Self-repairing concrete based on waxy rice slurry coated recycled aggregate immobilized microorganisms

Abstract

The present application relates to the field of self-repairing concrete, in particular to a self-repairing concrete based on waxy rice syrup wrapped recycled aggregate immobilized microorganisms, which is used to solve the problems of low survival rate of microorganisms in strong alkali environment of concrete, serious mixing shear damage, premature loss of nutrient components and insufficient performance of traditional carriers, and to improve the inherent defects of weak interface of recycled aggregate; the cement, mineral admixture, natural fine aggregate and natural coarse aggregate are dry-mixed in a forced mixer, the waxy rice syrup wrapped recycled coarse aggregate immobilized microorganisms is first stirred, then the waxy rice syrup wrapped recycled fine aggregate immobilized microorganisms is stirred, and then the mixing water, water reducing agent and nutrients are added for continuous stirring, and finally the self-repairing concrete is obtained after pouring, shaping and standard curing; the self-repairing concrete has more excellent mechanical strength, interface bonding performance and microcrack self-repairing ability, and realizes the collaborative high-value utilization of construction and agricultural waste.

Description

Technical Field

[0001] This invention relates to the field of self-healing concrete, specifically to a self-healing concrete based on glutinous rice paste encapsulating recycled aggregate and immobilizing microorganisms. Background Technology

[0002] Concrete is the most widely used building material, but its brittleness and low tensile strength make it highly susceptible to cracking during use. Cracks provide pathways for corrosive media such as water, chloride ions, and sulfates, accelerating steel corrosion and concrete deterioration, significantly reducing the durability and service life of structures. Traditional crack repair methods (such as surface coating and pressure grouting) are passive repair methods, which are costly, complex to operate, and difficult to detect and repair internal micro-cracks.

[0003] Microbial self-healing concrete is a smart repair technology that has been developed in recent years. Its principle is to pre-mix microorganisms and their nutrients that can induce calcium carbonate precipitation (MICP) into the concrete. When cracks appear, moisture and air enter the cracks, activating the metabolism of microorganisms, producing calcium carbonate precipitation, and sealing the cracks. This technology has the advantages of being green, long-lasting, and self-healing.

[0004] However, existing microbial self-healing concrete technology still faces many key bottlenecks in engineering applications: the microbial survival environment is harsh, with the internal pH value of concrete reaching 12-13 after hydration, making it difficult for most microorganisms to survive for a long time in this highly alkaline environment. Even when alkali-resistant strains are used, their activity will rapidly decline over time, leading to a loss of later repair capabilities; severe mechanical damage occurs during the mixing process, with the strong shearing and grinding action between cement particles and aggregates directly destroying the microbial cell structure and significantly reducing the number of viable bacteria in the system; low nutrient utilization rate, as nutrients such as urea and calcium sources are easily consumed by cement hydration products or lost with water migration in the early stages of hydration if directly added to concrete, failing to effectively supply microbial metabolism when cracks occur; and insufficient performance of carrier materials, such as porous ceramsite, diatomaceous earth, expanded perlite, and synthetic microcapsules, which have drawbacks including high cost, weak interfacial bonding with the concrete matrix, low self-strength, and limited protection and slow-release effects on microorganisms, making it difficult to meet the needs of engineering applications.

[0005] Recycled aggregates are aggregates produced from construction waste such as waste concrete, waste bricks, and waste mortar through processes such as crushing, screening, and washing. my country generates a large amount of construction waste annually, and the resource utilization of recycled aggregates is an important way to achieve sustainable development in the construction industry. However, recycled aggregates have a large amount of old cement mortar adhering to their surface, resulting in high water absorption, high crushing index, and a weak interfacial transition zone, which limits their application in high-performance concrete. It is worth noting that the porous structure of the mortar adhering to recycled aggregates naturally possesses the potential to serve as a carrier for microorganisms. However, directly using recycled aggregates to immobilize microorganisms presents two major problems: first, the cement hydration products remaining on the surface of the recycled aggregates make them highly alkaline, causing chemical damage to microorganisms; second, microorganisms easily escape from the aggregate pores, resulting in poor immobilization stability.

[0006] Glutinous rice paste is a traditional natural cementitious material. Its main component, branched-chain starch, has excellent binding, film-forming, and biocompatibility. Its solidified film can buffer alkaline environments, slowly release nutrients, and protect microorganisms. Currently, there is no research or application on using glutinous rice paste to coat recycled aggregates and construct a composite microbial support system to prepare self-healing concrete. Summary of the Invention

[0007] In order to overcome the above-mentioned technical problems, the purpose of this invention is to provide a self-healing concrete based on glutinous rice paste encapsulating recycled aggregate and immobilizing microorganisms.

