Concrete strength detection method and system

Abstract

The invention relates to the technical field of constructional engineering detection, in particular to a concrete strength detection method and system. The method comprises the following steps: placing a thermal reference block with known thermal physical characteristics in the center of a target area on the surface of to-be-detected concrete; taking the thermal reference block as a center, applying synchronous thermal pulses with the same energy to the surfaces of the concrete at the symmetrical positions on the two sides of the thermal reference block, recording the formed thermal response by using an infrared thermal imager, generating thermal response data, and forming two hot spots on the surface of the concrete; monitoring the environment temperature fluctuation by using the thermal reference block, and subtracting the quantity of the environment temperature fluctuation from the thermal response data in real time to obtain a thermal attenuation curve of the hot spots; and analyzing the isotherm contour form distortion degree of the thermal field corresponding to the thermal attenuation curve, and quantifying the isotherm contour form distortion degree as a thermal field structure polarization index. The problems of environmental interference and internal structure quantification in existing concrete strength detection are solved through a constructional engineering detection technology.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building engineering detection, and in particular to a concrete strength detection method and system. BACKGROUND

[0002] Traditional concrete strength detection methods include physical detection means such as rebound method and ultrasonic method, but these methods still face severe challenges in the field of low-strength concrete detection. Traditional rebound method and ultrasonic method show obvious insufficient sensitivity in low-grade concrete (C20 and below) detection, and the measurement curve tends to be flat in the low-strength interval, making it difficult to accurately distinguish between C15 and C10 and other similar strength grades, resulting in low detection accuracy and being easily affected by the surface hardening layer; at the same time, although the existing thermal detection method has potential, it is severely affected by external factors such as environmental temperature fluctuations, uneven surface emissivity, and air convection disturbance, lacks effective environmental noise elimination mechanism, making the measurement results have poor repeatability, and it is difficult to obtain reliable and stable data in complex on-site environment; more importantly, the existing thermal method mainly focuses on defect imaging and internal structure visualization, and has not established a stable quantitative relationship between thermal response characteristics and concrete strength, lacking effective models and theoretical support for converting thermal parameters into practical strength values.

[0003] In summary, there is an urgent need in the existing technology for a new non-destructive detection method that can accurately detect low-strength concrete in complex environments and establish a reliable correlation between thermal characteristics and strength. SUMMARY

[0004] Therefore, it is necessary to provide a concrete strength detection method and system to solve at least one of the above technical problems.

[0005] To achieve the above-mentioned purpose, a concrete strength detection method comprises the following steps:

[0006] Step S1: placing a thermal reference block with known thermal physical properties at the center of the target area on the surface of the concrete to be detected;

[0007] Step S2: applying synchronous thermal pulses with the same energy to the concrete surfaces symmetrically on both sides of the thermal reference block, and recording the thermal response formed by the infrared thermal imager to generate thermal response data, wherein two thermal spots are formed on the concrete surface;

[0008] Step S3: monitoring the environmental temperature fluctuations using the thermal reference block, and subtracting the amount of environmental temperature fluctuations from the thermal response data in real time to obtain the thermal decay curve of the thermal spot;

[0009] Step S4: analyzing the isotherm contour distortion degree of the thermal field corresponding to the thermal decay curve, and quantifying it as a thermal field structure polarization index;

[0010] Step S5: calculating the time required for the temperature of the hot spot to decay from the peak value to 37% of the peak temperature to obtain an initial effective thermal relaxation time; compensating the initial effective thermal relaxation time with a time constant using the thermal decay curve to obtain an effective thermal relaxation time;

[0011] Step S6: substituting the thermal field structure polarization index and the effective thermal relaxation time into the pre-calibrated correlation equation to calculate the estimated equivalent strength of the concrete.

[0012] The present application provides a stable reference point for subsequent measurement by introducing the thermal reference block in step S1 as a thermal reference; the signal strength is enhanced and redundancy verification is provided by using the double-sided symmetric thermal pulse method in step S2; the environmental interference factors are effectively eliminated by using the thermal reference block to monitor the environmental temperature fluctuation and compensate in real time in step S3, which greatly improves the anti-interference ability and repeatability of the measurement; the thermal field isotheral contour shape distortion degree is innovatively analyzed in step S4, which converts the internal structural inhomogeneity of the concrete into a quantifiable thermal field structure polarization index, breaking through the limitation of traditional thermal methods which only focus on the temperature decay rate; the thermal diffusion characteristics of the concrete are accurately captured by multiple time characteristic analysis and exponential fitting compensation in step S5, which improves the detection sensitivity of the low strength interval; the double-parameter strength mapping model used in step S6 considers two key factors of structural inhomogeneity and density, and introduces age and water content correction, realizing accurate non-destructive testing of low strength concrete (especially C20 and below) in complex environments on site, and providing fast and reliable technical support for safety evaluation of historical building reconstruction, temporary structure and rural self-built house.

[0013] Therefore, the present application provides a concrete strength detection method, which realizes real-time cancellation of environmental noise by introducing a thermal reference block as a dynamic environmental monitor; the shape of heat diffusion is taken as a quantitative index of the internal structural inhomogeneity of the concrete by analyzing the shape distortion degree of thermal field diffusion; and a double-parameter strength mapping model is established combined with the accurately calculated thermal relaxation time. This method ingeniously solves the problems of environmental interference and internal structure quantization, realizes an anti-interference, high-precision and simple-to-operate low-strength concrete non-destructive testing technology, and provides reliable technical support for safety evaluation of historical building reconstruction, temporary structure and rural self-built house.

[0014] Preferably, the present application also provides a concrete strength detection system for executing the concrete strength detection method as described above, which comprises:

[0015] The thermal reference block is made of silicon nitride ceramic sheet, coated with a high-emissivity black coating on the surface, and used to be placed at the center position of the surface of the concrete to be measured;

[0016] A double-head pulse heat source comprising two power-adjustable focused infrared lamps and a synchronous controller is used to apply synchronous heat pulses with the same energy to the concrete surface to form two heat spots on the concrete surface;

[0017] An infrared thermal imager with a thermal sensitivity of not less than 0.05℃ is used to continuously record the thermal response process and generate thermal response data;

[0018] A data processing unit is in communication connection with the infrared thermal imager to receive the thermal response data and in communication connection with the synchronous controller of the double-head pulse heat source to control the application of heat pulses, and the data processing unit is used to perform the following operations:

[0019] The thermal force reference block is used to monitor the environmental temperature fluctuation, and the amount of the environmental temperature fluctuation is subtracted from the thermal response data in real time to obtain a thermal decay curve of the heat spot;

[0020] The isotherm profile distortion degree of the thermal field corresponding to the thermal decay curve is analyzed, and is quantified as a thermal field structure polarization index;

[0021] The initial effective thermal relaxation time is obtained by calculating the time required for the temperature of the heat spot to decay from the peak value to 37% of the peak value, and the effective thermal relaxation time is obtained by time constant compensation on the initial effective thermal relaxation time;

[0022] The thermal field structure polarization index and the effective thermal relaxation time are substituted into a pre-calibrated correlation equation to calculate the estimated equivalent strength of the concrete;

[0023] A display unit is in communication connection with the data processing unit and is used to display the thermal response data, the thermal decay curve, the thermal field structure polarization index, the effective thermal relaxation time and the estimated equivalent strength value.

[0024] The concrete strength detection system provided by the application has precisely known thermal physical properties and stable radiation properties by using the thermal force reference block made of silicon nitride ceramic sheet, which provides a reliable reference for environmental interference elimination; the double-head pulse heat source design ensures precise control and spatial symmetry of energy input, thereby enhancing the reliability of measurement; the high-sensitivity infrared thermal imager realizes precise capture of small temperature differences, thereby improving the resolution of thermal field analysis; the data processing unit integrates core algorithms such as environmental fluctuation compensation, thermal field profile distortion analysis, thermal relaxation time calculation and strength mapping, thereby realizing automatic conversion from thermal response data to concrete strength; and the display unit intuitively presents the detection process and results, thereby facilitating on-site evaluation and decision-making. The entire system realizes portable, automated and intelligent nondestructive detection of concrete strength, is particularly suitable for on-site rapid detection of low-strength concrete, significantly reduces detection time and labor cost, improves detection accuracy and reliability, provides an efficient and practical technical means for building structure safety evaluation, and has a broad engineering application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0025] Fig. 1 It is a flow chart of steps of a concrete strength detection method;

[0026] Fig. 2 It is a structural schematic diagram of a concrete strength detection system in the application.

