repair construction, it will potentially reduce the bearing capacity of the repaired bridge and increase the risk of further damage, which is unacceptable for old bridges that may have insufficient bearing capacity.

[0006] The Chinese invention patent "Solvent-free high-elastic epoxy infusion adhesive and preparation method for repairing movable cracks in concrete" with application number 202210147501.7 provides a repair method, that is, modifying the adhesive injected into the crack into a material with a certain flexibility to adapt to the change in crack width. However, it should be noted that for bridge concrete structures, the cracks have the characteristics of narrow width and large variation. In addition, the stiffness of the adhesive bonding object-concrete is much greater than that of the adhesive, which will cause the flexible adhesive to be significantly laterally constrained by the rigid concrete during deformation. Depending on the performance design of the flexible adhesive, the result may be one or a combination of concrete cohesive failure, adhesive bonding failure, or adhesive cohesive failure, and the variation in crack width adapted will not be very large. According to the report of the American Concrete Institute (ACI224.1R-07), the repair effect of using flexible epoxy adhesive is close to that of rigid epoxy adhesive, that is, it is difficult to fully adapt to the change in crack width. Further laboratory evaluations showed that, with increasing flexibility, the flexible adhesive was only applicable to crack widths up to a maximum of about 60% change, which is clearly not enough to meet the wider range of crack width changes in bridge concrete structures.

[0007] The use of polymer materials, especially flexible polymer materials, to form a continuous film layer on the surface of concrete structures has been proven to be a relatively effective repair method. Compared with the adhesive layer formed in the crack perpendicular to the force direction, when the width of the concrete crack changes, the coating is consistent with the force direction, the force mode changes from surface force to line force, and the lateral constraint from rigid concrete is transformed from two-dimensional to one-dimensional, which greatly increases the deformation space of the polymer film layer.

[0008] However, there are also some problems with the repair of flexible polymer coatings. Most flexible polymer coatings have hiding power, which will make it impossible to implement key tasks such as daily bridge maintenance, identification during monitoring, and observation of structural cracks. Although it is possible to remove the color fillers in the flexible polymer coating material and make the coating transparent to facilitate observation of structural changes, engineering applications have shown that this construction method will cause the concrete surface to darken, that is, the concrete changes from the original grayish white to a darker dark gray, which is often difficult to accept in bridge maintenance work, and will also cover cracks and even make cracks difficult to observe.

[0009] In summary, the problem of repairing active cracks in bridge concrete structures has not yet been fully solved, and it mainly includes the following key points: (1) providing protection capabilities; (2) meeting the needs of crack activity; and (3) minimizing the impact on regular bridge maintenance and inspection work to meet operation and maintenance needs. Summary of the invention

[0010] In view of this, the present invention provides a concrete crack repair method which does not affect the observation of active cracks in the concrete structure, so as to solve the problems that the protective ability of concrete repaired by the existing repair method is poor, and the repair materials used for repair cannot meet the crack activity requirements and operation and maintenance requirements.

[0011] In order to achieve the above object, the present invention adopts the following technical solution:

[0012] The present invention provides a concrete crack repair method which does not affect the observation of active cracks in the concrete structure, comprising the following steps:

[0013] S1. Clean the crack surface of the concrete to be repaired;

[0014] S2, bury the grouting nozzle;

[0015] S3, crack closure;

[0016] S4. Sealing inspection;

[0017] S5. Preparation of injection materials;

[0018] S6, injection construction and maintenance;

[0019] S7, surface treatment;

[0020] S8, preparation of bottom functional layer materials;

[0021] S9, construction and maintenance of bottom functional layer;

[0022] S10, preparation of surface functional layer materials;

[0023] S11: Construction and maintenance of surface functional layer.

[0024] Preferably, the crack sealing adhesive is an epoxy resin adhesive.

[0025] Preferably, the injection material includes one or more of epoxy resin, polyurethane resin, acrylate, fluorocarbon resin, epoxy-modified silicone resin, and cement-based grouting material.

[0026] Preferably, the bottom functional layer material includes one or more of epoxy resin coating, cement-based waterproof coating, fluorocarbon resin coating, and inorganic coating.

[0027] Preferably, the bottom functional layer material is a brittle material, the elongation at break of the bottom functional layer material is ≤5%, the bonding strength of the bottom functional layer material to C40 concrete is ≥1.5MPa, and the failure form of the bottom functional layer material is concrete cohesive failure.

[0028] Preferably, the color difference between the bottom functional layer material and the concrete surface to be repaired is ≤20.

