Nano modified mineral self-repairing cement-based material and preparation method thereof

Abstract

The invention discloses a nano modified mineral self-repairing cement-based material and a preparation method thereof, and relates to the technical field of self-repairing cement-based materials. The nano modified mineral self-repairing cement-based material is prepared from the following raw materials in parts by weight: cement, water, sand, a pozzolanic mineral admixture, a calcium-based additive, an inorganic nano material and a calcium ion complexing agent, according to the self-repairing cement-based material provided by the invention, the self-repairing cement-based material is regulated and controlled on the basis of synergism of multiple action mechanisms of physical filling, expansion, nano material nucleation promotion and ion complexing, so that the self-repairing efficiency, durability and mechanical property of the self-repairing cement-based material are improved; the waterproof material has the advantages of high strength, good crack resistance, high shrinkage resistance, excellent waterproof performance, good durability, high self-repairing efficiency, low cost, low carbon, environmental protection and the like, the application range of the waterproof material is widened, and the waterproof material particularly has important application value in the protection application fields of ocean engineering, bridge engineering application, hydraulic engineering and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of self-repairing cement-based materials, and particularly relates to a nano-modified mineral self-repairing cement-based material and a preparation method thereof. BACKGROUND

[0002] Cement-based materials are the most widely used materials in construction engineering due to their good plasticity, durability, and low cost. However, cement-based materials are brittle in nature and have multi-scale characteristics, so they are prone to cracking and even failure when subjected to variable stress. Cracking not only reduces the strength of the material, but also provides a way for water and other harmful substances to penetrate into the material, thereby degrading the function and durability of the material and structure. Therefore, developing effective self-repairing concrete materials has been a hot research topic in the field of building materials.

[0003] Compared with conventional crack repair techniques with limited effectiveness, self-repairing cement-based materials have attracted widespread attention because they can repair micro-cracks without human intervention. Existing crack self-healing techniques for cement-based materials mainly include mineral self-repairing, adhesive self-repairing, shape memory alloy self-repairing, and microbial self-repairing. However, adhesive self-repairing, shape memory alloy self-repairing, and microbial self-repairing significantly increase the cost of concrete manufacturing, which severely limits the practical production application of these technologies. At the current stage, mineral self-repairing has been proven to be effective in healing or repairing concrete itself, and the use of inexpensive minerals to prepare self-repairing concrete can greatly reduce costs and take a major step towards commercialization.

[0004] Mineral self-repairing mainly refers to the pre-mixing of certain mineral materials in concrete, which can react with hydration products to generate calcium silicate gel, ettringite, calcium carbonate, and other crystal precipitates to heal cracks when water penetrates into the cement-based material through cracks. Mineral self-repairing mainly includes mineral additive-based self-repairing, expansion agent-based self-repairing, and chemical crystallization precipitate-based self-repairing. Due to the better compatibility of mineral materials and repair products with the cement matrix, and the low cost and simple operation, mineral self-repairing has good application prospects. However, current mineral self-repairing has the problems of low repair efficiency, poor material mechanical properties, poor durability, and high cost, so it is of great significance to develop a self-repairing cement-based composite material with high repair efficiency, good material performance, good durability, and low cost. SUMMARY

[0005] The present application aims to solve the technical problems of low repair efficiency, poor mechanical properties, poor durability and high cost of the current mineral self-repairing cement-based materials, and provides a nano-modified mineral self-repairing cement-based material and a preparation method thereof.

[0006] The present application is realized by the following technical solutions.

[0007] The present application aims to provide a nano-modified mineral self-repairing cement-based material, and the raw materials of the nano-modified mineral self-repairing cement-based material include cement, water, sand, a pozzolanic mineral admixture, a calcium-based additive, inorganic nano-materials and a calcium ion complexing agent, by weight.

