Photocured hydrogel encapsulating microorganisms for concrete repair and method of making and use

Abstract

This invention discloses a concrete repair agent encapsulated in photocurable hydrogel, its preparation method, and its application, belonging to the field of building materials technology. This invention solves problems in concrete repair technology such as bacterial inactivation under freeze-thaw conditions, significant deterioration of concrete mechanical properties after hydrogel incorporation, and easy debonding. This invention mixes cellulose nanofibers, water, surfactants, monomers, octadecyl methacrylate, photoinitiator, nano-silica, crosslinking agent, and Sunset Yellow. The resulting hydrogel precursor solution is mixed with a suspension of *Bacillus pseudosternus*, and printed layer by layer using DLP photocurable 3D printing technology to obtain concrete repair agent powder. This powder is then mixed with cement, sand, calcium lactate, polycarboxylate superplasticizer, and water to form a mold. This invention utilizes the synergistic effect of the bacterial protection provided by the photocurable dense network and the interface strengthening effect of nano-silica to achieve high strength and durability of concrete and self-healing of cracks. After cracking, the specimens can be cured in situ under normal temperature or freeze-thaw cycles.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, and relates to a concrete repair agent containing microorganisms encapsulated in photocurable hydrogel, its preparation method, and its application. Background Technology

[0002] Concrete, as the most widely used building material in modern infrastructure construction, is prone to microcracks during use due to load, shrinkage, carbonation, and drying. These microcracks not only compromise the integrity of the concrete structure but also provide channels for the transmission of corrosive media such as moisture and chloride ions, accelerating steel corrosion and matrix deterioration, and severely shortening the service life of concrete structures. To address this problem, microbial-induced calcium carbonate precipitation (MICP) technology has emerged. This technology utilizes microbial metabolism to generate calcium carbonate minerals in situ at the cracks, thereby achieving self-healing of concrete cracks. It has attracted significant attention due to its advantages such as in-situ mineralization, enormous self-repair potential, and environmental friendliness.

[0003] However, MICP technology faces two major challenges in practical applications: First, the continuous hydration process of concrete and the highly alkaline pore fluid significantly compress the living space of bacteria and kill cells; second, concrete used in cold regions undergoes repeated freeze-thaw cycles (FTCs), and the formation and melting of ice crystals causes fatal physical damage to the cell membranes of microorganisms, leading to the inactivation of a large number of bacteria before cracks appear, resulting in the loss of repair function. Therefore, to solve the problem of microbial survival in harsh environments, it is necessary to introduce a carrier to protect the microorganisms. Existing technologies mostly use porous inorganic materials such as biochar, ceramsite, and expanded perlite as carriers; however, these materials generally suffer from uneven pore size distribution and poor water retention. Although natural polysaccharides or synthetic polymer hydrogels have good biocompatibility, their mechanical strength is extremely low, and direct incorporation into cement easily leads to swelling and disintegration, significantly reducing the mechanical properties of the concrete matrix and failing to meet engineering load-bearing requirements. More importantly, traditionally extruded or molded hydrogels lack precise control over their morphology, size, and spatial distribution. Their interfacial bonding with the cement matrix is ​​relatively weak, and they are prone to interfacial debonding under external loads or freeze-thaw stress, leading to the failure of the repair system.

[0004] Therefore, how to achieve precise control of the microstructure of the carrier, alleviate or even compensate for the significant deterioration of matrix strength caused by traditional hydrogel carriers, solve the problem of interfacial debonding under freeze-thaw conditions, and achieve concrete repair under extreme conditions are the technical challenges that urgently need to be overcome in this field. Summary of the Invention

[0005] In order to solve the above-mentioned problems in the prior art, the present invention provides a concrete repair agent encapsulating microorganisms in photocurable hydrogel, its preparation method and application.

[0006] The technical solution of the present invention is as follows: One objective of this invention is to provide a method for preparing a concrete repair agent encapsulated in a photocurable hydrogel, the method comprising the following steps: S1. Preparation of photocurable dual crosslinked hydrogel precursor solution modified with nano-silica (NS): 0.25-2 parts of cellulose nanofibers, 40-60 parts of deionized water, 5-9 parts of surfactant, 20-40 parts of monomer A, 5-15 parts of monomer B, 0.1-1 parts of octadecyl methacrylate, 0.5-2 parts of photoinitiator, 2-5.5 parts of nano-silica and 0.2-1 parts of crosslinking agent are mixed, and finally 0.01-0.15 parts of Sunset Yellow are added to obtain the photocurable dual crosslinked hydrogel precursor solution modified with nano-silica; S2. Microbial spore encapsulation: The suspension of Bacillus pseudosturcium was mixed evenly with the precursor solution of photocurable double crosslinked hydrogel modified with nano-silica to obtain a bacterial precursor solution. S3, DLP photopolymerization 3D printing molding: DLP photopolymerization 3D printing technology is used to print the bacterial precursor solution layer by layer. The microbial spores are fixed in situ in the nano-silica modified double cross-linked hydrogel network by photo-initiated polymerization and cross-linking reaction. After printing, the micron-sized modified hydrogel powder is obtained by drying, grinding and sieving, which is the concrete repair agent with microorganism encapsulated by photopolymerization hydrogel.

