A method and device for repairing concrete cracks based on composite plant urease-induced calcium carbonate deposition.

Abstract

This patent application belongs to the field of concrete repair technology, specifically relating to a method for repairing concrete cracks based on calcium carbonate deposition induced by a composite plant urease, including the following steps: S1: extracting soybean urease and canavagoid urease; S2: preparing a composite urease solution and a cementitious liquid; S3: injecting the solution to repair the cracks. The use of composite urease improves reaction efficiency and shortens repair time. It also specifically relates to a concrete repair device, including an infusion tube, a suction tube, and a needle. One end of the infusion tube and the suction tube are respectively connected to the corresponding pump body pipe. Negative pressure is used to suction the residual solution, ensuring that the solution after subsequent injection maintains a low concentration of ammonium ions, thus ensuring reaction efficiency.

Description

Technical Field

[0001] This invention relates to the field of concrete repair technology, specifically to a method and device for repairing concrete cracks based on composite plant urease-induced calcium carbonate deposition. Background Technology

[0002] With the in-depth research on MMICP (microbial-induced calcium carbonate deposition) and EICP (enzyme-induced calcium carbonate deposition) technologies, their applications have expanded from traditional soil and rock repair to the field of concrete structure repair. To optimize mineralization effects, researchers have begun to introduce various admixtures as "synergists." Studies have shown that the synergistic use of additives such as skim milk powder, glutinous rice flour, brown sugar, and fiber can significantly improve reinforcement performance.

[0003] Existing patent (CN118163219A) discloses a method for repairing concrete cracks based on plant urease-induced calcium carbonate deposition (EICP), comprising the following steps: Step 1: preparing concrete test blocks and their cracks to obtain concrete test blocks with different cracks; Step 2: extracting urease and preparing a cementing solution; Step 3: adding quartz sand as a repair medium to the concrete test blocks with different cracks obtained in Step 1, mixing the urease extracted in Step 2 with the prepared cementing solution to form a solution, and using an injection method to extract the solution to perform EICP repair on the concrete test blocks with different cracks; In the above patent, the repair technology using soybean urease has the limitation of slow reaction speed, resulting in a long repair cycle. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention aims to provide a method for repairing concrete cracks based on calcium carbonate deposition induced by composite plant urease. By utilizing composite urease, the reaction efficiency is improved and the repair time is shortened.

[0005] The technical solution adopted in this invention is as follows: A method for repairing concrete cracks based on composite plant urease-induced calcium carbonate deposition includes the following steps: S1: Extract urease from soybeans and sword beans. Soybeans and sword beans are dried at 50℃±1℃ for 5 hours, pulverized, and passed through a 100-mesh sieve to obtain soybean flour. The soybean flour and distilled water are mixed in a 1:1 ratio by mass, stirred, and allowed to stand. The solution after standing is filtered through gauze to remove soybean residue, and the filtrate is obtained. After centrifuging the filtrate, the supernatant is collected as crude urease solution. S2: Prepare a composite urease solution and a cementing solution. Mix the crude urease solutions of sword bean and soybean extracted in step S1 at a volume ratio of 1:1 to obtain a composite urease solution. Mix urea: calcium acetate: chitosan in a mass ratio of 1:1:0.1 and stir. Finally, adjust the pH of the reaction solution to 8 to obtain a cementing solution. Mix the composite urease solution and the cementing solution at a volume ratio of 1:1 and react to obtain a repair solution. S3: Injection repair of cracks. Add quartz sand to the concrete cracks and inject the repair solution into the cracks multiple times. When the number of repairs reaches 20, 40 and 60 times, let it stand for 3 days to allow the calcium carbonate to harden fully.

[0006] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The compound urease combines the high calcium production characteristics of soybean urease with the high activity advantage of canavalia urease, resulting in a significant improvement in repair efficiency and a shorter reaction time compared to single urease. 2. The generated calcium carbonate is mainly in the stable calcite crystal form, with a bond strength to the crack wall >1.5MPa. After repair, the compressive strength of the concrete is improved, the splitting tensile strength is improved, the ultrasonic velocity is increased, the sound duration is shortened, and the impermeability is improved. 3. It has a good repair effect on cracks with a width of 0.75-1.25mm. Due to the space restriction effect, the calcium carbonate deposition is denser in narrow cracks (0.75mm), resulting in the best repair effect; wide cracks (1.25mm) can also be effectively filled by increasing the number of grouting injections. 4. Chitosan can effectively inhibit the growth of metastable aragonite or globular crystals, while guiding and stabilizing the formation and growth of the most thermodynamically stable calcite crystal.

