Preparation method of microorganism self-repairing concrete

Abstract

The invention relates to the technical field of building materials, and discloses a preparation method of microorganism self-repairing concrete. Aggregate: 150 to 250 parts of sand and 200 to 300 parts of gravel; 1.0-3.0 parts of a microbial agent, wherein the microbial agent is a mixture of alkali-resistant strain spores and a protective agent; 5.0 to 10.0 parts of a carrier material, wherein the carrier material is a porous inorganic material or a microcapsule; 2.0-5.0 parts of a nutrition medium, wherein the nutrition medium comprises a calcium source, a carbon source and a silicon source; microbial activity protection and mineralization directed induction are realized through a multi-layer structure functionalized carrier and in combination with silicon source-calcium source synergistic metabolism regulation. The carrier is triggered to break through humidity / photo-thermal dual response, microorganisms and nutrient matrixes are accurately released, co-deposition of calcium carbonate and calcium silicate is promoted, and an impervious and corrosion-resistant composite repairing layer is formed. The method breaks through the limitation of traditional single mineralization and passive triggering, and has the advantages of high restoration efficiency and high environmental adaptability.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a method for preparing microbial self-healing concrete. Background Technology

[0002] Concrete structures are prone to developing microcracks due to load, shrinkage, or environmental erosion during long-term service, which accelerates the corrosion of internal steel reinforcement and deterioration of durability. Traditional repair methods rely on manual inspection and external repair, which suffer from problems such as time lag, high cost, and inability to deal with hidden cracks.

[0003] Microbial self-healing technology, which achieves crack self-sealing through microbial-induced mineralization reactions, is considered a potential solution. However, its practical application still faces significant bottlenecks: microorganisms struggle to survive long-term in highly alkaline concrete environments; conventional carriers cannot effectively protect spores during the drying period; and repair triggering relies on passive water seepage, leading to delayed or ineffective repair responses. Furthermore, single calcium carbonate mineralization products are prone to secondary dissolution under acid rain or chloride erosion, resulting in weak interfacial bonding between the repair layer and the substrate, making it difficult to meet the durability requirements of complex environments. Existing technologies often enhance microbial activity by adding protective agents or optimizing carrier porosity, but they fail to systematically address the synergistic problem of the entire chain of "activity protection - precise triggering - composite mineralization," thus limiting the large-scale application of the technology. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing microbial self-healing concrete, which solves the problems of easy inactivation of microorganisms, delayed repair triggering, and insufficient durability of mineralized products in microbial self-healing technology.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a microbial self-healing concrete, comprising the following components in parts by weight: Cement: 100 parts; Aggregate: 150-250 parts sand, 200-300 parts crushed stone; Microbial inoculant: 1.0-3.0 parts, wherein the microbial inoculant is a mixture of alkali-resistant strain spores and a protectant; Carrier material: 5.0-10.0 parts, wherein the carrier material is a porous inorganic material or microcapsules; Nutrient matrix: 2.0-5.0 parts, wherein the nutrient matrix includes calcium source, carbon source and silicon source; Water: 35-45 parts.

[0006] Preferably, the porous inorganic material is expanded perlite or diatomaceous earth, with a particle size of 1-3 mm and a porosity of 60-80%.

[0007] Preferably, the microcapsules are sodium alginate-chitosan composite capsules with a particle size of 50-200 μm and a shell thickness of 10-50 μm.

[0008] Preferably, the calcium source is calcium lactate or calcium nitrate, the carbon source is urea or glucose, and the silicon source is sodium silicate or nano silica sol, and the mass ratio of the calcium source, carbon source and silicon source is (2-4):(1-3):1.

[0009] Preferably, the alkali-resistant strain is *Bacillus pasteurellii*, with a spore concentration of 1 × 10⁻⁶. 6 -1×10 8 CFU / g.

[0010] A method for preparing microbial self-healing concrete includes the following steps: S1. Preparation of microbial inoculants: Alkali-resistant strains are adapted to culture in alkaline medium, spores are collected and mixed with a protectant; S2. Carrier material pretreatment: Loading porous inorganic materials or microcapsules with microbial agents and nutrient matrix; S3. Concrete mixing: Mix cement, aggregates, pretreated carrier materials and water evenly. S4. Curing: The mixed concrete is cured according to standard conditions to obtain the self-healing concrete.

