A fast-hardening high-strength cement anchoring agent and a strength testing method thereof

Abstract

The application relates to a tunnel construction material and detection technology, and particularly discloses a fast-hard high-strength cement anchoring agent and a strength testing method thereof. The fast-hard high-strength cement anchoring agent comprises 50-70% of sulphoaluminate cement, 10-20% of silica fume, 10-20% of desulfurization gypsum, 3-10% of an expansive agent, 0.05-0.3% of a composite retarder, 0.01-0.1% of an early strength agent and 0.02-0.1% of a defoaming agent. The strength testing method is a piezoelectric impedance detection method based on a lead zirconate titanate transducer, a sensor embedded in the anchoring agent is used to generate harmonic excitation and receive piezoelectric signals, and a neural network is used to analyze the piezoelectric signals to obtain the strength of the anchoring agent. The application provides a high-performance anchoring agent and a solution for accurately monitoring the strength of the anchoring agent by combining the innovative fast-hard high-strength cement anchoring agent and the advanced piezoelectric impedance testing technology. Non-destructive and real-time monitoring of the strength change process is realized, and the comprehensive requirements of speed, strength and environmental friendliness of modern engineering are met.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of tunnel construction materials and detection technology, and particularly relates to a fast-hard high-strength cement anchoring agent and a strength testing method thereof. BACKGROUND

[0002] At present, the railway and highway construction in China is gradually advancing to the central and western regions. However, with the continuous uplift of the Qinghai-Tibet Plateau and its extrusion effect on the eastern region, the geological structure, hydrogeological conditions and stratum complexity of the southwestern region of China have significantly increased, and the distribution of fault fracture zones is particularly dense. This complex geological environment, accompanied by the rapid development of infrastructure construction in the southwestern mountainous area, makes tunnel engineering more frequent and challenging when crossing high-activity fault regions. Fault fracture zones are usually composed of broken rocks and loose soil, and the overall structure is loose and has poor stability, which is prone to cause a series of engineering disasters such as large-scale deformation of tunnel support structure and collapse of the working face. In addition, these geological risks pose a serious challenge to the safety of engineering construction and the long-term stability of the later structure. In order to effectively deal with the problem of large deformation of soft rock tunnel, experts in the relevant field have proposed a variety of innovative support strategies based on different design concepts, mainly including rapid and effective strong support, layered and multiple support and other methods.

[0003] The anchoring agent is mainly used for reinforcing rock and soil in tunnel construction to ensure the structural stability of the tunnel. Its working principle is to inject anchoring agent (such as cement-based or chemical-based anchoring agent) in the borehole, and after the anchoring agent solidifies, it firmly combines the anchor rod or other structures with the surrounding rock or soil, thereby providing support and uplift resistance. Through chemical reaction or physical hardening process, the anchoring agent forms strong bonding force with the surrounding medium, achieving the effect of stabilization and reinforcement. Chemical anchoring agent takes epoxy resin or polyester resin as the main component, with amine compound added as the curing agent to promote resin curing. The advantages of chemical anchoring agent are resin-based anchoring agent, fast solidification speed, suitable for projects requiring rapid reinforcement; strong bonding force with rock mass, can withstand large pulling force, suitable for anchoring of soft surrounding rock or unstable rock mass. The disadvantages of chemical anchoring agent are that the price of epoxy resin is high, the cost is high; in the curing process, chemical gas may be produced, which has health and environmental risks; resin is easy to age and decompose in high temperature or corrosive environment, with poor durability. Cement-based anchoring agent is usually composed of Portland cement or high-alumina cement, aggregate such as quartz sand or fine sand, additives to adjust the setting time and enhance the fluidity (such as water reducing agent, early strength agent) and water, etc., which promotes hardening through hydration reaction. Its advantages include low cost, easy to obtain materials, good corrosion resistance and long-term durability, and relatively environmentally friendly, without harmful substances in the construction process. However, the setting time of cement-based anchoring agent is longer, which is difficult to meet the requirements of rapid construction, and the solidification effect may be affected in low temperature or humid environment, with poor fluidity, which may lead to uneven anchoring. Due to the advantages of chemical anchoring agent, it is widely used in tunnel construction in the southwest mountainous area of China, however, the geological, hydrogeological and stratigraphic conditions in this area are extremely complex, resin-based chemical anchoring agent has poor durability and is easy to age and decompose. Therefore, it is necessary to provide a fast-hardening high-strength cement anchoring agent to better adapt to the requirements of immediate powerful support in tunnel engineering in the southwest mountainous area of China and the requirements of operation in complex environments with high temperature, high ground stress and high degree of groundwater development.

