Cement-based patching material for relieving sulfate crystallization and preparation method of cement-based patching material

Abstract

The invention relates to the technical field of cement-based patching materials, and discloses a cement-based patching material capable of relieving sulfate crystallization and a preparation method thereof.The cement-based patching material capable of relieving sulfate crystallization comprises a cementing material, an ionic permeation-resisting nanometer super-hydrophobic material, an air entraining agent and mineral powder; wherein ordinary Portland cement, aluminate cement and dihydrate gypsum in a cementing material are compounded, and mineral powder, an ion permeation-resistant nano super-hydrophobic material and an air entraining agent are doped, so that the early strength and the later strength of the repairing material are ensured, a large amount of ettringite and hydrated calcium aluminate can be generated in the early stage of hydration, and the material has relatively high early strength; the ettringite contains a large amount of crystal water, has certain expansion performance for the system, and can form good adhesion with basic concrete; in addition, the doping of the ionic permeation-resistant nano super-hydrophobic material improves the erosion performance of the repairing material to sulfate, and improves the concrete damage caused by expansion pressure generated by sulfate crystallization.

Description

Technical Field

[0001] The present invention belongs to the technical field of cement-based repair materials, and particularly relates to a cement-based repair material for alleviating sulfate crystallization and a preparation method thereof. Background Art

[0002] With the rapid development of infrastructure construction in China, the durability problems of concrete buildings and components have received increasing attention. During the service process of a large number of concrete structures, especially in the corrosive environments rich in high-concentration sulfates in the saline soil areas of the northwest and coastal areas, different problems such as concrete expansion cracking, surface protective layer cracking or even spalling, and steel bar corrosion are extremely likely to occur, seriously affecting the durability and use safety of concrete. If the damaged concrete structures are not treated in time, the hazards will increase rapidly. Therefore, developing a cement-based repair material that can effectively resist sulfate erosion and extend the durability and service life of concrete structures has become a key problem to be solved urgently at present.

[0003] Literature shows that sulfate physical erosion, namely sulfate crystallization expansion damage, is the main reason for the corrosion and damage of concrete structures in the saline soil areas of the northwest and coastal areas. At present, the research on anti-sulfate erosion repair materials commonly used in practical engineering mainly focuses on the chemical erosion caused by sulfates, and the concrete damage caused by sulfate physical erosion is often ignored. At the same time, various properties such as the early mechanical properties, volume stability, durability, and bonding properties with the original structure of the repair material are rarely comprehensively considered in practical applications and environments.

[0004] Chinese invention patent CN116396046A provides a repair material for sulfate-eroded concrete structures and a preparation method thereof. The invention uses silica fume, water glass, and UEA expansive agent as composite auxiliaries, and uses basalt fibers with a single-filament length of 12 mm as reinforcing materials to modify ordinary Portland cement-based materials, preparing a composite modified repair material with good workability, excellent volume stability, high early strength and good later strength development, strong anti-sulfate physical erosion ability, and high anti-salt corrosion, dry-wet cycle, and freeze-thaw cycle composite erosion ability. However, the preparation process is relatively cumbersome, and the incorporated fibers are not easy to stir evenly and are prone to agglomeration, affecting the compactness of the specimens.

[0005] Chinese invention patent CN113045285A discloses a rapid repair material based on magnesium phosphate cement-based anti-sulfate coating and its preparation method. The components and their mass fractions are as follows: magnesium phosphate cement-based gelling agent powder 68 - 73; phosphate 16 - 21; composite retarder 9 - 12; sodium silicate 2 - 4. The components and their mass fractions of the magnesium phosphate cement-based gelling agent powder include: over-burned magnesium oxide powder 82 - 88; nano-scale SiO2 powder 4 - 8; nano-scale CaO powder 3 - 7; metakaolin 5 - 8. The composite retarder is composed of borax, dodecahydrate phosphate, and polyphosphate. The magnesium phosphate cement-based rapid repair material prepared by this invention has the characteristics of fast setting and hardening, high early strength, strong anti-sulfate erosion resistance, strong wear resistance, and strong bonding with the old concrete structure matrix. However, it has a high cost, poor long-term durability, and does not consider solving the physical erosion damage of sulfates.

