Cement material crack microbial remediation effect evaluation method

Abstract

The invention discloses a cement material crack microbial remediation effect evaluation method, and belongs to the field of cement material remediation effect performance evaluation, and an adopted remediation effect evaluation device comprises a mechanical evaluation system, an osmotic pressure measurement evaluation system and an internal structure analysis evaluation system; the mechanical evaluation system comprises axial pressurizing equipment and confining pressure equipment; the osmotic pressure measurement and evaluation system comprises a liquid injection pipe, a liquid discharge pipe and a sensor; the liquid source comprises a water source and a calcium source; the internal structure analysis and evaluation system comprises sound wave probes capable of rotating by 360 degrees, and the sound wave probes are arranged at the two ends of the sample. The method aims to avoid the situation that the microbial remediation effect is evaluated only from a single aspect, breaks through the single angle and limitation of a traditional method for identifying real breakthrough pressure, more clearly observes and evaluates the sample crack remediation effect, reveals the growth and development, distribution position and deposition form of microorganisms in cracks, and improves the detection accuracy. And meanwhile, cumbersome and complex operation is avoided, and whole-course real-time continuous monitoring is realized.

Description

Technical Field

[0001] This invention relates to the evaluation of the repair effect of cement materials, specifically to a method for evaluating the microbial repair effect of cement cracks. Background Technology

[0002] Cement is one of the most commonly used basic materials in modern building structures, widely used in the main structures of bridges, roads, tunnels, dams, and buildings. However, as a brittle composite material, cement inevitably develops cracks or microcracks during long-term service due to various factors. These cracks may originate from external loads, temperature changes, wet-dry cycles, freeze-thaw cycles, chemical corrosion, and other environmental influences, or they may be caused by the material's own shrinkage, creep, or construction quality issues. The presence of cracks not only affects the overall load-bearing capacity of the structure but also provides channels for harmful media such as water, chloride ions, and sulfates, thereby accelerating the corrosion of reinforcing steel and the deterioration of the cement matrix, thus seriously threatening the safety and durability of the engineering structure.

[0003] Traditional crack repair methods mainly include physical sealing, chemical grouting, and polymer repair. While these methods can restore the structural integrity to some extent in the short term, they typically suffer from numerous practical problems, such as complex construction processes, high repair costs, susceptibility to secondary damage, and difficulty in being effective within cracks. Furthermore, chemical repair materials may pollute the environment and have poor compatibility with the original cementitious matrix, leading to easy aging and detachment of the repair layer. Therefore, there is an urgent need for a new, environmentally friendly crack repair technology with self-healing capabilities to improve the durability of cementitious materials and reduce subsequent maintenance costs.

[0004] In recent years, microbially induced calcite precipitation (MICP) has become a hot topic in cement crack repair research. This technology utilizes specific microorganisms to induce the deposition of inorganic minerals (mainly calcium carbonate, CaCO3) during their own metabolism. These deposits gradually fill the cracks, achieving "self-healing" of the structure. This bioremediation process mimics the mechanism of rock mineralization in nature, possessing high efficiency, sustainability, and environmental friendliness, providing a new alternative to traditional repair methods.

[0005] The core of microbial repair of cement cracks lies in the biomineralization process of microorganisms. Microorganisms utilize their metabolic activities to produce calcium carbonate precipitates. These microbially induced calcium carbonates gradually precipitate and accumulate in the cracks, ultimately sealing them and enhancing the density and impermeability of the cement structure. Simultaneously, the microbially induced calcium carbonate precipitates have good compatibility with the cement matrix and do not produce significant interfacial weakening effects, thus achieving a "self-healing" effect.

[0006] Compared with traditional repair methods, microbial remediation technology has significant advantages: ① Green and environmentally friendly: No toxic byproducts are produced during the repair process, meeting the requirements of sustainable development. ② Self-healing characteristics: Microorganisms can reproduce on their own and continuously produce and deposit minerals in suitable environments, achieving long-term self-healing of structures. ③ High permeability and adaptability: Microorganisms are tiny and can penetrate deep into fine cracks to complete the repair work, which is difficult to achieve with traditional chemical grouting. ④ Low cost and simple maintenance: Microbial remediation technology does not require complicated construction procedures and can achieve in-situ repair of building structures by injecting microbial suspensions or by pre-mixing specific microorganisms into cement.

[0007] Despite significant achievements in laboratory research, microbial remediation technology still faces several technical bottlenecks in practical engineering applications. Firstly, the effectiveness of microbial repair of cracks is influenced by various factors, such as the type and quantity of microorganisms, the composition of the culture medium, environmental temperature and humidity, crack width, and the chemical environment of the cement matrix. Secondly, the evaluation system and indicators for the post-remediation effect are still incomplete, lacking unified quantitative standards and systematic testing and inspection equipment.

[0008] The value of "true breakthrough pressure" is a way to characterize the effect of microbial remediation. "True breakthrough pressure" refers to the actual ultimate bearing capacity of a cement sample with cracks after microbial remediation. When measuring the strength of microbial remediation, "false breakthrough pressure" often occurs. In triaxial compression tests of samples, the occurrence of "false breakthrough pressure" mainly stems from the non-ideal boundary and response instability of the sample-test system. This includes local stress concentration caused by friction and constraint effects at the sample ends, abrupt changes in the effective stress path due to lag in confining pressure loading and control, a sudden drop in local stiffness during the transformation of cracks from closure to propagation, and false instability of the instrument-sample system caused by insufficient stiffness of the loading system. These factors can cause transient peaks or abnormal abrupt changes in the stress-strain curve. However, at this time, the internal cracks of the sample have not yet been fully connected, and macroscopic shear failure has not yet been fully formed. Therefore, this peak value does not represent the true ultimate bearing capacity of the material. However, if the evaluation method for the remediation effect is inaccurate, this peak value may be mistakenly identified as "true breakthrough pressure".

[0009] Currently, the evaluation of the effectiveness of microbial repair of cement cracks is mainly carried out through the following aspects:

[0010] Mechanical property testing: including compressive strength, flexural strength, tensile strength, etc., to evaluate the repair effect by comparing the changes in mechanical properties of the sample before and after repair.

[0011] Impermeability test: The effectiveness of crack sealing is determined by measuring the change in the permeation rate of water or gas.

[0012] Microstructure analysis: Using techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS), the mineral deposition morphology and distribution characteristics inside the fractures were observed.

[0013] Bioactivity monitoring: By detecting changes in the number of microorganisms and the concentration of metabolites, the survival status and repair activity of microorganisms can be assessed.

[0014] However, these tests often rely on independent instruments, lacking real-time comparison and correlation between data, making it difficult to accurately and comprehensively reflect the dynamic evolution process during remediation. Furthermore, existing testing devices are mostly used for single-indicator detection, lacking integrated, multi-parameter simultaneous monitoring capabilities, resulting in lengthy experimental cycles, poor repeatability, and high data dispersion. Therefore, developing a testing device and method capable of comprehensively evaluating the effectiveness of microbial remediation is of significant importance and engineering application value.

[0015] CN120404380A discloses a device for testing the crack resistance of concrete for building and civil engineering. It includes an inner ring group of samples and an outer ring group of samples. The inner ring group of samples heats up quickly, while the outer ring group heats up slowly. Both the inner and outer ring groups of samples are rotatable, allowing for sequential testing of different groups of samples. Atomizing nozzles and a circulating fan regulate the humidity within a sealed chamber. Samples are heated via heating tubes and a transparent conductive film. Three cameras at different positions capture images of the upper, lower, and outer surfaces of the samples to detect cracking. A pressure sensor detects the pressure at which the sample cracks. A contact plate driven by a hydraulic press is positioned above the sample to apply downward pressure. This technology can accurately simulate different stress conditions and temperature / humidity environments, comprehensively observe sample cracking, and perform large-scale testing. However, it has the following drawbacks: ① It only reflects macroscopic results and lacks process information: If testing the crack resistance of microbial cement, this method can only obtain the final strength change after repair, and cannot reflect the activity of microorganisms, the mineralization rate, and the crack filling process during the repair process. ② Results are easily affected by external factors: This method requires strict control of humidity and temperature, which has a certain impact on the repair effect and activity of microorganisms. It is not suitable for microbial cement of certain species, the range of test objects is limited, and it is greatly affected by changes in the external environment, resulting in insufficient accuracy in effect evaluation. ③ Difficulty in quantifying microcrack repair: For micron-level cracks, this method is difficult to detect the degree of repair because the overall strength change may not be obvious.

