An in-situ evaluation method for yield shear stress of wet sprayed concrete adhered to sprayed surface

Abstract

The present invention belongs to the technical field of underground engineering support, and specifically relates to an in-situ evaluation method for the yield shear stress of wet sprayed concrete adhered to the sprayed surface. The present invention mainly addresses the technical difficulty that the yield shear stress of wet sprayed concrete adhered to the sprayed surface cannot be evaluated in situ. Using ultrasonic velocity as a connecting link, a quantitative correlation expression between yield shear stress and penetration strength is established. By measuring the penetration strength of wet sprayed concrete adhered to the sprayed surface, an in-situ evaluation of the yield shear stress after the concrete is mixed with the accelerator and before initial setting is achieved, providing a core basis for judging whether the concrete jet rebounds or falls off on the sprayed surface and evaluating the thickness of a single spraying. The method of the present invention realizes the prediction of the yield shear stress of wet sprayed concrete at any time before initial setting after the concrete is mixed with the accelerator and under actual on-site application conditions.

Description

Technical Field

[0001] The invention belongs to the technical field of underground engineering support, and particularly relates to an in-situ evaluation method for the yield shear stress of wet sprayed concrete adhered to a sprayed surface. Background Art

[0002] Rebound rate is one of the three major technical indicators of wet shotcrete sprayability, and it is the most important of the three. The rebound rate is not only related to the economic cost of concrete construction, such as the effective concrete construction volume and slag removal workload, but also reduces the efficiency of shotcrete construction; the greater the rebound rate, the lower the construction efficiency. Especially for areas with risks of rock bursts and collapses, a high rebound rate is not conducive to the rapid formation of support capacity and is detrimental to construction safety. The rebound rate and the thickness of a single shot influence each other. The smaller the rebound rate, the greater the thickness of a single shot; the greater the thickness of a single shot, the smaller the rebound rate. Regardless of the rebound rate or the thickness of a single shot, both are the rebound or adhesion behaviors associated with wet shotcrete impacting the sprayed surface in the form of a jet. Whether the concrete jet can adhere or rebound is essentially a rheological issue, which depends on the magnitude of the real-time yield shear stress of the wet shotcrete adhering to the sprayed surface.

[0003] During wet shotcrete construction, concrete is mixed with an accelerator and then jetted onto the surface. Under the influence of the accelerator, the cementitious material hydrates rapidly, causing the concrete to lose fluidity almost instantly and undergo a rapid flow transition. Rheological parameters, such as yield shear stress, differ significantly from those without the accelerator. Whether the concrete jet adheres to the surface should be calculated based on the yield shear stress of the actual wet shotcrete containing the accelerator. Currently, yield shear stress testing relies primarily on rheometers. However, the properties of wet shotcrete containing accelerators evolve rapidly, making testing inadequate and potentially damaging the equipment. Furthermore, under the catalytic effect of the accelerator, the rheological behavior of the concrete changes rapidly. Rheological testing takes approximately 30 seconds, after which significant changes have already occurred, and the resulting parameters do not meet the objective requirements of real-time performance. Furthermore, wet shotcrete construction is typically carried out outdoors, where the concrete jet directly adheres to the surface. The yield shear stress is affected by multiple factors, including local climate, surrounding environment, and concrete raw materials, all of which differ from indoor environments. Real-time testing and feedback would not only provide a practical basis for theoretical research on concrete jet adhesion or shedding, but also provide a real-time basis for the dynamic regulation of concrete mix parameters and construction process parameters. In line with the dual requirements of timeliness and practicality in testing yield shear stress, the inventors aim to provide an in-situ method for assessing the yield shear stress of wet sprayed concrete adhered to the sprayed surface. Summary of the Invention

[0004] To address the technical challenge of estimating the yield shear stress during jet rebound or adhesion of wet shotcrete containing an accelerator, this paper proposes an in-situ method for assessing the yield shear stress of wet shotcrete adhered to the sprayed surface. First, penetration strength, yield shear stress, and ultrasonic velocity tests were conducted on the same wet shotcrete mix without an accelerator. Using ultrasonic velocity as the link, a quantitative relationship between yield shear stress and penetration strength was established. Next, penetration strength tests were conducted on wet shotcrete containing an accelerator in actual construction. The yield shear stress of the wet shotcrete was then determined at any point between mixing the concrete and the accelerator and initial setting.