[0006] Chinese invention patent CN115073076A discloses an anti-sulfate erosion mortar and its preparation method. The mortar is composed of high anti-sulfate cement, pozzolan, mineral powder, microsilica, gypsum, anhydrous calcium sulfoaluminate, medium sand, air-entraining agent, water-reducing agent, and water. The raw materials of the mortar of this invention are simple and easy to obtain, the preparation method is simple, the slurry prepared according to the mix ratio has good fluidity, good cohesion, strong anti-freezing and anti-sulfate erosion ability, and no volume shrinkage; it can be used in buildings rich in SO 4 2- ion erosion in saline-alkali areas. However, it is not applicable to all sulfate media, has a slightly lower early strength, and a longer setting time.

[0007] Chinese invention patent CN113321484B discloses a magnesium phosphate cement-based anti-sulfate marine repair and reinforcement material and its preparation method. The components and their mass percentages of this material are as follows: magnesium phosphate cement 53 - 60wt%; quartz sand 39 - 46wt%; polypropylene fiber 0.8 - 1.5wt%. The components and their mass percentages of the magnesium phosphate cement include: magnesium phosphate cement-based gelling powder 62 - 67wt%; monoammonium phosphate 18 - 22wt%; composite retarder 10 - 13wt%; sodium silicate 2 - 4wt%. The magnesium phosphate cement-based gelling agent powder contains: over-burned magnesium oxide powder 80 - 83wt%; limestone powder 5 - 7wt%; metakaolin 10 - 15wt%. The composite retarder is composed of borax, disodium hydrogen phosphate dodecahydrate, and organic acid. The material of this invention has the characteristics of strong anti-sulfate erosion resistance, fast setting and hardening, strong workability, high early strength, and good bonding. However, it has a high cost, the fibers incorporated may show uneven distribution, affecting the durability of the repair material, and it also does not solve the problem of physical erosion damage of sulfates.

[0008] Chinese Invention Patent CN110698147A discloses a cement-based repair material applicable to saline soil environment and its preparation method, which is made of raw materials including the following parts by mass: 500-680 parts of sulfoaluminate cement, 200-350 parts of ordinary Portland cement, 4.5-10 parts of nano-silica, 0.25-0.51 parts of dispersant, 1.15-1.75 parts of water reducer, 0.015-0.018 parts of air-entraining agent, 0.40-1.25 parts of retarder, 1.9-2.5 parts of defoamer, 800-900 parts of quartz sand, and 315-360 g of water. Although the cement-based repair material prepared by this invention has certain early strength and the late strength does not show reverse shrinkage, its sulfate resistance is weak (especially for sulfate crystallization phenomenon), and its volume stability and bonding performance are not fully optimized. Summary of the Invention

[0009] The purpose of the present invention is to overcome the above problems and provide a cement-based repair material for alleviating sulfate crystallization and its preparation method. The cement-based repair material provided by the present invention has high early strength, the late strength steadily increases and does not show reverse shrinkage, has good volume stability, good bonding performance with the original concrete, good sulfate resistance and can alleviate sulfate crystallization, is easy to prepare, and is convenient for construction.

[0010] To achieve the above purpose, the present invention adopts the following technical solutions: The present invention provides a cement-based repair material for alleviating sulfate crystallization, which is made of raw materials including the following parts by mass: 850-900 parts of cementitious material, 45-54 parts of ion-blocking nano-superhydrophobic material, 0.45-0.81 parts of water reducer, 0.03-0.045 parts of air-entraining agent, 0.6-0.9 parts of retarder, 0.45-0.81 parts of defoamer, 850-900 parts of quartz sand, and 227-270 parts of water; The cementitious material includes 410-684 parts of ordinary Portland cement, 86-144 parts of aluminate cement, 43-72 parts of gypsum dihydrate, and 90-360 parts of blast furnace slag powder.

