Modified plant fiber reinforced self-repairing microbial cement mortar and preparation method thereof

Abstract

The application discloses a modified plant fiber reinforced self-repairing microbial cement mortar and a preparation method thereof, and belongs to the technical field of building materials. 600 The bacillus pseudofirmus with OD of 0.6 is immobilized in EP to prepare a microbial self-healing agent, which is mixed with plant fibers modified by oxidation reduction pretreatment and GO, cement, standard sand, calcium lactate and water. 2+ The application constructs a double-interface synergistic self-healing system coupled by the EP immobilized microbial self-healing agent and the GO modified plant fibers, realizes long-term survival of the microorganism and Ca 2+ Efficient biochemical kinetics matching, and through the template induction effect of GO on calcium carbonate crystallization, the mineralization product is promoted to evolve into a continuous three-dimensional filling skeleton, and finally the early rapid closure of the wide crack and the efficient repair of high compactness are realized.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology and relates to a modified plant fiber reinforced self-healing microbial cement mortar and its preparation method. Background Technology

[0002] Concrete is prone to developing microcracks during long-term service, providing channels for the transport of corrosive media and accelerating material degradation. Traditional techniques struggle to achieve long-term in-situ repair of these microcracks. Microbial-induced calcium carbonate precipitation (MICP), a typical biomimetic mineralization technology, offers a sustainable pathway for concrete self-healing. However, the highly alkaline environment of the cement matrix (pH>12) severely inhibits the metabolic activity of microorganisms, leading to a significant decline in the activity of unencapsulated bacteria in the early stages. This has become a bottleneck restricting the practical application of this technology. Therefore, using porous carriers to immobilize and encapsulate bacteria, physically isolating them from the corrosive environment of highly alkaline conditions, has become a key means to overcome the difficulty of bacterial survival in concrete and break through the bottleneck in the application of MIP.

[0003] Although carrier encapsulation technology enhances the activity of microorganisms in cement matrix, its healing efficiency significantly decreases for wider cracks of 500-600 μm and above. The main reason is the insufficient density of effective heterogeneous nucleation sites within wider cracks, resulting in a discrete distribution of mineral deposits and difficulty in forming continuous spatial overlap structures. Existing technologies often introduce fibrous materials to provide a nucleation substrate, but synthetic fibers are energy-intensive and have high carbon emissions; while plant fibers, although environmentally friendly, are prone to swelling, alkali corrosion, and interfacial degradation in strongly alkaline environments, making it difficult for their surfaces to stably adsorb bacteria and effectively induce nucleation.

[0004] To mitigate interface degradation, existing technologies attempt to modify fibers. However, these technologies suffer from several drawbacks: Firstly, most studies treat fibers merely as passive physical supports, lacking a systematic understanding of the synergistic mechanisms for bacterial protection, ion enrichment, and space filling. This results in unclear coupling of functions within the repair system, leading to a spatiotemporal mismatch in biochemical reactions. Secondly, the intrinsic compositions of different plant fibers vary significantly, and existing technologies lack a systematic comparison of the differences in interactions between fibers. This fails to reveal fiber-dependent synergistic mechanisms and makes it difficult to regulate bacterial activity and the continuous deposition of CaCO3 under wide-crack conditions.

[0005] Therefore, how to construct a dual-interface repair system in which microorganisms immobilized on a carrier work synergistically with specific plant fibers, thereby overcoming the discrete nucleation defects in the existing concrete self-healing process, accelerating the evolution of healing products into a continuous three-dimensional filling skeleton, and achieving efficient and dense repair of wide cracks, is a key technical challenge that urgently needs to be overcome in this field. Summary of the Invention

[0006] In order to solve the above-mentioned problems in the prior art, the present invention provides a modified plant fiber reinforced self-healing microbial cement mortar and its preparation method.

[0007] The technical solution of the present invention is as follows: One objective of this invention is to provide a modified plant fiber reinforced self-healing microbial cement mortar. The raw materials of the cement mortar, by weight, include: 980-1020 parts of ordinary silicate cement, 480-520 parts of water, 1670-1730 parts of standard sand, 7.5-8.5 parts of calcium lactate, 31-35 parts of expanded perlite-supported microbial self-healing agent, and graphene oxide (GO) modified plant fiber. The amount of graphene oxide modified plant fiber added is 0.8-1.2 vol.% of the sum of the volumes of ordinary silicate cement and standard sand. The expanded perlite-supported microbial self-healing agent and the graphene oxide modified plant fiber constitute a dual-interface self-healing component.

[0008] Further specifying, the raw materials of cement mortar, by weight, include: 1000 parts of ordinary silicate cement, 500 parts of water, 1700 parts of standard sand, 8 parts of calcium lactate, 33 parts of expanded perlite-supported microbial self-healing agent, and graphene oxide-modified plant fiber, wherein the amount of graphene oxide-modified plant fiber added is 1.0 vol. of the sum of the volumes of ordinary silicate cement and standard sand.

[0009] Further specifying, the plant fiber is coconut fiber, bamboo fiber, or sisal fiber.