[0008] The present application uses a pozzolanic material as a mineral admixture, in which the active silicates, aluminosilicates and silico-aluminicalcium silicates can dissolve and react with the hydration products to form secondary C-S-H gel to heal fine cracks; the calcium-based additive generates calcium hydroxide after meeting water at the cracks, providing additional calcium ions for the self-repairing process, and these calcium ions can react with carbon dioxide or other substances in the atmosphere to generate calcium carbonate to fill the cracks; the inorganic nano-materials can act as nucleation points for calcium carbonate precipitation due to their high specific surface area, promoting rapid crack filling, forming a dense network structure and material organization to fill gaps and improving the self-repairing efficiency; the calcium ion complexing agent has ion complexation effect, which can directionally drive calcium ions to the cracks to improve the efficiency of mineral filling at the cracks; in addition, the calcium-based additive such as CaO has an expansion agent effect, which can make the cement stone produce a certain volume micro-expansion, effectively offsetting the self-shrinkage of the cement-based material in the later stage.

[0009] In summary, the self-repairing cement-based material of the present application is based on the synergistic effect of physical filling, expansion, nano-material nucleation promotion and ion complexation, and is used to regulate and control the self-repairing cement-based material, thereby improving the self-repairing efficiency, durability and mechanical properties of the self-repairing cement-based material, making the self-repairing cement-based material meet the requirements of high strength, crack resistance, durability and self-repairing, expanding its application range, and having advantages in the fields of marine engineering, bridge engineering application and water conservancy engineering protection application.

[0010] And, the self-repairing cement-based material of the present application has simple preparation process, good stability, low carbon and environmental protection, compared with traditional self-repairing cement-based materials, without adding high-cost materials such as fibers, microorganisms and microcapsules, using bulk low-cost mineral materials as self-repairing components, significantly reducing material cost, which is conducive to enterprise cost reduction and efficiency increase; in addition, the self-repairing cement-based material of the present application can improve the carbon neutralization ability of the material during the self-repairing process, and has low-carbon ecological and environmental protection characteristics; therefore, it has good environmental and economic effects.

[0011] Further, the inorganic nano material is selected from nano CaCO3 or nano SiO2.

[0012] Further, the calcium ion complexing agent is selected from any one or more of ethylenediaminetetraacetic acid, ethylene glycol bis-tetraacetic acid, and ethylenediamine.

[0013] As preferred, the calcium ion complexing agent is ethylenediaminetetraacetic acid.

[0014] Further, the pozzolanic mineral admixture is selected from any one or more of pozzolanic tuff, mineral powder, and fly ash.

[0015] Further, the calcium-based additive is quicklime.

[0016] Further, the mass of the pozzolanic mineral admixture is 10%-20% of the mass of the cement, the mass of the calcium-based additive is 2%-6% of the mass of the cement, the mass of the nano material is 0.6%-0.8% of the mass of the cement, the mass of the water is 40%-45% of the total mass of the cement, the pozzolanic mineral admixture and the nano material, the total mass of the cement, the pozzolanic mineral admixture and the nano material is 45%-50% of the mass of the sand, and the mass of the calcium ion complexing agent is 0.25%-0.75% of the mass of the cement.

[0017] Further, the 28d flexural strength of the nano-modified mineral self-repairing cement-based material is above 6.5 MPa, the compressive strength is above 45 MPa, and the dry shrinkage is below 350με; the flexural strength recovery rate after self-repairing is above 80%, the relative crack width is below 0.2, and the relative water permeability coefficient is less than 0.15.

[0018] The second object of the present application is to provide a preparation method of a nano-modified mineral self-repairing cement-based material, comprising the following steps: S1, pour the weighed water into the cement mortar mixer according to the mass ratio, and then pour the cement, the pozzolanic mineral admixture, the calcium-based additive, the nano material and the calcium ion complexing agent weighed according to the mass ratio into the cement mortar mixer, and stir for 30-60s; S2, sand is added to the mixture obtained in step S1, and stirred and mixed uniformly, to obtain a nano-modified mineral self-repairing cement-based material.

[0019] Further, the step S2 further comprises: Step S3, pouring the nano-modified mineral self-repairing cement-based material into a mold, demolding the next day, and then performing normal temperature curing, with a curing temperature of 19-21 DEG C and a relative humidity of more than 90%.

[0020] Compared with the prior art, the present application has the following advantages and beneficial effects.

[0021] 1. The self-repairing cement-based material of the present application is based on the synergistic effect of multiple action mechanisms such as physical filling, expansion, nano-material nucleation promotion, and ion complexation, to regulate and control the self-repairing cement-based material, thereby improving the self-repairing efficiency, durability, and mechanical properties of the self-repairing cement-based material, so that the self-repairing cement-based material can meet the requirements of higher strength, crack resistance, durability, and self-repairing, and the application range is widened, and it has important application value in the fields of marine engineering, bridge engineering, and water conservancy engineering protection applications.

