A device and method for detecting the hardness of concrete in road and bridge construction

Abstract

The application relates to the technical field of hardness detection, in particular to a device and method for detecting the hardness of concrete in road and bridge construction, which comprises the following steps: collecting the inclination angle of a probe, the rebound value of the concrete surface, the emission of ultrasonic waves from an ultrasonic detector in the probe to the concrete interior, the acquisition of the sound velocity value of the ultrasonic waves propagating at different depth positions in the concrete, and the collection of the temperature of the concrete surface at each time; correcting the rebound value and the sound velocity value, constructing a heat conduction differential equation and a definite condition, acquiring the temperature and temperature gradient of the concrete at each depth position, compensating the corrected sound velocity value, and calculating the rebound contribution weight; acquiring a rebound hardness model and a sound velocity hardness model; determining the hardness of the concrete at each depth position, and detecting the hardness of the concrete in road and bridge construction in real time. The application can more comprehensively reflect the internal quality of the concrete and improve the hardness detection accuracy of the concrete structure such as roads and bridges.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of hardness detection, in particular to a device and method for detecting the hardness of concrete in road and bridge construction. BACKGROUND

[0002] In the construction process of large concrete structures such as roads and bridges, as the core bearing material, the hardening process and internal quality of the concrete directly affect the load-carrying capacity, deformation resistance and durability of the structure. By detecting the hardness of the concrete structure, the strength and hardening state of the concrete from the surface to the interior can be determined in real time, and problems such as insufficient strength and internal defects caused by improper pouring process, curing conditions or material ratio can be found in time, so as to avoid safety accidents such as structure cracking, load failure and even collapse caused by insufficient concrete strength, and to ensure the long-term safety and stability of the road and bridge structure.

[0003] The traditional concrete hardness detection method generally performs single detection based on the assumption of vertical incidence, without considering the deviation of the incidence angle caused by the incomplete fitting of the curved surface structure such as the arch rib of the road and bridge, which can significantly affect the accuracy of the rebound value measured by the rebound method and the propagation path of the ultrasonic wave in the ultrasonic method, and further cause errors in the evaluation of the hardness of the concrete. Secondly, the gradient change of the internal temperature of the concrete can affect the sound velocity of the ultrasonic wave propagation, resulting in thermal distortion in the measurement of the sound velocity of the ultrasonic wave, so that the continuous hardness distribution of the concrete from the surface to the interior under the curved surface structure of the road and bridge cannot be accurately reflected, and it is difficult to accurately evaluate the hardness of the concrete structure such as the road and bridge. SUMMARY

[0004] In order to solve the above technical problems, a device and method for detecting the hardness of concrete in road and bridge construction are provided to solve the existing problems.

[0005] The technical problem of the application is solved by providing a device and method for detecting the hardness of concrete in road and bridge construction, comprising the following steps:

[0006] In the first aspect, the application provides a method for detecting the hardness of concrete in road and bridge construction, which comprises the following steps:

[0007] The probe integrating multiple detection instruments is attached to the surface of the concrete in road and bridge construction, the inclination angle of the probe, the rebound value of the concrete surface, the ultrasonic detector in the probe emitting ultrasonic waves to the interior of the concrete, the sound velocity value of the ultrasonic waves propagating at different depths in the concrete, and the temperature of the concrete surface at different times are collected; based on the inclination angle, the rebound value and the sound velocity value are corrected respectively;

[0008] Based on Fourier's law of heat conduction and energy conservation, a differential equation for heat conduction and boundary conditions are constructed. Based on the boundary conditions, the differential equation for heat conduction is solved using the finite difference method to obtain the temperature of the concrete at each depth. Combined with the temperature of the concrete surface, the temperature gradient of the concrete at each depth is determined. The corrected sound velocity value is then compensated to obtain the compensated sound velocity value of the concrete at each depth.

[0009] By drilling and sampling multiple groups of concrete test blocks of different strength grades, the rebound value and hardness of the core samples measured during the rebound test were analyzed, and the rebound contribution weight of the concrete at each depth was calculated.

[0010] After conducting rebound tests and ultrasonic tests on multiple groups of concrete specimens of different strength grades, the relationship between the rebound value and ultrasonic velocity measured on the surface of the concrete specimens and the strength of the concrete specimens was analyzed, and rebound hardness model and ultrasonic velocity hardness model were obtained respectively.

[0011] Based on the corrected rebound value and rebound hardness model, the compensated sound velocity value and sound velocity hardness model, and combined with the rebound contribution weight, the hardness of concrete at each depth is determined, and the hardness of concrete in road and bridge construction is detected in real time.

[0012] Preferably, the correction of the rebound value and the speed of sound includes:

[0013] Corrected rebound value The calculation formula is: ,in, The rebound value is the original measurement. The tilt angle, It is a cosine-valued function;

[0014] Concrete at depth Corrected sound speed value The calculation formula is: ,in, In depth The original measured sound speed value.