[0027] The purposes, functional features and advantages of the application will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0028] The technical method of the application will be described clearly and completely below with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0029] In addition, the accompanying drawings are only schematic diagrams of the application, and are not necessarily drawn to scale. The same reference signs in the drawings represent the same or similar parts, and thus repeated descriptions thereof will be omitted. Some block diagrams shown in the drawings are functional entities, and do not necessarily correspond to physically or logically independent entities. The functional entities can be implemented in the form of software, or in one or more hardware modules or integrated circuits, or in different network and / or processor methods and / or microcontroller methods.

[0030] It should be understood that although the terms "first", "second" and the like can be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of the exemplary embodiments, a first element can be called a second element, and similarly a second element can be called a first element. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0031] To achieve the above-mentioned purposes, please refer to Figs. 1-2 The application provides a concrete strength detection method, comprising the following steps:

[0032] Step S1: placing a thermal force reference block with known thermal physical properties at the center of a target area on the surface of the concrete to be detected;

[0033] In the embodiment of the present application, a test area of 1m x 1m is marked on the surface of the concrete to be tested, a thermal reference block made of silicon nitride ceramic sheet with a size of 10mm x 10mm x 1mm is placed at the center of the area, the reference block has known thermal physical properties (specific heat capacity 700J / kg·K, thermal conductivity 30W / m·K), and the surface is coated with a high-emissivity black coating with a thickness of 25±5μm and an emissivity of ε=0.95±0.02 to make it have stable radiation characteristics in the infrared wave band. The reference block is fixed to the surface of the concrete using silicone glue with a thermal conductivity of less than 0.2W / m·K, the thickness of the glue layer is controlled within 0.1mm to ensure good contact. The ambient temperature, humidity and other parameters are measured and recorded, the temperature of the reference block is collected for 30 seconds, the standard deviation of the temperature is calculated to ensure that it is less than 0.05℃, which indicates that the reference block has reached a state of thermal equilibrium, and finally the actual heat capacity value of the reference block at the current ambient temperature is calculated as the calibration heat capacity reference.

[0034] Step S2: taking the thermal reference block as the center, synchronous thermal pulses with the same energy are applied to the concrete surfaces symmetrically located on both sides of the thermal reference block, and the thermal response formed is recorded by an infrared thermal imager to generate thermal response data, wherein two thermal spots are formed on the concrete surface;

[0035] In the embodiment of the present application, two heating point positions are marked at 10cm on both sides of the thermal reference block. Two focused infrared lamps with a power of 800W are adjusted so that their beam centers are accurately aligned with the marked points, and the spot diameter is controlled within 20±2mm. The actual output energy of the two heat sources is measured using a heat flux meter, and the output energy difference of the two heat sources is controlled to be not more than ±2% by adjusting the power controller, and the typical heat flux is 3.5kW / m². An infrared thermal imager with a thermal sensitivity of not less than 0.05℃ is set, the field of view covers the entire test area, and the sampling frequency is set to 25Hz. The pulse duration of the electronic synchronization controller is set to 0.5 seconds to ensure that the two heat sources are strictly synchronized to start and stop. Start the infrared thermal imager to record, then trigger the synchronization controller to apply a 0.5-second thermal pulse to the two heating points at the same time, and continue to record the thermal response process for 60 seconds to obtain a complete double-peak thermal response spectrum.

[0036] Step S3: monitor the ambient temperature fluctuation using the thermal reference block, and subtract the amount of ambient temperature fluctuation from the thermal response data in real time to obtain the thermal decay curve of the thermal spot;

[0037] In the embodiment of the present application, the average temperature value in the 5mm*5mm area around the center point of the thermal reference block in the bimodal thermal response map is extracted to form a time series. The average value of the reference block temperature within 10 seconds before the thermal pulse is calculated as the ambient reference temperature, and then the difference between the reference block temperature series and the reference temperature is calculated to obtain the temperature fluctuation series caused by environmental factors. The temperature fluctuation series is applied to a Butterworth low-pass filter with a cutoff frequency of 0.5Hz to obtain a smooth environmental fluctuation series. The time delay (about 3.5 seconds) and the attenuation coefficient (about 0.85) are calculated according to the thermal diffusion coefficient ratio (about 30) of the thermal reference block to the concrete. The smooth environmental fluctuation series is time-shifted and amplitude-adjusted according to the conduction correction parameter to generate an environmental fluctuation compensation matrix. The corresponding value of the corresponding position in the environmental fluctuation compensation matrix is subtracted from the original thermal spot temperature curve extracted from the thermal response data to obtain a pure thermal decay curve that eliminates the environmental impact.

[0038] Step S4: analyze the isotherm contour distortion degree of the thermal field corresponding to the thermal decay curve, and quantify it as a thermal field structure polarization index;

[0039] In the embodiment of the present application, the pure thermal decay curve is analyzed to determine three characteristic time points at which the thermal spot temperature decays to 75%, 50% and 25% of the peak value. At these three time points, the isotherm contours of the thermal spot are extracted from the corrected thermal field map. The geometric center coordinates of each contour are calculated, the contour is translated to the coordinate origin, and it is converted to polar coordinates. The radial distance in 72 directions is calculated at intervals of 5°, and the average radius value is taken as the radius of the ideal circular contour. The radial distance difference between the actual contour and the ideal circular contour is calculated to form a radial deviation sequence. The radial deviation sequence is subjected to Fourier transform, and the amplitudes of the first and second components are extracted to represent the elliptical degree and biaxial asymmetry of the contour, respectively. The ratio of the standard deviation of the radial deviation sequence to the average radius is calculated to obtain a dimensionless distortion coefficient. The distortion coefficients at the three time points are weighted and averaged to obtain a comprehensive distortion index. The average value and the difference of the comprehensive distortion indexes of the two thermal spots are calculated, and finally the thermal field structure polarization index is calculated.

[0040] Step S5: calculate the time required for the temperature of the thermal spot to decay to 37% of the peak value from the peak value to obtain an initial effective thermal relaxation time; and compensate the initial effective thermal relaxation time with a time constant according to the thermal decay curve to obtain an effective thermal relaxation time;

[0041] In the embodiment of the present application, the highest temperature value and its corresponding time point are found from the pure thermal decay curve to determine the peak temperature and the peak time. The 37% (i.e. 1 / e) of the peak temperature is calculated as the characteristic threshold of heat decay. The three-point moving average filter is applied to the thermal decay curve to eliminate minor data fluctuations. Starting from the peak time, the time point when the temperature first drops to the threshold temperature is accurately determined by linear interpolation. The time interval experienced from the peak time to the threshold time point is calculated to obtain the characteristic decay time. The arithmetic mean of the characteristic decay times of the two heat spots is calculated, and the correction formula is applied according to the ambient temperature to obtain the initial effective thermal relaxation time. The exponential function fitting is performed on the thermal decay curve to extract the time constant τ_fit in the fitting parameter. The deviation rate of the initial effective thermal relaxation time and the fitting time constant is calculated, and different strategies are adopted according to the deviation rate to adjust the effective thermal relaxation time τ.

[0042] Step S6: Substitute the thermal field structure polarization index and the effective thermal relaxation time into the pre-calibrated correlation equation to calculate the estimated equivalent strength of the concrete;

[0043] In the embodiment of the present application, the thermal field structure polarization index PI and the effective thermal relaxation time τ are divided by the preset standard reference value to obtain the normalized characteristic value. The strength base value is calculated by using the binary linear regression formula. The product term of the normalized characteristic value is calculated, multiplied by the interaction coefficient, as the adjustment amount reflecting the mutual influence of the parameters. According to the estimated age and the surface water content of the concrete, the age correction coefficient and the humidity correction coefficient are calculated. The strength base value is added to the adjustment amount to obtain the corrected strength value, and then the multi-factor correction value is calculated according to the corrected strength value (F_corr), the age correction coefficient (K_age) and the humidity correction coefficient (K_moisture). The standard deviation of the multi-factor correction value and the upper and lower limit values of the 95% confidence interval are calculated. The multi-factor correction value is compared with the standard concrete strength grade (C10, C15, C20, etc.), and the concrete strength grade is determined according to the overlapping relationship of the confidence interval and the standard strength grade. Finally, the estimated equivalent strength result is output, including the numerical strength estimate value (accurate to 0.1 MPa), the 95% confidence interval and the estimated concrete strength grade, completing the whole concrete strength detection process.