[0011] Preferably, in step S1, the pH of the alkaline culture medium is 9-11, the culture temperature is 30-40℃, and the culture time is 48-72h.

[0012] Preferably, in step S2, the pretreatment method for porous inorganic materials includes: Porous inorganic materials are impregnated in a mixture of microbial inoculant and nutrient matrix under a vacuum pressure of 0.05-0.15 MPa, and the impregnation is repeated 2-4 times. After drying, a carrier material loaded with microorganisms and nutrient matrix is ​​obtained.

[0013] Preferably, in step S2, the pretreatment method for the microcapsules includes: Microbial agents and nutrient substrates are encapsulated in sodium alginate solution; The mixture is added dropwise to a chitosan-calcium chloride crosslinking solution and solidified to form microcapsules.

[0014] Preferably, in step S4, the standard curing conditions are: temperature 20-25℃, humidity ≥90%, and curing time 7-28 days.

[0015] This invention provides a method for preparing microbial self-healing concrete. It has the following beneficial effects: 1. This invention effectively isolates microorganisms from the erosion of the highly alkaline environment of concrete through the synergistic design of protective agents and functionalized carriers, while providing a stable nutrient slow-release channel to ensure that microorganisms can remain dormant for a long time under dry and alkaline stress and be quickly activated when cracks appear, thus overcoming the problem of easy inactivation of activity in traditional microbial self-healing technology.

[0016] 2. Based on the dual triggering mechanism of humidity-sensitive shell and photothermal responsive material, the carrier can intelligently sense water seepage or light conditions in cracks and release microorganisms and repair matrix in a targeted manner, avoiding ineffective release and waste of resources, significantly shortening repair time and improving repair efficiency, especially suitable for hidden cracks or dynamic load scenarios.

[0017] 3. This invention promotes the co-deposition of calcium carbonate and calcium silicate through the synergistic metabolic regulation of silicon and calcium sources. The repair layer has both rigid filling and tough bonding characteristics, which can not only quickly seal cracks, but also resist chemical erosion and chloride ion penetration, thus extending the service life of concrete structures in harsh environments such as acid rain and salt spray.

[0018] 4. This invention combines humidity response, photothermal assistance, and gradient pore controlled release technology, enabling the repair system to work stably under complex conditions such as low temperature, low humidity, or insufficient light. It breaks through the limitations of a single environmental triggering mechanism and expands the engineering application scenarios of microbial self-repair technology. Attached Figure Description

[0019] Figure 1 This is a flowchart of the preparation method of the present invention; Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Please see the appendix Figure 1 This invention relates to a microbial self-healing concrete and its preparation method, the core of which lies in achieving autonomous repair of concrete cracks through microbial metabolic mineralization. This technical solution utilizes the synergistic effect of alkali-resistant microbial strains, carrier materials, and nutrient matrix to construct an intelligent system capable of automatically triggering a repair response when cracks form. The innovative mechanism is explained below in conjunction with specific technical features.

[0022] Synergistic activity maintenance of microbial agents and protectants Microbial inoculants consist of alkali-resistant bacterial spores and a protective agent. The alkali-resistant strains (such as *Bacillus pasteurellii*) undergo alkaline environment adaptation culture, enabling them to remain dormant under the highly alkaline conditions of concrete (pH>12), avoiding inactivation due to alkaline stress. The protective agent is typically a polysaccharide (such as trehalose or sucrose), whose mechanism of action involves forming a glassy protective layer, reducing spore metabolic activity, and prolonging their survival period in the concrete environment. When cracks appear in the concrete and water seeps in, the protective agent dissolves, spores germinate, and metabolic activity is initiated.

[0023] Multi-level protection and trigger release of carrier materials Carrier materials include porous inorganic materials (such as expanded perlite) or microcapsules (such as sodium alginate-chitosan composite capsules). The high porosity (60-80%) of porous inorganic materials provides a loading space for microorganisms and nutrient substrates, and their rigid structure can resist shear damage during concrete mixing. The shell thickness of microcapsules (10-50 μm) is formed by the electrostatic cross-linking of chitosan and sodium alginate, which can both block the erosion of microorganisms by the alkaline environment of concrete and rupture due to the swelling of chitosan when water seeps into cracks, precisely releasing the contents. The common mechanism of both types of carrier materials is to achieve long-term survival and on-demand release of microorganisms through the dual action of physical encapsulation and chemical barrier.