[0005] In order to achieve the above technical objectives and the above technical effects, the present invention is implemented through the following technical solutions:

[0006] An in-situ evaluation method for yield shear stress of wet sprayed concrete adhered to a sprayed surface comprises the following steps:

[0007] 1) Based on the actual wet spraying concrete mix ratio and the type and flow rate of the matching accelerator, the ultrasonic velocity of the wet spraying concrete mixture without accelerator is first observed. The change of ultrasonic velocity with hydration time from the time the concrete leaves the machine to the time of initial setting is recorded. The "linear growth section" of ultrasonic velocity is intercepted to determine the hydration time range of this stage;

[0008] 2) Within the specified time range of the ultrasonic velocity "linear growth section", the penetration strength, ultrasonic velocity and yield shear stress are tested simultaneously. The three technical indicators are tested at one-to-one time, and the number of measuring points for each indicator is not less than 5;

[0009] 3) Based on the quantitative relationship expression between the penetration strength and ultrasonic velocity in the "linear growth section" of ultrasonic velocity, combined with the measured data of penetration strength and ultrasonic velocity, the least squares method is used to calculate the parameters α, β, ζ, and ε in the quantitative relationship expression;

[0010] 4) Based on the quantitative relationship between the yield shear stress and ultrasonic velocity in the "linear growth section" of ultrasonic velocity, combined with the measured data of yield shear stress and ultrasonic velocity, the least squares method is used to calculate the parameters θ, λ, and δ in the quantitative relationship expression;

[0011] 5) According to the quantitative relationship expression between yield shear stress and penetration strength, the above-mentioned known parameters α, β, ζ, ε, θ, λ and δ are substituted as the basis for in-situ evaluation of yield shear stress of wet shotcrete;

[0012] 6) Record the mixing time of wet spraying concrete and accelerator, wait for the concrete jet to adhere to the sprayed surface, and then start testing the penetration strength. Record each penetration strength measurement and test time. Combined with the quantitative relationship expression between yield shear stress and penetration strength, convert the yield shear stress according to the measured penetration strength.

[0013] Furthermore, the ultrasonic velocity "linear growth section" is the "wave velocity linear growth" stage among the three stages of ultrasonic velocity change with the extension of concrete mixture hydration time: "wave velocity almost no increase", "wave velocity linear growth", and "wave velocity slow growth", and the change slope in this stage is the largest.

[0014] Furthermore, the quantitative relationship between the penetration intensity and ultrasonic velocity is expressed as follows:

[0015]

[0016] Where: P is the penetration strength, unit is MPa; υ is the ultrasonic velocity, unit is m / s; α, β, ζ, ε are all constants.

[0017] Furthermore, the quantitative relationship between the yield shear stress and the ultrasonic velocity is expressed as follows:

[0018] τ0=θe υ / λ +δ

[0019] Where: τ0 is the yield shear stress, θ, λ, and δ are all constants.

[0020] Furthermore, the quantitative relationship between the yield shear stress and the penetration strength is expressed as follows:

[0021]

[0022] Furthermore, the penetration strength is tested using a handheld penetration resistance device. The probe cross-section is circular, with a diameter of 4mm to 6mm, a measuring range of 200N to 500N, a penetration depth of 25mm, and a loading method of slow and uniform loading. The single-point test takes 10s. The penetration strength is calculated as follows:

[0023]

[0024] Where: F is the penetration resistance, unit is N; d is the diameter of the measuring needle, unit is mm.

[0025] Furthermore, the yield shear stress of the wet sprayed concrete without accelerator was tested by a paddle type rotational rheometer, using a ramp acceleration shear rate control mode with a shear rate change acceleration of 0.1s. -2 ~0.5s -2 To ensure that the test time is in the "linear growth section" of ultrasonic velocity, the sample is first loaded into the rheometer, and the test is started at the scheduled time. The shear stress and shear rate are recorded simultaneously, and the yield shear stress is calculated in combination with the Bingham model. The model expression is:

[0026]

[0027] Where: τ is shear stress, unit is Pa; η is plastic viscosity, unit is Pa·s; is the shear rate, unit is s -1 .

[0028] Furthermore, the ultrasonic velocity observation is the ratio of the ultrasonic observation distance to the time taken to pass the observation distance, i.e., the wave time, and the calculation expression is as follows:

[0029]

[0030] Where: s is the ultrasonic observation distance, unit is mm; t is the ultrasonic time, unit is μs.

[0031] Furthermore, the ultrasonic observation distance is not less than 150 mm.