[0007] Further specifying, the surfactant in S1 is sodium dodecyl sulfate (SDS), hexadecyltrimethylammonium bromide (CTAB), polyoxyethylene sorbitan monooleate (Tween-80) or sorbitan monooleate (Span-80), monomer A is at least one of acrylamide (AM), N,N-dimethylacrylamide (DMAA), and methacrylamide (MAM), monomer B is at least one of acrylic acid (AA), methacrylic acid (MAA), and itaconic acid (IA), photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO), 1-hydroxycyclohexylphenyl ketone (HCPK) or bisacylphosphine oxide (BAPO), and crosslinking agent is polyethylene glycol diacrylate (PEGDA), N,N'-methylenebisacrylamide (MBA), ethylene glycol dimethacrylate (EGDMA) or N-hydroxymethylacrylamide (NMA).

[0008] Further specifying, in S1, 1 part cellulose nanofibers, 50.1 parts deionized water, 7 parts sodium dodecyl sulfate, 30 parts acrylamide, 10 parts acrylic acid, 0.1-1 part octadecyl methacrylate, 1 part 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 3.6 parts nano silica, and 0.5 parts polyethylene glycol diacrylate are mixed, and finally 0.01-0.15 parts sunset yellow are added to obtain a nano silica-modified photocurable double crosslinked hydrogel precursor solution; Further specified, the amount of nano-silica added in S1 is 8-10 wt.% of the total mass of the monomers, and the particle size of the nano-silica is 10-30 nm.

[0009] To further define the specific mixing process in S1, it is as follows: Step 1: Disperse cellulose nanofibers in deionized water, add surfactant, and stir at 50 °C for 0.5 h to obtain a uniform dispersion system; Step 2: Maintain a constant temperature of 50 °C, and add monomer A, monomer B, photoinitiator and octadecyl methacrylate sequentially to the uniformly dispersed system, and continue stirring for 2 h until a uniform and transparent micelle solution is formed. Step 3: Add the ultrasonically dispersed nano-silica to the micelle solution and continue stirring. Then add the crosslinking agent and finally add Sunset Yellow to obtain the nano-silica modified photocurable double crosslinked hydrogel precursor solution.

[0010] To further refine the process, sunset yellow is added in step three to reduce light scattering and improve print resolution.

[0011] Further specifying the optical density (OD) value of the *Bacillus pseudostrongylus* suspension in S2, 600 The volume ratio of the nano-silica modified photocurable double crosslinked hydrogel precursor solution to the Bacillus pseudostrongylus suspension is (4-6):1.

[0012] Furthermore, the volume ratio of the nano-silica modified photocurable double crosslinked hydrogel precursor solution to the Bacillus pseudostrongylus suspension is 5:1.

[0013] Further specifying, the light source wavelength in the S3 printing process is 405 nm, and the printing parameters are: single-layer printing thickness is set to 0.05-0.15 mm, single-layer exposure time is controlled to 5-12 s, and light intensity is 3.0-5.0 mW / cm². 2 Printing is performed at 25°C.

[0014] To further refine the specifications, the printing parameters are as follows: single-layer printing thickness is set to 0.1 mm, single-layer exposure time is controlled at 8 seconds, and light intensity is 4.0 mW / cm². 2 .

[0015] Further specifying, the particle size of the concrete repair agent containing microorganisms encapsulated in the photocurable hydrogel in S3 is <75 μm.

[0016] The second objective of this invention is to provide a concrete repair agent containing microorganisms encapsulated in a photocurable hydrogel obtained by the above preparation method.

[0017] The third objective of this invention is to provide a self-healing concrete, which is obtained by mixing and stirring 1-5 parts of the above-mentioned light-cured hydrogel-encapsulated microorganism concrete repair agent, 800-1200 parts of ordinary silicate cement, 400-600 parts of mixing water, 1500-2500 parts of standard sand, 1-6 parts of polycarboxylate superplasticizer and 5-15 parts of calcium lactate, and then casting it into shape.

[0018] Further specifying, the self-healing concrete is made by mixing and stirring 3 parts of the above-mentioned light-cured hydrogel-encapsulated microorganism concrete repair agent, 1000 parts of ordinary silicate cement, 500 parts of mixing water, 2000 parts of standard sand, 6 parts of polycarboxylate superplasticizer and 10 parts of calcium lactate, and then casting it into shape.

[0019] Further specified, the dosage of calcium lactate is 0.417-1.875% of the mass of ordinary Portland cement, and the amount of polycarboxylate superplasticizer added is adjusted according to the flow performance requirements of concrete to ensure that the paste has good workability and uniform dispersion performance.

[0020] Furthermore, the amount of calcium lactate is specified as 1% of the mass of ordinary Portland cement.

[0021] Furthermore, self-healing concrete is suitable for self-repairing cracks in normal temperature environments or freeze-thaw cycles of -20 to 20 ℃.