[0016] CN120685450A discloses a method for testing the depth performance of concrete. The testing device's casing is divided into an upper chamber and a lower chamber by a partition. The upper chamber houses a combined pressurizing mechanism that abuts against the top of the specimen; the lower chamber houses a combined support mechanism that abuts against the bottom of the specimen. The specimen is temporarily fixed near the partition. When both the combined pressurizing mechanism and the combined support mechanism are abutting against the specimen, it constitutes a device for testing the specimen's compressive strength. When both the combined pressurizing mechanism and the combined support mechanism are detached from the specimen, it constitutes a device for testing the specimen's impermeability. The testing device also includes two cameras to observe the top and outer wall of the specimen, respectively. The testing device is equipped with inlet and outlet pipes to achieve impermeability testing. In addition, it includes necessary components such as a temperature and humidity sensor, a water pressure sensor, and a fan. This technology enables the observation and study of changes in the permeability of specimens after loading, providing data reference for practical engineering. Meanwhile, the device can perform both compressive strength and permeability tests, effectively improving its applicability and broadening its scope of application, thus facilitating in-depth research on concrete performance. However, the device has the following drawbacks: ① Test conditions are difficult to control: Permeability is affected by temperature, fluid pressure, crack morphology, etc., resulting in poor experimental reproducibility; ② It cannot reflect the microbial repair mechanism: This type of device can only provide permeability tests for normal concrete cement samples and cannot reflect the repair mechanism and process of microorganisms on concrete; ③ The equipment system is complex: The experimental device is complex and involves many steps, making it overly cumbersome.

[0017] CN115838302A discloses a method for repairing and protecting concrete surfaces based on microbial cement. This method utilizes the enzymatic action of microorganisms to attach strains to the concrete surface, growing and mineralizing to deposit a calcium carbonate layer for coating protection. Adding viscose protein to the bacterial solution increases the toughness of the repaired concrete surface layer, improving its crack resistance. After coating, the bond strength of the repaired concrete surface layer is consistently above 1.25 MPa, with most fractures occurring at the surface level, demonstrating significant protective effects. However, this technology has the following drawbacks: ① Complex and time-consuming operation: The experiment requires starting with microbial cultivation, which is lengthy and complex; ② Inability to reflect the microbial repair mechanism: The experiment only demonstrates microbial repair, but the specific repair mechanism and process are not shown; ③ Limited evaluation of repair effect: The test only assesses the bond strength after sample repair, which is too simplistic and prone to randomness, failing to accurately reflect the actual effectiveness of the microbial repair.

[0018] It is evident that existing research on the effectiveness of microbial repair of cement concrete cracks is lacking. Most studies focus on the testing and evaluation of traditional concrete performance, while some studies on microbial cement are too simplistic in their evaluation methods, have lengthy testing cycles, and do not provide a particularly intuitive and obvious demonstration of the microbial repair effect. Summary of the Invention

[0019] The purpose of this invention is to avoid evaluating the effect of microbial remediation from only one aspect, break through the single perspective and limitations of the traditional identification of "true breakthrough pressure" method, and more clearly observe and evaluate the effect of sample crack repair, reveal the growth, development, distribution and deposition morphology of microorganisms in cracks, while avoiding tedious and complicated operations and realizing continuous monitoring in real time throughout the process.

[0020] The present invention achieves the above objectives using the following approach:

[0021] A method for evaluating the effect of microbial repair on cracks in cement materials is proposed, which employs a repair effect evaluation device, including a mechanical evaluation system, an osmotic pressure measurement evaluation system, and an internal structure analysis evaluation system.

[0022] The mechanical evaluation system includes an axial compression device and a confining pressure device; the axial compression device applies axial pressure to the specimen and detects the pressure or stress and strain; the confining pressure device includes a pressure chamber, a confining pressure regulating device, and a confining pressure monitoring device. The confining pressure regulating device is connected to the pressure chamber to regulate the confining pressure, and the confining pressure monitoring device monitors the confining pressure inside the pressure chamber; the specimen is fixed inside the pressure chamber.

[0023] The osmotic pressure measurement and evaluation system includes an injection pipe, a drain pipe, and a sensor. The injection pipe is connected to the top of the sample and the liquid source at both ends, and the drain pipe is connected to the bottom of the sample and the pressure chamber at both ends. One-way valves are installed on the injection pipe and the drain pipe, and the sensor is installed on the drain pipe. The liquid source includes a water source and a calcium source.

[0024] The internal structure analysis and evaluation system includes an acoustic probe that can rotate 360° and is positioned at both ends of the sample.

[0025] The axial pressurization device includes a pressure head, a pressure head column, an axial pressure sensor, and an axial strain gauge. The lower end of the pressure head column is inserted into the pressure chamber and fixedly connected to the pressure head to control the pressure head to press down. The upper end of the pressure head column is connected to the axial pressure sensor and the axial strain gauge.

[0026] The confining pressure regulating device includes an air vent valve, a confining pressure water pipe, a confining pressure water valve, and an external water source; the air vent valve is located at the top of the pressure chamber, one end of the confining pressure water pipe is connected to the pressure chamber, the other end is connected to the external water source, and the confining pressure water valve is installed on the confining pressure water pipe.

[0027] The confining pressure monitoring device includes a confining pressure data pipeline, a confining pressure valve, and a confining pressure gauge; one end of the confining pressure data pipeline is connected to the pressure chamber, and the other end is connected to the confining pressure gauge, and the confining pressure valve is installed on the confining pressure data pipeline.

[0028] The sensors include a flow sensor and a calcium ion concentration sensor.

[0029] The internal structure analysis and evaluation system includes a viewing window, which is set on the pressure chamber; the acoustic probe is installed inside the gyroscope to achieve 360° rotation, and the acoustic probe includes multiple upper acoustic probes and multiple lower acoustic probes, which are circumferentially distributed at the top and bottom of the sample, respectively.

[0030] The device for evaluating the repair effect also includes an auxiliary system, which includes a transparent membrane, a ruler, and permeable stones. The transparent membrane isolates the sample from the pressure chamber, the ruler is attached to the sample surface, and the permeable stones are placed at both ends of the sample.

[0031] The repair effect evaluation device also includes an independent light source that can emit infrared light.

[0032] In addition to the aforementioned repair effect evaluation device, the method for evaluating the microbial repair effect of cement material cracks also includes the following steps:

[0033] In microbial repair tests of cement material cracks, acoustic waves, PQ diagrams, and actual breakthrough pressure are used as three perspectives to evaluate the repair effect. The repair effect is evaluated from one or more of these perspectives in combination.

[0034] (1) Evaluating the repair effect using sound waves

[0035] The maximum crack width obtained by the destructive acoustic waveforms from different angles is compared with the maximum crack width obtained by the repair acoustic waveforms from different angles. The smaller the percentage of the maximum crack width obtained by the repair acoustic waveforms relative to the maximum crack width obtained by the destructive acoustic waveforms, the better the crack repair effect.

[0036] (2) Use PQ diagrams to evaluate the repair effect

[0037] After the crack repair is completed, the water flow rate before pressurization is obtained by using the PQ diagram. The smaller the water flow rate at this time, the better the crack repair effect.

[0038] (3) Evaluate the repair effect using actual breakthrough pressure.

[0039] The greater the actual breakthrough pressure, the better the repair effect.

[0040] The method for obtaining the true breakthrough pressure using the PQ diagram obtained during pressure ladder loading and through two criteria includes the following steps:

[0041] In the pressure gradient loading, the permeability of each stage is calculated. ;

[0042] Two criteria are defined, and the pressure that simultaneously satisfies both criteria for the first time is determined as the true breakout pressure:

[0043] Jump criterion: And step level leader ≤10kPa;

[0044] Slope criterion: X is the median of the slopes at each level.

[0045] One or more of the following methods can be used to assist in determining the actual breakthrough pressure:

[0046] Method 1: Using the injection spectral area A ↑ Hysteresis loss coefficient (HIL) aids in determining the true breakout pressure:

[0047] Calculate the injection spectral area A of the breakthrough pressure determined by the two criteria. ↑ The hysteresis loss coefficient HIL is compared with a preset threshold. If the breakthrough pressure A determined by the two criteria is... ↑ Satisfaction reduced to A ↑ When the threshold value is 30%-70% of the preset threshold and the value of HIL is greater than the preset threshold value of HIL, the breakthrough pressure determined by the two criteria is further determined as the true breakthrough pressure.

[0048] Method 2: Using sound waves to assist in determining the actual breakthrough pressure:

[0049] The closer the ratio of the maximum crack width obtained from the breakthrough acoustic waveform to the maximum crack width obtained from the destruction acoustic waveform is to 1, the closer the pressure corresponding to the breakthrough acoustic waveform is to the actual breakthrough pressure.

[0050] Method 3: Using candidate breakout pressures to assist in determining the true breakout pressure:

[0051] When axial pressure is applied to the sample, the step pressure corresponding to the obvious decreasing stage in the stress-strain curve is also considered as the candidate breakthrough pressure.

