A carbonation-resistant sulfoaluminate cement repair mortar and its preparation method

Abstract

This invention discloses a carbonation-resistant sulfoaluminate cement repair mortar and its preparation method, belonging to the field of building materials technology. The mortar of this invention is composed of sulfoaluminate cement, quartz sand, dual nanocrystalline nuclei, microencapsulated CO2 adsorbent, zeolite, lithium sulfate, redispersible latex powder, hydrophobically modified nanocellulose, polycarboxylate-based water-reducing agent, and water. The dual nanocrystalline nuclei are composite powders composed of nano-trisulfate calcium sulfoaluminate and nano-hydrated calcium silicate in a mass ratio of 6:4 to 8:2. The microencapsulated CO2 adsorbent is a material with polyethyleneimine as the core material and a pH-responsive polymer as the wall material. This invention achieves a synergistic improvement in the mortar's ultra-early strength, high bond strength, continuous growth in later strength without shrinkage, and excellent carbonation resistance, making it particularly suitable for rapid repair projects of concrete in high CO2 concentration environments.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and more specifically, to a carbonation-resistant sulfoaluminate cement repair mortar and its preparation method, which is particularly suitable for rapid concrete repair projects in high CO2 concentration environments (such as underground pipe corridors, industrial plants, tunnels, marine structures, etc.). Background Technology

[0002] To meet the rapid repair needs of pipe corridors, factories, tunnels, marine engineering, buildings, airport runways, highways, high-speed railways, and dam repair, various special cementitious materials have been developed and used, including geopolymers, magnesium phosphate cement, magnesium oxychloride cement, aluminate cement, and sulfoaluminate cement (CSA). Among these, CSA has the advantages of short setting time, high early strength, early micro-expansion, and low shrinkage in the later stage, which can better meet the service performance requirements of special service environments and working conditions, and its application is particularly widespread.

[0003] Rapid repair engineering demands high early-stage performance, but inevitably faces challenges related to long-term service stability. Extensive research has reported advantages such as early-stage strength, high strength, and good volume stability in CSA (Continuous Susceptible Autoclave), but it also suffers from poor long-term performance stability, for example, due to SO42-. 2- The deficiency leads to the transformation of the internal hydration product ettringite into monosulfide-type hydrated calcium sulfoaluminate. This is because, on the one hand, as ettringite transforms into a new product, the microscopic volume begins to decrease, which in turn causes the volume stability of CSA to become unstable, resulting in shrinkage and cracking of CSA. On the other hand, due to the appearance of cracks, the internal density of CSA decreases, and the mechanical strength of CSA begins to decline and shrink.

[0004] The environment in which CSA (Compact Steel Aqueduct) operates significantly impacts its service performance, including sulfate attack, chloride attack, freeze-thaw cycles, and carbonization. Carbonization has a particularly widespread effect. It leads to the decomposition and transformation of the critical internal hydration product, ettringite (AFt), accelerating internal crack formation and strength reduction. Over long-term use, as carbonization deepens, building structures may experience cracking and spalling, drastically shortening their lifespan and increasing maintenance costs and safety risks. Therefore, improving the carbonization resistance of CSA is crucial for its long-term service in rapid repair projects.

[0005] Existing repair mortars often focus on improving "early strength" while neglecting long-term durability, resulting in rapid performance degradation under complex environments. Some studies have also paid attention to carbonation resistance. For example, existing technology CN120423841A discloses an early-strength, fast-hardening, carbonation-resistant cement-based repair mortar, which improves carbonation resistance through anti-carbonation fibers and admixtures. However, this technology only demonstrates the compressive strength retention rate after 14 days of carbonation and does not address the issues of later strength reduction and carbonation depth. Existing technology CN120025132A discloses a road repair mortar that emphasizes 4-hour early strength performance but lacks research on carbonation resistance.

