Anti-carbonization sulphoaluminate cement repair mortar and preparation method thereof

Abstract

The invention discloses anti-carbonization sulphoaluminate cement repair mortar and a preparation method thereof, and belongs to the technical field of building materials. The mortar is prepared from sulphoaluminate cement, quartz sand, double nanocrystal nucleuses, a microencapsulated CO2 adsorbent, zeolite, lithium sulfate, redispersible latex powder, hydrophobic modified nanocellulose, a polycarboxylic acid water reducer and water. Wherein the double nanocrystal nucleus is composite powder composed of nano trisulfide calcium sulphoaluminate and nano calcium silicate hydrate according to the mass ratio of 6: 4-8: 2, and the microencapsulated CO2 adsorbent is a material with polyethyleneimine as a core material and a pH response type polymer as a wall material. According to the invention, the synergistic improvement of super early strength, high bonding strength, continuous increase of later strength without shrinkage and excellent carbonization resistance of the mortar is realized, and the mortar is especially suitable for rapid repair engineering of concrete in a high CO2 concentration environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building materials, and more particularly to an anti-carbonization sulphoaluminate cement repair mortar and a preparation method thereof, which is particularly suitable for rapid repair engineering of concrete under high CO2 concentration environment (such as underground pipe gallery, industrial plant, tunnel, marine structure, etc.). BACKGROUND

[0002] In order to meet the rapid repair requirements of pipe gallery, plant, tunnel, marine engineering, building, airport runway, highway, high-speed railway, dam repair, etc., various special cementitious materials have been developed and used, including geopolymer, magnesium phosphate cement, oxychloride magnesium cement, aluminate cement and sulphoaluminate cement (CSA), etc. Among them, CSA has the advantages of short setting time, high early strength, early micro-expansion and low shrinkage in later period, etc., and can better meet the performance requirements of special service environment and working conditions, so its application is particularly widespread.

[0003] Rapid repair engineering has high requirements on early performance, but it inevitably needs to face problems such as long-term service stability. Researchers have carried out a lot of research, and reported the advantages of CSA such as early strength, high strength and good volume stability, but there are also problems such as poor long-term performance stability. For example, due to the deficiency of SO4 2- , the internal hydration product AFt is converted into monosulfate type calcium sulphoaluminate, which is caused by: on the one hand, due to the conversion of AFt into new products, the micro volume begins to decrease, thereby causing the volume stability of CSA to be unstable, resulting in shrinkage and cracking of CSA, on the other hand, due to the presence of cracks, the internal density of CSA decreases, and the mechanical strength of CSA begins to decrease and shrink.

[0004] The environment has a great influence on the service performance of CSA, including sulphate attack, chloride attack, freeze-thaw cycle, carbonization, etc. The influence of carbonization is particularly widespread. Carbonization will cause the decomposition and conversion of internal key hydration product AFt, accelerate the appearance of internal cracks and strength shrinkage. In the long-term use process, with the deepening of carbonization degree, the building structure may appear cracks, peeling and other phenomena, which greatly shortens the service life of the building structure, increases the maintenance cost and safety risk. Therefore, improving the anti-carbonization ability of CSA is particularly important for its long-term service use in rapid repair engineering.

[0005] The existing repair mortar focuses on improving the "early strength", ignores the long-term durability, and the performance decays quickly in complex environment. Some studies also focus on the carbonation resistance performance, for example, the prior art CN120423841A discloses an early strength fast hardening type carbonation resistant cement-based repair mortar, which improves the carbonation resistance performance by using carbonation resistant fibers and additives, but the technology only shows the compressive strength retention rate after 14 days of carbonation, and does not involve solving the problems of late strength reduction and carbonation depth; the prior art CN120025132A discloses a road repair mortar, which focuses on the 4h early strength performance, and lacks the study on the carbonation resistance performance.

[0006] The present application is aimed at the problem that the repair mortar, especially the sulphoaluminate cement-based repair mortar, is prone to service failure due to carbonation during service, and the performance breakthrough is achieved through the synergy of active CO2 capture, simultaneous matrix reinforcement, stable crystal structure, etc. SUMMARY

[0007] The present application aims to overcome the shortcomings of the prior art, and provides an anti-carbonation sulphoaluminate cement repair mortar and a preparation method thereof. Through the "induction-adsorption-stabilization-shielding" four-in-one mechanism, the early strength, high strength, continuous growth of late strength without reduction, high bonding strength and significant improvement of carbonation resistance performance are achieved, and the performance bottleneck problem of concrete structure repair material is solved.