[0015] Preferably, the differential equation for heat conduction is: ,in, represent t At this moment, the concrete is at a certain depth The temperature at that location This indicates the depth of the concrete, where t represents time. First, the thermal diffusivity; second, the thermal diffusivity. ,in, This indicates the thermal conductivity of concrete. and These represent the density and specific heat capacity of concrete, respectively. The change per unit time This represents a differential unit of concrete in the depth direction.

[0016] Preferably, the boundary conditions include initial conditions and boundary conditions, specifically:

[0017] Initial conditions: ,in, This indicates the depth of the concrete at the initial time t=0. The temperature at that location For pouring temperature;

[0018] First type of boundary condition: ,in, For concrete surface at t Temperature at any moment The concrete surface measured by the temperature sensor t Temperature at any moment;

[0019] Second type of boundary condition: ,in, For a given heat flow, The thermal conductivity of concrete;

[0020] Third type of boundary condition: ,in, The surface heat transfer coefficient, The temperature of the surrounding medium.

[0021] Preferably, the concrete at a depth Temperature gradient at The calculation formula is: .

[0022] Preferably, the concrete at a depth Compensated sound speed value The calculation formula is: ,in, For concrete at depth The corrected speed of sound value, This is the preset influence coefficient.

[0023] Preferably, the calculation of the rebound contribution weight of concrete at each depth location includes:

[0024] Multiple sets of concrete test blocks of different strength grades were selected. Core samples were drilled from each concrete test block at preset depth intervals. Rebound tests were performed on the surface of the core samples and the surface of each concrete test block using a rebound hammer. The rebound values ​​at the corresponding depths of the core samples were recorded and denoted as . , record the rebound value of the surface of each concrete test block as ;

[0025] Place the core sample and each concrete test block under the pressure testing machine respectively, measure the true hardness of the depth corresponding to the core sample, record it as , and record the true hardness of the surface of each concrete test block as ;

[0026] The calculation formula of the rebound reliability of each concrete test block at the depth is: ; the slope of the fitting straight line is taken as the attenuation coefficient by linear fitting the rebound reliability of all concrete test blocks at different depths;

[0027] The calculation formula of the rebound contribution weight of concrete at the depth is: , wherein is the attenuation coefficient, represents the depth.

[0028] Preferably, the rebound hardness model and the sound velocity hardness model are obtained respectively, comprising:

[0029] Select multiple groups of concrete test blocks with different strength grades, perform rebound tests on the surface of the concrete test blocks, select multiple test points on the surface of each concrete test block, and take the average value of the rebound values of all test points as the rebound value of the surface of each concrete test block;

[0030] Emit ultrasonic waves to the concrete test block multiple times through the ultrasonic detector, and obtain the average value of the multiple measured sound velocity values as the sound velocity value of each concrete test block;

[0031] Drill core samples from each concrete test block, and test the compressive strength of the core sample by the pressure testing machine as the true hardness of each concrete test block;

[0032] Perform quadratic polynomial fitting on the rebound value and the true hardness corresponding to all concrete test blocks, obtain the fitted quadratic polynomial function, and record it as the rebound hardness model;

[0033] Perform exponential fitting on the sound velocity value and the true hardness corresponding to all concrete test blocks, obtain the fitted exponential function, and record it as the sound velocity hardness model.

[0034] Preferably, the calculation formula of the hardness of concrete at the depth L is: , wherein is the rebound contribution weight of concrete at the depth L, is the corrected rebound value, the compensated sound velocity value, representing a rebound hardness model, representing a sound velocity hardness model.

[0035] In a second aspect, the embodiments of the present application also provide a device for detecting the hardness of concrete in road and bridge construction, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, and the processor implements the steps of the method for detecting the hardness of concrete in road and bridge construction according to any one of the preceding embodiments when executing the computer program.

[0036] The present application has at least the following beneficial effects:

[0037] The present application corrects the rebound value and the sound velocity value by the inclination angle of the probe to obtain the corrected rebound value and the corrected sound velocity value, which has the beneficial effect of correcting by the inclination angle to eliminate the incident deviation phenomenon caused by the incomplete adhesion of the probe to the curved surface structure of the road and bridge arch rib, so that the corrected rebound value and the corrected sound velocity value both reflect the measurement results when the incident is perpendicular; the heat conduction differential equation and the definite condition are constructed, the heat conduction differential equation is solved based on the definite condition by using the finite difference method, and the temperature of the concrete at each depth position is obtained, which has the beneficial effect of considering the temperature field distribution in the concrete structure to facilitate subsequent temperature compensation of the sound velocity value of the ultrasonic wave based on the temperature at different depth positions; the temperature gradient of the concrete at each depth position is determined to compensate the corrected sound velocity value to obtain the compensated sound velocity value of the concrete at each depth position, which has the beneficial effect of eliminating the influence of the gradient change of the temperature of the concrete structure on the sound velocity value by temperature compensation of the sound velocity value of the ultrasonic wave, avoiding the interference of the thermal effect on the propagation speed of the ultrasonic wave, and improving the accuracy of the ultrasonic detection; the rebound contribution weight of the concrete at each depth position is calculated, which has the beneficial effect of considering the change relationship between the rebound value and the hardness to evaluate the reference of the rebound value to the hardness at different depth positions and quantify the reliability of the rebound method at different depths; the rebound hardness model and the sound velocity hardness model are obtained respectively, which has the beneficial effect of evaluating the change relationship between the rebound value and the hardness of the concrete test block and the change relationship between the sound velocity value and the hardness of the concrete test block through experiments, and constructing the prediction method of the hardness of the concrete based on the rebound value and the prediction method of the hardness of the concrete based on the sound velocity value respectively; the hardness of the concrete at each depth position is determined, which has the beneficial effect of fusing the hardness of the two hardness detection methods by the rebound contribution weight, comprehensively evaluating the hardness distribution of the concrete structure, and more comprehensively reflecting the internal quality of the concrete to improve the accuracy of the hardness detection of the concrete structure such as road and bridge. BRIEF DESCRIPTION OF DRAWINGS

[0038] A method for detecting the hardness of road and bridge construction concrete is further described in detail below with reference to the accompanying drawings.

[0039] Figure 1 A step flow chart of the method for detecting the hardness of road and bridge construction concrete provided by the embodiment of the application is shown in

[0040] Figure 2 A step flow chart of the method for detecting the hardness of road and bridge construction concrete provided by the embodiment of the application is shown in DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the application more clear, the device and method for detecting the hardness of road and bridge construction concrete are further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the application and do not limit the application.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0043] Reference is made to Figure 1 A step flow chart of the method for detecting the hardness of road and bridge construction concrete provided by the embodiment of the application is shown in

[0044] Step 1, the probe integrated with multiple detection instruments is attached to the surface of the road and bridge construction concrete, the inclination angle of the probe, the rebound value of the concrete surface, the ultrasonic detector in the probe emitting ultrasonic waves to the inside of the concrete, the sound speed value of the ultrasonic waves propagating at different depth positions in the concrete, and the temperature of the concrete surface at different time are collected; based on the inclination angle, the rebound value and the sound speed value are corrected respectively to obtain the corrected rebound value and the corrected sound speed value.

[0045] As the main material of bridge structure, the hardness of concrete directly affects the stability and service life of the whole bridge. In the process of road and bridge construction, the detection of concrete hardness is not only the core link of engineering quality control, but also an important guarantee for the bridge to withstand various loads and resist environmental influences in the use process. The traditional concrete hardness detection method generally uses ultrasonic method or rebound method for detection. Among them, the rebound method uses a spring-driven weight to measure the rebound distance after the concrete surface is hit, to evaluate the hardness of the concrete. The ratio of this distance to the initial spring length is the rebound value. The ultrasonic method is a non-destructive detection method that uses the characteristics of sound wave propagation in concrete to evaluate the elastic properties and internal quality of concrete, to realize the detection of concrete hardness. When ultrasonic waves pass through concrete, they interact with particles, pores, cracks and other materials in the material, causing changes in ultrasonic velocity. The velocity can be used to infer the hardness of the concrete. Specifically, the greater the density of the concrete, the higher the hardness and the higher the velocity. If the internal pores of the concrete are more, the density of the concrete is smaller, and the velocity of the ultrasonic wave in the concrete is lower, and the corresponding hardness is lower.

[0046] However, the detection process of single ultrasonic method or rebound method has certain limitations. When using the rebound method, only the hardness of the concrete surface can be reflected, and the internal hardness cannot be evaluated. In addition, the rebound needs to maintain the flatness of the concrete surface. The ultrasonic method uses a single velocity to estimate the hardness of the concrete, and the velocity mainly reflects the dynamic elasticity of the concrete. When the hardness of the concrete is high, the dynamic elasticity index changes very little, causing the velocity to change slightly, which leads to inaccurate velocity detection and greatly affects the accuracy. Therefore, the ultrasonic rebound comprehensive method is used to measure the hardness of the concrete, to compensate for the shortcomings of the two detection methods.

[0047] However, in the concrete pouring of bridge arch ribs and other curved structures, due to the curvature characteristics of the arch rib curve, the rebound instrument and ultrasonic detector are difficult to completely vertically adhere to the concrete surface, causing the rebound instrument and ultrasonic detector to rebound and signal emission at an incident angle, resulting in deviation in the detection results. Secondly, in the road and bridge construction concrete, there is a temperature gradient inside the concrete, and the temperature change will affect the propagation speed of the ultrasonic wave, further causing deviation in the calculation of the velocity.

