Self-repairing composite cement as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of concrete materials, and particularly discloses self-repairing composite cement as well as a preparation method and application thereof, and the composite cement comprises the following components: Portland cement, a water reducing agent, nano silicon dioxide and bacillus pasteurii bacterial sludge; wherein relative to 100 parts by weight of Portland cement, the content of the water reducing agent is 0.5 to 1 part, the content of the nano silicon dioxide is 1.5 to 2 parts, and the content of the bacillus pasteurii bacterial sludge is 5 to 8 parts. According to the composite cement, three mechanisms of physical filling, structure optimization and bioremediation are combined, the defects of high brittleness, poor crack resistance, insufficient durability and the like of traditional concrete can be overcome, multi-dimensional synergistic improvement of material performance is achieved, a material system is chemically compatible with a cement matrix, the problem of expansion stress secondary cracks does not exist, and the composite cement has the good comprehensive performance. Meanwhile, the corrosion inhibitor has alkali environment tolerance and long-term activity, can remarkably reduce diffusion coefficients of oxygen and chloride ions, delays corrosion of steel bars, and prolongs the service life of the structure.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of concrete materials, and more particularly relates to a self-repairing composite cement as well as a preparation method and application thereof. BACKGROUND

[0002] As one of the most widely used building materials in modern construction engineering, the performance of concrete directly affects the safety and durability of the structure. However, since concrete is essentially a heterogeneous porous material, there are inevitably many microstructure defects in the preparation and service process. These defects mainly manifest as self-shrinkage, drying shrinkage, plastic settlement, and temperature gradient changes caused by hydration reactions in the early stage, which in turn lead to the formation of microcracks. With the extension of service time, the original microcracks in hardened concrete gradually expand under the action of multiple factors such as external load, environmental temperature and humidity changes, and chemical corrosion, and eventually evolve into macro cracks. The presence of cracks not only destroys the continuity of concrete, but also provides a channel for the infiltration of harmful substances such as oxygen, carbon dioxide, moisture, and chloride ions, thereby triggering a series of chain reactions such as steel corrosion and cement-based material degradation, forming a vicious cycle of "deterioration-cracking-re-deterioration-re-cracking". This phenomenon seriously threatens the safety and service life of the building structure, and has become a key technical problem to be solved in the field of civil engineering.

[0003] In view of the above problems, in recent years, domestic and foreign scholars and technical personnel have proposed a variety of technical means to improve the crack resistance and durability of concrete. On the one hand, at the material level, by optimizing the mix design, introducing high-performance admixtures (such as fly ash, slag powder, silica fume, etc.) and using low water-binder ratio, etc., to reduce the porosity and improve the density of concrete; on the other hand, in terms of construction technology, widely popularizing the use of temperature control curing, layered pouring, and strengthening vibration, etc., to reduce the occurrence of early shrinkage cracks. In addition, in order to inhibit the expansion of cracks, some studies attempt to add fiber reinforced materials (such as steel fiber, polypropylene fiber) to concrete to improve its tensile strength and ductility. Some technical solutions propose to coat the surface of concrete with a waterproof coating or a penetrating protective agent to prevent the intrusion of harmful external media, thereby delaying the deterioration process of the structure. At the same time, in some engineering practices, post-tensioned prestressed concrete structures are also used, which can effectively control the development of cracks by applying a pre-compressive stress to offset part of the tensile stress.

[0004] Although the prior art has alleviated the problem of concrete cracks to some extent, its effect is still difficult to meet the growing demand for engineering safety and durability, such as: although the traditional mix optimization and admixture application can improve the compactness of concrete, it still cannot fundamentally eliminate its inherent brittle characteristics, and has limited ability to control early shrinkage; secondly, although the fiber material can improve the toughness of concrete, due to its high cost, complex construction process, and difficulty in uniform distribution in mass concrete, its practical application is limited; thirdly, the waterproof coating and protective agent can only form a physical barrier on the surface of the concrete, and once there are microcracks in the concrete, harmful substances can still penetrate through capillary action, and the long-term effect is not good; in addition, although the prestressed structure can effectively control cracks, it has high precision requirements in the design and construction process, and it is difficult to deal with secondary cracks caused by environmental changes during service. SUMMARY

[0005] In view of the above defects or improvement needs of the prior art, the present application provides a self-repairing composite cement and its preparation method and application, which can overcome the defects of traditional concrete such as high brittleness, poor crack resistance and insufficient durability, realize multi-dimensional collaborative improvement of material performance, and the material system is chemically compatible with the cement matrix without secondary cracks caused by expansion stress, and has alkali environment resistance and long-term activity, which can significantly reduce the oxygen and chloride diffusion coefficient, delay steel corrosion and prolong the service life of the structure.

