Pole surface self-repairing mortar containing microbial mineralization microcapsules and preparation method thereof

Abstract

The application relates to the technical field of building materials, and particularly discloses a pole surface self-repairing mortar containing microbial mineralization microcapsules and a preparation method thereof, which is prepared by mixing a base dry powder, microbial mineralization microcapsules and mixed water; the external admixture amount of the microbial mineralization microcapsules is 8%-14% of the total mass of the base dry powder, and the mixed water admixture amount is 22%-26% of the total mass of the base dry powder; the microbial mineralization microcapsules have a three-layer core-shell structure, and from inside to outside, the three-layer core-shell structure comprises an integrated mineralization core liquid inner core, a sodium alginate inner layer hydrogel wall and an ultra-fine metakaolin-sodium silicate inorganic alkali-resistant outer layer wall. The application can synchronously release the mineralization components to efficiently plug the pole microcracks by adopting the integrated sterile mineralization core liquid and the three-layer core-shell microcapsules, and can improve the flexibility and impermeability of the mortar by compounding the base with a retarding agent, fibers and a hydrophobic agent, so that the repair layer is prevented from being cracked again, and the defects of traditional materials, such as easy inactivation of bacteria and short repair time, are solved.

Description

Technical Field

[0001] This application relates to the field of building materials technology, and more specifically, to a self-healing mortar for the surface of utility poles containing microbial mineralization microcapsules and its preparation method. Background Technology

[0002] Concrete poles are core load-bearing components of overhead transmission lines. Operating outdoors for extended periods, they are constantly subjected to diurnal temperature variations, alternating wet and dry conditions, rainwater erosion, freeze-thaw cycles, and minor loads. This makes the surface of the poles highly susceptible to developing micro-cracks of 0.05–0.6 mm. Rainwater, carbon dioxide, and chloride ions penetrate these cracks into the structure, accelerating steel corrosion and concrete carbonation, significantly reducing the pole's load-bearing capacity and service life.

[0003] Currently, in the field of power grid operation and maintenance, ordinary repair mortar, epoxy resin coating, and carbon fiber wrapping are mainly used to treat surface cracks on power poles. However, after a long time, the repair mortar and coating are not coordinated with the deformation of the power pole substrate, and are prone to cracking and oxidation again in a short period of time.

[0004] A search revealed Chinese Patent Publication No. CN116730685B, which discloses a self-healing ordinary silicate cement-based material for crack repair based on Bacillus pasteurellium mineralization deposition and its preparation method. The material comprises ordinary silicate cement substrate, premix one, and premix two. Premix one contains urease-producing bacteria that have adsorbed calcium ions and a carrier, while premix two contains urease-producing bacteria that have not adsorbed calcium ions and a carrier. This invention divides the microbially loaded diatomaceous earth into two parts: one part consists of diatomaceous earth loaded with microorganisms that have not pre-adsorbed calcium ions, and the other part consists of diatomaceous earth loaded with microorganisms that have pre-adsorbed calcium ions. This ensures timely repair of cracks in the ordinary silicate cement-based material and improves the durability of the repaired material. The self-healing recycled ordinary silicate cement-based material for crack repair based on Bacillus pasteurellium mineralization deposition prepared in this application is a green and environmentally friendly recycled ordinary silicate cement-based material that combines crack self-diagnosis and self-repair, meeting the current economic and social requirements for green, environmentally friendly, and intelligent building materials.

[0005] The above-mentioned self-healing ordinary silicate cement-based material, which uses porous inorganic powder to adsorb microorganisms, has the following problems in actual use: First, it lacks a complete core-shell microcapsule encapsulation structure. Microorganisms, urea, and calcium sources are dispersed in the mortar pores, resulting in a large loss of nutrients during the mixing process. The microorganisms lack long-term protection and only have a weak repair effect in the short term. Second, it cannot meet the requirements of long-term outdoor service of power poles for many years. Moreover, the early hydration exothermic reaction of ordinary silicate cement is prone to high-temperature inactivation of spores, making it difficult to balance the mechanical strength of the mortar and the survival rate of microorganisms. Summary of the Invention

[0006] To address the shortcomings of existing technologies and solve the aforementioned technical problems, this application provides a self-healing mortar for pole surfaces containing microbial mineralization microcapsules and its preparation method.

[0007] Firstly, this application provides a self-healing mortar for the surface of utility poles containing microbial mineralization microcapsules, employing the following technical solution: The self-healing mortar for the surface of utility poles containing microbial mineralization microcapsules is made by mixing matrix dry powder, microbial mineralization microcapsules, and mixing water. By weight, the matrix powder comprises: 40-48 parts ordinary silicate cement, 8-12 parts ultrafine metakaolin, 3-5 parts silica fume, 30-38 parts fine quartz sand, 1.5-2.5 parts redispersible latex powder, 0.2-0.6 parts polycarboxylate superplasticizer, 0.1-0.3 parts polypropylene short fiber, 0.2-0.4 parts organosilicon water-repellent agent, and 0.08-0.16 parts citric acid retarder; The amount of microbial mineralization microcapsules added is 8% to 14% of the total mass of the matrix dry powder, and the amount of mixing water added is 22% to 26% of the total mass of the matrix dry powder; the microbial mineralization microcapsules have a three-layer core-shell structure, consisting of an integrated mineralization core liquid core, an inner layer hydrogel wall of sodium alginate, and an outer layer of ultrafine metakaolin-water glass inorganic alkali resistant material, from the inside out. The integrated mineralized core solution is a pre-mixed homogeneous sterile liquid phase, and is composed of the following components based on the total mass of the integrated mineralized core solution: 32-38 parts of Bacillus pasteurellii spore suspension, 10-14 parts of urea, 16-20 parts of calcium acetate, 1-3 parts of yeast extract, and 30-36 parts of deionized water.