[0011] A further improvement of the present invention is that the Portland cement is P·O42.5 ordinary Portland cement with SO 3 content less than 5%, the aluminate cement is CA-50 aluminate cement, and the blast furnace slag powder is S95 grade granulated blast furnace slag powder.

[0012] A further improvement of the present invention is that the ion-blocking nano-superhydrophobic material includes nano material and superhydrophobic material.

[0013] A further improvement of the present invention lies in that the nano-material is one or more of nano-calcium silicate hydrate seeds, nano-silica, nano-aluminum oxide and nano-titanium dioxide.

[0014] A further improvement of the present invention lies in that the superhydrophobic material is one or more of carboxylic acid esters, siloxanes and stearic acid.

[0015] A further improvement of the present invention lies in that the water reducing agent is a high-performance polycarboxylate water reducing agent.

[0016] A further improvement of the present invention lies in that the air-entraining agent is an AOS-type air-entraining agent and the setting retarder is borax.

[0017] A further improvement of the present invention lies in that the defoaming agent is a P803-type powder defoaming agent.

[0018] A further improvement of the present invention lies in that the particle size of the quartz sand is 16 - 48 mesh.

[0019] The present invention also provides a preparation method of a cement-based repair material for alleviating sulfate crystallization, comprising the following steps: Step 1: Add the superhydrophobic material to the nano-material suspension according to the ratio, magnetically stir for 1 - 2 h to cause a liquid-phase reaction, and then use an ultrasonic disperser to ultrasonically disperse the stirred solution for 20 - 40 min to finally obtain an ion-blocking nano-superhydrophobic material, wherein the ratio of the superhydrophobic material to the nano-material suspension is 10:1; Step 2: Wet the mixer, and uniformly mix the gelling material, water reducing agent, air-entraining agent, setting retarder, defoaming agent and quartz sand in the mixer according to the ratio to obtain a main material mixture, wherein the stirring speed is 450 - 650 rpm and the stirring time is 1 - 5 min; Step 3: Sequentially add the ion-blocking nano-superhydrophobic material and water to the main material mixture in Step 2, and stir at 450 - 650 rpm for 1 - 5 min until uniform; Step 4: Increase the mixer speed to 1200 - 1500 rpm and stir for 1 - 5 min to obtain the cement-based repair material.

[0020] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a cement-based repair material for alleviating sulfate crystallization. By compounding ordinary Portland cement, aluminate cement and gypsum dihydrate, and incorporating mineral powder, ion-blocking nano-superhydrophobic material and air-entraining agent, the early strength and late strength of the repair material are ensured. A large amount of ettringite and calcium aluminohydrate can be generated in the early stage of hydration, endowing the material with high early strength. Moreover, ettringite contains a large amount of crystal water, which has a certain swelling property for the system and can form a good bond with the base concrete. In addition, the incorporation of the ion-blocking nano-superhydrophobic material improves the erosion resistance of the repair material to sulfates and alleviates the concrete damage caused by the swelling pressure generated by sulfate crystallization.

[0021] The nano-materials in the ion-blocking nano-superhydrophobic material not only have small sizes but also large specific surface areas, which is conducive to the adsorption of ions, making the growth of hydration products in the system more dispersed and uniform, thus obtaining a denser repair material and further enhancing the sulfate erosion resistance of the cement-based repair material. At the same time, the nano-materials can provide nucleation sites for the hydration products of cement, reduce the nucleation barrier of the hydration products, further promote the hydration of the cement-based material, and improve the early strength of the system. The superhydrophobic material can form a barrier on the surface of the repair material, effectively blocking the penetration of erosion ions, thereby improving the sulfate erosion resistance of the cement-based repair material and alleviating the damage caused by sulfate crystallization.

