A self-healing cementitious material and method of manufacture

Abstract

The application discloses a kind of based on bacillus pasteurii mineralization deposition crack self-repair cement-based material and preparation method, including cement base material, premix one and premix two, the premix one includes urease-producing bacteria and carrier that have adsorbed calcium ion, and the premix two includes urease-producing bacteria and carrier that are not adsorbed calcium ion.The diatomite of the microorganism of the present application is divided into two parts, one part is diatomite load not in advance adsorbed calcium ion microorganism, and another part is diatomite load in advance adsorbed calcium ion microorganism.Therefore, both can ensure that cement-based material crack is repaired in time after cracking, and the durability of cement-based material after repair can be improved.The crack self-repair renewable cement-based material based on bacillus pasteurii mineralization deposition prepared by the present application is a kind of renewable cement-based material with crack self-diagnosis and self-repair, green and environmental protection, meets the current economic society to the green, environmental protection and intelligent requirements of building material.

Description

Technical Field

[0001] This invention relates to a self-healing cement-based material, and more particularly to a self-healing cement-based material for cracks based on Bacillus pasteurellium mineralization deposition and its preparation method. Background Technology

[0002] Concrete is currently the most widely used and applied building material. However, due to its low tensile strength, it is prone to cracking, which reduces its strength. Furthermore, harmful chemicals (such as chloride ions) can easily enter the concrete through cracks, leading to concrete deterioration and steel corrosion, thus reducing its service life.

[0003] Traditional crack repair methods, while capable of filling cracks to some extent, suffer from drawbacks such as complex operation, high labor costs, damage to concrete structures, and inability to repair in a timely manner. In contrast, the application of microbial self-healing cement-based materials not only meets the requirements for crack repair but also eliminates the need for manual inspection and repair, resulting in low energy consumption and environmental friendliness.

[0004] Pasteurella multocida is a bacterium that produces urease through its metabolism, breaking down urea into... and The microorganism *Pasteurella multocida* possesses strong mineralization capabilities, a certain degree of alkali resistance, and high urease production, making it a high-quality microorganism suitable for self-healing mortars. The mineralization process induced by *Pasteurella multocida* is as follows: when microcracks form in concrete, the environment surrounding the spores changes; oxygen and moisture enter the cracks, causing the spores to germinate into vegetative cells. These cells then undergo normal metabolic activities, producing urease, which promotes the hydrolysis of urea. and In an alkaline environment, It reacts with calcium ions to form calcium carbonate, which fills the cracked areas, enabling self-repair of the cracks and protecting the concrete and internal reinforcing steel. Figure 5 As shown. However, although the extremely high urease production rate of Bacillus pasteurellii can accelerate the deposition of mineral products, the resulting mineral products are mostly large-diameter, loose calcium carbonate precipitates, which is not conducive to improving the durability of cement-based materials.

[0005] The literature (Qian C, Wang J, Wang R, et al. Corrosion protection of cement-based building materials by surface deposition of CaCO3 by Bacillus pasteurii[J]. Materials Science and Engineering:C,2009,29(4):1273-1280.) shows that when calcium ions are added to the mineralization system first, the pre-adsorption of calcium ions by Bacillus pasteurii can inhibit the rate of urease generation to a certain extent, resulting in calcite with smaller, denser, and more stable precipitates (such as...) Figure 1 and Figure 2 As shown, Figure 2 The first group (where urea and calcium source were added simultaneously); the second group (where urea was added 24 hours after the calcium source); and the third group (where urea was added 48 hours after the calcium source) significantly increased the likelihood that *Pasteurella multocida*, which pre-adsorbed calcium ions, would become nucleation sites. This further improved the utilization efficiency of *Pasteurella multocida* and the likelihood of mineralization products forming throughout the cement-based material, thus increasing the potential for repair after cracking. However, pre-adsorption of calcium ions slowed down the urease production rate of *Pasteurella multocida*, reduced the precipitation rate, and slowed the repair rate, potentially leading to the problem that early-stage cracking in cement-based materials might not be repaired in a timely manner. Summary of the Invention

[0006] Objective of this invention: The objective of this invention is to provide a self-healing cement-based material for cracks based on Bacillus pasteurellium mineralization deposition, addressing the problem that existing self-healing materials using Bacillus pasteurellium mineralization to repair cracks cannot simultaneously achieve both repair speed and durability. Another objective of this invention is to propose a method for preparing the self-healing cement-based material for cracks, solving the problem of how to apply Bacillus pasteurellium to prepare the aforementioned self-healing cement-based material for cracks.