[0008] By adopting the above technical solutions, a complete system is constructed, consisting of an integrated mineralized core liquid combined with a three-layer gradient protective capsule and a special dry powder for pole repair. The integrated sterile homogeneous liquid core liquid premixes urease-producing bacteria, urea nitrogen source, calcium ion supply source, and nutrient additives. After the capsule breaks and leaks water, multiple components dissolve simultaneously, resulting in a balanced ratio of raw materials for the mineralization reaction and higher calcium carbonate deposition efficiency. The three-layer core-shell structure features an inner flexible gel that encapsulates the liquid core liquid to buffer the mixing and impact, while the outer inorganic alkali-resistant shell isolates the mortar from the high-alkali environment, preventing microorganisms from prematurely inactivating due to strong alkali. The matrix dry powder is compounded with citric acid retarder to reduce the peak heat release during hydration of ordinary silicate cement, protecting spores from high-temperature damage. Fiber and latex powder enhance the flexibility of the mortar to adapt to the temperature difference deformation of the pole, and organosilicon water-repellent agent reduces... The overall water absorption rate is reduced, and the capsules dissolve prematurely without differentiation. The components work together to solve the defects of traditional microbial self-healing materials, such as easy loss and inactivation of bacterial strains, short repair time, and repeated cracking of the repair layer. This enables long-term self-sealing and repair of microcracks of 0.05-0.6mm on concrete poles. Among them, polycarboxylate superplasticizer is less than 0.2 parts, and the mortar mix is ​​viscous and has many air bubbles; more than 0.6 parts, and serious bleeding and stratification occur; citric acid retarder is less than 0.08 parts, and the hydration exothermic peak is too high, killing the spores; more than 0.16 parts, and the mortar does not set for a long time and has insufficient strength; the external admixture of microcapsules is less than 8%, and the mineralized substrate is insufficient; more than 14%, and the mortar bonding strength is significantly reduced; the core liquid spore suspension is less than 32 parts, and the viable bacterial base is insufficient; more than 38 parts, and the system osmotic pressure is too high, damaging the spores.

[0009] Preferably, the quartz sand has a particle size of 0.15–0.6 mm, the polypropylene short fiber has a length of 6 mm, and the concentration of the Bacillus pasteurellii spore suspension is 1 × 10⁻⁶. 9 CFU / mL.

[0010] By adopting the above technical solution, 0.15-0.6mm fine quartz sand forms a dense skeleton, suitable for 3-5mm thin-layer spraying, avoiding problems such as coarse aggregate protrusion and uneven coating thickness; 6mm short-cut polypropylene fibers are evenly dispersed, forming a three-dimensional network anti-crack structure inside the mortar, effectively suppressing the formation of new microcracks on the surface under minor deformation; 1×10 9 The high concentration of CFU / mL spore suspension ensures a sufficient number of live bacteria inside each capsule, and even after long-term storage and loss, it still retains a sufficient amount of urease-producing microorganisms, ensuring that the mineralization reaction at the cracks continues.

[0011] Preferably, the microbial mineralization microcapsules have a particle size of 0.8–1.5 mm; the inner hydrogel wall of the sodium alginate is prepared by cross-linking and solidifying a 2.0% (w / w) sterile sodium alginate aqueous solution by dripping it into a calcium chloride coagulation bath.

[0012] By adopting the above technical solution, microcapsules with a particle size of 0.8-1.5mm can be uniformly dispersed in the mortar system without floating, agglomerating, or settling. They are subjected to uniform stress during mixing and have a lower probability of breakage. Sodium alginate with a concentration of 2.0% has a moderate viscosity and forms a hydrogel inner layer with moderate toughness after cross-linking with calcium chloride ions. The membrane is intact and free of pinholes, which can firmly encapsulate the liquid mineralized core liquid and has a certain buffering deformation capacity. If the concentration is too low, the membrane layer will be too thin and leak. If the concentration is too high, the viscosity will be too high and it will not be able to stably form droplets.

[0013] Preferably, the mass ratio of the inorganic alkali-resistant outer wall material of the ultrafine metakaolin-water glass is 2:5:3.

[0014] By adopting the above technical solution, the coating slurry with a ratio of ultrafine metakaolin: sodium silicate: deionized water of 2:5:3 has moderate fluidity. Fluidized bed spraying can form a continuous, dense, and alkali-resistant inorganic shell on the surface of a single layer of microspheres. Sodium silicate acts as an inorganic binder to ensure film integrity, ultrafine metakaolin enhances the shell's alkali resistance and wear resistance, and deionized water controls the consistency to suit the spraying process. The shell is slowly eroded only under long-term rainwater immersion, realizing a controllable release mechanism of "repair triggered only by water seepage through cracks". The intact areas of the capsule remain stable and do not fail for a long time.

[0015] Preferably, the ratio of mixing water to the total mass of cementitious materials in the mortar is 0.32 to 0.38, wherein the cementitious materials consist only of ordinary silicate cement, ultrafine metakaolin, and silica fume; the total construction thickness is 3 to 5 mm, applied in two layers by spraying or plastering, with a single layer thickness of 1.5 to 2.5 mm.

[0016] By adopting the above technical solutions, the 0.32-0.38 low water-cement ratio mortar has low internal porosity and dense structure, resulting in excellent impermeability and carbonation resistance, reducing the indiscriminate infiltration of rainwater. The cementitious materials are clearly defined to include only ordinary silicate cement, ultrafine metakaolin, and silica fume, with unified and unambiguous measurement standards. The 3-5mm layered thin coating and 1.5-2.5mm single-layer construction mode avoids large cracks caused by shrinkage of a single thick layer of mortar. The thin layer of mortar has better deformation coordination with the concrete pole substrate, and the interface bonding is strong, significantly reducing the risk of secondary cracking of the repair layer in the later stage.

[0017] Secondly, this application provides a method for preparing self-healing mortar for pole surfaces containing microbial mineralization microcapsules, using the following technical solution: A method for preparing self-healing mortar for utility pole surfaces containing microbial mineralization microcapsules includes the following steps: (1) Preparation of integrated mineralized core solution: Bacillus pasteurellii was expanded in liquid culture medium and concentrated by centrifugation to obtain 1×10 9CFU / mL spore suspension, according to the mass ratio, spore suspension, urea, calcium acetate, yeast extract and deionized water are aseptically mixed to obtain a uniform integrated mineralized core solution; (2) Molding of the inner layer hydrogel wall of sodium alginate: Prepare a 2.0wt% sterile sodium alginate aqueous solution, mix the integrated mineralized core liquid in step (1) with the sterile sodium alginate aqueous solution at a volume ratio of 1:3, and drip it into a 4wt% calcium chloride coagulation bath through a 0.8mm needle to crosslink and solidify to obtain wet microspheres. After sterile water washing, dry at 40℃ under low temperature vacuum until the water content is ≤8%, which is a single-layer bacterial microsphere; (3) Coating of the outer wall of the inorganic alkali resistant layer of ultrafine metakaolin-water glass: prepare ultrafine metakaolin-sodium water glass slurry, use fluidized bed to double-coat the single-layer bacterial microspheres in step (2), dry at low temperature of 45℃, and store in a sealed and light-proof container to obtain three-layer core-shell microbial mineralization microcapsules. (4) Premixing of matrix dry powder: Put ordinary silicate cement, ultrafine metakaolin, silica fume and quartz fine sand into a dry powder mixer and dry mix for 5 minutes. Then add redispersible latex powder, polycarboxylate superplasticizer, polypropylene short fiber, organosilicon water repellent and citric acid retarder in sequence. Continue to dry mix for 8 minutes and seal for later use. (5) On-site mixing construction: Take the premixed dry matrix powder in step (4), mix it manually at low speed for 2 minutes, add the microbial mineralization microcapsules in step (3), add the mixing water in batches and mix at low speed for 3-4 minutes to obtain the sprayable repair mortar.