[0022] The incorporation of the air-entraining agent can cause internal voids to form in the cement-based repair material during use. These fine void structures can effectively block the connected pores in the hardened paste, thereby enhancing the impermeability of the material. At the same time, the voids can also relieve the pressure generated during sulfate crystallization.

[0023] The incorporation of mineral powder can not only refine the pore structure but also react with substances such as calcium hydroxide in the cement to generate calcium silicate hydrate gel (pozzolanic effect), thereby further improving the density and sulfate erosion resistance of the mortar.

[0024] By compounding and incorporating a water reducer and a retarder, the setting time of the repair material can be appropriately extended, and at the same time, the fluidity of the paste can be increased to facilitate on-site construction operations.

[0025] The present invention also provides a preparation method for the cement-based repair material for alleviating sulfate crystallization. This preparation method is simple, easy to formulate, and convenient for construction. It is applicable to cement-based repair projects after sulfate erosion, has a large market space, and strong practicability. Specific embodiments

[0026] To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meanings understood by those skilled in the art regarding the present invention. In case of conflicts, the definitions in this specification shall prevail.

[0027] The theories or mechanisms described and disclosed herein, whether right or wrong, shall not limit the scope of the present invention in any way, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0028] In this article, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are only for the sake of brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be regarded as having covered and specifically disclosed all possible sub-ranges and individual numerical values within the range (including integers and fractions).

[0029] In this article, unless otherwise specified, the terms "comprising", "including", "containing", "having", or similar terms cover the meanings of "consisting of" and "consisting essentially of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A consists only of a".

[0030] In this article, for the sake of concise description, all possible combinations of all technical features in each embodiment or example are not described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered as within the scope described in this specification.

[0031] The present invention provides a cement-based repair material for alleviating sulfate crystallization, which is made from raw materials including the following components in parts by mass: 850 - 900 parts of cementitious materials, 45 - 54 parts of ion-blocking nano-superhydrophobic materials, 0.45 - 0.81 parts of water-reducing agents, 0.03 - 0.045 parts of air-entraining agents, 0.6 - 0.9 parts of retarders, 0.45 - 0.81 parts of defoamers, 850 - 900 parts of quartz sand, and 227 - 270 parts of water; wherein the cementitious materials include 410 - 684 parts of ordinary Portland cement, 86 - 144 parts of aluminate cement, 43 - 72 parts of gypsum dihydrate, and 90 - 360 parts of mineral powder.

[0032] As a preferred solution, the Portland cement is P·O 42.5 ordinary Portland cement with an SO 3 content of less than 5%, the aluminate cement is CA-50 aluminate cement, and the mineral powder is S95 grade granulated blast furnace slag powder.

[0033] The ion-blocking nano superhydrophobic material includes a nano material and a superhydrophobic material, where the nano material is one or more of nano hydrated calcium silicate seeds, nano silicon dioxide, nano aluminum oxide, and nano titanium dioxide; the superhydrophobic material is one or more of carboxylic acid esters, siloxanes, and stearic acid.

[0034] As a preferred solution, the water reducing agent is a high-performance polycarboxylate water reducing agent, the air-entraining agent is an AOS-type air-entraining agent, the setting retarder is borax, the defoaming agent is a P803-type powder defoaming agent, and the particle size of the quartz sand is 16 - 48 mesh.

[0035] In the present invention, a ternary system composed of ordinary Portland cement, aluminate cement, and gypsum dihydrate is adopted as the matrix, and mineral powder is compounded at the same time, so that the density of the repair material is improved, which can not only improve the mechanical strength of the repair material, but also enhance the sulfate erosion resistance of the repair material.