[0022] The beneficial effects of this invention are as follows: (1) In this invention, an NS-modified photocurable dual crosslinked hydrogel precursor solution is combined with OD 600 A 0.6% suspension of *Bacillus pseudosturcium* was mixed, and the resulting mixture was exposed layer by layer using DLP photopolymerization 3D printing technology. *Bacillus pseudosturcium* was in situ encapsulated within a dense cross-linked network formed by NS modification. After drying and grinding, a modified hydrogel powder was obtained, which is a photopolymerized hydrogel-encapsulated microorganism concrete repair agent. This powder was then mixed with cement, water, standard sand, polycarboxylate superplasticizer, and calcium lactate and cast into a mold. The resulting specimens, after cracking, could be in situ cured under ambient temperature or freeze-thaw cycles of -20 to 20 °C. This invention utilizes the synergistic effect of the photopolymerized dense network's bacterial protection and NS's interface strengthening to effectively suppress the significant mechanical property degradation caused by traditional hydrogel carriers. It overcomes the problems of easy debonding and bacterial inactivation under freeze-thaw conditions, achieving high strength, durability, and self-healing of cracks under extreme environments.

[0023] (2) This invention proposes a nano-silica modified hydrogel based on photocuring 3D printing. DLP photocuring 3D printing technology is applied to a hydrogel carrier containing microorganisms. A high-precision, dense cross-linked network is constructed through photocuring additive manufacturing. In the presence of a photoinitiator, light irradiation induces efficient polymerization and cross-linking reactions in the precursor system, forming an extremely dense double-cross-linked three-dimensional network. This network not only precisely controls the carrier morphology, allowing *Bacillus pseudosturcium* to be uniformly immobilized in situ within the network structure, but also, in conjunction with the interfacial strengthening effect of NS, effectively resists the rapid invasion of strong alkali ions and the physical penetration of ice crystal growth. Without sacrificing the material exchange channels, it provides excellent physical shielding against high alkali and freeze-thaw conditions for the microorganism *Bacillus pseudosturcium*, significantly improving the long-term survival rate of *Bacillus pseudosturcium* in high-alkali and freeze-thaw environments, ultimately achieving high strength, durability, and self-healing properties in concrete under normal temperature and freeze-thaw conditions. The photocuring hydrogel-encapsulated microorganism concrete repair agent of this invention has a porous network structure, which can be used for the uniform dispersion of subsequent cement-based materials and the construction of microbial self-healing functions.

[0024] (3) The NS introduced in this invention enhances the mechanical strength of the hydrogel carrier itself through the filling effect and hydrogen bond network. On the other hand, the extremely high pozzolanic activity of NS can undergo a secondary hydration reaction with the cement hydration product Ca(OH)2 to generate additional CSH gel, which greatly enhances the adhesion between the carrier and the cement matrix interface and effectively resists the interface debonding caused by freeze-thaw cycles.

[0025] (4) This invention utilizes the dual synergistic effect of NS-promoted interfacial hydration and Bacillus pseudostrongylus-induced calcium carbonate mineralization to achieve crack repair under both ambient temperature and freeze-thaw environments. Experiments show that at ambient temperature of 23 ℃, the specimen can achieve complete surface healing in 7 days; even under extreme freeze-thaw environments of -20~20 ℃, crack healing can be achieved in 28 days. At the same time, the ultrasonic pulse velocity (UPV) achieves the highest level of recovery, the resistance to chloride ion penetration is significantly improved, the repair performance of damaged concrete is excellent, and the integrity after repair is high. Attached Figure Description

[0026] Figure 1 The process flow diagrams are for embodiments 1-2 of the present invention; Figure 2 SEM images of the concrete repair agent containing microorganisms encapsulated in photocurable hydrogel in Example 1 and Comparative Example 2, where (a) is Comparative Example 2 and (b) is Example 1; Figure 3 The diagram shows the viable bacterial concentrations in simulated cement pore solutions of the bacterial solutions in Example 1 and Comparative Example 4, as well as the concrete repair agent powder containing microorganisms encapsulated by photocurable hydrogel. Figure 4The compressive strength and flexural strength at 3 days, 7 days, and 28 days of the mortar specimens of Example 1 and Comparative Examples 1-4 are shown. Figure 5 The crack morphology of mortar specimens with cracks in Examples 1-2 and Comparative Examples 1-8 at different ages under 23°C and freeze-thaw conditions; Figure 6 Statistical graphs of UPV recovery rate for mortar specimens at healing ages of 0 days and 28 days; Figure 7 The images show scanning electron microscope (SEM) images and magnified views of the filling material at the cracks of mortar specimens from Examples 1-2, Comparative Examples 2-4, and Comparative Examples 6-8 at 28 days of healing age. In Example 1, (a1) is a magnified view of the red area in (a); in Comparative Example 2, (b1) is a magnified view of the red area in (b); in Comparative Example 3, (c1) is a magnified view of the red area in (c); in Comparative Example 4, (d1) is a magnified view of the red area in (d); in Example 2, (e1) is a magnified view of the red area in (e); in Comparative Example 6, (f1) is a magnified view of the red area in (f); in Comparative Example 7, (g1) is a magnified view of the red area in (g); and in Comparative Example 8, (h1) is a magnified view of the red area in (h). Detailed Implementation