[0018] By adopting the above technical solution, the entire preparation process is implemented step by step in the order of strain expansion and core preparation liquid - flexible inner layer coating - alkali-resistant inorganic outer shell protection - dry powder premixing - on-site low-damage mixing construction; Step (1) Integrated mineralized core preparation: Bacillus pasteurellis is first liquid-expanded and centrifuged to obtain a stable concentration of 1×10 9CFU / mL spore suspension, then under sterile conditions, the spore suspension, urea, calcium acetate, yeast extract and deionized water are thoroughly mixed to form an integrated mineralization core solution. Aseptic operation can prevent the invasion of miscellaneous bacteria that consume nutrients and destroy spore activity. The pre-mixed system allows the bacteria, urea nitrogen source and calcium ion supply source to coexist synchronously. After the capsule is broken and comes into contact with water, various mineralization reaction raw materials can be released synchronously to ensure the balanced and efficient calcium carbonate deposition reaction. Step (2) Forming the inner layer hydrogel wall of sodium alginate: Prepare a 2.0% sterile sodium alginate aqueous solution. Mix the integrated mineralization core solution with this solution at a volume ratio of 1:3 and then drip it into a 4wt% calcium chloride coagulation bath through a 0.8mm needle. Utilize the calcium ions and sodium alginate The ion crosslinking reaction quickly solidifies to form wet microspheres encapsulating the core liquid. After sterile water washing to remove residual calcium chloride on the surface, the microspheres are dried at 40°C under low temperature vacuum until the water content is ≤8% to obtain single-layer bacterial microspheres. Low temperature vacuum drying can avoid high temperature damage to spores. The inner layer of sodium alginate flexible hydrogel formed by crosslinking can buffer the impact and friction during the stirring process and prevent premature leakage of the liquid core liquid. In particular, it avoids the water content being higher than 8%, which would cause the microspheres to stick together during storage and the outer shell to crack easily. Step (3) Coating the outer wall of the ultrafine metakaolin-water glass inorganic alkali resistant slurry with a stable ratio of ultrafine metakaolin, sodium water glass and deionized water. The single-layer bacterial microspheres are coated with a fluidized bed to complete the double-layer coating. After the coating is completed, the microspheres are dried at 45°C and then sealed and stored in the dark to obtain a three-layer coating. The core-shell microbial mineralization microcapsules have an outer inorganic shell that is resistant to strong alkali erosion of ordinary silicate cement matrix. This shell can isolate the high-alkali environment and kill the internal spores. It can also slowly dissolve and release the microorganisms only when the cracks are water-permeable for a long time. Low-temperature drying and sealed storage can isolate water vapor and light, ensuring the integrity of the capsule shell and the non-decay of microbial activity throughout the process. Step (4) Premixing the dry powder of the matrix: First, put ordinary silicate cement, ultrafine metakaolin, silica fume and quartz fine sand into the dry powder mixer and dry mix for 5 minutes. Then, add redispersible latex powder, polycarboxylate high-efficiency water-reducing agent, polypropylene short fiber, organosilicon water-repellent agent and citric acid retarder in sequence and continue to dry mix for 8 minutes. Then seal for later use. Adding materials in stages and extending the dry mixing time can achieve uniform dispersion of various powder raw materials. Citric acid retarder After the coagulant is evenly distributed, it can reduce the early hydration heat release peak of ordinary silicate cement. Fiber and latex powder work together to improve the flexibility and crack resistance of mortar. The uniform distribution of water-repellent agent can reduce the overall water absorption rate of mortar. Sealed storage prevents the powder from absorbing moisture and clumping, which affects the subsequent mixing performance. Step (5) On-site mixing construction: Take the pre-mixed matrix dry powder, first mix manually at low speed for 2 minutes, then add microbial mineralization microcapsules, and then add mixing water in batches and mix at low speed for 3-4 minutes to obtain sprayable repair mortar. Low-speed mixing and low-speed stirring throughout the process avoid strong shearing action, reduce the grinding and crushing of the three-layer core-shell capsules by hard quartz fine sand, and add water in batches to accurately control the mortar consistency to adapt to thin-layer spraying construction, retain the complete structure of microcapsules to the greatest extent, and ensure the long-term self-repair function of mortar.

[0019] Preferably, in step (1), the liquid culture medium consists of 10 g / L peptone, 5 g / L yeast extract and 10 g / L NaCl, sterilized at 121°C for 30 min, cooled to 30°C and inoculated with Bacillus pasteurellis, and cultured at 30°C and 160 r / min for 24 h with shaking.

[0020] By adopting the above technical solution, the culture medium formula can provide complete carbon, nitrogen and inorganic salt nutrition for the proliferation of Bacillus pasteurellis; the high temperature and high pressure at 121℃ completely eliminates interference from other bacteria; the constant temperature at 30℃ and shaking culture at 160r / min improves the dissolved oxygen efficiency of the bacteria; and the 24-hour culture cycle can stably obtain a highly active spore suspension, ensuring that the number of live bacteria in the core liquid meets the standard and avoiding insufficient mineralization reaction intensity in the later stage due to insufficient bacterial culture.

[0021] Preferably, in step (3), the storage and transportation of microbial mineralization microcapsules require sealing and protection from light at room temperature.