[0036] In the present invention, by incorporating the ion-blocking nano superhydrophobic material, on the one hand, due to the surface effect and volume effect of the nano material, the cement-based repair material can be made denser, enhancing the erosion resistance of the repair material. At the same time, the nano material, as the nucleation matrix of cement hydration products, can improve the early strength of the cement-based repair material; on the other hand, the superhydrophobic material will form a dense waterproof barrier on the concrete surface, fundamentally preventing sulfate ions from the outside from entering the interior of the concrete, not only improving the durability and sulfate erosion resistance of the cement-based repair material, but also alleviating the crystallization phenomenon of sulfates at the source.

[0037] In the present invention, a large number of tiny air bubbles are introduced by incorporating an air-entraining agent, improving the defective voids in the repair material, reducing the porosity of the concrete, making the pore distribution more uniform, and at the same time, it can relieve the expansion pressure caused by sulfate crystallization, thereby reducing the damage of the concrete caused by the expansion pressure.

[0038] In the present invention, through the above technologies, the chemical erosion caused by sulfate erosion ions and the physical erosion caused by sulfate crystallization are improved, solving the problem that the existing repair materials mainly focus on the chemical erosion caused by sulfates during sulfate erosion resistance research and often ignore the concrete damage caused by the physical erosion of sulfate crystallization.

[0039] The present invention also provides a preparation method of a cement-based repair material for relieving sulfate crystallization, including the following steps: Step 1, add the superhydrophobic material to the nano material suspension according to the ratio, magnetically stir for 1 - 2 h to make it undergo a liquid-phase reaction, and then use an ultrasonic disperser to ultrasonically disperse the stirred solution for 20 - 40 min to finally obtain the ion-blocking nano superhydrophobic material, where the ratio of the superhydrophobic material to the nano material suspension is 10:1; Step 2: Wet the mixer, and uniformly mix the cementitious material, water reducer, air-entraining agent, retarder, defoamer and quartz sand in the mixer according to the ratio to obtain the main material mixture, where the stirring speed is 450 - 650 rpm and the stirring time is 1 - 5 min; Step 3: Sequentially add the ion-blocking nano superhydrophobic material and water to the main material mixture in Step 2, and stir at 450 - 650 rpm for 1 - 5 min until uniform; Step 4: Increase the mixer speed to 1200 - 1500 rpm and stir for 1 - 5 min to obtain the cement-based repair material.

[0040] The following will further illustrate the present invention in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0041] Conventional instrument equipment in the art is used in the following embodiments. For the experimental methods without specific conditions noted in the following embodiments, they are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. Various raw materials are used in the following embodiments. Unless otherwise stated, commercially available products are used, and their specifications are conventional specifications in the art. In the specification of the present invention and the following embodiments, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratio represents weight ratio.

[0042] Example 1 Prepare materials according to the following components: 684 g of ordinary Portland cement, 144 g of aluminate cement, 72 g of gypsum dihydrate, 90 g of mineral powder, 227 g of water, 54 g of ion-blocking nano superhydrophobic material, 0.81 g of high-efficiency polycarboxylate water reducer, 0.045 g of AOS-type air-entraining agent, 0.9 g of borax, 0.81 g of P803-type powder defoamer, and 900 g of quartz sand.

[0043] Prepare the above raw materials into a cement-based repair material suitable for saline soil environment according to the following steps: Step 1: Add the superhydrophobic material to the nano material suspension according to the ratio, magnetically stir for 1 h to cause a liquid-phase reaction, and then use an ultrasonic disperser to ultrasonically disperse the stirred solution for 30 min to finally obtain the ion-blocking nano superhydrophobic material; Step 2: Wet the mixer, and uniformly mix the ordinary Portland cement, aluminate cement, gypsum dihydrate, mineral powder, high-efficiency polycarboxylate water reducer, borax, P803-type powder defoamer, AOS-type air-entraining agent and quartz sand in the mixer according to the ratio to obtain the main material mixture, where the stirring speed is 600 rpm and the stirring time is 1 min; Step 3: Sequentially add an ion-blocking and moisture-repellent nano-superhydrophobic material and water to the main material mixture obtained in Step 2, and stir for 1 min at 600 rpm until homogeneous; Step 4: Increase the rotational speed of the blender to 1500 rpm and stir for 1 min to obtain a cement-based repair material.