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0028] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0029] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0030] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0031] The ordinary silicate cement described below is PO 42.5 cement. The polycarboxylate superplasticizer was purchased from Sichuan Dongrun Baisheng New Material Co., Ltd., and is a standard type of high-performance polycarboxylate superplasticizer. Bacillus pseudosturcium was purchased from the China Industrial Microbial Culture Collection Center (CICC), with the accession number CICC10722.

[0032] Example 1 Step 1: Preparation of *Bacillus pseudostrongylus* suspension: The liquid culture medium was prepared by adding 5.0 g / L peptone, 3.0 g / L beef extract, 5.0 g / L sodium chloride, 0.0015 g / L manganese sulfate, and 1 L distilled water. After steam sterilization at 121℃ and 0.1 MPa for 20 min, the medium was cooled to room temperature. *Bacillus pseudostrongylus* was inoculated at 1% of the total liquid culture medium volume in a laminar flow hood. The inoculated culture was then placed in a shaker and cultured at 27℃ and 120 rpm for 24 h. The culture was centrifuged at 6000 rpm for 5 min to obtain a precipitate, which was diluted with sterile water and its OD value was adjusted. 600 To a concentration of 0.6, a suspension of *Bacillus pseudostrongylus* was obtained; Step 2: Preparation of NS-modified photocurable double crosslinked hydrogel precursor solution: One part of cellulose nanofibers with a diameter of 10-50 nm and a length of 1-3 µm was dispersed in 50.1 parts of deionized water. Seven parts of sodium dodecyl sulfate were added, and the mixture was magnetically stirred at 50 °C for 0.5 h to obtain a uniform dispersion. Then, 30 parts of acrylamide, 10 parts of acrylic acid, 1 part of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and 0.4 parts of octadecyl methacrylate were added to the system, and stirring was continued for 2 h until a uniform and transparent micelle solution was formed. Ultrasonically dispersed nano-silica with a particle size of 10-30 nm was added to the micelle solution at an amount of 9 wt.% of the total monomer mass. After ultrasonic dispersion, stirring was continued for 1 h to utilize the hydrogen bond interaction between the hydroxyl groups on the surface of the nano-silica and the carboxyl groups of the acrylamide monomer. Finally, 0.5 parts of polyethylene glycol diacrylate and 0.05 parts of sunset yellow dye were added, and stirring was continued for 30 min to ensure uniform mixing of the components, thus obtaining a nano-silica-modified photocurable double crosslinked hydrogel precursor solution. Store in the dark at ℃ and 100 r / min. Step 3: Encapsulation of microbial spores: The photocurable double crosslinked hydrogel precursor solution modified with nano-silica was cooled to room temperature to avoid high temperature damage to bacterial activity. The precursor solution was mixed with the Bacillus pseudostrongylus suspension prepared in step one at a volume ratio of 5:1 and gently stirred until uniformly dispersed to complete the microbial spore encapsulation and obtain the bacterial precursor solution. Step 4: DLP (Digital Light Processing) photopolymerization 3D printing molding: A commercial DLP 3D printer equipped with a 405 nm light source was used to print the bacterial precursor solution layer by layer: the single-layer exposure thickness was set to 0.1 mm, the single-layer exposure time was 8 s, and the light intensity was controlled at 4.0 mW / cm². Under controlled light-induced polymerization, Bacillus pseudosternum was in situ immobilized in a dense double cross-linked network modified with nano-silica using a layer-by-layer molding process. After printing, the molded block was placed in a vacuum drying oven at 40 ℃ and dried for 24-48 h until constant weight. After grinding and sieving, a concrete repair agent powder containing photocurable hydrogel encapsulating microorganisms with a particle size of less than 75 µm was obtained. Step 5: Preparation of mortar specimens: First, 500 parts of water and 6 parts of polycarboxylate superplasticizer were premixed to obtain a homogeneous mixture. Then, 1000 parts of dry cement, 2000 parts of standard sand, 8 parts of calcium lactate, and 3 parts of light-cured hydrogel-encapsulated microorganism concrete repair agent powder were added to the mortar mixer and mixed at a low speed of 140 r / min for 1 min. Then, the homogeneous mixture was added and the mixing was continued at a low speed for 1 min. The mixing was paused, and the mortar adhering to the inner wall and blades of the mixer was scraped off. The mixture was then continued to be mixed at a high speed of 285 r / min for 1 min 30 s to obtain a uniform mortar mixture. This mixture was poured into molds and cured for 3, 7, and 28 days respectively under standard curing conditions of 23±1 ℃ and 95% relative humidity. Step Six: Preparation of Microcracks When the standard curing age of the mortar specimens reached 28 days, microcracks were prepared. A steel wire was placed horizontally parallel to the cross-section of the specimen at the center of the contact surface between the specimen and the lower pressure plate. A central load was applied at a loading rate of 0.2 kN / s. When the load reached 60-65% of the specimen's ultimate load, the loading was stopped and the load was unloaded immediately, thereby inducing visible microcracks on the specimen surface. After the cracks were pre-cracked, the pre-cracked specimens were completely immersed in water at 23 ℃ for continuous healing curing. The curing times were 3, 7, 14, and 28 days, respectively.