[0008] The objective of this invention can be achieved through the following technical solutions: This application provides a self-healing concrete based on recycled aggregate encapsulated in glutinous rice paste and supported by microorganisms, comprising the following components by weight: The mixture consists of 350-420 parts cement, 60-90 parts mineral admixtures, 450-850 parts natural coarse aggregate, 200-500 parts recycled coarse aggregate coated with glutinous rice paste containing microorganisms, 460-730 parts natural fine aggregate, 70-240 parts recycled fine aggregate coated with glutinous rice paste containing microorganisms, 175-195 parts mixing water, 3.8-5.1 parts water-reducing agent, and 1.0-2.5 parts nutrients. The recycled coarse aggregate and the recycled fine aggregate coated with glutinous rice paste containing microorganisms are prepared by the following steps: Step a1: Construction waste is crushed by a jaw crusher and then further crushed by a cone crusher. The waste is then graded using a vibrating screen to obtain recycled coarse aggregate and recycled fine aggregate. The two types of aggregate are placed separately in a drum washing machine and rinsed with high-pressure water for 10-15 minutes. Afterward, they are transferred to a soaking tank and soaked in room temperature water for 24-48 hours, with the water changed every 12 hours. The aggregates are then drained and soaked in acetic acid solution for 30-60 minutes. After rinsing with water until the pH of the filtrate is 7-8, the aggregates are placed in a forced-air drying oven and dried at 55-60℃ for 12-18 hours. After removal, the aggregates are allowed to cool naturally to room temperature and then placed in a muffle furnace. The temperature is increased to 300-400℃ at a rate of 5℃ / min and calcined at a constant temperature for 1-2 hours. Afterward, the aggregates are allowed to cool naturally to room temperature and then sieved to remove fine powder with a particle size <0.15mm to obtain pretreated recycled aggregate. Step a2: Soak glutinous rice in deionized water at room temperature for 2-4 hours. Then transfer it to a stainless steel cooking pot, bring it to a boil over high heat, and immediately reduce to a simmer. Stir constantly with a glass rod while cooking for 30-60 minutes. After turning off the heat, let it cool naturally to below 40°C. Filter it through a 40-mesh standard sieve, add glutinous rice slurry modifier and stir. Then place it in a vacuum drying oven and degas at -0.06MPa for 10-12 minutes to obtain modified glutinous rice slurry. Step a3: Inoculate the urease-producing microorganisms into liquid culture medium and culture them with shaking at a temperature of 30-37℃ and a stirring rate of 150-200 r / min until OD. 600 A value of 1.2 indicates the presence of microbial inoculum. Step a4: The pretreated recycled aggregates are subjected to immobilization treatment and placed in a vacuum impregnation tank. The vacuum is drawn to -0.09MPa and maintained for 20-30 minutes. Microbial inoculum is injected until the liquid surface completely submerges the aggregates by more than 5cm. After restoring normal pressure, the aggregates are soaked for 1-2 hours. The inoculum is drained and the surface of the aggregates is drained. The aggregates are then immersed in glutinous rice slurry and soaked at normal pressure for 15-30 minutes. The aggregates are then removed and drained. Afterward, they are placed in a constant temperature and humidity incubator and dried for 24-36 hours at a temperature of 25℃ and a relative humidity of 60%. This yields recycled coarse aggregates and recycled fine aggregates encapsulated in glutinous rice slurry with immobilized microorganisms.

[0009] In a preferred embodiment of the present invention, the particle size range of the recycled coarse aggregate in step a1 is 5-10 mm; the particle size range of the recycled fine aggregate is 0.15-2.36 mm.

[0010] In a preferred embodiment of the present invention, the pretreated recycled aggregate in step a1 includes pretreated recycled coarse aggregate and pretreated recycled fine aggregate.

[0011] In a preferred embodiment of the present invention, the molar concentration of the acetic acid solution in step a1 is 0.3 mol / L.

[0012] In a preferred embodiment of the present invention, the mass ratio of glutinous rice to deionized water in step a2 is 1:8.

[0013] In a preferred embodiment of the present invention, the glutinous rice paste modifier in step a2 includes 0.05-0.2 mol / L calcium salt, 0.1-0.5 mol / L urea, 0.5-2 g / L nutrient broth, and 0.1-0.5% sodium alginate.

[0014] In a preferred embodiment of the present invention, the urease-producing microorganism in step a3 is Bacillus pasteurellii.

[0015] As a preferred embodiment of the present invention, a method for preparing self-healing concrete based on microorganisms immobilized by recycled aggregate encapsulated in glutinous rice paste includes the following steps: Step 1: Weigh out the following components by weight: 350-420 parts cement, 60-90 parts mineral admixture, 450-850 parts natural coarse aggregate, 200-500 parts recycled coarse aggregate coated with glutinous rice paste containing microorganisms, 460-730 parts natural fine aggregate, 70-240 parts recycled fine aggregate coated with glutinous rice paste containing microorganisms, 175-195 parts mixing water, 3.8-5.1 parts water-reducing agent, and 1.0-2.5 parts nutrients. Set aside. Step 2: Add cement, mineral admixtures, natural fine aggregate, and natural coarse aggregate to a forced mixer and dry mix for 30 seconds at an online speed of 1.2-1.8 m / s. First, add glutinous rice paste containing microorganisms to coat the recycled coarse aggregate and mix for 15 seconds at an online speed of 0.6-1.0 m / s. Then, add glutinous rice paste containing microorganisms to coat the recycled fine aggregate and continue mixing for 10 seconds. After that, add mixing water, water-reducing agent, and nutrients and continue mixing for 100-120 seconds at an online speed of 0.9-1.4 m / s. Then, pour the mixture into shape and cure it for 14 days at a temperature of 18-22℃ and a relative humidity of ≥95% to obtain self-healing concrete.

[0016] In a preferred embodiment of the present invention, the cement is ordinary Portland cement of grade PO 42.5 or higher; the mineral admixture is one or both of fly ash and mineral powder; the natural coarse aggregate is 5-20mm continuously graded granite crushed stone; the natural fine aggregate is medium sand with a fineness modulus of 2.3-3.0; the water-reducing agent is PCA®-Ⅰ series polycarboxylate high-performance water-reducing agent; the nutrient is a mixture of urea and calcium salt in a mass ratio of 1:1, and the calcium salt is calcium chloride or calcium acetate.