[0008] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0009] An anti-carbonation sulphoaluminate cement repair mortar, by weight, the mortar comprises the following components: sulphoaluminate cement 80-90 parts, quartz sand 90-120 parts, double nanocrystalline core 1-3 parts, microencapsulated CO2 adsorbent 1.5-3 parts, zeolite 2-5 parts, lithium sulfate 0.3-0.5 parts, redispersible latex powder 2-4 parts, hydrophobically modified nanocellulose 0.15-0.3 parts, polycarboxylate superplasticizer 0.3-0.8 parts, and water 22-30 parts.

[0010] The double nanocrystalline core is a composite powder composed of nano calcium sulphoaluminate of three sulfur type and nano hydrated calcium silicate in a mass ratio of 6:4~8:2; the microencapsulated CO2 adsorbent is a material with polyethyleneimine as core material and pH-responsive polymer as wall material.

[0011] The present application further provides that the double nanocrystalline core is prepared by the following method: nano calcium sulphoaluminate of three sulfur type sol is prepared by co-precipitation of CaCl2 solution and Al2(SO4)3 solution; nano hydrated calcium silicate sol is prepared by reaction of Na2SiO3 solution and saturated calcium hydroxide solution; the two sols are uniformly dispersed and mixed by taking polycarboxylate superplasticizer as dispersant, and then centrifuged, washed, freeze-dried and ball milled and sieved to obtain the double nanocrystalline core.

[0012] The application is further provided with the microencapsulated CO2 adsorbent prepared by complex coacervation method: the polyethyleneimine aqueous solution is dispersed in the emulsifier to form an emulsion; then chitosan and sodium alginate are added for complex coacervation, followed by glutaraldehyde crosslinking, alkali washing, and freeze-drying treatment to obtain the microencapsulated CO2 adsorbent.

[0013] The application is further provided with the dual-nanocrystal core dispersion particle size ≤ 100 nm.

[0014] The application is further provided with the microencapsulated CO2 adsorbent being broken to release the core material at pH ≤ 10.5; and the pH-responsive polymer being a chitosan-sodium alginate complex.

[0015] The application is further provided with the sulphoaluminate cement being a fast-hardening sulphoaluminate cement, wherein the anhydrous calcium sulphoaluminate content is ≥ 60%, the dicalcium silicate content is 15% to 25%, the initial setting time is ≤ 30 min, and the final setting time is ≤ 90 min.

[0016] The application is further provided with the zeolite being a 13X type or NaA type zeolite with a specific surface area ≥ 500 m² / g.

[0017] The application is further provided with the redispersible latex powder being an ethylene-vinyl acetate copolymer latex powder, the mass ratio of vinyl acetate to ethylene being 80:20, the film forming temperature being -5°C, and the elongation at break being ≥ 300%.

[0018] The application is further provided with the hydrophobically modified nanocellulose being nanocellulose surface modified by a silane coupling agent.

[0019] A preparation method of an anti-carbonization sulphoaluminate cement repair mortar, wherein a uniform mixture of sulphoaluminate cement, quartz sand, and zeolite is mixed with a uniform mixture of dual-nanocrystal core, microencapsulated CO2 adsorbent, redispersible latex powder, hydrophobically modified nanocellulose, lithium sulfate, and polycarboxylate superplasticizer, stirred uniformly, and then water is added and stirred until the slurry is uniform to obtain the repair mortar.

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

[0021] 1. Dual-nanocrystal core reinforcement: The trithio type calcium sulphoaluminate nanocrystal core in the dual-nanocrystal core acts as a template for the growth of tobermorite crystals, inducing tobermorite to nucleate heterogeneously on the surface of the seed, significantly accelerating the formation rate of ettringite and providing a large number of nucleation sites, leading to the formation of more and smaller tobermorite crystals. Small-sized crystals have higher specific surface area and lower defect density, and the crystal structure is more stable. In addition, the trithio type calcium sulphoaluminate nanocrystal core itself or the fine tobermorite formed early reacts preferentially with the invading CO2, consuming part of the CO2 and providing a certain buffer time for the internal tobermorite. The hydrated calcium silicate nanocrystal core in the dual-nanocrystal core acts as a template and nucleation site for the formation of C-S-H gel, strongly promoting the hydration of the silicate phase, leading to the early, large and rapid generation of C-S-H gel. The rapidly generated C-S-H gel fills capillary pores, refines pore size, and blocks connected pore channels, significantly reducing the total porosity, average pore size and permeability of the cement stone, forming a highly dense matrix, which constitutes a strong physical diffusion barrier, effectively hindering the migration of CO2 gas and moisture into the interior. When the mass ratio of nanometer trithio type calcium sulphoaluminate sol to nanometer hydrated calcium silicate sol is 6:4~8:2, the synergistic effect of "macro-pore skeleton reinforcement + micro-pore gel filling" can be achieved, and the pore structure of the mortar is optimized comprehensively.