[0007] Technical solution: The present invention provides a self-healing cement-based material for cracks, comprising a cement base material, a premix one, and a premix two. The premix one contains urease-producing bacteria that have adsorbed calcium ions and a carrier, and the premix two contains urease-producing bacteria that have not adsorbed calcium ions and a carrier. The total weight of the premix one and the premix two is 1%-25% of the weight of the cement base material.

[0008] This invention innovatively proposes adding two types of premixes to cement-based materials: one is a porous adsorption carrier loaded with *Pasteurella multocida* without pre-adsorbed calcium ions, and the other is a porous adsorption carrier loaded with *Pasteurella multocida* that has pre-adsorbed calcium ions. After the cement-based material cracks, the mineralization process can be divided into two steps. First, the *Pasteurella multocida* without pre-adsorbed calcium ions produces urease to decompose urea, rapidly generating loose precipitates to initially repair the cracks. The *Pasteurella multocida* with pre-adsorbed calcium ions generates urease at a relatively slower rate, which can be considered the second step of the mineralization process. The denser precipitate generated at this stage improves the durability of the repaired cement-based material.

[0009] Preferably, the urease-producing bacterium is *Bacillus pasteurellii*, the carrier is a porous adsorption substrate, and the cement substrate comprises cement, sand, water, and nutrients for the metabolism and growth of *Bacillus pasteurellii*. As a urease-producing microorganism, *Bacillus pasteurellii* can produce urease to hydrolyze urea into ammonia and carbon dioxide. Ammonia increases the pH of the surrounding environment, promoting the conversion of carbon dioxide into carbonate ions, leading to CaCO3 precipitation. Furthermore, its cell wall is negatively charged, making it an ideal nucleation site for calcium carbonate crystals. *Bacillus pasteurellii* that has pre-adsorbed calcium ions is more likely to become a nucleation site, increasing the likelihood of repairing cracks in the cement-based material after cracking. The *Bacillus pasteurellii* used in this invention is highly adaptable to highly alkaline environments and can survive well in the alkaline environment inside the cement-based material. Simultaneously, *Bacillus pasteurellii* is in a dormant state when the cement-based material is not cracked, which can significantly extend the service life of the cement-based material. The nutrients are mainly used for the germination and metabolic activities of *Bacillus pasteurellii*.

[0010] Preferably, the porous adsorption substrate includes one or more of diatomaceous earth, porous carbon materials, attapulgite, zeolite, vermiculite, and perlite. Porous adsorption substrates such as diatomaceous earth possess advantages such as porosity, light weight, chemical stability, and biological inertness, making them suitable as carriers for immobilizing Bacillus pasteurellii. Their nanoscale pore structure not only facilitates the adsorption of Bacillus pasteurellii, protecting it from the alkaline environment within cement-based materials, but also promotes the uniform dispersion of Bacillus pasteurellii within the cement matrix, thereby significantly improving the self-healing performance of cement-based materials.

[0011] Preferably, the formulation of the above-mentioned self-healing cement-based material for cracks comprises the following raw materials by weight: 3500-4500 parts cement base material, 135-215 parts premix one and 135-215 parts premix two.

[0012] Preferably, the weight ratio of premix one to premix two is 1:(1-1.5). A reasonable ratio of the two premixes can effectively avoid interference between the rapid repair action in the first step and the dense repair action in the second step, thus resolving the contradiction between achieving both rapid repair and durable repair.

[0013] The preparation method of the above-mentioned self-healing cement-based material for cracks according to the present invention includes the following steps:

[0014] (1) Preparation of premix 1: The carrier is added to the suspension of Bacillus pasteurellii that has pre-adsorbed calcium ions and mixed thoroughly;

[0015] (2) Preparation of premix 2: The carrier was added to the suspension of Bacillus pasteurellium that had not adsorbed calcium ions and mixed thoroughly;

[0016] (3) Mix the cement base material with premix one and premix two according to the proportion to obtain the self-healing cement base material.