[0017] The beneficial effects of this invention are: This invention discloses a self-healing concrete based on recycled aggregate encapsulated with glutinous rice paste and immobilized with microorganisms. The process involves dry mixing cement, mineral admixtures, natural fine aggregate, and natural coarse aggregate in a forced mixer. First, recycled coarse aggregate encapsulated with microorganisms is added and mixed. Then, recycled fine aggregate encapsulated with microorganisms is added and mixed further. Next, mixing water, a water-reducing agent, and nutrients are added, and mixing continues. The mixture is then poured into molds and cured according to standard conditions to obtain self-healing concrete. The recycled aggregate encapsulated with microorganisms in the glutinous rice paste can improve defects in the recycled aggregate and strengthen the concrete interface transition zone to enhance the matrix's mechanical properties through the filling and bonding effects of the glutinous rice paste and the mineralization effect of the microorganisms. Furthermore, the alkaline environment buffering and nutrient slow-release effect of the glutinous rice paste can maintain the activity of the microorganisms for a long time, endowing the concrete with long-term self-healing crack repair capabilities. This self-healing concrete exhibits superior mechanical strength, interfacial bonding performance, and self-repairing ability for microcracks. It also achieves high-value synergistic utilization of construction and agricultural waste, is environmentally friendly, has low preparation costs, and is easy to scale up for industrial application.

[0018] In the preparation of self-healing concrete, a type of recycled aggregate encapsulated in glutinous rice paste with microorganisms was first prepared. This recycled aggregate includes two types: recycled coarse aggregate encapsulated in glutinous rice paste with microorganisms and recycled fine aggregate encapsulated in glutinous rice paste with microorganisms. Firstly, in the aggregate pretreatment stage, acetic acid was used to selectively dissolve the loose surface of the old mortar, combined with low-temperature calcination. This avoided damage to the silicate skeleton from high temperatures and effectively reduced water absorption. Combined with particle size control and fine powder removal, a uniform and interconnected microporous reaction channel was constructed for subsequent microbial mineralization. Then, in the glutinous rice paste modification stage, appropriate amounts of calcium salts and urea constituted the ideal substrate environment required for MIP (microbially induced calcium carbonate precipitation). Sodium alginate was added to form a three-dimensional gel network, which further extended… The biodegradation rate of glutinous rice starch was slowed down, and the microbial fixation effect was enhanced through physical encapsulation. At the same time, vacuum degassing eliminated air bubble interference, ensuring the continuity and uniformity of the aggregate surface coating. Finally, in the microbial fixation and encapsulation stage, a step-by-step dual penetration process was adopted, which first vacuum impregnates the bacterial solution and then soaks the glutinous rice slurry at normal pressure. This allows the bacterial solution to penetrate deep into the pores of the aggregate under the pressure difference, increasing the fixation load. The subsequent glutinous rice slurry coating layer not only effectively fills the open pores on the surface of the aggregate, but also forms a physical barrier against the high alkaline environment of cement slurry on the outside of the microorganisms, giving them the potential for self-repair when activated by water. Combined with controlled humidity drying, cell rupture due to rapid water loss is effectively avoided, and the survival rate of microorganisms is stabilized, thus achieving efficient strengthening and long-term protection of recycled aggregates.

[0019] This invention achieves the synergistic high-value utilization of both construction and agricultural waste. It is the first to propose combining recycled aggregate from construction waste with glutinous rice paste from agricultural byproducts as a microbial immobilization system. The recycled aggregate provides a natural porous load-bearing framework, while the glutinous rice paste simultaneously acts as a microbial protective layer, a nutrient slow-release layer, and an interfacial bonding layer. This truly realizes waste-to-waste transformation, breaking through the traditional single application of glutinous rice paste as a binder. It integrates three functions: forming a dense organic protective film on the aggregate surface to isolate the high-alkaline environment inside the concrete and resist damage from mixing shear forces, thus increasing the survival rate of microorganisms; utilizing the water-absorbing, swelling, and slow-degrading properties of starch to achieve on-demand release of microorganisms and mineralized substrates, preventing premature nutrient consumption; and simultaneously enhancing the interfacial adhesion between microorganisms and aggregates, and between aggregates and cement paste through physical adsorption and chemical cross-linking. This technology enhances the structural strength of recycled aggregates. It breaks the conventional limitations of using recycled aggregates merely as inert filler aggregates, transforming their inherent defects of high porosity and high water absorption into advantages. Through pretreatment to optimize pore structure and the creation of a microenvironment via rice paste encapsulation, ordinary recycled aggregates are upgraded into intelligent repair micro-compartments, achieving integrated modification of defect repair, performance enhancement, and functional enhancement. Employing a green, low-cost, and large-scale preparation process, all raw materials are inexpensive and readily available. The preparation process encompasses vacuum impregnation, atmospheric pressure soaking, and constant temperature drying, and can be carried out using conventional equipment in the construction industry. More importantly, it resolves the common contradiction in existing self-healing technologies where repair and strength are mutually exclusive. After recycled aggregates are encapsulated in rice paste containing microorganisms and incorporated into concrete, the filling and bonding effects of the rice paste significantly improve the interfacial transition zone, resulting in an increase in the 28-day compressive strength of the concrete. Detailed Implementation