[0010] Further specifying, coconut fiber has a single fiber diameter of 20-50 μm, an aspect ratio of 200-500, a surface roughness of 3.5-5.0 μm, and a specific surface area of ​​1.60 m² / g; bamboo fiber has a single fiber diameter of 15-35 μm, an aspect ratio of 286-667, a surface roughness of 2.0-3.2 μm, and a specific surface area of ​​1.90 m² / g; sisal fiber has a single fiber diameter of 20-40 μm, an aspect ratio of 250-500, a surface roughness of 4.0-6.5 μm, and a specific surface area of ​​2.45 m² / g. 2 / g.

[0011] Further specifying the preparation method of the expanded perlite-supported microbial self-healing agent, the method is as follows: Expanded perlite (EP) with a particle size of 1.00 mm-3.00 mm and a water absorption rate of 298.2% is selected as the carrier, and the expanded perlite is immersed in an optical density (OD) value... 600 Expanded perlite-supported microbial self-healing agent was prepared by immersing the agent in a solution of Bacillus pseudostrongylus with a concentration of 0.6 for 20-28 hours.

[0012] Further specifying the preparation method of graphene oxide modified plant fiber, the method is as follows: the plant fiber is immersed in an oxidant for treatment, dried and then immersed in a reducing agent for treatment, washed and dried to complete the oxidation-reduction pretreatment, the pretreated plant fiber is immersed in a graphene oxide dispersion for 1.5-2.5 hours, and then washed and dried to obtain graphene oxide modified plant fiber.

[0013] Further specifying, the oxidant is a 0.3% (w / w) sodium periodate solution, hydrogen peroxide solution, or sodium hypochlorite solution; the treatment temperature after immersion in the oxidant is 35-55℃, and the time is 1.5-2.5h; the reducing agent is a 0.02% (w / w) sodium borohydride solution, dilute hydrazine hydrate solution, or citric acid solution; the treatment after immersion in the reducing agent is at room temperature, and the treatment time is 1.5-2.5h; the concentration of the graphene oxide dispersion is 1.0-3.0mg / mL.

[0014] A second objective of this invention is to provide a method for preparing the above-mentioned cement mortar, which includes the following steps: Step 1: Preparation of expanded perlite-supported microbial self-healing agent: A solution of Bacillus pseudostrongylus with an optical density of 0.6 was mixed with expanded perlite to prepare the expanded perlite-supported microbial self-healing agent. Step 2, Preparation of graphene oxide modified plant fiber: The plant fiber is first subjected to oxidation-reduction pretreatment, and then immersed in graphene oxide dispersion for loading to obtain graphene oxide modified plant fiber. Step 3: Preparation of cement mortar: Dry mix expanded perlite-supported microbial self-healing agent, graphene oxide-modified plant fiber, ordinary silicate cement, standard sand and calcium lactate, then add water and stir, and pour into molds to obtain cement mortar.

[0015] Further specified, the dry mixing speed is 100-150 r / min, and the time is 20-60 s.

[0016] Further specifying, in step three, an equal-volume substitution method is used to replace part of the standard sand with expanded perlite-supported microbial self-healing agent, so that the sand-binder ratio of the cement mortar is always maintained at 2.

[0017] The beneficial effects of this invention are as follows: (1) The present invention uses the optical density value OD 600An EP-immobilized microbial self-healing agent was prepared by immobilizing 0.6% *Bacillus pseudosturcium* in expanded perlite (EP). Simultaneously, coconut fiber, bamboo fiber, or sisal fiber were selected and pretreated with redox reactions to reduce water absorption, increase surface roughness, and enhance the relative exposure abundance of cellulose. Then, GO was loaded onto the fibers to prepare GO-modified plant fibers. The GO-modified fibers, EP-immobilized microbial self-healing agent, cement, standard sand, calcium lactate, and water were mixed according to a predetermined ratio and cast into a mold. When cracking of the cement mortar matrix caused water infiltration, the MIP system was activated in situ. This invention constructs a dual-interface synergistic self-healing system coupled with EP-immobilized microbial self-healing agent and GO-modified plant fibers, achieving long-term survival of microorganisms and calcium lactate. 2+ The highly efficient enrichment of biochemical dynamics overcame the problems of discrete nucleation of traditional microbial repair products and slow early healing. Furthermore, the template-inducing effect of GO on calcium carbonate crystallization promoted the evolution of mineralized products into a continuous three-dimensional filling framework, ultimately achieving early and rapid closure of wide cracks and highly efficient repair with high density.

[0018] (2) This invention proposes a method for synergistically enhancing the self-healing of cement mortar cracks based on GO-modified plant fibers and microbial Bacillus pseudostrongylus. By constructing a dual-interface repair system with synergistic effects of "bacterial protection and release" and "crack mineralization regulation," the intrinsic microstructure and abundant oxygen-containing functional groups of the GO-modified plant fibers form a mutually dependent dynamic enhancement relationship with the Bacillus pseudostrongylus immobilized within the system. On the one hand, the modified plant fibers provide bacteria with a large number of nucleation sites and Ca2+. 2+ On the one hand, the enrichment of calcium carbonate and on the other hand, the maintenance of bacterial activity drove the efficient heterogeneous nucleation of calcium carbonate along the fiber template. The two worked together to successfully promote the rapid evolution of the healing products from a discrete distribution to a continuous three-dimensional support skeleton in wide cracks and early healing stages, thereby improving the overall repair quality of the crack.