[0004] Fast hardening high strength cement anchoring agent is a typical cement material, which is widely used in civil engineering and plays an irreplaceable role throughout the construction industry. The early hydration and setting of cement involve complex physicochemical reactions between clinker minerals and water, which are crucial to the performance of cement and cement mortar and other cementitious materials. This process directly determines the formation of the microstructure and affects the physical, mechanical and durability properties of hardened cement hydrates. For engineers, it is necessary to continuously monitor and evaluate the early hydration and setting process of cement, as it can provide key construction information to help determine the best time to remove formwork or temporary support and minimize unnecessary delays in the construction cycle. Real-time monitoring can also determine the hardening state of the cement. At present, there are many destructive and non-destructive testing methods (NDT), such as conventional Vicat needle penetration test, isothermal calorimetry and hydration condition monitoring, etc. However, the current detection methods have the disadvantages of being unable to realize continuous measurement, low precision, complex equipment and difficult operation. Therefore, it is crucial to develop a reliable, real-time, autonomous and intelligent non-destructive strength testing method for fast hardening high strength cement anchoring agent to accurately monitor and evaluate the early hydration and setting process of the material. SUMMARY

[0005] To solve the problems in the prior art, the present application provides a fast hardening high strength cement anchoring agent and a strength testing method thereof, aiming to solve the problems of insufficient durability, slow setting time, poor early strength of existing anchoring agents, and the difficulty of real-time and accurate monitoring of anchoring agent strength by existing methods.

[0006] To solve the problems of difficult control of setting time, poor anti-cracking performance, insufficient early strength and uneven expansion of existing anchoring agents during use, the present application successfully adjusts the setting time of the anchoring agent by changing the raw material composition and additive ratio of the anchoring agent, improves the anti-cracking ability, while maintaining a small expansion coefficient, and significantly improves the early strength and anchoring force, meeting the construction requirements of complex engineering environments. A fast hardening high strength cement anchoring agent according to the present application comprises the following raw materials in mass fraction: 50-70% sulphoaluminate cement, 10-20% silica fume, 10-20% desulfurized gypsum, 3-10% expansion agent, 0.05-0.3% composite retarder, 0.01-0.1% early strength agent, and 0.02-0.1% defoaming agent.

[0007] The main components of the sulphoaluminate cement are calcium sulphoaluminate and gypsum.

[0008] The core component of the present application is sulphoaluminate cement, which occupies a dominant position in the anchoring agent due to its rapid setting and high early strength. Its main components are calcium sulphoaluminate and gypsum, which can quickly generate high-strength hydration products in the hydration reaction, thereby accelerating the setting process of the anchoring agent and significantly shortening the construction cycle. At the same time, the use of sulphoaluminate cement also makes the anchoring agent exhibit high compressive strength in the early stage, ensuring the formation of effective anchoring effect in the engineering construction.

[0009] In order to further improve the performance of the anchoring agent, 10% to 20% of silica fume is also introduced. Silica fume is a kind of super-fine mineral admixture, which has small particle size and large specific surface area. It can act as a filling material in the anchoring agent, filling the tiny pores in the cement matrix, and enhancing the density and durability of the anchoring agent. At the same time, the incorporation of silica fume can also significantly improve the crack resistance of the anchoring agent, because silica fume can generate additional cementitious materials with cement hydration products, reduce the generation of shrinkage cracks, and enhance the overall crack resistance of the material

[0010] Desulfurized gypsum also plays an important role as a regulating material in the present application. Its dosage is controlled at 10% to 20%. By adding desulfurized gypsum, not only can the early strength of the anchoring agent be further improved, but also the expansion performance can be adjusted. During the hydration reaction, desulfurized gypsum can work together with sulphoaluminate cement to generate hydration products with expansion properties, thereby controlling the volume change of the anchoring agent and keeping it in a slightly swelling state during the setting process, avoiding the generation of excessive shrinkage cracks. In addition, the use of desulfurized gypsum can also effectively adjust the setting time of the anchoring agent, ensuring good operability during construction.