[0033] Example 2 The difference between this embodiment and Embodiment 1 is that after the microcracks are pre-fabricated in step six, the pre-cracked specimen is frozen in air at -20 ℃ for 12 h, and then thawed in water at 20 ℃ for 12 h. This constitutes a complete freeze-thaw cycle. The pre-cracked specimens undergo 3, 7, 14 and 28 complete freeze-thaw cycles respectively. Since the ice-water phase change process provides sufficient moisture, the freeze-thaw cycle itself serves as a healing and curing process simulating extreme environments. After the cycle is completed, the crack healing rate is tested directly without additional immersion in room temperature water.

[0034] Comparative Example 1 The difference between this embodiment and Embodiment 1 is that steps one through four are not performed, and the concrete repair agent powder containing light-cured hydrogel encapsulating microorganisms and the polycarboxylate superplasticizer are not added in step five. This is because the hydrogel powder has water absorption properties. In order to ensure that the initial fluidity of the mortar mixture in this comparative example is consistent with that in Embodiment 1, the polycarboxylate superplasticizer needs to be removed simultaneously when the concrete repair agent powder is not added. The remaining process operations and parameter settings are the same as in Embodiment 1.

[0035] Comparative Example 2 The difference between this embodiment and Embodiment 1 is that step one is not performed, NS is not added in step two, and Bacillus pseudostrongylus suspension is not added in step three. The remaining process operations and parameter settings are the same as in Embodiment 1.

[0036] Comparative Example 3 The difference between this embodiment and embodiment 1 is that step one is not performed, and Bacillus pseudostrongylus suspension is not added in step three. The remaining process operations and parameter settings are the same as in embodiment 1.

[0037] Comparative Example 4 The difference between this embodiment and embodiment 1 is that NS is not added in step two, while the remaining process operations and parameter settings are the same as in embodiment 1.

[0038] Comparative Example 5 The difference between this embodiment and embodiment 2 is that steps one to four are not performed, and the concrete repair agent powder containing light-cured hydrogel encapsulating microorganisms and polycarboxylate superplasticizer are not added in step five. The remaining process operations and parameter settings are the same as in embodiment 2.

[0039] Comparative Example 6 The difference between this embodiment and embodiment 2 is that step one is not performed, NS is not added in step two, and Bacillus pseudostrongylus suspension is not added in step three. The remaining process operations and parameter settings are the same as in embodiment 2.

[0040] Comparative Example 7 The difference between this embodiment and embodiment 2 is that step one is not performed, and Bacillus pseudostrongylus suspension is not added in step three. The remaining process operations and parameter settings are the same as in embodiment 2.

[0041] Comparative Example 8 The difference between this embodiment and embodiment 2 is that NS is not added in step two, while the remaining process operations and parameter settings are the same as in embodiment 2.

[0042] Figure 2SEM images of the concrete repair agent powder encapsulated with microorganisms in photocurable hydrogels of Example 1 and Comparative Example 2 are shown. It can be seen that the unmodified hydrogel in Comparative Example 2 has a porous network structure, while the modified hydrogel in Example 1 has a compact structure with reduced pore size. This means that NS is encapsulated within the three-dimensional network structure of the hydrogel, thereby increasing the degree of cross-linking.

[0043] Figure 3 The graph shows the viable bacterial concentrations in simulated cement pore solutions of the bacterial-containing solutions and the concrete repair agent powder encapsulated with photocured hydrogel in Examples 1 and 4. The test data shows that the DLP photocuring process used in this invention can significantly improve the survival level of *Bacillus pseudostrongylus* in a strongly alkaline environment, as can be seen from the viable bacterial counts before and after photocuring in Examples 1 and 4. Specifically, in Comparative Example 4, which contained only *Bacillus pseudostrongylus* and no NS, the viable bacterial concentration in the bacterial-containing solution before photocuring was 12.55 × 10⁻⁶. 8 After light curing, the concentration of viable bacteria in the concrete repair agent increased to 17.33 × 10⁻⁶ CFU / mL. 8 CFU / mL; the same situation occurred in Example 1, where the viable bacteria concentration in the bacterial solution was 13.76 × 10⁻⁶ before photocuring. 8 After light curing, the concentration of viable bacteria in the concrete repair agent increased to 19.27 × 10⁻⁶ CFU / mL. 8 CFU / mL.