[0044] The performance measurement conclusion of this example is as follows: The compressive strengths of this cement-based repair material after being immersed in tap water for 1 d, 7 d, and 28 d are 49.5 MPa, 65.7 MPa, and 77.3 MPa, respectively. After 28 d, the compressive strengths after 30, 60, 90, and 120 dry-wet cycles in a sulfate solution are 79.3 MPa, 83.0 MPa, 85.1 MPa, and 82.7 MPa, respectively, and the expansion rates are 0.007%, 0.013%, 0.017%, and 0.023%, respectively. After 120 dry-wet cycles in the sulfate solution, the mass increases by 1.42% compared to before erosion. The sulfate ion contents after 30, 60, 90, and 120 dry-wet cycles in the sulfate solution are 0.16%, 0.27%, 0.36%, and 0.47%, respectively.

[0045] Example 2 Prepare materials according to the following components: 547 g of ordinary Portland cement, 115 g of aluminate cement, 57.5 g of dihydrate gypsum, 225 g of mineral powder, 223.5 g of water, 49.5 g of superhydrophobic material, 0.63 g of high-performance polycarboxylate water reducer, 0.0375 g of AOS-type air-entraining agent, 0.75 g of borax, 0.63 g of P803-type powder defoamer, and 875 g of quartz sand.

[0046] The method for preparing the cement-based repair material applicable to the saline soil environment from the above raw materials in this example is the same as that in Example 1.

[0047] The performance measurement conclusion of this example is as follows: The compressive strengths of this cement-based repair material after being immersed in tap water for 1 d, 7 d, and 28 d are 50.6 MPa, 68.5 MPa, and 80.3 MPa, respectively. After 28 d, the compressive strengths after 30, 60, 90, and 120 dry-wet cycles in a sulfate solution are 85.0 MPa, 88.4 MPa, 89.5 MPa, and 86.5 MPa, respectively, and the expansion rates are 0.009%, 0.016%, 0.022%, and 0.029%, respectively. After 120 dry-wet cycles in the sulfate solution, the mass increases by 1.34% compared to before erosion. The sulfate ion contents after 30, 60, 90, and 120 dry-wet cycles in the sulfate solution are 0.14%, 0.21%, 0.29%, and 0.37%, respectively.

[0048] Example 3 Prepare materials according to the following components: 441 g of ordinary Portland cement, 93 g of aluminate cement, 46 g of gypsum dihydrate, 270 g of mineral powder, 220 g of water, 45 g of ion-blocking nano superhydrophobic material, 0.54 g of high-performance polycarboxylate water reducer, 0.03 g of AOS-type air-entraining agent, 0.66 g of borax, 0.54 g of P803-type powder defoamer, and 850 g of quartz sand.

[0049] The method for preparing the above raw materials into a cement-based repair material suitable for saline soil environment in this example is the same as that in Example 1.

[0050] The performance measurement conclusion of this example is as follows: The compressive strengths of the cement-based repair material immersed in tap water for 1 d, 7 d, and 28 d are 49.8 MPa, 66.5 MPa, and 78.9 MPa respectively. After 28 d, the compressive strengths of the cement-based repair material after 30, 60, 90, and 120 dry-wet cycles in sulfate solution are 80.1 MPa, 83.7 MPa, 82.1 MPa, and 78.7 MPa respectively, and the expansion rates are 0.011%, 0.017%, 0.024%, and 0.031% respectively. After 120 dry-wet cycles in sulfate solution, the mass increases by 1.52% compared with that before erosion. The sulfate ion contents of the cement-based repair material after 30, 60, 90, and 120 dry-wet cycles in sulfate solution are 0.18%, 0.28%, 0.37%, and 0.46% respectively.