[0006] This invention patent addresses the problem that repair mortars, especially sulfoaluminate cement-based repair mortars, are prone to failure due to carbonization during service. It achieves a performance breakthrough through the synergistic effects of actively capturing CO2, simultaneously strengthening the matrix, and stabilizing the crystal structure. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a carbonation-resistant sulfoaluminate cement repair mortar and its preparation method. Through a four-in-one mechanism of "induction-adsorption-stabilization-shielding", it achieves early strength and high strength, continuous growth of later strength without shrinkage, high bond strength and significantly improved carbonation resistance, thus solving the performance bottleneck problem of concrete structure repair materials.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A carbonization-resistant sulfoaluminate cement repair mortar, comprising the following components by weight: 80-90 parts sulfoaluminate cement, 90-120 parts quartz sand, 1-3 parts dual nanocrystal nuclei, 1.5-3 parts microencapsulated CO2 adsorbent, 2-5 parts zeolite, 0.3-0.5 parts lithium sulfate, 2-4 parts redispersible latex powder, 0.15-0.3 parts hydrophobically modified nanocellulose, 0.3-0.8 parts polycarboxylate superplasticizer, and 22-30 parts water;

[0010] Among them, the dual nanocrystal core is a composite powder composed of nano-trisulfate calcium sulfoaluminate and nano-hydrated calcium silicate in a mass ratio of 6:4 to 8:2; the microencapsulated CO2 adsorbent is a material with polyethyleneimine as the core material and pH-responsive polymer as the wall material.

[0011] The present invention is further configured such that the dual nanocrystal nuclei are prepared by the following method: nano-trisulfate calcium sulfoaluminate sol is prepared by co-precipitation of CaCl2 solution and Al2(SO4)3 solution; nano-hydrated calcium silicate sol is prepared by reacting Na2SiO3 solution with saturated calcium hydroxide solution; using polycarboxylate superplasticizer as dispersant, the two sols are dispersed and mixed evenly, and then centrifuged, washed, freeze-dried, ball-milled and sieved to obtain the dual nanocrystal nuclei.

[0012] The present invention is further configured such that the microencapsulated CO2 adsorbent is prepared by a complex coagulation method: an aqueous solution of polyethyleneimine is dispersed in an emulsifier to form an emulsion; then chitosan and sodium alginate are added for complex coagulation, followed by glutaraldehyde crosslinking, alkali washing, and freeze drying to obtain the microencapsulated CO2 adsorbent.

[0013] The present invention is further configured such that the particle size of the dual nanocrystal nuclei after dispersion is ≤100nm.

[0014] The present invention is further configured such that the microencapsulated CO2 adsorbent ruptures and releases the core material when pH ≤ 10.5; the pH-responsive polymer is a chitosan-sodium alginate complex.

[0015] The present invention is further configured such that the sulfoaluminate cement is a rapid-hardening sulfoaluminate cement, wherein the content of anhydrous calcium sulfoaluminate is ≥60%, the content of dicalcium silicate is 15%~25%, the initial setting time is ≤30min, and the final setting time is ≤90min.

[0016] The present invention is further configured such that the zeolite is a 13X type or a NaA type zeolite with a specific surface area ≥ 500 m² / g.

[0017] The present invention is further configured such that the redispersible latex powder is an ethylene-vinyl acetate copolymer latex powder, the mass ratio of vinyl acetate to ethylene is 80:20, the film-forming temperature is -5℃, and the elongation at break is ≥300%.

[0018] The present invention is further configured such that the hydrophobically modified nanocellulose is nanocellulose with a surface modified by a silane coupling agent.

[0019] A method for preparing a carbonization-resistant sulfoaluminate cement repair mortar involves mixing a homogeneous mixture of sulfoaluminate cement, quartz sand, and zeolite with a homogeneous mixture of dual nanocrystal nuclei, microencapsulated CO2 adsorbent, redispersible latex powder, hydrophobically modified nanocellulose, lithium sulfate, and polycarboxylate superplasticizer. Water is then added and stirred until the slurry is homogeneous, thus obtaining the repair mortar.

[0020] In summary, the present invention has the following beneficial effects:

[0021] 1. Dual Nanocrystal Nucleus Reinforcement: The trisulfate-type calcium sulfoaluminate nanocrystal nuclei in the dual nanocrystal nucleus structure serve as templates for the growth of calcite crystals, inducing heterogeneous nucleation of calcite on the seed surface, significantly accelerating the formation rate of ettringite, and providing numerous nucleation sites. This promotes the formation of more and finer calcite crystals, which have higher specific surface areas and lower defect densities, resulting in a more stable crystal structure. Furthermore, the trisulfate-type calcium sulfoaluminate nanocrystal nuclei themselves, or the fine calcite formed early on, preferentially react with intruding CO2, consuming some CO2 and providing a buffer time for the internal calcite. The hydrated calcium silicate nanocrystal nuclei in the dual nanocrystal nucleus structure serve as templates and nucleation sites for CSH gel formation, strongly promoting the hydration of the silicate phase, leading to early, abundant, and rapid formation of CSH gel. This rapidly formed CSH gel fills capillaries, refines pore size, and blocks interconnecting channels, significantly reducing the total porosity, average pore size, and permeability of the cement stone, forming a highly dense matrix and constituting a strong physical diffusion barrier, effectively hindering the migration of CO2 gas and moisture into the interior. When the mass ratio of nano-trisulfate calcium sulfoaluminate sol to nano-hydrated calcium silicate sol is 6:4 to 8:2, a synergistic effect of "large pore skeleton reinforcement + micro pore gel filling" can be achieved, comprehensively optimizing the pore structure of mortar.

[0022] 2. Active Anti-Carbonization and Synergistic Adsorption: The microcapsule wall material uses a chitosan-sodium alginate composite. When the pH drops to ≤10.5 due to carbonization on the surface and inside the repair mortar, the protonation degree of chitosan decreases, and the carboxyl groups of sodium alginate deprotonate, causing the wall material structure to dissociate and break, precisely releasing the core material, polyethyleneimine. The amino groups in the polyethyleneimine molecule can undergo a chemical adsorption reaction with CO2 to generate carbamate, achieving in-situ CO2 capture; the zeolite selected has a specific surface area ≥500 m². 2 / g of 13X or NaA type, its microporous structure can physically adsorb residual CO2 that has not been captured by polyethyleneimine, while the ion exchange performance of zeolite can buffer the pH change of the system, prolong the response window of the microcapsule release core material, and form a dual anti-carbonization barrier of "chemical adsorption + physical adsorption".

[0023] 3. Hydrophobic Network Constructs an Impermeable Barrier: Redispersible latex powder forms a continuous polymer film in the later stages of hydration, enhancing the interfacial bond with the old concrete substrate through "molecular chain penetration-mechanical anchoring." Hydroxyl groups on the surface of hydrophobically modified nanocellulose form hydrogen bonds with the silicate groups of the old concrete substrate, further enhancing the bonding strength in conjunction with the polymer film. Its nanoscale fibers are uniformly dispersed in the cement mortar, forming a three-dimensional network structure that strengthens and toughens the surface. Simultaneously, the hydrophobic groups of the hydrophobically modified nanocellulose are oriented on the pore surface, forming a continuous hydrophobic film that reduces water intrusion and blocks the transport path of the carbonization medium.

[0024] 4. Ion Regulation for Stabilizing Crystal Structure: Lithium ions released from lithium sulfate can enter the hexagonal channels of ettringite, competing with water molecules for coordination to form a Li-AFt solid solution, thus improving the thermodynamic stability of the crystal. This invention, by adding lithium sulfate, provides Li... + Stable AFt, and also provides SO4 2- Supplementing the sulfur source prevents AFt from converting to monosulfide form, achieving "one agent, two effects". Attached Figure Description

[0025] Figure 1 This is a carbonation depth diagram of the mortar in Example 1;

[0026] Figure 2 This is a carbonation depth diagram of the mortar in Example 2;

[0027] Figure 3 This is a carbonation depth diagram of the mortar in Example 3;

[0028] Figure 4 The carbonation depth diagram is shown for the mortar in Comparative Example 1.

[0029] Figure 5 The carbonation depth diagram is shown for the mortar in Comparative Example 2.

[0030] Figure 6 The carbonation depth diagram is for Comparative Example 3 mortar.

[0031] Figure 7 The carbonation depth diagram is for Comparative Example 4 mortar.

[0032] Figure 8 This is a carbonation depth diagram of the mortar in Comparative Example 5. Detailed Implementation

[0033] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1

[0035] Mortar formulation composition: 80 parts sulfoaluminate cement, 120 parts quartz sand, 1 part double nanocrystal nuclei, 1.5 parts microencapsulated CO2 adsorbent, 2 parts zeolite, 0.3 parts lithium sulfate, 2 parts redispersible latex powder, 0.15 parts hydrophobically modified nanocellulose, 0.3 parts polycarboxylate superplasticizer, and 22 parts water.