[0007] In a preferred embodiment of the present invention, in step S1, the ratio of soybean urease to canavagase is 3:2.

[0008] In a preferred embodiment of the present invention, in step S2, the concentration of the composite urease solution is 100 g / L.

[0009] In a preferred embodiment of the present invention, in step S3, saturation is achieved by repairing a narrow gap with a width of 0.75mm 30-40 times, and saturation is achieved by repairing a wide gap with a width of 1.25mm 50-60 times.

[0010] In a preferred embodiment of the present invention, when the number of repairs reaches 20, 40, and 60 times, the device is left to stand for 3 days.

[0011] In a preferred embodiment of the present invention, in step S3, when injecting to repair the crack, the repair solution is first injected for 2 minutes, then left to stand for 90 minutes, and finally pulsed aspiration for 10 minutes, waiting for the next injection repair. During the pulsed aspiration process, after aspiration for 13-16 seconds, it is stopped for 4-6 seconds before the next aspiration is performed.

[0012] Beneficial effects: The micropores formed by the quartz sand in the cracks generate strong capillary forces, which lock in the waste liquid. Continuous suction can easily form an airlock before the fluid is completely pumped out. By adopting a pulse mode of 13-16 seconds of operation and 4-6 seconds of pause, the trapped liquid is allowed to re-converge towards the suction port under capillary action during the pause period, so that it can be effectively extracted in the next working period, thus improving the waste liquid replacement efficiency.

[0013] This invention also provides a concrete repair device that applies the above-described method for repairing concrete cracks based on the induction of calcium carbonate deposition by composite plant urease. The device includes an infusion tube, a suction tube, and a needle. One end of the infusion tube and the suction tube are respectively connected to the corresponding pump body pipe. The other end of the infusion tube and the suction tube are connected to the needle through a switching valve. A rubber layer covering the crack is provided on the outside of the needle. During injection repair, injection and aspiration are performed alternately. During injection, the switching valve connects the infusion tubing to the needle, and the corresponding pump provides positive pressure to the infusion tubing to deliver the repair solution. During aspiration, the switching valve connects the aspiration tubing to the needle, and the corresponding pump provides negative pressure to the aspiration tubing to draw out the remaining liquid from the crack.

[0014] Beneficial effects: Repairing concrete cracks is essentially a controlled biomineralization process catalyzed by urease. The hydrolysis of urea gradually leads to an increase in ammonium ions in the solution. High concentrations of ammonium ions cause the pH of the reaction solution to rise, thereby inhibiting urease activity and affecting the next injection repair. This device seals the crack to a certain extent through an elastic layer after the injection has been stationary for a period of time, and uses negative pressure to suction out the residual solution, ensuring that the solution after subsequent injections always maintains a low concentration of ammonium ions, thus ensuring reaction efficiency.

[0015] In a preferred embodiment of the present invention, the infusion tube and the suction tube are coaxially arranged, the inner diameter of the suction tube is larger than the inner diameter of the infusion tube, the inner wall of the suction tube is provided with a first limiting ring, the infusion tube is provided with a second limiting ring, the switching valve includes a sliding cylinder, the outer wall of the sliding cylinder is provided with a first sliding part, the inner wall of the sliding cylinder is provided with a second sliding part, the second sliding part and the second limiting ring are provided with corresponding through holes, and a compression spring is vertically arranged between the sliding cylinder and the infusion tube; Under positive pressure, the through hole between the second sliding part and the second limiting ring is connected, and the first sliding part blocks the suction tube; When there is negative pressure, the first sliding part disengages from the first limiting ring, and the through hole between the second sliding part and the second limiting ring is misaligned, thus blocking the infusion tube.

[0016] Beneficial effects: 1. The above structure facilitates automatic switching between positive and negative pressure channels, ensuring that only one of the injection and suction channels is open at any given time, and preventing excessive contamination of fresh repair fluid by waste liquid reflux. 2. This switching valve does not require additional electrical components for control, reducing equipment costs and providing timely response; 3. The coaxial infusion tubing and suction tubing provide effective protection for the infusion tubing, making its internal structure less prone to damage; 4. If a separate suction tube is installed, prolonged use under negative pressure may cause quartz sand particles or impurities to clog the needle. However, by using a coaxial design, the clogging particles will be flushed out during positive pressure delivery, thus preventing clogging. Attached Figure Description

[0017] Figure 1 This invention relates to a precast concrete test block crack diagram using the steel sheet insertion and extraction method based on a concrete crack repair method using composite plant urease-induced calcium carbonate deposition.