[0022] 2. Active anti-carbonation and synergistic adsorption: The microcapsule wall material uses a chitosan-sodium alginate complex. When the pH of the repaired mortar surface and interior caused by carbonation decreases to ≤10.5, the degree of protonation of chitosan decreases and the carboxyl group of sodium alginate deprotonates, the wall material structure dissociates and breaks, and the core material polyethyleneimine is accurately released. The amino group in the polyethyleneimine molecule can chemically adsorb CO2 to generate carbamate, achieving in-situ capture of CO2; zeolite is selected as 13X type or NaA type with specific surface area ≥500 m 2 / g, its microporous structure can physically adsorb residual CO2 not captured by polyethyleneimine, and the ion exchange performance of zeolite can buffer the pH change of the system, prolong the response window period of the microcapsule releasing the core material, forming a dual anti-carbonation barrier of "chemical adsorption + physical adsorption".

[0023] 3. Hydrophobic network construction anti-permeability barrier: Redispersible latex powder forms a continuous polymer film at the late hydration stage, and enhances the interfacial bonding with the old concrete base layer through the "molecular chain penetration-mechanical anchoring" effect; the hydroxyl groups on the surface of the hydrophobically modified nanocellulose form hydrogen bonds with the silicate groups of the old concrete base layer, together with the polymer film to improve the bonding strength; its nanoscale fibers can be uniformly dispersed in the cement mortar to form a three-dimensional network structure, playing a role in strengthening and toughening. At the same time, the hydrophobic groups of the hydrophobically modified nanocellulose are arranged in a continuous hydrophobic film on the pore surface, reducing the invasion of water and blocking the transmission path of carbonation medium.

[0024] 4. Ion regulation stabilizes crystal structure: Lithium ions released by lithium sulfate can enter the hexagonal channels of ettringite and compete with water molecules for coordination, forming a Li-AFt solid solution to improve the thermodynamic stability of the crystal. By adding lithium sulfate, the present application not only provides Li + stabilizes AFt, but also provides SO4 2- supplemental sulfur source to prevent the conversion of AFt to monosulfate type, achieving "one dose, double effect". BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 Carbonation depth map of the mortar of Example 1;

[0026] Figure 2 Carbonation depth map of the mortar of Example 2;

[0027] Figure 3 Carbonation depth map of the mortar of Example 3;

[0028] Figure 4 Carbonation depth map of the mortar of Comparative Example 1;

[0029] Figure 5 Carbonation depth map of the mortar of Comparative Example 2;

[0030] Figure 6 Carbonation depth map of the mortar of Comparative Example 3;

[0031] Figure 7 Carbonation depth map of the mortar of Comparative Example 4;

[0032] Figure 8 Carbonation depth map of the mortar of Comparative Example 5. DETAILED DESCRIPTION

[0033] The technical solutions of the present application will be described in detail below with reference to the accompanying drawings and embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0034] Example 1

[0035] Mortar formula composition: 80 parts of sulphoaluminate cement, 120 parts of quartz sand, 1 part of double-nanometer crystal core, 1.5 parts of microencapsulated CO2 adsorbent, 2 parts of zeolite, 0.3 parts of lithium sulfate, 2 parts of redispersible latex powder, 0.15 parts of hydrophobically modified nanocellulose, 0.3 parts of polycarboxylate superplasticizer, and 22 parts of water.

[0036] (1) Add sulphoaluminate cement, quartz sand, zeolite into a mixer, dry mix for 2-3 minutes; (2) Disperse double nanocrystal core, microencapsulated CO2 adsorbent, re-dispersible latex powder, hydrophobically modified nanocellulose, lithium sulfate and polycarboxylate superplasticizer in a high-speed disperser for 3-5 minutes, then add the mixture of step (1), continue to dry mix for 3 minutes; (3) Add water, stir for 5-8 minutes until the slurry is uniform, to obtain the carbonation-resistant sulphoaluminate cement repair mortar.