[0006] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a self-repairing composite cement, comprising the following components: Portland cement, water reducing agent, nano-silicon dioxide and bacillus pasteurii slurry;

[0007] Among them, the content of the water reducing agent is 0.5-1 parts, the content of the nano-silicon dioxide is 1.5-2 parts, and the content of the bacillus pasteurii slurry is 5-8 parts, relative to 100 parts by weight of the Portland cement.

[0008] Further, the bacillus pasteurii slurry comprises a second bacterial solution, which comprises: a first bacterial solution, a sodium alginate solution and a calcium hydroxide solution;

[0009] Among them, the volume of the sodium alginate solution is 1-2 parts, and the volume of the calcium hydroxide solution is 5-10 parts, relative to 1 volume part of the first bacterial solution.

[0010] Further, the concentration of bacillus pasteurii in the first bacterial solution is 8x10 7 CFU / mL to 1.2x10 8 CFU / mL.

[0011] Further, the concentration of sodium alginate in the sodium alginate solution is 1% to 3%, and the molecular weight of the sodium alginate is 80kDa to 120kDa.

[0012] Further, the content of calcium hydroxide in the calcium hydroxide solution is 2% to 5%.

[0013] Further, the bacillus pasteurii slurry further comprises a carrier material mixed with the second bacterial solution, which comprises at least one of bentonite, silica ash and starch gel.

[0014] Further, when the carrier material is bentonite, the particle size thereof is not greater than 20μm, and the mass ratio of the second bacterial solution to the bentonite is 1:1 to 2:1.

[0015] Further, when the carrier material is silica ash, the particle size thereof ranges from 0.1μm to 1μm, and the mass ratio of the second bacterial solution to the silica ash is 5:1 to 10:1.

[0016] Further, when the carrier material is starch gel, the molecular weight thereof is 10kDa to 50kDa, and the mass ratio of the second bacterial solution to the starch gel is 1:1 to 2:1.

[0017] Further, the particle size of the nanosilica ranges from 10nm to 30nm.

[0018] Further, the water reducing agent is a polycarboxylic acid type water reducing agent.

[0019] The second aspect of the present application provides a preparation method of a self-repairing composite cement, which is applied to the composite cement as described above, and comprises the following steps:

[0020] S1: Culturing bacillus pasteurii in a liquid culture medium to the logarithmic production phase, centrifuging to collect the bacterial cells, and resuspending and diluting with a buffer solution to obtain a first bacterial solution;

[0021] S2: Adding a sodium alginate solution to the first bacterial solution, and slowly adding a calcium hydroxide solution under continuous stirring until the mixture reaches a uniform state, and obtaining a second bacterial solution;

[0022] S3: Mixing the second bacterial solution with a carrier material, and uniformly mixing to obtain a bacillus pasteurii slurry;

[0023] S4: Adding a silicate cement, a water reducing agent and nanosilica to the bacillus pasteurii slurry, and uniformly mixing to obtain a composite cement;

[0024] The content of the water reducing agent is 0.5-1 parts, the content of the nano-silicon dioxide is 1.5-2 parts, and the content of the bacillus pasteurii slurry is 5-8 parts, relative to 100 parts of the portland cement by weight.

[0025] Further, in step S1, calcium hydroxide saturated solution is added to the second bacterial solution to make the pH value of the second bacterial solution in the range of 9 to 9.5.

[0026] Further, in step S4, after water is added to the composite cement to obtain cement slurry, pouring is completed within 30 minutes.

[0027] The third aspect of the application provides an application of the self-repairing composite cement, which is prepared by using the composite cement preparation method described above, and comprises the following steps:

[0028] S10: complete water and power supply, remove dangerous stones, and determine the composite cement ratio;

[0029] S20: lay out the hole position at a spacing of 1.2 m in the ring direction and 0.8 m in the longitudinal direction;

[0030] S30: sequentially connect the drill bit, the self-drilling hollow anchor rod body, the connecting sleeve and the drill bit tail;

[0031] S40: install the drilling machine, lengthen the self-drilling hollow anchor rod by using the connecting sleeve, and once form a hole to the designed depth, and the hole direction is perpendicular to the main structure surface of the surrounding rock;

[0032] S50: set a grout stopping plug at a position 250 mm away from the hole mouth in the anchor hole, and if the surrounding rock is broken to a large extent, use an anchoring agent to replace the hole sealing;

[0033] S60: add water to the composite cement in the mixing station to obtain cement slurry, use a screw pump to inject the slurry into the rod body through a quick connector, the hole mouth pressure is 0.1-0.5 MPa, and stop after the slurry injection is full;

[0034] S70: after the strength of the grouting body is greater than or equal to 10 MPa, install a pad plate and tighten a nut to make the pad plate closely attached to the shotcrete surface;

[0035] S80: after the strength of the initial support concrete and the anchor rod mortar is greater than or equal to 70% of the designed strength, prestress is tensioned and locked.