[0032] The beneficial effects of the present invention are:

[0033] 1. The present invention solves the technical problem of being unable to evaluate the yield shear stress of wet-sprayed concrete with accelerated setting agent adhering to the sprayed surface, breaking through the limitation that its yield shear stress cannot be directly tested by a rheometer or obtained indirectly. It provides an important rheological parameter basis for judging jet rebound or shedding, evaluating the thickness of a single spraying, and dynamically controlling concrete mix parameters and construction process parameters.

[0034] 2. The present invention realizes the prediction of the yield shear stress of wet sprayed concrete at any time after the concrete is mixed with the accelerator and before the initial setting, under actual on-site application environment.

[0035] Of course, any product implementing the present invention does not necessarily need to achieve all of the above advantages at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0037] Figure 1 This is a flow chart of the yield shear stress prediction method involved in the present invention;

[0038] Figure 2 Schematic diagram of the change of ultrasonic velocity of wet shotcrete without accelerator as a function of hydration time in the embodiment;

[0039] Figure 3 Schematic diagram of the change of ultrasonic velocity of wet-sprayed concrete with hydration time in the embodiment;

[0040] Figure 4This is a graph showing the ramp accelerated shear rate loading control curve used in the yield shear stress test in the embodiment;

[0041] Figure 5 Schematic diagram of the results of formula fitting of penetration strength and ultrasonic velocity measured data in the embodiment;

[0042] Figure 6 Schematic diagram of the formula fitting results of the yield shear stress and ultrasonic velocity measured data in the embodiment. DETAILED DESCRIPTION

[0043] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0044] The present invention is mainly achieved from three aspects:

[0045] First, previous studies have found that the ultrasonic velocity of wet-sprayed concrete with an accelerator increases linearly with the extension of hydration time before initial setting, while the ultrasonic velocity of wet-sprayed concrete without an accelerator goes through three stages: "almost no increase in wave velocity", "linear increase in wave velocity", and "slow increase in wave velocity". Taking advantage of the fact that the ultrasonic velocity of wet-sprayed concrete with an accelerator always maintains a linear increase with the extension of hydration time, it is compared with the "linear increase section" of the ultrasonic velocity of wet-sprayed concrete without an accelerator. By taking advantage of the similarity in the staged changes in ultrasonic velocity between the two, wet-sprayed concrete without an accelerator can be approximately regarded as wet-sprayed concrete with an accelerator whose setting process is "slowed down".

[0046] Secondly, taking the "linear growth section" of ultrasonic velocity of wet sprayed concrete without accelerator as the main investigation stage, the changes in penetration strength, ultrasonic velocity, and yield shear stress with hydration time in this stage were tested and obtained. That is, the logarithmic correlation between penetration strength and hydration time, the linear correlation between ultrasonic velocity and hydration time, and the exponential correlation between yield shear stress and hydration time were established, and a quantitative relationship between yield shear stress and penetration strength was established.

[0047] Third, when evaluating the yield shear stress of wet shotcrete during actual construction, concrete mixed with an accelerator was used as the investigation object. The penetration strength of the wet shotcrete adhered to the sprayed surface was tested. The quantitative relationship between the yield shear stress and the penetration strength, established based on the "linear growth segment" of ultrasonic velocity in wet shotcrete without an accelerator, was substituted into the equation to calculate the corresponding yield shear stress. Since a yield shear stress can be obtained for each penetration strength, an estimate of the yield shear stress at any time before the initial setting time of the wet shotcrete can be obtained.

[0048] The in-situ evaluation method for the yield shear stress of wet sprayed concrete adhered to a sprayed surface comprises the following steps: first, without adding an accelerator, synchronously testing the ultrasonic velocity, penetration strength and yield shear stress of the wet sprayed concrete at different hydration times before initial setting, and intercepting the hydration time range of the ultrasonic velocity "linear growth section"; establishing a quantitative relationship expression between the yield shear stress and the penetration strength based on the quantitative relationship between the penetration strength and the ultrasonic velocity, and the quantitative relationship between the yield shear stress and the ultrasonic velocity in the "linear growth section"; combining measured data of the ultrasonic velocity, penetration strength and yield shear stress at different times in the "linear growth section" to obtain relevant parameters of the quantitative relationship expression between the yield shear stress and the penetration strength, so as to concretize the quantitative correlation formula; and then, under the condition of adding an accelerator, measuring the penetration strength of the wet sprayed concrete adhered to the sprayed surface, substituting it into the quantitative relationship expression between the yield shear stress and the penetration strength, and converting the yield shear stress.