[0022] 2. The self-repairing cement-based material of the present application has simple preparation process, good stability, low carbon and environmental protection, and compared with traditional self-repairing cement-based materials, it does not need to add high-cost materials such as fibers, microorganisms, and microcapsules, but uses bulk low-cost mineral materials as self-repairing components, which significantly reduces the material cost and is beneficial to the enterprise to reduce cost and increase benefit; in addition, the self-repairing cement-based material of the present application can improve the carbon neutralization ability of the material during the self-repairing process, and has the characteristics of low-carbon ecological protection; therefore, it has good environmental and economic effects. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments, and it should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope, and for those skilled in the art, other related drawings can also be obtained without creative labor. In the drawings: Figure 1 Figure 1 is a crack change graph during the self-repairing process of Example 1; Figure 2 Figure 2 is a crack change graph during the self-repairing process of Example 2; Figure 3 Figure 3 is a crack change graph during the self-repairing process of Example 3; Figure 4 Figure 4 is a crack change graph during the self-repairing process of Example 4; Figure 5 Figure 5 is a crack change graph during the self-repairing process of Example 5; Figure 6 Figure 6 is a plot of crack evolution during the self-repair process of Example 6. DETAILED DESCRIPTION

[0024] In order to make the objects, technical solutions, and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be described below in conjunction with the examples and drawings. Obviously, the illustrative embodiments of the present application and their descriptions are only used to explain the present application and not to limit it.

[0025] The embodiments of the present application will be described below in detail with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description and repeated description are omitted. For example, there will be cases where detailed description of matters known to those skilled in the art and repeated description are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art.

[0026] The "range" disclosed in the present application is defined in the form of lower limit and upper limit, a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range.

[0027] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0028] If not specifically stated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0029] If not specifically stated, "including" and "comprising" mentioned in the present application means open-ended, and can also be closed. For example, "including" and "comprising" can mean that other substances not listed can also be included or contained, or only the listed substances can be included or contained.

[0030] If not specifically stated, all steps of the present application can be performed in sequence or randomly, and are preferably performed in sequence. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, the method can also include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or steps (a), (c), and (b), or steps (c), (a), and (b), etc.

[0031] The technical solutions of the present application are further described in detail below in combination with the embodiments.

[0032] It should be noted that the experimental methods used in the embodiments are conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are conventional materials, reagents, methods and instruments in the art unless otherwise specified, and can be obtained by commercial channels by those skilled in the art.

[0033] Example 1 A nano-modified mineral self-repairing cement-based material, by weight, comprises the following components: cement 100 parts, slag 10 parts, quicklime 2 parts, nano-calcium carbonate 0.6 parts, water 45 parts, sand 250 parts, ethylene glycol bis-tetraacetic acid 0.25 parts.

[0034] A preparation method of a nano-modified mineral self-repairing cement-based material, comprising the following steps: Step one: pour the weighed water according to the mass ratio into the cement mortar mixer, then pour the weighed cement, mineral admixture, calcium-based additive, nano material and calcium ion complexing agent according to the mass ratio; Step two: open the cement mortar mixer and stir for 30s, then add sand into the pot, stir for 30s, pause for 90s, and finally stir for 60s to obtain the self-repairing cement-based material; Step three: pour the self-repairing cement-based material into the mold, and demold the next day. After demolding, normal temperature curing is carried out, and the curing temperature is 19-21℃, and the relative humidity of the wet curing is above 90%.

[0035] Example 2 A nano-modified mineral self-repairing cement-based material, by weight, comprises the following components: cement 100 parts, fly ash 10 parts, quicklime 4 parts, nano-calcium carbonate 0.8 parts, water 52 parts, sand 230 parts, ethylene glycol bis-tetraacetic acid 0.75 parts.