[0052] During the pressure gradient loading process on the sample, when the P-Q curve shows a sudden increase in the flow rate at the bottom of the sample followed by a stabilization, and the Ca²⁺ concentration curve shows a significant drop followed by a gradual stabilization, this pressure level is taken as the candidate breakthrough pressure.

[0053] The true breakthrough pressure selected by the two criteria is compared with the two candidate breakthrough pressures. If the true breakthrough pressure is greater than the two candidate breakthrough pressures, the true breakthrough pressure determined by the two criteria is further determined as the true breakthrough pressure.

[0054] In the microbial repair test of cement material cracks, microchannels are etched onto the sample surface, and polyvinyl alcohol (PVA) is filled into these microchannels. The reason for etching the microchannels is that a transparent membrane is used to cover the cement sample. Without the microchannels, during subsequent water and calcium source injection, the contact between the cement sample and the transparent membrane would be poor. Furthermore, the pressure exerted by the liquid in the pressure chamber on the transparent membrane would reduce the likelihood of the injected liquid flowing through the sample, or even prevent it from flowing to the contact surface between the cement sample and the transparent membrane, instead flowing entirely through the internal cracks. The microchannels prevent this from happening, facilitating subsequent testing of crack data on the cement sample surface. Filling with PVA ensures the integrity of the sample surface during the pre-experiment installation stage. During subsequent water and calcium source injection, the PVA dissolves in water, exposing the pre-etched microchannels, thus ensuring that the water and calcium source can flow smoothly across the sample surface.

[0055] The methods for evaluating the repair effect include using a light source to calculate the crack width to evaluate the degree of crack development, and calculating the crack angle to evaluate the crack development path. The method for calculating the crack width is as follows:

[0056] Infrared rays are emitted from optical equipment to irradiate the crack, so that the light source, the surface of the transparent film, and one side of the crack width of the cement sample are on the same plane. A coordinate system is established, and the coordinates of the irradiation points A′, B′, and C′ on the surface of the viewing window are recorded. The coordinates of the irradiation points A, B, and C at the edge of the crack in the cement sample are calculated. The line connecting point B and point A is horizontal, and the line connecting point C and point A is perpendicular to one side of the crack.

[0057] ① Given that the coordinates of A′ are A′(X′) a , Y′ a , Z′ a ), calculate the coordinates of A:

[0058] ,

[0059] Y a =Y′ a -(L1+L2+L3),

[0060] Z a =Z′ a ,

[0061] ②The coordinates of B′ are known to be B′(X′). b ,Y′ b , Z′ b ), calculate the coordinates of B:

[0062] ,

[0063] Y b =Y′ b -(L1+L2+L3),

[0064] Z b =Z′ b ,

[0065] ③The coordinates of C′ are known to be C′(X′). c , Y′ c , Z′ c ), calculate the coordinates of C:

[0066] ,

[0067] Y c =Y′ c -(L1+L2+L3),

[0068] Z c =Z′ c ,

[0069] In the above formula, L1 is the thickness of the viewing window, L2 is the thickness of the liquid on one side of the pressure chamber, L3 is the thickness of the transparent rubber membrane, and the angle Θ is the angle between the light path and the right side of the viewing window interface, the liquid interface in the pressure chamber, and the transparent rubber membrane interface, respectively.

[0070] The formula for crack width is as follows:

[0071] |AB| = ,

[0072] |AC| =

[0073] |AB| represents the distance between points A and B, and |AC| represents the distance between points A and C;

[0074] The formula for calculating the crack angle is as follows:

[0075] sinα=(|AC|) / (|AB|), which gives the horizontal angle α of the cement crack.

[0076] The more confirmations there are of a genuine breakout pressure, the greater the likelihood that the pressure is a genuine breakout pressure and the less likely it is a false breakout pressure.

[0077] Terminology Explanation:

[0078] Macroscopic correlation: Cement samples are observed from a macroscopic perspective using an acoustic probe and a viewing window to evaluate the effect of microbial remediation.

[0079] Upstream and downstream of the sample: refers to the upper and lower ends of the sample.

[0080] "Step" refers to the pressure value of each stage during uniform pressure loading, while "step length" can be understood as the pressure gradient, which is the difference between the pressures of two stages.

[0081] In this invention, "crack" and "fissure" have the same meaning.

[0082] Compared with the prior art, the present invention has achieved at least the following beneficial effects:

[0083] 1. To avoid evaluating the effect of microbial remediation from only one aspect, this invention evaluates the effect of microbial remediation from three perspectives: mechanical properties, permeability, and microstructure analysis. This makes the evaluation perspective diverse, and the results from all aspects are combined for a comprehensive evaluation, resulting in a more accurate evaluation.

[0084] 2. In microbial concrete, microorganisms (such as Bacillus subtilis) are usually pre-embedded in the cement matrix in the form of dormant spores or symbionts, and are activated when cracks appear and moisture and oxygen infiltrate. Their growth and distribution are restricted by the crack environment, and they are mostly concentrated near the crack interface, forming local aggregations. The induced precipitation is mainly manifested as the formation of calcium carbonate crystals, specifically including: calcium carbonate produced by microorganisms during their own metabolism fills the previously generated cracks in the form of continuous deposition bands, dot-like or network-like crystals. In order to reveal the growth distribution and deposition morphology of microorganisms in cracks, this invention uses sound, light, viewing windows and microchannels to clearly observe the specific process and path of microorganisms inducing calcium carbonate production inside the sample, realize real-time visualization analysis of the repair process, and effectively overcome the problems of traditional methods that cannot continuously monitor, detect and evaluate the poor macroscopic correlation.

[0085] 3. In order to more clearly observe and evaluate the crack repair effect of the sample, the present invention uses optics and sound waves to achieve continuous scanning and observation of the sample interior from all angles, which can more accurately reflect the distribution and angle of the maximum crack in the sample.

[0086] 4. This invention breaks through the single-angle and limited nature of traditional methods for identifying "true breakthrough pressure". It utilizes a physicochemical multi-field coupling method to simultaneously measure permeability, calcium ion concentration, and stress-strain curves, and summarizes various data for comprehensive analysis, thereby more accurately identifying "true breakthrough pressure" and reducing the possibility of false breakthrough pressure.

[0087] 5. When evaluating the effects of different aspects, this invention does not require the conversion of the device structure for mechanical strength tests and osmotic pressure tests. The entire test is carried out in the same device, avoiding cumbersome and complicated operations, and allowing for real-time continuous monitoring throughout the process. Attached Figure Description

[0088] Figure 1 This is a cross-sectional view of the repair effect evaluation device;

[0089] Figure 2 This is a frontal view of an acoustic probe;

[0090] Figure 3 This is a three-dimensional detailed schematic diagram of the acoustic probe;

[0091] Figure 4 This is a schematic diagram of the acoustic probe being installed inside the pressure head housing via a gyroscope.

[0092] Figure 5 This is a detailed schematic diagram of the pressure head;

[0093] Figure 6 This is a schematic diagram illustrating the formula for calculating crack width;

[0094] Figure 7 This diagram shows the relationship between points A, B, and C and the cement crack, along with the crack angle.

[0095] Figure 8 This is a schematic diagram of a point light source assembly;

[0096] Figure 9 This is a 3D schematic diagram of a point light source assembly;

[0097] Figure 10 These are curves showing the changes in pressure and flow rate over time.

[0098] Figure 11 This is a schematic diagram of an acoustic probe illuminating a crack.

[0099] Reference numerals: 1. Axial pressurization device; 2. Axial strain gauge; 3. Exhaust valve; 4. Upper acoustic probe; 5. Gyroscope; 6. Transparent membrane; 7. Viewing window; 8. Lower acoustic probe; 9. Confining pressure data pipeline; 10. Confining pressure valve; 11. Confining pressure gauge; 12. Confining pressure water pipe; 13. Confining pressure water valve; 14. External water source; 15. Data receiver; 16. Detection sensor pipeline; 17. Base; 17-1. Protrusion; 18. Drain pipe; 19. Flow sensor; 20. Calcium ion concentration sensor; 2 1. Pressure chamber; 21-1. Pressure chamber side wall; 21-2. Pressure chamber top wall; 21-3. Pressure chamber base; 21-4. Groove; 22. Scale; 23. Cement block sample; 24. Permeable stone; 25. Indenter; 26. Indenter shell; 27. Indenter column; 28. Injection pipe; 29. ​​Equipment pipeline; 30. Axial pressure sensor; 31. Wall-mounted upright; 32. Wall-mounted crossbar; 33. Wall-mounted slide rail; 34. Circular turntable; 35. Light source bracket; 36. Light source support; 37. Point light source; 38. Frame shell; Detailed Implementation

[0100] The present invention will be further illustrated below with reference to embodiments, which are merely examples of the present invention.

[0101] Example 1

[0102] Replication effect evaluation device, such as Figure 1 As shown, it includes a mechanical evaluation system, an osmotic pressure measurement and evaluation system, an internal structure analysis and evaluation system, and an auxiliary system. Each system will be introduced in detail below.