[0044] Preferably, the monitoring process of the environmental temperature fluctuation in step S3 includes:

[0045] The temperature average value of the thermal reference block before the heat pulse is calculated as the temperature reference point under the stable environment;

[0046] The temperature sequence of the thermal reference block region changing with time is extracted, and the temperature reference point is subtracted to obtain the temperature fluctuation sequence caused by environmental factors;

[0047] A low-pass filter is applied to the temperature fluctuation sequence to remove random noise but retain the real environmental temperature variation trend, obtaining a smooth environmental fluctuation sequence;

[0048] According to the difference in thermal physical properties of the thermal reference block and the concrete, the attenuation coefficient and time delay of the environmental fluctuation from the thermal reference block to the thermal spot area are calculated, and a conduction correction parameter is obtained;

[0049] According to the conduction correction parameter, the smooth environmental fluctuation sequence is time-shifted and amplitude-adjusted to generate an environmental fluctuation compensation matrix;

[0050] Subtract the corresponding environmental fluctuation compensation matrix from the original thermal spot temperature curve extracted from the thermal response data to obtain a thermal decay curve that eliminates the environmental impact.

[0051] In the embodiment of the present application, when monitoring the environmental temperature fluctuation, first, the temperature values of the thermal reference block area within the first 10 seconds of the thermal pulse are sampled, the sampling frequency is 10Hz, and a total of 100 temperature data points are obtained. The sum of the 100 temperature data points is divided by 100 to calculate the average temperature value T_base, which is used as the temperature reference point under stable environment. Then, the average temperature value in the 5mm×5mm area around the center point of the thermal reference block is extracted from the double-peak thermal response map to form a time sequence T_ref(t), where t represents the time from the start of the thermal pulse, the total recording time is 60 seconds, and the sampling interval is 0.04 seconds. The environmental fluctuation sequence ΔT_env(t) is obtained by calculating T_ref(t)-T_base, which reflects the temperature fluctuation caused by pure environmental factors (such as air flow, radiation change, etc.). A Butterworth low-pass filter with a cutoff frequency of 0.5Hz is applied to the environmental fluctuation sequence ΔT_env(t), and the filter order is 3. The filter processing formula is ΔT_smooth(t)=LPF[ΔT_env(t)], where LPF represents the low-pass filtering operation. After filtering, the smooth environmental fluctuation sequence ΔT_smooth(t) is obtained, which retains the real change trend of the environmental temperature and removes the high-frequency random noise. According to the difference in thermal physical properties of the thermal reference block and the concrete, the conduction correction parameter is calculated. Specifically, the thermal diffusivity α_ref of the thermal reference block is 1.5× m² / s, and the thermal diffusivity α_conc of the concrete is 5.0× m² / s, and the ratio is 30. According to the heat diffusion theory, the time delay At of the environmental fluctuation from the thermal reference block to the hot spot area is the square of the distance between the two points divided by the difference of the heat diffusion coefficient, and for the hot spot area with a distance of 10 cm, the time delay At is calculated to be 3.5 seconds. The attenuation coefficient K is calculated according to the thermal resistance ratio of the two materials, K = (λ_ref × ρ_ref × c_ref) / (λ_conc × ρ_conc × c_conc), where λ_ref is the thermal conductivity of the thermal reference block (silicon nitride ceramic), ρ_ref is the density of the thermal reference block, c_ref is the specific heat capacity of the thermal reference block, λ_conc is the thermal conductivity of the concrete to be tested, ρ_conc is the density of the concrete to be tested, and c_conc is the specific heat capacity of the concrete to be tested. Substituting the specific parameter values, K = 0.85 is calculated. According to the conduction correction parameter, the smooth environmental fluctuation sequence is processed to generate the environmental fluctuation compensation matrix ΔT_comp(t, x, y). The specific operation is as follows: for each pixel point (x, y) in the thermal response map, the time delay correction amount At_d = At × (d / 10cm)² is calculated according to the distance d from the center of the reference block, and then the smooth environmental fluctuation sequence is time-shifted and amplitude-adjusted: ΔT_comp(t, x, y) = K × ΔT_smooth(t-At_d) × exp(-d / d_0), where d_0 is the characteristic attenuation distance, and the value is 15 cm. Subtract the value of the corresponding position in the environmental fluctuation compensation matrix from the original hot spot temperature curve T_orig(t) extracted from the thermal response data to obtain the corrected thermal decay curve T_corr(t) = T_orig(t) - ΔT_comp(t, x_0, y_0), where (x_0, y_0) is the center point coordinate of the hot spot. The corrected thermal decay curve T_corr(t) only reflects the thermal conduction characteristics of the concrete itself, eliminating the influence of external factors such as environmental temperature fluctuations and air flow disturbances.

[0052] Preferably, the analysis process of the isotherm contour profile distortion degree of the thermal field in step S4 includes:

[0053] determining the decay time point of the hot spot from the peak temperature to 50%;

[0054] extracting the closed isotherm contour of the hot spot at the decay time point;

[0055] calculating the geometric center coordinates of the closed isotherm contour, translating the closed isotherm contour to the coordinate origin to obtain a standardized profile;

[0056] calculating the average radius value of the standardized profile;

[0057] taking the average radius value as an ideal circular profile, calculating the radial distance difference between the standardized profile and the ideal circular profile to obtain a radial deviation sequence;

[0058] Perform a Fourier transform on the radial deviation sequence to extract the amplitudes of the first and second order components;

[0059] The ratio of the standard deviation of the radial deviation sequence to the mean radius is calculated to obtain the dimensionless distortion coefficient that characterizes the degree of profile irregularity.

[0060] The comprehensive distortion index is obtained by weighted averaging of thermal field morphology distortion of hot spots at multiple time points based on the dimensionless distortion coefficient.

[0061] The polarization index of the thermal field structure is calculated based on the comprehensive distortion index.

[0062] In this embodiment of the invention, the precise time point t_50% when the hot spot temperature drops from its highest temperature value Tmax to 50% (i.e., 0.5 × Tmax) is determined by analyzing the pure thermal decay curve T_corr(t). Specifically, starting from the peak time tmax, the search proceeds backward along the time axis, using linear interpolation to find the moment when the temperature is exactly 0.5 × Tmax. For typical C15 strength concrete, this time point usually occurs 8 to 12 seconds after the end of the thermal pulse. At the determined t_50% time, the isothermal contour of the hot spot is extracted from the corrected thermal field map. The extraction method involves marking pixels with a temperature value set to 0.5 × Tmax ± 0.1℃ as contour points, and then connecting these contour points using an edge tracking algorithm to form a closed isothermal contour C(x,y). For each hot spot, typically 200 to 300 contour point coordinates are obtained, forming a complete closed curve.

[0063] Calculate the profile of a closed isotherm Geometric center coordinates The calculation formula is:

[0064] , ;

[0065] in For the outline of the first The coordinates of the points This represents the total number of contour points.

[0066] outline Translate to the origin, i.e. To obtain a standardized profile Standardize the profile Convert to polar coordinates ,in This represents the distance from the origin to the contour point. This represents the polar angle, ranging from 0 to 2π. In the polar coordinate system, radial distances in 72 directions are calculated at 5° intervals. ,in = ×5°×π / 180, =0,1,2,...,71. Calculate the average of these 72 radial distances. ,Will The radius is taken as the ideal circular profile. For each angle... Calculate the radial distance difference between the actual profile and the ideal circular profile. , forming a radial deviation sequence { }, =0,1,2,...,71.