[0036] A preparation method of a nano-modified mineral self-repairing cement-based material, comprising the following steps: Step one: pour the weighed water according to the mass ratio into the cement mortar mixer, then pour the weighed cement, mineral admixture, calcium-based additive, nano material and calcium ion complexing agent according to the mass ratio; Step two: open the cement mortar mixer and stir for 60s, then add sand into the pot, stir for 60s, pause for 90s, and finally stir for 90s to obtain the self-repairing cement-based material; Step three: pour the self-repairing cement-based material into the mold, and demold the next day. After demolding, normal temperature curing is carried out, and the curing temperature is 19-21℃, and the relative humidity of the wet curing is above 90%.

[0037] Embodiment 3 A nano-modified mineral self-repairing cement-based material, comprising the following components by weight parts: cement 100 parts, volcanic ash tuff 10 parts, quicklime 4 parts, nano-calcium carbonate 0.6 parts, water 46 parts, sand 230 parts, ethylene diamine 0.25 parts.

[0038] A preparation method of a nano-modified mineral self-repairing cement-based material, comprising the following steps: Step one: pour the weighed water according to the mass ratio into the cement mortar mixer, and then pour the weighed cement, mineral admixture, calcium-based additive, nano material and calcium ion complexing agent according to the mass ratio; Step two: open the cement mortar mixer and stir for 40s, then add sand into the pot, stir for 40s, stop for 90s, and finally stir for 70s to obtain the self-repairing cement-based material.

[0039] Step three: pour the self-repairing cement-based material into the mold, and demold the next day. After demolding, normal temperature curing is carried out, and the curing temperature is 19-21℃, and the relative humidity of the wet curing is above 90%.

[0040] Embodiment 4 A nano-modified mineral self-repairing cement-based material, comprising the following components by weight parts: cement 100 parts, volcanic ash tuff 20 parts, quicklime 4 parts, nano-calcium carbonate 0.8 parts, water 45 parts, sand 240 parts, ethylenediaminetetraacetic acid 0.25 parts.

[0041] A preparation method of a nano-modified mineral self-repairing cement-based material, comprising the following steps: Step one: pour the weighed water according to the mass ratio into the cement mortar mixer, and then pour the weighed cement, mineral admixture, calcium-based additive, nano material and calcium ion complexing agent according to the mass ratio; Step two: open the cement mortar mixer and stir for 45s, then add sand into the pot, stir for 45s, stop for 90s, and finally stir for 80s to obtain the self-repairing cement-based material; Step three: pour the self-repairing cement-based material into the mold, and demold the next day. After demolding, normal temperature curing is carried out, and the curing temperature is 19-21℃, and the relative humidity of the wet curing is above 90%.

[0042] Embodiment 5 A nano-modified mineral self-repairing cement-based material, comprising the following components by weight parts: cement 100 parts, volcanic ash tuff 20 parts, quicklime 6 parts, nano-calcium carbonate 0.8 parts, water 48 parts, sand 250 parts, ethylenediaminetetraacetic acid 0.4 parts.

[0043] A preparation method of a nano-modified mineral self-repairing cement-based material, comprising the following steps: Step one: pour the weighed water into the cement mortar mixer according to the mass ratio, and then pour the cement, mineral admixture, calcium-based additive, nano material and calcium ion complexing agent weighed according to the mass ratio; Step two: open the cement mortar mixer and stir for 60s, then add sand into the pot, stir for 60s, stop for 90s, and finally stir for 90s to obtain the self-repairing cement-based material; Step three: pour the self-repairing cement-based material into the mold, and demold the next day. After demolding, normal temperature curing is carried out, and the curing temperature is 19-21℃, and the relative humidity of the wet curing is above 90%.

[0044] Example 6 A nano-modified mineral self-repairing cement-based material, comprising the following components by weight: cement 100 parts, volcanic ash tuff 20 parts, quicklime 4 parts, nano calcium carbonate 0.8 parts, water 50 parts, sand 240 parts, and ethylenediaminetetraacetic acid 0.5 parts.

[0045] A preparation method of a nano-modified mineral self-repairing cement-based material, comprising the following steps: Step one: pour the weighed water into the cement mortar mixer according to the mass ratio, and then pour the cement, mineral admixture, calcium-based additive, nano material and calcium ion complexing agent weighed according to the mass ratio; Step two: open the cement mortar mixer and stir for 60s, then add sand into the pot, stir for 60s, stop for 90s, and finally stir for 90s to obtain the self-repairing cement-based material; Step three: pour the self-repairing cement-based material into the mold, and demold the next day. After demolding, normal temperature curing is carried out, and the curing temperature is 19-21℃, and the relative humidity of the wet curing is above 90%.