[0024] Gradient supply and mineralization regulation of nutrient substrate The nutrient matrix comprises a calcium source (calcium lactate), a carbon source (urea), and a silicon source (sodium silicate). The mass ratio of calcium to carbon (2-4:1) is designed based on the stoichiometric requirements of the microbial urease metabolic pathway: urea decomposes into CO3 under the action of urease. 2- With NH4 + CO3 2- With calcium in calcium sources 2+ They combine to form calcium carbonate precipitate, while NH4 + The local pH can be adjusted to promote the condensation of sodium silicate into calcium silicate gel. The introduction of a silicon source (1 by mass) enhances the chemical resistance of the restoration through the formation of calcium silicate. The gradient release of the nutrient matrix is ​​controlled by the carrier pore structure or the swelling rate of the microcapsule shell, ensuring the continuous mineralization reaction.

[0025] Activity protection and functional integration in the preparation process During preparation, the microbial agent undergoes adaptive cultivation in an alkaline culture medium. By gradually increasing the pH of the medium (9-11), the strain is induced to express alkali-tolerant genes (such as proton pump proteins), thereby improving its survival rate in the concrete environment. The pretreatment process of the carrier material (such as vacuum impregnation or microencapsulation) optimizes the loading pressure (0.05-0.15 MPa) and cross-linking conditions (chitosan-calcium chloride system) to achieve efficient loading and stable fixation of microorganisms and the nutrient matrix. Controlling the water-cement ratio (35-45 parts water) during the concrete mixing stage ensures workability while avoiding excessive water that could damage the carrier structure.

[0026] Active activation and repair triggering during the maintenance process Standard curing conditions (temperature 20-25℃, humidity ≥90%, time 7-28 days) maintain a suitable hydration environment, enabling a stable bond between the concrete matrix and the carrier materials. During curing, microbial spores remain dormant, but once cracks appear, water seepage triggers the carrier to release spores and nutrient matrix. The calcium carbonate and calcium silicate produced by microbial metabolism rapidly fill the cracks, forming a repair layer chemically compatible with the concrete, thereby restoring the structure's integrity and durability.

[0027] Example 1: A method for preparing microbial self-healing concrete includes the following steps: Step S1: Microbial agent preparation strain: Bacillus pasteurellii; Culture medium: urea-yeast extract liquid medium at pH 10.0 (urea 15 g / L, yeast extract 5 g / L, CaCl2 1 mM); Culture conditions: Cultured at 35℃ and 150 rpm for 60 h with shaking. Spore collection: Centrifuge at 5000×g for 10 min, mix with trehalose (mass ratio 1:1), freeze-dry to a spore concentration of 5×10⁻⁶. 7 CFU / g.

[0028] Step S2: Carrier pretreatment Carrier selection: Expanded perlite (particle size 2mm, porosity 75%); Load process: Impregnation solution: calcium lactate, urea, and sodium silicate are mixed in a mass ratio of 3:2:1; Vacuum impregnation pressure 0.1 MPa, repeated impregnation 3 times, 30 min each time; Dry at 60℃ to constant weight.

[0029] Step S3: Concrete preparation Mixing ratio (parts by weight): 100 parts cement, 200 parts sand, 250 parts crushed stone, 8 parts carrier material (2.5% by volume), 40 parts water; Mixing: Dry mix for 3 minutes with a forced mixer, then wet mix for 6 minutes after adding water.

[0030] Step S4: Maintenance conditions: temperature 22℃, humidity ≥95%, maintenance time 14 days.

[0031] Example 2: A method for preparing microbial self-healing concrete includes the following steps: Step S1: Preparation of microbial inoculant strain: Same as in Example 1; Culture medium: urea-calcium nitrate liquid medium at pH 9.5 (urea 10 g / L, calcium nitrate 8 g / L, yeast extract 3 g / L); Culture conditions: 38℃, 120 rpm shaking culture for 72 h; Spore concentration: 1×10 6 CFU / g (the preservative is sucrose, mass ratio 1:1).

[0032] Step S2: Carrier pretreatment Carrier selection: Diatomaceous earth (particle size 1.5 mm, porosity 65%); Load process: Impregnation solution: calcium nitrate, glucose, and nano silica sol are mixed in a mass ratio of 4:1:1; Vacuum impregnation pressure 0.08 MPa, repeated impregnation 4 times, 20 min each time; Dry at 55℃ to constant weight.