[0036] Overall, compared with the prior art, the above technical solutions conceived by the application can achieve the following beneficial effects:

[0037] 1.The composite cement of the present application, which can overcome the defects of traditional concrete such as high brittleness, poor crack resistance and insufficient durability by combining the three mechanisms of physical filling, structural optimization and biological repair, realize the multidimensional collaborative improvement of material performance, and has chemical compatibility with the cement matrix, no secondary crack problem of expansion stress, alkali environment resistance and long-term activity, which can significantly reduce the oxygen and chloride diffusion coefficient, delay the corrosion of steel bars and prolong the service life of the structure.

[0038] 2.The composite cement of the present application, which can effectively fill the pore structure in the cement matrix, optimize the pore size distribution, reduce the porosity, thereby significantly improve the compactness and compressive strength of the concrete, and improve the uniformity of its microstructure, reduce the early shrinkage and dry shrinkage deformation, and inhibit the generation of microcracks, by virtue of the high specific surface area and pozzolanic activity of the nano-silicon dioxide; secondly, the introduction of the water reducing agent can significantly reduce the water-binder ratio without reducing the workability, further improve the compactness and durability of the concrete, and improve the construction performance and efficiency; in addition, the bacillus pasteurii can trigger the MICP reaction by metabolizing the calcium ions and nutrients in the environment after the cracks are formed, and continuously deposit calcium carbonate crystals on the crack surface to realize the active healing of microcracks and effectively seal the water seepage channels to delay the invasion of harmful media. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The figure is a schematic diagram of the preparation method of the self-repairing composite cement of the present application;

[0040] Figure 2 The figure is a schematic diagram of the application steps of the self-repairing composite cement of the present application. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0042] As shown in Figure 1 The first aspect of the present application provides a self-repairing composite cement, which comprises the following components: Portland cement, water reducing agent, nano-silicon dioxide and bacillus pasteurii paste; wherein, the content of the water reducing agent is 0.5-1 parts, the content of the nano-silicon dioxide is 1.5-2 parts, and the content of the bacillus pasteurii paste is 5-8 parts, relative to 100 parts by weight of the Portland cement.

[0043] It can be understood that, in actual use, through the extremely high specific surface area of the nano-silicon dioxide and the activity of the volcanic ash, the pore structure in the cement matrix can be effectively filled, the pore size distribution can be optimized, and the porosity can be reduced, thereby significantly improving the compactness and compressive strength of the concrete, improving the uniformity of the microstructure, reducing the early shrinkage and dry shrinkage deformation, and inhibiting the generation of micro-cracks; secondly, the introduction of the water reducing agent can significantly reduce the water-binder ratio without reducing the workability, further improve the compactness and durability of the concrete, and improve the construction performance and construction efficiency; in addition, the bacillus pasteurii can utilize calcium ions and nutrients in the environment for metabolic activity and trigger a MICP (Microbially Induced Calcite Precipitation) reaction after the formation of cracks, continuously depositing calcium carbonate crystals on the crack surface to achieve active healing of the micro-cracks, effectively sealing the water seepage channels, and delaying the invasion of harmful media. The composite cement of the present application can overcome the defects of traditional concrete, such as high brittleness, poor crack resistance, and insufficient durability, through the combination of physical filling, structure optimization, and biological repair, realize the multi-dimensional collaborative improvement of material performance, and the material system is chemically compatible with the cement matrix, without the problem of secondary cracks caused by expansion stress, and has alkali environment resistance and long-term activity, which can significantly reduce the oxygen and chloride ion diffusion coefficients, delay the corrosion of steel bars, and prolong the service life of the structure.

[0044] Preferably, the portland cement is P.O. 42.5 grade cement, which is used to improve the adaptability of the composite cement and reduce the use cost.

[0045] Preferably, the water reducing agent is a polycarboxylate-based water reducing agent, which is used to realize the dual optimization of high water-reducing rate and slump retention performance at a very low dosage, thereby significantly reducing the water-binder ratio, reducing the initial porosity of the matrix, and providing a low-viscosity and high-homogeneity environment for the close packing of the nano-silicon dioxide and the uniform dispersion of the bacillus pasteurii.