[0067] For radial deviation sequence { The discrete Fourier transform is calculated using the following formula:

[0068] ;

[0069] in =0,1,2,...,71 The imaginary unit commonly used in engineering (i.e. ), to distinguish it from the circular index value Extracting first-order components from the Fourier transform results. and second-order components amplitude and The first-order component characterizes the degree of ellipticization of the profile, while the second-order component characterizes the degree of "dumbbell-shaped" distortion of the profile. The radial deviation sequence is calculated. Standard deviation Then calculate the dimensionless distortion coefficient. This coefficient characterizes the degree of irregularity in the profile; a larger value indicates a more significant non-uniformity in the internal structure of the concrete. Repeat the above steps to calculate the dimensionless distortion coefficients D_25%, D_50%, and D_75% for the hot spot at 25% (t_25%) and 75% (t_75%) of the peak temperature decay.

[0070] The comprehensive distortion index DI is calculated according to the preset weights as 0.2×D_25%+0.5×D_50%+0.3×D_75%. The average comprehensive distortion index of the two hot spots is calculated as DI_avg=(DI_1+DI_2) / 2 and the difference in comprehensive distortion index is calculated as DI_diff=|DI_1-DI_2| / DI_avg, where DI_1 is the comprehensive distortion index of the first hot spot and DI_2 is the comprehensive distortion index of the second hot spot.

[0071] Finally, the polarization index of the thermal field structure was calculated:

[0072] PI = 0.6 x DI avg + 0.2 x DI diff + 0.2 x (Z_1+Z_2) / 4;

[0073] Z_1 = |F_1(1)| / r_avg + |F_1(2)| / r_avg;

[0074] Z_2 = |F_2(1)| / r_avg + |F_2(2)| / r_avg;

[0075] wherein PI is the hot spot structure polarization index, Z_1 is the normalized harmonic distortion coefficient of the first hot spot, Z_2 is the normalized harmonic distortion coefficient of the second hot spot, F_1(1), F_1(2) are the first-order and second-order components of the Fourier transform of the radial deviation of the first hot spot at t_50%, F_2(1), F_2(2) are the first-order and second-order components of the Fourier transform of the radial deviation of the second hot spot at t_50%, DI avg is the average value of the comprehensive distortion index, DI diff is the difference degree of the comprehensive distortion index, and r avg is the average radius value of the isotherm contour. The hot spot structure polarization index PI is a dimensionless parameter, and the numerical range is usually between 0.05 and 0.5, wherein the PI value of low-strength concrete (such as C10) is usually above 0.3, and the PI value of higher-strength concrete (such as C20) is usually below 0.2.

[0076] Preferably, the calculation process of the initial effective thermal relaxation time in step S5 includes:

[0077] Finding the highest temperature value of the thermal decay curve and its corresponding time point, and determining the peak temperature and the peak time;

[0078] Calculating 37% of the peak temperature as a characteristic threshold of heat decay;

[0079] Applying a three-point moving average filter to the thermal decay curve to eliminate minor data fluctuations and obtain a smooth decay curve;

[0080] Searching the thermal decay curve backward from the peak time to determine the time point when the temperature first drops to the characteristic threshold, which is recorded as the characteristic threshold time point;

[0081] Calculating the time interval experienced from the peak time to the characteristic threshold time point to obtain the characteristic decay time;

[0082] Calculating the arithmetic mean of the characteristic decay times of the two hot spots to obtain the hot spot decay time;

[0083] Obtaining and applying a temperature correction formula to the hot spot decay time according to the ambient temperature at the time of testing to calibrate the initial effective thermal relaxation time.

[0084] In the embodiment of the present application, the pure thermal decay curve T corr(t) is analyzed, and the highest temperature value Tmax and its corresponding peak time tmax are found by traversing the entire time sequence, to determine the peak temperature and the peak time. For typical C15 strength concrete, the peak temperature is reached within 0.5 to 1.5 seconds after the end of the thermal pulse, and the peak temperature is usually 3 to 5°C higher than the ambient temperature. The characteristic threshold temperature T threshold = 0.37 x Tmax + T ambient is calculated, where T ambient is the ambient reference temperature. The characteristic threshold temperature corresponds to a heat decay of 37% (i.e. 1 / e, e is the base of the natural logarithm) of the peak value, and this threshold selection is based on the characteristic decay ratio in the heat diffusion theory, which can accurately reflect the thermal conductivity characteristics of the material. The three-point moving average filter is applied to the pure thermal decay curve T corr(t), i.e. T smooth(i) = [T corr(i-1) + T corr(i) + T corr(i+1)] / 3, where T smooth(i) is the temperature value of the i th point in the discrete data point sequence after three-point moving average filtering, T corr(i-1), T corr(i) and T corr(i+1) are the temperature values of the corrected thermal decay curve at the (i-1) th, i th and (i+1) th sampling time, respectively, and i is from 1 to n-1, where n is the total number of data points. This filtering operation eliminates small data fluctuations in the curve, ensuring the accuracy of subsequent time point judgments. Starting from the peak time tmax, the smooth decay curve T smooth(t) is searched along the time axis, and the time point t threshold at which the temperature first falls to the characteristic threshold T threshold is found. Since the temperature data is discretely sampled, the linear interpolation method is usually used to determine the accurate threshold crossing time between the adjacent two sampling points:

[0085] t_threshold = t_i + (t_i+1 - t_i) x (T_threshold - T_smooth(i)) / (T_smooth(i+1) - T_smooth(i)), where t_i and t_i+1 are two adjacent sampling times, and T_smooth(i) > T_threshold > T_smooth(i+1). The characteristic decay time τ = t_threshold - tmax is calculated, with the unit of seconds. The characteristic decay time reflects the rate of heat diffusion in concrete, which is directly related to the density and internal structure of concrete. The characteristic decay times τ1 and τ2 are calculated for the two hot spots respectively, and then their arithmetic mean τ_avg = (τ1 + τ2) / 2 is calculated to obtain the hot spot decay time. The average of the two hot spots eliminates the influence of local non-uniformity and improves the representativeness of the measurement. According to the environmental temperature T_test at the time of testing, the hot spot decay time is calibrated, and the initial effective thermal relaxation time τ_0 = τ_avg x [1 + α x (T_test - T_ref)] is calculated, where T_ref is the standard reference temperature 20℃, and α is the temperature correction coefficient, which is 0.015 / ℃. This calibration process takes into account the influence of environmental temperature on the thermal diffusion performance of concrete, ensuring that the thermal relaxation time measured under different environmental conditions is comparable. For low-strength concrete (such as C10-C15), the initial effective thermal relaxation time τ_0 is usually in the range of 15 to 25 seconds, while for higher-strength concrete (such as C20-C25), τ_0 is usually in the range of 8 to 15 seconds. The initial effective thermal relaxation time is an important indicator of concrete density, providing a key parameter for subsequent strength evaluation.

[0086] Preferably, the calculation process of estimating the equivalent strength in step S6 includes:

[0087] Divide the thermal field structure polarization index and the effective thermal relaxation time by the respective preset standard reference values to obtain normalized characteristic values;

[0088] According to the thermal field structure polarization index and the effective thermal relaxation time, calculate the strength base value using a binary linear regression formula;

[0089] Calculate the product term of the normalized characteristic values as an adjustment quantity reflecting the mutual influence of parameters;

[0090] Obtain and calculate the age correction coefficient and the humidity correction coefficient according to the estimated age and the surface water content of the concrete;

[0091] Add the strength base value and the adjustment quantity to obtain the corrected strength value, and then calculate the multi-factor correction value according to the corrected strength value, the age correction coefficient and the humidity correction coefficient;

[0092] Calculate the standard deviation and the 95% confidence interval of the multi-factor correction value;

[0093] The concrete strength grade is determined as the presumed equivalent strength by comparing the multi-factor correction value with the standard concrete strength grade according to the standard deviation and the 95% confidence interval.