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

[0021] Example 1: This embodiment describes a method for preparing self-healing concrete based on recycled aggregate encapsulated in glutinous rice paste and supported by microorganisms, comprising the following steps: Step S1: 1000g of construction waste is crushed by a jaw crusher, then further crushed by a cone crusher, and classified using a vibrating screen to obtain recycled coarse aggregate (particle size range of 5-10mm) and recycled fine aggregate (particle size range of 0.15-2.36mm). The two types of aggregate are placed separately in a drum washer and rinsed with high-pressure water for 10 minutes. Afterwards, they are transferred to a soaking tank and soaked in room temperature water for 24 hours, changing the water every 12 hours. The aggregates are then drained and rinsed with 0.3mol... Soak in 1 / L acetic acid solution for 30 min, then rinse with water until the pH of the filtrate is 7. Then place in a forced-air drying oven and dry at 55℃ for 12 h. After removal, allow to cool naturally to room temperature, then place in a muffle furnace and heat to 300℃ at a rate of 5℃ / min, calcine at a constant temperature for 1 h. After that, allow to cool naturally to room temperature with the furnace, and sieve to remove fine powder with a particle size <0.15 mm to obtain pretreated recycled aggregate (pretreated recycled coarse aggregate and pretreated recycled fine aggregate). Step S2: Soak 100g of glutinous rice in 800mL of deionized water at room temperature for 2 hours. Then transfer it to a stainless steel cooking pot, bring it to a boil over high heat, and immediately reduce to a simmer. Stir constantly with a glass rod while cooking for 30 minutes. After turning off the heat, let it cool naturally to below 40℃. Filter it through a 40-mesh standard sieve. Add glutinous rice paste modifier (0.05mol / L calcium salt, 0.1mol / L urea, 0.5g / L nutrient broth, and 0.1% sodium alginate in sequence). Stir for 5 minutes after each addition. Then place it in a vacuum drying oven and degauss at -0.06MPa for 10 minutes to obtain modified glutinous rice paste. Step S3: Inoculate the urease-producing microorganism (Bacillus pasteurellii) into the liquid culture medium and culture it under shaking conditions at 30°C and a stirring rate of 150 r / min until OD. 600 A value of 1.2 indicates the presence of microbial inoculum. Step S4: The pretreated recycled aggregates (400g of pretreated recycled coarse aggregate and 400g of pretreated recycled fine aggregate) were subjected to immobilization treatment and placed in a vacuum impregnation tank. The vacuum was drawn to -0.09MPa and maintained for 20min. Microbial liquid was injected until the liquid surface completely submerged the aggregate by more than 5cm. After restoring normal pressure, the aggregate was soaked for 1h. The liquid was drained and the surface of the aggregate was drained. The aggregate was then immersed in glutinous rice slurry and soaked at normal pressure for 15min. The aggregate was then removed and drained. Afterward, the aggregate was placed in a constant temperature and humidity incubator and dried for 24h at a temperature of 25℃ and a relative humidity of 60%. This yielded microbially immobilized glutinous rice slurry-coated recycled coarse aggregate and microbially immobilized glutinous rice slurry-coated recycled fine aggregate.

[0022] Step S5: Weigh out 350 parts of cement, 60 parts of mineral admixture, 450 parts of natural coarse aggregate, 200 parts of recycled coarse aggregate coated with glutinous rice paste containing microorganisms, 460 parts of natural fine aggregate, 70 parts of recycled fine aggregate coated with glutinous rice paste containing microorganisms, 175 parts of mixing water, 3.8 parts of water-reducing agent, and 1.0 part of nutrients according to weight, and set aside. Step S6: Add cement (ordinary Portland cement of grade PO 42.5 or higher), mineral admixture (fly ash), natural fine aggregate (medium sand with a fineness modulus of 2.3), and natural coarse aggregate (5-20mm continuously graded granite crushed stone) to a forced mixer and dry mix for 30 seconds at an online speed of 1.2 m / s. First, add glutinous rice paste containing microorganisms to coat the recycled coarse aggregate and mix for 15 seconds at an online speed of 0.6 m / s. Then, add the microorganisms... The glutinous rice paste is used to coat recycled fine aggregate, and the mixture is stirred for 10 seconds. Then, mixing water, water-reducing agent (PCA®-Ⅰ series polycarboxylate high-performance water-reducing agent) and nutrients (a mixture of urea and calcium salts in a mass ratio of 1:1, with calcium salts being calcium chloride or calcium acetate) are added. The mixture is stirred for 100 seconds at an online speed of 0.9 m / s, and then poured into molds. The mixture is then cured for 14 days under standard conditions at a temperature of 18℃ and a relative humidity of ≥95% to obtain self-healing concrete.

[0023] Example 2: This embodiment describes a method for preparing self-healing concrete based on recycled aggregate encapsulated in glutinous rice paste and supported by microorganisms, comprising the following steps: Step S1: The construction waste is crushed by a jaw crusher and then further crushed by a cone crusher. It is then classified using a vibrating screen to obtain recycled coarse aggregate (5-10mm particle size) and recycled fine aggregate (0.15-2.36mm particle size). Both types of aggregate are placed separately in a drum washing machine and rinsed with high-pressure water for 12 minutes. Afterward, they are transferred to a soaking tank and soaked in room temperature water for 36 hours, changing the water every 12 hours. The aggregates are then drained and rinsed with 0.3mol / L vinegar. The aggregate was soaked in acid solution for 45 minutes, then rinsed with water until the pH of the filtrate was 7.5. It was then placed in a forced-air drying oven and dried at 57°C for 15 hours. After being removed, it was allowed to cool naturally to room temperature and then placed in a muffle furnace. The temperature was increased to 350°C at a rate of 5°C / min and calcined at a constant temperature for 1.5 hours. After that, it was allowed to cool naturally to room temperature with the furnace. Fine powder with a particle size <0.15mm was removed by sieving to obtain pretreated recycled aggregate (pretreated recycled coarse aggregate and pretreated recycled fine aggregate). Step S2: Soak 100g of glutinous rice in 800mL of deionized water at room temperature for 3 hours. Then transfer it to a stainless steel cooking pot, bring it to a boil over high heat, and immediately reduce to a simmer. Stir constantly with a glass rod while cooking for 45 minutes. After turning off the heat, let it cool naturally to below 40℃. Filter it through a 40-mesh standard sieve. Add glutinous rice paste modifier (0.12mol / L calcium salt, 0.3mol / L urea, 1.3g / L nutrient broth, and 0.3% sodium alginate in sequence). Stir for 5 minutes after each addition. Then place it in a vacuum drying oven and degauge it at -0.06MPa for 11 minutes to obtain modified glutinous rice paste. Step S3: Inoculate the urease-producing microorganism (Bacillus pasteurellii) into the liquid culture medium and culture it under shaking conditions at 33°C and a stirring rate of 170 r / min until OD. 600 A value of 1.2 indicates the presence of microbial inoculum. Step S4: The pretreated recycled aggregates were subjected to immobilization treatment and placed in a vacuum impregnation tank. The vacuum was drawn to -0.09 MPa and maintained for 25 min. Microbial liquid was injected until the liquid surface completely submerged the aggregates by more than 5 cm. After restoring normal pressure, the aggregates were soaked for 1.5 h. The microbial liquid was drained and the surface of the aggregates was drained. The aggregates were then immersed in glutinous rice slurry and soaked at normal pressure for 23 min. The aggregates were then removed and drained. Afterward, they were placed in a constant temperature and humidity incubator and dried for 30 h at a temperature of 25℃ and a relative humidity of 60%. This yielded recycled coarse aggregates and recycled fine aggregates encapsulated in glutinous rice slurry with immobilized microorganisms.