[0048] Therefore, the rebound hammer, the ultrasonic detector, the MEMS three-axis tilt sensor and the patch Pt100 temperature sensor are integrated into the same detection device probe, the test points on the concrete surface of the bridge arch rib are selected for the rebound experiment, the MEMS three-axis tilt sensor in the probe collects the tilt angle of the probe by detecting the component of the gravity acceleration on the sensitive axis, the rebound hammer in the probe collects the rebound value of the concrete surface, the ultrasonic detector in the probe obtains the ultrasonic signal, and the ultrasonic velocity value of the concrete at different depth positions is calculated according to the time interval from the emission to the reception of the ultrasonic signal, and the temperature sensor in the probe collects the temperature of the concrete surface at different time;

[0049] In the embodiment, the collection frequency of the temperature sensor is 10 Hz, and as other implementation manners, the implementer can set it according to the actual situation.

[0050] It should be noted that the transmitting end of the ultrasonic detector is a 1MHz piezoelectric transducer, the receiving end is a same-frequency piezoelectric transducer, the distance between the transducers is 50mm, and as other implementation manners, the implementer can set it according to the actual situation, wherein the calculation of the ultrasonic velocity value is a known technology, and will not be described here.

[0051] In an ideal case, the probe is completely perpendicular to the concrete surface, at this time, the impact energy is completely transmitted along the normal direction of the concrete surface, and the rebound value measured reflects the true hardness of the concrete surface; however, when the concrete surface of the curved structure such as the bridge arch rib is detected, due to the difficulty of the probe to completely vertically adhere to the concrete surface, there is an inclination angle between the probe and the concrete surface, then the impact energy is no longer completely transmitted along the normal direction, but is divided into two components, respectively, the component perpendicular to the concrete surface and the component parallel to the concrete surface, the component parallel to the surface energy will be lost, resulting in low or distorted rebound value, therefore, the rebound value is corrected by the inclination angle, to represent the component perpendicular to the concrete surface, specifically:

[0052]

[0053] wherein, is the corrected rebound value, is the original measured rebound value, is the inclination angle, is the cosine value function.

[0054] Secondly, when the ultrasonic wave incidence direction deviates from the normal, the propagation path is lengthened due to the angle inclination, and the reflection and refraction characteristics of the ultrasonic wave at the concrete-air interface change, which directly affects the accuracy of the velocity calculation; wherein the propagation of the ultrasonic wave in the concrete can be approximated as straight line propagation, when the incidence angle of the ultrasonic wave is When the actual propagation path length is longer than the vertical path length, the relationship between the actual propagation path length and the vertical path length is as follows:

[0055]

[0056] in, This is the actual propagation path length. This represents the vertical path length. The tilt angle, It is a cosine-valued function.

[0057] With the propagation time of ultrasound remaining constant, since the speed of sound equals the path length divided by the propagation time, the original speed of sound value is corrected to characterize the speed of sound under perpendicular incidence. Specifically:

[0058]

[0059] in, For concrete at depth The corrected speed of sound value, In depth The original measured sound speed value, The tilt angle, It is a cosine-valued function.

[0060] It should be noted that, This indicates the speed of sound when an ultrasonic wave is incident perpendicularly.

[0061] It should be noted that by correcting the rebound value, the mechanical properties of the concrete surface layer are accurately reflected in the rebound test, avoiding measurement deviations caused by the tilt angle. Secondly, the sound velocity value is corrected to rectify path errors in the sound velocity calculation, ensuring the inversion accuracy of signals from the subsurface layer and internal structure of the concrete, and providing reliable basic data for multimodal fusion. Therefore, by eliminating the influence of the tilt angle caused by incomplete surface fit on the deviation of the rebound test and ultrasonic testing, the unique errors in the testing scenarios of curved structures such as bridge arch ribs are resolved.

[0062] Thus, the temperature of the concrete surface at each moment, the rebound value of the concrete surface after correction, and the sound velocity value of the concrete at different depths inside the concrete after correction are obtained.

[0063] Step 2: Based on Fourier's law of heat conduction and energy conservation, construct the differential equation of heat conduction and boundary conditions. Based on the boundary conditions, solve the differential equation of heat conduction using the finite difference method to obtain the temperature of the concrete at each depth. Combined with the temperature of the concrete surface, determine the temperature gradient of the concrete at each depth. Compensate the corrected sound velocity value to obtain the compensated sound velocity value of the concrete at each depth.

[0064] In the concrete structure of road and bridge construction, there is often an imbalance in the exchange of internal and external heat and generation. For example, the hydration reaction after concrete pouring will continuously release heat, and the internal heat in large volume or thick layer structure is difficult to dissipate quickly, which is easy to form heat accumulation. Secondly, the surface layer of concrete is directly in contact with the external environment, and is affected by environmental factors such as temperature, sunlight, wind, and precipitation, and the heat dissipation speed is much faster than the internal, resulting in a significant temperature difference along the depth direction. Among them, the surface temperature of the concrete fluctuates more obviously with the environment, while the internal temperature is higher due to heat accumulation and changes gently. This temperature gradient along the depth direction is formed, and the greater the pouring thickness, the more intense the hydration heat release, and the more significant the environmental temperature change, the more obvious the temperature gradient.