[0017] In some embodiments, the method for preparing the Bacillus pasteurellium suspension that pre-adsorbs calcium ions in step (1) is as follows:

[0018] Calcium salts are added to a liquid culture medium or bacterial resuspension. *Bacillus pasteurellii* is activated and cultured using the liquid culture medium to obtain a bacterial culture solution. The bacterial culture solution is centrifuged, and the supernatant is discarded to obtain a bacterial precipitate. The bacterial precipitate is resuspended in the bacterial resuspension solution to obtain a bacterial concentration of 10. 6 ~10 9 A suspension of *Pasteurella multocida* pre-adsorbed with calcium ions (cFU / mL). This method involves adding an extra concentration of calcium ions during the culture or resuspension of *Pasteurella multocida* to pre-adsorb calcium ions, thereby improving the durability of cement-based materials after repair. Pre-addition of calcium ions helps maintain osmotic pressure balance within the cells, promoting *Pasteurella multocida* growth. Furthermore, the pre-adsorption of calcium ions around the cell wall reduces the rate of urease production by *Pasteurella multocida*, resulting in a denser calcium carbonate precipitate. This also improves the utilization efficiency of *Pasteurella multocida*, enhancing the feasibility and durability of cement-based material repair.

[0019] Preferably, in step (1), the amount of carrier added is 20wt%-70wt% of the Bacillus pasteurellium suspension that has pre-adsorbed calcium ions; in step (2), the amount of carrier added is 20wt%-70wt% of the Bacillus pasteurellium suspension that has not adsorbed calcium ions; and calcium salt is added at a ratio of 7.8-10.4 g / L.

[0020] Preferably, the calcium salt is an organic acid calcium salt, and the liquid used to suspend the bacterial cells is distilled water or physiological saline. The method for activating and culturing *Bacillus pasteurellii* is as follows: under aseptic conditions, *Bacillus pasteurellii* lyophilized powder is inoculated into an alkaline liquid bacterial culture medium at pH 9.0, cultured by shaking, and the bacterial culture at the plateau phase is passaged. The passage culture is repeated at least twice to obtain the bacterial culture medium. The organic acid calcium salt can be selected from calcium formate, calcium acetate, calcium propionate, calcium acetate, etc.

[0021] Preferably, the method for preparing the cementitious substrate is as follows:

[0022] (1) The nutrients are prepared by thoroughly mixing 40-50 parts by weight of urea, 8-11 parts by weight of calcium formate, 15-25 parts by weight of peptone, 15-25 parts by weight of yeast powder, and 4-6 parts by weight of sodium chloride.

[0023] (2) A cement base material is prepared by mixing 900-1100 parts by weight of cement, 2700-3000 parts by weight of sand, 225-325 parts by weight of water and 25-40 parts by weight of nutrients.

[0024] Beneficial Effects: Compared with existing technologies, this invention has the following significant advantages: The self-healing cement-based material prepared by this invention can not only rapidly fill and repair cracks in their early stages, meeting the requirements for early water penetration resistance repair, but also continuously and densely repair cracks, ultimately achieving a high water penetration resistance repair rate and effectively improving the durability of the self-healing cement-based material. This invention successfully utilizes porous adsorption carriers and Bacillus pasteurellii to prepare a green and environmentally friendly cement-based material with self-diagnosis and self-repair capabilities for cracks, while also considering repair speed and durability. The preparation method is simple and reliable, and it has good application prospects. Attached Figure Description

[0025] Figure 1 SEM image of the precipitate formed by Bacillus pasteurellii;

[0026] In the figure, (a) shows the precipitate formed when urea and calcium source are added simultaneously; (b) shows the precipitate formed when urea is added after calcium source.

[0027] Figure 2 XRD patterns of precipitates obtained under different urea addition methods;

[0028] Figure 3 This is a schematic diagram illustrating the self-healing principle of concrete cracks.