[0046] Preferably, the particle size of the nano-silicon dioxide ranges from 10 nm to 30 nm, thereby significantly improving the mechanical properties and durability through the filling effect and the volcanic ash reaction, and enabling effective dispersion through conventional processes and reducing the possibility of agglomeration.

[0047] Further, the bacillus pasteurii slurry includes a second bacterial solution, which includes: the first bacterial solution, a sodium alginate solution, and a calcium hydroxide solution; wherein, relative to 1 volume part of the first bacterial solution, the volume of the sodium alginate solution is 1-2 parts, and the volume of the calcium hydroxide solution is 5-10 parts.

[0048] Preferably, the concentration of bacillus pasteurii in the first bacterial solution is 8x10 7 CFU / mL to 1.2x108 CFU / mL was used to enhance the metabolic activity of Bacillus pasteurellii through high concentrations of live bacteria and optimize the rate of calcium carbonate formation.

[0049] Preferably, the concentration of sodium alginate in the sodium alginate solution is 1% to 3% (by mass and volume), and the molecular weight of the sodium alginate is 80kDa to 120kDa. This is used to optimally balance bacterial encapsulation, reaction controllability, and cement mechanical properties, thereby ensuring that the bacteria are encapsulated within the gel microspheres and avoiding potential oxygen deficiency problems.

[0050] Preferably, the calcium hydroxide solution contains 2% to 5% (by mass) calcium hydroxide to form stable calcium alginate microcapsules.

[0051] Furthermore, the Bacillus pasteurized mud also includes a carrier material, which is mixed with the second bacterial liquid phase and includes at least one of bentonite, silica fume and starch gel, to form particles with a certain strength and delay the initial high alkalinity of the cement slurry.

[0052] In an optional embodiment, when the carrier material is bentonite, its particle size is no greater than 20 μm, and the mass ratio of the second bacterial solution to the bentonite is 1:1 to 2:1, in order to adapt to high-salt and dynamic load environments, especially suitable for wharf piers.

[0053] In an optional embodiment, when the carrier material is silica fume, its particle size ranges from 0.1 μm to 1 μm, and the mass ratio of the second bacterial solution to the silica fume is from 5:1 to 10:1, in order to adapt to high-intensity and high-durability scenarios, especially suitable for cross-sea bridges.

[0054] In an optional embodiment, when the carrier material is a starch gel with a molecular weight of 10kDa to 50kDa, and the mass ratio of the second bacterial solution to the starch gel is 1:1 to 2:1, it is suitable for short-term remediation or ecological engineering, and is especially suitable for soil solidification.

[0055] It should be noted that when two or more materials are used as carrier materials, the amount added can be adjusted according to the usage requirements, but the amount used is within the range of its individual use, in order to achieve a triangular balance between functional requirements, cost and sustainability.

[0056] like Figure 1 As shown, a second aspect of the present invention provides a method for preparing self-healing composite cement, comprising the following steps:

[0057] S1: Bacillus pasteurellii was cultured in liquid culture medium to the logarithmic production phase, the bacterial cells were collected by centrifugation, and the cells were resuspended and diluted with buffer solution to obtain the first bacterial solution;

[0058] S2: After adding sodium alginate solution into the first bacteria solution, slowly drop calcium hydroxide solution under the condition of continuous stirring until the mixture reaches a uniform state, and a second bacteria solution is obtained;

[0059] S3: Mix the second bacteria solution with the carrier material, and after uniform mixing, obtain the bacillus pasteurii slurry;

[0060] S4: Add Portland cement, water reducing agent, and nano silicon dioxide to the bacillus pasteurii slurry, and after uniform dry mixing, obtain a composite cement;

[0061] In the composite cement, relative to 100 parts by weight of the Portland cement, the content of the water reducing agent is 0.5-1 parts, the content of the nano silicon dioxide is 1.5-2 parts, and the content of the bacillus pasteurii slurry is 5-8 parts.

[0062] It should be noted that the liquid medium and the buffer solution are common solvents in the prior art to at least meet the basic growth needs of bacillus pasteurii, such as a medium containing urea, yeast extract, and sodium chloride, a phosphate buffer solution with a pH value in the range of 7-8. Of course, other types of solvents can also be used in other embodiments, which are not limited here.

[0063] In optional embodiments, in step S1, the centrifugal treatment conditions include a rotation speed of 3500-4500 rpm and a time of 15-20 min.