[0022] By adopting the above technical solution, the outer inorganic water glass shell of the three-layer core-shell microcapsule is prone to moisture absorption, softening and cracking, and the internal spores will be oxidized and deactivated when exposed to ultraviolet light. The room temperature sealed and light-proof storage and transportation can isolate air moisture and light, maintain the integrity of the capsule shell and the stability of spore activity, avoid premature failure of the finished capsules in the storage and transportation process, and ensure that it still has complete self-repair capability after being transported to the construction site.

[0023] Preferably, in step (5), the mixing stage is carried out at a low speed of 30-60 r / min to prevent the three-layer core-shell microcapsule wall from breaking.

[0024] By adopting the above technical solution, high-speed stirring will generate strong shearing and grinding action with the help of hard quartz fine sand particles, causing large-area breakage of the three-layer capsule shell, and premature release of the core liquid into the strong alkaline mortar, resulting in spore inactivation; low-speed stirring at 30-60 r / min relies only on the overall convection of materials to achieve uniform mixing, with weak mechanical impact force, which can minimize the capsule mixing breakage rate, preserve the microcapsules with controllable release function, and ensure the long-term self-healing performance of the mortar.

[0025] Preferably, in step (5), before construction, the surface of the concrete pole is ground and cleaned of laitance and loose layer, the base surface is moistened with clean water without standing water, and after construction, it is kept moist at room temperature for 7 days.

[0026] By adopting the above technical solution, the surface laitance and loose concrete layer of the pole are removed by grinding, which can eliminate the weak area of ​​the interface. The water wetting without standing water can ensure that the repair mortar and the original concrete are fully hydrated and bonded. After construction, the cementitious material is fully hydrated by maintaining room temperature and humidity for 7 days, and the early strength of the mortar is steadily improved. This avoids the interface delamination and surface shrinkage cracking caused by insufficient curing, and provides a stable and durable matrix service environment for the internal microcapsules.

[0027] In summary, this application has the following beneficial effects: 1. This application utilizes an integrated sterile mineralized core liquid combined with three-layer core-shell microcapsules to simultaneously release mineralized components and efficiently seal microcracks in utility poles. The inner and outer double shells isolate strong alkalis, buffer stirring and impact, and protect spore activity. The matrix is ​​compounded with retarder, fiber, and water-repellent agent to reduce hydration high-temperature damage, improve mortar flexibility and impermeability, prevent repair layer cracking, and provide long-term adaptability to outdoor dry and wet temperature conditions, solving the shortcomings of traditional materials such as easy inactivation of microorganisms and short repair time.

[0028] 2. This application employs a process of limited sodium alginate cross-linking molding, fluidized bed double-layer coating, 45℃ low-temperature drying, and sealed light-proof storage and transportation. This gentle processing avoids the loss of spore activity due to high temperature and light exposure throughout the entire process. The capsule shell is continuous and dense, making it less prone to premature breakage, thus ensuring that the microcapsules retain their long-term repair function intact from the time they leave the factory until they are used for construction.

[0029] 3. This application uses a special sterile culture medium to amplify Bacillus pasteurella at a constant temperature and with shaking to stably obtain a highly active spore suspension. The sufficient number of live bacteria ensures the potential for mineralization reaction inside the capsule and avoids the problem of poor crack filling effect caused by insufficient bacterial activity.

[0030] 4. This application avoids high-speed shearing and quartz fine sand grinding that breaks the capsule by using low-speed stirring with limited mixing, which greatly reduces the capsule breakage rate, reduces premature leakage and deactivation of mineralized core fluid, and completely preserves the targeted self-healing core carrier.

[0031] 5. This application strengthens the bond between the mortar and the pole substrate by cleaning the loose layer before construction, wetting the base surface and maintaining moisture for 7 days, reducing interface cracking and water seepage, and providing a stable and durable service environment for the internal microcapsules. Attached Figure Description

[0032] Figure 1 This is a flowchart of the preparation method of self-healing mortar for pole surfaces containing microbial mineralization microcapsules provided in this application; Figure 2 These are experimental comparison images of the self-healing mortar for pole surfaces containing microbial mineralization microcapsules provided in this application. Detailed Implementation

[0033] The present application will be further described in detail below with reference to embodiments and comparative examples. Unless otherwise specified, the experimental methods used below are conventional methods. Unless otherwise specified, the materials, reagents, methods and instruments used are all conventional materials, reagents, methods and instruments in the art, which can be obtained by those skilled in the art through commercial channels or prepared according to literature methods.

[0034] Concrete power transmission poles are subjected to long-term outdoor exposure to varying temperatures and humidity, leading to the formation of microcracks (0.05–0.6 mm) on the surface. Rainwater, chloride ions, and carbon dioxide can penetrate these cracks, causing corrosion of the internal steel reinforcement and carbonation of the concrete. Traditional repair mortars have poor compatibility with the substrate, resulting in re-cracking shortly after repair. Existing microbial self-healing solutions use diatomaceous earth powder to adsorb bacteria and calcium ions separately, but lack a sealed protective structure. During mixing, significant amounts of urea and nutrients are lost. Ordinary silicate cement is susceptible to inactivation of urease-producing spores due to early hydration at high temperatures and in a highly alkaline environment. Furthermore, the separate loading of bacteria and calcium sources prevents simultaneous mineralization reactions, resulting in low calcium carbonate deposition efficiency. These solutions only provide short-term repair effects and are unsuitable for the long-term outdoor service requirements of power poles.

[0035] Based on the multiple defects of the existing technology, this application constructs a three-layer core-shell microbial capsule and pole-specific repair mortar synergistic system. The core functional core is an integrated homogeneous sterile liquid mineralization core liquid. Pasteurella spores, urea, calcium acetate, and nutrients are pre-mixed and blended to achieve the simultaneous release of bacteria, calcium source, and substrate after water seepage into the crack, efficiently generating calcium carbonate to seal microcracks. The system is designed with a double-layer coating structure of sodium alginate flexible inner layer and ultrafine metakaolin-water glass inorganic alkali-resistant outer layer to isolate the mortar from the high-alkali environment. Repair is triggered only by slow dissolution when water seeps into the crack, protecting the activity of microorganisms throughout the process. Meanwhile, the mortar matrix is ​​optimized. Ordinary silicate cement, ultrafine metakaolin, and silica fume are compounded to form a dense cementitious system. Citric acid retarder reduces the heat of hydration and prevents spore inactivation at high temperatures. Polypropylene short fibers and redispersible latex powder improve the flexibility of the mortar to adapt to the expansion and contraction of utility poles. Organosilicon water-repellent agent reduces the penetration of indiscriminate rainwater and delays the premature failure of capsules. All components work together to take into account the strength of thin-layer repair, crack resistance and long-term self-healing ability.