[0019] (3) This invention effectively reduces the water absorption rate of plant fibers through redox pretreatment, while increasing their surface roughness and improving the relative exposure abundance of cellulose-related components, providing favorable surface conditions for the subsequent efficient loading of GO. In addition, GO modification not only alleviates the swelling and interface degradation problems that easily occur in plant fibers in strongly alkaline cement matrices, but its abundant oxygen-containing functional groups on the surface can also effectively buffer the highly alkaline microenvironment in cracks, thereby improving the survival ability of bacteria.

[0020] (4) This invention breaks through the limitations of single carrier or single fiber repair. The EP carrier mainly undertakes the long-term immobilization and internal protection of bacteria, while the GO modified fiber interspersed in the cracks can efficiently enrich Ca in the cement matrix environment due to its large specific surface area and rich surface functional groups. 2+This synergistic mechanism provides excellent attachment sites and heterogeneous nucleation substrates for freed bacteria, solving the problems of insufficient effective nucleation sites and low bacterial survival rate in traditional MIP technology.

[0021] (5) In this invention, the strengthening effect of GO-modified plant fiber on MIP repair focuses on the early kinetic stage. Through the template-induced effect of GO at the fiber interface, it promotes efficient heterogeneous nucleation and continuous crystallization of calcium carbonate. This causes the healing products (calcite-type CaCO3 with a crystal interplanar spacing of about 0.304 nm) in the crack to evolve rapidly from discrete surface deposition to a continuous three-dimensional filling skeleton. The test results of this invention show that when the crack healing age is 28 days, the ultrasonic pulse velocity (UPV) of the specimen jumps to a maximum of 4413 m / s, the water permeability drops to an extremely low level of 0.84%, and the compressive strength recovers to 48.6 MPa. This indicates that this invention successfully solves the traditional problem of discrete surface crusting and transforms it into deep repair of wide cracks with high density and high crystallinity. Attached Figure Description

[0022] Figure 1 The above are flow charts of the cement mortar preparation process in Examples 1-3 of this invention. Figure 2 The TG-DTG analysis curves are for sisal fiber, bamboo fiber and coconut fiber before modification and after redox pretreatment according to the modification methods in Examples 1-3. (a) is for sisal fiber, (b) is for bamboo fiber and (c) is for coconut fiber. Figure 3 The residual Ca in the simulated pore solution of specimens in Examples 1-3 and Comparative Examples 1-4 2+ The concentration and bacterial survival count in the specimens at 3 days and 28 days of healing time, (a) is Ca 2+ Concentration, (b) bacterial survival count; Figure 4 Microscopic images of crack closure morphology of specimens from Examples 1-3 at different healing ages of 0 days, 3 days, 7 days, 14 days, and 28 days. Figure 5 Microscopic images of crack closure morphology of specimens from Comparative Examples 1-4 at different healing ages of 0 days, 3 days, 7 days, 14 days, and 28 days. Figure 6 The apparent healing rates of specimens from Examples 1-3 and Comparative Examples 1-4 at different healing ages of 3 days, 7 days, 14 days, and 28 days were determined. Figure 7 The UPV of specimens in Examples 1-3 and Comparative Examples 1-4 at healing ages of 0 days and 28 days; Figure 8 The water permeability of specimens from Examples 1-3 and Comparative Examples 1-4 at 7 days and 28 days of healing age; Figure 9 The images show the SEM, TEM, and HR-TEM characterization results of the healing products at the cracks of specimens from Examples 1-3 and Comparative Examples 1-4 at a healing age of 28 days. Figure 10 The thermogravimetric analysis (TG) curves of the healing products of specimens from Examples 1-3 and Comparative Examples 1-4 after 28 days of healing are shown in (a) and (b) respectively. Detailed Implementation

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] The following ordinary Portland cement is PO 42.5.