[0018] Figure 2 This is a graph showing the changes in urease activity at different concentrations under different conditions in the concrete crack repair method based on composite plant urease-induced calcium carbonate deposition, according to the present invention.

[0019] Figure 3 This is a graph showing the relationship between the urease incorporation ratio and the actual amount of calcium carbonate generated in the concrete crack repair method based on composite plant urease-induced calcium carbonate deposition according to the present invention.

[0020] Figure 4 This is a graph showing the variation of different reaction times in the concrete crack repair method based on composite plant urease-induced calcium carbonate deposition, as described in this invention.

[0021] Figure 5 These are diagrams of crack sealing treatment and injection repair of a test block based on the concrete crack repair method induced by composite plant urease-induced calcium carbonate deposition.

[0022] Figure 6 This is a diagram showing the distribution of calcium carbonate in different cracks in the concrete crack repair method based on composite plant urease-induced calcium carbonate deposition, as described in this invention.

[0023] Figure 7 The diagram shows the relationship between ultrasonic time and crack width, and the relationship between ultrasonic velocity and crack width, based on the concrete crack repair method induced by composite plant urease.

[0024] Figure 8 This invention includes a diagram showing the placement of compressive strength test specimens and a diagram showing the relationship between compressive strength and crack width.

[0025] Figure 9 This invention presents a diagram showing the arrangement of splitting tensile strength specimens and the relationship between splitting tensile strength and crack width in a concrete crack repair method based on composite plant urease-induced calcium carbonate deposition.

[0026] Figure 10 This is a schematic diagram of the concrete repair device of the present invention.

[0027] Figure 11 This is a partial cross-sectional view of the concrete repair device of the present invention under positive pressure.

[0028] Figure 12 This is a partial cross-sectional view of the concrete repair device of the present invention under negative pressure.

[0029] Figure 13 This is a flowchart illustrating the preparation of soybean urease solution and cementitious liquid in the concrete crack repair method based on composite plant urease-induced calcium carbonate deposition, according to the present invention.

[0030] Figure 14 The present invention relates to the relationship between the proportion of canavalialinase in concrete crack repair method based on composite plant urease-induced calcium carbonate deposition and the actual amount of calcium carbonate generated and the setting time.

[0031] The reference numerals in the attached drawings include: infusion tube 1, second limiting ring 11, suction tube 2, first limiting ring 21, needle 3, rubber layer 4, pressure plate 5, sliding cylinder 6, first sliding part 61, second sliding part 62, and compression spring 63. Detailed Implementation

[0032] Typical embodiments embodying the features and advantages of the present invention will be specifically described in the following description. It should be understood that the present invention can have various variations in different embodiments without departing from the scope of the present invention, and the descriptions and illustrations herein are for illustrative purposes only and not intended to limit the present invention.

[0033] In the description of this application, the terms "first", "second", etc. are used only for the convenience of describing this application and simplifying the description, and are not intended to indicate or imply that the structure referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0034] Example 1 See Figures 1 to 14As shown, this embodiment discloses a method for repairing concrete cracks based on composite plant urease-induced calcium carbonate deposition. The method involves pre-preparing concrete test blocks and cracks using ordinary Portland cement, medium sand as fine aggregate, and 5-20mm continuously graded crushed stone as coarse aggregate. The following proportions are used: 310 parts cement, 840 parts fine aggregate, 1080 parts coarse aggregate, 170 parts water, and 1 part polycarboxylate superplasticizer. The mixture is stirred in a forced mixer for 120 seconds. A 100mm×100mm×100mm triple mold is used, with steel plates of thicknesses of 0.75mm, 1.0mm, and 1.25mm inserted to a depth of 35mm. The mixture is vibrated on a vibrating table for 25 seconds, then smoothed. The steel plates are inserted and removed every 2 hours. The mold is removed after 24 hours, and standard curing is performed for 28 days. (See reference...) Figure 1 Concrete test blocks with crack widths of 0.75 mm, 1.0 mm, and 1.25 mm were obtained, with initial compressive strengths of 25-28 MPa. Includes the following steps: S1: Take 600g of fresh soybeans and 400g of sword beans, dry them in an oven at 50℃ for 5 hours until the moisture content is <5%. Grind them in a high-speed grinder and pass them through a 100-mesh standard sieve. Mix 100g of soybean powder with 100mL of distilled water, stir with a magnetic stirrer at 45℃ for 45 minutes at 300r / min, let it stand in a refrigerator at 4℃ for 4 hours, filter with double-layer gauze, dispense the filtrate into 50mL centrifuge tubes, place them symmetrically in a centrifuge, centrifuge at 4000r / min for 15 minutes, and take the supernatant, which is the crude urease solution with an enzyme activity of about 200-300 U / mL. Mix soybean urease and sword bean urease at a 1:1 volume ratio to obtain a compound urease solution, increasing the total enzyme activity to 350-450 U / mL.