[0036] Furthermore, a dedicated microcapsule preparation and low-damage mixing and construction process is designed. After freshly preparing the integrated mineralization core liquid, it undergoes drop ball crosslinking, fluidized bed double-layer coating, low-temperature drying, and sealed light-proof storage and transportation to completely produce three-layer core-shell microcapsules. On-site construction is limited to low-speed stirring of 30-60 r / min to avoid high-speed shearing and capsule breakage. Simultaneously, the pretreatment of the pole base surface, layered thin coating, and moisturizing curing processes are standardized. By precisely controlling the efficiency by limiting the ratio range of each raw material, capsule size, water-binder ratio, and construction thickness, the existing technologies address the problems of easy loss and inactivation of microorganisms, low mineralization efficiency, repeated cracking of the repair layer, and inability to adapt to the outdoor working conditions of poles in a long-term manner from multiple dimensions, including mineralization repair core, capsule protective structure, special mortar compatibility, and complete preparation and construction process.

[0037] The raw materials selected are as follows: Ordinary Portland cement of grade P·O42.5; ultrafine metakaolin with a particle size D90 ≤ 3μm; silica fume specific surface area ≥ 18000m² 2 / kg; Sodium silicate modulus 2.8, Baume degree 40°Bé; Redispersible latex powder is ethylene-vinyl acetate type; Polypropylene short fiber diameter 20μm; Intermittent bottom spray fluidized bed is selected; Vacuum drying oven vacuum degree -0.08MPa; Dry powder mixer horizontal double ribbon type; Mixing mixer planetary type.

[0038] Example 1: This application provides a self-healing mortar for the surface of utility poles containing microbial mineralization microcapsules, which is made by mixing matrix dry powder, microbial mineralization microcapsules, and mixing water; By weight, the dry matrix powder contains: 44 parts ordinary silicate cement, 10 parts ultrafine metakaolin, 4 parts silica fume, 34 parts quartz fine sand, 2 parts redispersible latex powder, 0.4 parts polycarboxylate superplasticizer, 0.2 parts polypropylene short fiber, 0.2 parts organosilicon water-repellent agent, and 0.12 parts citric acid retarder. The amount of microbial mineralization microcapsules added is 11% of the total mass of the matrix dry powder, and the amount of mixing water added is 24% of the total mass of the matrix dry powder. The microbial mineralization microcapsules have a three-layer core-shell structure, consisting of an integrated mineralization core liquid core, an inner layer of sodium alginate hydrogel wall, and an outer layer of ultrafine metakaolin-water glass inorganic alkali resistant wall, from the inside out. The integrated mineralized core solution is a pre-mixed homogeneous sterile liquid phase, which consists of the following components based on the total mass of the integrated mineralized core solution: 35 parts of Bacillus pasteurellii spore suspension, 12 parts of urea, 18 parts of calcium acetate, 2 parts of yeast extract, and 33 parts of deionized water. The quartz fine sand has a particle size of 0.15–0.6 mm, the polypropylene short fiber length is 6 mm, and the concentration of the Bacillus pasteurellium spore suspension is 1 × 10⁻⁶. 9 CFU / mL; The microbial mineralization microcapsules have a particle size of 0.8–1.5 mm; the inner layer hydrogel wall of sodium alginate is prepared by cross-linking and solidifying a 2.0% (w / w) sterile sodium alginate aqueous solution by dripping it into a calcium chloride coagulation bath. The mass ratio of the inorganic alkali-resistant outer wall material of ultrafine metakaolin-water glass is 2:5:3: ultrafine metakaolin: sodium water glass: deionized water. The ratio of mixing water to total mass of cementitious materials in the mortar is 0.35. The cementitious materials consist only of ordinary Portland cement, ultrafine metakaolin, and silica fume. The total construction thickness is 4mm, applied in two layers by spraying or plastering, with each layer being 2mm thick. A method for preparing self-healing mortar for utility pole surfaces containing microbial mineralization microcapsules includes the following steps: (1) Preparation of integrated mineralized core solution: Bacillus pasteurellii was expanded in liquid culture medium and concentrated by centrifugation to obtain 1×10 9CFU / mL spore suspension, according to the mass ratio, spore suspension, urea, calcium acetate, yeast extract and deionized water are aseptically mixed to obtain a uniform integrated mineralized core solution; The liquid culture medium consisted of 10 g / L peptone, 5 g / L yeast extract and 10 g / L NaCl. It was sterilized at 121°C for 30 min, cooled to 30°C and inoculated with Bacillus pasteurellis. It was then cultured at 30°C and 160 r / min for 24 h with shaking. (2) Molding of the inner layer hydrogel wall of sodium alginate: Prepare a 2.0wt% sterile sodium alginate aqueous solution, mix the integrated mineralized core liquid in step (1) with the sterile sodium alginate aqueous solution at a volume ratio of 1:3, and drip it into a 4wt% calcium chloride coagulation bath through a 0.8mm needle to crosslink and solidify to obtain wet microspheres. After sterile water washing, dry at 40℃ under low temperature vacuum until the water content is ≤8%, which is a single-layer bacterial microsphere; (3) Coating of the outer wall of the inorganic alkali resistant layer of ultrafine metakaolin-water glass: prepare ultrafine metakaolin-sodium water glass slurry, use fluidized bed to double-coat the single-layer bacterial microspheres in step (2), dry at low temperature of 45℃, and store in a sealed and light-proof container to obtain three-layer core-shell microbial mineralization microcapsules. Among them, the storage and transportation of microbial mineralization microcapsules must be sealed and protected from light at room temperature; (4) Premixing of matrix dry powder: Put ordinary silicate cement, ultrafine metakaolin, silica fume and quartz fine sand into a dry powder mixer and dry mix for 5 minutes. Then add redispersible latex powder, polycarboxylate superplasticizer, polypropylene short fiber, organosilicon water repellent and citric acid retarder in sequence. Continue to dry mix for 8 minutes and seal for later use. (5) On-site mixing construction: Take the premixed dry matrix powder in step (4), mix it manually at low speed for 2 minutes, add the microbial mineralization microcapsules in step (3), add the mixing water in batches and mix at low speed for 3-4 minutes to obtain the sprayable repair mortar. During the mixing stage, a low-speed mixing of 45r / min is used throughout to prevent the three-layer core-shell microcapsule wall from breaking. Before construction, the surface of the concrete pole is ground and cleaned of laitance and loose layer. The base surface is moistened with clean water without standing water. After construction, it is kept moist at room temperature for 7 days.