[0029] Figure 4 A comparison of calcium carbonate production in different Bacillus pasteurellium culture media at the same in vitro mineralization time.

[0030] Figure 5 The water penetration resistance repair rate of the concrete samples after 8 and 28 days of self-healing.

[0031] Figure 6 This is a schematic diagram of a testing device used to determine the water penetration resistance and repair rate of a specimen. Detailed Implementation

[0032] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0033] Example 1: The composition ratio and preparation method of the self-healing cement-based material are as follows:

[0034] (1) Dissolve 5g yeast extract, 5g peptone and 1.25g sodium chloride in 225mL distilled water, adjust the pH of the above culture medium to 9.0 with Tris, sterilize at 120℃ for 30 minutes to prepare the first type of liquid culture medium;

[0035] (2) Dissolve 5g yeast extract, 5g peptone, 1.25g sodium chloride and 2.03g calcium formate in 225mL distilled water, adjust the pH of the above culture medium to 9.0 with Tris, and sterilize at 120℃ for 30 minutes to prepare the second type of liquid culture medium; the calcium formate in this example can also be conventionally replaced with other organic acid calcium salts such as calcium acetate, calcium propionate, and calcium acetate, or inorganic calcium salts such as calcium nitrate.

[0036] (3) Under aseptic conditions, the freeze-dried Bacillus pasteurellii powder was activated and inoculated into the first type of liquid culture medium and the second type of liquid culture medium, respectively, and cultured by shaking.

[0037] (4) Set the wavelength of the microbial reader to 600 nm and roughly measure the concentration of microorganisms in the culture medium at 2-4 hour intervals. When the OD value in the culture medium reaches the maximum, that is, the plateau phase of the bacterial growth curve, take 1% of the culture medium containing Bacillus pasteurellii and inoculate it into a new culture medium for subculture.

[0038] (5) Step (3) is repeated twice to obtain third-generation Pasteurella multocida that pre-adsorbed calcium ions and those that did not pre-adsorb calcium ions.

[0039] (6) The bacterial cultures of the third-generation Bacillus pasteurellium with pre-adsorbed calcium ions and those without pre-adsorbed calcium ions were centrifuged at 4000 r / min for 20 min to collect bacterial sludge. The bacterial sludge was resuspended in physiological saline with a sodium chloride concentration of 8.5 g / L to prepare 1×10⁻⁶ cells / mL of bacterial culture. 9 A bacterial suspension of cells / mL;

[0040] (7) Add 45g of diatomaceous earth to 160g of bacterial suspension that has pre-adsorbed calcium ions and mix for 1 hour on a shaker at 30℃ and 100rpm to prepare premix one.

[0041] (8) Add 45g of diatomaceous earth to 159.5g of bacterial suspension that has not pre-adsorbed calcium ions, and mix for 1 hour on a shaker at 30℃ and 100rpm to prepare premix two.

[0042] (9) Pour 900g of cement, 2400g of sand, 225g of water, the two types of premixes (135g of premix one and 135g of premix two), 8.95g of urea, 3.65g of calcium formate, 9.04g of peptone, 9.04g of yeast powder, and 2.25g of sodium chloride into a mixer and stir evenly to obtain the self-healing and regenerated cement-based material.

[0043] Example 2: The composition ratio and preparation method of the self-healing cement-based material are as follows:

[0044] (1) Dissolve 5g yeast extract, 5g peptone, and 1.25g sodium chloride in 250mL distilled water, adjust the pH of the culture medium to 9.0 with Tris, and sterilize at 120℃ for 30 minutes to prepare liquid culture medium;

[0045] (2) Under aseptic conditions, the freeze-dried powder of Bacillus pasteurellii was activated and inoculated into liquid culture medium and cultured by shaking.

[0046] (3) Set the wavelength of the microbial reader to 600 nm and roughly measure the concentration of microorganisms in the culture medium at 2-4 hour intervals. When the OD value in the culture medium reaches its maximum, take 1% of the culture medium containing Bacillus pasteurellii and inoculate it into a new culture medium for subculture.