[0035] S2: Weigh out urea and calcium acetate in a ratio of 1:1:0.1 by mass. Add distilled water to a final volume of 1L. Add 10g of chitosan and heat in a 60℃ water bath with stirring until completely dissolved. Cool to room temperature and adjust the pH to 8.0 with 0.1mol / L NaOH solution. Add 1L of composite urease solution (urease participation ratio 0.5) and mix thoroughly. Under this formula, the calcium carbonate yield can reach 85%-95% of the theoretical value. The crystals are mainly calcite type with a particle size of 10-50μm.

[0036] S3: Injection repair of cracks, specifically including the following: S31: Quartz sand pretreatment. Select 20-40 mesh quartz sand, rinse with clean water, and dry at 105℃ for 2 hours. The filling rate is controlled at 60% of the crack volume. Gently tap the side of the test block with a rubber mallet to compact the quartz sand.

[0037] S32: Grouting process. Before the first grouting, inject 5mL of repair solution to wet the crack. Then, extract 30mL of repair solution each time and inject it slowly at a rate of 5mL / min. Stop when you observe the grout overflowing from the micropores on the surface of the crack. Repeat 12 times a day.

[0038] S33: Process control: Before each grouting, use medical cotton swabs to absorb the accumulated liquid and unreacted liquid at the crack opening. After 20 groutings, let it stand for 3 days to observe the hardening of the sediment. Continue grouting up to 40 times, then let it stand for another 3 days. Finally, grout up to 60 times to complete the repair.

[0039] In step S1, refer to Figure 2 Under the same conditions, sword bean showed the highest urease activity, followed by mixed beans, and then soybeans. Urease activity increased with increasing soybean flour solution concentration, with peak concentrations all around 200 g / L, specifically 67.155 mM / min (sword bean), 51.171 mM / min (mixed beans), and 36.852 mM / min (soybean). The lowest urease concentration was 20 g / L, corresponding to 11.211 mM / min, 9.8568 mM / min, and 6.8709 mM / min for sword bean, mixed beans, and soybeans, respectively. Sword bean showed a more significant increase in urease activity, with the most rapid increases (64.5% to 68.2%) at soybean flour solution concentrations of 40 g / L–60 g / L and 80 g / L–100 g / L, respectively; while the slowest increase (only 4.91%) occurred at concentrations of 100 g / L–150 g / L. Soybeans exhibit a relatively milder urease activity compared to sword beans. The fastest growth rate (75.4% and 39% respectively) is observed at soybean flour concentrations of 20-40 g / L and 100-150 g / L, while the slowest growth rate (5.8%) occurs at concentrations of 80-100 g / L. Finally, the mixed urease shows the most moderate and uniform activity change, falling between that of sword beans and soybeans under the same conditions. Overall, at the same solution concentration, sword beans generally exhibit higher urease activity than soybeans and the mixed species, with the largest variation in activity. The growth rate is faster for sword beans, soybeans, and the mixed species at concentrations of 40-100 g / L, but slows down significantly above 100 g / L. Considering urease activity, economic efficiency, and the rate of increase, a urease concentration of 100 g / L was chosen.

[0040] In step S2, refer to Figure 3 For soybeans, mixed urease, and sword bean urease, the participation ratio of the two ureases was gradually increased. Considering both economic efficiency and urease activity, a participation ratio of 0.5 was selected. (See reference...) Figure 4Soybeans, mixed urease, and canavagase were reacted with the cementing solution at a ratio of 0.5. Compared with canavagase, soybean urease reacted more slowly and produced more calcium carbonate, while canavagase reacted more quickly and produced less calcium carbonate. However, the mixed urease produced similar amounts of calcium carbonate without significantly reducing the reaction rate. This may be because the different molecular compositions of the different urease sources lead to different bonding forms between the calcium carbonate and the quartz sand. The calcium carbonate bonds more tightly with the sand particles, thus ensuring the strength of the repaired area.