[0039] Example 2: This application provides a self-healing mortar for the surface of a power pole containing microbial mineralization microcapsules. Unlike Example 1, the integrated mineralization core liquid is a pre-mixed homogeneous sterile liquid phase, which consists of the following components based on the total mass of the integrated mineralization core liquid: 32 parts of Bacillus pasteurellii spore suspension, 10 parts of urea, 16 parts of calcium acetate, 1 part of yeast extract, and 30 parts of deionized water; the remaining raw material components, proportions, and preparation processes are the same as in Example 1.

[0040] Example 3: This application provides a self-healing mortar for the surface of a power pole containing microbial mineralization microcapsules. Unlike Example 1, the integrated mineralization core liquid is a pre-mixed homogeneous sterile liquid phase, which consists of the following components based on the total mass of the integrated mineralization core liquid: 38 parts of Bacillus pasteurellii spore suspension, 14 parts of urea, 20 parts of calcium acetate, 3 parts of yeast extract, and 36 parts of deionized water; the remaining raw material components, proportions, and preparation processes are the same as in Example 1.

[0041] Example 4: This application provides a self-healing mortar for the surface of utility poles containing microbial mineralization microcapsules. Unlike Example 1, the mortar contains 40 parts of ordinary silicate cement, 8 parts of ultrafine metakaolin, 3 parts of silica fume, 30 parts of fine quartz sand, 1.5 parts of redispersible latex powder, 0.2 parts of polycarboxylate superplasticizer, 0.1 parts of polypropylene short fiber, 0.2 parts of organosilicon water-repellent agent, and 0.08 parts of citric acid retarder. The external admixture of microcapsules is 8%, and the mixing water is 22%. The integrated mineralization core liquid is the same as in Example 2, and the remaining raw material components, proportions, and preparation processes are the same as in Example 1.

[0042] Example 5: This application provides a self-healing mortar for the surface of utility poles containing microbial mineralization microcapsules. Unlike Example 1, the mortar contains 48 parts ordinary silicate cement, 12 parts ultrafine metakaolin, 5 parts silica fume, 38 parts fine quartz sand, 2.5 parts redispersible latex powder, 0.6 parts polycarboxylate superplasticizer, 0.3 parts polypropylene short fiber, 0.4 parts organosilicon water-repellent agent, and 0.16 parts citric acid retarder; the external microcapsule dosage is 14%, and the mixing water is 26%; the integrated mineralization core liquid is the same as in Example 3; the remaining raw material components, proportions, and preparation processes are the same as in Example 1.

[0043] Comparative Example 1: The only difference between this comparative example and Example 1 is that all microbial mineralization microcapsules are removed and replaced with two types of diatomaceous earth adsorption powders: Powder A: diatomaceous earth adsorbs calcium acetate; Powder B: diatomaceous earth adsorbs Bacillus pasteurellii and urea; the total amount of the two types of powders is equal to the mass of the microcapsules in Example 1; the remaining raw material components, proportions and preparation processes are the same as in Example 1.

[0044] Comparative Example 2: The only difference between this comparative example and Example 1 is that the ultrafine metakaolin-water glass double-layer coating step is omitted, and it is directly dried and then mixed into mortar; the other raw material components, proportions and preparation processes are the same as those in Example 1.

[0045] Comparative Example 3: The only difference between this comparative example and Example 1 is that the matrix dry powder, the three-layer structure of the capsule, the preparation process, and the mixing parameters are the same as in Example 2; only the core liquid ratio is changed: 25 parts of spore suspension, 6 parts of urea, 12 parts of calcium acetate, 0.5 parts of yeast extract, and 56.5 parts of deionized water; the other raw material components, ratios, and preparation processes are the same as in Example 1.

[0046] Comparative Example 4: The only difference between this comparative example and Example 1 is that the mixing step is changed to high-speed stirring at 90 r / min, while the rest of the operation remains the same; the other raw material components, proportions and preparation processes are the same as in Example 1.

[0047] Comparative Example 5: The only difference between this comparative example and Example 1 is that the citric acid retarder is removed from the dry matrix powder, and the early hydration heat release of ordinary silicate cement is not buffered; the other raw material components, proportions and preparation processes are the same as those in Example 1.

[0048] Performance comparison experiment of self-healing mortar for pole surfaces containing microbial mineralization microcapsules and its preparation method: In this application, four parallel tests were conducted: microcapsule mixing breakage rate, Bacillus pasteurellosis spore survival rate after mixing, 0.05-0.6 mm microcrack closure rate after 28 days, and simulated open-air cracking after 180 days. Each group of parallel samples had no less than 6 pieces, and the average value was taken as the final result. The compressive strength at 7 days and 28 days was tested according to GB / T17671; the interfacial bond strength with the concrete substrate was tested according to GB / T50448. In Example 1, the 28-day compressive strength was 36.2 MPa and the interfacial bond strength was 1.85 MPa, meeting the mechanical requirements for thin-layer repair of utility poles. The microcapsule breakage rate was tested according to the JC / T681 cement mortar mixer standard, using a planetary mortar mixer, a 0.075 mm standard sieve, a 10-40x optical microscope, and an electronic balance with an accuracy of 0.001 g. The number of intact capsules before and after mixing was counted, and the breakage percentage was calculated based on the difference. The spore survival rate was determined according to the GB4789.2 standard for the determination of total microbial colonies. Using a clean bench, sterilizer, constant temperature incubator, and nutrient agar medium, the plate-coated viable count method was employed, comparing the viable count of the unmixed blank group and the mortar sample to obtain the survival rate. The 28-day crack closure rate was... The closure rate was determined according to GB / T50081 Concrete Mechanical Testing Standard. 40mm×40mm×160mm specimens with standard microcracks were prepared and cured under dry-wet cycles for 28 days. The closure rate was calculated by statistically analyzing the calcium carbonate filling area using scanning electron microscopy combined with image software. The 180-day re-cracking test followed GB / T50082 Concrete Durability Performance Standard. A high-low temperature dry-wet aging chamber was used to simulate outdoor temperature changes from -10℃ to 60℃ and periodic spraying conditions. After the test, the surface cracking status was recorded under a microscope. The quantitative grading criteria for cracks were as follows: No new microcracks: no cracks wider than 0.02mm in the crack area; a few extremely fine cracks: only 0.02–0.05mm micro-cracks exist, with no through cracks; multiple surface cracks: multiple 0.05–0.3mm through cracks appear on the surface; numerous re-crackings: multiple 0.1–0.5mm through cracks, with large-area detachment of the mineralized filling layer.