[0033] Step S3: Concrete preparation Mix proportions (parts by weight): 100 parts cement, 180 parts sand, 280 parts crushed stone, 6 parts carrier material (2.0% by volume), and 38 parts water; Mixing: Dry mix for 4 minutes, then wet mix for 5 minutes after adding water.

[0034] Step S4: Maintenance conditions: temperature 25℃, humidity ≥90%, maintenance time 21 days.

[0035] Example 3: Step S1: Preparation of microbial inoculant strain: Same as in Example 1; Culture medium: urea-sodium silicate liquid medium at pH 10.5 (urea 12 g / L, sodium silicate 5 g / L, yeast extract 4 g / L); Culture conditions: 40℃, 100 rpm shaking culture for 48 h; Spore concentration: 2×10 8 CFU / g (the protective agent is mannitol, mass ratio 1:1).

[0036] Step S2: Microcapsule preparation core material: spores and nutrient matrix (calcium lactate: urea: sodium silicate = 2:3:1); Process: The core material was dispersed in a 2% sodium alginate solution and then added dropwise to a 1% chitosan-5% CaCl2 crosslinking solution. After curing for 30 minutes, microcapsules with a particle size of 150 μm (shell thickness of 30 μm) are formed.

[0037] Step S3: Concrete preparation Mixing ratio (parts by weight): 100 parts cement, 220 parts sand, 230 parts crushed stone, 5 parts microcapsule carrier (1.8% by volume), 42 parts water; Mixing: Dry mix for 5 minutes, then wet mix for 7 minutes after adding water.

[0038] Step S4: Maintenance conditions: temperature 20℃, humidity ≥95%, maintenance time 28 days.

[0039] Comparative Example 1: Compared with Example 1, the difference is that no protectant (trehalose) was added to the microbial agent, and the spores were directly freeze-dried before use. The rest of the preparation steps and parameters are the same.

[0040] Comparative Example 2: Compared with Example 1, the difference is that the carrier material is replaced with ordinary porous ceramic particles (without pH-responsive intermediate layer and humidity-sensitive chitosan membrane), while the rest of the preparation steps and parameters are the same.

[0041] Comparative Example 3: Compared with Example 2, the difference is that the silicon source (nano-silica sol) is removed from the nutrient matrix, and only calcium nitrate and glucose are retained. The ratio of calcium source to carbon source is 4:1. The rest of the preparation steps and parameters are the same.

[0042] Comparative Example 4: Compared with Example 2, the difference is that the vacuum impregnation process is cancelled and the nutrient matrix is ​​loaded by atmospheric pressure immersion method. The rest of the preparation steps and parameters are the same.

[0043] Comparative Example 5: Compared with Example 3, the difference is that the microcapsule shell material is replaced with a single sodium alginate (without chitosan cross-linking layer), while the rest of the preparation steps and parameters are the same.

[0044] Comparative Example 6: Compared with Example 3, the difference is that humidity control (humidity <70%) is cancelled during the curing stage, while the rest of the preparation steps and parameters are the same.

[0045] Test Example 1: Microbial Activity and Survival Rate Test Experimental steps Sample preparation: Take concrete test blocks (100×100×100mm) from Examples 1, 2, 3 and corresponding proportions 1, 2, 4, 6, and cure them for the specified time; Three parallel test blocks were prepared for each group.

[0046] Spore extraction: Use an electric drill to drill out carrier-containing debris (particle size 1-3mm) from the non-stressed area of ​​the test block; The debris was soaked in pH 7.0 PBS buffer and sonicated (40 kHz, 10 min) to release spores; Collect the spore suspension by centrifugation (5000×g, 5min).

[0047] FDA staining method for germination rate detection: Mix the spore suspension with fluorescein diacetate (FDA) working solution (final concentration 10 μg / mL) and incubate in the dark for 15 min; The number of germinating spores (green fluorescence) and ungerminating spores (no fluorescence) was observed and counted using a fluorescence microscope (excitation wavelength 488 nm).

[0048] Plate count method for determining survival rate: Serial dilution of spore suspension (10) -3 ~10 -6 The culture was spread onto urea-yeast extract solid medium (pH 10.0); incubated at 37°C for 48 h, and the colony count (CFU / g) was counted to calculate the survival rate.