[0028] Example 1 Step 1: Preparation of the microbial self-healing agent: Preparation of *Bacillus pseudosternae* solution: The liquid culture medium for *Bacillus pseudosternae* was prepared by adding 5.0 parts peptone, 3.0 parts beef extract, 5.0 parts sodium chloride, and 0.0015 parts manganese sulfate to 1000 parts (equivalent to 1 L) of distilled water. After preparation, the liquid culture medium was dispensed into Erlenmeyer flasks and then autoclaved at 121℃. After the culture medium cooled to room temperature, *Bacillus pseudosternae* was inoculated at 1% of the total volume of the liquid culture medium in a clean bench. The inoculated culture medium was then placed in a constant temperature shaker and cultured at 27℃ and 120 r / min for 24 h. After the culture was completed, the bacterial suspension was transferred to centrifuge tubes and centrifuged at 6000 r / min for 5 min. The supernatant was discarded, and the bacterial cells were resuspended in deionized water. The optical density of the bacterial suspension was adjusted to OD. 600 =0.6, a solution of Bacillus pseudostrongylus with an absorbance of 0.6 at a wavelength of 600 nm was prepared; EP particles with a particle size of 1.00 mm-3.00 mm and a water absorption rate of 298.2% were selected and immersed in the Bacillus pseudostrongylus solution for 24 h to obtain EP immobilized microbial self-healing agent. Step 2: Preparation of GO-modified sisal fiber: Sisal fibers with a diameter of 20-40 μm and an aspect ratio of 250-500 were selected and immersed in a 0.3% sodium periodate solution. The fibers were oxidized at 45°C for 2 hours. After the reaction, the fibers were washed with distilled water to remove residual oxidant and dried at 40°C to constant weight. They were then immersed in a 0.02% sodium borohydride solution at room temperature for another 2 hours. The treated fibers were washed with distilled water until neutral and dried to constant weight, completing the fiber oxidation-reduction pretreatment. A 2 mg / mL GO aqueous dispersion was placed in an ultrasonic disperser and treated for 30 minutes. The pretreated sisal fibers were then immersed in the GO aqueous dispersion for 2 hours to load GO onto the surface of the sisal fibers. Unloaded GO was removed by washing with distilled water, and the fibers were dried at 40°C for 24 hours, completing the fiber modification and obtaining GO-modified sisal fibers. Step 3: Preparation of cement mortar: First, 1000 parts of dry PO42.5 ordinary Portland cement, 1570 parts of ISO standard sand, 33 parts of EP immobilized microbial self-healing agent, 8 parts of calcium lactate, and GO modified sisal fiber with a volume of 1.0 vol.% of the sum of the volumes of ordinary Portland cement and standard sand are added to a mortar mixer and dry-mixed at a low speed of 140 r / min for 30 s to achieve initial uniform dispersion of each component. Then, 500 parts of water are added and low-speed mixing continues for 60 s. Then, mixing is paused and the mortar adhering to the mixing blades and the inner wall of the mixing pot is scraped off with a scraper to make it evenly mixed with the system. Then, the mixer is restarted and high-speed mixing is carried out at 285 r / min for 120 s. The mixture is then poured into a mold and cast to obtain a uniform cement mortar. Step 4: Place the cement mortar mixture in a standard curing chamber (20±1℃, RH≥99%) for 28 days to obtain specimens. Prepare pre-cracked specimens using a fully automatic bending testing machine. The specific method is as follows: fix steel needles to the loading plate, then place the specimen under the loading device. Induce crack formation through localized concentrated loading, controlling the loading rate at 20 N / s. Stop loading when the crack width on the specimen surface reaches 350-650 μm. The target load is 65% of the ultimate load. After crack formation, immerse the specimen in water at 30±1℃ with continuous oxygen supply to ensure sufficient oxygen for bacterial healing.

[0029] Example 2 The difference between this embodiment and Embodiment 1 is that the fiber in step two is a single bamboo fiber with a diameter of 15-35μm and an aspect ratio of 286-667. The remaining process operations and parameter settings are the same as in Embodiment 1.

[0030] Example 3 The difference between this embodiment and embodiment 1 is that the fiber in step two is a single coconut fiber with a diameter of 20-50 μm and an aspect ratio of 200-500. The remaining process operations and parameter settings are the same as in embodiment 1.

[0031] Comparative Example 1 The difference between this comparative example and Example 1 is that no fibers are added, while the remaining process operations and parameter settings are the same as in Example 1.

[0032] Comparative Example 2 The difference between this comparative example and Example 1 is that the sisal fiber is not modified, i.e., step two is not performed. The remaining process operations and parameter settings are the same as in Example 1.

[0033] Comparative Example 3 The difference between this comparative example and Example 2 is that the bamboo fiber is not modified, i.e., step two is not performed. The remaining process operations and parameter settings are the same as in Example 2.

[0034] Comparative Example 4 The difference between this comparative example and Example 3 is that the coconut fiber is not modified, i.e., step two is not performed. The remaining process operations and parameter settings are the same as in Example 3.

[0035] The compressive strength and flexural strength of the specimens from Examples 1-3 and Comparative Examples 1-4 that were cured for 28 days without pre-existing cracks were tested, and the results are detailed in Table 1.

[0036] Table 1. Results of 28-day compressive and flexural strength tests

[0037] As shown in Table 1, the 28-day compressive strength of unmodified Comparative Examples 2, 3, and 4 was slightly lower than that of Comparative Example 1, with decreases of 0.68% (Comparative Example 2), 2.26% (Comparative Example 3), and 3.16% (Comparative Example 4), respectively. However, the 28-day compressive strength of Examples 1-3, which were synergistically modified with fiber and *Bacillus pseudostearate*, significantly increased to 48.6, 47.0, and 46.6 MPa, respectively, compared to the unmodified examples, representing increases of 10.45%, 8.55%, and 8.62% compared to the corresponding unmodified Comparative Examples 2-4. This is because the modification increased the active sites and roughness of the plant fibers, enhancing interfacial adhesion; simultaneously, the oxygen-containing functional groups on the GO surface provided heterogeneous nucleation sites for hydration products, promoting CSH gel formation and highly densifying the interfacial transition zone. Regarding 28-day flexural strength, Comparative Example 1 showed 11.4 MPa, while the unmodified Comparative Example 2 showed 11.2 MPa, Comparative Example 3 showed 11.0 MPa, and Comparative Example 4 showed 10.5 MPa, all lower than Comparative Example 1. Examples 1, 2, and 3 showed significant increases compared to the unmodified form, reaching 11.9, 11.6, and 11.5 MPa, respectively. This indicates that GO modification not only improves the interfacial adhesion between the fiber and the matrix but also greatly enhances the stress transfer capacity of the plant fiber under bending conditions. Therefore, the specimens from Examples 1-3 exhibited superior 28-day flexural and compressive strengths. Among them, Example 1, due to its high cellulose content and excellent intrinsic structural characteristics, possessed the best intrinsic mechanical properties and interfacial reinforcement potential, demonstrating the best load-bearing capacity.