[0049] The present invention mainly addresses the technical difficulty of being unable to in-situ evaluate the yield shear stress of wet sprayed concrete adhering to the sprayed surface. Using ultrasonic velocity as a connecting link, a quantitative correlation expression between yield shear stress and penetration strength is established. By measuring the penetration strength of wet sprayed concrete adhering to the sprayed surface, in-situ evaluation of the yield shear stress after the concrete and the accelerator are mixed and before initial setting is achieved, providing a core basis for judging whether the concrete jet will rebound or fall off on the sprayed surface and for evaluating the thickness of a single spraying.

[0050] The relevant specific embodiments of the present invention are:

[0051] Example:

[0052] 1) Based on the actual wet spraying construction concrete mix ratio and the matching accelerator type and flow rate (dosage), the concrete mix ratio is shown in Table 1, with a water-binder ratio of 0.40, a silica fume content of 10%, and a sand ratio of 55%.

[0053] Table 1 Wet shotcrete mix ratio (kg / m 3 )

[0054] cement silica fume fine aggregate coarse aggregate water water reducer Accelerator 416 46 952 779 185 4.63 32.4

[0055] The cement is "Hunhe Brand" P·O42.5 ordinary Portland cement produced by Fushun Cement Co., Ltd.; the silica fume is 920 semi-densified silica fume provided by Elkem International Trading (Shanghai) Co., Ltd.; the fine aggregate and coarse aggregate are artificial limestone aggregates crushed from the same parent rock, with a saturated compressive strength of 116 MPa, a fineness modulus of 2.9, and a coarse aggregate particle size range of 5 mm to 10 mm; the water reducer is an early-strength, high-performance water reducer provided by Changchun Dongkan New Building Materials Co., Ltd., with a dosage of 1.0% and a water reduction rate of 28.8%; the accelerator is an alkali-free liquid accelerator provided by Changchun Dongkan New Building Materials Co., Ltd., with a dosage of 7.0%, an initial setting time of 2 minutes 32 seconds, and a final setting time of 6 minutes 44 seconds.

[0056] 2) Before ultrasonic observation, stir the sample evenly and quickly put it into a 180mm×180mm×100mm special organic glass test mold. A pair of center lines of the test mold are pre-buried with the receiving end and transmitting end of the ultrasonic transducer. The observation distance is 180mm. Start timing from the contact between the accelerator and the concrete, record the time it takes for the ultrasonic wave to pass through the observation distance, that is, the wave time, and calculate the ultrasonic velocity.

[0057] First, the ultrasonic velocity of the wet sprayed concrete mixture without accelerator in Table 1 was observed. The change of ultrasonic velocity with hydration time from the time the concrete leaves the machine to the time before initial setting is shown in the figure. Figure 2 The ultrasonic velocity “linear growth section” was intercepted and the hydration time range of this stage was determined to be 120 min to 253 min.

[0058] In order to more clearly illustrate the technical points of the present invention, the change of ultrasonic velocity of wet sprayed concrete with accelerating setting agent in Table 1 is given as follows: Figure 3 As shown, the ultrasonic velocity exhibits a "linear growth phase" initially after contact with the accelerator, lasting from 0.70 to 2.50 minutes. The yield shear stress prediction for wet-shot concrete with an accelerator primarily leverages the similarity in the phased changes in the ultrasonic velocity "linear growth phase" between wet-shot concrete with and without an accelerator. By approximating wet-shot concrete without an accelerator to wet-shot concrete with an accelerator, which has a "slowed-down setting process," the ultrasonic velocity during this phase serves as a connecting link, providing a basis for establishing a quantitative correlation between the yield shear stress and penetration strength.

[0059] 3) Within the specified time range of the ultrasonic velocity "linear growth section", the penetration strength, ultrasonic velocity and yield shear stress are tested simultaneously. The test times of the three technical indicators correspond one to one, and the number of measuring points for each indicator is not less than 5.