[0024] Step S5: Weigh out 385 parts of cement, 75 parts of mineral admixture, 650 parts of natural coarse aggregate, 350 parts of recycled coarse aggregate coated with glutinous rice paste containing microorganisms, 595 parts of natural fine aggregate, 155 parts of recycled fine aggregate coated with glutinous rice paste containing microorganisms, 185 parts of mixing water, 4.45 parts of water-reducing agent, and 1.75 parts of nutrients according to weight, and set aside. Step S6: Add cement (ordinary Portland cement of grade PO 42.5 or higher), mineral admixture (fly ash), natural fine aggregate (medium sand with a fineness modulus of 2.6), and natural coarse aggregate (5-20mm continuously graded granite crushed stone) to a forced mixer and dry mix for 30 seconds at an online speed of 1.5 m / s. First, add glutinous rice paste containing microorganisms to coat the recycled coarse aggregate and mix for 15 seconds at an online speed of 0.8 m / s. Then, add the microorganisms... The glutinous rice paste is used to coat recycled fine aggregate, and the mixture is stirred for 10 seconds. Then, mixing water, water-reducing agent (PCA®-Ⅰ series polycarboxylate high-performance water-reducing agent) and nutrients (a mixture of urea and calcium salts in a mass ratio of 1:1, with calcium salts being calcium chloride or calcium acetate) are added. The mixture is stirred for 110 seconds at an online speed of 1.2 m / s, and then poured into molds. The mixture is then cured for 14 days under standard conditions at a temperature of 20℃ and a relative humidity of ≥95% to obtain self-healing concrete.

[0025] Example 3: This embodiment describes a method for preparing self-healing concrete based on recycled aggregate encapsulated in glutinous rice paste and supported by microorganisms, comprising the following steps: Step S1: The construction waste is crushed by a jaw crusher and then further crushed by a cone crusher. It is then classified using a vibrating screen to obtain recycled coarse aggregate (5-10mm particle size range) and recycled fine aggregate (0.15-2.36mm particle size range). Both types of aggregate are placed separately in a drum washing machine and rinsed with high-pressure water for 15 minutes. Afterward, they are transferred to a soaking tank and soaked in room temperature water for 48 hours, changing the water every 12 hours. The aggregates are then drained and treated with 0.3mol / L... The aggregate was soaked in acetic acid solution for 60 min, then rinsed with water until the pH of the filtrate was 8. It was then placed in a forced-air drying oven and dried at 60℃ for 18 h. After being removed, it was allowed to cool naturally to room temperature and then placed in a muffle furnace. The temperature was increased to 400℃ at a rate of 5℃ / min and calcined at a constant temperature for 2 h. After that, it was allowed to cool naturally to room temperature with the furnace. Fine powder with a particle size <0.15 mm was removed by sieving to obtain pretreated recycled aggregate (pretreated recycled coarse aggregate and pretreated recycled fine aggregate). Step S2: Soak 100g of glutinous rice in 800mL of deionized water at room temperature for 4 hours. Then transfer it to a stainless steel cooking pot, bring it to a boil over high heat, and immediately reduce to a simmer. Stir constantly with a glass rod while cooking for 60 minutes. After turning off the heat, let it cool naturally to below 40℃. Filter it through a 40-mesh standard sieve. Add glutinous rice paste modifier (0.2mol / L calcium salt, 0.5mol / L urea, 2g / L nutrient broth, and 0.5% sodium alginate in sequence). Stir for 5 minutes after each addition. Then place it in a vacuum drying oven and degauge it at -0.06MPa for 12 minutes to obtain modified glutinous rice paste. Step S3: Inoculate the urease-producing microorganism (Bacillus pasteurellii) into the liquid culture medium and culture it under shaking conditions at 37°C and a stirring rate of 200 r / min until OD. 600 A value of 1.2 indicates the presence of microbial inoculum. Step S4: The pretreated recycled aggregates were subjected to immobilization treatment and placed in a vacuum impregnation tank. The vacuum was drawn to -0.09MPa and maintained for 30 minutes. Microbial liquid was injected until the liquid surface completely submerged the aggregates by more than 5 cm. After restoring normal pressure, the aggregates were soaked for 2 hours. The liquid was drained and the surface of the aggregates was drained. The aggregates were then immersed in glutinous rice slurry and soaked at normal pressure for 30 minutes. The aggregates were then removed and drained. Afterward, they were placed in a constant temperature and humidity incubator and dried for 36 hours at a temperature of 25℃ and a relative humidity of 60%. This yielded recycled coarse aggregates and recycled fine aggregates encapsulated in glutinous rice slurry with immobilized microorganisms.