[0038] Figure 2 Table 2 shows the thermogravimetric analysis results of unmodified fibers and fibers pretreated by redox according to the modification methods in Examples 1-3. These results can be used to characterize the mass loss of plant fibers before and after modification in different temperature ranges.

[0039] Table 2. Mass loss of plant fibers in different temperature ranges before and after modification.

[0040] Combining the data in Table 2 and Figure 2It can be observed that in the 200-350℃ range, the weight loss of the three fibers pretreated with redox treatment was lower than that of the corresponding untreated fibers. This result indicates that pretreatment reduces the thermal decomposition of hemicellulose and some amorphous components in the fibers within this temperature range. Correspondingly, in the 350-400℃ range, the mass loss of the three fibers pretreated with redox treatment increased, indicating that the relative exposure of cellulose-related components in the fibers increased after pretreatment, resulting in more concentrated and significant thermal weight loss characteristics during the main decomposition stage. Furthermore, among the three fibers, modified sisal fiber consistently exhibited the highest mass loss in the 350-400℃ range, suggesting that its proportion of cellulose-related components may be relatively higher. This characteristic implies that sisal fiber, after surface pretreatment, has a higher degree of exposure of active sites, thus providing a more favorable structural basis for subsequent GO loading and interfacial interactions.

[0041] Figure 3 Tables 1-3 and 3 show the Ca2+ values ​​in simulated cement mortar solutions after 3 days, respectively, for Examples 1-3 and Comparative Examples 1-4. 2+ Concentration test results, and the number of bacteria surviving inside the precast crack specimens at 3 and 28 days of healing age (i.e., the survival rate of Bacillus pseudostrongylus).

[0042] Table 3. Ca in the simulated pore solution of the specimen 2+ Concentration test and bacterial survival count test results at 3 and 28 days of healing period

[0043] Table 3 and Figure 3 The residual Ca in the simulated pore solutions of each embodiment and comparative example are shown respectively. 2+ Concentration, and the number of surviving bacteria inside the specimens at 3 days and 28 days of healing time. Overall, each group showed an effect on Ca... 2+ The enrichment and consumption of bacteria showed a significant difference compared to the number of bacterial survivors. In the residual Ca... 2+ Regarding concentration, Examples 1-3 of this invention exhibit extremely low residual Ca. 2+ Concentration and extremely high bacterial viability, with residual Ca in Example 1 2+ The lowest concentration was observed, while the highest number of bacteria survived at different healing stages. This result indicates that the introduction of plant fibers can promote the absorption of Ca²⁺ by the cement mortar system. + The enrichment or consumption of plant fibers can be further enhanced by GO modification because, on the one hand, the surface and pore structure of plant fibers are rich in Ca²⁺. + Enrichment and mineralization deposits provide more interfacial sites; on the other hand, oxygen-containing functional groups such as hydroxyl, carboxyl, and epoxy groups on the GO surface interact with Ca²⁺ through electrostatic and coordination interactions. + The interaction simultaneously increases fiber surface roughness and nucleation site density, thus favoring Ca²⁺.+ Local enrichment and subsequent mineralization deposition on the fiber surface. Because the mortar specimens of this invention also contain immobilized bacteria, the residual Ca²⁺... + The reduction reflects the combined effect of GO-modified plant fiber and microbial-induced mineralization, rather than a single adsorption effect.

[0044] From the bacterial survival results, during the early healing stage (3 days), the viable bacterial counts in all groups were at a high level, with Example 1 showing the highest viable bacterial count. Compared to Comparative Example 1, Examples 1-3 and Comparative Examples 2-4, which used fabric fibers, all had higher bacterial survival counts. Furthermore, the bacterial survival counts in Examples 1-3 were higher than those in the corresponding unmodified Comparative Examples 2-4. This is because the fiber surface and its porous structure provide additional attachment sites and physical barriers for bacteria, reducing the direct inhibition of bacteria by the high-alkaline environment. After GO modification, the roughness and functional sites on the fiber surface further increase, which is more conducive to bacterial attachment, nutrient enrichment, and local interfacial microenvironment regulation, thereby enhancing bacterial survival. At the 28-day healing period, the bacterial survival counts in all groups decreased significantly, but the pattern between different groups remained consistent with that at 3 days, meaning the Example groups were still significantly higher than the corresponding unmodified fiber Comparative groups. This indicates that although the continuous consumption of nutrients, the gradual closure of cracks, and the limited local oxygen supply inhibit bacterial metabolism and reduce their survival as the healing period lengthens, GO-modified plant fibers can still provide a relatively more favorable survival interface during the long-term healing process.