[0094] In the embodiment of the present application, the thermal field structure polarization index PI and the effective thermal relaxation time τ are divided by the preset standard reference value to obtain the normalized characteristic value. The standard reference values are PI_ref=0.25 and τ_ref=15 seconds respectively, which represent the characteristic parameters of typical C15 strength concrete. The normalized characteristic value is calculated as PI_norm=PI / PI_ref and τ_norm=τ / τ_ref. The normalization processing makes the two parameters of different dimensions comparable, which is convenient for subsequent multi-parameter comprehensive analysis. According to the thermal field structure polarization index and the effective thermal relaxation time, the strength base value F_base is calculated by using the binary linear regression formula + ×PI_norm+ ×τ_norm, wherein 、 、 is the coefficient calibrated by experiment. For the low strength concrete interval (C10-C20), =15.0, =-8.5, =-4.2. This regression formula reflects the basic relationship between the concrete strength and the thermal characteristic parameters, in which PI_norm is negatively correlated with the strength (the larger the PI value, the more uneven the internal structure, and the lower the strength), and τ_norm is also negatively correlated with the strength (the longer the thermal relaxation time, the slower the heat diffusion, the lower the density, and the lower the strength). The product item PI_norm×τ_norm of the normalized characteristic values is multiplied by the interaction coefficient =2.1 to obtain the parameter interaction adjustment amount Δ_interact= ×PI_norm×τ_norm. This interaction item reflects the nonlinear interaction between the two parameters, especially in the extremely low strength concrete, the superimposed effect of internal structure unevenness and low density is more significant. The estimated age Age (unit: days) and the surface water content W (percentage) of the concrete are obtained, and the age correction coefficient K_age and the humidity correction coefficient K_moisture are calculated.

[0095] The age correction coefficient calculation formula is: K_age=1.0-0.2×exp(-Age / 7);

[0096] For mature concrete with an age of more than 28 days, K_age is close to 1.0; for early concrete with an age of only 7 days, K_age is about 0.85.

[0097] The humidity correction coefficient calculation formula is:

[0098] K_moisture = 1.0 - 0.05 x (W - 3);

[0099] When the surface water content W is 3%, K_moisture = 1.0; when the water content increases to 8%, K_moisture decreases to 0.75. The corrected strength value F_corr = F_base + Δ_interact is obtained by adding the strength base value to the interaction adjustment value, and the multi-factor correction value F_multi = F_corr x K_age x K_moisture is calculated according to the corrected strength value, the age correction coefficient and the humidity correction coefficient, with the unit of MPa. This multi-factor correction value comprehensively considers the influencing factors such as the thermal properties, age and water content of the concrete. The standard deviation σ_F = 0.5 + 0.1 x F_multi is calculated, with the unit of MPa. The standard deviation increases with the increase of the strength value, reflecting the characteristics of relatively large measurement uncertainty in the high strength interval. The upper and lower limit values F_upper = F_multi + 1.96 x σ_F and F_lower = F_multi - 1.96 x σ_F of the 95% confidence interval are calculated, where F_upper is the upper limit value of the 95% confidence interval, and F_lower is the lower limit value of the 95% confidence interval, and the confidence interval reflects the reliability range of the strength estimation. The multi-factor correction value F_multi is compared with the standard concrete strength grade to determine the concrete strength grade. The specific comparison rules are as follows: when F_lower ≤ 10.0 and F_upper ≥ 10.0, it is determined as C10; when F_lower ≤ 15.0 and F_upper ≥ 15.0, it is determined as C15; when F_lower ≤ 20.0 and F_upper ≥ 20.0, it is determined as C20. If F_lower < 10.0 and F_multi < 10.0, it is determined as C10 or below; if F_lower > 20.0, it is determined as C20 or above. Finally, the estimated equivalent strength result is output, including the numerical strength estimation value F_multi (accurate to 0.1 MPa), the 95% confidence interval [F_lower, F_upper] and the estimated concrete strength grade, such as "estimated equivalent strength: 13.5 MPa, 95% confidence interval [11.8, 15.2] MPa, estimated strength grade C15".

[0100] Preferably, step S4 further comprises analyzing the thermal field morphology distortion degree at a plurality of time points:

[0101] In addition to the time point at which the hot spot decays from the peak temperature to 50%, isotheral contour is extracted at the time point at which the hot spot decays from the peak temperature to 25% and 75%;

[0102] The distortion coefficient values at the three time points are calculated according to the isotherm profile, respectively;

[0103] The distortion coefficients at the three time points are weighted and averaged to obtain a comprehensive distortion index, wherein the weights corresponding to the 50% time point, the 25% time point and the 75% time point are 0.2, 0.5 and 0.3, respectively.

[0104] In the embodiments of the present application, by analyzing the pure thermal decay curve T_corr(t), the three characteristic time points t_25%, t_50% and t_75% are determined, at which the hot spot decays from the highest temperature value Tmax to 25%, 50% and 75% respectively. The specific determination method is to start from the peak time tmax, search backward along the time axis, and find the three time points at which the temperature is exactly 0.75 Tmax, 0.5 Tmax and 0.25 Tmax by linear interpolation. For typical C15 strength concrete, t_75% usually occurs at 4 to 6 seconds after the end of the thermal pulse, t_50% occurs at 8 to 12 seconds, and t_25% occurs at 18 to 25 seconds. These three time points represent the early, middle and late stages of heat diffusion, capturing the complete dynamic characteristics of the heat diffusion process. At the determined three time points t_25%, t_50% and t_75%, the isotherm contours of the hot spot are extracted from the corrected thermal field map. The extraction method is to mark the pixel points with temperature values of 0.75 Tmax ± 0.1℃, 0.5 Tmax ± 0.1℃ and 0.25 Tmax ± 0.1℃ as contour points, and then connect these contour points using an edge tracking algorithm to form three closed isotherm contours C_75%(x, y), C_50%(x, y) and C_25%(x, y). For each time point of each hot spot, usually 200 to 300 contour point coordinates are obtained to form a complete closed curve. The isotherm contours at the three time points are respectively subjected to standardization processing: calculate the geometric center coordinates, translate the contours to the coordinate origin, convert to polar coordinate representation, calculate the average radius, generate an ideal circular reference contour, calculate the radial deviation sequence, and finally calculate the dimensionless distortion coefficient D_75%, D_50% and D_25%. The specific calculation process is the same as the distortion coefficient calculation method for a single time point described above, but is applied to the contour data at the three different time points respectively. The distortion coefficients D_75%, D_50% and D_25% at the three time points are weighted and averaged to calculate the comprehensive distortion index DI = 0.2 × D_25% + 0.5 × D_50% + 0.3 × D_75%. In this weighting scheme, the distortion coefficient D_50% at the middle stage (50% decay point) is given the highest weight of 0.5, because the thermal field morphology at this time best reflects the internal structural characteristics of the concrete; the distortion coefficient D_75% at the early stage (75% decay point) is given a weight of 0.3, at which time the thermal field morphology mainly reflects the surface characteristics; the distortion coefficient D_25% at the late stage (25% decay point) is given a weight of 0.2, at which time the heat field has diffused far away, and the influence of boundary effect and deep structure is enhanced. The multi-time point comprehensive analysis overcomes the limitations of single time point evaluation, and comprehensively captures the structural characteristics of concrete at different depths and different scales.The comprehensive distortion indexes DI_1 and DI_2 are calculated for the two hot spots respectively, and then the average value DI_avg=(DI_1+DI_2) / 2 and the difference degree DI_diff=|DI_1-DI_2| / DI_avg are calculated.

[0105] Finally, the thermal field structure polarization index under the multi-time point analysis is calculated again by using the comprehensive distortion index average value DI_avg and the comprehensive distortion index difference degree DI_diff obtained through the multi-time point analysis.

[0106] This multi-time point analysis method significantly improves the stability and representativeness of the thermal field form distortion degree evaluation, and provides a more reliable index for the accurate quantification of the internal structure inhomogeneity of concrete.

[0107] Preferably, the time constant compensation of the initial effective thermal relaxation time by using the thermal decay curve in step S5 comprises:

[0108] The exponential function fitting is performed on the thermal decay curve to obtain fitting parameters;

[0109] The time constant is extracted from the fitting parameters;

[0110] The initial effective thermal relaxation time is verified and adjusted by using the time constant to obtain the effective thermal relaxation time.