[0026] Step S5: Weigh out 420 parts of cement, 90 parts of mineral admixture, 850 parts of natural coarse aggregate, 500 parts of recycled coarse aggregate coated with glutinous rice paste containing microorganisms, 730 parts of natural fine aggregate, 240 parts of recycled fine aggregate coated with glutinous rice paste containing microorganisms, 195 parts of mixing water, 5.1 parts of water-reducing agent, and 2.5 parts of nutrients according to weight, and set aside. Step S6: Add cement (ordinary Portland cement of grade PO 42.5 or higher), mineral admixtures (mineral admixtures are mineral powder), natural fine aggregate (natural fine aggregate is medium sand with a fineness modulus of 3.0), and natural coarse aggregate (natural coarse aggregate is 5-20mm continuously graded granite crushed stone) to a forced mixer and dry mix for 30 seconds at an online speed of 1.8 m / s. First, add glutinous rice paste containing immobilized microorganisms to coat the recycled coarse aggregate, and mix for 15 seconds at an online speed of 1.0 m / s. Then, add the immobilized microorganisms... The recycled fine aggregate is coated with glutinous rice paste and stirred for 10 seconds. Then, mixing water, water-reducing agent (PCA®-Ⅰ series polycarboxylate high-performance water-reducing agent) and nutrients (a mixture of urea and calcium salts in a mass ratio of 1:1, with calcium salts being calcium chloride or calcium acetate) are added. The mixture is stirred for 120 seconds at an online speed of 1.4 m / s. After that, it is poured into shape and cured for 14 days under standard conditions of 22℃ and relative humidity ≥95% to obtain self-healing concrete.

[0027] Comparative Example 1: This comparative example illustrates a method for preparing ordinary concrete, comprising the following steps: Step S1: Weigh out 385 parts of cement, 75 parts of mineral admixture, 1000 parts of natural coarse aggregate, 700 parts of natural fine aggregate, 185 parts of mixing water, and 4.45 parts of water-reducing agent according to the weight ratio, and set aside. Step S2: Add cement (ordinary Portland cement of grade PO 42.5 or higher), mineral admixture (fly ash), natural fine aggregate (medium sand with a fineness modulus of 2.6), and natural coarse aggregate (5-20mm continuously graded granite crushed stone) to a forced mixer and dry mix for 30 seconds at an online speed of 1.5 m / s. Then add mixing water and water-reducing agent (PCA®-Ⅰ series polycarboxylate high-performance water-reducing agent). Continue mixing for 110 seconds at an online speed of 1.2 m / s. Then pour the mixture into shape and cure it for 14 days at a temperature of 20℃ and a relative humidity of ≥95% to obtain ordinary concrete.

[0028] Comparative Example 2: This comparative example illustrates a method for preparing directly inoculated concrete, comprising the following steps: Step S1: Inoculate the urease-producing microorganism (Bacillus pasteurellii) into the liquid culture medium and culture it under shaking conditions at 33℃ and a stirring rate of 170 r / min until OD. 600 A value of 1.2 indicates the presence of microbial inoculum. Step S2: Weigh out 385 parts of cement, 75 parts of mineral admixture, 1000 parts of natural coarse aggregate, 700 parts of natural fine aggregate, 165 parts of mixing water, 4.45 parts of water-reducing agent, and 1.75 parts of nutrients according to the weight ratio, and set aside. Step S3: Add the nutrients (a mixture of urea and calcium salt in a mass ratio of 1:1, with calcium salt being calcium chloride or calcium acetate) to the mixing water and stir at 300 rpm for 2 minutes. Then add 4.45 parts of water-reducing agent (PCA®-Ⅰ series polycarboxylate high-performance water-reducing agent) and continue stirring for 3 minutes. Finally, add 20 parts of microbial inoculum and stir at 100 rpm for 30 seconds to obtain the mixture. Step S4: Add cement (ordinary Portland cement of grade PO 42.5 or above), mineral admixture (fly ash), natural fine aggregate (medium sand with a fineness modulus of 2.6), and natural coarse aggregate (5-20mm continuously graded granite crushed stone) to a forced mixer and dry mix for 30 seconds at an online speed of 1.5 m / s. Add the liquid mixture and continue mixing for 110 seconds at an online speed of 1.2 m / s. Then pour the mixture into shape and cure it for 14 days at a temperature of 20℃ and a relative humidity of ≥95% to obtain directly inoculated concrete.

[0029] Comparative Example 3: This comparative example describes a method for preparing concrete with recycled aggregate fixation but without rice paste coating, including the following steps: Step S1: The construction waste is crushed by a jaw crusher and then further crushed by a cone crusher. It is then classified using a vibrating screen to obtain recycled coarse aggregate (5-10mm particle size) and recycled fine aggregate (0.15-2.36mm particle size). Both types of aggregate are placed separately in a drum washing machine and rinsed with high-pressure water for 12 minutes. Afterward, they are transferred to a soaking tank and soaked in room temperature water for 36 hours, changing the water every 12 hours. The aggregates are then drained and rinsed with 0.3mol / L vinegar. The aggregate was soaked in acid solution for 45 minutes, then rinsed with water until the pH of the filtrate was 7.5. It was then placed in a forced-air drying oven and dried at 57°C for 15 hours. After being removed, it was allowed to cool naturally to room temperature and then placed in a muffle furnace. The temperature was increased to 350°C at a rate of 5°C / min and calcined at a constant temperature for 1.5 hours. After that, it was allowed to cool naturally to room temperature with the furnace. Fine powder with a particle size <0.15mm was removed by sieving to obtain pretreated recycled aggregate (pretreated recycled coarse aggregate and pretreated recycled fine aggregate). Step S2: Inoculate the urease-producing microorganism (Bacillus pasteurellii) into the liquid culture medium and culture it under shaking conditions at 33°C and a stirring rate of 170 r / min until OD. 600 A value of 1.2 indicates the presence of microbial inoculum. Step S3: The pretreated recycled aggregates are subjected to immobilization treatment and placed in a vacuum impregnation tank. The vacuum is drawn to -0.09 MPa and maintained for 25 min. Microbial inoculum is injected until the liquid surface completely submerges the aggregates by more than 5 cm. After restoring normal pressure, the aggregates are soaked for 1.5 h. The inoculum is drained and the surface of the aggregates is drained. Then, the aggregates are placed in a constant temperature and humidity incubator and dried for 30 h at a temperature of 25℃ and a relative humidity of 60% to obtain microbial-immobilized recycled aggregates (microbial-immobilized recycled aggregates include microbial-immobilized recycled coarse aggregates and microbial-immobilized recycled fine aggregates).