[0011] Expanding agent is also an important component of the present application, and its dosage is controlled between 3% and 10%. The main role of the expanding agent is to produce appropriate expansion during the hydration process of the anchoring agent, offsetting the stress caused by the shrinkage during the cement hardening process, and preventing the anchoring agent from cracking after setting. The preferred type of expanding agent is at least one of calcium oxide, sulphoaluminate and magnesium oxide. By reasonably matching the expanding agent, the anchoring agent can maintain high strength while having a slightly swelling property, thereby enhancing the anchoring effect.

[0012] In order to delay the setting time of the anchoring agent, the present application uses 0.05% to 0.3% of a composite retarder, preferably a combination of sucrose and citric acid, or a combination of borax and sodium citrate. These retarders can effectively prolong the setting time of the cement, ensuring sufficient operation time during construction. Especially in the case of sulphoaluminate cement with fast setting speed, the use of retarder is particularly important, which can balance the fast setting property of the material, making the anchoring agent have better construction adaptability.

[0013] In the selection of early strength agents, the present application particularly employs 0.01% to 0.1% of ethylene glycol. Ethylene glycol is a commonly used early strength agent that can significantly improve the early strength of the anchoring agent by accelerating the hydration reaction process of the cement. In the preparation of the anchoring agent, the use of lithium carbonate ensures that the anchoring agent reaches the required strength level in a short time, meeting the high requirements of engineering on early strength. At the same time, the addition amount of ethylene glycol is precisely controlled, which not only ensures the early strength effect, but also avoids the negative effects caused by excessive addition, such as material embrittlement, etc.

[0014] The defoaming agent plays a role in removing air and improving material density in the present application. The dosage of the defoaming agent is controlled between 0.02% and 0.1%. By adding an appropriate amount of defoaming agent, the bubble content in the anchoring agent can be effectively reduced, preventing the occurrence of pores inside the material, thereby improving the overall density and mechanical properties of the anchoring agent.

[0015] After the scientific proportioning of the components in the present application, the anchoring agent can achieve the comprehensive effects of adjusting the setting time, enhancing the anti-cracking performance, maintaining the micro-expansion, and improving the early strength. Among them, the sulphoaluminate cement is the basic cementitious material, silica fume and desulfurized gypsum play the roles of improving the density, adjusting the expansion, and improving the setting time, ethylene glycol as an early strength agent ensures the rapid strength growth of the anchoring agent, and the retarder and defoaming agent further optimize the construction performance of the material.

[0016] On the other hand, as an innovation in concrete strength monitoring technology, the present application combines long short-term memory network (LSTM) and piezoelectric impedance technology for the strength monitoring of fast high-strength cement anchoring agent. Based on the electromechanical coupling characteristics of piezoelectric ceramic sheet (PZT) and the time series data processing capability of LSTM neural network, the neural network model is trained by acquiring piezoelectric impedance data, thereby realizing real-time and non-destructive monitoring of the strength of the anchoring agent. In order to achieve the above purpose, the present application further provides the following technical scheme: a strength testing method for fast hardening high strength cement anchoring agent, comprising the following steps:

[0017] S1: collecting piezoelectric impedance signal data of the cement anchoring agent by a piezoelectric ceramic sensor;

[0018] S2: collecting actual strength data of the cement anchoring agent at different strength stages by the rebound method;

[0019] S3: preprocessing the piezoelectric impedance signal data set and the strength data set, and constructing a time series data set;

[0020] S4: using long short-term memory network (LSTM) for model training, learning the relationship between piezoelectric impedance signal and strength, and establishing a cement anchoring agent strength prediction model;

[0021] S5: verifying and optimizing the model;

[0022] S6: Apply the optimized model to the actual project to realize real-time nondestructive monitoring of the strength of the cement anchoring agent.

[0023] Preferably, in step S3, specifically comprises the following:

[0024] S301: Preprocess the piezoelectric impedance signal, including empirical mode decomposition (EMD) and Hilbert transform of the signal, and extract the instantaneous amplitude;

[0025] S302: Divide the processed signal data set into training set and validation set in proportion;

[0026] S303: Label the data set to ensure that each signal data corresponds to the corresponding cement anchoring agent strength.

[0027] Preferably, in step S5, specifically comprises the following:

[0028] S501: Input the validation set into the trained model for prediction;

[0029] S502: Compare the strength prediction result output by the model with the actual strength using the loss function;

[0030] S503: Adjust the weight parameters and network topology structure of the LSTM network based on the comparison result to optimize the model performance.