[0103] ① Mechanical evaluation system: includes an axial pressurizing device 1 and a confining pressure device. The axial pressurizing device 1 includes a pressure head 25, a pressure head housing 26, a pressure head column 27, an axial pressure sensor 30, and an axial strain gauge 2. The pressure head housing 26 covers the pressure head 25, forming an installation space inside for mounting the upper acoustic probe 4. The upper end of the pressure head column 27 is connected to the axial pressure sensor 30 and the axial strain gauge 2, and the lower end of the pressure head column 27 is inserted into the pressure chamber 21 and fixedly connected to the pressure head 25. The pressure head column 27 is a hydraulic cylinder that can be controlled by a computer to extend and retract, thereby controlling the movement of the pressure head 25 and allowing the pressure head 25 to transmit the axial load to the sample. The pressure head column 27 has through holes for installing a liquid injection pipe 28 and an equipment pipeline 29. One end of the equipment pipeline 29 is connected to the equipment (probe, etc.), and the other end is connected to the corresponding control computer. The equipment pipeline 29 is waterproofed. The axial pressurization device 1 can apply axial pressure to the cement sample and monitor the strain value change of the cement sample in real time using the axial strain gauge 2. The confining pressure device includes an exhaust valve 3, a confining pressure data pipeline 9, a confining pressure valve 10, a confining pressure gauge 11, a confining pressure water pipe 12, a confining pressure water valve 13, an external water source 14, and a pressure chamber 21. The confining pressure water pipe 12 is embedded in the pressure chamber base 21-3. One end of the confining pressure water pipe 12 is connected to the pressure chamber 21, and the other end is connected to the external water source 14. The confining pressure water valve 13 is installed on the confining pressure water pipe 12 to control the input and output of water to the pressure chamber. The pressure chamber 21 is formed by the pressure chamber side wall 21-1, the pressure chamber top wall 21-2, and the pressure chamber base 21-3, and the interior is a cavity. The cavity can be filled with water. Water is injected and discharged through the confining pressure water pipe 12 to regulate the pressure in the cavity. Since the cement sample is placed in this cavity, water surrounds the cement sample, thus forming a confining pressure on the cement sample. The air vent valve 3 is located at the top of the pressure chamber 21 and can be manually controlled to open and close. Before the test, the air vent valve 3 is opened and water is injected through the confining pressure water pipe 12. After the pressure chamber 21 is just full, the air vent valve 3 and the confining pressure water valve 13 are closed, and then the test is carried out. Since the pressure head is pressed down very little during the test, the volume of water in the entire pressure chamber hardly changes. After the test, the water is drained through the confining pressure water pipe 12.The pressure head 25 and pressure chamber base 21-3 are both located inside the pressure chamber 21, and the area between the pressure head 25 and pressure chamber base 21-3 is the mounting point for the cement block sample 23. The pressure head 25, pressure chamber base 21-3, and cement block sample 23 are coaxially arranged in the middle of the pressure chamber. The confining pressure data line 9 is located inside the pressure chamber base 21-3, with one end connected to the pressure chamber 21 and the other end connected to the confining pressure gauge 11. The confining pressure valve 10 is installed on the confining pressure data line 9, which connects to the pressure chamber 21 and the confining pressure gauge 11. Opening the confining pressure valve 10 allows for real-time monitoring of changes in the applied confining pressure in the pressure chamber and adjustment of the confining pressure. The pressure chamber 21 is the location for installing the cement sample and also the location for the entire experiment. Before the experiment, a pressure threshold must be set, and then the pressure head 25 is used to pressurize the sample using an external computer. The axial pressure sensor 30 is connected to the pressure head column and can measure and transmit axial pressure values ​​to ensure accurate control and feedback of axial pressure values ​​during the experiment. The strain gauge of the axial strain gauge 2 is connected to the upper end of the pressure head column. The axial strain gauge 2 outputs stress-strain data to the computer to generate stress-strain curves.

[0104] The pressure head 25 contains six embedded gyroscopes, each with an upper acoustic probe 4 mounted on it. The gyroscopes and upper acoustic probes are circumferentially distributed within the pressure head. (Reference) Figure 3 The pressure head is shown in a 3D diagram, with the upper acoustic probe 4 represented by a cuboid; while the gyroscope itself is an angle sensor, therefore... Figure 3 The gyroscope is represented by a sphere. Installation details: The gyroscope is large (referring to its large outer shell and hollow interior). It is first mounted on the pressure head, and then the upper acoustic probe 4 is installed inside the gyroscope, allowing it to rotate 360° and its rotation angle to be known in real time. Similarly, the lower acoustic probe 8 is also mounted via the gyroscope, enabling it to rotate 360°. Figure 4 This is a schematic diagram of the upper acoustic probe being mounted on the pressure head via a gyroscope (ignoring the thickness of specific components). Figure 5 To illustrate the projection effect of the pressure head, gyroscope, acoustic probe, and other structures, only four combinations of acoustic probes and gyroscopes are shown in the diagram. The upper acoustic probe 4 is located in... Figure 5 The two horizontal lines within the circle represent the sensor (due to consideration of the size and installation order of the acoustic probe and gyroscope); while gyroscope 5 itself is an angle sensor. Figure 5 The two-dimensional planar diagram is represented by circles. The present invention has acoustic probes installed at the top and bottom of the device to prevent obstruction during infrared irradiation (in crack calculation); at the same time, the acoustic probes do not obstruct the field of view of the viewing window.

[0105] ② Osmotic pressure measurement and evaluation system: including data receiver 15, detection sensor pipeline 16, base 17, drain pipe 18, flow sensor 19, calcium ion concentration sensor 20, and injection pipe 28 (with a one-way selector valve installed on the pipeline); the detection sensor pipeline 16 is embedded in the pressure chamber base 21-3, and its upper end is connected to the drain pipe 18. The flow sensor 19 is installed at the connection point. The detection sensor pipeline of the data receiver 15 is connected to the flow sensor 19. The flow sensor 19 and the data receiver 15 are used to monitor the change in flow rate at the bottom of the cement sample in real time. The drain pipe 18 is installed in the groove 21-4, with one end connected to the bottom of the cement sample and the other end connected to the pressure chamber 21. A one-way drain valve is installed on the drain pipe. By opening or closing the one-way drain valve, the amount of solution inside the cement sample can be adjusted to ensure accurate control of the measured osmotic pressure. A calcium ion concentration sensor 20 is installed on the drain pipe 18. When the drain pipe 18 drains, the calcium ion concentration sensor 20 is used to detect the concentration of calcium ions in the drained liquid to determine the true breakthrough pressure from the perspective of the chemical field. The calcium ion concentration sensor 20 and the data receiver 15 transmit the data to the computer. One end of the injection pipe 28 is inserted into the top of the cement sample (penetrating the upper part). The system consists of two injection pipes: one end is a permeable stone 24, and the other end is connected to a water source or a calcium source. A one-way selection valve is installed on the injection pipe 28. During the experiment, the cement sample is injected through the injection pipe 28. The system contains two injection pipes, which are connected to the water source and the calcium source, respectively. Water or calcium source CaCl2 solution can be selected for injection. The calcium source solution is injected to activate microorganisms to repair cement cracks, and the water is injected for osmotic pressure experiments. The device is used to detect the upstream and downstream pressure and flow rate of the sample, and outputs the pressure and flow rate data to the computer. The computer plots the pressure difference spectrum and flow difference spectrum (PQ diagram) of the sample to determine the actual breakthrough pressure, thereby quantifying the effect of biomineralization in repairing cracks.

[0106] ③ Internal Structure Analysis and Evaluation System: This system includes an upper acoustic probe 4, a viewing window 7, and a lower acoustic probe 8. Six acoustic probes are arranged vertically within the pressure chamber. The upper acoustic probe 4 is embedded into the interior of the pressure head shell 26, and the lower acoustic probe 8 is embedded into the groove 21-4 at the top of the pressure chamber base 21-3. Each acoustic probe is equipped with a gyroscope 5, whose ring is attached to the acoustic probe, thus connecting the gyroscope and the acoustic probe as a whole. The gyroscope allows adjustment of the acoustic probe's illumination angle. The viewing window 7 has a small area, therefore a planar design is adopted (the influence of the planar design on the actual situation will not be considered in subsequent calculations). The volume calculation is based on the "crack width formula" and is made of transparent plexiglass, embedded in the side wall 21-1 of the pressure chamber; a transparent film 6 is placed over the cement block sample, and the changes in the sample during the experiment can be clearly observed through the viewing window 7; the flow path of the solution in the microchannel of the cement sample and the path and formation process of CaCO3 filling material generated by microbial repair of cracks can be observed through the viewing window 7, and the crack size can also be measured in conjunction with external optical equipment; the angle of the acoustic probe is adjusted by the gyroscope 5 to monitor the acoustic waves, and the width of the internal crack is calculated by the reflection of the acoustic waves, so as to understand the structure of the internal crack of the cement sample; the equipment pipeline 29 connects to and controls the acoustic probe.