[0051] Example 4 Prepare materials according to the following components: 410 g of ordinary Portland cement, 86 g of aluminate cement, 43 g of gypsum dihydrate, 360 g of mineral powder, 227 g of water, 54 g of ion-blocking nano superhydrophobic material, 0.45 g of high-performance polycarboxylate water reducer, 0.045 g of AOS-type air-entraining agent, 0.9 g of borax, 0.45 g of P803-type powder defoamer, and 900 g of quartz sand.

[0052] The method for preparing the above raw materials into a cement-based repair material suitable for saline soil environment in this example is the same as that in Example 1.

[0053] The performance measurement conclusion of this embodiment is as follows: The compressive strengths of this cement-based repair material after being immersed in tap water for 1 day, 7 days, and 28 days are 48.5 MPa, 66.7 MPa, and 74.8 MPa respectively. After 28 days, the compressive strengths after 30, 60, 90, and 120 dry-wet cycles in sulfate solution are 76.5 MPa, 78.3 MPa, 79.3 MPa, and 76.8 MPa respectively, and the expansion rates are 0.011%, 0.018%, 0.025%, and 0.033% respectively. After 120 dry-wet cycles in sulfate solution, the mass increases by 1.61% compared with that before erosion. The sulfate ion contents after 30, 60, 90, and 120 dry-wet cycles in sulfate solution are 0.18%, 0.26%, 0.36%, and 0.49% respectively.

[0054] Comparative example Prepare materials according to the following components: 684 g of ordinary Portland cement, 144 g of aluminate cement, 72 g of dihydrate gypsum, 227 g of water, 54 g of superhydrophobic material, 0.81 g of high-efficiency polycarboxylate water reducer, 0.045 g of AOS-type air-entraining agent, 0.9 g of borax, 0.81 g of P803-type powder defoamer, and 900 g of quartz sand.

[0055] Prepare the above raw materials into a cement-based repair material suitable for saline soil environment according to the following steps: Step 1: Add the superhydrophobic material into the nanomaterial suspension according to the ratio, stir magnetically for 1 h to cause a liquid-phase reaction, and then use an ultrasonic disperser to ultrasonically disperse the stirred solution for 30 min to finally obtain an ion-blocking nano-superhydrophobic material; Step 2: Wet the mixer, and uniformly mix ordinary Portland cement, aluminate cement, dihydrate gypsum, high-efficiency polycarboxylate water reducer, borax, P803-type powder defoamer, AOS-type air-entraining agent, and quartz sand in the mixer according to the ratio to obtain a main material mixture, where the stirring speed is 600 rpm and the stirring time is 1 min; Step 3: Add the ion-blocking nano-superhydrophobic material and water to the main material mixture in Step 2 in sequence, and stir at 600 rpm for 1 min until uniform; Step 4: Increase the mixer speed to 1500 rpm and stir for 1 min to obtain the cement-based repair material.

[0056] The performance measurement conclusion of this embodiment is as follows: The compressive strengths of this cement-based repair material after being immersed in tap water for 1 day, 7 days, and 28 days are 44.5 MPa, 60.7 MPa, and 74.4 MPa respectively. After 28 days, the compressive strengths after 30, 60, 90, and 120 dry-wet cycles in sulfate solution are 76.4 MPa, 77.9 MPa, 76.8 MPa, and 74.6 MPa respectively, and the expansion rates are 0.011%, 0.019%, 0.026%, and 0.033% respectively. After 120 dry-wet cycles in sulfate solution, the mass increases by 1.49% compared with that before erosion. The sulfate ion contents after 30, 60, 90, and 120 dry-wet cycles in sulfate solution are 0.20%, 0.31%, 0.43%, and 0.51% respectively.