[0041] See Figure 14 According to the graph showing the relationship between the proportion of canavon urease in total urease and the actual amount of calcium carbonate produced and the setting time, it can be seen that as the proportion increases, the amount of calcium carbonate produced gradually decreases and the setting time gradually shortens. However, according to the graph, when the proportion is 0.4, there is still a relatively high amount of calcium carbonate produced and a relatively fast setting time.

[0042] After performing the repairs according to the above steps, the repair effect will be tested and evaluated. Because concrete is a heterogeneous mixture, it exhibits significant absorption and scattering of high-frequency ultrasonic pulses during ultrasonic testing. Therefore, lower frequencies are typically selected for testing. If the concrete material composition, construction process, internal condition, and testing distance are consistent, its acoustic parameters should be relatively similar. When defects such as pores and cracks exist within the concrete, the ultrasonic wave propagation path changes, resulting in reflection or diffraction, leading to prolonged acoustic duration and reduced amplitude and frequency. Therefore, ultrasonic testing is performed on concrete specimens before and after repair, and the changes in parameters are used to evaluate the repair effect of concrete cracks. Before testing, coupling agent should be applied to both ends of the specimen to ensure stable signal transmission. The measuring points are placed on opposite sides of the specimen, 1.5 cm from the top surface. Instrument parameters are generally set to a sampling period of 0.8 μs and a transmission voltage of 500 V.

[0043] When sound waves propagate through concrete, cracks cause diffraction along the propagation path. Wider cracks result in longer diffraction paths and longer acoustic durations. As the crack width increased from 0.75mm to 1.25mm, the acoustic duration of the unrepaired group continuously increased from 21.7μs to 22.4μs. After EICP repair, the acoustic duration decreased to varying degrees for different crack widths, with the largest decrease observed in the 0.75mm crack width and the smallest decrease in the 1.25mm crack width. Under the same crack width condition, the repaired acoustic duration was consistently shorter than the unrepaired acoustic duration. This is because EICP technology fills the concrete cracks, improving the continuity of ultrasonic wave propagation and thus shortening the acoustic duration. However, as the crack width increases, the filling difficulty of the repair material increases, leading to a slightly poorer acoustic duration repair effect for wider cracks.

[0044] EICP technology improves the density and uniformity of concrete by filling cracks, making the ultrasonic propagation path more continuous. Therefore, for the same crack width, the sound velocity in the repaired group is higher than that in the unrepaired group, and the sound velocity decreases as the crack width increases. In the unrepaired group, the concrete with a crack width of 0.75 mm has the fastest sound velocity, at 4.62 km / s; the sound velocity in a crack width of 1.25 mm is the slowest, at 4.51 km / s. After EICP repair, all groups with different crack widths showed varying degrees of improvement. The 0.75 mm crack width group showed the best improvement, increasing by 0.07 km / s; the 1.0 mm crack width group was second best, increasing by 0.05 km / s; and the 1.25 mm crack width group was slightly less effective, increasing by 0.04 km / s. The mineralization reaction of EICP technology fills the concrete cracks, improving the density of the concrete and thus increasing the sound velocity. As the crack width increases, the filling effect deteriorates, and the improvement effect on wide cracks is also slightly weaker. The filling effect is best for 0.75mm cracks, followed by 1.0mm, and worst for 1.25mm. In summary, EICP combined with chitosan technology has a relatively significant repair effect on concrete cracks, which is reflected by shortening the ultrasonic propagation time and increasing the ultrasonic propagation speed. However, the repair effect is affected by the crack width; the wider the crack, the worse the ultrasonic properties (sound time and sound velocity) of the repaired concrete, indicating that this technology is more effective in repairing narrow cracks.

[0045] like Figure 9 As shown, the arrangement of the compressive strength specimens and the relationship between compressive strength and crack width are illustrated. The specific method for placing the compressive strength specimens and determining the relationship between compressive strength and crack width is as follows: Compressive strength is the most fundamental mechanical property of concrete, and its test value directly reflects the strength improvement after EICP technology combined with chitosan repair. This study conducted concrete compressive strength tests to explore the influence of different urea sources on the repair effect of cracked concrete's mechanical properties and to analyze the correlation between crack size and repair effect. Compressive strength tests were performed on unrepaired and repaired specimens measuring 100mm × 100mm × 100mm, in accordance with the relevant provisions of the "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" (GB / T 50081-2019).