[0029] Preferably, the surface functional layer material includes one or more of epoxy resin coating, polyurethane coating, acrylate coating, fluorocarbon resin coating, epoxy-modified silicone resin coating, and polyurea coating.

[0030] Preferably, the elongation at break of the surface functional layer material is ≥200%, the tensile strength of the surface functional layer material is ≥1.5 MPa, and the 100% elongation at break of the surface functional layer material is ≤1.0 MPa; the bonding strength of the surface functional layer material to C40 concrete after composite construction with the bottom functional layer is ≥1.5 MPa, and the form of failure after composite construction with the bottom functional layer material is concrete cohesive failure.

[0031] Preferably, the coverage rate of the surface functional layer material is ≤15%.

[0032] It can be seen from the above technical solution that compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The repair method provided by the present invention has little impact on the identification and observation of cracks, and has little impact on the regular maintenance and inspection of bridges. In concrete structures, the appearance and development of cracks have important indicative significance for the performance and durability of concrete structures. Therefore, crack detection is one of the important contents in the current highway bridge maintenance and inspection standards. In the current standards, visual observation and measurement are still irreplaceable methods for detecting cracks such as direction, location, length, width and other indicators. It is difficult to achieve this goal with the design of traditional paint protective coating systems.

[0034] (2) The repair material provided by the present invention is designed with a double-layer structure of a bottom functional layer and a surface functional layer. The bottom functional layer mainly plays the role of accompanying cracking, indicating cracks and beautifying the surface of concrete. The present invention endows the bottom functional layer with high adhesion and low deformation capacity through the design of mechanical properties of the bottom functional layer, so that when the concrete cracks, the bottom functional layer will crack accordingly, and the timing and position of the cracking are close to those of the concrete cracking. In addition, the color difference index design of the bottom functional layer ensures that the appearance of the repaired concrete structure is closer to the original concrete. And the cracks can be clearly distinguished visually, which is convenient for detection;

[0035] The surface functional layer mainly plays the role of aesthetics, protection and reducing the impact on visual detection. The present invention ensures that the surface functional layer can withstand large changes in crack width and will not fail to bond through the design of the mechanical properties of the surface functional layer, and has high protection performance and long life. At the same time, the coverage design of the surface functional layer can avoid the coating of the surface functional layer from having an adverse effect on the appearance of the bottom functional layer, such as darkening; at the same time, it reduces the absorption of light by the surface functional layer, creating better conditions for visual detection of cracks.

[0036] (2) The repair method provided by the present invention can meet a wider range of crack width variations. The surface functional layer of the present invention is designed to use a highly deformable material. After the repair is completed, it will overcome the unfavorable factors recommended in the current standards when the crack is repaired by glue injection during service, and convert the lateral constraints from the rigid concrete from two dimensions to one dimension, greatly improving the deformation capacity before failure. It can ensure that the surface functional layer has a higher deformation capacity and adapts to a larger crack width change.

[0037] (3) The repair method provided by the present invention has a more excellent durability protection effect. Studies have shown that the diffusion ability of external corrosive substances into concrete is greatly affected by the width of the crack. On the basis of surface protection of concrete cracks, the present invention adds a crack gap filling process, which can reduce the actual size of the passage for external corrosive substances to enter the concrete to nearly 0. Under the repair method provided by the present invention, after coating protection, external corrosive substances will be greatly reduced; at the same time, with the filling of the gaps, the ability of external corrosive substances to erode the interior of the concrete will be further reduced.

[0038] (4) The repair method provided by the present invention has a longer-lasting repair effect. In the current standards, crack repair mainly adopts the glue injection repair process. Due to the limitations of the process and crack size, only a small number of materials can be injected, including epoxy resin, methacrylate resin, cement-based crack grouting materials, etc. Most of these materials are very rigid and cannot be used for the effective repair of active cracks. The flexible injection material is basically a non-elastic material. When subjected to reciprocating force, there is energy accumulation, which will cause the repair to fail prematurely and the repair life is short. The repair method adopted by the present invention changes the traditional crack glue injection repair process into a crack filling + surface protection repair process. The repair and protection of the crack site are mainly provided by the surface functional layer, which has more selectivity. The surface functional layer has the performance of low energy accumulation under fatigue, so it has stronger dynamic load performance and has a significantly longer protection effect.