[0045] The self-healing properties of the specimens with cracks in Examples 1-3 and Comparative Examples 1-4 were tested, and the results are detailed in Table 4. Figure 4-6 .

[0046] Table 4 Specimen healing test results

[0047] The crack area healing morphology of each embodiment and comparative example is as follows: Figure 4 and Figure 5 As shown. (Combined with Table 4 and...) Figure 4-6The results show that, in Comparative Example 1, without the introduction of fiber interface support, mineralization products within the crack could only be discretely deposited relying on a limited number of nucleation sites, making it difficult to form a continuous filling structure in the wide crack. Its apparent healing rate at 28 days was only 79.51%, failing to achieve complete closure. After incorporating unmodified plant fibers (Comparative Examples 2-4), the fiber surface and its pores provided additional interface sites for the attachment of *Bacillus pseudostrongylus* and the deposition of CaCO3. Its bridging and skeletal support promoted the continuous growth of healing products. The unmodified fiber samples in Comparative Examples 2-4 all achieved a 100% apparent healing rate at 28 days. Among them, sisal fiber, due to its higher porosity and more anchoring sites, performed best in the mid-to-late stages. Furthermore, Examples 1-3 of this invention exhibited superior repair efficacy, with particularly significant early kinetic advantages. At 3 days, the apparent healing rate of Examples 1-3 was significantly higher than the corresponding unmodified group; by 14 days, Examples 1 and 2 had achieved 100% complete closure of the crack surface ahead of schedule. The advantage of this early and rapid repair mechanism lies in the fact that GO modification increases the roughness and active sites on the fiber surface, which is more conducive to bacterial adhesion and Ca²⁺. + Enrichment and heterogeneous nucleation of CaCO3; simultaneously, GO may also improve the local microenvironment at the fiber-matrix interface, thereby promoting the continuous deposition of healing products in the crack space and improving the overall repair efficiency. Although the final apparent healing rates of Comparative Examples 1-3 were also high, their crack healing ability was still inferior to that of the corresponding Examples 1-3 at the same healing age. At 7 days, Examples 1-3 were able to repair most of the cracks, with only a very small portion of the cracks in Example 1. At this time, the crack area healing rate was 86.41%, while Comparative Examples 2-4 still had a large degree of unhealed cracks, and obvious cracks still existed until 14 days. However, Examples 1-2 had achieved 100% self-healing of cracks, thus demonstrating that the present invention can shorten the self-healing time of cracks.

[0048] Figure 7 The UPV test results are for specimens of Examples 1-3 and Comparative Examples 1-4 at healing ages of 0d and 28d. The higher the UPV value, the fewer internal defects in the material, the more fully the cracks are filled, and the better the healing effect. Figure 8 The results of water permeability tests on specimens of Examples 1-3 and Comparative Examples 1-4 at healing ages of 7 days and 28 days show that the lower the relative water permeability, the more fully the crack seepage channels are blocked and the higher the effective healing degree of the specimen.

[0049] Depend on Figure 7 and Figure 8It can be seen that the UPV of Comparative Example 1 increased by only about 5.59% after 28 days, and the water permeability was only 33.53% at the 28-day healing age. This indicates that under the condition of relying solely on EP-based microbial self-healing agents without the addition of plant fibers, although some mineralization and filling occurred in the crack area, the overall densification effect was limited. In contrast, the UPV values ​​of Comparative Examples 2-4 were all higher than those of Comparative Example 1, indicating that the introduction of plant fibers is beneficial to improving the internal density of the crack after healing. This is because plant fibers provide a bridging framework and additional interface sites in the crack space, which is conducive to the attachment of Bacillus pseudostrongylus and the deposition of CaCO3. At the same time, the water absorption and release behavior of the fibers also plays a certain role in internal maintenance, promoting continuous hydration and pore filling. Examples 1-3 showed good effects in terms of both UPV and water permeability. The UPV value was significantly higher than that of Comparative Examples 1-4, and the water permeability was significantly lower than that of Comparative Examples 1-4. This result indicates that the surface roughness and active sites of the fibers increased after GO modification, which is beneficial to CaCO3 deposition. 2+ Enrichment, bacterial attachment, and heterogeneous CaCO3 nucleation promote the formation of a more continuous and denser sealing layer of mineralized products within the fracture, thereby significantly increasing UPV and reducing permeability.