[0046] The repair effect of EICP technology on concrete cracks can be characterized by changes in compressive strength. The compressive strength of unrepaired specimens decreases with increasing crack width, from 25.73 MPa for a 0.75 mm crack to 22.85 MPa for a 1.25 mm crack, indicating that the integrity of the concrete specimen has a significant impact on compressive strength. The compressive strength of the repaired concrete specimens all increased, with the largest increase (0.89 MPa) observed in the 0.75 mm crack width specimen, followed by the 0.7 MPa increase in the 1.0 mm crack width specimen, and the smallest increase (0.4 MPa) in the 1.25 mm crack width specimen. The corresponding strength improvement rate decreased with increasing crack width, at 3.4% (0.75 mm), 2.8% (1.0 mm), and 1.8% (1.25 mm). This is attributed to the densest distribution of calcium carbonate within the 0.75 mm crack width, compared to a sparser distribution in the 1.25 mm crack width specimen. The denser the calcium carbonate distribution, the better it fills cracks and bonds to the crack walls in concrete, improving the stress transfer path between aggregates and making the specimen less prone to failure due to stress concentration at the cracks under pressure, thus increasing compressive strength. Conversely, in wide cracks, the calcium carbonate distribution is sparse, resulting in weaker filling and bonding effects, limited restoration of structural continuity at the crack, and the crack area easily becoming a stress concentration point under pressure, leading to premature specimen failure and thus limited improvement in compressive strength. Furthermore, the wider the concrete crack, the more severe the damage to the integrity of its internal structure, making it difficult for EICP technology alone to completely compensate for structural defects. In summary, the calcium carbonate generated by EICP technology mainly serves to fill cracks; its ability to improve compressive strength through precipitation is limited for addressing internal concrete cracks. The wider the crack, the less significant the improvement in compressive strength.

[0047] like Figure 10 As shown, the arrangement of splitting tensile strength specimens and the relationship between splitting tensile strength and crack width are illustrated. The specific method for placing the splitting tensile strength specimen and determining the relationship between splitting tensile strength and crack width in step 10 is as follows: Concrete is a brittle material with a tensile strength far lower than its compressive strength. Splitting tensile strength is a crucial indicator for assessing the crack resistance of concrete. According to the "Test Procedure for Hydraulic Concrete" SL / T352-2020, the splitting clamp is precisely installed at the center of the lower pressure plate of the testing machine. Then, spacers are accurately placed on pre-marked positioning lines on both sides of the specimen to ensure uniform load distribution along the diameter. Subsequently, unrepaired specimens after reaching the specified curing period and repaired specimens are placed centered in the clamp, ensuring the splitting surface is perpendicular to the top surface. Finally, a continuous load of 0.06 MPa / s is applied until the specimen splits and fails, and the maximum load is recorded.

[0048] To analyze the repair effect of EICP technology on the splitting tensile strength of concrete cracks, the splitting tensile strengths of unrepaired concrete specimens were 2.15 MPa (0.75 mm), 2.05 MPa (1.0 mm), and 1.98 MPa (1.25 mm), respectively. The splitting tensile strength gradually decreased with increasing crack width. After EICP repair, the splitting tensile strength increased in all specimens. The 0.75 mm specimen showed the largest average increase of 2.32%, the 1.0 mm crack width specimen showed an increase of 1.95%, and the 1.25 mm crack width specimen showed an increase of 1.01%. The narrower the crack, the more significant the increase in splitting tensile strength after repair. This phenomenon may be due to the fact that the concrete cracks repaired by EICP technology are filled with calcium carbonate, resulting in varying degrees of enhancement. Secondly, calcium carbonate fills narrow cracks more densely, resulting in better synergistic bonding with chitosan and a better improvement in the splitting tensile strength of concrete. In wide cracks, the distribution of calcium carbonate is sparser, and the bonding effect with the crack walls is weaker, thus the improvement in splitting tensile strength is slight. Finally, in the ultrasonic analysis, the narrower the crack, the higher the sound velocity and the shorter the sound duration after repair. This indicates that the concrete after repairing narrow cracks has better density and structural continuity, and can provide a certain degree of support. In contrast, the structural continuity after repairing wide cracks is poor, thus the strength improvement is limited.

[0049] After repairing cracks of different widths using EICP combined with chitosan technology, the distribution of calcium carbonate showed significant differences. The calcium carbonate precipitation effect was the best and the distribution was the densest in the 0.75mm narrow crack, followed by the 1.0mm crack, while the distribution was relatively sparse and there were blank areas in the 1.25mm wide crack.