[0039] (5) The repair method provided by the present invention can reduce the adverse effects of the "breathing" effect of cracks on directly applied coatings. The direct manifestation of active cracks in bridge concrete structures is the opening and closing of concrete cracks, which is similar to the "breathing" effect. The process is accompanied by changes in air pressure in the gaps inside the cracks. This change will cause the directly applied coating to bulge. As time passes after the repair, the bulging bubbles will gradually expand from the cracks, causing repair failure or appearance problems. The repair method provided by the present invention fills the gaps between cracks, greatly reducing the change in air volume when the crack width changes, and can reduce the adverse effects of the "breathing" effect of cracks on the coating.

[0040] In summary, the repair of active cracks in bridge concrete structures is a complex issue, which requires not only a long-term repair method, but also the return of the repaired concrete structure to the existing inspection and evaluation standard system, so that the concrete structure can continue to serve under effective monitoring. The repair method provided by the present invention does not affect the observation of active cracks in concrete structures, and is designed from aspects such as construction technology, functional layer setting, material type, mechanical properties, and appearance, to achieve long-term and effective repair of active cracks in bridge concrete structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0042] Figure 1 The diagrams are of the C40 concrete beams to be repaired in Example 1 and Comparative Examples 1 to 5, wherein the left diagram is a front view and the right diagram is a left view;

[0043] Figure 2 The crack design diagram of the C40 concrete beam to be repaired in Example 1 and Comparative Examples 1 to 5;

[0044] Figure 3 This is a diagram of the buried positions of the grouting nozzles and exhaust ports described in Example 1 and Comparative Examples 1 to 5. DETAILED DESCRIPTION

[0045] The present invention provides a concrete crack repair method which does not affect the observation of active cracks in the concrete structure, comprising the following steps:

[0046] S1. Clean the crack surface of the concrete to be repaired;

[0047] S2, bury the grouting nozzle;

[0048] S3, crack closure;

[0049] S4. Sealing inspection;

[0050] S5. Preparation of injection materials;

[0051] S6, injection construction and maintenance;

[0052] S7, surface treatment;

[0053] S8, preparation of bottom functional layer materials;

[0054] S9, construction and maintenance of bottom functional layer;

[0055] S10, preparation of surface functional layer materials;

[0056] S11: Construction and maintenance of surface functional layer.

[0057] In the present invention, the crack sealing glue is a paste-like epoxy resin adhesive, which has the ability to be constructed on the facade and top surface, can form a continuous film layer on the surface of the concrete to be repaired, and adhere to the concrete to be repaired, meeting the sealing requirements of pressure grouting construction.

[0058] In the present invention, the injection material includes one or more of epoxy resin, polyurethane resin, acrylate, fluorocarbon resin, epoxy-modified silicone resin, and cement-based grouting material.

[0059] In the present invention, the bottom functional layer material includes one or more of epoxy resin coating, cement-based waterproof coating, fluorocarbon resin coating, and inorganic coating.

[0060] In the present invention, the bottom functional layer material is a brittle material; the elongation at break of the bottom functional layer material is preferably ≤5%, further preferably ≤4%, and more preferably ≤3%; the bonding strength of the bottom functional layer material to C40 concrete is preferably ≥1.5MPa, further preferably ≥1.8MPa, and more preferably ≥1.9MPa; the failure form of the bottom functional layer material is concrete cohesive failure.

[0061] In the present invention, the color difference between the bottom functional layer material and the concrete surface to be repaired is preferably ≤20, more preferably ≤19, and even more preferably ≤18.

[0062] In the present invention, the surface functional layer material includes one or more of epoxy resin coating, polyurethane coating, acrylate coating, fluorocarbon resin coating, epoxy-modified silicone resin coating, and polyurea coating.

[0063] In the present invention, the elongation at break of the surface functional layer material is preferably ≥200%, further preferably ≥210%, and more preferably ≥220%; the tensile strength of the surface functional layer material is preferably ≥1.5MPa, further preferably ≥1.6MPa, and more preferably ≥1.7MPa; the 100% elongation at break of the surface functional layer material is preferably ≤1.0MPa, further preferably ≤0.9MPa, and more preferably ≤0.8MPa; the bonding strength of the surface functional layer material to C40 concrete after composite construction with the bottom functional layer is preferably ≥1.5MPa, further preferably ≥1.6MPa, and more preferably ≥1.7MPa; the form of failure after composite construction of the surface functional layer material and the bottom functional layer is concrete cohesive failure.

[0064] In the present invention, the coverage rate of the surface functional layer material is preferably ≤15%, more preferably ≤14%, and even more preferably ≤13%.