[0111] In the embodiment of the present application, the temperature data point set {t_i, T_i} after the peak time tmax is extracted from the pure thermal decay curve T_corr(t), where i=1, 2,..., n, t_i represents a time point, T_i represents a corresponding temperature value, n is the total number of data points, and is usually taken as the data points within 60 seconds. The exponential function model T(t)=T_ambient+ΔT×exp(-(t-tmax) / τ_fit) is applied to the extracted temperature data point set for fitting, where T_ambient is the ambient reference temperature, ΔT is the temperature increment parameter, and τ_fit is the time constant to be solved. The least square method is used to determine the optimal fitting parameters, that is, to solve the residual sum of squares S=∑[T_i-T(t_i)] The minimum parameter value. The implementation employs an iterative optimization algorithm, with initial values set to T ambient = end-of-data temperature, ΔΤ = peak temperature - T ambient, τ fit = initial effective thermal relaxation time τ 0. Iterative calculations continue until the parameter change rate is less than 0.1% or a maximum number of iterations of 50 is reached. From the fitting results, the time constant τ fit is extracted, which characterizes the characteristic time scale of heat decay in concrete and reflects the overall thermal diffusion performance of concrete. Two thermal spots are fitted respectively to obtain the time constant τ fit1 of the first thermal spot and the time constant τ fit2 of the second thermal spot, and the average value τ fit_avg = (τ fit1 + τ fit2) / 2 is calculated. The goodness of fit R = 1 - ∑[T i - T(t i)] / ∑[T i - T mean] , where T mean is the average value of all temperature data. The goodness of fit R² is used to evaluate the accuracy of the exponential model in describing the actual heat decay process, and the closer the value of R is to 1, the more accurate the fitting is. For a typical concrete heat decay curve, R Generally above 0.95. Calculate the deviation rate δ = |τ_0 - τ_fit_avg| / τ_0 of the initial effective thermal relaxation time τ_0 and the fitting time constant τ_fit_avg. If the deviation rate δ is less than 10%, it is verified, and the initial effective thermal relaxation time τ_0 is directly used as the final effective thermal relaxation time τ; if the deviation rate δ is between 10% and 30%, a weighted adjustment is made, and τ = (2 × τ_0 + τ_fit_avg) / 3 is calculated; if the deviation rate δ is greater than 30%, it indicates that the thermal decay process has obvious non-exponential characteristics or measurement abnormalities, at this time a more complex double exponential model T(t) = T_ambient + ΔT1 × exp(-(t-tmax) / τ1) + ΔT2 × exp(-(t-tmax) / τ2) is used for re-fitting, and then the equivalent time constant τ_eq = (ΔT1 × τ1 + ΔT2 × τ2) / (ΔT1 + ΔT2) is calculated, and finally the effective thermal relaxation time τ = (τ_0 + τ_eq) / 2 is determined, where ΔT1 is the initial temperature increment of the fast decay component, in °C, representing the temperature rise amplitude caused by the heat absorbed by the surface layer of the concrete, τ1 is the time constant of the fast decay component, in seconds, representing the characteristic time of heat diffusion in the surface layer, with a small value (usually 3-8 seconds), ΔT2 is the initial temperature increment of the slow decay component, in °C, representing the temperature rise amplitude caused by the heat penetrating into the deep layer of the concrete, τ2 is the time constant of the slow decay component, in seconds, representing the characteristic time of heat diffusion in the deep layer, with a large value (usually 15-30 seconds). The equivalent time constant τ_eq is calculated by weighted average of the temperature increments of each component to comprehensively represent the thermal relaxation characteristics. The initial effective thermal relaxation time is verified and adjusted by exponential function fitting, which enhances the robustness of the thermal relaxation time measurement, especially for low-strength concrete with complex internal structure, whose thermal decay process often shows multi-time scale characteristics. The final effective thermal relaxation time τ combines the advantages of direct measurement and model fitting, providing a more accurate thermal characteristic parameter for concrete strength evaluation.

[0112] Preferably, the thermal reference block in step S1 is made of silicon nitride ceramic sheet, and its surface is coated with a uniform high-emissivity black coating, so that it has stable radiation characteristics in the infrared wave band.

[0113] In the embodiment of the present application, the thermal reference block is made of a silicon nitride ceramic sheet with a size of 10mmx10mmx1mm. The material has high thermal conductivity (30W / m·K), low heat capacity (700J / kg·K) and high temperature stability (temperature resistance range -50℃ to 500℃). The silicon nitride ceramic is selected from high-purity (purity≥99.5%) and high-density (density≥3.1g / cm³) materials to ensure the consistency and stability of physical properties. The surface of the thermal reference block is coated with a layer of high-emissivity black coating with a thickness of 25±5μm. The coating material is carbon black filled polyacrylate, with an emissivity of ε=0.95±0.02 (in the 8-14μm infrared waveband), ensuring stable and near blackbody radiation characteristics in the working waveband of the infrared thermal imager. The coating is achieved by precise spraying process, with a coating thickness variation coefficient controlled within 5%, and a surface roughness Ra<1.0μm to ensure the spatial uniformity of the emissivity. The thermal reference block is strictly calibrated for thermal physical properties before use, including measurement of its thermal conductivity, specific heat capacity and thermal diffusivity at 20℃, 30℃ and 40℃, to ensure the accuracy of the parameters. The thermal reference block is installed at the center of the target area on the surface of the concrete to be tested, and is fixed with silicone glue with a thermal conductivity less than 0.2W / m·K, with a glue layer thickness controlled within 0.1mm to ensure full contact between the reference block and the concrete surface but minimize thermal coupling effect. After fixing, stand for 15 minutes to make the reference block reach thermal equilibrium with the environment, and monitor the surface temperature of the reference block during this period. The temperature fluctuation is controlled within ±0.1℃ before the subsequent test can be carried out. The thermal reference block serves as a thermal reference standard and environmental fluctuation monitor in the detection system. Its high thermal conductivity and low heat capacity characteristics enable it to quickly respond to environmental temperature changes, while the stable emissivity ensures the accuracy of infrared temperature measurement, providing a reliable reference point for subsequent environmental noise cancellation.

[0114] Preferably, the synchronous thermal pulse in step S2 is realized by two side-by-side focused infrared lamps, with a pulse duration of 0.5 seconds, and the output energy difference of the two focused infrared lamps does not exceed ±2%.

[0115] In the embodiment of the present application, the synchronous thermal pulse is realized by two side-by-side installed focused infrared lamps. The infrared lamps use halogen quartz bulbs with a rated power of 800 W and a working voltage of 220 V. The emission spectrum is concentrated in the 1.0-3.0 μm band, and the thermal radiation efficiency is ≥ 85%. The infrared lamps are equipped with an elliptical reflecting cup with a focal length of 150 mm. The inner surface of the reflecting cup is coated with aluminum and polished, and the reflectivity is ≥ 95%. The two infrared lamps are installed on a precision adjustment bracket, which allows fine adjustment in three directions by ± 10 mm to ensure accurate positioning of the light spot. The distance between the two infrared lamps is fixed at 200 mm, and the vertical distance from the concrete surface is 300 mm. The irradiation angle is perpendicular to the concrete surface. The centers of the light spots of the two infrared lamps are located 100 mm apart on both sides of the thermal reference block, forming a symmetrical layout. The diameter of the light spot of the infrared lamp is controlled within the range of 20 ± 2 mm, which is realized by adjusting the focusing device. The two infrared lamps are connected to the same electronic synchronous controller. The controller uses a solid-state relay driving circuit with a switching time of < 1 ms to ensure synchronous starting and closing of the two lamps. The pulse duration is accurately set to 0.5 seconds with a time error of < ± 5 ms, which is controlled by a high-precision timing circuit. Before applying the thermal pulse, the heat flux at the target position of the two infrared lamps is measured using a heat flux meter. The power input of the infrared lamps is adjusted to control the heat flux difference between the two light spots within ± 2%, and the typical value is 3.5 kW / m². Before the pulse is triggered, the system performs self-checking to confirm that the infrared thermal imager has started recording, and then the synchronous controller sends a trigger signal to activate the two infrared lamps simultaneously. After accurately lasting for 0.5 seconds, the two infrared lamps are turned off simultaneously. This precisely controlled synchronous thermal pulse method ensures that the two heat spots receive exactly the same amount of heat input, providing reliable initial conditions for subsequent thermal field analysis. At the same time, the short pulse characteristic avoids excessive heating of the concrete surface, maintaining the non-destructive nature of the measurement.