[0050] In ultrasonic analysis, different crack widths resulted in a decrease in acoustic duration and an increase in acoustic velocity after repair. A crack width of 0.75 mm showed the best repair effect, while a crack width of 1.25 mm showed a poor improvement. This indicates that EICP combined with chitosan technology can effectively fill cracks, improve the density and structural continuity of concrete, and that the wider the crack, the smaller the decrease in acoustic duration and the weaker the increase in acoustic velocity after repair.

[0051] The compressive strength of unrepaired specimens decreased with increasing crack width. The specimen with a crack width of 0.75 mm exhibited the highest compressive strength (25.73 MPa), while the specimen with a crack width of 1.25 mm showed the lowest strength (22.85 MPa). After repair, the strength of all specimens increased. Influenced by the distribution of calcium carbonate within the concrete cracks, the 0.75 mm specimen showed the best improvement (3.4%), while the 1.25 mm specimen showed the worst improvement (1.8%).

[0052] The splitting tensile strength of concrete test blocks repaired by EICP technology was improved. The narrower the crack width, the higher the improvement rate. The crack width of the test block increased by 2.32% for 0.75mm crack width specimens, 1.95% for 1.0mm crack width specimens, and 1.01% for 1.25mm crack width specimens.

[0053] See Figures 10 to 12 This embodiment of a concrete repair device applies the above-described method for repairing concrete cracks based on composite plant urease-induced calcium carbonate deposition. It includes an infusion tube 1, a suction tube 2, and a needle 3. One end of the infusion tube 1 and the suction tube 2 are respectively connected to the corresponding pump body (using a peristaltic pump). The other end of both the infusion tube 1 and the suction tube 2 are connected to the needle 3 via a switching valve. A rubber layer 4 covering the crack is provided on the outside of the needle 3, and a pressure plate 5 is provided above the rubber layer 4 for limiting its position. During injection repair, injection and aspiration are performed alternately. During injection, the switching valve connects the infusion tube 1 to the needle 3, and the corresponding pump body provides positive pressure to the infusion tube 1 to input the repair solution. During aspiration, the switching valve connects the suction tube 2 to the needle 3, and the corresponding pump body provides negative pressure to the suction tube 2 to draw out the remaining liquid from the crack.

[0054] The infusion tube 1 and the suction tube 2 are coaxially arranged. The inner diameter of the suction tube 2 is larger than that of the infusion tube 1. The inner wall of the suction tube 2 is provided with a first limiting ring 21, and the infusion tube 1 is provided with a second limiting ring 11. The switching valve includes a sliding cylinder 6. The outer wall of the sliding cylinder 6 is provided with a first sliding part 61, and the inner wall of the sliding cylinder 6 is provided with a second sliding part 62. A corresponding through hole is provided between the second sliding part 62 and the second limiting ring 11. A compression spring 63 is vertically arranged between the sliding cylinder 6 and the infusion tube 1. Under positive pressure, the through hole between the second sliding part 62 and the second limiting ring 11 is connected, and the first sliding part 61 blocks the suction tube 2. Under negative pressure, the first sliding part 61 disengages from the first limiting ring 21, and the through hole between the second sliding part 62 and the second limiting ring 11 is misaligned, blocking the infusion tube 1. By providing the compression spring 63, the device can return to the middle position by elasticity when not in operation.

[0055] In this embodiment, the needle 3 is welded to the suction tube 2. In other embodiments, the inner wall of the needle 3 and the outer wall of the suction tube 2 can be provided with corresponding threads to achieve a detachable connection and facilitate disassembly and assembly.

[0056] The working steps of the concrete repair device in this embodiment are as follows: During each injection repair process, first inject for 2 minutes, then let it stand for 90 minutes, and finally perform pulse aspiration for 10 minutes, waiting for the next injection repair. During the pulse aspiration process, after aspirating for 13-16 seconds, stop for 4-6 seconds before performing the next aspiration.

[0057] By using the above settings, the residual solution is aspirated under negative pressure, ensuring that the solution after subsequent injection always maintains a low concentration of ammonium ions, thus guaranteeing reaction efficiency. If a separate suction tube 2 is used, prolonged use under negative pressure may cause quartz sand particles or impurities to clog the needle. However, this solution uses a coaxial design, which flushes out the clogging particles during positive pressure delivery, thus preventing blockage.

[0058] Comparative Example 1 Based on Example 1, the bonding solution formulation in Comparative Example 1 was as follows: urea:calcium acetate:skimmed milk powder in a ratio of 1:1:0.1 was weighed and mixed by weight. After mixing the above bonding solution with the mixed-selective urease, the same method was used to repair 0.75mm, 1.0mm, and 1.25mm sections, respectively. The experimental comparison data with Example 1 are shown in the table below: As shown in the table above, after repair using the gelling liquid formulation made from skim milk powder, the increase in ultrasonic velocity, compressive strength, and tensile strength was lower than that in Example 1 (using chitosan).