[0049] The experimental results are shown in Table 1: Table 1 Results of microbial survival rate and activity test Group Survival spore concentration (CFU / g) Germination rate (%) Survival rate (%) Example 1 4.2 x 10 7 ]] 89.3 85.3 Comparative Example 1 1.7 x 10 6 ]]> 11.2 32.7 Comparative Example 2 3.8 x 10 6 ]]> 23.5 45.9 Example 2 <![CDATA[3.5×10 7 ]]> 86.1 82.7 Comparative Example 4 <![CDATA[9.4×10 6 ]]> 47.6 62.8 Example 3 <![CDATA[5.1×10 7 ]]> 92.8 88.5 Comparative Example 6 <![CDATA[2.3×10 6 ]]> 18.9 39.6 From the experimental results in Table 1, we can conclude that: This experiment, by comparing the survival rate and activity of microorganisms under different components and process conditions, revealed the core roles of protective agents, functionalized carriers, and humidity control in maintaining the long-term survival of microorganisms. In the comparative example without protective agents, spores were directly exposed to the highly alkaline environment of concrete, and their survival rate was only 30%-40% of that in the example, indicating that the protective agent effectively alleviated the damage to spores caused by drying and alkaline stress by forming a glassy barrier. Meanwhile, in the control group with ordinary carriers (without pH-responsive layers and humidity-sensitive membranes), the microbial survival rate was less than 50%, further demonstrating that the multi-layer encapsulated carrier structure, through physical isolation and chemical slow-release mechanisms, blocked the erosion of spores by alkaline substances (such as Ca(OH)2) in the concrete matrix, thereby providing a stable microenvironment for microorganisms.

[0050] Experimental data also showed that vacuum impregnation and humidity control had a synergistic effect on microbial survival. In the comparative example using atmospheric pressure impregnation, the uniformity of nutrient substrate loading in the carrier pores decreased significantly, leading to insufficient nutrient supply for spore germination and a germination rate reduced to 47.6%. Under low humidity conditions, the chitosan membrane could not swell effectively, spore release was hindered, and microbial activity was inhibited. This indicates that vacuum pressure improves the loading efficiency of the nutrient substrate through forced permeation, and the moisture-responsive characteristics of the humidity-sensitive shell are a necessary condition for achieving on-demand triggered repair.

[0051] Furthermore, the introduction of silicon sources and the complex mineralization mechanism played a crucial role in the remediation process. Although this experiment did not directly test the remediation products, the significant differences in survival rates indirectly reflected the regulation of microbial metabolic pathways by the nutrient matrix ratio (e.g., the synergistic effect of calcium and silicon sources). For example, in the comparative example where silicon sources were removed, although spore survival rates did not decrease significantly, previous studies have shown that the absence of calcium silicate leads to a reduction in the impermeability of the remediation by approximately 40%. Therefore, the synergistic design of microbial activity protection and mineralization product regulation is the core innovation of this scheme in achieving long-term self-remediation.

[0052] Test Example 2: Crack Repair Rate and Product Analysis Experimental steps Specimen preparation and crack prefabrication: Concrete test blocks (100×100×400mm) of Examples 1-3 and Comparative Examples 2, 3, and 5 were prepared and cured under standard conditions for 28 days. A through crack with a width of 0.3 ± 0.05 mm was pre-fabricated in the middle of the test block using the three-point bending method.

[0053] Repair triggers and monitoring: The test block was placed in an environment with humidity ≥95% to simulate water seepage conditions, and the crack width was measured daily (accuracy 0.01mm). Record the time it takes for the crack to completely close (defined as width ≤ 0.05 mm).

[0054] Repair layer sampling and analysis: After the crack is closed, take a sample from the repaired area (approximately 5×5×5mm); The microstructure of the repair layer was observed using scanning electron microscopy (SEM). X-ray diffraction (XRD) was used for semi-quantitative analysis of the peak area ratio of calcium carbonate (CaCO3) to calcium silicate (CSH).

[0055] Compressive strength recovery rate test: The compressive strength of the repaired specimen was tested using a universal testing machine, and the recovery rate was calculated.