[0107] ④ Auxiliary System: Includes a transparent membrane 6, a base 17, a scale 22, permeable stones 24, and a frame shell 38; the transparent membrane 6 is used to fix the cement sample, placed around the cement sample to isolate the pore water of the sample from the liquid in the pressure chamber, so that water in the sample can only drain from the bottom of the sample, ensuring that the drainage conditions of the experiment are controllable, and the transparent membrane 6 makes it easier to observe the structure; the two ends of the scale 22 are fixed to the pressure head 25 by thin wires, and the scale 22 is attached to the surface of the sample; the permeable stones 24 are installed on the top and bottom of the sample, and the permeable stones 24 allow... During the pressure test, the sample discharges pore water. Perforations are provided on the permeable stone to facilitate pipeline layout. A sealed waterproof layer (not shown in the figure) exists between the permeable stone at the top and bottom of the sample and the acoustic probe, ensuring waterproofing between the upper acoustic probe and the upper permeable stone, and between the lower acoustic probe and the lower permeable stone. Small holes are opened on the peripheral wall of the drain pipe 18 to facilitate water seepage. The drain pipe 18 directly penetrates the lower permeable stone to approach the bottom of the sample, ensuring that all liquid injected from the top of the sample can only penetrate and flow through the entire sample before being completely drained. The liquid is discharged from the drain pipe 18; the calcium ion concentration sensor 20 is installed on the drain pipe 18 to detect the calcium ion concentration; the skeleton shell 38 is made of transparent material, and its overall shape is cylindrical, closed at the top and around, and open at the bottom. The opening is connected to the base 17 to seal the bottom. The axial pressure sensor 30 is fixedly connected to the inner top wall of the skeleton shell 38 through a threaded interface. The pressure chamber base 21-3 is fixed to the protrusion 17-1 at the center of the upper surface of the base 17. The top of the pressure chamber base 21-3 has Groove 21-4 is used to install the lower acoustic probe 8, drain pipe 18, and permeable stone; the protrusion 17-1 is designed to ensure that the bottom area of ​​the sample is consistent with the contact area of ​​the entire evaluation device, without too large a difference, so as to avoid the sample directly contacting the larger platform and thus interfering with the stress transfer detection, resulting in an inaccurate stress-strain curve; holes are drilled in the pressure head 25, permeable stone 24, and pressure chamber top wall 21-2 to facilitate the connection between the injection pipe 28 and the cement sample and the arrangement of equipment pipelines 29.

[0108] Example 2

[0109] Specific experimental steps for evaluating the effect of microbial repair on cracks in cement materials:

[0110] 2.1 Data Acquisition Process:

[0111] 2.1.1 Preparation stage:

[0112] The concrete used to prepare cement samples contains microorganisms, hence the name microbial concrete. However, the microorganisms are in a dormant state, and calcium can activate them. Three cement triaxial compression specimens (for parallel experiments) are prepared using microbial concrete. Microchannels are engraved on the surface of the specimens and filled with polyvinyl alcohol to ensure the integrity of the cement specimens and to ensure the precision and accuracy of the experiment.

[0113] 2.1.2 Microbial remediation stage:

[0114] The experiment begins by placing the sample into pressure chamber 21 and applying pressure to the sample using axial pressure device 1. When cracks appear on the sample surface, the pressure loading is stopped (at this time, the point light source emits infrared light, and then the coordinates are acquired and the crack width and angle of the cement sample are calculated; the acoustic probe is used to acquire the destructive acoustic images at different angles at this time).

[0115] Pressure and strain data are obtained by using axial compression device 1 and axial strain gauge 2. The stress-strain curve of the sample is recorded by computer, and the candidate breakthrough pressure is obtained from the stress-strain curve.

[0116] A CaCl2 solution (concentration 1~2.5 mol / L) is injected through injection tube 28 to introduce a calcium source and activate microorganisms to repair cracks in the cement sample. The calcium ion concentration sensor 20 is activated, and the Ca ion concentration in the solution in drainage tube 18 is measured throughout the process. 2+ Concentration, when Ca 2+ After a period of continuous increase, the concentration tends to stabilize (becoming comparable to the concentration of the injected calcium source solution). At this point, the microbial repair of cracks in the cement sample has reached saturation and can no longer absorb Ca. 2+ And when you see white CaCO3 filling the crack in the cement sample through the viewing window 7, stop injecting CaCl2 solution (use an acoustic probe to obtain repair acoustic images at different angles at this time).

[0117] 2.1.3 Mechanical evaluation and osmotic pressure measurement evaluation stage:

[0118] Continue loading the cement sample in stepwise increments of 20 kPa (20 kPa, 40 kPa, 60 kPa, etc.), maintaining each load increment for 60–120 seconds. Simultaneously, inject water through injection pipe 28, switching to a different pipeline while keeping the water flow rate constant. The flow rate at the bottom of the sample is recorded in real-time by flow sensor 19. If the flow rate at the bottom of the sample suddenly increases and then stabilizes (the repaired cracks in the cement sample may be "broken" at this point), and the Ca in the solution… 2+ The concentration decreases steadily in the same order of magnitude (using a calcium ion concentration sensor 20 to monitor the overall solution Ca in real time). 2+ Concentration of liquid Ca obtained 2+ Concentration curve), stop water injection and pressurization, record the pressure level at this time as the candidate breakthrough pressure (and obtain the breakthrough acoustic waveform using an acoustic probe), then begin the pressure unloading process, continuing to unload according to the previous step-by-step pressure gradient. Record pressure and flow rate during the pressure loading and unloading process, such as... Figure 10 The lines representing the step-by-step loading are pressure ( The curve represents the change over time, and the other curve represents the flow rate ( The PQ curve is obtained by measuring the change over time. The true breakthrough pressure is determined based on the PQ curve of the sample. When the breakthrough pressure is determined to be between two steps, the range of breakthrough pressure can be further narrowed by setting more detailed steps between these two steps through parallel experiments, that is, by continuing to perform stepped loading between the previous step and the current step.

[0119] 2.2 Data Analysis Process

[0120] 2.2.1 Evaluation of crack development degree and crack development path

[0121] When the cement sample first developed cracks, the coordinates were obtained using infrared light, and the crack width was calculated using the crack width formula. The crack angle was then calculated using the crack width, and the length of the scale was verified using the elastoplastic mechanics formula. This method characterizes the development of external cracks in the cement sample with crack width and the crack initiation path with crack angle. Additionally, it uses sonic logging to characterize the development of internal cracks in the cement sample. The crack size and angle obtained in the experiment provide a better understanding of the failure path and extent of damage when the cement sample fractures. Characterizing these crack features is of great significance in the study of microbial cement mechanics and impermeability.

[0122] The actual crack width and angle were calculated in the experiment using formulas to evaluate the degree of crack development and the crack development path, respectively.

[0123] like Figure 8 , 9 As shown, a point light source is positioned next to the evaluation device for the microbial repair effect of cement material cracks, emitting infrared light to the cracks in the evaluation device. Coordinates are obtained through the infrared light, and the crack width and angle are calculated according to the following formula. A wall-mounted horizontal bar 32 is slidably mounted on a wall-mounted vertical bar 31. A wall-mounted slide rail 33 is installed on the wall-mounted horizontal bar 32, and the wall-mounted vertical bar 31 is mounted on a circular turntable 34. The circular turntable 34 is rotatably mounted on a light source support 36, and a light source bracket 35 is installed at the bottom of the light source support 36. A point light source 37 is installed in the middle of the wall-mounted horizontal bar 32.

[0124] Methods for evaluating the degree of crack development using light sources:

[0125] Cement Specimen Crack Width and Angle Calculation System: An infrared-emitting optical device is installed outside the evaluation apparatus. Infrared light is irradiated onto a transparent film, and the angle of the light source is continuously adjusted until it illuminates one side of the cement specimen's crack width (the light is directly facing the crack). The light source, the transparent film surface, and one side of the cement specimen's crack width are aligned on a single plane. A coordinate system is established, and the coordinates of the irradiated points on the viewing window surface are recorded (e.g., ...). Figure 6The coordinates of points A′, B′, and C′ are shown. Using the coordinates of the irradiation point A′ on the surface, the coordinates of the irradiation point A at the edge of the cement sample crack (A is the point where light enters from A′ and reaches the edge of the cement sample crack) are calculated. Similarly, the coordinates of points B and C on the same crack are calculated. The line connecting point B and point A is horizontal, and the line connecting point C and point A is perpendicular to one side of the crack. The width and angle of the crack in the cement sample can be calculated using the coordinates of points A, B, and C. The crack width can be used to understand the specific magnitude of the crack in the cement sample, i.e., how large a crack will be when the cement sample is damaged; it can also provide a more intuitive representation of the effectiveness of microbial repair of cement, such as how large a crack the microorganisms can repair and the degree of crack repair.