[0046] Comparative Example 1 The difference between this comparative example and Example 6 is that no nano material is added.

[0047] A mineral self-repairing cement-based material, comprising the following components by weight: cement 100 parts, volcanic ash tuff 20 parts, quicklime 4 parts, water 50 parts, sand 240 parts, and ethylenediaminetetraacetic acid 0.5 parts.

[0048] A mineral self-repairing cement-based material and a preparation method thereof, comprising the following steps: Step one: pour the weighed water into the cement mortar mixer according to the mass ratio, and then pour the cement, mineral admixture, calcium-based additive, nano material and calcium ion complexing agent weighed according to the mass ratio; Step two: open the cement mortar mixer for 60s, then add sand into the pot, stir for 60s, stop for 90s, and finally stir for 90s, to obtain the self-repairing cement-based material; Step three: pour the self-repairing cement-based material into a mold, and demold the next day. After demolding, normal temperature curing is performed, the curing temperature is 19-21℃, and the relative humidity of the wet curing is above 90%.

[0049] Comparative Example 2 The difference between this comparative example and Example 6 is that no calcium ion complexing agent is added.

[0050] A nano-modified mineral self-repairing cement-based material, comprising the following components by weight parts: cement 100 parts, volcanic ash tuff 20 parts, quicklime 4 parts, nano calcium carbonate 0.8 parts, water 50 parts, and sand 240 parts.

[0051] A preparation method of a nano-modified mineral self-repairing cement-based material, comprising the following steps: Step one: pour the weighed water into a cement mortar mixer according to the mass ratio, and then pour the weighed cement, mineral admixture, calcium-based additive, and nano material into the cement mortar mixer according to the mass ratio; Step two: open the cement mortar mixer for 30-60s, then add sand into the pot, stir for 30-60s, stop for 90s, and finally stir for 60-90s, to obtain the self-repairing cement-based material.

[0052] Step three: pour the self-repairing cement-based material into a mold, and demold the next day. After demolding, normal temperature curing is performed, the curing temperature is 19-21℃, and the relative humidity of the wet curing is above 90%.

[0053] Comparative Example 3 The difference between this comparative example and Example 6 is that no nano material and calcium ion complexing agent are added.

[0054] A mineral self-repairing cement-based material, comprising the following components by weight parts: cement 100 parts, volcanic ash tuff 20 parts, quicklime 4 parts, water 50 parts, and sand 240 parts.

[0055] A mineral self-repairing cement-based material and a preparation method thereof, comprising the following steps: Step one: pour the weighed water into a cement mortar mixer according to the mass ratio, and then pour the weighed cement, mineral admixture, and calcium-based additive into the cement mortar mixer according to the mass ratio; Step two: open the cement mortar mixer for 60s, then add sand into the pot, stir for 60s, stop for 90s, and finally stir for 90s, to obtain the self-repairing cement-based material. Step 3: Pour the self-repairing cement-based material into the mold and demold the next day. After demolding, perform room temperature curing at a temperature of 19-21°C and a relative humidity of 90% or higher.

[0056] The performance tests of the samples prepared in the above examples and comparative examples were carried out as follows: 1. After the cement-based material has been cured for the required 28 days, the compressive and flexural strengths are measured according to the national standard GB / T 17671-1. The flexural specimens are sized 40mm x 40mm x 160mm, and the compressive specimens are sized 70mm x 70mm x 70mm. Both the flexural and compressive strength tests are repeated six times.

[0057] 2. Prepare and cure cement-based materials according to the standard method in the industry recommended standard JC / T 603-2004. Each group has three parallel samples, and the average value is taken as the final result. The test uses a standard specimen with a size of 25mm×25mm×280mm. After the specimen is cured under standard conditions (20℃±2℃, ≥95% relative humidity) for 7 days, it is moved to 20±3℃ and 50%±4% relative humidity for drying shrinkage test. After measuring the initial length of the specimen, place it in a length comparator and measure the length change within 28 days. The shrinkage rate of cement-based materials is calculated as the ratio of the length change of the cement-based specimen to the initial length. The drying shrinkage rate of cement-based materials is calculated according to the following formula (the calculated value is accurate to 0.001%):

[0058] Among them, S n Indicates the drying shrinkage of cement-based materials after 28 days of curing, με; L0 indicates the initial measurement length of cement-based materials, mm; L n It represents the measured length of cement-based material after 28 days of curing, in mm; 250 represents the effective length of the specimen, in mm.