[0064] Further, in step S1, saturated calcium hydroxide solution is added to the second bacteria solution to adjust the pH value of the second bacteria solution to a pre-equilibrium state, so that the bacteria adapt to the high alkaline environment and reduce the alkaline impact of the cement.

[0065] In optional embodiments, in step S3, under the continuous stirring action of a magnetic stirrer (rotation speed 300-500 rpm), calcium hydroxide solution is added dropwise at a rate of 0.5-1.0 mL / min to form stable calcium alginate microcapsules.

[0066] Further, in step S4, after adding water to the composite cement and stirring uniformly to obtain cement slurry, pouring is completed within 30 min, and plastic film is covered after pouring is completed to avoid the bacillus pasteurii being exposed to the high alkaline environment for too long.

[0067] In optional embodiments, in steps S3 and S4, the stirring time is 10-15 min to reduce labor intensity under the condition of meeting the stirring requirement.

[0068] In an optional embodiment, the water-cement ratio of the cement slurry is 0.38 to 0.45, and the water includes the water content of the components and the water added in solution preparation.

[0069] It should be noted that, in the mixing process of the components, if no special instructions are given, the components are mixed by adding and stirring simultaneously, so as to realize sufficient mixing of the components and accurate adjustment of the pH value.

[0070] As shown in Figure 2 The third aspect of the present application provides an application of the self-repairing composite cement, which comprises the following steps:

[0071] S10: complete water and power supply, remove dangerous stones, and determine the proportion of the composite cement;

[0072] S20: lay out the hole position at a spacing of 1.2 m in the circumferential direction and 0.8 m in the longitudinal direction;

[0073] S30: sequentially connect the drill bit, the self-drilling hollow anchor rod body, the connecting sleeve, and the drill tail;

[0074] S40: install the drilling machine, lengthen the self-drilling hollow anchor rod by using the connecting sleeve, and once form a hole to the designed depth, and the hole is perpendicular to the main structural surface of the surrounding rock;

[0075] S50: set a grout stopper at a position 250 mm away from the hole mouth in the anchor hole, and if the surrounding rock is broken to a large extent, use an anchoring agent to replace the hole sealing;

[0076] S60: add water to the composite cement in the mixing station and stir to obtain a cement slurry, use a screw pump to inject the slurry into the rod body through a quick connector, the hole mouth pressure is 0.1-0.5 MPa, and stop after the slurry injection is full;

[0077] S70: after the strength of the grouting body is greater than or equal to 10 MPa, install a pad plate and tighten a nut, so that the pad plate is closely attached to the shotcrete surface;

[0078] S80: after the strength of the initial support concrete and the anchor rod mortar is greater than or equal to 70% of the designed strength, tension and lock the prestress.

[0079] It can be understood that, through the above design, the self-drilling hollow anchor rod is used to cooperatively support the tunnel surrounding rock with the composite cement, so that continuous operation of one-time hole forming, grouting and anchoring can be realized in the construction stage, the work efficiency is significantly improved, and the secondary disturbance to the surrounding rock is reduced; the composite cement can significantly inhibit the cracking of the slurry caused by train vibration, stress redistribution of the surrounding rock or environmental temperature cycle; at the same time, the self-repairing mechanism is combined with the grouting channel of the hollow cavity of the anchor rod, so that the bacterial liquid and nutrient salt can be supplemented for multiple times during the operation period, long-term performance maintenance is realized, and in addition, the field pulling test shows that in the hard-soft weak surrounding rock such as sandstone and mudstone, the bonding strength between the composite cement slurry and the rock wall interface is increased by 20%-30% compared with the traditional cement-based slurry, and the ultimate slip amount of the anchor rod is reduced by about 25%, which significantly reduces the risk of slip failure; in addition, the alkalinity of the slurry tends to be neutral after being optimized by the mineral admixture, which slows down the corrosion of the anchor rod steel, prolongs the service life of the anchoring system, and provides reliable protection for the long-term safe operation of the tunnel.

[0080] In order to further illustrate the present application, a self-repairing composite cement provided by the present application is described in detail below in combination with comparative examples and examples, but it should not be understood as limiting the protection scope of the present application.

[0081] Comparative Example 1

[0082] In the present comparative example 1, the content of the water reducing agent is 0.75 parts relative to 100 parts by weight of the Portland cement, and then water is added and stirred uniformly to obtain a cement slurry, and the water-cement ratio of the cement slurry is 0.4.