[0059] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A method for repairing concrete cracks based on composite plant urease-induced calcium carbonate deposition, characterized in that, Includes the following steps: S1: Extract urease from soybeans and sword beans. Soybeans and sword beans are dried at 50℃±1℃ for 5 hours, pulverized, and passed through a 100-mesh sieve to obtain soybean flour. The soybean flour and distilled water are mixed in a 1:1 ratio by mass, stirred, and allowed to stand. The solution after standing is filtered through gauze to remove soybean residue, and the filtrate is obtained. After centrifuging the filtrate, the supernatant is collected as crude urease solution. S2: Prepare a composite urease solution and a cementing solution. Mix the crude urease solutions of sword bean and soybean extracted in step S1 at a volume ratio of 1:1 to obtain a composite urease solution. Mix urea: calcium acetate: chitosan in a mass ratio of 1:1:0.1 and stir. Finally, adjust the pH of the reaction solution to 8 to obtain a cementing solution. Mix the composite urease solution and the cementing solution at a volume ratio of 1:1 and react to obtain a repair solution. S3: Injection repair of cracks involves adding quartz sand into the concrete cracks and injecting the repair solution into the cracks multiple times to allow the calcium carbonate to fully harden.

2. The method for repairing concrete cracks based on composite plant urease-induced calcium carbonate deposition according to claim 1, characterized in that: In step S1, the ratio of soybean urease to canavagase is 3:

2.

3. The method for repairing concrete cracks based on composite plant urease-induced calcium carbonate deposition according to claim 1, characterized in that: In step S2, the concentration of the composite urease solution is 100 g / L.

4. The method for repairing concrete cracks based on composite plant urease-induced calcium carbonate deposition according to claim 1, characterized in that: In step S3, a narrow gap with a width of 0.75mm can be saturated after 30-40 repairs, while a wide gap with a width of 1.25mm requires 50-60 repairs to reach saturation.

5. The method for repairing concrete cracks based on composite plant urease-induced calcium carbonate deposition according to claim 1, characterized in that, In step S3: When the number of repairs reaches 20, 40, and 60, let it stand for 3 days each time.

6. The method for repairing concrete cracks based on composite plant urease-induced calcium carbonate deposition according to claim 1, characterized in that, In step S3: When performing injection repair of cracks, first inject the repair solution for 2 minutes, then let it stand for 90 minutes, and finally perform pulse aspiration for 10 minutes, waiting for the next injection repair. During the pulse aspiration process, aspirate for 13-16 seconds, stop for 4-6 seconds, and then perform the next aspiration.

7. A concrete repair device, applied to the concrete crack repair method based on composite plant urease-induced calcium carbonate deposition according to any one of claims 1-6, characterized in that: It includes an infusion tube, a suction tube, and a needle. One end of the infusion tube and the suction tube are respectively connected to the corresponding pump body pipes. The other end of the infusion tube and the suction tube are connected to the needle through a switching valve. The needle is provided with a rubber layer covering the crack. During injection repair, injection and aspiration are performed alternately. During injection, the switching valve connects the infusion tubing to the needle, and the corresponding pump provides positive pressure to the infusion tubing to deliver the repair solution. During aspiration, the switching valve connects the aspiration tubing to the needle, and the corresponding pump provides negative pressure to the aspiration tubing to draw out the remaining liquid from the crack.

8. The concrete repair device according to claim 6, characterized in that: The infusion tube and the suction tube are coaxially arranged. The inner diameter of the suction tube is larger than that of the infusion tube. The inner wall of the suction tube is provided with a first limiting ring, and the infusion tube is provided with a second limiting ring. The switching valve includes a sliding cylinder. The outer wall of the sliding cylinder is provided with a first sliding part, and the inner wall of the sliding cylinder is provided with a second sliding part. A corresponding through hole is provided between the second sliding part and the second limiting ring. A compression spring is vertically arranged between the sliding cylinder and the infusion tube. Under positive pressure, the through hole between the second sliding part and the second limiting ring is connected, and the first sliding part blocks the suction tube; When there is negative pressure, the first sliding part disengages from the first limiting ring, and the through hole between the second sliding part and the second limiting ring is misaligned, thus blocking the infusion tube.

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