[0065] Furthermore, there is a significant temperature gradient in the concrete, and temperature changes will affect the change of ultrasonic speed value. If the temperature interference is not eliminated, the reliability of ultrasonic detection will be greatly reduced, and then the hardness detection will have errors.

[0066] Based on the above analysis, the patch type Pt100 temperature sensor can only collect the temperature of the surface of the concrete, while the heat conduction in the concrete is a one-dimensional stable or unstable heat diffusion process along the depth. Based on the Fourier heat conduction law, the heat conduction differential equation is:

[0067]

[0068] Among them, represents t the temperature of the concrete at depth at time t, represents the depth position of the concrete, t represents time, is the thermal diffusion coefficient, is the change per unit time, is the differential unit of the concrete in the depth direction;

[0069] Secondly, the thermal diffusion coefficient , wherein, represents the thermal conductivity of the concrete, represents the density of the concrete and represents the specific heat capacity of the concrete.

[0070] It should be noted that the thermal conductivity, density and specific heat capacity are inherent parameters of the concrete material, which can be obtained through the construction manual. Secondly, the heat conduction equation describes the change of temperature with time and depth in the process of heat conduction in the concrete. By measuring the temperature of the surface of the concrete, the hardness of the internal structure of the concrete can be inferred.

[0071] Second, in order to solve the heat conduction partial differential equation, the heat conduction differential equation needs to be designed to determine the condition, including: initial condition and boundary condition:

[0072] Initial condition: is the temperature field state of concrete at initial time, that is, the temperature of concrete at the time of concrete pouring, at the initial time =0, Wherein, The pouring temperature, in this embodiment, the temperature of concrete at the time of pouring Obtained through the construction manual.

[0073] The first type of boundary condition: the temperature of the concrete boundary Wherein, L=0, represents the surface of the concrete, The temperature of the concrete surface at the time of t The temperature of the concrete surface at the time of Measured by the temperature sensor; t

[0074] The second type of boundary condition: the heat flux of the given concrete surface is a function of time, that is:

[0075]

[0076] Wherein, The given heat flux, The thermal conductivity of concrete;

[0077] It should be noted that before the concrete is poured, the thermocouple is pre-embedded at an interval of 5 cm. During the pouring process and the initial stage of solidification, the temperature at each depth position is recorded in real time, the ratio between the temperature difference at adjacent depth positions and the interval of adjacent depth positions is calculated, the initial temperature gradient is calculated, and the heat flux is determined through the initial temperature gradient and the thermal conductivity of concrete.

[0078] The third type of boundary condition: the concrete is in contact with the external medium such as air, and there is a phenomenon of convective heat transfer, that is:

[0079]

[0080] Wherein, The thermal conductivity of concrete, The surface heat release coefficient, The temperature of the surrounding medium, such as air temperature, Indicates the depth; second, the size of the surface heat release coefficient Affects the heat release rate of concrete, and the surface heat release coefficient is related to factors such as wind speed, wherein the approximate calculation method of the surface heat release coefficient of concrete is:

[0081] ​

[0082] wherein, represents the wind speed, is an exponential function with a natural constant as a base.

[0083] Based on the definite condition, the heat conduction differential equation is solved by using the finite difference method, the time derivative is approximated by the forward difference, and the spatial second-order derivative is approximated by the central difference, so as to calculate the temperature at different depth positions at each time;

[0084] It should be noted that the process of calculating the heat conduction differential equation by using the finite difference method is a known technology, which will not be described here.

[0085] Based on the temperature of the concrete at each depth position at the time and the temperature of the concrete surface, the temperature gradient of the concrete at the depth position at each time is calculated;

[0086]

[0087] wherein, is the temperature gradient of the concrete at the depth position at the time, is the temperature of the concrete surface at the time, is the temperature of the concrete at the depth position at the time, represents the depth.

[0088] Further, based on the temperature gradient, the corrected sound speed value at different depth positions is compensated, specifically:

[0089]

[0090] wherein, is the compensated sound speed value of the concrete at the depth position, is the corrected sound speed value of the concrete at the depth position, is a preset influence coefficient, which represents the change amount of the sound speed value of the ultrasonic wave caused by a unit temperature gradient;

[0091] Therefore, the corrected sound speed value is compensated by the temperature gradient of the concrete at different depth positions at this time.

[0092] In this embodiment, under the condition of controllable temperature, for example, in a constant temperature box, by applying different temperature gradients Wherein, the concrete test block is same with the concrete at the bridge arch rib in mix proportion and age, using the ultrasonic detector, recording the sound velocity value change corresponding to different temperature gradient, after forming two-dimensional array of each temperature gradient and its corresponding sound velocity value change, linear fitting is carried out, the slope of the fitting straight line is obtained, that is, the preset influence coefficient It should be noted that the least square method is used for linear fitting, wherein the least square method is a known technology and will not be described here. Thus, the sound velocity value of the ultrasonic wave is compensated by the temperature change, and the influence of temperature on the sound velocity value is eliminated.