[0083] Example 1

[0084] In the present example 1, the composite cement is prepared by using the preparation method of the aforementioned self-repairing composite cement:

[0085] S1: Bacillus pasteurii is cultured in a liquid culture medium to the logarithmic production phase, the bacterial cells are collected by centrifugation, and a buffer solution is used to resuspend and dilute to obtain a first bacterial liquid with a concentration of 1×10 8 CFU / mL of Bacillus pasteurii;

[0086] S2: After adding sodium alginate solution to the first bacterial liquid, calcium hydroxide solution is slowly added dropwise under continuous stirring until the mixture reaches a uniform state, and a second bacterial liquid is obtained;

[0087] S3: The second bacterial liquid is mixed with the carrier material, and after uniform mixing, a Bacillus pasteurii bacterial paste is obtained;

[0088] S4: Portland cement, water reducing agent and nano-silicon dioxide are added to the Bacillus pasteurii bacterial paste, and after dry mixing, a composite cement is obtained.

[0089] The content of the water reducing agent is 0.75 parts, the content of the nano-silicon dioxide is 1.5 parts, and the content of the bacillus pasteurii slurry is 5 parts relative to 100 parts by weight of the portland cement; then, water is added, and stirring is uniformly performed to obtain a cement slurry, and the water-cement ratio of the cement slurry is 0.4.

[0090] Example 2

[0091] The method and process conditions of this example are similar to those of example 1, except that the content of the nano-silicon dioxide is 1.75 parts, and the content of the bacillus pasteurii slurry is 5 parts relative to 100 parts by weight of the portland cement.

[0092] Example 3

[0093] The method and process conditions of this example are similar to those of example 1, except that the content of the nano-silicon dioxide is 2 parts, and the content of the bacillus pasteurii slurry is 5 parts relative to 100 parts by weight of the portland cement.

[0094] Example 4

[0095] The method and process conditions of this example are similar to those of example 1, except that the content of the nano-silicon dioxide is 1.5 parts, and the content of the bacillus pasteurii slurry is 6.5 parts relative to 100 parts by weight of the portland cement.

[0096] Example 5

[0097] The method and process conditions of this example are similar to those of example 1, except that the content of the nano-silicon dioxide is 1.75 parts, and the content of the bacillus pasteurii slurry is 6.5 parts relative to 100 parts by weight of the portland cement.

[0098] Example 6

[0099] The method and process conditions of this example are similar to those of example 1, except that the content of the nano-silicon dioxide is 2 parts, and the content of the bacillus pasteurii slurry is 6.5 parts relative to 100 parts by weight of the portland cement.

[0100] Example 7

[0101] The method and process conditions of this example are similar to those of example 1, except that the content of the nano-silicon dioxide is 1.5 parts, and the content of the bacillus pasteurii slurry is 8 parts relative to 100 parts by weight of the portland cement.

[0102] Example 8

[0103] The embodiment and the embodiment 1 adopt similar method and process condition, different is: relative to each 100 weight parts of the silicate cement, the content of the nano silicon dioxide is 1.75 parts, the content of the bacillus pasteurii mud is 8 parts.

[0104] Embodiment 9

[0105] The embodiment and the embodiment 1 adopt similar method and process condition, different is: relative to each 100 weight parts of the silicate cement, the content of the nano silicon dioxide is 2 parts, the content of the bacillus pasteurii mud is 8 parts.

[0106] It needs to be explained that the concentration of bacillus pasteurii in all the embodiments 1-9 is 1×10 8 CFU / mL; the proportion of each component in the first bacterial solution is the same, the type of the carrier material is the same, and the mass fraction of the bacillus pasteurii mud in the composite cement in each embodiment is satisfied; the water-cement ratio of the final cement slurry is the same, and the water amount added in the composite cement is increased or decreased based on the aforementioned additive materials, to ensure the accuracy of the experiment.