[0044] The significant improvement in the survival rate of *Bacillus pseudosturcium* is attributed to the reshaping of the hydrogel carrier's microstructure by the photocuring process: the uncured system mainly consists of low-density chemical bonds, with a large polymer network pore size, leading to increased OH- ions in the highly alkaline pore liquid. - Ions can rapidly diffuse into the carrier, directly disrupting bacterial cell membranes; conversely, during DLP photocuring, the photoinitiator induces a rapid free radical polymerization reaction, promoting the formation of a highly dense and robust three-dimensional covalent cross-linked network between hydrogel monomers. This network acts as a robust physical barrier, significantly hindering the diffusion of free OH groups. - Inward diffusion of ions. Meanwhile, the increase in viable bacterial concentration in the specimen of Example 1 was significantly higher than that of Comparative Example 4, further confirming that NS modification and photocuring molding process have a synergistic protective effect on bacterial survival. Specifically, this synergistic mechanism is mainly reflected in the dual effects of "physical inhibition enhancement" and "chemical buffering": On the one hand, NS, as a nanoscale filler, is uniformly dispersed and embedded in the three-dimensional polymer network formed by photocuring. Through hydrogen bond cross-linking between its abundant active hydroxyl groups and polymer segments, the network micropore size is further reduced, greatly increasing the OH- ion concentration. -The path curvature and steric hindrance of ion diffusion inwards; on the other hand, NS has high pozzolanic activity, enabling it to preferentially react with trace amounts of highly alkaline solution that have penetrated the outer defenses and seeped into the shallow surface of the hydrogel, consuming some of the invading OH groups in situ. - The ions create a relatively mild local chemical buffer microenvironment for microorganisms within the concrete repair agent. The combination of the physical shielding provided by the DLP photocuring network and the nanofilling and chemical consumption of NS, with their complementary advantages, provides dual protection against high-alkali damage for *Bacillus pseudostrongylus*, thus ensuring its long-term survival in extreme environments.

[0045] Figure 4 The compressive strength and flexural strength at 3 days, 7 days, and 28 days for mortar specimens without pre-existing cracks in Examples 1 and Comparative Examples 2-4 are shown. The mechanical strength of specimens in Examples 1 and Comparative Examples 2-4 at all test ages is lower than that of Comparative Example 1 without a carrier. This is because the hydrogel inevitably introduces additional pores and forms an interfacial transition zone within the matrix during the initial water absorption and expansion of cement hydration and the subsequent water release and shrinkage. However, Comparative Example 2, using a conventional unmodified hydrogel, showed a significant deterioration in its 28-day compressive strength to 38.3 MPa. In contrast, Comparative Example 3, modified only with NS, significantly improved its local microstructure by promoting secondary CSH gel formation due to the high pozzolanic effect of NS, resulting in an approximately 14.4% increase in its 28-day compressive strength. Comparative Example 4, encapsulated only with bacteria, also partially mitigated the strength deterioration by filling the pores in situ with CaCO3 crystals generated through metabolism. Example 1, employing the NS-modified + bacterial synergistic system, exhibited the best mechanical properties, with 28-day compressive and flexural strengths reaching 46.4 MPa and 10.7 MPa, respectively, recovering to 91.5% and 95.5% of Comparative Example 1, significantly superior to Comparative Example 2. This demonstrates that the interfacial chemical enhancement and microbial mineralization effects of NS in this invention achieved a significant synergistic gain, greatly improving matrix density and interfacial adhesion. While endowing the matrix with excellent self-healing capabilities, it also maximized compensation for the mechanical losses caused by the introduction of the carrier, minimizing the negative impact of hydrogel on the initial strength of concrete.

[0046] The self-healing properties of the specimens with cracks in Examples 1-2 and Comparative Examples 1-8 were tested, and the results are detailed in Table 1. Figure 5 The crack morphology of mortar specimens with cracks in Examples 1-2 and Comparative Examples 1-8 at different ages under 23 ℃ and freeze-thaw conditions.

[0047] Table 1. Healing test results of mortar specimens in Examples 1-2 and Comparative Examples 1-8

[0048] According to Table 1 and Figure 5It can be seen that under 23℃ conditions, all groups showed a certain self-healing trend, but freeze-thaw cycles (-20~20℃) significantly inhibited the repair process of the conventional system. Comparative Example 8, under freeze-thaw ice crystal expansion damage, had a 28-day healing rate of only 72.37%. Conversely, Example 2, utilizing the dense network formed by NS modification and DLP photocuring, effectively resisted freeze-thaw damage, allowing the mineralization process to continue under extreme conditions, ultimately achieving 100% complete surface closure within 28 days. Considering the results from different healing environments and ages, the specimens from Examples 1 and 2 exhibited the most stable crack healing ability and the highest healing rate.

[0049] Figure 6 The UPV test results are for mortar specimens from Examples 1-2 and Comparative Examples 1-8 at 0 days and 28 days of healing age. This non-destructive test is mainly used to evaluate the internal density of the mortar specimens. The larger the value and the higher the growth rate, the denser the healing product fills the crack and the better the self-healing effect.