[0049] All experiments in this application adopted the single-variable control principle. Except for the differential variables set for each group, the basic parameters such as microbial culture, microcapsule preparation, and mortar mixing and curing were kept uniform: the bacterial strains were uniformly cultured in sterile medium at 121℃ with shaking at 30℃ and 160r / min for 24h; the microcapsules were uniformly formed by cross-linking 2.0wt% sodium alginate and 4wt% calcium chloride, with a particle size controlled between 0.8 and 1.5 mm; the single-layer microspheres were vacuum-dried at 40℃, and the encapsulated capsules were dried at a low temperature of 45℃; the mortar was cured at standard room temperature with moisture for 7 days; and the water-cement ratio of the non-variable groups was uniformly controlled between 0.32 and 0.38 to minimize interference from irrelevant conditions and ensure the objectivity and reliability of the experimental data for each group. The experimental results are shown in Table 1.

[0050] Table 1:

[0051] In conjunction with Examples 1-5 and Comparative Example 1, and in conjunction with Table 1, Figure 2 It can be seen that canceling the integrated sterile liquid mineralization core liquid and the three-layer core-shell microcapsule and replacing it with diatomaceous earth-loaded powder will significantly degrade the overall self-healing performance of the mortar. The reaction principle is that diatomaceous earth simply wraps bacteria and calcium source through physical pores without airtight isolation and protection. During the mixing process, nutrients are continuously lost, and the strong alkali of ordinary silicate cement and the high temperature of hydration continuously kill spores. Although there is no capsule breakage loss, the long-term loss of live bacteria and mineralized substrate is serious. At the synergistic level, the integrated premixed core liquid of this invention can realize the simultaneous release of bacteria, urea and calcium ions. The inner gel of the three-layer capsule buffers the impact, and the outer alkali-resistant shell isolates the erosion. The two work together to greatly improve the spore survival rate and calcium carbonate deposition efficiency. The comparative data shows that the spore survival rate and 28-day crack closure rate of the example are much higher than those of the comparative example 1. There is no cracking phenomenon after long-term open-air service, which proves that the integrated core liquid and the three-layer capsule are the core synergistic structure for achieving long-term repair.

[0052] In conjunction with Examples 1-5 and Comparative Example 2, and in conjunction with Table 1, Figure 2 It can be seen that removing the inorganic alkali-resistant outer wall of ultrafine metakaolin-water glass and retaining only a single layer of sodium alginate microspheres significantly reduces the survival of microorganisms and the ability to repair cracks. The reaction principle is that sodium alginate hydrogel alone has poor alkali resistance and is prone to swelling and damage when in direct contact with ordinary silicate cement high-alkali slurry. After the core liquid leaks out in advance, the spores are quickly inactivated and there is no controllable erosion triggering mechanism. In terms of synergistic effect, the inner layer of sodium alginate provides flexible buffering to prevent mechanical damage, while the inorganic outer layer isolates strong alkali and achieves controllable shell breaking upon contact with water. The double-layer coating structure synergistically protects the capsule integrity and bacterial activity. In Comparative Example 2, the capsule mixing breakage rate increased significantly and the 28-day crack closure rate decreased significantly after the absence of the inorganic alkali-resistant outer shell, verifying the necessity of the double-layer coating synergistic protection.

[0053] Combined with Examples 1-5 and Comparative Example 3, and in conjunction with Table 1 and Figure 2It can be seen that deviating from the specified ratio range of the mineralized core solution significantly weakens the self-healing effect. The reaction principle is that the imbalance of the ratio of spore-forming liquid, urea, and calcium source in the core solution either results in insufficient substrate limiting calcium carbonate production or high osmotic pressure damaging spore cells and reducing the activity of viable bacteria. In terms of synergistic effect, the ratio of each component in the core solution of this invention has been optimized, and the molar ratios of bacterial strains, nitrogen sources, and calcium ions are matched. Any deviation of any component from the range will disrupt the mineralization reaction balance. Even if the capsule structure is intact, the spore survival rate and crack closure rate are still significantly lower than those in the example, proving that there is a synergistic adaptation relationship among the components in the core solution ratio range.

[0054] In conjunction with Examples 1-5 and Comparative Example 4, and in conjunction with Table 1, Figure 2 It can be seen that high-speed shearing and mixing at 90 r / min causes large-scale damage to the three-layer core-shell capsules, completely weakening the self-healing function. The reaction principle is that high-speed mixing combined with hard quartz fine sand particles produces strong grinding and tearing effects. After the capsule shell breaks, the core liquid is released prematurely at one time, and the spores are rapidly inactivated in a strong alkaline and high-temperature environment. There is no reserve repair carrier in the mortar. In terms of synergistic effect, the low-speed mixing process of 30-60 r / min is compatible with the three-layer capsule structure. The low speed reduces mechanical damage and the capsule resists slight friction. The two work together to ensure that most capsules remain intact. In Comparative Example 4, high-speed mixing destroys the synergistic matching relationship between the capsule and the low-speed mixing process. The capsule mixing damage rate is the highest, the crack closure rate at 28 days is the lowest, and the spore survival rate is only higher than that of Comparative Example 1, resulting in the worst overall self-healing performance.

[0055] In conjunction with Examples 1-5 and Comparative Example 5, and in conjunction with Table 1, Figure 2 It can be seen that removing the citric acid retarder from the matrix dry powder significantly reduces the spore survival rate after mixing. The reaction principle is that without the retarder to regulate the early hydration exothermic peak of ordinary silicate cement, the high temperature directly kills the Pasteurella spores inside the capsule. In terms of synergistic effect, the citric acid retarder slows down the hydration rate and reduces the temperature rise of the system. It forms a synergistic system of dual protection against temperature and alkaline environment with the three-layer alkali-resistant capsule. Without the retarder, the capsule alone cannot resist high temperature damage, the spore survival rate decreases significantly, and the long-term repair durability of cracks deteriorates. This proves that the retarder and microcapsules have a synergistic effect in protecting the microbial species.