[0036] (1) Add sulfoaluminate cement, quartz sand and zeolite to a mixer and dry mix for 2-3 minutes; (2) Disperse the double nanocrystal nuclei, microencapsulated CO2 adsorbent, redispersible latex powder, hydrophobically modified nanocellulose, lithium sulfate and polycarboxylic acid water-reducing agent in a high-speed disperser for 3-5 minutes, then add them to the mixture in step (1) and continue to dry mix for 3 minutes; (3) Add water and stir for 5-8 minutes until the slurry is uniform to obtain carbonation sulfoaluminate cement repair mortar.

[0037] Example 2

[0038] Mortar formulation composition: 90 parts sulfoaluminate cement, 90 parts quartz sand, 3 parts dual nanocrystal nuclei, 3 parts microencapsulated CO2 adsorbent, 5 parts zeolite, 0.5 parts lithium sulfate, 4 parts redispersible latex powder, 0.3 parts hydrophobically modified nanocellulose, 0.8 parts polycarboxylate superplasticizer, and 30 parts water. Preparation method is the same as in Example 1.

[0039] Example 3

[0040] The mortar formulation consists of: 85 parts sulfoaluminate cement, 105 parts quartz sand, 2 parts dual nanocrystal nuclei, 2.3 parts microencapsulated CO2 adsorbent, 3.5 parts zeolite, 0.4 parts lithium sulfate, 3 parts redispersible latex powder, 0.2 parts hydrophobically modified nanocellulose, 0.5 parts polycarboxylate superplasticizer, and 26 parts water. The preparation method is the same as in Example 1.

[0041] Comparative Example 1

[0042] Mortar formulation (existing repair mortar): 80 parts sulfoaluminate cement, 120 parts quartz sand, 2 parts redispersible latex powder, 0.3 parts polycarboxylate superplasticizer, and 22 parts water. Preparation method is the same as in Example 1.

[0043] Comparative Example 2

[0044] The mortar formulation consists of: 80 parts sulfoaluminate cement, 120 parts quartz sand, 1.5 parts microencapsulated CO2 adsorbent, 2 parts zeolite, 0.3 parts lithium sulfate, 2 parts redispersible latex powder, 0.15 parts hydrophobically modified nanocellulose, 0.3 parts polycarboxylate superplasticizer, and 22 parts water. The preparation method is the same as in Example 1. Compared to Example 1, this formulation uses an equal mass of quartz sand instead of the dual nanocrystal nuclei.

[0045] Comparative Example 3

[0046] The mortar formulation consists of: 80 parts sulfoaluminate cement, 120 parts quartz sand, 1 part dual nanocrystal nuclei, 3.5 parts zeolite, 0.3 parts lithium sulfate, 2 parts redispersible latex powder, 0.15 parts hydrophobically modified nanocellulose, 0.3 parts polycarboxylate-based water-reducing agent, and 22 parts water. The preparation method is the same as in Example 1. Compared to the formulation in Example 1, this formulation uses an equal mass of zeolite to replace the microencapsulated CO2 adsorbent.

[0047] Comparative Example 4

[0048] The mortar formulation consists of: 80 parts sulfoaluminate cement, 120 parts quartz sand, 1 part dual nanocrystal nuclei, 1.5 parts microencapsulated CO2 adsorbent, 2 parts zeolite, 0.3 parts lithium sulfate, 2 parts redispersible latex powder, 0.15 parts unmodified nanocellulose (molecular weight 80,000 Da), 0.3 parts polycarboxylate superplasticizer, and 22 parts water. The preparation method is the same as in Example 1. Compared to the formulation in Example 1, this formulation replaces the hydrophobically modified nanocellulose with an equal mass of unmodified nanocellulose.

[0049] Comparative Example 5

[0050] Formulation composition: 80 parts sulfoaluminate cement, 120 parts quartz sand, 1 part dual nanocrystal nuclei, 1.5 parts microencapsulated CO2 adsorbent, 2 parts zeolite, 2 parts redispersible latex powder, 0.15 parts hydrophobically modified nanocellulose, 0.3 parts polycarboxylate superplasticizer, and 22 parts water. The preparation method is the same as in Example 1. Compared to the formulation in Example 1, this formulation lacks lithium sulfate.