[0031] Preferably, in step S502, mean square error (MSE) is used as the loss function to measure the error between the network predicted strength value and the true strength value, and the formula is as follows:

[0032]

[0033] Wherein, y i is the actual strength, is the model predicted strength.

[0034] The present application has the advantages that: the present application provides a rapid setting type cement anchoring agent with excellent performance by reasonably proportioning sulphoaluminate cement, silica fume, desulfurization gypsum and various additives. The anchoring agent not only has the advantages of rapid setting and high early strength, but also has good anti-cracking performance, micro-expansion characteristics and operation adaptability, and can be applied in various complex engineering environments to meet the high standard requirements in actual construction. The present application can automatically extract the time sequence characteristics of the strength of the cement anchoring agent by combining piezoelectric impedance technology and LSTM neural network, realize rapid and accurate nondestructive detection, greatly improve the strength monitoring efficiency and precision, and once an abnormality is detected, timely warning and remedial measures can be taken. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1A flowchart of a strength test method of the fast-hardening high-strength cement anchoring agent of the present application is shown in the figure.

[0036] Figure 2 A schematic diagram of the piezoelectric impedance principle of the present application is shown in the figure.

[0037] Figure 3 A schematic diagram of the long short-term memory network (LSTM) of the present application is shown in the figure.

[0038] Figure 4 A schematic diagram of the piezoelectric ceramic sensor test device for collecting the piezoelectric impedance signal of the cement anchoring agent is shown in the figure. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0040] Embodiment 1

[0041] The present embodiment provides a fast-hardening high-strength cement anchoring agent, which comprises the following raw materials: 50wt% sulphoaluminate cement, 15wt% silica fume, 15wt% desulfurized gypsum, 7wt% expanding agent, 0.2wt% composite retarder (sucrose and citric acid are prepared in a mass ratio of 4:1), 0.1wt% early strength agent, and 0.05wt% defoaming agent.

[0042] The preparation method is as follows: the silica fume and the desulfurized gypsum are mixed with water in a mass ratio of 1:100, stirred at a speed of 1000rpm for 5 minutes, then the sulphoaluminate cement is added, stirred at a speed of 5000rpm for 5 minutes, and then anhydrous ethanol is added and stirred at a speed of 5000rpm for 4 minutes to obtain a modified mineral admixture dispersion liquid. The modified mineral admixture is dried at 110℃ and ground to a particle size of not more than 20μm. The mass ratio of the silica fume to water is 100:3, and the mass of the anhydrous ethanol is 20wt% of the water.

[0043] The composite retarder is sucrose and citric acid prepared in a mass ratio of 4:1. The sulphoaluminate cement, silica fume, desulfurized gypsum, expanding agent, composite retarder, early strength agent, and defoaming agent are mixed uniformly, loaded into a packaging bag with a diameter of 33mm, and made into a cylindrical anchoring bag to form a fast-setting cement anchoring agent.

[0044] Embodiment 2

[0045] The embodiment provides a fast-hardening high-strength cement anchoring agent, and raw materials used in the embodiment include: 60wt% of sulphoaluminate cement, 12wt% of silica fume, 13wt% of desulfurization gypsum, 6wt% of expanding agent, 0.15wt% of composite retarder (sucrose and citric acid are prepared according to a mass ratio of 4.5:1), 0.08wt% of early strength agent and 0.03wt% of defoaming agent.

[0046] The preparation steps are as follows: the silica fume is mixed with water according to a mass ratio of 1:100, stirring is carried out at a speed of 1200 rpm for 4 minutes, then the sulphoaluminate cement is added, stirring is carried out at a speed of 5000 rpm for 5 minutes, then anhydrous ethanol is added, and stirring is carried out for 4 minutes, so that a modified mineral admixture dispersion liquid is obtained, and the modified mineral admixture dispersion liquid is dried at 110 DEG C and ground to a particle size of not more than 20 μm. The water and ethanol ratio is 100:3, and the ethanol accounts for 20wt% of the mass of the water.

[0047] The composite retarder is prepared by mixing sucrose and citric acid according to a mass ratio of 4.5:1. After the sulphoaluminate cement, the silica fume, the desulfurization gypsum, the expanding agent, the composite retarder, the early strength agent and the defoaming agent are mixed, the mixture is filled into a packaging bag, and a cylindrical anchoring bag with a diameter of 35 mm is formed.