[0116] Preferably, the present application also provides a concrete strength detection system for performing the concrete strength detection method as described above, which comprises:

[0117] A thermal reference block made of silicon nitride ceramic sheet, coated with a high-emissivity black coating, for placing at the center of the surface of the concrete to be measured;

[0118] A double-head pulse heat source comprising two power-adjustable focused infrared lamps and a synchronous controller for applying synchronous thermal pulses with the same energy to the concrete surface to form two heat spots on the concrete surface;

[0119] An infrared thermal imager with a thermal sensitivity of not less than 0.05℃ for continuously recording the thermal response process to generate thermal response data;

[0120] A data processing unit is in communication connection with the infrared thermal imager to receive the thermal response data and in communication connection with the synchronous controller of the double-head pulse heat source to control the application of the thermal pulse, and the data processing unit is used to perform the following operations:

[0121] The thermal decay curve of the hot spot is obtained by monitoring the environmental temperature fluctuation with the thermal reference block and subtracting the amount of the environmental temperature fluctuation from the thermal response data in real time;

[0122] The isotherm profile distortion degree of the thermal field corresponding to the thermal decay curve is analyzed, and is quantified as a thermal field structure polarization index;

[0123] The initial effective thermal relaxation time is obtained by calculating the time required for the temperature of the hot spot to decay to 37% of the peak value from the peak value, and the effective thermal relaxation time is obtained by time constant compensation on the initial effective thermal relaxation time;

[0124] The estimated equivalent strength of the concrete is calculated by substituting the thermal field structure polarization index and the effective thermal relaxation time into the pre-calibrated correlation equation;

[0125] A display unit is in communication connection with the data processing unit and is used to display the thermal response data, the thermal decay curve, the thermal field structure polarization index, the effective thermal relaxation time and the estimated equivalent strength value.

[0126] In the examples of the present application:

[0127] 1. System initialization phase: first start the data processing unit, the system performs self-checking to confirm the connection state of each component. The data processing unit establishes a data communication link with the infrared thermal imager and establishes a control communication link with the synchronous controller of the double-head pulse heat source. The system loads the pre-calibrated strength correlation equation and the reference database.

[0128] 2. Test preparation phase: the operator cleans the surface of the concrete to be tested to ensure that the surface is dry and free of obvious contaminants. Mark a 1m x 1m square area in the center of the area to be tested. Fix the thermal reference block (10mm x 10mm x 1mm silicon nitride ceramic sheet, surface coated with high-emissivity black coating) at the center of the marked area. Adjust the position of the double-head pulse heat source so that the two focused infrared lamps are respectively aimed at the positions 10 cm away from the two sides of the thermal reference block, and adjust the power output to ensure that the output energy difference of the two infrared lamps does not exceed ±2%.

[0129] 3. Environmental parameter acquisition phase: the system measures and records environmental temperature, humidity and other parameters. The infrared thermal imager starts continuous monitoring of the test area, and collects the initial temperature distribution of the thermal reference block and the surrounding concrete surface, and establishes a temperature reference for 10 seconds.

[0130] 4. Heat pulse excitation phase: The data processing unit sends a trigger signal to the synchronization controller, which precisely controls the two focused infrared lamps to turn on simultaneously for 0.5 seconds and then turn off, applying the same heat pulse to the concrete surface and forming two thermal spots on the surface. The infrared thermal imager continuously records the temperature changes of the entire area at a frequency of not less than 25 Hz, including the complete thermal response process of 60 seconds before, during, and after the heat pulse application.

[0131] 5. Data processing phase: The data processing unit receives the thermal response data transmitted by the infrared thermal imager and performs the following processing:

[0132] Extract the temperature sequence of the thermal reference block area, calculate the environmental temperature fluctuation, and generate an environmental fluctuation compensation matrix;

[0133] Subtract the environmental fluctuation compensation from the original thermal response data to obtain the corrected thermal decay curve;

[0134] Extract the isotheral contour at multiple time points (peak temperature decay to 25%, 50%, and 75%);

[0135] Analyze the morphological distortion degree of the isotheral contour and calculate the thermal field structure polarization index;

[0136] Determine the time required for the thermal spot temperature to decay from the peak to 37%, and calculate the initial effective thermal relaxation time;

[0137] Perform exponential function fitting on the thermal decay curve, extract the time constant, and compensate the initial effective thermal relaxation time;

[0138] Substitute the thermal field structure polarization index and effective thermal relaxation time into the pre-calibrated correlation equation to calculate the estimated equivalent strength of the concrete.

[0139] 6. Result output phase: The data processing unit transmits the processing results to the display unit. The display unit displays key data in graphical and numerical form, including:

[0140] Thermal response original image and corrected thermal field distribution map;

[0141] Thermal decay curve of the thermal spot center point;

[0142] Isothermal contour and its distortion analysis results;

[0143] Thermal field structure polarization index value (dimensionless);

[0144] Effective thermal relaxation time value (seconds);

[0145] Estimated equivalent strength value (MPa) and its 95% confidence interval;

[0146] The estimated concrete strength grade (such as C10, C15, C20, etc.).

[0147] 7. Data storage and report generation phase: the system stores test results, raw data and processing procedures in the database, generates test reports containing test point location information, environmental parameters, measurement results and strength evaluation conclusions. Reports can be viewed through the display unit or exported as standard format files.

[0148] Please refer to Fig. 2 The structure diagram of the concrete strength detection system in the present application is shown in the figure, which adopts a symmetrical design with the thermal reference block as the center axis, and the components are reasonably distributed to form a complete detection link from excitation to detection to result output. Among them Fig. 2 The specific description is as follows:

[0149] Detection object area: the concrete to be tested is located at the bottom of the figure as the target object to be detected; the thermal reference block is a small black block on the center of the concrete surface, which is used as a temperature reference and environmental monitoring reference point; the thermal spot is two symmetrical red oval areas generated by the double-head pulse heat source, which is the temperature response area formed by the thermal pulse on the concrete surface.

[0150] Excitation component: the double-head pulse heat source is composed of two focused infrared lamps, which are orange oval in shape and symmetrically distributed on both sides of the thermal reference block; each infrared lamp in the focused infrared lamp contains a focusing lens system, which emits synchronous thermal pulses to the concrete surface; the synchronous controller is located between the two infrared lamps to ensure the accurate synchronous operation of the double-head heat source.

[0151] Detection component: the infrared thermal imager is a blue device located in the center of the upper part of the figure, which has a large-size lens system and continuously captures the temperature distribution changes of the entire test area.

[0152] Data processing and display component: the data processing unit is a green rectangular module located in the upper left of the figure, which is the control and analysis core of the entire system; the display unit is an orange rectangular module located in the upper right of the figure, which contains a white display screen and displays the detection results in real time (for example, the strength grade "C25" is displayed in the figure).

[0153] Data flow (the data flow in the figure is clearly indicated by different colored connecting lines):

[0154] 1. Control flow:

[0155] The data processing unit sends "control signals" to the synchronous controller through the green thick line;

[0156] The synchronous controller sends synchronous control instructions to the two focused infrared lamps through the purple line;

[0157] 2. Data acquisition flow:

[0158] The infrared thermography transmits "thermal response data" to the data processing unit through the blue thick line;

[0159] The data processing unit transmits "processing results" to the display unit through the green thick line;

[0160] 3. Physical excitation process:

[0161] Two focused infrared lamps emit thermal pulses to the concrete surface through the orange radiation line;

[0162] The infrared thermography observes the entire test area through the blue dotted triangle area;

[0163] Fig. 2 Working principle: Based on the thermal pulse excitation-infrared response analysis technology, the symmetrical double-head heat source generates a standardized thermal excitation on the concrete surface, the infrared thermography monitors the thermal response process in real time, the data processing unit analyzes the thermal field characteristics and time response characteristics, and finally outputs the concrete strength grade evaluation results.

[0164] Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting, the scope of the present application being defined by the appended claims and not by the above description, therefore all variations falling within the meaning and scope of the equivalent elements of the application file are intended to be included in the present application.