[0093] Thus, the compensated sound velocity value of the concrete at each depth position is obtained.

[0094] Step 3, by drilling core sampling on multiple groups of concrete test blocks with different strength grades, analyzing the rebound value measured in the rebound test and the hardness change of the core sample after core sampling, calculating the rebound contribution weight of the concrete at each depth position; after the rebound test and ultrasonic detection of multiple groups of concrete test blocks with different strength grades, analyzing the change relationship between the rebound value measured on the surface of the concrete test block, the sound velocity value of the ultrasonic wave and the strength of the concrete test block, respectively, obtaining the rebound hardness model and the sound velocity hardness model; based on the corrected rebound value and the rebound hardness model, the compensated sound velocity value and the sound velocity hardness model, combining the rebound contribution weight, determining the hardness of the concrete at each depth position, and detecting the hardness of the road and bridge construction concrete in real time.

[0095] Further, the rebound method is sensitive to the surface hardness, but the impact energy decays sharply with depth, and cannot accurately reflect the hardness characteristics of the concrete inside the subsurface; although the ultrasonic detection method can penetrate the subsurface, its accuracy is affected by temperature. The reliability of the two methods at different depths presents complementary characteristics, the rebound value is more reliable in the shallow layer, and the ultrasonic signal is more stable in the subsurface. Therefore, the advantages of the two methods need to be dynamically integrated through weight distribution, and in the hardness detection of the bridge arch rib mass concrete, if the same weight is given to all depths, it will lead to excessive dependence on unreliable rebound value for deep layer hardness evaluation, resulting in large deviation. By setting dynamic distribution weight changing with depth, the rebound value plays a dominant role in its surface layer, avoiding detection deviation of single mode at non-advantageous depth, and realizing continuous hardness evaluation from surface layer to subsurface.

[0096] Based on the above analysis, the attenuation characteristics of the rebound value at different depth positions in the concrete are designed as an exponential function, and thus the rebound contribution weight at each depth position is:

[0097]

[0098] Wherein, is the rebound contribution weight of the concrete at the depth The rebound contribution weight at the depth L, The preset attenuation coefficient is The depth is represented.

[0099] In the embodiment, the preset attenuation coefficient is The specific experimental operation is that: 3 groups of concrete test blocks with different intensity grades are selected, for example, 3 groups of C25, C30 and C35 concrete test blocks are selected, a core sample is drilled every 5 cm in the 0-50 cm depth interval of each concrete test block, the surface of the core sample is tested by the rebound hammer, the rebound value corresponding to the depth of the core sample is recorded, and the rebound value is recorded as ; secondly, the core sample is placed under the pressure testing machine, the real hardness of the depth corresponding to the core sample is measured, and the real hardness is recorded as , and the surface of each concrete test block is rebound tested, the rebound value of the surface of each concrete test block is recorded, and the rebound value is recorded as , and the real hardness of the surface of each concrete test block is measured, and the real hardness is recorded as , then the rebound reliability is calculated , the rebound reliability of all concrete test blocks at different depths is linearly fitted, the slope of the fitted straight line is taken as the attenuation coefficient , in the embodiment, the preset attenuation coefficient is ; the depth is inversely calculated by the propagation time of the ultrasonic wave and the compensated sound velocity value, and then the rebound contribution weight is calculated.

[0100] It should be noted that the greater the depth L is, the smaller the rebound contribution weight is, which indicates that the contribution of the rebound value to the hardness decays with the depth, at this time, the reference of the rebound value should be reduced, and the reference of the ultrasonic velocity to the hardness detection should be increased.

[0101] Secondly, the rebound value and the velocity of the ultrasonic wave are physical signals that indirectly reflect the hardness of the concrete, rather than direct hardness indicators. The rebound method characterizes the surface plastic deformation ability by the rebound energy of the impact hammer, and the ultrasonic method reflects the material density and elastic properties by the sound velocity, both of which need to establish a quantitative mapping relationship with the actual hardness of the concrete to be used for engineering evaluation. In addition, the mix proportion and curing conditions of the concrete will significantly affect the correlation between the signal and the hardness, therefore, a specific mapping model must be established through experimental calibration to avoid scene adaptation deviation of the general empirical formula and ensure the engineering reliability of the detection result.

[0102] Therefore, by selecting multiple groups of concrete test blocks of different strength grades, for example, three groups of concrete test blocks of C25, C30, and C35, and curing the three groups of concrete test blocks for 28 days, a rebound test was conducted on the surface of the concrete test blocks. Sixteen test points were selected on the surface of each concrete test block, and the average value of the rebound values ​​corresponding to the 10 valid test points was taken as the rebound value of each concrete test block. At the same time, the sound velocity was measured using an ultrasonic testing instrument with a transducer spacing of 100 mm. The average value of the sound velocity measured three times for each concrete test block was taken as the sound velocity value of each concrete test block. Core samples were drilled from each concrete test block, with a core sample diameter of 100 mm and a height-to-diameter ratio of 1:1. The compressive strength of the core sample was tested using a pressure testing machine as the true hardness of each concrete test block.