[0048] Embodiment 3

[0049] The fast-hardening high-strength cement anchoring agent of the embodiment includes the following raw materials: 55wt% of sulphoaluminate cement, 10wt% of silica fume, 20wt% of desulfurization gypsum, 0.07wt% of lithium carbonate, 5wt% of expanding agent, 0.1wt% of composite retarder (borax and sodium citrate are prepared according to a mass ratio of 10:1), 0.1wt% of ethylene glycol and 0.02wt% of defoaming agent.

[0050] The preparation method is as follows: the silica fume and water are mixed according to a mass ratio of 1:100, stirring is carried out at a speed of 1000 rpm for 5 minutes, then the sulphoaluminate cement is added, and stirring is carried out at a speed of 5000 rpm for 5 minutes, then anhydrous ethanol is added, and stirring is carried out for 4 minutes, so that a modified mineral admixture dispersion liquid is obtained. After drying at 110 DEG C, the modified mineral admixture dispersion liquid is ground to a particle size of not more than 20 μm.

[0051] The composite retarder is prepared by mixing borax and sodium citrate according to a mass ratio of 10:1. All the raw materials are uniformly mixed according to the proportions, and an anchoring bag with a diameter of 33 mm is prepared.

[0052] Embodiment 4

[0053] The fast-hardening high-strength cement anchoring agent provided in the embodiment includes the following raw materials: 70wt% of sulphoaluminate cement, 10wt% of silica fume, 10wt% of desulfurization gypsum, 0.05wt% of lithium carbonate, 4wt% of expanding agent, 0.2wt% of composite retarder (sodium phosphate and phosphoric acid are prepared according to a mass ratio of 4:1), 0.02wt% of early strength agent and 0.05wt% of defoaming agent.

[0054] The preparation method is: mixing silica fume and water at a mass ratio of 1:100, stirring at 1000 rpm for 5 minutes, then adding sulphoaluminate cement, continuing to stir at 5000 rpm for 5 minutes, then adding anhydrous ethanol and continuing to stir at 5000 rpm for 4 minutes to obtain a modified mineral admixture dispersion liquid, drying and grinding to a particle size of not more than 20 μm. The mass of the ethanol is 20 wt% of the water.

[0055] Mixing all raw materials in proportion to make cylindrical anchor bags with a diameter of 33 mm for construction of anchors.

[0056] Comparative Example 1

[0057] The composition of the rapid-setting cement anchor provided by this comparative example is the same as that of Example 1, except that no desulfurized gypsum is added. Tests show that this proportion results in a significant shortening of the initial setting time of the anchor, a 1-hour compressive strength of 25.4 MPa, and a decrease in expansion performance.

[0058] Mixing silica fume and water at a mass ratio of 1:100, stirring at 1000 rpm for 5 minutes, then adding sulphoaluminate cement, continuing to stir at 5000 rpm for 5 minutes, then adding anhydrous ethanol and continuing to stir at 5000 rpm for 4 minutes to obtain a modified mineral admixture dispersion liquid, drying and grinding to a particle size of not more than 20 μm. The mass of the ethanol is 20 wt% of the water.

[0059] Comparative Example 2

[0060] The composition of the rapid-setting cement anchor provided by this comparative example is the same as that of Example 2, except that no composite retarder is added. Test results show that the absence of the composite retarder significantly shortens the initial setting time to 2:30, and the 1-hour compressive strength is 22.1 MPa, which is too fast for construction adaptability.

[0061] Comparative Example 3

[0062] The composition of the rapid-setting cement anchor provided by this comparative example is the same as that of Example 3, except that no ethylene glycol is used as an early strength agent. Test results show that the absence of ethylene glycol results in an initial setting time of 8:15, a 1-hour compressive strength of 18.7 MPa, and a significant lack of early strength.

[0063] Comparative Example 4

[0064] The composition of the rapid-setting cement anchor provided by this comparative example is the same as that of Example 4, except that no expansion agent is added. Test results show that the absence of the expansion agent significantly reduces the expansion performance of the anchor, with a 28-day expansion rate of only 0.015%, and a 1-hour compressive strength of 20.9 MPa, as shown in Table 1.