[0050] Figure 9 The images show the SEM, TEM, and HR-TEM characterization results of the healing products at the cracks in specimens of Examples 1-3 and Comparative Examples 1-4 at a healing age of 28 days. Specifically, Figure 9 (a) is a SEM image of Example 1. Figure 9 (d) is the SEM image of Example 2. Figure 9 (g) is the SEM image of Example 3. Figure 9 (j) is the SEM image of Comparative Example 1. Figure 9 (m) is the SEM image of Comparative Example 2. Figure 9 (p) is the SEM image of Comparative Example 3. Figure 9 (s) is the SEM image of Comparative Example 4; Figure 9 (b) is a TEM image of Example 1. Figure 9 (e) is a TEM image of Example 2. Figure 9 (h) is a TEM image of Example 3. Figure 9 (k) is the TEM image of Comparative Example 1. Figure 9 (n) is the TEM image of Comparative Example 2. Figure 9 (q) is the TEM image of Comparative Example 3. Figure 9 (t) is the TEM image of Comparative Example 4; Figure 9 (c) is the HR-TEM image of Example 1. Figure 9 (f) is the HR-TEM image of Example 2. Figure 9 (i) is the HR-TEM image of Example 3. Figure 9(l) is the HR-TEM image of Comparative Example 1. Figure 9 (o) is the HR-TEM image of Comparative Example 2. Figure 9 (r) is the HR-TEM image of Comparative Example 3. Figure 9 (u) is the HR-TEM image of Comparative Example 4. The SEM images show that the calcium carbonate crystals in the specimens of Examples 1-3 are more densely deposited, with clearer crystal edges and a more compact inter-crystal packing. Numerous complete *Bacillus pseudostrongylus* spores and bacteria, as well as a continuous biofilm network composed of extracellular polymeric substances (EPS), can also be observed. Low-magnification TEM images show that the calcium carbonate particles in the healing products of Examples 1-3 have more regular morphology and clearer boundaries, exhibiting higher morphological integrity. HR-TEM images further reveal the local crystal structure characteristics of the healing products in the specimens of Examples 1-3. The lattice fringes of the specimens containing GO-modified fibers in Examples 1-3 are more continuous and clearer, with more regular boundaries, indicating higher local crystal order and a more complete calcium carbonate crystal structure. The microscopic characterization results of SEM and TEM indicate that GO-modified fibers can further promote the deposition and growth of healing products at the fiber interface and crack region, optimizing the crystallization integrity and packing density of the mineralized crystals. The abundant oxygen-containing functional groups on the GO surface can enhance the Ca2+ content at the plant fiber interface through chemical adsorption. 2+ The enrichment capacity provides ample nucleation sites for heterogeneous nucleation of calcium carbonate. Simultaneously, the increased surface roughness of the fibers after GO modification provides more active interface sites for initial bacterial attachment, colonization, and biofilm formation, promoting early nucleation and directional growth of calcium carbonate crystals, ultimately optimizing crystal morphology and improving density. Among these, the healing product of Example 1 exhibited the clearest lattice fringes and more complete crystal boundaries, indicating that GO-modified sisal fibers are most conducive to the formation of more structurally complete CaCO3 crystals. Figure 9 (j) The SEM images show that only a small number of discrete calcium carbonate crystals exist on the surface of the crack in the specimen of Comparative Example 1, and the crystal morphology is not fully developed. At the same time, a small number of spores were observed. Figure 9 (k) Low-magnification TEM images show that the particle boundaries of the healing product in Comparative Example 1 are relatively blurred and the morphological integrity is poor. Figure 9 (l) HR-TEM images show that the lattice fringes of the healing product in Comparative Example 1 specimen are relatively blurred, with poor local order. This indicates that no fibers were incorporated, and the healing product relied solely on CO2- and Ca produced by microbial metabolism. 2+ Random collisions result in a lack of effective nucleation sites on the crack surface, leading to a discrete distribution of healing products. Figure 9The SEM images (m), (p), and (s) show that the deposition products on the fiber surface of Comparative Examples 2-4 have increased coverage and continuous calcium carbonate crystals. Furthermore, biofilm structures formed by extracellular polymers secreted by a small number of microorganisms and colonization of some bacilli can be observed in the intercrystalline spaces and at the fiber-matrix interface. The SEM images also show that Comparative Example 2 has better crystal morphology compared to Comparative Examples 3 and 4, which is attributed to the high porosity of the sisal fibers themselves. Figure 9 The low-magnification TEM results of (n), (q), and (t) show that the particle outlines of the healing products in Comparative Examples 2-4 are relatively clear, but the local edges are still relatively rounded. Figure 9 High-magnification HR-TEM images (o), (r), and (u) show relatively clear lattice fringes of the healing products, but slight bending and discontinuity are still present in local areas. This indicates that the introduction of plant fibers is beneficial to promoting mineralization deposition in the crack region. This is because the fiber surface and its porous structure provide more interface sites for bacterial attachment and heterogeneous CaCO3 nucleation, thereby enhancing the mineralization reaction in the crack region.

[0051] Figure 10 Table 5 shows the TG and DTG test results of the healing products of specimens from Examples 1-3 and Comparative Examples 1-4 at a healing age of 28 days. The test results can measure the mass loss of the specimens in the temperature range of 650-800 ℃ at the crack, i.e. the mass loss of calcium carbonate.