[0103] Because the impact energy and plastic deformation in the rebound test exhibit nonlinear characteristics, the rebound value of the construct has a quadratic polynomial relationship with the surface hardness; the sound velocity increases with the density or strength of the concrete, but a threshold effect exists due to the influence of microcracks. Therefore, the sound velocity value of the construct has an exponential relationship with the internal hardness.

[0104] For all concrete test blocks, the rebound value and the true hardness are fitted with a quadratic polynomial to obtain the fitted quadratic polynomial function, which is denoted as the rebound hardness model.

[0105] The expression for the springback hardness model is as follows: ,in, , , The fitting coefficients for the springback hardness model are denoted as . This is the rebound value. This indicates the hardness corresponding to the rebound value R.

[0106] In this embodiment, a non-least squares method is used for quadratic polynomial fitting. The least squares method is a well-known technique and will not be described in detail here.

[0107] For all concrete test blocks, the sound velocity value and the actual hardness are subjected to exponential fitting to obtain the fitted exponential function, which is denoted as the sound velocity hardness model.

[0108] The expression for the sound velocity hardness model is as follows: ,in Indicates the speed of sound. , , These are the fitting parameters for the sound velocity hardness model. Indicates the speed of sound The corresponding hardness.

[0109] In this embodiment, a non-least squares method is used for exponential fitting. The least squares method is a well-known technique and will not be described in detail here.

[0110] The formula for calculating the hardness of the concrete at each depth position is:

[0111]

[0112] wherein, is the hardness of the concrete at depth L, is the rebound contribution weight of the concrete at depth L, is the corrected rebound value, is the compensated sound speed value, represents a rebound hardness model, represents a sound speed hardness model.

[0113] It should be noted that the fusion is performed by the corrected rebound value and the corrected and temperature compensated sound speed value, in the shallow layer of the concrete, the hardness detection mainly depends on the rebound value, in the deep layer of the concrete, the hardness detection mainly depends on the sound speed value, so as to comprehensively evaluate the hardness condition of the concrete inside, wherein the step flow chart of the hardness acquisition method provided in the embodiment is as shown in Figure 2 .

[0114] Based on the interpolation of the hardness at different depth positions in the concrete in the road and bridge construction, the continuous three-dimensional hardness profile is converted, the inside of the concrete is visualized, the three-dimensional hardness cloud chart is generated, so as to reflect the hardness condition of the inside of the concrete, and the high-precision, full-depth, three-dimensional visualized detection of the hardness of the concrete is realized.

[0115] It should be noted that the generation of the three-dimensional hardness cloud chart is a known technology, which will not be repeated here.

[0116] Based on the same inventive concept as the above method, the embodiment of the present application also provides a detection device for the hardness of the concrete in the road and bridge construction, which comprises a memory, a processor and a computer program stored in the memory and running on the processor, and the processor executes the computer program to realize the steps of the method in any one of the above-mentioned detection methods for the hardness of the concrete in the road and bridge construction.

[0117] It should be understood that, although Figure 1 the steps in the flow chart are displayed in sequence according to the arrow, these steps are not necessarily executed in sequence according to the arrow. Unless otherwise stated herein, the execution of these steps has no strict order limitation, and these steps can be executed in other order. Moreover, Figure 1At least one of the steps in the above embodiments can include a plurality of sub-steps or a plurality of stages, which are not necessarily executed at the same time, but can be executed at different times, and the order of execution of the sub-steps or stages is not necessarily sequential, but can be executed in rotation or alternation with other steps or at least a part of the sub-steps or stages of other steps.

[0118] The technical features of the above embodiments can be combined in any manner. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described, but it should be understood that any combination of the technical features is within the scope of the present disclosure as long as there is no contradiction.

[0119] The above embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the present application. It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present application, and therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application, as long as it does not depart from the technical solution of the present application, is within the protection scope of the technical solution of the present application.