[0050] Combined with Table 1 Figure 6 The data shows that the UPV of specimens in Comparative Examples 1 and 5 increased only slightly by 9.01% and 8.00% after 28 days, respectively, with extremely low maximum repaired crack widths of 88 µm and 41 µm, respectively. This is due to the limited secondary hydration of the cement matrix, resulting in very weak crack repair capabilities. While Comparative Examples 3-4, using either NS or *Bacillus pseudostrongylus* alone, showed improved crack repair compared to Comparative Example 2, and Comparative Examples 7-8, compared to Comparative Example 6, they exhibited significant decreases in crack area healing rate, maximum repaired crack width, and UPV growth rate at different ages under freeze-thaw conditions. In contrast, Examples 1 and 2, using the NS-modified + *Bacillus pseudostrongylus* binary system, demonstrated outstanding synergistic repair performance, with their absolute UPV values ​​increasing dramatically from 3.217 km / s and 3.017 km / s to 4.456 km / s and 4.167 km / s, respectively, reaching peak growth rates of 38.51% and 38.12%. Meanwhile, the maximum repaired crack widths in Examples 1 and 2 reached 573 µm and 417 µm, respectively. The maximum crack widths corroborate the UPV test results: repair agents lacking NS modification are prone to debonding and breakage under environmental stress, resulting in incomplete internal repair; while the present invention utilizes photopolymerization 3D printing technology to encapsulate bacteria, which works synergistically with NS interface chemical enhancement, not only ensuring efficient closure of the crack surface but also achieving effective filling of large-width cracks.

[0051] The compressive strength loss rate and mass loss rate of the mortar specimens of Example 2 and Comparative Examples 5-8 were tested under different cycles. These two indicators directly reflect the structural integrity and durability of the specimens under extreme cold environment. The results are detailed in Table 2.

[0052] Table 2. Compressive strength loss rate and mass loss rate of mortar specimens from Example 2 and Comparative Examples 5-8

[0053] As can be seen from the data in Table 2, Comparative Example 5 deteriorated severely under repeated freeze-thaw stress. After 100 cycles, its compressive strength loss rate reached 67.02%, and its mass loss rate surged to 19.9%, indicating that its internal structure had undergone severe macroscopic spalling and loosening. Although Comparative Examples 6 and 8 could delay the failure to some extent, their strength loss rates after 100 cycles were still as high as 37.86% and 33.18%, respectively, indicating that conventional flexible carriers are prone to interfacial debonding failure under freeze-thaw water pressure.

[0054] Compared to Comparative Example 6, the specimen in Comparative Example 7 showed a strength loss rate of only 29.68% after 100 cycles, confirming that the pozzolanic and filling effects of NS can effectively enhance the interfacial bonding between the hydrogel repair agent and the cement matrix. Example 2, using NS modification and synergistic effects with *Bacillus pseudostrongylus*, exhibited the best freeze-thaw resistance: after 100 cycles, its compressive strength loss rate was controlled at an extremely low 26.51%, and its mass loss rate was only 0.83%, demonstrating the best durability performance.

[0055] The test results further confirm that the highly dense cross-linked network formed by the DLP photocuring process, combined with the interfacial chemical reinforcement of NS, fundamentally overcomes the swelling and debonding defects of traditional hydrogels during freeze-thaw cycles. This system not only constructs a physical barrier for bacteria to resist ice crystal penetration, ensuring the in-situ mineralization ability of *Bacillus pseudosturcica* under extremely cold conditions, but also densifies the pores of the cement matrix through the synergistic filling of the mineralization product CaCO3 and the secondary hydration product CSH, significantly blocking the water penetration path, thereby achieving a comprehensive leap in the freeze-thaw durability of the specimens.

[0056] Figure 7The images show scanning electron microscope (SEM) images of the filling material at the cracks in the mortar specimens of Examples 1-2, Comparative Examples 2-4, and Comparative Examples 6-8 at 28 days of healing age. Under normal temperature water curing conditions of 23 °C, Example 1 of the present invention exhibits an extremely dense and continuous filling characteristic. Its healing zone is filled with large-sized lamellar stacked and spindle-shaped deposits, deeply interwoven with hydration products. This microstructure confirms a significant synergistic effect between NS modification and bacterial mineralization, achieving optimal crack and pore sealing. In Comparative Example 2, the healing zone is mainly composed of lamellar Ca(OH)₂ and a small amount of gel-like CSH, indicating limited internal curing hydration. In Comparative Example 3, lamellar crystals are reduced and transformed into flocculent CSH and locally carbonized granular CaCO₃, indicating that NS effectively promotes secondary hydration. Comparative Example 4 mainly produces well-developed CaCO₃ polyhedral crystals, demonstrating basic microbial mineralization. Under alternating -20℃ / 20℃ freeze-thaw cycles, the pores of the specimen in Example 2 remained tightly filled with high-density CaCO3 crystals. Although the size of the mineralized products decreased due to the thermodynamic limitations of low temperature, the bacterial survival space provided by the DLP photocuring crosslinking network and the strong coupling mechanism of NS effectively compensated for the decrease in mineralization efficiency caused by low temperature. This microscopic feature proves that the NS + Bacillus pseudostrongylus + DLP photocuring synergistic system of this invention still has excellent densification filling performance in the freeze-thaw environment, which is the fundamental mechanism for the comprehensive improvement of the macroscopic freeze-thaw resistance of the specimen. In contrast, low temperature and ice crystal expansion severely inhibited the conventional or single-modification systems of Comparative Examples 6-8: the internal structure of the specimen in Comparative Example 6 was extremely loose and full of pores; the mineralized products in the specimen in Comparative Example 7 were transformed into fibrous structures, lacking effective crack-filling minerals; the crack healing phenomenon in the specimen in Comparative Example 8 was more obvious, the CaCO3 crystal development was extremely irregular and accompanied by a large number of unfilled voids, indicating that the single mineralization technology of Bacillus pseudostrongylus alone is very easy to fail in the freeze-thaw environment.