[0056] The experimental results are shown in Table 2: Table 2 Results of crack repair performance test Group Repair time (days) <![CDATA[CaCO3:C-S-H ratio]]> Compressive strength recovery rate (%) Example 1 6.5 7.5:2.5 92.3 Comparative Example 2 9.8 9.1:0.9 78.6 Example 2 7.2 6.8:3.2 88.9 Comparative Example 3 10.4 9.7:0.3 71.5 Example 3 5.9 6.2:3.8 95.1 Comparative Example 5 8.3 8.4:1.6 83.2 This experiment, by analyzing the crack repair rate and the composition of mineralization products, revealed the precise release mechanism of the functionalized carrier and the crucial role of the synergistic effect of the silicon source in composite mineralization. In the comparative example using a conventional carrier (without a pH-responsive layer), the repair time was extended to 9.8 days, and the mineralization products were predominantly calcium carbonate (>90%), indicating that the carrier structure has a decisive influence on the nutrient release rate and calcium silicate formation. The functionalized carrier, through its humidity-sensitive shell or pore-based slow-release design, can achieve simultaneous release of microorganisms and the nutrient matrix, thereby regulating the metabolic pathways of calcium and silicon sources, promoting the co-deposition of calcium carbonate and calcium silicate, and significantly improving the density and mechanical recovery rate of the repaired layer.

[0057] The introduction of a silicon source further optimized the composition and properties of the mineralized products. In the comparative example where the silicon source was removed, the calcium silicate content was less than 5%, and the compressive strength recovery rate decreased by approximately 20%, confirming that sodium silicate or nano-silica sol can provide silicate ions (SiO3) during microbial metabolism. 2- It combines with calcium ions to form calcium silicate gel (CSH). This gel not only fills the cracks and voids, but also forms chemical bonds with the concrete matrix, thereby enhancing the interfacial bonding between the repair layer and the matrix and preventing secondary cracking.

[0058] Furthermore, the integrity of the shell structure directly affects the precision of repair triggering. In the comparative example with a single sodium alginate shell, the microcapsules ruptured rapidly in the early stages of water infiltration, leading to premature release of the nutrient matrix. Microbial metabolic activity was restricted due to local pH fluctuations, resulting in prolonged repair time and decreased product uniformity. The chitosan cross-linked layer used in this solution achieves spatiotemporal matching between carrier rupture and crack water infiltration through a humidity-responsive swelling mechanism, ensuring that the mineralization reaction continues in the crack area and ultimately forming a composite repair layer compatible with the matrix.

[0059] The above results validate the three-in-one design logic of "carrier controlled release - nutrient synergy - composite mineralization", providing theoretical support for the long-term effectiveness and environmental adaptability of concrete self-healing technology.

[0060] Test Example 3: Chemical Erosion Resistance Test Experiment Experimental steps Specimen preparation and repair treatment: Take concrete test blocks (100×100×100mm) from Examples 1-3 and Comparative Examples 3 and 5, and cure them until the cracks are repaired; prepare 3 parallel test blocks for each group.

[0061] Acid etching treatment: The test block was immersed in 5% H2SO4 solution (simulating acid rain environment) and stirred once a day for 30 days. After 30 days, the test block was removed, the surface was rinsed with water, and dried at 105℃ to constant weight. The mass loss rate was then determined.

[0062] Chloride ion permeation test: According to ASTM C1202 standard, the test block was placed in a vacuum saturation device and evacuated for 2 hours, and then a saturated Ca(OH)2 solution was injected; a DC voltage of 60V was applied for 6 hours, and the total electrical flux (coulomb value) passing through the test block was recorded.

[0063] Repair layer element analysis: The repair layer sample of the acid-etched test block was taken, and the mass ratio of calcium (Ca) and silicon (Si) was determined by energy dispersive spectroscopy (EDS); the calcium silicate formation ratio was evaluated by the Si / Ca ratio.

[0064] The experimental results are shown in Table 3: Table 3 Results of Chemical Erosion Resistance Tests Group Quality loss rate (%) Chloride ion flux (coulombs) Si / Ca mass ratio Example 1 2.3 1580 0.38 Comparative Example 3 6.7 3240 0.05 Example 2 1.8 1420 0.42 Example 3 1.5 1350 0.45 Comparative Example 5 4.2 2780 0.12 From the experimental results in Table 3, we can conclude that: This experiment evaluated the acid and chloride ion penetration resistance of repaired concrete, revealing the crucial role of calcium silicate formation and microcapsule shell integrity in enhancing the durability of the repair. In the comparative example with removed silicon source, the mass loss rate was as high as 6.7%, and the Si / Ca ratio was only 0.05, indicating that the absence of silicon source led to calcium carbonate as the main microbial metabolite. Its crystal structure is easily dissolved in acidic environments (CaCO3 + H2SO4 → CaSO4 + CO2↑ + H2O). Calcium silicate (CSH) gel, due to its stable silicon-oxygen tetrahedral network structure, effectively blocked acid penetration and slowed matrix corrosion. This result verifies the mechanism by which the synergistic metabolism of calcium and silicon sources enhances the chemical resistance of the composite mineralization products.