[0107] The cement pastes of Comparative Example 1, Example 1 to Example 9 were subjected to performance tests, and the above mortar was used to prepare test piece samples with a size of 40 mm x 40 mm x 160 mm and Φ100 mm x 50 mm. After initial setting, the test piece samples were removed from the mold and placed in a standard curing box (temperature 20 ± 1 °C, humidity ≥ 90%) for curing until the test age (7 days and 28 days, and the flexural / compressive strength test was performed after 28 days). Specifically, according to GB / T 17671-1999 “Cement mortar strength test method (ISO method)”, the compressive and flexural strength of the samples were tested under the conditions of compressive strength 2.4 kN / s and flexural strength 50 N / s; the microstructure of the samples was observed, and scanning electron microscopy was used to observe the C-S-H gel, CH crystal (calcium hydroxide) refinement degree and CaCO3 precipitation distribution (resolution ≥ 5 nm); CH crystal size (half-height width method calculation), CaCO3 crystallinity (diffraction peak intensity) were analyzed by X-ray diffraction; porosity (target ≤ 15%) and pore size distribution (micropore filling effect) were determined by mercury intrusion method; the mortar-aggregate interface transition zone pull-out test was performed, and standard sand was used as aggregate, and the chemical cementation (C-S-H + CaCO3) and mechanical anchoring effect (CaCO3 crystal filling pores) were analyzed according to ASTM C1583 to obtain the interface bonding performance of the samples; the samples were artificially pre-prepared microcracks (width 0.1-0.3 mm, depth 5 mm), and the moisture environment (humidity ≥ 85%) during curing was simulated to activate the bacterial mineralization reaction, and the crack closure rate was observed after 28 days of curing; the impermeability of the samples was tested based on the impermeability grade test (GB / T 50082-2009, target P12 or above, i.e. water pressure 1.2 MPa); the Cl - invasion of the samples was tested by electric flux method (ASTM C1202, 56-day electric flux ≤ 1000 C, high resistance to chloride ion penetration); SO4 2- invasion of the samples was tested by immersion method (5% Na2SO4 solution, 90-day strength loss ≤ 10%); in addition, the fluidity of the cement mortar was directly tested by mortar slump method, and the pumping performance of the cement mortar (pressure loss ≤ 10%) was evaluated. The sample performance test results are shown in the following table:

[0108] Table 1 Sample performance test results

[0109] As can be seen from the sample performance test results in Table 1, by incorporating the nano-silica and Bacillus pasteurii synergistic system, the compressive strength / flexural strength of Examples 1-9 is increased from 45 MPa / 7 MPa to a maximum of 64 MPa / 9.5 MPa, the porosity is reduced from 20% to 13%, the CH crystal is refined from >10 μm to 3-8 μm with uniform filling of 1-2 μm CaCO3, and the interfacial bonding strength is increased by 20-35%; a 0.1-0.3 mm pre-prepared crack is completely self-healed within 3-7 d, the impermeability grade is increased from P8 to P12-P13, the Cl - diffusion coefficient is reduced by 30-40%, the SO4 2- erosion rate is reduced by >40%, the slump is stabilized at 215-220 mm and the pumping performance is excellent. Among them, the comprehensive index of Example 5 is the best, which verifies the significant advantages of the synergistic mechanism in improving strength, dense microstructure, crack self-repair and durability. The above performance test results show that the composite cement can be applied to concrete engineering scenarios that require durability, crack control and long-term service performance, such as road, bridge, tunnel, underground pipe gallery, etc. The composite cement can effectively improve the crack resistance and durability of the concrete structure, especially suitable for complex service environments that bear dynamic load, temperature and humidity changes and chemical corrosion for a long time, which helps to prolong the service life of the structure and reduce the maintenance cost in the later period; for high-rise buildings, basements, pools, sewage treatment plants and other occasions that require high impermeability and durability of concrete, the composite cement can significantly improve the waterproof performance and long-term stability of the structure, meeting the higher requirements of modern buildings for safety and sustainability; crack repair, old concrete structure reinforcement, bridge pier column coating, etc., use its self-repair function to realize active repair of structural damage, improve repair efficiency and quality.

[0110] It should be noted that if the description of "first", "second" and the like is involved in the embodiments of the present application, the description of "first", "second" and the like is only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features with "first", "second" can explicitly or implicitly include at least one of the features. In addition, the technical solutions of each embodiment can be combined with each other, but it must be based on the realization of ordinary skilled in the art, when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, nor within the protection scope required by the present application.

[0111] In this disclosure, the terms "including", "containing" or any other similar words are intended to encompass non-exclusive inclusions, such that a process, method, article, or apparatus including a list of elements does not necessarily include only those elements, but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without more limitations, the elements defined by the phrase "comprising" do not exclude the presence of additional identical elements in the process, method, article, or apparatus including the elements.

[0112] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; those skilled in the art can easily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application, and any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A self-healing composite cement, characterized in that, It includes the following components: silicate cement, water-reducing agent, nano-silica and Bacillus pasteurized mud; Of which, relative to every 100 parts by weight of the silicate cement, the content of the water-reducing agent is 0.5-1 parts, the content of the nano-silica is 1.5-2 parts, and the content of the Bacillus pasteurized mud is 5-8 parts.

2. The composite cement according to claim 1, characterized in that, The Bacillus pasteurized mud includes a second bacterial solution, which comprises: a first bacterial solution, sodium alginate solution, and calcium hydroxide solution; Wherein, relative to each volume part of the first bacterial solution, the volume of the sodium alginate solution is 1-2 parts, and the volume of the calcium hydroxide solution is 5-10 parts.