[0057] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a concrete repair agent encapsulated in a photocurable hydrogel, characterized in that, The method includes the following steps: S1. Preparation of the precursor solution of photocurable dual crosslinked hydrogel modified with nano-silica: 0.25-2 parts of cellulose nanofibers, 40-60 parts of deionized water, 5-9 parts of surfactant, 20-40 parts of monomer A, 5-15 parts of monomer B, 0.1-1 parts of octadecyl methacrylate, 0.5-2 parts of photoinitiator, 2-5.5 parts of nano-silica and 0.2-1 parts of crosslinking agent are mixed, and finally 0.01-0.15 parts of Sunset Yellow are added to obtain the precursor solution of photocurable dual crosslinked hydrogel modified with nano-silica; S2. Microbial spore encapsulation: The suspension of Bacillus pseudosturcium was mixed evenly with the precursor solution of photocurable double crosslinked hydrogel modified with nano-silica to obtain a bacterial precursor solution. S3, DLP photopolymerization 3D printing molding: DLP photopolymerization 3D printing technology is used to print the bacterial precursor solution layer by layer. After printing, the solution is dried, ground and sieved to obtain a concrete repair agent with photopolymerized hydrogel encapsulating microorganisms.

2. The preparation method according to claim 1, characterized in that, (1) The surfactant is sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, polyoxyethylene sorbitan monooleate or sorbitan monooleate, monomer A is at least one of acrylamide, N,N-dimethylacrylamide or methacrylamide, and monomer B is at least one of acrylic acid, methacrylic acid or itaconic acid.

3. The preparation method according to claim 1, characterized in that, In S1, the photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 1-hydroxycyclohexylphenyl ketone, or bisacylphosphine oxide, and the crosslinking agent is polyethylene glycol diacrylate, N,N'-methylenebisacrylamide, ethylene glycol dimethacrylate, or N-hydroxymethylacrylamide.

4. The preparation method according to claim 1, characterized in that, The amount of nano-silica added in S1 is 8-10 wt.% of the total mass of the monomers, and the particle size of the nano-silica is 10-30 nm.

5. The preparation method according to claim 1, characterized in that, The specific mixing process in S1 is as follows: (1) Disperse cellulose nanofibers in deionized water, add surfactant, and stir at 50 °C for 0.5 h to obtain a uniform dispersion system; (2) Keep the temperature constant at 50 °C, add monomer A, monomer B, photoinitiator and octadecyl methacrylate to the uniformly dispersed system in sequence, and stir continuously for 2 h until a uniform and transparent micelle solution is formed. (3) Add the ultrasonically dispersed nano-silica to the micelle solution and continue stirring, then add the crosslinking agent, and finally add Sunset Yellow to obtain the nano-silica modified photocurable double crosslinked hydrogel precursor solution.

6. The preparation method according to claim 1, characterized in that, The optical density of the *Bacillus pseudostrongylus* suspension in S2 was 0.6, and the volume ratio of the nano-silica modified photocurable double crosslinked hydrogel precursor solution to the *Bacillus pseudostrongylus* suspension was (4-6):

1.

7. The preparation method according to claim 1, characterized in that, The light source wavelength of the printing process in S3 is 405 nm, and the printing parameters are: the single layer printing layer thickness is set to 0.05-0.15 mm, the single layer exposure time is controlled to 5-12 s, and the light intensity is 3.0-5.0 mW / cm 2 .

8. The preparation method according to claim 1, characterized in that, The particle size of the S3 light-cured hydrogel-encapsulated microorganism concrete repair agent is <75 μm.

9. A concrete repair agent containing microorganisms encapsulated in a photocurable hydrogel obtained by the preparation method according to any one of claims 1-8.

10. A self-healing concrete, characterized in that, The concrete is prepared by mixing and stirring 1-5 parts of the light-cured hydrogel-encapsulated microorganism concrete repair agent as described in claim 9, 800-1200 parts of ordinary silicate cement, 400-600 parts of mixing water, 1500-2500 parts of standard sand, 1-6 parts of polycarboxylate superplasticizer, and 5-15 parts of calcium lactate, and then casting it into shape.

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