[0047] (4) Repeat step (3) twice to obtain third-generation Pasteurella multocida;

[0048] (5) The third-generation Bacillus pasteurellium culture was centrifuged at 4000 r / min for 20 min to collect the bacterial sludge. Half of the bacterial sludge was resuspended in an aqueous solution with a sodium chloride concentration of 8.5 g / L and a calcium formate concentration of 62.5 mM to prepare Bacillus pasteurellium with a pre-adsorbed calcium ion concentration of 1 × 10⁻⁶. 9 A bacterial suspension of 10⁶ cells / mL was prepared by resuspending the remaining bacterial sludge in an 8.5 g / L sodium chloride aqueous solution to obtain *Bacillus pasteurellis* with a concentration of 1 × 10⁶ cells / mL before calcium ion adsorption. 9 A bacterial suspension of cells / mL;

[0049] (6) Add 45g of diatomaceous earth to 160g of bacterial suspension that has not pre-adsorbed calcium ions and mix for 1 hour on a shaker at 30℃ and 100rpm to prepare premix one.

[0050] (7) Add 45g of diatomaceous earth to 159.5g of bacterial suspension that has pre-adsorbed calcium ions and mix for 1 hour on a shaker at 30℃ and 100rpm to prepare premix two.

[0051] (8) Pour 900g of cement, 2700g of sand, 225g of water, the two types of premixes (135g of premix one and 135g of premix two), 8.95g of urea, 3.65g of calcium formate, 9.04g of peptone, 9.04g of yeast powder, and 2.25g of sodium chloride into a mixer and stir evenly to obtain the self-healing and regenerated cement-based material.

[0052] Example 3: The composition ratio and preparation method of the self-healing cement-based material are as follows:

[0053] (1) Dissolve 5g yeast extract, 5g peptone and 1.25g sodium chloride in 225mL distilled water, adjust the pH of the above culture medium to 9.0 with Tris, sterilize at 120℃ for 30 minutes to prepare the first type of liquid culture medium;

[0054] (2) Dissolve 5g yeast extract, 5g peptone, 1.25g sodium chloride and 2.03g calcium formate in 225mL distilled water, adjust the pH of the above culture medium to 9.0 with Tris, and sterilize at 120℃ for 30 minutes to prepare the second type of liquid culture medium.

[0055] (3) Under aseptic conditions, the freeze-dried Bacillus pasteurellii powder was activated and inoculated into the first type of liquid culture medium and the second type of liquid culture medium, respectively, and cultured by shaking.

[0056] (4) Select a wavelength of 600 nm to roughly determine the concentration of microorganisms in the culture medium at intervals of 2-4 hours. When the OD value in the culture medium reaches its maximum, take 1% of the culture medium containing Bacillus pasteurellii and inoculate it into a new culture medium for subculture.

[0057] (5) Repeat the subculture twice to obtain third-generation Pasteurella multocida that pre-adsorbed calcium ions and those that did not pre-adsorb calcium ions.

[0058] (6) The bacterial cultures of the third-generation Bacillus pasteurellium with pre-adsorbed calcium ions and those without pre-adsorbed calcium ions were centrifuged at 4000 r / min for 20 min to collect bacterial sludge. The bacterial sludge was resuspended in physiological saline with a sodium chloride concentration of 8.5 g / L to prepare 1×10⁻⁶ cells / mL of bacterial culture. 9 A bacterial suspension of cells / mL;

[0059] (7) Add 67.5g of diatomaceous earth to 112.5g of bacterial suspension that has pre-adsorbed calcium ions and mix for 1 hour at 30℃ and 100rpm to prepare premix one.

[0060] (8) Add 67.5g of diatomaceous earth to 112.5g of bacterial suspension that has not pre-adsorbed calcium ions and mix for 1 hour at 30℃ and 100rpm to prepare premix two.

[0061] (9) Pour 900g of cement, 2700g of sand, 225g of water, the two types of premixes (182.5g of premix one and 182g of premix two), 8.95g of urea, 3.08g of calcium formate, 9.04g of peptone, 9.04g of yeast powder, and 2.25g of sodium chloride into a mixer and stir evenly to obtain the self-healing cement-based material.