[0037] Example 2

[0038] Mortar formulation composition: sulphoaluminate cement 90 parts, quartz sand 90 parts, double nanocrystal core 3 parts, microencapsulated CO2 adsorbent 3 parts, zeolite 5 parts, lithium sulfate 0.5 parts, re-dispersible latex powder 4 parts, hydrophobically modified nanocellulose 0.3 parts, polycarboxylate superplasticizer 0.8 parts, water 30 parts. Preparation method same as Example 1.

[0039] Example 3

[0040] Mortar formulation composition: sulphoaluminate cement 85 parts, quartz sand 105 parts, double nanocrystal core 2 parts, microencapsulated CO2 adsorbent 2.3 parts, zeolite 3.5 parts, lithium sulfate 0.4 parts, re-dispersible latex powder 3 parts, hydrophobically modified nanocellulose 0.2 parts, polycarboxylate superplasticizer 0.5 parts, water 26 parts. Preparation method same as Example 1.

[0041] Comparative Example 1

[0042] Mortar formulation composition (existing repair mortar): sulphoaluminate cement 80 parts, quartz sand 120 parts, re-dispersible latex powder 2 parts, polycarboxylate superplasticizer 0.3 parts, water 22 parts. Preparation method same as Example 1.

[0043] Comparative Example 2

[0044] Mortar formulation composition: sulphoaluminate cement 80 parts, quartz sand 120 parts, microencapsulated CO2 adsorbent 1.5 parts, zeolite 2 parts, lithium sulfate 0.3 parts, re-dispersible latex powder 2 parts, hydrophobically modified nanocellulose 0.15 parts, polycarboxylate superplasticizer 0.3 parts, water 22 parts. Preparation method same as Example 1. Compared with Example 1, this formulation replaces double nanocrystal core with equal mass of quartz sand.

[0045] Comparative Example 3

[0046] Mortar formulation composition: sulphoaluminate cement 80 parts, quartz sand 120 parts, double nanocrystal core 1 part, zeolite 3.5 parts, lithium sulfate 0.3 parts, re-dispersible latex powder 2 parts, hydrophobically modified nanocellulose 0.15 parts, polycarboxylate superplasticizer 0.3 parts, water 22 parts. Preparation method same as Example 1. Compared with Example 1 formulation, this formulation replaces microencapsulated CO2 adsorbent with equal mass of zeolite.

[0047] Comparative Example 4

[0048] Mortar formulation composition: sulphoaluminate cement 80 parts, quartz sand 120 parts, double nanocrystalline core 1 part, microencapsulated CO2 adsorbent 1.5 parts, zeolite 2 parts, lithium sulfate 0.3 parts, redispersible latex powder 2 parts, unmodified nanocellulose 0.15 parts (molecular weight 80000 Da), polycarboxylate based superplasticizer 0.3 parts, water 22 parts. Preparation method same as Example 1. Compared to the formulation of Example 1, this formulation replaces the same amount of hydrophobically modified nanocellulose with unmodified nanocellulose.

[0049] Comparative Example 5

[0050] Formulation composition: sulphoaluminate cement 80 parts, quartz sand 120 parts, double nanocrystalline core 1 part, microencapsulated CO2 adsorbent 1.5 parts, zeolite 2 parts, redispersible latex powder 2 parts, hydrophobically modified nanocellulose 0.15 parts, polycarboxylate based superplasticizer 0.3 parts, water 22 parts. Preparation method same as Example 1. Compared to the formulation of Example 1, this formulation lacks lithium sulfate.

[0051] In the present invention:

[0052] The sulphoaluminate cement is a fast hardening sulphoaluminate cement, wherein the anhydrous calcium sulphoaluminate content is > 60%, the dicalcium silicate content is 15-25%, the initial setting time is < 30 min, and the final setting time is < 90 min. The quartz sand is a continuous graded fine quartz sand with a maximum particle size of < 1.18 mm and a fineness modulus of 2.3-3.0. The zeolite is a 13X or NaA type zeolite with a specific surface area of > 500 m² / g. The lithium sulfate is anhydrous lithium sulfate with a particle size of 1-5 pm. 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°C, and an elongation at break of > 300%. The polycarboxylate based superplasticizer is a powdered superplasticizer with a water-reducing 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 nanocellulose with a γ-aminopropyltriethoxysilane surface modified.

[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; 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.

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 after dispersion of the dual nanocrystal nuclei is ≤100nm.

5. The anti-carbonation sulfoaluminate cement repair mortar according to claim 1, characterized in 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.

6. 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.

7. 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.

8. 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%.

9. 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.

10. A method for preparing the anti-carbonation sulfoaluminate cement repair mortar as described in any one of claims 1-9, 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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