[0065] Table 1 Performance comparison of examples and comparative examples

[0066]

[0067] As can be seen from Table 1, compared with the examples, although the main components are the same in Comparative Example 1, the initial setting time is shortened and the 0.5 hour and 1 hour compressive strength is significantly reduced due to the absence of desulfurized gypsum, which shows that the setting time is too fast and is not conducive to construction operation. The initial setting time is too short and the 1 hour compressive strength is significantly reduced in Comparative Example 2 due to the absence of composite retarder, which affects the stability and strength performance of the material due to the too fast setting speed. The initial setting time is greatly prolonged and the early strength performance is poor in Comparative Example 3 due to the absence of early strength agent, and the compressive strength is significantly lower than that of the examples, which reflects the importance of lithium carbonate in improving the early strength. Although the initial setting time is prolonged in Comparative Example 4 due to the absence of expanding agent, the expansion performance is significantly reduced, and the 0.5 hour and 1 hour compressive strength is significantly reduced, which affects the overall performance of the material.

[0068] In summary, the formulation in the examples optimizes the setting time and early strength of the anchoring agent by reasonable material proportioning, ensuring the comprehensive performance of the material, while the different formulation adjustments in the comparative examples have a negative impact on the performance of the anchoring agent. Therefore, balancing the setting time and compressive strength and maintaining the reasonable proportion of each component in the formulation are the key to ensuring the performance of the anchoring agent.

[0069] A strength testing method for a fast-hardening high-strength cement anchoring agent, the fast-hardening high-strength cement anchoring agent used in the testing method is made according to the formulation in Example 1, as shown in Figure 1 The method comprises the following steps:

[0070] S1: Collecting piezoelectric impedance signal data of the cement anchoring agent by a piezoelectric ceramic sensor

[0071] Specifically, a lead zirconate titanate piezoelectric ceramic (PET) is used as an intelligent sensor to test the fast-hardening high-strength cement anchoring agent in a standard column mold after sufficient stirring, and the signal spectrum of a specified frequency interval is obtained. Or the PZT sensor is attached to the surface of the cement anchoring agent, and the conductance and impedance data of the anchoring agent at different strength stages are collected by an impedance analyzer to obtain time domain signals. The piezoelectric ceramic sensor collects the piezoelectric impedance signal of the cement anchoring agent, as shown in Figure 4 The signal data collection specifically comprises the following:

[0072] S101: The fast-hardening high-strength cement anchoring agent is prepared according to the above standard, and the anchoring agent mixture is fully stirred using an electric mixer, and then the fresh mortar is poured into a standard prism mold with a size of 60.0x60.0x170.0mm.

[0073] S102: EMI measurements were performed using a circular original PZT patch with a diameter of 19.8 mm and a thickness of 1.0 mm. Before practical application of the PZT patch as an impedance sensor, it was completely covered with a thin film of dielectric and water-resistant coating, and two wires were soldered to its electrodes.

[0074] S103: Immediately after the mortar was mixed, a fine PZT sensor was installed in the center of the test sample and aligned longitudinally with the prism mold, and a self-made wooden stick was used to assist in precise positioning of the sensor.

[0075] S104: EMI measurements were performed using an Agilent 4294A impedance analyzer with an excitation frequency ranging from 40.0 Hz to 110.0 MHz.

[0076] S105: In each measurement, the EMI spectrum was measured in two different frequency ranges, 0-1000 kHz and 0-3000 kHz, corresponding to the d31 and d33 resonance modes of the piezoelectric sensor, respectively. The EMI test of the PZT sensor was performed every 10 minutes before the mortar reached the final setting. After that, the impedance signal was collected every hour during the early hydration and setting process of the mortar, lasting for a total of 72 hours.

[0077] Principle of piezoelectric impedance technology

[0078] As shown in Figure 2 , the piezoelectric effect is divided into positive piezoelectric effect and inverse piezoelectric effect. The positive piezoelectric effect refers to the generation of electric charge in piezoelectric materials under mechanical force, while the inverse piezoelectric effect refers to the deformation of piezoelectric materials under electric field. Using this characteristic, a piezoelectric ceramic sheet can be used as both a driver and a sensor. When an alternating voltage is applied to the PZT, it drives the vibration and transmits the vibration to the cement anchoring agent structure being measured; conversely, the mechanical impedance of the anchoring agent structure will change the vibration response of the PZT, which is reflected in the changes in the electric conductance and impedance of the piezoelectric sheet.