[0065] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0066] The concrete to be repaired in the following examples and comparative examples is a prefabricated C40 concrete beam with a crack width of 0.2 mm and a depth of 80 mm (such as Figure 1 shown).

[0067] Example 1

[0068] The repair method described in this embodiment includes the following steps:

[0069] S1. Clean the crack surface: clean the cracks and surface positions of the concrete to be repaired;

[0070] S2. Bury the grouting nozzle: press Figure 3 The grouting nozzle and exhaust port are buried as shown;

[0071] S3, crack sealing: Use paste epoxy resin adhesive to seal the cracks;

[0072] S4. Sealing inspection: After closing the exhaust port, pressurize and inflate to check the sealing and observe whether there is any leakage;

[0073] S5. Preparation of injection materials: prepare epoxy resin;

[0074] S6, pressure injection construction and curing: inject epoxy resin into the vent under pressure until the glue flows out stably and becomes transparent; seal the vent and grouting nozzle; maintain the normal temperature environment and start curing;

[0075] S7. Surface treatment: Grind to remove crack sealant, and use epoxy putty to seal large and small holes on the concrete surface to be repaired;

[0076] S8. Preparation of bottom functional layer materials: preparation of inorganic coating;

[0077] S9. Construction and maintenance of bottom functional layer: Apply the mixed inorganic coating evenly on the concrete surface to be repaired, and control the dry film thickness of the coating to be 0.2mm.

[0078] S10, surface functional layer material preparation: prepare polyurethane coating component A and component B;

[0079] S11: Construction and maintenance of surface functional layer: Component A and component B of the polyurethane coating are accurately weighed and mixed evenly according to the ratio information provided by the manufacturer (the mass ratio of component A to component B is 1:3.5); the mixed polyurethane coating is evenly applied in 2 layers on the surface of the concrete to be repaired, and the total thickness of the coating dry film is controlled to be 0.3mm;

[0080] The above inorganic coating is a brittle material; the elongation at break is ≤0.1%; the bonding strength to C40 concrete is 2.7MPa, and the failure form is concrete cohesive failure; the color difference value with the concrete surface to be repaired is 5;

[0081] The elongation at break of the polyurethane coating is 400%, the tensile strength is 2.5 MPa, and the 100% elongation strength is 0.8 MPa. After composite construction with the inorganic coating, the bonding strength to the C40 concrete to be repaired is 2.3 MPa, and the failure form is concrete cohesive failure; the coverage rate is 12%.

[0082] Comparative Example 1

[0083] The repair method described in this comparative example comprises the following steps:

[0084] S1. Clean the crack surface: clean the cracks and surface positions of the concrete to be repaired;

[0085] S2. Bury the grouting nozzle: press Figure 3 The grouting nozzle and exhaust port are buried as shown;

[0086] S3, crack sealing: Use paste epoxy resin adhesive to seal the cracks;

[0087] S4. Sealing inspection: After closing the exhaust port, pressurize and inflate to check the sealing and observe whether there is any leakage;

[0088] S5. Preparation of injection materials: prepare flexible epoxy resin adhesive;

[0089] S6, pressure injection construction and curing: pressure-inject the flexible epoxy resin adhesive until the adhesive flows out of the exhaust port stably and becomes transparent; seal the exhaust port and the grouting nozzle; maintain the normal temperature environment and start curing;

[0090] The above-mentioned flexible epoxy resin adhesive has a tensile strength of 2.4 MPa and an elongation at break of 120%. The bonding strength to C40 concrete is 2.4 MPa, and the failure mode is concrete cohesive failure.

[0091] Comparative Example 2

[0092] The difference from Example 1 is that the "inorganic coating" is replaced by "fluorocarbon resin coating"; the fluorocarbon resin coating is a flexible material; the elongation at break is 30%; the bonding strength to C40 concrete is 2.1 MPa, and the failure form is concrete cohesive failure; the color difference value with the concrete surface to be repaired is 8. Others are the same as Example 1.

[0093] Comparative Example 3

[0094] The difference from Example 1 is that the color difference between the inorganic coating and the C40 concrete surface to be repaired is 30. Other aspects are the same as Example 1.

[0095] Comparative Example 4

[0096] The difference from Example 1 is that the "polyurethane coating" is replaced by "epoxy modified silicone resin coating"; the elongation at break of the epoxy modified silicone resin coating is 35%; the tensile strength is 10 MPa; the bonding strength to C40 concrete after composite construction with the inorganic coating is 2.6 MPa, and the failure form is concrete cohesive failure; the covering rate is 10%. Others are the same as Example 1.