[0060] The ultrasonic velocity test method is as described above; the penetration strength test is conducted using a handheld penetration resistance device with a measuring range of 200 N, a probe diameter of 6 mm, a penetration depth of 25 mm, and a single test time of approximately 10 s. The loading is performed at a slow and uniform rate. The test process is conducted in accordance with the "Test Procedures for Hydraulic Concrete" (DL / T 5150-2017). The yield shear stress is measured using a paddle-type rotational rheometer with a shear time of 60 s and a constant shear rate acceleration of 0.3 s. -2 , the loading process is as follows Figure 4 , record the shear stress and shear rate within 60s, and calculate the yield shear stress in combination with the Bingham model τ=τ0+ηγ. The so-called yield shear stress of different hydration times is that the concrete sample is installed on the rheometer in advance, and the test is started after a predetermined time without any disturbance to the concrete before. The starting test time is approximately regarded as the hydration time.

[0061] The penetration strength, ultrasonic velocity and yield shear stress of the wet sprayed concrete mix ratio in Table 1 without accelerator at five hydration times of 120min, 150min, 180min, 210min and 240min are summarized in Table 2.

[0062] Table 2 Penetration strength, ultrasonic velocity and yield shear stress at five hydration times

[0063] Hydration time (min) Penetration strength (MPa) Ultrasonic speed (m / s) Yield shear stress (Pa) 120 0.12 438 144 150 0.15 658 165 180 0.35 950 212 210 0.60 1254 478 240 1.45 1675 891

[0064] 4) According to the quantitative relationship expression between the penetration strength and ultrasonic velocity in the “linear growth section” of ultrasonic velocity, combined with the measured data of penetration strength and ultrasonic velocity in Table 2, the least square method is used to obtain the parameters α, β, ζ, and ε in the quantitative relationship expression. The formula fitting results are shown in Figure 5 The parameter results are: α = 27.73; β = 3770.90; ζ = -15.47; ε = -12133.75. The quantitative relationship between penetration intensity and ultrasonic velocity is expressed as follows:

[0065]

[0066] 5) According to the quantitative relationship expression between the yield shear stress and ultrasonic velocity in the “linear growth section” of ultrasonic velocity, combined with the measured data of yield shear stress and ultrasonic velocity in Table 2, the least squares method is used to obtain the parameters θ, λ and δ in the quantitative relationship expression. The formula fitting results are shown in Figure 6 , the parameter results are: θ = 43.98; λ = 560.81; δ = 25.89, and the quantitative relationship between yield shear stress and ultrasonic velocity is as follows:

[0067] G=43.98×e υ / 560.81 +25.89

[0068] Where: G-yield shear stress, θ, λ, δ are all constants.

[0069] 6) Combining the above known parameters α, β, ζ, ε, θ, λ and δ, the quantitative relationship expression between yield shear stress and penetration strength is obtained:

[0070]

[0071] Based on the measured penetration strength in Table 2, the predicted yield shear stress was calculated in combination with the above formula. The comparison between the predicted yield shear stress and the measured yield shear stress is shown in Table 3. The correlation coefficient r between the two is 0.9907, the number of data (samples) is 5, and the degree of freedom is (n-2)3. According to the critical value table of the significance test correlation coefficient, when the correlation coefficient is greater than or equal to 0.95874, the confidence level exceeds 99%. Therefore, the yield shear stress predicted by the above formula is in good agreement with the measured yield shear stress.

[0072] Table 3 Comparison of measured yield shear stress and predicted yield shear stress at five hydration times

[0073]

[0074]

[0075] 7) When predicting the actual yield shear stress of wet shotcrete, first record the mixing time of wet shotcrete and accelerator, which is approximately the starting point of hydration time. Wait for the concrete jet to adhere to the sprayed surface, then test the penetration strength, record each penetration strength measurement and test time, and combine the quantitative relationship expression between yield shear stress and penetration strength to convert the yield shear stress according to the measured penetration strength.

[0076] Based on the wet spraying concrete mix ratio in Table 1, the alkali-free liquid accelerator dosage is 7%, and a large-scale wet spraying concrete machine is used at the construction site with a construction efficiency of 20m 3 / h, the injection angle is right angle, the injection air pressure is 0.8MPa, the injection distance is 1.5m~2.0m, and the measured penetration strength and predicted yield shear stress at different hydration times are summarized in Table 4, which realizes the prediction of yield shear stress.