[0079] The electric displacement of the PZT in the coupled system is:

[0080]

[0081] The current is calculated as:

[0082] I = iω∫∫D3dxdy

[0083] where:

[0084]

[0085] Further, in most cases, the experimental frequency is much lower than the resonance frequency of the PZT:

[0086]

[0087] The formula of the coupled admittance of PZT can be simplified as:

[0088]

[0089] More specifically, the admittance (Y) of PZT is related to the mechanical impedance of the anchoring agent, expressed as:

[0090]

[0091] where ω is the angular frequency of the excitation signal, C0 is the baseline capacitance of PZT, Z S is the mechanical impedance of the anchoring agent, and Z A is the mechanical impedance of PZT.

[0092] S2: Collect the actual strength data of the cement anchoring agent at different strength stages by rebound method. Specifically, it includes the following:

[0093] S201: Determine the area of the concrete surface that is clean, flat, and free of obvious defects as the test point. Each test area should have 10 to 12 test points, and repeated tests should be avoided at the same location on the concrete surface.

[0094] S202: Clean the test point to ensure that the surface is free of dust, coatings, oil stains, and other substances that affect the rebound value. If the concrete surface is rough or has loose substances, use sandpaper or grinding stone to lightly polish it to ensure flatness and smoothness.

[0095] S203: Before formal testing, ensure that the Schmidt rebound hammer is calibrated. Calibration should be performed on a standard hardness block that meets the requirements, and the device should be in normal working condition.

[0096] S204: Touch the rebound hammer vertically to the concrete surface, apply light pressure, keep the rebound hammer stable and close to the surface, quickly press the trigger device to release the impact force, and the instrument will automatically record the rebound value. Test multiple times (usually more than 10 times) in the same area and record the rebound value of each test point.

[0097] S205: Calculate the average rebound value of each test area.

[0098] S206: Repeat steps S201-S205 every fixed time Δt, determine the rebound strength curve of the cement anchoring agent according to the change of the average rebound value with time (provided by the instrument or referred to relevant specifications), and convert the measured rebound average value to the concrete strength value.

[0099] S3: Preprocess the piezoelectric impedance signal dataset and the strength dataset, and construct a time series dataset. Specifically, it includes:

[0100] S301: Preprocessing the piezoelectric impedance signal, including empirical mode decomposition (EMD) and Hilbert transform of the signal, and extracting the instantaneous amplitude; obtaining the instantaneous amplitude dataset of the conductance.

[0101] Mathematically, the instantaneous amplitude of the Hilbert transform can be expressed as:

[0102]

[0103] where y(t) is the original signal, is its Hilbert transform.

[0104] S302: Divide the processed signal dataset into training set and validation set in proportion;

[0105] S303: Label the dataset, ensuring that each signal data corresponds to the corresponding cement anchoring agent strength.

[0106] S4: Use long short-term memory network (LSTM) for model training, learn the relationship between piezoelectric impedance signal and strength, and establish the cement anchoring agent strength prediction model.

[0107] As Figure 3 shown, long short-term memory network (LSTM) is used to process time series data, such as the change of piezoelectric impedance signal with time. LSTM can remember past states and handle long-time dependence problems, making it suitable for complex time series feature extraction of piezoelectric impedance data. The specific network structure is represented by the following formula:

[0108] The calculation formula of LSTM unit is:

[0109] f t =σ(W f ·[h t-1 ,x t ]+b f )

[0110] i t =σ(W i ·[h t-1 ,x t ]+b i )

[0111]

[0112] o t =σ(W o ·[h t-1 ,x t ]+b o )

[0113] h t =ot tanh(C t )

[0114] where f t is the forget gate, controlling how much historical information to discard; i t is the input gate, determining the degree of memory for current information; C t is the cell state; o t is the output gate, ultimately determining the output.

[0115] The collected instantaneous amplitude dataset is input into the LSTM network for training. The network input is time series data, and the output is the strength prediction value of the cement anchoring agent. The LSTM network learns the complex nonlinear relationship between the piezoelectric impedance signal and the anchoring agent strength through multiple iterations.

[0116] S5: Verify and optimize the model; specifically including the following:

[0117] S501: Input the validation set into the trained model for prediction;

[0118] S502: Compare the strength prediction results output by the model with the actual strength using the loss function;

[0119] The mean square error (MSE) is used as the loss function to measure the error between the predicted strength value and the true strength value, as follows:

[0120]

[0121] where y i is the actual strength, is the model predicted strength.