[0030] Step S4: Weigh out 385 parts of cement, 75 parts of mineral admixture, 650 parts of natural coarse aggregate, 350 parts of recycled coarse aggregate immobilized with microorganisms, 595 parts of natural fine aggregate, 155 parts of recycled fine aggregate immobilized with microorganisms, 185 parts of mixing water, 4.45 parts of water-reducing agent, and 1.75 parts of nutrients according to the weight ratio, and set aside. Step S5: Add cement (ordinary Portland cement of grade PO 42.5 or higher), mineral admixture (fly ash), natural fine aggregate (medium sand with a fineness modulus of 2.6), and natural coarse aggregate (5-20mm continuously graded granite crushed stone) to a forced mixer and dry mix for 30 seconds at an online speed of 1.5 m / s. First, add the recycled coarse aggregate with immobilized microorganisms and mix for 15 seconds at an online speed of 0.8 m / s. Then, add the recycled fine aggregate with immobilized microorganisms. Add the aggregate and continue mixing for 10 seconds. Then add mixing water, water-reducing agent (the water-reducing agent is PCA®-Ⅰ series polycarboxylate high-performance water-reducing agent), and nutrients (the nutrients are a mixture of urea and calcium salts in a mass ratio of 1:1, and the calcium salts are calcium chloride or calcium acetate). Continue mixing for 110 seconds at an online speed of 1.2 m / s. Then pour the mixture into shape and cure it for 14 days under standard conditions of 20℃ and relative humidity ≥95% to obtain recycled aggregate-supported concrete without rice paste coating.

[0031] Performance testing: The self-healing concrete of Examples 1-3, the ordinary concrete of Comparative Example 1, the directly inoculated concrete of Comparative Example 2, and the recycled aggregate-supported concrete without glutinous rice paste coating of Comparative Example 3 were tested according to the following methods. 28-day compressive strength test: The test was conducted according to GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete". Standard cubic specimens of 150mm×150mm×150mm were used, and three parallel specimens were prepared for each group. After the specimens were cast, they were cured for 28 days in a standard environment of 20℃ and relative humidity ≥95%. The specimens were removed, the surface moisture was wiped off, and they were placed in the center of the bearing plate of the pressure testing machine to ensure geometric centering. The load was continuously and uniformly applied at a rate of 0.7MPa / s until the specimen failed. The ultimate failure load was recorded. The compressive strength = failure load / bearing area. The arithmetic mean of the test values ​​of the three specimens was taken, and the result was accurate to 0.1MPa.

[0032] 7-day and 28-day crack repair rate tests: 40mm×40mm×160mm prism specimens were used, with 3 parallel specimens prepared for each group. The specimens were placed on the three-point bending device of a universal testing machine and loaded at a rate of 0.05mm / min to create a pre-existing crack with a mid-span width of 0.5mm. Initial crack images were captured and recorded using a stereomicroscope. The cracked specimens were then immersed in 25℃ clean water for static curing. They were removed on the 7th and 28th days, the surface moisture was wiped dry, and high-resolution images of the cracks (magnified 50 times) were captured at the same location. The initial crack area and the remaining crack area after repair were identified and calculated using ImageJ software. Crack repair rate = (initial crack area - remaining crack area after repair) / initial crack area × 100%, and the average value of parallel samples was taken.

[0033] Strength recovery rate test after repair: According to GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete", a 40mm×40mm×160mm prism was used. During the precast crack stage, the ultimate flexural load at the time of cracking was recorded as the initial cracking load. After the crack was repaired by immersion in water for 28 days, the specimen was placed back into the three-point bending device and reloaded at the same loading rate until failure. The failure load after repair was recorded. Strength recovery rate = failure load after repair / initial cracking load × 100%. The average value of parallel samples was taken.

[0034] 180-day microbial survival rate test: The plate colony counting method (dilution coating method) was adopted. Finished fixed aggregates not incorporated into concrete were taken, ground into powder under sterile conditions, and washed with sterile physiological saline for 30 min. The eluent was serially diluted and coated onto nutrient agar plates containing urea. After incubation at 30℃ for 48 h, the colony count was counted and converted into the initial viable number per gram of aggregate. After 180 days of standard curing, the concrete specimens were crushed, and the internal recycled aggregates were aseptically screened. The same method was used for grinding, washing, dilution, coating, and incubation. The counts were converted into the viable number per gram of aggregate. Microbial survival rate = viable number of viable bacteria after curing / initial fixed aggregate viable number × 100%. The average value of parallel samples was taken.

[0035] The test results are shown in Table 1: Table 1: Test Results Summary Table

[0036] Referring to Table 1, based on the comparison between Examples 1-3 and Comparative Examples 1-3, it can be seen that self-healing concrete can autonomously seal cracks, restore mechanical strength, and has a high long-term survival rate of microorganisms. It also takes into account both mechanical strength and durability, and has outstanding comprehensive application advantages.

[0037] Based on the comparison between Example 1 and Comparative Example 1, it can be seen that ordinary concrete does not have the ability to actively self-heal, and its strength recovery is limited after cracking; by replacing part of the natural aggregate with recycled aggregate, while disposing of construction waste, cracks can be effectively sealed, structural strength can be restored, and the durability of concrete can be significantly improved.

[0038] Based on the comparison between Example 1 and Comparative Example 2, it can be seen that the microorganisms directly added lack protection and are largely inactivated under alkaline environment and stirring, resulting in weak self-repair effect and no long-term effectiveness; the dual solidification protection system can significantly improve the survival rate of microorganisms, significantly enhance the crack repair efficiency, and ensure long-term self-repair capability.