[0051] In this invention:

[0052] The sulfoaluminate cement is a rapid-hardening sulfoaluminate cement, containing ≥60% anhydrous calcium sulfoaluminate and 15%~25% dicalcium silicate, with an initial setting time ≤30min and a final setting time ≤90min. The quartz sand is continuously graded fine quartz sand with a maximum particle size not exceeding 1.18mm and a fineness modulus of 2.3-3.0. The zeolite is 13X type or NaA type zeolite with a specific surface area ≥500 m² / g. The lithium sulfate is anhydrous lithium sulfate with a particle size of 1-5μm. The redispersible latex powder is ethylene-vinyl acetate copolymer latex powder with a vinyl acetate to ethylene mass ratio of 80:20, a film-forming temperature of -5℃, and an elongation at break ≥300%. The polycarboxylate superplasticizer is a powdered superplasticizer with a water reduction rate of 30%-50%.

[0053] The dual nanocrystal nuclei are a composite powder composed of nano-trisulfate calcium sulfoaluminate and nano-hydrated calcium silicate in a mass ratio of 6:4 to 8:2, and the particle size of the dual nanocrystal nuclei after dispersion is ≤100nm. The preparation method of the dual nanocrystalline nuclei is as follows: (1) 0.6 mol / L CaCl2 solution and 0.2 mol / L Al2(SO4)3 solution are co-precipitated at 5℃ and pH=12.5. After aging for 2h, filtration and washing, nano-trisulfate calcium sulfoaluminate sol is obtained; (2) 0.2 mol / L Na2SiO3 solution is reacted with saturated calcium hydroxide solution at 20℃ and pH=12.5. After aging for 2h, filtration and washing, nano-hydrated calcium silicate sol is obtained; (3) The sols obtained in steps (1) and (2) are mixed at a mass ratio of 6:4~8:2. 1% of the total mass of the two sols before mixing is added as a dispersant and stirred evenly; (4) The mixed sol is centrifuged, washed, freeze-dried at -50℃ and 10Pa for 24h, and then ball-milled and sieved to obtain dual nanocrystalline nuclei powder.

[0054] The core material of the microencapsulated CO2 adsorbent is polyethyleneimine, and the wall material is a pH-responsive polymer (chitosan-sodium alginate complex). The core material is released when the pH is ≤10.5. The microencapsulated CO2 adsorbent is prepared by the complex coagulation method: (1) dissolve polyethyleneimine in water to form a core material solution; (2) disperse the core material solution in a continuous phase in the presence of an emulsifier to form an emulsion; (3) add chitosan and sodium alginate, and complex coagulation occurs under pH=5.0-5.5 conditions, depositing on the surface of the core material; (4) crosslink with glutaraldehyde, wash with alkali, freeze dry to obtain microcapsules with a particle size of 5-50μm.

[0055] The hydrophobically modified nanocellulose is nanocellulose surface-modified with a silane coupling agent, which is selected from at least one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, or octadecyltrichlorosilane. The specific modification steps are as follows: nanocellulose (diameter 10-20 nm, length 100-500 nm) is dispersed in anhydrous ethanol to prepare a 2 wt% suspension; γ-aminopropyltriethoxysilane is added, with the amount being 8% of the nanocellulose mass; the pH is adjusted to 4.5 with acetic acid, and the reaction is stirred at 60℃ for 4 h; after the reaction, the nanocellulose is centrifuged, washed, and vacuum dried at 60℃ for 12 h to obtain the hydrophobically modified nanocellulose.

[0056] In the above embodiments and comparative examples:

[0057] The sulfoaluminate cement used was purchased from Tangshan Arctic Bear Building Materials Co., Ltd., and was a rapid-hardening sulfoaluminate cement grade 52.5.

[0058] When preparing the dual nanocrystal nuclei, the molar ratio of CaCl2 to Al2(SO4)3 was 3:1, the molar ratio of Na2SiO3 to calcium hydroxide was 1:1, the mass ratio of nano-trisulfate calcium sulfoaluminate sol to nano-hydrated calcium silicate sol was 7:3, and the polycarboxylate superplasticizer was PCA-I type powdered polycarboxylate superplasticizer with a water reduction rate of 35%, purchased from Jiangsu Bote New Materials Co., Ltd.