[0062] Example 4: Everything else is the same as in Example 1, except that the bacterial cell concentration in the resuspended bacterial suspension is 1×10⁻⁶. 6 The amount of cement base material used is 1100g cement, 3000g sand, and 325g water. The amount of premix added is 215g of premix one and 215g of premix two.

[0063] Example 5: Everything else is the same as in Example 1, except that:

[0064] In premix one, the amount of diatomaceous earth added is 70 wt% of the Bacillus pasteurellium suspension that has pre-adsorbed calcium ions; in premix two, the amount of diatomaceous earth added is 70 wt% of the Bacillus pasteurellium suspension that has not adsorbed calcium ions.

[0065] Diatomaceous earth can be replaced by one or more of the following materials, depending on actual needs: activated carbon, porous graphite, attapulgite, zeolite, vermiculite, and perlite.

[0066] Comparative Example 1: The rest is the same as in Example 1, except that only premix 2 is added, and premix 1 is replaced with an equal amount of premix 2.

[0067] Comparative Example 2: Everything else is the same as Comparative Example 1, except that an equal amount of Pasteurella multocida suspension without pre-adsorbed calcium ions is used to replace premix one.

[0068] Comparative Example 3: The rest is the same as Comparative Example 1, except that an equal amount of distilled water is used instead of the bacterial suspension.

[0069] Example 6: Using the weight ratio of premix 1 loaded with pre-adsorbed calcium ions and premix 2 loaded with unadsorbed calcium ions as variables, the weight ratios of premix 1 and premix 2 were set to 4:1, 2:1, 1:1, 1:2, 1:3, and 1:4. Self-healing cement-based material samples were prepared using the method of Example 2, and the crack water penetration resistance repair rate was measured at 8 days and 28 days. The water penetration resistance repair rate was tested by permeability testing. (1) The concrete specimen with repair time t was installed in the following way: Figure 6(1) In the container shown, Vaseline is applied to the sides and bottom of the specimen to ensure that the sides and bottom of the concrete specimen are in close contact with the container; (2) Water is continuously poured into the container from the top to keep the water level constant and ensure that the water pressure on the specimen remains stable; (3) When water seeps out from the bottom of the specimen, the timing is started, and the volume of water that seeps through the specimen in 1 minute is recorded and the mass of the water out is recorded as M.

[0070] Using the formula:

[0071]

[0072] In the formula: ε—water penetration resistance repair rate (%)

[0073] M0—Initial seepage flow rate of the specimen (g / s)

[0074] M t —Infiltration flow rate (g / s) of the specimen at a repair age of t days.

[0075] The results are as follows:

[0076] Table 1. Effects of different proportions of premix 1 and premix 2 on the water penetration resistance repair rate of cracks.

[0077] Group 8-day water penetration resistance repair rate (%) 28-day water penetration resistance repair rate (%) 4:1 34.3 89.2 2:1 43.2 87.6 1:1 49.4 86.8 1:2 52.7 84.3 1:3 53.2 74.2 1:4 54.6 66.7

[0078] Table 1 shows that when a relatively large amount of premix one was added, the 8-day water penetration resistance repair rate of the crack was low, but the 28-day water penetration resistance repair rate was high. This indicates that the self-healing material has a low rapid repair capability and cannot provide effective repair in the early stages of crack formation. It requires a longer period of slow densification repair, eventually achieving a better water penetration resistance repair rate at 28 days, thus improving the durability of the repair material. However, when the proportion of premix two gradually increased, especially when the proportion exceeded 1:3, although the early repair capability of the self-healing material was enhanced, the subsequent densification repair effect was significantly weakened. The 28-day water penetration resistance repair rate was significantly lower than other proportions. This may be because premix two, which plays an early repair role, quickly produces a large amount of loose mineralized products to fill the crack. Although it can quickly seal the crack, water and oxygen cannot enter the crack. Instead, it hinders the densification mineralization of Bacillus pasteurellii, which pre-adsorbs calcium ions, leading to the stagnation of the subsequent slow densification repair stage, ultimately affecting the durability repair of the self-healing material.