[0122] S503: Adjust the weight parameters and network topology structure of the LSTM network based on the comparison results to optimize the model performance. Ensure its learning ability for piezoelectric impedance data. Evaluate the network performance through the validation set. If the accuracy and recall rate meet the expected effect, stop optimization.

[0123] Input the test data that did not participate in training into the model to compare the predicted strength value with the actual measured anchoring agent strength value, verify the accuracy and generalization ability of the model. The model can be further optimized by adjusting network parameters such as learning rate and number of layers.

[0124] S6: Apply the optimized model to actual engineering to realize real-time non-destructive monitoring of cement anchoring agent strength. Collect data through PZT sensors and input them into the LSTM network to automatically predict the strength value of the cement anchoring agent, ensuring construction quality and safety.

[0125] The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in the description of the application and the appended claims, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0126] It should be understood that, the term "and / or" used herein is merely an association relationship of the associated objects, and means that there can be three relationships, for example, A and / or B, which can represent the three cases of A existing alone, A and B existing together, and B existing alone. In addition, the character " / " herein generally represents that the front and rear associated objects are in an "or" relationship.

[0127] Depending on the context, the word "if" as used herein can be interpreted to mean "when" or "upon" or "in response to determining" or "in response to detecting." Similarly, the phrase "if determined" or "if detecting (a stated condition or event)" can be interpreted to mean "when determined" or "in response to determining" or "when detecting (a stated condition or event)" or "in response to detecting (a stated condition or event)," depending on the context.

[0128] Although the application has been described in detail with reference to the foregoing embodiments, the technical solutions recorded in the foregoing embodiments can be modified by those skilled in the art, or some technical features can be replaced by equivalent ones, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A method for testing the strength of a fast-hardening high-strength cement anchoring agent, characterized by: The method comprises the following steps: S1: collecting piezoelectric impedance signal data of the cement anchoring agent by a piezoelectric ceramic sensor; the cement anchoring agent comprises the following raw materials in mass fraction: 50-70% of sulphoaluminate cement, 10-20% of silica fume, 10-20% of desulfurized gypsum, 3-10% of expansive agent, 0.05-0.3% of composite retarder, 0.01-0.1% of early strength agent, and 0.02-0.1% of defoaming agent; S2: collecting actual strength data of the cement anchoring agent at different strength stages by a rebound method; S3: pre-processing the piezoelectric impedance signal data set and the strength data set, and constructing a time series data set; specifically comprising the following: S301: pre-processing the piezoelectric impedance signal, including EMD (empirical mode decomposition) and Hilbert transform on the signal, and extracting instantaneous amplitude; S302: dividing the processed signal data set into a training set and a validation set in proportion; S303: marking the data set to ensure that each signal data corresponds to the strength of the cement anchoring agent; S4: training a model using an LSTM (long short-term memory) network to learn the relationship between the piezoelectric impedance signal and the strength, and establishing a cement anchoring agent strength prediction model; S5: verifying and optimizing the model; specifically comprising the following: S501: inputting the validation set into the trained model for prediction; S502: comparing the strength prediction result output by the model with the actual strength by using a loss function; S503: adjusting the weight parameters and network topology structure of the LSTM network based on the comparison result, and optimizing the performance of the model; S6: applying the optimized model to an actual project to realize real-time and non-destructive monitoring of the strength of the cement anchoring agent.

2. The strength testing method of the fast-hardening high-strength cement anchoring agent according to claim 1, characterized by: The composite retarder is sucrose and citric acid, or the composite retarder is borax and sodium citrate, or the composite retarder is sodium phosphate and phosphoric acid.

3. The strength testing method of the fast-hardening high-strength cement anchoring agent according to claim 2, characterized by: When the composite retarder is sucrose and citric acid, the mass ratio is 4:1; when the composite retarder is borax and sodium citrate, the mass ratio is 10:1; and when the composite retarder is sodium phosphate and phosphoric acid, the mass ratio is 4:

1.

4. The strength testing method of the fast-hardening high-strength cement anchoring agent according to claim 1, characterized by: The early strength agent is ethylene glycol.

5. The strength testing method of the fast-hardening high-strength cement anchoring agent according to claim 1, characterized by: In the step S502, the MSE (mean square error) is used as the loss function for measuring the error between the network prediction strength value and the true strength value, and the formula is as follows:

6. The strength testing method of a fast hardening high strength cement anchoring agent according to claim 1, characterized by: ​ where y i is the actual intensity, is the model predicted intensity.

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