[0165] The above description is merely one specific implementation of the present application, which enables those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method of concrete strength detection, characterized by, The method comprises the following steps: Step S1: placing a thermal reference block with known thermal physical properties at the center of a target area on the surface of the concrete to be tested; Step S2: applying synchronous thermal pulses with the same energy to the concrete surfaces on both sides of the thermal reference block, recording the thermal responses formed thereby using an infrared thermal imager, and generating thermal response data, wherein two thermal spots are formed on the surface of the concrete; Step S3: monitoring the environmental temperature fluctuations using the thermal reference block, subtracting the amount of environmental temperature fluctuations from the thermal response data in real time to obtain the thermal decay curve of the thermal spots; Step S4: analyzing the isotherm profile distortion degree of the thermal field corresponding to the thermal decay curve, and quantifying it as a thermal field structure polarization index; Step S5: calculating the time required for the temperature of the thermal spot to decay from the peak value to 37% of the peak temperature to obtain the initial effective thermal relaxation time; compensating the initial effective thermal relaxation time using the thermal decay curve to obtain the effective thermal relaxation time; Step S6: substituting the thermal field structure polarization index and the effective thermal relaxation time into the pre-calibrated correlation equation to calculate the estimated equivalent strength of the concrete.

2. The method of concrete strength detection according to claim 1, wherein, The monitoring process of the environmental temperature fluctuations in step S3 comprises: calculating the average temperature of the thermal reference block before the thermal pulse as a temperature reference point under the stable environment; extracting the temperature sequence of the thermal reference block region over time, subtracting the temperature reference point to obtain the temperature fluctuation sequence caused by environmental factors; applying a low-pass filter to the temperature fluctuation sequence to remove random noise but retain the true environmental temperature change trend to obtain a smoothed environmental fluctuation sequence; calculating the attenuation coefficient and time delay of the environmental fluctuations from the thermal reference block to the thermal spot region according to the difference in thermal physical properties between the thermal reference block and the concrete to obtain a conduction correction parameter; generating an environmental fluctuation compensation matrix by time-shifting and amplitude-adjusting the smoothed environmental fluctuation sequence according to the conduction correction parameter; subtracting the corresponding environmental fluctuation compensation matrix from the original thermal spot temperature curve extracted from the thermal response data to obtain the thermal decay curve that eliminates the environmental impact.

3. The method of concrete strength testing according to claim 1, wherein, The analysis process of the isotherm profile distortion degree of the thermal field in step S4 comprises: determining the decay time point of the thermal spot from the peak temperature to 50%; extracting the closed isotherm profile of the thermal spot at the decay time point; calculating the geometric center coordinates of the closed isotherm profile, shifting the closed isotherm profile to the coordinate origin to obtain a standardized profile; calculating the average radius value of the standardized profile; taking the average radius value as an ideal circular profile, calculating the radial distance difference between the standardized profile and the ideal circular profile to obtain a radial deviation sequence; performing Fourier transform on the radial deviation sequence to extract the amplitude of the first and second components thereof; calculating the ratio of the standard deviation of the radial deviation sequence to the average radius to obtain a dimensionless distortion coefficient representing the irregularity degree of the profile; performing a weighted average of the thermal field profile distortion degree of the thermal spot at multiple time points according to the dimensionless distortion coefficient to obtain a comprehensive distortion index; calculating the thermal field structure polarization index according to the comprehensive distortion index.

4. The method for detecting the strength of concrete according to Claim 1, wherein The calculation process of the initial effective thermal relaxation time in step S5 comprises: finding the highest temperature value of the thermal decay curve and its corresponding time point to determine the peak temperature and the peak time; 37% of the peak temperature is calculated as the characteristic threshold of heat decay; A three-point moving average filter is applied to the heat decay curve to eliminate minor data fluctuations and obtain a smooth decay curve; The heat decay curve is searched backward from the peak time to determine the time point when the temperature first drops to the characteristic threshold, which is recorded as the characteristic threshold time point; The time interval experienced from the peak time to the characteristic threshold time point is calculated to obtain the characteristic decay time; The arithmetic mean of the characteristic decay times of the two heat spots is calculated to obtain the heat spot decay time; The ambient temperature at the time of testing is obtained and used to apply a temperature correction formula to calibrate the heat spot decay time to obtain the initial effective thermal relaxation time.

5. The method for detecting the strength of concrete according to Claim 1, wherein The calculation process of the estimated equivalent strength in step S6 includes: Divide the thermal field structure polarization index and the effective thermal relaxation time by the respective preset standard reference values to obtain normalized characteristic values; According to the thermal field structure polarization index and the effective thermal relaxation time, calculate the strength base value using a binary linear regression formula; Calculate the product term of the normalized characteristic values as an adjustment amount reflecting the mutual influence of parameters; Obtain and calculate the age correction coefficient and the humidity correction coefficient according to the estimated age and the surface water content of the concrete; Add the strength base value and the adjustment amount to obtain the corrected strength value, and then calculate the multi-factor correction value according to the corrected strength value, the age correction coefficient, and the humidity correction coefficient; Calculate the standard deviation and the 95% confidence interval of the multi-factor correction value; Compare the multi-factor correction value with the standard concrete strength grade according to the standard deviation and the 95% confidence interval to determine the concrete strength grade as the estimated equivalent strength.

6. The method for detecting the strength of concrete according to Claim 1, wherein Step S4 also includes analyzing the thermal field shape distortion degree at multiple time points: In addition to the time point when the heat spot decays from the peak temperature to 50%, isothermal contour profiles are also extracted at the time points when the heat spot decays from the peak temperature to 25% and 75%; According to the isothermal contour profiles, calculate the distortion coefficient values at the three time points respectively; Weighted average the distortion coefficients at the three time points to obtain a comprehensive distortion index, wherein the weights corresponding to the 50% time point, the 25% time point, and the 75% time point are 0.2, 0.5, and 0.3 respectively.

7. The method for detecting the strength of concrete according to Claim 1, wherein In step S5, the initial effective thermal relaxation time is compensated for the time constant using the heat decay curve, which includes: Exponential function fitting is performed on the heat decay curve to obtain fitting parameters; Extract the time constant from the fitting parameters; Verify and adjust the initial effective thermal relaxation time using the time constant to obtain the effective thermal relaxation time.

8. The method for detecting the strength of concrete according to Claim 1, wherein The thermal reference block in step S1 is made of silicon nitride ceramic sheet, and its surface is coated with a uniform high-emissivity black coating, so that it has stable radiation characteristics in the infrared band.

9. The method for detecting the strength of concrete according to Claim 1, wherein The synchronous heat pulse in step S2 is realized by two side-by-side focused infrared lamps, with a pulse duration of 0.5 seconds, and the output energy difference between the two focused infrared lamps does not exceed ±2%.

10. A concrete strength detection system characterized by, A concrete strength detection system for performing the concrete strength detection method as claimed in claim 1, the concrete strength detection system comprising: A thermal reference block made of silicon nitride ceramic sheet, coated with a high-emissivity black coating on its surface, for placement at the center of the surface of the concrete to be tested; The double-head pulse heat source comprises two power-adjustable focused infrared lamps and a synchronous controller, and is used for applying synchronous heat pulses with the same energy to a concrete surface to form two heat spots on the concrete surface. The infrared thermal imager has a thermal sensitivity of not less than 0.05 DEG C, is used for continuously recording a thermal response process, and generates thermal response data. The data processing unit is in communication connection with the infrared thermal imager to receive the thermal response data, and is in communication connection with the synchronous controller of the double-head pulse heat source to control the application of the heat pulses. The thermal decay curve of the heat spot is obtained by monitoring the environmental temperature fluctuation by using the thermal reference block, and subtracting the amount of the environmental temperature fluctuation from the thermal response data in real time. The isotherm profile distortion degree of the thermal field corresponding to the thermal decay curve is analyzed, and is quantified as a thermal field structure polarization index. The initial effective thermal relaxation time is obtained by calculating the time required for the temperature of the heat spot to decay to 37% of the peak value, and the effective thermal relaxation time is obtained by performing time constant compensation on the initial effective thermal relaxation time. The estimated equivalent strength of the concrete is calculated by substituting the thermal field structure polarization index and the effective thermal relaxation time into a pre-calibrated correlation equation. The display unit is in communication connection with the data processing unit, and is used for displaying the thermal response data, the thermal decay curve, the thermal field structure polarization index, the effective thermal relaxation time and the estimated equivalent strength value.

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