[0097] Comparative Example 5

[0098] The difference from Example 1 is that the covering rate of the polyurethane coating is 20%. The other aspects are the same as Example 1.

[0099] Static load and dynamic load tests (crack width change rate is 100%) were used to evaluate the repair effects of the repair methods described in Example 1 and Comparative Examples 1 to 5. The results are shown in Table 1.

[0100] Table 1 Repair effects of the repair methods described in Example 1 and Comparative Examples 1 to 5

[0101]

[0102]

[0103] The following conclusions can be drawn from Table 1: (1) Compared with the traditional glue injection repair method in Comparative Example 1, the bridge concrete structure active crack repair method provided by the present invention has a larger crack width change rate and can adapt to a larger range of crack activities; and has a higher number of dynamic loads, showing a longer service life. (2) Compared with Comparative Example 1, Comparative Example 2 is different in that a more flexible bottom functional layer is provided. It can be found in the test that when the crack width changes by no more than 25%, the bottom functional layer does not crack, while the actual cracks in the concrete are already expanding; when observing the development of the cracks, there is a delay in the cracking timing of Comparative Example 2, which is not conducive to timely, rapid and intuitive display of the structural state. (3) Comparative Examples 3 and Comparative Examples 5 respectively provide repair materials with color difference values ​​and hiding power that exceed the range relative to Example 1. It can be seen that the color difference value and hiding power exceeding the range will affect the visual observation of cracks and will have an adverse effect on crack observation. (4) The repair material provided by Comparative Example 4 has a lower elongation at break. It can be found that it can only adapt to relatively small crack width changes. It also fails quickly in the dynamic load test and has a weak repair ability.

[0104] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for repairing concrete cracks without affecting the observation of active cracks in concrete structures, characterized in that: The steps include: S1. Clean the crack surface of the concrete to be repaired; S2, bury the grouting nozzle; S3, crack closure; S4. Sealing inspection; S5. Preparation of injection materials; S6, injection construction and maintenance; S7, surface treatment; S8, preparation of bottom functional layer materials; S9, construction and maintenance of bottom functional layer; S10, preparation of surface functional layer materials; S11: Construction and maintenance of surface functional layer.

2. The method for repairing concrete cracks without affecting the observation of active cracks in concrete structures according to claim 1, characterized in that: The crack sealing glue is an epoxy resin adhesive.

3. The method for repairing concrete cracks without affecting the observation of active cracks in concrete structures according to claim 2, characterized in that: The injection material includes one or more of epoxy resin, polyurethane resin, acrylate, fluorocarbon resin, epoxy-modified silicone resin, and cement-based grouting material.

4. The method for repairing concrete cracks without affecting the observation of active cracks in concrete structures according to any one of claims 1 to 3, characterized in that: The bottom functional layer material includes one or more of epoxy resin coating, cement-based waterproof coating, fluorocarbon resin coating and inorganic coating.

5. The method for repairing concrete cracks without affecting the observation of active cracks in concrete structures according to claim 4, characterized in that: The bottom functional layer material is a brittle material, the elongation at break of the bottom functional layer material is ≤5%, the bonding strength of the bottom functional layer material to C40 concrete is ≥1.5MPa, and the failure form of the bottom functional layer material is concrete cohesive failure.

6. The method for repairing concrete cracks without affecting the observation of active cracks in concrete structures according to claim 5, characterized in that: The color difference between the bottom functional layer material and the concrete surface to be repaired is ≤20.

7. The method for repairing concrete cracks without affecting the observation of active cracks in concrete structures according to claim 5 or 6, characterized in that: The surface functional layer material includes one or more of epoxy resin coating, polyurethane coating, acrylate coating, fluorocarbon resin coating, epoxy-modified silicone resin coating, and polyurea coating.

8. The method for repairing concrete cracks without affecting the observation of active cracks in concrete structures according to claim 7, characterized in that: The elongation at break of the surface functional layer material is ≥200%, the tensile strength of the surface functional layer material is ≥1.5MPa, and the 100% elongation strength of the surface functional layer material is ≤1.0MPa; the bonding strength of the surface functional layer material to C40 concrete after composite construction with the bottom functional layer is ≥1.5MPa, and the form of failure after composite construction with the bottom functional layer material is concrete cohesive failure.

9. The method for repairing concrete cracks without affecting the observation of active cracks in concrete structures according to claim 8, characterized in that: The coverage rate of the surface functional layer material is ≤15%.

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