Claims

1. A method for detecting the hardness of concrete for road and bridge construction, characterized by, The method comprises the following steps: The probe integrating multiple detection instruments is attached to the surface of the road and bridge construction concrete, the inclination angle of the probe, the rebound value of the concrete surface, the ultrasonic detector in the probe emitting ultrasonic waves to the concrete interior, the sound velocity value of the ultrasonic waves propagating at different depth positions in the concrete, and the temperature of the concrete surface at different time are collected; the rebound value and the sound velocity value are corrected based on the inclination angle; According to the Fourier heat conduction law and the energy conservation, the heat conduction differential equation and the definite condition are constructed, the heat conduction differential equation is solved by using the finite difference method based on the definite condition, the temperature of the concrete at each depth position is obtained, the temperature gradient of the concrete at each depth position is determined in combination with the temperature of the concrete surface, the corrected sound velocity value is compensated, and the compensated sound velocity value of the concrete at each depth position is obtained; A plurality of concrete test blocks of different strength grades are selected, core sampling is performed, the rebound value measured in the rebound test and the hardness change of the core sample after the core sampling are analyzed, and the rebound contribution weight of the concrete at each depth position is calculated; After the rebound test and the ultrasonic wave detection of the plurality of concrete test blocks of different strength grades, the change relationship between the rebound value and the sound velocity value measured on the surface of the concrete test block and the strength of the concrete test block is analyzed, and the rebound hardness model and the sound velocity hardness model are obtained respectively; Based on the corrected rebound value and the rebound hardness model, the compensated sound velocity value and the sound velocity hardness model, and in combination with the rebound contribution weight, the hardness of the concrete at each depth position is determined, and the hardness of the road and bridge construction concrete is detected in real time; The correction of the rebound value and the sound velocity value comprises: The corrected rebound value The calculation formula is: Wherein, is the original measured rebound value, is the inclination angle, is the cosine value function; The sound velocity value corrected at the depth The formula for calculating the sound velocity value corrected at the depth wherein, is the sound velocity value originally measured at the depth ​​ The heat conduction differential equation is: wherein, represents t the temperature of the concrete at a depth at a time t, denotes the depth position of the concrete, t represents time, is a thermal diffusion coefficient; secondly, the thermal diffusion coefficient wherein, denotes the thermal conductivity of the concrete, and denote the density and the specific heat capacity of the concrete, respectively, is a change amount per unit time, is a differential unit in the depth direction of the concrete; The definite condition comprises an initial condition and a boundary condition, and specifically comprises: Initial conditions: wherein, T (0, x) represents the temperature of the concrete at the start time t = 0 at the depth x, is the casting temperature; First type of boundary condition: wherein, Tc(t) is the temperature of the concrete surface at time t, t Tc(t) is the temperature of the concrete surface at time t, Tc(t) is the temperature of the concrete surface at time t, t Tc(t) is the temperature of the concrete surface at time t, Second type of boundary condition: wherein, is the heat flow for a given temperature difference, is the thermal conductivity of the concrete; Third type boundary condition: wherein, is the surface heat emission coefficient, is the temperature of the surrounding medium; Concrete at depth Compensated sound speed value The calculation formula is: ,in, For concrete at depth The corrected speed of sound value, The preset influence coefficient; The calculation of the rebound contribution weight of the concrete at each depth position comprises: Selecting multiple groups of concrete test blocks of different strength grades, drilling core samples at every preset depth distance for each concrete test block, performing rebound tests on the surface of the core samples and the surface of each concrete test block respectively by using a rebound hammer, recording the rebound value of the depth corresponding to the core sample, denoted as , and recording the rebound value of the surface of each concrete test block, denoted as ; Respectively, the core sample, each concrete test block is placed under the pressure testing machine, measuring the true hardness of the core sample corresponding depth, recorded as The true hardness of each concrete test block surface is recorded as ; The rebound modulus of each concrete test block at a depth of 0.5 m is calculated according to the formula: The slope of the fitted straight line is taken as the attenuation coefficient.​ Concrete at depth rebound contribution weight at the location The calculation formula is: ,in, The attenuation coefficient is... Indicates depth; The obtaining of the rebound hardness model and the sound velocity hardness model comprises: A plurality of concrete test blocks of different strength grades are selected, the rebound test is performed on the surface of the concrete test block, a plurality of test points are selected on the surface of each concrete test block, and the average value of the rebound values corresponding to all the test points is taken as the rebound value of the surface of each concrete test block; The ultrasonic detector emits ultrasonic waves to the concrete test block multiple times, the average value of the multiple measured sound velocity values is taken as the sound velocity value of each concrete test block; Each concrete test block is core sampled, and the compressive strength of the core sample is tested by using a pressure testing machine as the true hardness of each concrete test block; The rebound value corresponding to each concrete test block and the true hardness are fitted by using a quadratic polynomial, a fitted quadratic polynomial function is obtained, and the fitted quadratic polynomial function is denoted as a rebound hardness model; The sound velocity value corresponding to each concrete test block and the true hardness are fitted by using an exponential function, a fitted exponential function is obtained, and the fitted exponential function is denoted as a sound velocity hardness model; Hardness of concrete at depth L The formula for calculating the hardness of concrete at depth L is: wherein, is the rebound contribution weight of concrete at depth L, is the corrected rebound value, is the compensated sound velocity value, denotes the rebound hardness model, denotes the sound velocity hardness model.

2. The method for detecting the hardness of concrete for road and bridge construction according to claim 1, wherein The formula for calculating the temperature gradient of concrete at depth is: .​ 3. A device for detecting the hardness of concrete in road and bridge construction, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that, The processor executes the computer program to realize the steps of the detection method of the hardness of the road and bridge construction concrete according to any one of claims 1-2.

Images