[0059] 3. Strength recovery rate is one of the most important indicators to characterize self-repair performance. In the present invention, strength recovery rate refers to the flexural strength recovery rate, and the formula is as follows:

[0060] in, is the flexural strength recovery rate, %; is the flexural strength of the pre-damaged specimen after self-repair, MPa; It is the flexural strength of the specimen without pre-damage treatment at the same curing age, MPa.

[0061] 4. Relative crack width indicates the change in crack width before and after self-repair. The calculation formula is as follows:

[0062] wherein, w 0 is the relative crack width, mm; w 1 is the initial crack width, mm; w 2 is the crack width after self-repairing of the pre-damaged test piece, mm.

[0063] The crack changes of the samples prepared by the method of Examples 1-6 during self-repairing are shown in Table 1. Figures 1-6

[0064] 5. The direct measurement index of the impermeability is the permeability coefficient. The test method of the permeability coefficient is that a cylindrical test piece with a diameter of 100 mm and a height of 100 mm is placed in a PVC pipe with a diameter of 100 mm and a height of 250 mm. The contact surface between the PVC pipe and the test piece is sealed with epoxy resin. During the entire experiment, the water column height in the PVC pipe is kept at 200 mm, and the water seeping from the crack area is collected in a beaker. After 8 minutes, the water in the beaker is measured by a precision balance. The permeability coefficient is calculated according to Darcy's law, and the formula is as follows:

[0065] wherein, k1 is the permeability coefficient, m / s; Qw is the water flow, m / s; L is the height of the test piece, m; A is the cross-sectional area, m2; and h is the water surface difference, m. 3 2

[0066] The calculation formula of the relative permeability coefficient k2 is as follows:

[0067] wherein, kt is the permeability coefficient after self-repairing, m / s; and k1 is the initial permeability coefficient, m / s.

[0068] The test results are shown in Table 1.

[0069] Table 1, Test results of the samples prepared in Examples and Comparative Examples

[0070] As can be seen from the data in Table 1, the material of the present application has excellent performance, the 28d flexural strength is above 6.5 MPa, the 28d compressive strength is above 45 MPa, the 28d drying shrinkage is less than 350 με; the flexural strength recovery rate after self-repairing is above 80%, the relative crack width is less than 0.2, the relative water permeability coefficient is less than 0.15, and the material has the advantages of high strength, good crack resistance, strong anti-shrinkage ability, excellent waterproof performance, good durability, high self-repairing efficiency, low cost, low carbon and environmental protection, etc.

[0071] ​​​​Comparative Example 1: Without adding nano calcium carbonate, the compactness of the material as a whole is reduced, so that the mechanical properties are significantly reduced. And the high reactivity of nanoparticles can accelerate mineral deposition. Therefore, after the material is damaged, larger cracks are formed, and the self-repairing effect of this comparative example is poor.

[0072] Comparative Example 2: Without adding calcium ion complexing agent, the main role of calcium ion complexing agent is to form a soluble complex to improve the migration efficiency of calcium ions in the crack water environment and drive CaCO3 precipitation. Without the complexing agent, the diffusion rate of calcium ions is reduced, resulting in a decrease in the healing reaction rate. Without the complexing agent, the repair product cannot fill the wide crack. In addition, the hydrolysis of the complex can control the directional deposition of CaCO3 to avoid local accumulation. Without the complexing agent, CaCO3 randomly crystallizes on the surface of the crack to form a loose and porous structure rather than a dense filling layer, reducing the repair compactness.