[0056] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A self-healing mortar for utility pole surfaces containing microbial mineralization microcapsules, characterized in that, It is made by mixing a dry matrix powder, microbial mineralization microcapsules, and mixing water; By weight, the matrix powder comprises: 40-48 parts ordinary silicate cement, 8-12 parts ultrafine metakaolin, 3-5 parts silica fume, 30-38 parts fine quartz sand, 1.5-2.5 parts redispersible latex powder, 0.2-0.6 parts polycarboxylate superplasticizer, 0.1-0.3 parts polypropylene short fiber, 0.2-0.4 parts organosilicon water-repellent agent, and 0.08-0.16 parts citric acid retarder; The amount of microbial mineralization microcapsules added is 8% to 14% of the total mass of the matrix dry powder, and the amount of mixing water added is 22% to 26% of the total mass of the matrix dry powder; the microbial mineralization microcapsules have a three-layer core-shell structure, consisting of an integrated mineralization core liquid core, an inner layer hydrogel wall of sodium alginate, and an outer layer of ultrafine metakaolin-water glass inorganic alkali resistant material, from the inside out. The integrated mineralized core solution is a pre-mixed homogeneous sterile liquid phase, and is composed of the following components based on the total mass of the integrated mineralized core solution: 32-38 parts of Bacillus pasteurellii spore suspension, 10-14 parts of urea, 16-20 parts of calcium acetate, 1-3 parts of yeast extract, and 30-36 parts of deionized water.

2. The self-healing mortar for pole surfaces containing microbial mineralization microcapsules according to claim 1, characterized in that, The quartz sand has a particle size of 0.15–0.6 mm, the polypropylene short fibers have a length of 6 mm, and the *Bacillus pasteurellii* spore suspension concentration is 1 × 10⁻⁶. 9 CFU / mL.

3. The self-healing mortar for pole surfaces containing microbial mineralization microcapsules according to claim 1, characterized in that, The microbial mineralization microcapsules have a particle size of 0.8–1.5 mm; the inner hydrogel wall of the sodium alginate is prepared by cross-linking and solidifying a 2.0% (w / w) sterile sodium alginate aqueous solution by dripping it into a calcium chloride coagulation bath.

4. The self-healing mortar for pole surfaces containing microbial mineralization microcapsules according to claim 1, characterized in that, The mass ratio of the inorganic alkali-resistant outer wall material of the ultrafine metakaolin-water glass is 2:5:3: ultrafine metakaolin: sodium water glass: deionized water.

5. The self-healing mortar for pole surfaces containing microbial mineralization microcapsules according to claim 1, characterized in that, The ratio of mixing water to total mass of cementitious materials in the mortar is 0.32 to 0.

38. The cementitious materials consist only of ordinary Portland cement, ultrafine metakaolin, and silica fume. The total construction thickness is 3 to 5 mm, applied in two layers by spraying or plastering, with each layer being 1.5 to 2.5 mm thick.

6. A method for preparing self-healing mortar for utility pole surfaces containing microbial mineralization microcapsules, characterized in that, The method for preparing the self-healing mortar for pole surfaces containing microbial mineralization microcapsules as described in any one of claims 1-5 comprises the following steps: (1) Preparation of integrated mineralized core solution: Bacillus pasteurellii was expanded in liquid culture medium and concentrated by centrifugation to obtain 1×10 9 CFU / mL spore suspension, according to the mass ratio, spore suspension, urea, calcium acetate, yeast extract and deionized water are aseptically mixed to obtain a uniform integrated mineralized core solution; (2) Molding of the inner layer hydrogel wall of sodium alginate: Prepare a 2.0wt% sterile sodium alginate aqueous solution, mix the integrated mineralized core liquid in step (1) with the sterile sodium alginate aqueous solution at a volume ratio of 1:3, and drip it into a 4wt% calcium chloride coagulation bath through a 0.8mm needle to crosslink and solidify to obtain wet microspheres. After sterile water washing, dry at 40℃ under low temperature vacuum until the water content is ≤8%, which is a single-layer bacterial microsphere; (3) Coating of the outer wall of the inorganic alkali resistant layer of ultrafine metakaolin-water glass: prepare ultrafine metakaolin-sodium water glass slurry, use fluidized bed to double-coat the single-layer bacterial microspheres in step (2), dry at low temperature of 45℃, and store in a sealed and light-proof container to obtain three-layer core-shell microbial mineralization microcapsules. (4) Premixing of matrix dry powder: Put ordinary silicate cement, ultrafine metakaolin, silica fume and quartz fine sand into a dry powder mixer and dry mix for 5 minutes. Then add redispersible latex powder, polycarboxylate superplasticizer, polypropylene short fiber, organosilicon water repellent and citric acid retarder in sequence. Continue to dry mix for 8 minutes and seal for later use. (5) On-site mixing construction: Take the premixed dry matrix powder in step (4), mix it manually at low speed for 2 minutes, add the microbial mineralization microcapsules in step (3), add the mixing water in batches and mix at low speed for 3-4 minutes to obtain the sprayable repair mortar.

7. The method for preparing self-healing mortar for pole surfaces containing microbial mineralization microcapsules according to claim 6, characterized in that, In step (1), the liquid culture medium consists of 10 g / L peptone, 5 g / L yeast extract and 10 g / L NaCl. It is sterilized at 121°C for 30 min, cooled to 30°C and inoculated with Bacillus pasteurellis. It is then cultured at 30°C and 160 r / min for 24 h with shaking.

8. The method for preparing self-healing mortar for pole surfaces containing microbial mineralization microcapsules according to claim 6, characterized in that, In step (3), the storage and transportation of microbial mineralization microcapsules require sealing and protection from light at room temperature.

9. The method for preparing self-healing mortar for pole surfaces containing microbial mineralization microcapsules according to claim 6, characterized in that, In step (5), the mixing stage is carried out at a low speed of 30-60 r / min to prevent the three-layer core-shell microcapsule wall from breaking.

10. The method for preparing self-healing mortar for pole surfaces containing microbial mineralization microcapsules according to claim 6, characterized in that, In step (5), before construction, the surface of the concrete pole is ground and cleaned of laitance and loose layer, and the base surface is moistened with clean water without standing water. After construction, it is kept moist at room temperature for 7 days.

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