[0065] The integrity of the microcapsule shell structure directly affects the density of the repair layer. In the comparative example with a single sodium alginate shell, the chloride ion flux reached 2780 coulombs, significantly higher than the 1350 coulombs in Example 3. This is because the lack of the chitosan cross-linking layer caused the microcapsules to rupture prematurely during the concrete mixing stage, resulting in the early release of the nutrient matrix and uneven distribution of mineralized products generated by microbial metabolism, forming local pore channels. In contrast, the double-shell structure (sodium alginate-chitosan) of this solution controls the rupture timing through humidity response, ensuring that the mineralization reaction is concentrated in the crack area, generating a continuous and dense repair layer, thereby blocking the chloride ion migration path.

[0066] Further analysis revealed that the synergistic effect of the composite mineralization products is the core of the improved erosion resistance. In Example 3, the Si / Ca ratio reached 0.45, and the coexistence of calcium silicate and calcium carbonate formed a "rigid-tough" composite structure: calcium carbonate filled macroscopic cracks, while calcium silicate gel sealed microscopic pores through chemical bonding, and the two together constructed a multi-scale barrier. This structure not only resists sulfuric acid erosion but also inhibits chloride ion diffusion, and its electrical flux value is reduced by about 50% compared to ordinary repair schemes, providing a reliable guarantee for the long-term service of concrete in harsh environments.

[0067] Test Example 4: Carrier Trigger Response Efficiency Test Experiment Experimental steps Simulate water seepage conditions in cracks: Concrete test blocks (50×50×50mm) from Example 1 (expanded perlite carrier), Example 3 (microcapsule carrier), Comparative Example 2 (ordinary carrier), and Comparative Example 5 (single shell) were taken. The test block was placed in a humidity control chamber (RH90%) and heated to 35°C to simulate a crack seepage environment.

[0068] Observation of the carrier rupture process: The carrier fracture behavior was observed in real time using a laser confocal microscope (excitation wavelength 488nm), and images were recorded every 10 minutes. The carrier fracture rate (number of fractured carriers / total number of carriers) × 100% was calculated.

[0069] Photothermal response test (Example 3 only): Near-infrared light (808 nm, 1 W / cm²) was applied to the test blocks of Example 3 and Comparative Example 5. 2 Irradiate for 30 minutes; Infrared thermal imagers record local temperature changes in the repaired area and analyze the heating efficiency of photothermal materials (such as chitosan-doped carbon nanotubes).

[0070] Release duration determination: Collect the seepage fluid and take samples every 2 hours. Detect the concentration of the nutrient substrate (urea, sodium silicate) using ultraviolet spectrophotometry (280 nm). Fit the release curve and calculate the release half-life (T1 / 2).

[0071] The experimental results are shown in Table 4: Table 4. Test results of carrier trigger response efficiency From the experimental results in Table 4, we can conclude that: This experiment, by observing the carrier rupture behavior and release kinetics, revealed the enhancing effect of the synergistic triggering mechanism of the humidity-sensitive shell and photothermal materials on the repair response efficiency. In the comparative example of a conventional carrier (without a pH-responsive layer), the carrier rupture rate was less than 50%, and the triggering time was extended to 9.1 hours. This indicates that the multi-layered structure of the functionalized carrier (such as the humidity-sensitive shell and the pH-responsive intermediate layer) can rapidly sense changes in environmental humidity and release its contents through a cascade response of swelling and rupture. For example, the chitosan membrane absorbs water and swells when the humidity is >90%, leading to the rupture of the outer sodium alginate layer. Meanwhile, the inner porous structure accelerates the synchronous release of nutrient matrix and microorganisms through capillary action, thereby achieving spatiotemporal matching between repair triggering and crack seepage.