[0073] Comparative Example 3: Without adding nano materials and calcium ion complexing agent, nano materials and calcium ion complexing agent are key components for synergistically improving repair efficiency. The absence of nano materials leads to a lack of nucleation sites, and nano calcium carbonate can provide a large number of active surfaces to promote heterogeneous nucleation of calcium carbonate. Without it, the repair product crystallizes slowly and loosely. Calcium ion migration is blocked, and the complexing agent forms a soluble complex by chelating calcium ions to drive their migration to the crack. Without the complexing agent, the diffusion rate of calcium ions decreases significantly, resulting in a significant decrease in the self-repairing effect of the crack. Nano materials are the "skeletal support" of the repair product, providing nucleation sites and micro-filling; the complexing agent is the "transport engine" of calcium ions, enabling directional migration and deposition. The double absence will cause the self-repairing mechanism to be severely imbalanced from molecular migration to product crystallization, so the self-repairing effect is poor.

[0074] Finally, it should be noted that the above specific examples are only used to explain the purpose, technical solutions and beneficial effects of the present application in detail. It should be understood that the above description is only a specific embodiment of the present application and does not limit the protection scope of the present application; although the present application has been described in detail with reference to the foregoing specific embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent replacement, improvement, etc. to part or all of the technical features; and these modifications, equivalent replacement, improvement, etc. do not make the essence of the corresponding technical solution deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and description of the present application.

Claims

1. A nano-modified mineral self-repairing cement-based material, characterized in that: The raw materials of the nano-modified mineral self-repairing cement-based material include, by weight, cement, water, sand, pozzolanic mineral admixture, calcium-based admixture, inorganic nanomaterial and calcium ion complexing agent.

2. A nano-modified mineral self-repairing cement-based material according to claim 1, characterized in that: The inorganic nanomaterial is selected from nano-CaCO3 or nano-SiO2.

3. The nano-modified mineral self-repairing cement-based material according to claim 1, characterized in that: The calcium ion complexing agent is selected from any one or more of ethylenediaminetetraacetic acid, ethylene glycol ditetraacetic acid, and ethylenediene pentamine.

4. The nano-modified mineral self-repairing cement-based material according to claim 1, characterized in that: The calcium ion complexing agent is ethylenediaminetetraacetic acid.

5. The nano-modified mineral self-repairing cement-based material according to claim 1, characterized in that: The pozzolanic mineral admixture is selected from any one or more of pozzolanic tuff, mineral powder, and fly ash.

6. The nano-modified mineral self-repairing cement-based material according to claim 1, characterized in that: The calcium-based admixture is quicklime.

7. A nano-modified mineral self-repairing cement-based material according to any one of claims 1 to 6, characterized in that: The mass of the pozzolanic mineral admixture is 10%-20% of the mass of cement, the mass of the calcium-based admixture is 2%-6% of the mass of cement, the mass of the nanomaterial is 0.6%-0.8% of the mass of cement, the mass of the water is 40%-45% of the total mass of cement, pozzolanic mineral admixture and nanomaterial, the total mass of cement, pozzolanic mineral admixture and nanomaterial is 45%-50% of the mass of sand, and the mass of the calcium ion chelating agent is 0.25%-0.75% of the mass of cement.

8. The nano-modified mineral self-repairing cement-based material according to claim 1, characterized in that: The nano-modified mineral self-repairing cement-based material has a 28d flexural strength of more than 6.5 MPa, a compressive strength of more than 45 MPa, and a drying shrinkage of less than 350 με; the flexural strength recovery rate after self-repair is more than 80%, the relative crack width is less than 0.2, and the relative permeability coefficient is less than 0.

15.

9. A method for preparing a nano-modified mineral self-repairing cement-based material, characterized in that: The following steps are involved: S1. Pour the water weighed according to the mass ratio into the cement mortar mixer, and then pour in the cement, pozzolanic mineral admixture, calcium-based admixture, nanomaterial and calcium ion complexing agent weighed according to the mass ratio, and stir for 30-60 seconds; S2. Add sand to the mixture obtained in step S1 and stir to mix well to obtain the nano-modified mineral self-repairing cement-based material.

10. The method for preparing a nano-modified mineral self-repairing cement-based material according to claim 9, characterized in that: After step S2, the following steps are further included: Step S3: pour the nano-modified mineral self-repairing cement-based material into the mold, demold the mold the next day, and then perform room temperature curing after demolding. The curing temperature is 19-21° C. and the relative humidity is above 90%.

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