[0079] Example 7: Two types of culture media as described in Example 1 were prepared, and after autoclaving, five experimental groups were prepared. The composition of the two types of culture media in each group is shown in the table below. The media were incubated at 30°C with shaking for three days. The precipitates from each group were collected by filtration, dried, and weighed to obtain the weight of the precipitates in each group.

[0080] Group Type I culture medium (mL) Second type of culture medium (mL) A 100 0 B 75 25 C 50 50 D 25 75 E 0 100

[0081] Among them, Group A consisted of 100 mL of Pasteurella multocida suspension with pre-adsorbed calcium ions; Group B consisted of 75 mL of Pasteurella multocida suspension with pre-adsorbed calcium ions and 25 mL of untreated Pasteurella multocida suspension; Group C consisted of 50 mL of Pasteurella multocida suspension with pre-adsorbed calcium ions and 50 mL of Pasteurella multocida culture medium without calcium ions; Group D consisted of 25 mL of Pasteurella multocida suspension with pre-adsorbed calcium ions and 75 mL of Pasteurella multocida suspension without calcium ions; and Group E consisted of 100 mL of Pasteurella multocida suspension without calcium ions.

[0082] Depend on Figure 4 The results show that, under the same short-term mineralization time, the mineralization rate of *Pasteurella multocida* that pre-adsorbed calcium ions was slower, and less mineralization products were produced. Conversely, the higher the proportion of *Pasteurella multocida* that did not pre-adsorb calcium ions, the faster the mineralization process, and the significantly higher the amount of mineralization products produced compared to the group with a lower proportion. Analysis reveals that when the proportion of *Pasteurella multocida* that did not pre-adsorb calcium ions in the groups was less than 50%, the factor of whether or not calcium ions were pre-adsorbed significantly affected the mineralization rate of *Pasteurella multocida*, but the influence decreased after the proportion exceeded 50%. Considering the overall impact of whether *Pasteurella multocida* pre-adsorbed calcium ions on the crack repair effect after concrete cracking, there is an optimal value for the proportion of *Pasteurella multocida* that did not pre-adsorb calcium ions.

[0083] Example 8: Five groups of concrete were prepared, of which group A was the cement-based material prepared in Example 1; group B was the cement-based material prepared in Example 2; group C was the cement-based material prepared in Comparative Example 1; group D was the cement-based material prepared in Comparative Example 2; and group E was the cement-based material prepared in Comparative Example 3. Cracks were prepared and cured under standard conditions, and permeability tests were conducted at 8 days and 28 days. The steps are as follows: (1) The concrete specimen with a repair time of t was installed in the following way: Figure 6 (1) In the container shown, Vaseline was applied to the sides and bottom of the specimen to ensure that the sides and bottom of the concrete specimen were in close contact with the container; (2) Water was continuously poured into the container from the top to keep the water level constant and to ensure that the water pressure on the specimen remained stable; (3) Timing was started when water seeped out from the bottom of the specimen.

[0084] Record the volume of water that permeates through the specimen within 1 minute and record the mass of the water exiting the specimen, M.

[0085] Using the formula:

[0086]

[0087] In the formula: ε—water penetration resistance repair rate (%)

[0088] M0—Initial seepage flow rate of the specimen (g / s)

[0089] M t —Infiltration flow rate (g / s) of the specimen at a repair age of t days.

[0090] Experimental results are as follows Figure 5 As shown, Group A is the cement-based material prepared in Example 1; Group B is the cement-based material prepared in Example 2; Group C is the cement-based material prepared in Comparative Example 1; Group D is the cement-based material prepared in Comparative Example 2; and Group E is the cement-based material prepared in Comparative Example 3.

[0091] Depend on Figure 5 The results show that the material in group E, which did not contain Bacillus pasteurellii, lacked mineralization repair capabilities. A comparison between groups D and E shows that diatomaceous earth, as a carrier, can effectively enhance the mineralization repair effect of Bacillus pasteurellii, but the improvement is limited. Compared to group C, groups A and B, while exhibiting good rapid repair capabilities without pre-adsorbing calcium ions, showed poor improvement in material durability in the later stages (the 28-day water penetration resistance repair rate of group C was significantly lower than that of groups A and B). In contrast, the self-healing materials prepared in Examples 1 and 2 not only possessed good early-stage rapid repair capabilities but also slow, dense repair capabilities, ensuring continuous slow, dense repair after rapid crack filling, effectively improving the material's durability.