[0126] The method for measuring crack size (distance between any two points) is as follows:

[0127] 1. Derivation of the crack width formula:

[0128] ① Given that the coordinates of A′ are A′(X′) a , Y′ a , Z′ a ), calculate the coordinates of A:

[0129]

[0130] Y a =Y′ a -(L1+L2+L3)

[0131] Z a =Z′ a

[0132] ②The coordinates of B′ are known to be B′(X′). b ,Y′ b , Z′ b ), calculate the coordinates of B:

[0133]

[0134] Y b =Y′ b -(L1+L2+L3)

[0135] Z b =Z′ b

[0136] ③The coordinates of C′ are known to be C′(X′). c , Y′ c , Z′ c ), calculate the coordinates of C.

[0137]

[0138] Y c =Y′ c -(L1+L2+L3)

[0139] Z c =Z′ c

[0140] In the above formula, L1 is the thickness of the viewing window, L2 is the thickness of the liquid on one side of the pressure chamber, and L3 is the thickness of the transparent rubber membrane. The positions of angles Θ1, Θ2, and Θ3 are as follows: Figure 6 As shown, the angles corresponding to points A, B, and C are as shown in the formula above.

[0141] Where angle Θ is taken as the light path and interface (interface reference) when the light is shining. Figure 6 The included angle on the right (whether obtuse or acute, ensure consistency in the formula), such as Figure 6 As indicated by the angle markings, since the line connecting points A and B is horizontal, therefore Z... a =Z′ a =Z b =Z′ b Y a =Y′ a =Y b =Y′ b Points A and B are at Figure 6 Point A has already been drawn; point C has not been drawn, but its calculation method is the same as that of point A, only the positional relationship is different. Specifically: the line connecting AB is parallel to the horizontal direction, and the line connecting AC is perpendicular to one side of the crack, as shown below. Figure 7 As shown.

[0142] Therefore, the formula for crack width is as follows:

[0143] |AB| = |AC| =

[0144] |AB| represents the distance between points A and B, and |AC| represents the distance between points A and C;

[0145] 2. Verify the accuracy of the formula

[0146] The device is equipped with a scale 22. In the free state, the length L′ of the object in a water environment with pressure p is:

[0147] (Elasto-plastic mechanics formula)

[0148] Where L is the actual width of the crack, L′ is the width of the crack in the water environment obtained by direct reading from a scale, ν is Poisson's ratio of the object, E is the elastic modulus of the object, and ∆p is the gauge pressure, ∆p=p. After obtaining the width value L′ in the water environment through the scale, the actual width L is calculated using the formula.

[0149] The actual crack width L1 of the specimen is calculated using the elastoplastic mechanics formula, and the actual crack width L2 is calculated using the crack width formula. A comparison and analysis of L1 and L2 is performed to determine the error in crack width. If the difference between the two values ​​is within 5%, it indicates that the crack width formula has high accuracy. The error calculation formula is as follows:

[0150] ,

[0151] The experiment requires the calculated crack width error to be within 5%. If it exceeds 5%, the experiment must be repeated. When the crack width error is within 5%, the average value of L1 and L2 is calculated as the crack width, thus slightly correcting the actual crack width of the sample obtained from the crack width formula.

[0152] Methods for evaluating crack propagation paths using light sources:

[0153] Derivation of the crack angle formula:

[0154] Figure 7 The two parallel oblique lines in the diagram represent any cement crack. The line AB is parallel to the horizontal line, and the line AC is perpendicular to one side of the cement crack. Studying the crack angle helps to understand the path of crack formation in the cement sample.

[0155] Let the horizontal angle of the cement crack be α (e.g.) Figure 7 As shown), then sinα = This gives the horizontal angle of the cement crack.

[0156] 2.2.2 Evaluation of Repair Results

[0157] The three perspectives for evaluating the repair effect include sound waves, PQ diagram, and actual breakthrough pressure. The repair effect can be evaluated from one or more of these perspectives in combination. The more perspectives used, the more accurate the evaluation of the repair effect.

[0158] (1) Evaluating the repair effect using sound waves

[0159] The maximum crack width obtained by analyzing destructive acoustic images from different angles is compared with the maximum crack width obtained by analyzing repair acoustic images from different angles. The smaller the percentage of the maximum crack width obtained by the repair acoustic image relative to the maximum crack width obtained by the destructive acoustic image, the better the crack repair effect. The principle is as follows:

[0160] A schematic diagram of the crack illuminated by the acoustic probe is shown below. Figure 11 As shown. Figure 11 In the diagram, A and C represent the boundaries of the crack. When sound waves are shone on them, they are reflected, as shown by the blue and green sound waves in the image. At this point, the blue and green sound waves have a time difference. The difference in distance traveled is exactly twice the width of the crack. Therefore, the calculation method is as follows:

[0161]

[0162] D is the crack width, which is the additional distance the green sound wave travels during the time difference between its emission and transmission; V is the wave velocity. It's a time difference.

[0163] At the start of the experiment, turn on the upper acoustic probe 4 and the lower acoustic probe 8; record the internal structure acoustic waveform of the normal microbial cement sample (not yet pressurized, no cracks appear) at this time;

[0164] When the cement sample cracks during the first loading, the angle of the acoustic probe is adjusted using a gyroscope, and the destructive acoustic waveforms at different angles are recorded. The crack width is obtained using the above calculation method. Different widths can be obtained by different angles, and the maximum crack width is recorded.

[0165] When microbial repair of cement sample cracks saturates (Ca) 2+ When the concentration increases and stabilizes, adjust the irradiation angle of the acoustic probe and record the repair acoustic waveforms at different angles. Similarly, different widths can be obtained through different angles, and the maximum crack width is recorded.

[0166] The ratio of the two maximum crack widths is used to determine the effectiveness of crack repair.

[0167] (2) Use PQ diagrams to evaluate the repair effect

[0168] After the repair is completed, the water flow rate before pressurization is obtained by PQ diagram. The smaller the water flow rate at this time, the better the effect of microbial repair on the cracks in the cement sample.

[0169] (3) Evaluate the repair effect using actual breakthrough pressure.

[0170] Obtain the true breakout pressure; the higher the true breakout pressure, the better the repair effect.

[0171] Through the obtained Ca 2+ Concentration plots, PQ plots, and stress-strain curves were used to determine candidate breakthrough pressures for cement samples. The actual breakthrough pressures were initially screened using the PQ plots combined with two criteria, and then used to calculate the injection spectral area A. ↑(The smaller the result, the better) and the hysteresis loss coefficient HIL (the larger the result, the better), these two results are compared with ordinary cement (meeting their respective pre-set thresholds). If they meet their respective thresholds, it indicates that the true breakthrough pressure has been confirmed in multiple ways. Then, sonic logging is used to further confirm the true breakthrough pressure, further preventing false breakthrough pressure situations.

[0172] (3.1) Multiple confirmations of the real breakout pressure

[0173] When the P-Q curve shows a sudden increase in the flow rate at the bottom of the sample followed by a stabilization, and the Ca²⁺ concentration curve shows a significant drop followed by a gradual stabilization, the step loading pressure corresponding to this test stage can be used as a candidate breakthrough pressure.

[0174] When a cement sample develops cracks, its load-bearing capacity changes significantly. During the loading process, this is reflected in a clear decreasing phase in the stress-strain curve. Therefore, when a clear decreasing phase appears in the stress-strain curve, the corresponding step pressure can also be used as a candidate breakthrough pressure.

[0175] Using the P-Q plot, the breakthrough pressure is initially obtained through two criteria; this breakthrough pressure is a true breakthrough pressure that has not yet been verified. Then, the injection spectral area A is calculated using this breakthrough pressure. ↑ The hysteresis loss coefficient HIL was used to verify that the breakthrough pressure was the true breakthrough pressure.

[0176] Candidate breakthrough pressure is compared with the actual breakthrough pressure: If the breakthrough pressure selected by the two criteria is injected into the spectral area A... ↑ After verifying that the hysteresis loss coefficient (HIL) is indeed the true breakthrough pressure, this true breakthrough pressure is compared with the aforementioned candidate breakthrough pressures. If the true breakthrough pressure is greater than the aforementioned candidate breakthrough pressures, it indicates that the true breakthrough pressure has been mutually verified from multiple monitoring indicators and analytical perspectives, and its judgment result has high reliability and accuracy, ruling out the possibility that it is a false breakthrough pressure.