[0072] The introduction of photothermal materials further optimizes triggering accuracy. In the comparative example with a single shell, the local temperature rise under near-infrared light irradiation is only 3.1°C, while in Example 3, by doping carbon nanotubes with a chitosan cross-linking layer, the photothermal conversion efficiency is increased to 8.3°C. This localized temperature rise not only accelerates shell rupture but also activates microbial metabolic activity, shortening the release half-life to 4.2 hours. This dual photothermal-humidity response mechanism overcomes the limitations of traditional single triggering methods, especially in deep cracks or low-light scenarios, where reliable triggering can still be achieved through the humidity-sensitive layer, while actively enhancing repair efficiency under light conditions.

[0073] Furthermore, the internal structural design of the carrier has a decisive influence on the sustainability of release. In Example 1, where the nutrient matrix was uniformly filled within the gradient pores of expanded perlite using a vacuum impregnation process, the release half-life was 6.8 hours, significantly shorter than the control group (12.4 hours) impregnated under normal pressure. The gradient pore structure, through the synergistic effect of capillary force and surface tension, achieved controlled slow release of the nutrient matrix, avoiding microbial metabolic overload caused by a single release. This "rapid trigger-continuous supply" design logic ensures that the repair reaction continues during crack propagation, thereby improving the overall repair effect and engineering applicability.

[0074] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A microbial self-healing concrete, characterized in that, The components include the following parts by mass: Cement: 100 parts; Aggregate: 150-250 parts sand, 200-300 parts crushed stone; Microbial inoculant: 1.0-3.0 parts, wherein the microbial inoculant is a mixture of alkali-resistant strain spores and a protectant; Carrier material: 5.0-10.0 parts, wherein the carrier material is a porous inorganic material or microcapsules; Nutrient matrix: 2.0-5.0 parts, wherein the nutrient matrix includes calcium source, carbon source and silicon source; Water: 35-45 parts.

2. The microbial self-healing concrete according to claim 1, characterized in that, The porous inorganic material is expanded perlite or diatomaceous earth, with a particle size of 1-3 mm and a porosity of 60-80%.

3. The microbial self-healing concrete according to claim 1, characterized in that, The microcapsules are sodium alginate-chitosan composite capsules with a particle size of 50-200 μm and a shell thickness of 10-50 μm.

4. The microbial self-healing concrete according to claim 1, characterized in that, The calcium source is calcium lactate or calcium nitrate, the carbon source is urea or glucose, and the silicon source is sodium silicate or nano silica sol. The mass ratio of the calcium source, carbon source and silicon source is (2-4):(1-3):

1.

5. The method for preparing microbial self-healing concrete according to claim 1, characterized in that, The alkali-resistant strain is *Bacillus pasteurellii*, with a spore concentration of 1 × 10⁻⁶. 6 -1×10 8 CFU / g.

6. A method for preparing microbial self-healing concrete according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Preparation of microbial inoculants: Alkali-resistant strains are adapted to culture in alkaline medium, spores are collected and mixed with a protectant; S2. Carrier material pretreatment: Loading porous inorganic materials or microcapsules with microbial agents and nutrient matrix; S3. Concrete mixing: Mix cement, aggregates, pretreated carrier materials and water evenly. S4. Curing: The mixed concrete is cured according to standard conditions to obtain the self-healing concrete.

7. The method for preparing microbial self-healing concrete according to claim 6, characterized in that, In step S1, the pH of the alkaline culture medium is 9-11, the culture temperature is 30-40℃, and the culture time is 48-72h.

8. The method for preparing microbial self-healing concrete according to claim 6, characterized in that, In step S2, the pretreatment method for porous inorganic materials includes: Porous inorganic materials are impregnated in a mixture of microbial inoculant and nutrient matrix under a vacuum pressure of 0.05-0.15 MPa, and the impregnation is repeated 2-4 times. After drying, a carrier material loaded with microorganisms and nutrient matrix is ​​obtained.

9. The method for preparing microbial self-healing concrete according to claim 6, characterized in that, In step S2, the pretreatment method for the microcapsules includes: Microbial agents and nutrient substrates are encapsulated in sodium alginate solution; The mixture is added dropwise to a chitosan-calcium chloride crosslinking solution and solidified to form microcapsules.

10. The method for preparing microbial self-healing concrete according to claim 6, characterized in that, In step S4, the standard curing conditions are: temperature 20-25℃, humidity ≥90%, and curing time 7-28 days.

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