[0052] Table 5. Mass loss at the crack in the specimen within the temperature range of 650-800 ℃

[0053] Combination Figure 10 As shown in Table 5, all samples exhibited significant mass loss in the 650-800℃ range, corresponding to the thermal decomposition of CaCO3. The mass loss percentages in this temperature range were as follows: Example 1 (11.49%) > Example 2 (9.52%) > Example 3 (8.84%) > Comparative Example 2 (8.23%) > Comparative Example 3 (6.55%) > Comparative Example 4 (5.34%) > Comparative Example 1 (3.59%). This result indicates that the introduction of plant fibers is beneficial to increasing the deposition of calcium carbonate in the crack region, and GO modification can further enhance this effect. Among them, Example 1 showed the highest mass loss in this temperature range, indicating that its crack region had the highest relative CaCO3 content. Figure 10(b) The DTG curves show that there are significant differences in the peak temperatures of the CaCO3 decomposition temperature range among the different groups of samples: the peak temperatures of Comparative Examples 1-4 are 697, 723, 717, and 715 °C, respectively; while the peak temperatures of Examples 1-3 are further increased to 748, 736, and 730 °C, respectively. Overall, the decomposition peak temperatures of Examples 1-3 with GO modified fibers are higher than those of the corresponding unmodified fiber groups, while the peak temperatures of Comparative Examples 2-4 with unmodified fibers are higher than those of Comparative Example 1. This result indicates that the CaCO3 induced by GO modified fibers has higher thermal stability, corresponding to a more complete crystal structure and higher local order.

[0054] 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 modified plant fiber reinforced self-healing microbial cement mortar, characterized in that, The raw materials of cement mortar, by weight, include: 980-1020 parts of ordinary Portland cement, 480-520 parts of water, 1670-1730 parts of standard sand, 7.5-8.5 parts of calcium lactate, 31-35 parts of expanded perlite-supported microbial self-healing agent, and graphene oxide-modified plant fiber. The amount of graphene oxide-modified plant fiber added is 0.8-1.2 vol.% of the sum of the volumes of ordinary silicate cement and standard sand. Expanded perlite-supported microbial self-healing agent and graphene oxide-modified plant fiber form a dual-interface self-healing component. Plant fibers include coconut fiber, bamboo fiber, or sisal fiber; The preparation method of graphene oxide modified plant fiber is as follows: plant fiber is immersed in an oxidant for treatment, dried and then immersed in a reducing agent for treatment, washed and dried to complete the oxidation-reduction pretreatment, the pretreated plant fiber is immersed in a graphene oxide dispersion for 1.5-2.5 h, and then washed and dried to obtain graphene oxide modified plant fiber. The reducing agent is a 0.02% sodium borohydride solution, a dilute hydrazine hydrate solution, or a citric acid solution; after immersion in the reducing agent, the sample is treated at room temperature for 1.5-2.5 hours.

2. The cement mortar according to claim 1, characterized in that, The raw materials of the cement mortar, by weight, include: 1000 parts of ordinary silicate cement, 500 parts of water, 1700 parts of standard sand, 8 parts of calcium lactate, 33 parts of expanded perlite-supported microbial self-healing agent, and graphene oxide-modified plant fiber. The amount of graphene oxide-modified plant fiber added is 1.0 vol. of the sum of the volumes of ordinary silicate cement and standard sand.

3. The cement mortar according to claim 1, characterized in that, Coconut fiber has a single fiber diameter of 20-50 μm, an aspect ratio of 200-500, a surface roughness of 3.5-5.0 μm, and a specific surface area of ​​1.60 m² / g; bamboo fiber has a single fiber diameter of 15-35 μm, an aspect ratio of 286-667, a surface roughness of 2.0-3.2 μm, and a specific surface area of ​​1.90 m² / g; sisal fiber has a single fiber diameter of 20-40 μm, an aspect ratio of 250-500, a surface roughness of 4.0-6.5 μm, and a specific surface area of ​​2.45 m² / g.

4. The cement mortar according to claim 1, characterized in that, The preparation method of expanded perlite-supported microbial self-healing agent is as follows: Expanded perlite with a particle size of 1.00 mm-3.00 mm and a water absorption rate of 298.2% is selected as a carrier, and the expanded perlite is soaked in a solution of Bacillus pseudostrongylus with an optical density of 0.6 for 20-28 h to obtain the expanded perlite-supported microbial self-healing agent.

5. The cement mortar according to claim 1, characterized in that, The oxidant is a sodium periodate solution, hydrogen peroxide solution, or sodium hypochlorite solution with a mass fraction of 0.3%; the treatment temperature after immersion in the oxidant is 35-55 ℃, and the time is 1.5-2.5h; the concentration of the graphene oxide dispersion is 1.0-3.0 mg / mL.

6. A method for preparing cement mortar according to any one of claims 1-5, characterized in that, The preparation method includes the following steps: Step 1: Preparation of expanded perlite-supported microbial self-healing agent: A solution of Bacillus pseudostrongylus with an optical density of 0.6 was mixed with expanded perlite to prepare the expanded perlite-supported microbial self-healing agent. Step 2, Preparation of graphene oxide modified plant fiber: The plant fiber is first subjected to oxidation-reduction pretreatment, and then immersed in graphene oxide dispersion for loading to obtain graphene oxide modified plant fiber. Step 3: Preparation of cement mortar: Dry mix expanded perlite-supported microbial self-healing agent, graphene oxide-modified plant fiber, ordinary silicate cement, standard sand and calcium lactate, then add water and stir, and pour into molds to obtain cement mortar.

7. The preparation method according to claim 6, characterized in that, In step three, the dry mixing speed is 100-150 r / min, and the time is 20-60 s.

8. The preparation method according to claim 6, characterized in that, In step three, an equal-volume substitution method is used to replace part of the standard sand with expanded perlite-supported microbial self-healing agent, so that the sand-binder ratio of the cement mortar is always maintained at 2.

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