[0039] Based on the comparison between Example 1 and Comparative Example 3, it can be seen that relying solely on recycled aggregate to fix microbial protection is insufficient, resulting in low repair effect and low long-term survival rate of microorganisms. After adding glutinous rice paste coating, it can not only isolate microorganisms from alkaline erosion and slow-release nutrients, but also improve the aggregate interface properties, thereby achieving simultaneous improvement in repair effect and mechanical properties.

[0040] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0041] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in this application, they should all fall within the protection scope of the present invention.

Claims

1. A self-healing concrete based on recycled aggregate encapsulated in glutinous rice paste and immobilized with microorganisms, characterized in that, Includes the following components by weight: The mixture consists of 350-420 parts cement, 60-90 parts mineral admixtures, 450-850 parts natural coarse aggregate, 200-500 parts recycled coarse aggregate coated with glutinous rice paste containing microorganisms, 460-730 parts natural fine aggregate, 70-240 parts recycled fine aggregate coated with glutinous rice paste containing microorganisms, 175-195 parts mixing water, 3.8-5.1 parts water-reducing agent, and 1.0-2.5 parts nutrients. The recycled coarse aggregate and the recycled fine aggregate coated with glutinous rice paste containing microorganisms are prepared by the following steps: Step a1: The construction waste is crushed and finely crushed, and then graded by a vibrating screen to obtain recycled coarse aggregate and recycled fine aggregate. The two types of aggregate are placed in a drum washing machine and washed with high-pressure water. Then they are soaked in room temperature water, drained, soaked in acetic acid solution, rinsed, dried, cooled, calcined, cooled, and sieved to obtain pretreated recycled aggregate. Step a2: Soak glutinous rice in deionized water, then boil, cool, filter, add glutinous rice paste modifier, stir, and then deaerate to obtain modified glutinous rice paste; Step a3: Inoculate the urease-producing microorganisms into a liquid culture medium, shake and culture to obtain the microbial culture solution; Step a4: The pretreated recycled aggregates are subjected to immobilization treatment and placed in a vacuum impregnation tank. Vacuum is drawn, and microbial liquid is injected until the liquid surface completely submerges the aggregates. After restoring normal pressure, the aggregates are soaked, the liquid is drained, and the surface of the aggregates is drained. Then, the aggregates are soaked in glutinous rice slurry under normal pressure. The aggregates are then removed, drained, and then air-dried to obtain recycled coarse aggregates coated with glutinous rice slurry immobilized with microorganisms and recycled fine aggregates coated with glutinous rice slurry immobilized with microorganisms.

2. The self-healing concrete based on glutinous rice paste-encapsulated recycled aggregate and microorganisms as described in claim 1, characterized in that, The recycled coarse aggregate in step a1 has a particle size range of 5-10 mm; the recycled fine aggregate has a particle size range of 0.15-2.36 mm.

3. The self-healing concrete based on glutinous rice paste-encapsulated recycled aggregate and microorganisms as described in claim 1, characterized in that, The pretreated recycled aggregate in step a1 includes pretreated recycled coarse aggregate and pretreated recycled fine aggregate.

4. The self-healing concrete based on glutinous rice paste-encapsulated recycled aggregate and microorganisms as described in claim 1, characterized in that, The molar concentration of the acetic acid solution in step a1 is 0.3 mol / L.

5. The self-healing concrete based on glutinous rice paste-encapsulated recycled aggregate and microorganisms as described in claim 1, characterized in that, The mass ratio of glutinous rice to deionized water in step a2 is 1:

8.

6. The self-healing concrete based on glutinous rice paste-encapsulated recycled aggregate and microorganisms as described in claim 1, characterized in that, The glutinous rice paste modifier in step a2 includes 0.05-0.2 mol / L calcium salt, 0.1-0.5 mol / L urea, 0.5-2 g / L nutrient broth, and 0.1-0.5% sodium alginate.

7. The self-healing concrete based on glutinous rice paste-encapsulated recycled aggregate and microorganisms as described in claim 1, characterized in that, The urease-producing microorganism in step a3 is one of Bacillus pasteurellii, Bacillus licheniformis, or Bacillus coliformis.

8. The self-healing concrete based on glutinous rice paste-encapsulated recycled aggregate and microorganisms as described in claim 1, characterized in that, The method for preparing self-healing concrete based on recycled aggregate encapsulated in glutinous rice paste and immobilized with microorganisms includes the following steps: Step 1: Weigh out the following components by weight: 350-420 parts cement, 60-90 parts mineral admixture, 450-850 parts natural coarse aggregate, 200-500 parts recycled coarse aggregate coated with glutinous rice paste containing microorganisms, 460-730 parts natural fine aggregate, 70-240 parts recycled fine aggregate coated with glutinous rice paste containing microorganisms, 175-195 parts mixing water, 3.8-5.1 parts water-reducing agent, and 1.0-2.5 parts nutrients. Set aside. Step 2: Add cement, mineral admixtures, natural fine aggregate, and natural coarse aggregate to a forced mixer and dry mix. First, add glutinous rice paste containing microorganisms to coat the recycled coarse aggregate and mix. Then, add glutinous rice paste containing microorganisms to coat the recycled fine aggregate and continue mixing. After that, add mixing water, water-reducing agent, and nutrients and continue mixing. Then, pour the mixture into shape and cure it according to standard to obtain self-healing concrete.

9. The self-healing concrete based on glutinous rice paste-encapsulated recycled aggregate and microorganisms as described in claim 8, characterized in that, The cement is ordinary Portland cement of grade PO 42.5 or above; the mineral admixture is one or two of fly ash and mineral powder; the natural coarse aggregate is 5-20mm continuously graded granite crushed stone; the natural fine aggregate is medium sand with a fineness modulus of 2.3-3.0; the nutrient is a mixture of urea and calcium salt in a mass ratio of 1:1, and the calcium salt is calcium chloride or calcium acetate.

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