[0059] When preparing the microencapsulated CO2 adsorbent, the concentration of polyethyleneimine in the core material solution was 18 wt%, the emulsifier was Tween 80, and the mass ratio of emulsifier to polyethyleneimine, chitosan, sodium alginate, and glutaraldehyde was 1:10:2:2:0.5. The molecular weight of polyethyleneimine was 70,000 Da, the molecular weight of chitosan was 200,000 Da, and the molecular weight of sodium alginate was 120,000 Da.

[0060] The zeolite was type 13X zeolite, purchased from Shanghai Aladdin Reagent Bioscience Co., Ltd.

[0061] The ethylene-vinyl acetate copolymer latex powder was purchased from Celanese (Nanjing) Chemical Co., Ltd., model Fx2350.

[0062] The hydrophobically modified nanocellulose is γ-aminopropyltriethoxysilane-modified nanocellulose;

[0063] The polycarboxylate superplasticizer is a PCA-I type powdered polycarboxylate superplasticizer with a water reduction rate of 35%, purchased from Jiangsu Bote New Materials Co., Ltd.

[0064] Performance tests were conducted on the mortars of each embodiment and each comparative example, and the results are shown in Table 1. The carbonation depth diagrams of the mortars of each embodiment and each comparative example are shown in the figure below. Figures 1-8 As shown. The test method is as follows:

[0065] 1. Compressive strength and flexural strength: According to GB / T 17671-2021, 40 mm × 40 mm × 160 mm prism specimens were cured to standard for 1 day, 28 days and 90 days for testing. Three parallel specimens were used in each group and the average value was taken.

[0066] 2. Tensile bond strength: Tested according to GB / T 29756-2013. A 50 mm × 50 mm × 5 mm molding frame was placed on a concrete slab and molded. After curing at (20±3)℃ and (60±5)% relative humidity for 28 days, the test was conducted. Ten parallel specimens were tested in each group.

[0067] 3. Carbonization depth: The specimen size is 40 mm × 40 mm × 160 mm. It is tested according to GB / T 50082-2024. The CO2 concentration is (20±3)%, the temperature is (20±2)℃, and the humidity is (70±5)%. After carbonization for 90 days, the carbonization depth is measured by the phenolphthalein indicator method. There are 3 specimens in each group, and 10 points are measured for each specimen and the average value is taken.

[0068] 4. Water absorption rate: Tested according to DL / T 5126-2021. The specimen size is 40 mm × 40 mm × 160 mm. After curing at (20±3)℃ and (60±5)% relative humidity for 28 days, it is dried at 80±2℃ for 48 hours. After cooling, it is weighed and then soaked for 48 hours and weighed again. The water absorption rate is calculated. There are 3 parallel specimens in each group.

[0069] Table 1: Performance test results of each embodiment and comparative example

[0070]

[0071] As can be seen from Table 1, (1) Strength performance: The 1-day compressive strength of Examples 1-3 is ≥30.0MPa, which meets the requirements for rapid repair; the 90-day flexural and compressive strength increases by 7%-9% compared with 28 days, and there is no strength reduction phenomenon; while Comparative Examples 1-5 all show 90-day strength reduction, of which the compressive strength reduction rate of Comparative Example 1 reaches 2.6%, and the reduction rate of Comparative Example 5 (without lithium sulfate) reaches 4.8%, proving the key role of lithium sulfate in crystal stability. (2) Anti-carbonization performance: The 90-day carbonization depth of Examples 1-3 is only 2.6-3.1mm, which is 75%-80% lower than that of Comparative Example 1 (12.3mm); the compressive strength ratio after carbonization is ≥91%, which is much higher than that of Comparative Example 1 (63%). Comparative Example 2 (lacking dual nanocrystal nuclei) showed a 161.3% increase in carbonization depth compared to Example 1, demonstrating that the dense matrix constructed with dual nanocrystal nuclei is the physical basis for carbonization resistance; Comparative Example 3 (lacking microcapsules) showed a 203.2% increase in carbonization depth, highlighting the necessity of the active carbon capture mechanism. (3) Adhesion and impermeability performance: The 28-day tensile bond strength of Examples 1-3 was ≥2.23 MPa, and the water absorption rate was ≤4.5%, which was 22% lower than the 5.8% water absorption rate of Comparative Example 4 (unmodified nanocellulose), demonstrating the impermeability effect of the hydrophobic network.