[0077] Table 4 Measured penetration strength and predicted yield shear stress at five hydration times

[0078] Hydration time (min) Measured penetration strength (MPa) Predicted yield shear stress (Pa) 0.15 0.97 637 0.56 1.18 752 0.95 1.43 886 1.25 1.66 1009 1.93 2.33 1358

[0079] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to specific embodiments. Obviously, many modifications and variations are possible based on the contents of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. An in-situ evaluation method for yield shear stress of wet sprayed concrete adhered to a sprayed surface, characterized in that: The following steps are involved: 1) Based on the actual wet spraying concrete mix ratio and the type and flow rate of the matching accelerator, ultrasonic velocity observations were first conducted on wet spraying concrete mixtures without accelerators. The change in ultrasonic velocity with hydration time from the time the concrete leaves the concrete machine to the time of initial setting was recorded. The "linear growth segment" of ultrasonic velocity was intercepted to determine the hydration time range of this stage. The "linear growth segment" of ultrasonic velocity is the "linear growth segment" of the three stages of ultrasonic velocity change with concrete mixture hydration time: "almost no velocity increase", "linear velocity increase", and "slow velocity increase". The slope of change in this stage is the largest. 2) Within the specified time range of the ultrasonic velocity "linear growth section", the penetration strength, ultrasonic velocity and yield shear stress are tested simultaneously. The three technical indicators are tested at corresponding times, and the number of measuring points for each indicator is not less than 5; 3) Based on the quantitative relationship between penetration strength and ultrasonic velocity in the "linear growth section" of ultrasonic velocity, and combined with the measured data of penetration strength and ultrasonic velocity, the least squares method is used to calculate the parameters α, β, ζ, and ε in the quantitative relationship expression; The quantitative relationship between the penetration intensity and ultrasonic velocity is expressed as follows: Where: P is the penetration strength, unit is MPa; υ is the ultrasonic velocity, unit is m / s; α, β, ζ, ε are all constants; 4) Based on the quantitative relationship between the yield shear stress and ultrasonic velocity in the "linear growth section" of ultrasonic velocity, and combined with the measured data of yield shear stress and ultrasonic velocity, the least squares method was used to determine the parameters θ, λ, and δ in the quantitative relationship. The quantitative relationship between the yield shear stress and the ultrasonic velocity is expressed as follows: τ0=θe υ / λ +d Where: τ0 is the yield shear stress, unit: Pa; θ, λ, and δ are all constants; 5) According to the quantitative relationship expression between yield shear stress and penetration strength, the above-mentioned known parameters α, β, ζ, ε, θ, λ and δ are substituted as the basis for in-situ evaluation of yield shear stress of wet shotcrete; The quantitative relationship between the yield shear stress and the penetration strength is expressed as follows: 6) Record the mixing time of wet spraying concrete and accelerator, wait for the concrete jet to adhere to the sprayed surface, and then start testing the penetration strength. Record each penetration strength measurement and test time. Combined with the quantitative relationship expression between yield shear stress and penetration strength, convert the yield shear stress according to the measured penetration strength.

2. The in-situ evaluation method for yield shear stress of wet sprayed concrete adhered to a sprayed surface according to claim 1, characterized in that: The penetration strength is tested using a handheld penetration resistance device. The probe cross-section is circular, with a diameter of 4mm to 6mm, a measuring range of 200N to 500N, a penetration depth of 25mm, and a slow and uniform loading method. The single-point test takes 10s. The penetration strength is calculated as follows: Where: F is the penetration resistance, unit is N; d is the diameter of the measuring needle, unit is mm.

3. The in-situ evaluation method for yield shear stress of wet sprayed concrete adhered to a sprayed surface according to claim 1, characterized in that: The yield shear stress of the wet sprayed concrete mixture without accelerator was tested by a paddle rotational rheometer using a ramp acceleration shear rate control mode with a shear rate change acceleration of 0.1s. -2 ~0.5s -2 To ensure that the test time is in the "linear growth section" of ultrasonic velocity, the sample is first loaded into the rheometer, and the test is started at the scheduled time. The shear stress and shear rate are recorded simultaneously, and the yield shear stress is calculated in combination with the Bingham model. The model expression is: Where: τ is shear stress, unit: Pa; η is the plastic viscosity, unit is Pa·s; is the shear rate, unit is s -1 .

4. The in-situ evaluation method for yield shear stress of sprayed concrete adhered to a sprayed surface according to claim 1, characterized in that: The ultrasonic velocity observation is the ratio of the ultrasonic observation distance to the time taken to pass the observation distance, i.e., the wave time, and the calculation expression is as follows: Where: s is the ultrasonic observation distance, unit is mm; t is the ultrasonic time, unit is μs.

5. The in-situ evaluation method for yield shear stress of wet sprayed concrete adhered to a sprayed surface according to claim 4, characterized in that: The ultrasonic observation distance is not less than 150 mm.

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