3. The composite cement according to claim 2, characterized in that, The concentration of Bacillus pasteurellii in the first bacterial culture was 8 × 10⁻⁶. 7 CFU / mL up to 1.2 × 10⁻⁶ 8 CFU / mL.

4. The composite cement according to claim 2, characterized in that, The sodium alginate solution contains 1% to 3% sodium alginate, and the molecular weight of the sodium alginate is 80 kDa to 120 kDa.

5. The composite cement according to claim 2, characterized in that, The calcium hydroxide solution contains 2% to 5% calcium hydroxide.

6. The composite cement according to any one of claims 2-5, characterized in that, The Bacillus pasteurized mud also includes a carrier material, which is mixed with the second bacterial liquid phase and includes at least one of bentonite, silica fume and starch gel.

7. The composite cement according to claim 6, characterized in that, When the carrier material is bentonite, its particle size is no greater than 20µm, and the mass ratio of the second bacterial solution to the bentonite is 1:1 to 2:

1.

8. The composite cement according to claim 6, characterized in that, When the carrier material is silica fume, its particle size ranges from 0.1µm to 1µm, and the mass ratio of the second bacterial solution to the silica fume is from 5:1 to 10:

1.

9. The composite cement according to claim 6, characterized in that, When the carrier material is starch gel, its molecular weight is 10kDa to 50kDa, and the mass ratio of the second bacterial solution to the starch gel is 1:1 to 2:

1.

10. The composite cement according to any one of claims 1-5, characterized in that, The particle size of the nano-silica ranges from 10 nm to 30 nm.

11. The composite cement according to any one of claims 1-5, characterized in that, The water-reducing agent is a polycarboxylate-based water-reducing agent.

12. A method for preparing self-healing composite cement, applied to the composite cement according to any one of claims 1-11, characterized in that, Includes the following steps: S1: Bacillus pasteurellii was cultured in liquid culture medium to the logarithmic production phase, the bacterial cells were collected by centrifugation, and the cells were resuspended and diluted with buffer solution to obtain the first bacterial solution; S2: After adding sodium alginate solution to the first bacterial solution, calcium hydroxide solution is slowly added dropwise under continuous stirring until the mixture reaches a homogeneous state and a second bacterial solution is obtained. S3: Mix the second bacterial solution with the carrier material and stir evenly to obtain Bacillus pasteurellium sludge; S4: Add silicate cement, water-reducing agent and nano-silica to the Bacillus paste, and dry mix evenly to obtain composite cement; In the composite cement, relative to every 100 parts by weight of the silicate cement, the content of the water-reducing agent is 0.5-1 parts, the content of the nano-silica is 1.5-2 parts, and the content of the Bacillus pasteurized mud is 5-8 parts.

13. The preparation method according to claim 12, characterized in that, In step S1, a saturated calcium hydroxide solution is added to the second bacterial solution until the pH value of the second bacterial solution is in the range of 9 to 9.

5.

14. The preparation method according to claim 12, characterized in that, In step S4, water is added to the composite cement and stirred evenly to obtain cement slurry, which is then poured within 30 minutes.

15. An application of a self-healing composite cement, implemented using the composite cement preparation method as described in any one of claims 12-14, characterized in that, Includes the following steps: S10: Complete the site's water and electricity supply, remove dangerous rocks, and determine the composite cement mix ratio; S20: Lay out the hole positions at intervals of 1.2m circumferentially and 0.8m longitudinally; S30: Connect the drill bit, self-drilling hollow anchor rod body, connecting sleeve and drill bit in sequence; S40: Install the drilling rig, use a connecting sleeve to extend the self-drilling hollow anchor rod, and drill a hole to the design depth in one go, with the hole direction perpendicular to the main structural surface of the surrounding rock; S50: Install a grout stop plug 250mm away from the hole opening inside the anchor hole. If the surrounding rock is highly fractured, use an anchoring agent instead of sealing the hole. S60: Water is added to the composite cement in the mixing plant and stirred evenly to obtain cement slurry. A screw pump is used to inject grout into the rod body through a quick connector. The orifice pressure is 0.1-0.5MPa. The machine is stopped after the grout is fully injected. S70: After the grout strength reaches ≥10MPa, install the pad and tighten the nut to ensure that the pad is in close contact with the shotcrete surface. S80: After the initial support concrete and anchor mortar strength are both ≥70% of the design strength, the prestress is tensioned and locked.

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