[0072] In summary, this invention solves the problem of strength reduction and carbonization deterioration of sulfoaluminate cement repair mortar during long-term service through the synergistic effect of multiple mechanisms, namely, "dual nanocrystal nucleus-induced densification + pH-responsive microcapsule active carbon capture + zeolite buffer adsorption + lithium sulfate crystal stabilization + polymer toughening and impermeability".

[0073] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A mortar for repairing sulfoaluminate cement that resists carbonation, characterized in that, By weight, the mortar comprises the following components: 80-90 parts sulfoaluminate cement, 90-120 parts quartz sand, 1-3 parts dual nanocrystal nuclei, 1.5-3 parts microencapsulated CO2 adsorbent, 2-5 parts zeolite, 0.3-0.5 parts lithium sulfate, 2-4 parts redispersible latex powder, 0.15-0.3 parts hydrophobically modified nanocellulose, 0.3-0.8 parts polycarboxylate superplasticizer, and 22-30 parts water; The dual nanocrystal nuclei are composite powders composed of nano-trisulfate calcium sulfoaluminate and nano-hydrated calcium silicate in a mass ratio of 6:4 to 8:2; the microencapsulated CO2 adsorbent is a material with polyethyleneimine as the core material and a pH-responsive polymer as the wall material; the microencapsulated CO2 adsorbent ruptures and releases the core material when pH ≤ 10.5; the pH-responsive polymer is a chitosan-sodium alginate complex.

2. The anti-carbonation sulfoaluminate cement repair mortar according to claim 1, characterized in that, The dual nanocrystalline nuclei were prepared by the following method: nano-trisulfate calcium sulfoaluminate sol was prepared by co-precipitation of CaCl2 solution and Al2(SO4)3 solution; nano-hydrated calcium silicate sol was prepared by reacting Na2SiO3 solution with saturated calcium hydroxide solution; the two sols were dispersed and mixed evenly with polycarboxylic acid water-reducing agent, and then centrifuged, washed, freeze-dried, ball-milled and sieved to obtain the dual nanocrystalline nuclei.

3. The anti-carbonation sulfoaluminate cement repair mortar according to claim 1, characterized in that, Microencapsulated CO2 adsorbents are prepared by a complex coagulation method: an aqueous solution of polyethyleneimine is dispersed in an emulsifier to form an emulsion; then chitosan and sodium alginate are added for complex coagulation, followed by glutaraldehyde crosslinking, alkali washing, and freeze drying to obtain microencapsulated CO2 adsorbents.

4. The anti-carbonation sulfoaluminate cement repair mortar according to claim 1, characterized in that, The particle size of the dispersed dual nanocrystal nuclei is ≤100nm.

5. The anti-carbonation sulfoaluminate cement repair mortar according to claim 1, characterized in that, The sulfoaluminate cement is a rapid-hardening sulfoaluminate cement, wherein the content of anhydrous calcium sulfoaluminate is ≥60%, the content of dicalcium silicate is 15%~25%, the initial setting time is ≤30min, and the final setting time is ≤90min.

6. The anti-carbonation sulfoaluminate cement repair mortar according to claim 1, characterized in that, The zeolite is of type 13X or type NaA, with a specific surface area ≥ 500 m² / g.

7. The anti-carbonation sulfoaluminate cement repair mortar according to claim 1, characterized in that, The redispersible latex powder is an ethylene-vinyl acetate copolymer latex powder, with a mass ratio of vinyl acetate to ethylene of 80:20, a film-forming temperature of -5℃, and an elongation at break of ≥300%.

8. The anti-carbonation sulfoaluminate cement repair mortar according to claim 1, characterized in that, The hydrophobically modified nanocellulose is nanocellulose with a surface modified by a silane coupling agent.

9. A method for preparing the anti-carbonation sulfoaluminate cement repair mortar as described in any one of claims 1-8, characterized in that, The sulfoaluminate cement, quartz sand, and zeolite are mixed evenly with a uniform mixture of double nanocrystal nuclei, microencapsulated CO2 adsorbent, redispersible latex powder, hydrophobically modified nanocellulose, lithium sulfate, and polycarboxylate superplasticizer. Water is then added and stirred until the slurry is homogeneous to obtain the repair mortar.

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