[0057] By comparing the performance data of the comparative example and Examples 1-4, it can be found that the compressive strengths of Examples 1-4 after 1 day, 7 days, and 28 days in tap water are higher than those of the comparative example. Especially the compressive strength after 28 days. This is because the micro-aggregate effect and pozzolanic reaction of the mineral powder improve the compressive strength of the system. At the same time, the compressive strength of the specimens in Example with added mineral powder after dry-wet cycles in sulfate solution is also higher than that of the comparative example, and the sulfate ion content after dry-wet cycles is also lower. This is because the mineral powder undergoes pozzolanic reaction to generate more C-S-H gels, making the system denser and having better resistance to sulfate erosion.

[0058] The above content is only to illustrate the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the claims of the present invention.

Claims

1. A cement-based repair material for alleviating sulfate crystallization, characterized in that: The invention is made of the following raw materials in parts by weight: 850-900 parts of gelling material, 45-54 parts of ion-blocking nano-super-hydrophobic material, 0.45-0.81 parts of water reducing agent, 0.03-0.045 parts of air entraining agent, 0.6-0.9 parts of retarder, 0.45-0.81 parts of defoaming agent, 850-900 parts of quartz sand and 227-270 parts of water; The cementitious material comprises 410-684 parts of ordinary Portland cement, 86-144 parts of aluminate cement, 43-72 parts of dihydrate gypsum and 90-360 parts of mineral powder.

2. A cement-based repair material for alleviating sulfate crystallization according to claim 1, characterized in that: The silicate cement is P·O42.5 ordinary silicate cement with a SO3 content of less than 5%, the aluminate cement is CA-50 aluminate cement, and the mineral powder is S95 grade granulated blast furnace slag powder.

3. The cement-based repair material for alleviating sulfate crystallization according to claim 1, characterized in that: The ion-blocking nanometer super-hydrophobic material comprises nanometer materials and super-hydrophobic materials.

4. A cement-based repair material for alleviating sulfate crystallization according to claim 3, characterized in that: The nano material is one or more of nano calcium silicate hydrate seeds, nano silicon dioxide, nano aluminum oxide and nano titanium dioxide.

5. The cement-based repair material for alleviating sulfate crystallization according to claim 3, characterized in that: The super hydrophobic material is one or more of carboxylates, siloxanes and stearic acid.

6. The cement-based repair material for alleviating sulfate crystallization according to claim 1, characterized in that: The water reducer is a high-efficiency polycarboxylate water reducer.

7. The cement-based repair material for alleviating sulfate crystallization according to claim 1, characterized in that: The air entraining agent is an AOS type air entraining agent, and the retarder is borax.

8. The cement-based repair material for alleviating sulfate crystallization according to claim 1, characterized in that: The defoamer is a P803 powder defoamer.

9. The cement-based repair material for alleviating sulfate crystallization according to claim 1, characterized in that: The particle size of the quartz sand is 16-48 meshes.

10. A method for preparing a cement-based repair material for alleviating sulfate crystallization, characterized in that: The following steps are involved: Step 1: adding the super-hydrophobic material to the nano-material suspension according to the ratio, magnetically stirring for 1-2 hours to make it react in the liquid phase, and then using an ultrasonic disperser to ultrasonically disperse the stirred solution for 20-40 minutes to finally obtain an ion-blocking nano-super-hydrophobic material, wherein the ratio of the super-hydrophobic material to the nano-material suspension is 10:1; Step 2, wetting the mixer, uniformly mixing the cementitious material, water reducing agent, air entraining agent, retarder, defoaming agent and quartz sand in the mixer according to the proportion to prepare the main material mixture, wherein the stirring speed is 450-650rpm, and the stirring time is 1-5min; Step 3, adding ion-blocking nano-super hydrophobic material and water to the main material mixture of step 2 in sequence, and stirring at 450-650 rpm for 1-5 min until uniform; Step 4: Increase the mixer speed to 1200-1500 rpm and stir for 1-5 minutes to obtain a cement-based repair material.