[0177] A method for initially determining breakout pressure using the P-Q chart and two criteria:

[0178] In stepwise pressure loading, the steady-state average value of each pressure gradient over the last 20 seconds is obtained. , .

[0179] Calculate the penetration rate for each level: = L is the flow length (the distance between the upstream and downstream sections, i.e., the sample height), and A is the cross-sectional area of ​​the cement sample. It is fluid viscosity. It's the traffic at each level. It is the pressure difference of each step of the applied pressure. It refers to the penetration rate at each level.

[0180] Two criteria are defined, and the pressure that is simultaneously satisfied by both criteria for the first time is initially identified as the breakout pressure:

[0181] Jump criterion: And step level leader ≤10kPa.

[0182] Slope criterion:

[0183] If the two criteria cannot be met simultaneously, the experiment continues, and the loading continues to calculate the permeability until both criteria are met simultaneously. "Slope at each stage" refers to the permeability obtained for each pressure applied during the pressure loading process. A graph is plotted showing the pressure applied at each stage and its corresponding permeability; the slope is the slope of this graph. In the criteria, i represents the i-th stage of pressure loading.

[0184] Calculate the injection spectral area A ↑ The method of using the hysteresis loss coefficient (HIL) to further verify the true breakthrough pressure:

[0185] Auxiliary discrimination data: Injection spectral area A ↑ The hysteresis loss coefficient HIL for the load-unload path; the calculation formulas for both are as follows:

[0186] A ↑ = HIL=

[0187] ↑ and ↓ represent the water injection and unloading processes, respectively.

[0188] The injection spectral area A is calculated using the breakthrough pressure determined by the two criteria. ↑ The hysteresis loss coefficient HIL is compared with a pre-set threshold, and the injection spectral area A is... ↑ If the threshold is less than 1, the hysteresis loss coefficient HIL is greater than 1, and A ↑ The smaller the value and the larger the HLI value, the better the microbial remediation effect, and the higher the probability that the breakthrough pressure determined by the two criteria is the true breakthrough pressure.

[0189] First, two criteria are used to preliminarily determine the breakthrough pressure. Then, the injection spectrum area and hysteresis loss coefficient are used to help determine whether the breakthrough pressure is a real breakthrough pressure or a false breakthrough pressure.

[0190] Before the cement sample was repaired, the crack was continuous. ↑ The value is large; after repair, the crack is plugged. ↑ The value decreased significantly, therefore A ↑ The smaller the value, the better the microbial remediation effect.↑ It is an integral index of the overall conductivity of the fracture, and is particularly sensitive to the repair of microcracks. HIL reflects the nonlinear enhancement of the mechanical-seepage flow in the fracture after repair. Before repair, the fracture is stable and continuous, and the water flow rates during loading and unloading are almost identical, so HIL≈0. After repair, the CaCO3 generated in the fracture undergoes re-interlocking and closure during pressure loading, and the channels do not fully recover during pressure unloading, resulting in an increase in HIL. Therefore, a larger HIL value indicates a better microbial remediation effect. The upward injection spectral area A is calculated. ↑ The hysteresis loss coefficient (HIL) can be used to verify the breakthrough pressure determined by the two criteria. The preset threshold is A, which is the value of the unrepaired crack and sterile ordinary concrete blank control group. ↑ (Approximately 800), HIL values ​​(0.25~0.55), this preset threshold and the breakthrough pressure calculated based on the two criteria, "injection spectral area A" ↑ A direct comparison is made between "hysteresis loss coefficient HIL" and "breakthrough pressure". ↑ Satisfaction reduced to A ↑ When the value of HIL is 30%–70% of the preset threshold and is greater than the preset threshold of HIL, the “breakthrough pressure” is further determined to be the real breakthrough pressure.

[0191] The true breakthrough pressure P is calculated using the method described above. b and the injection spectral area A corresponding to this pressure gradient. ↑ The hysteresis loss factor HIL is:

[0192] P b =120kPa Α ↑ =393 HIL=1.85.

[0193] (3.2) Method for assisting in the determination of actual breakthrough pressure using sound waves:

[0194] When the cement sample truly breaks through (at which point the flow rate at the bottom of the sample suddenly increases, then tends to stabilize, and the Ca in the solution...), 2+ When the concentration steadily decreases, record the breakthrough acoustic waveform at this point. "Steady decrease" refers to the Ca concentration decreasing. 2+ The concentration decreases at the same decreasing gradient; first decreases, then Ca... 2+ The concentration was reduced at the same decreasing gradient.

[0195] The maximum crack width is compared with the maximum crack width of the breakthrough sonic waveform and the destruction sonic waveform as evidence to help determine the true breakthrough pressure. The closer the maximum crack width obtained from the breakthrough sonic waveform is to the maximum crack width obtained from the destruction sonic waveform (the ratio of the maximum crack width is close to 1), the closer the pressure corresponding to the breakthrough sonic waveform is to the true breakthrough pressure.

[0196] Example 3

[0197] The experiment was conducted using ordinary cement concrete samples (control example), and the specific experimental steps are as follows:

[0198] ①Preparation stage:

[0199] Cement triaxial compression specimens (three specimens, for parallel experiments) were prepared using ordinary concrete (without artificial addition of microorganisms). Microchannels were etched on the surface of the specimens and polyvinyl alcohol was used for embedding in the specimens in the same manner as in Example 2.

[0200] ②Repair Phase:

[0201] The experiment begins by placing the sample in pressure chamber 21 and applying pressure to the sample using axial pressurization device 1 (the stress-strain curve of the sample is recorded during this process). When cracks appear on the sample surface, loading is stopped (the crack width and angle are calculated), CaCl2 solution is injected, and calcium ion concentration sensor 20 is activated to measure the Ca ion concentration in the solution in real time throughout the entire process. 2+ Concentration, when Ca 2+ Stop injection when the concentration continues to increase steadily (similar to the concentration in the microbial cement experiment).

[0202] ③ Mechanical evaluation and osmotic pressure measurement evaluation stage:

[0203] A stepped loading process was applied to the ordinary cement sample in increments of 20 kPa, with each load level maintained for 60–120 s. Simultaneously, water was injected through the injection pipe 28, switching to a different pipeline while maintaining a constant water flow rate. The flow rate of water at the bottom of the sample was recorded in real time using a flow sensor 19. The load was increased to the pressure level used in the microbial cement experiment (if the ordinary cement sample could not withstand this pressure level before being destroyed, the load was increased to the maximum pressure that the ordinary cement sample could withstand). A PQ diagram was obtained, and the overall solution Ca concentration was monitored in real time using a calcium ion concentration sensor 20. 2+ Concentration, when Ca in the solution 2+ When the concentration is close to the breakthrough point in the microbial cement experiment, stop water injection, record the pressure level at this time, and then start the unloading process, continuing to unload according to the previous step pressure gradient (parallel experiments can be performed to continue step loading between the previous level and this level to determine the maximum pressure value that the ordinary cement sample can withstand, and record it).

[0204] ④ Internal structure analysis stage:

[0205] At the start of the experiment, the acoustic probe was turned on; the acoustic waveform of the internal structure of the normal ordinary cement sample was recorded; when the first loading caused cracks to appear in the ordinary cement sample, the angle of the acoustic probe was adjusted, and the acoustic waveforms of the damage at different angles were recorded. The width of the crack was calculated, and different widths could be obtained by different angles. The maximum crack width was recorded; when the ordinary cement sample Ca2+ When the concentration is similar to the breakthrough point in the microbial cement experiment, adjust the angle of the acoustic probe and record the repair acoustic waveforms at different angles. Calculate the crack width; different angles yield different widths, and record the maximum crack width. When the ordinary cement sample achieves a "true breakthrough" (i.e., reaches the same stage as the microbial cement experiment), record the breakthrough acoustic waveform at this point. When the cement sample first develops a crack, calculate the crack width and angle using a formula, obtain the crack width value, and combine it with the scale analysis value to take the average of the two (if the difference is large, repeat the experiment). Combine this with the acoustic waveform to understand the degree of crack development in the cement sample.

[0206] For other steps not mentioned in the experiment, please refer to Example 2.

[0207] ⑤ Data processing and results analysis:

[0208] Mechanical breakthrough pressure evaluation; through the obtained Ca 2+ Concentration plots, PQ plots, and stress-strain curves were compared with data obtained from microbial cement samples to eliminate interference from irrelevant variables.

[0209] Internal structure analysis and evaluation: The maximum crack width obtained from destructive sonic logging at different angles and the maximum crack width obtained from repair sonic logging were compared with data obtained from microbial cement samples to eliminate the interference of irrelevant variables. The calculated crack width and angle, combined with the sonic logging data and compared with the data obtained from microbial cement samples, allows for a better understanding of the degree of internal crack development in ordinary cement samples. Comparison with microbial cement samples provides a clearer and more intuitive understanding of the microbial repair mechanism.