Claims

1. A self-healing cement-based material for cracks, characterized in that, The product comprises a cement-based material, a premix one, and a premix two. The premix one contains urease-producing bacteria that have adsorbed calcium ions and a carrier, and the premix two contains urease-producing bacteria that have not adsorbed calcium ions and a carrier. The total weight of the premix one and the premix two is 1%-25% of the weight of the cement-based material. The urease-producing bacterium is Bacillus pasteurellii, the carrier is a porous adsorption substrate, and the cement substrate contains cement, sand, water, and nutrients for the metabolism and growth of Bacillus pasteurellii. The nutrient is prepared by thoroughly mixing 40-50 parts by weight of urea, 8-11 parts by weight of calcium formate, 15-25 parts by weight of peptone, 15-25 parts by weight of yeast powder, and 4-6 parts by weight of sodium chloride.

2. The self-healing cement-based material for cracks according to claim 1, characterized in that, The porous adsorption substrate includes one or more of diatomaceous earth, porous carbon materials, attapulgite, zeolite, vermiculite, and perlite.

3. The self-healing cement-based material for cracks according to claim 1, characterized in that, It contains the following raw materials by weight: 3,500-4,500 parts cement base material, 135-215 parts premix one and 135-215 parts premix two.

4. The self-healing cement-based material for cracks according to claim 3, characterized in that, The weight ratio of premix one to premix two is 1:1-1.

5.

5. A method for preparing a self-healing cementitious material for cracks as described in any one of claims 1-4, characterized in that, Includes the following steps: (1) Preparation of premix 1: The carrier is added to the suspension of Bacillus pasteurellii that has pre-adsorbed calcium ions and mixed thoroughly; (2) Preparation of premix 2: The carrier was added to the suspension of Bacillus pasteurellium that had not adsorbed calcium ions and mixed thoroughly; (3) Mix the cement base material with premix one and premix two according to the proportion to obtain the self-healing cement base material.

6. The method for preparing the self-healing cement-based material for cracks according to claim 5, characterized in that, The method for preparing the Bacillus pasteurellium suspension with pre-adsorbed calcium ions in step (1) is as follows: calcium salt is added to a liquid culture medium or bacterial resuspension; Bacillus pasteurellium is activated and cultured in the liquid culture medium to obtain a bacterial culture solution; the bacterial culture solution is centrifuged and the supernatant is discarded to obtain a bacterial precipitate; the bacterial precipitate is resuspended in the bacterial resuspension to obtain a bacterial concentration of 10. 6 -10 9 A suspension of Bacillus pasteurellii pre-adsorbed calcium ions per mL.

7. The method for preparing the self-healing cement-based material for cracks according to claim 5, characterized in that, In step (1), the amount of carrier added is 20wt%-70wt% of the Bacillus pasteurellium suspension that has pre-adsorbed calcium ions; in step (2), the amount of carrier added is 20wt%-70wt% of the Bacillus pasteurellium suspension that has not adsorbed calcium ions; calcium salt is added at a ratio of 7.8-10.4 g / L.

8. The method for preparing the self-healing cement-based material for cracks according to claim 7, characterized in that, The calcium salt is an organic acid calcium salt, and the liquid for resuspending the bacterial cells is distilled water or physiological saline. The method for activating and culturing Bacillus pasteurellis is as follows: under aseptic conditions, Bacillus pasteurellis lyophilized powder is inoculated into an alkaline liquid bacterial culture medium, cultured by shaking, and the bacterial culture at the plateau phase is taken for subculturing. The subculturing is repeated at least twice to obtain the bacterial culture medium.

9. The method for preparing the self-healing cement-based material for cracks according to claim 8, characterized in that, The method for preparing the cement substrate is as follows: Cement base material is prepared by mixing 900-1100 parts by weight of cement, 2700-3000 parts by weight of sand, 225-325 parts by weight of water, and 25-40 parts by weight of nutrients.

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