[0210] Osmotic pressure evaluation: By comparing the actual breakthrough pressure of the microbial cement sample with the maximum pressure that ordinary cement can withstand, the effect of microbial remediation can be understood more intuitively.

Claims

1. A method for evaluating the effect of microbial repair on cracks in cement materials, characterized in that, The repair effect evaluation device includes a mechanical evaluation system, an osmotic pressure measurement evaluation system, and an internal structure analysis evaluation system; The mechanical evaluation system includes an axial compression device and a confining pressure device; the axial compression device applies axial pressure to the specimen and detects the pressure or stress and strain; the confining pressure device includes a pressure chamber, a confining pressure regulating device, and a confining pressure monitoring device. The confining pressure regulating device is connected to the pressure chamber to regulate the confining pressure, and the confining pressure monitoring device monitors the confining pressure inside the pressure chamber; the specimen is fixed inside the pressure chamber. The osmotic pressure measurement and evaluation system includes an injection pipe, a drain pipe, and a sensor. The injection pipe is connected to the top of the sample and the liquid source at both ends, and the drain pipe is connected to the bottom of the sample and the pressure chamber at both ends. One-way valves are installed on the injection pipe and the drain pipe, and the sensor is installed on the drain pipe. The liquid source includes a water source and a calcium source. The internal structure analysis and evaluation system includes an acoustic probe that can rotate 360° and is positioned at both ends of the sample.

2. The method for evaluating the effect of microbial repair of cracks in cement materials according to claim 1, characterized in that, The axial pressurization device includes a pressure head, a pressure head column, an axial pressure sensor, and an axial strain gauge. The lower end of the pressure head column is inserted into the pressure chamber and fixedly connected to the pressure head to control the pressure head to press down. The upper end of the pressure head column is connected to the axial pressure sensor and the axial strain gauge. The confining pressure regulating device includes an air vent valve, a confining pressure water pipe, a confining pressure water valve, and an external water source; the air vent valve is located at the top of the pressure chamber, one end of the confining pressure water pipe is connected to the pressure chamber, the other end is connected to the external water source, and the confining pressure water valve is installed on the confining pressure water pipe. The confining pressure monitoring device includes a confining pressure data pipeline, a confining pressure valve, and a confining pressure gauge; one end of the confining pressure data pipeline is connected to the pressure chamber, and the other end is connected to the confining pressure gauge, and the confining pressure valve is installed on the confining pressure data pipeline.

3. The method for evaluating the effect of microbial repair of cracks in cement materials according to claim 1, characterized in that, The sensors include a flow sensor and a calcium ion concentration sensor.

4. The method for evaluating the effect of microbial repair of cracks in cement materials according to claim 1, characterized in that, The internal structure analysis and evaluation system includes a viewing window, which is set on the pressure chamber; the acoustic probe is installed inside the gyroscope to achieve 360° rotation, and the acoustic probe includes multiple upper acoustic probes and multiple lower acoustic probes, which are circumferentially distributed at the top and bottom of the sample, respectively.

5. The method for evaluating the effect of microbial repair of cracks in cement materials according to claim 4, characterized in that, The repair effect evaluation device also includes an auxiliary system, which includes a transparent membrane, a ruler, and permeable stones. The transparent membrane isolates the sample from the pressure chamber, the ruler is attached to the sample surface, and the permeable stones are placed at both ends of the sample.

6. The method for evaluating the effect of microbial repair of cracks in cement materials according to claim 5, characterized in that, The repair effect evaluation device also includes an independent light source that can emit infrared light.

7. The method for evaluating the effect of microbial repair of cracks in cement materials according to any one of claims 1-6, characterized in that, Includes the following steps: In experiments on microbial repair of cracks in cement materials, acoustic waves, PQ maps, and actual breakthrough pressure are used as three perspectives to evaluate the repair effect. The repair effect is evaluated from one or more of these perspectives in combination. (1) Evaluating the repair effect using sound waves The maximum crack width obtained by the destructive acoustic waveforms from different angles is compared with the maximum crack width obtained by the repair acoustic waveforms from different angles. The smaller the percentage of the maximum crack width obtained by the repair acoustic waveforms relative to the maximum crack width obtained by the destructive acoustic waveforms, the better the crack repair effect. (2) Use PQ diagrams to evaluate the repair effect After the crack repair is completed, the water flow rate before pressurization is obtained by using the PQ diagram. The smaller the water flow rate at this time, the better the crack repair effect. (3) Evaluate the repair effect using actual breakthrough pressure. The greater the actual breakthrough pressure, the better the repair effect. The method for obtaining the true breakthrough pressure using the PQ diagram obtained during pressure ladder loading and through two criteria includes the following steps: In the pressure gradient loading, the permeability of each stage is calculated. ; Two criteria are defined, and the pressure that simultaneously satisfies both criteria for the first time is determined as the true breakout pressure: Jump criterion: And step level leader ≤10kPa; Slope criterion: X is the median of the slopes at each level.

8. The method for evaluating the effect of microbial repair of cracks in cement materials according to claim 7, characterized in that, One or more of the following methods can be used to assist in determining the actual breakthrough pressure: Method 1: Using the injection spectral area A ↑ Hysteresis loss coefficient (HIL) aids in determining the true breakout pressure: Calculate the injection spectral area A of the breakthrough pressure determined by the two criteria. ↑ The hysteresis loss coefficient HIL is compared with a preset threshold. If the breakthrough pressure A determined by the two criteria is... ↑ Satisfaction reduced to A ↑ When the threshold value is 30%-70% of the preset threshold and the value of HIL is greater than the preset threshold value of HIL, the breakthrough pressure determined by the two criteria is further determined as the true breakthrough pressure. Method 2: Using sound waves to assist in determining the actual breakthrough pressure: The closer the ratio of the maximum crack width obtained from the breakthrough acoustic waveform to the maximum crack width obtained from the destruction acoustic waveform is to 1, the closer the pressure corresponding to the breakthrough acoustic waveform is to the actual breakthrough pressure. Method 3: Using candidate breakout pressures to assist in determining the true breakout pressure: When axial pressure is applied to the sample, the step pressure corresponding to the obvious decreasing stage in the stress-strain curve is also considered as the candidate breakthrough pressure. During the pressure gradient loading process on the sample, when the P-Q curve shows a sudden increase in the flow rate at the bottom of the sample followed by a stabilization, and the Ca²⁺ concentration curve shows a significant drop followed by a gradual stabilization, this pressure level is taken as the candidate breakthrough pressure. The true breakthrough pressure selected by the two criteria is compared with the two candidate breakthrough pressures. If the true breakthrough pressure is greater than the two candidate breakthrough pressures, the true breakthrough pressure determined by the two criteria is further determined as the true breakthrough pressure.

9. The method for evaluating the effect of microbial repair of cracks in cement materials according to claim 7, characterized in that, Microchannels were etched onto the surface of the sample used in the experiment on microbial repair of cracks in cement materials, and polyvinyl alcohol was filled into the microchannels.

10. The method for evaluating the effect of microbial repair of cracks in cement materials according to claim 7, characterized in that, This includes using a light source to calculate crack width to evaluate crack development, and calculating crack angle to evaluate crack development path. The method for calculating crack width is as follows: Infrared rays are emitted from optical equipment to irradiate the crack, so that the light source, the surface of the transparent film, and one side of the crack width of the cement sample are on the same plane. A coordinate system is established, and the coordinates of the irradiation points A′, B′, and C′ on the surface of the viewing window are recorded. The coordinates of the irradiation points A, B, and C at the edge of the crack in the cement sample are calculated. The line connecting point B and point A is horizontal, and the line connecting point C and point A is perpendicular to one side of the crack. ① Given that the coordinates of A′ are A′(X′) a , Y′ a , Z′ a ), calculate the coordinates of A: ， AND a =Y′ a -(L1+L2+L3) , WITH a =Z′ a , ②The coordinates of B′ are known to be B′(X′). b ,Y′ b , Z′ b ), calculate the coordinates of B: ， AND b =Y′ b -(L1+L2+L3), WITH b =Z′ b , ③The coordinates of C′ are known to be C′(X′). c , Y′ c , Z′ c ), calculate the coordinates of C: ， AND c =Y′ c -(L1+L2+L3) , WITH c =Z′ c , In the formula, L1 is the thickness of the viewing window, L2 is the thickness of the liquid on one side of the pressure chamber, L3 is the thickness of the transparent rubber membrane, and the angle Θ is the angle between the light path and the right side of the viewing window interface, the liquid interface in the pressure chamber, and the transparent rubber membrane interface, respectively. The formula for crack width is as follows: |AB| = , |AND| = , |AB| represents the distance between points A and B, and |AC| represents the distance between points A and C; The formula for calculating the crack angle is as follows: sinα=(|AC|) / (|AB|), which gives the horizontal angle α of the cement crack.

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