Bridge deck concrete strength nondestructive testing system and method based on ultrasonic rebound

Abstract

The invention provides a bridge deck concrete strength nondestructive testing system and method based on ultrasonic springback, and relates to the technical field of concrete nondestructive testing. Parameters of all measuring points are obtained by dividing measuring grids, and test pieces with different concrete layer thicknesses and reinforcement protection layer thicknesses are prepared for fitting acoustic path correction factors; the interference of the reinforcing steel bars on ultrasonic propagation is corrected; the ratio of the basic sound velocity to the thickness of the reinforcing steel bar is obtained through ultrasonic opposite measurement, the real sound velocity is calculated, and a state datum line is correspondingly generated according to the springback value; and finally, by calculating the residual error and the included angle of each measuring point deviating from the datum line, generating a state correction factor in combination with a sound velocity-rebound coupling term, and correcting the datum strength, thereby realizing accurate and nondestructive evaluation of the bridge deck concrete strength.

Description

Technical Field

[0001] This invention relates to the field of non-destructive testing technology for concrete, specifically to a non-destructive testing system and method for bridge deck concrete strength based on ultrasonic rebound. Background Technology

[0002] In the field of non-destructive testing (NDT) for bridge engineering, accurately assessing the strength of bridge deck concrete has always been a key challenge. Traditional strength testing methods suffer from problems such as being destructive, inefficient, and having limited representativeness, making them unsuitable for large-scale, continuous bridge deck inspections. Although ultrasonic and rebound methods are widely used as common NDT techniques, both have significant limitations in practical applications: ultrasonic velocity is significantly affected by the distribution of reinforcing steel within the concrete, the thickness of the protective layer, and the geometric dimensions of the component, leading to substantial deviations in the measurement results; while rebound values ​​primarily reflect surface hardness and are insensitive to internal defects and homogeneity of the concrete. Furthermore, existing methods often simply combine ultrasonic and rebound data, failing to systematically correct for interference from reinforcing steel and cross-sectional dimensions on the acoustic path, and lacking a quantitative assessment mechanism for the degree of deviation between the measurement point and the overall condition. This results in insufficient reliability and poor adaptability of the test results, making it difficult to meet the engineering requirements for refined, non-destructive, and efficient testing of bridge deck concrete strength.

[0003] In the prior art, CN120741637A discloses a method and system for comprehensive ultrasonic rebound testing of the concrete strength of bridge piers, including acquiring ultrasonic propagation velocity data of the part of the bridge pier to be tested; acquiring rebound value data of the part of the bridge pier to be tested; coupling the ultrasonic propagation velocity data and rebound value data, and determining the concrete strength of the part to be tested by combining the pouring bedding direction of the bridge pier concrete and the strength growth coefficient corresponding to the curing age.

[0004] The main problems with the above scheme are: bridge pier concrete is usually poured vertically, with complex internal steel reinforcement distribution, and may have structural features such as layered pouring joints and formwork effects. The above scheme fails to consider the interference of changes in steel reinforcement direction and protective layer thickness on the ultrasonic wave propagation path, resulting in distortion of sound velocity data and affecting the accuracy of strength estimation; the piers are often in outdoor variable environments, and humidity and temperature affect ultrasonic velocity and rebound value. The above scheme lacks real-time correction measures and is prone to deviations under different working conditions.

[0005] The information disclosed in the background section is only intended to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to provide a non-destructive testing system and method for the strength of bridge deck concrete based on ultrasonic rebound, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A non-destructive testing system for bridge deck concrete strength based on ultrasonic rebound specifically includes: The measurement point division module is used to select the inspection area on the bridge deck to be inspected, uniformly divide the inspection area into measurement grids to form measurement points, obtain the concrete slab thickness of each measurement point, and calculate the average concrete slab thickness and average steel reinforcement cover thickness of the inspection area. The path correction module is used to prepare several sets of specimens with different average concrete slab thicknesses or different average steel reinforcement cover thicknesses. Ultrasonic tests are performed on the reinforced and unreinforced areas of each specimen, and an acoustic path correction factor is fitted based on the ultrasonic test results. The sound velocity correction module is used to perform ultrasonic measurements at each measurement point to obtain the basic sound velocity of the ultrasonic wave at each measurement point, and to calculate the ratio of the steel reinforcement thickness to the concrete slab thickness at each measurement point, denoted as the steel reinforcement thickness ratio. Based on the basic sound velocity, steel reinforcement thickness ratio and acoustic path correction factor at each measurement point, the actual sound velocity at each measurement point is calculated. The baseline calculation module is used to obtain the rebound value of each measurement point, normalize the rebound value of each measurement point and correspond it one-to-one with the true sound speed of that measurement point, and generate a state baseline based on the linear regression relationship between the rebound value and the true sound speed of the bridge surface to be tested. The integrated output module is used to calculate the residuals and included angles of each measurement point's deviation from the state baseline, and then calculate the state correction factor for each measurement point. Based on the state correction factor, the reference strength of each measurement point is corrected, and the concrete strength of each measurement point is generated.

[0008] Further, a square inspection area of ​​300mm×300mm is marked on the bridge surface to be inspected, avoiding cracks, joints and damaged areas; the inspection area is evenly divided into 4 rows and 4 columns, totaling 16 measurement grids, each measuring grid is 75mm×75mm in size, the nodes of the measurement grid are used as measurement points, and measurement points located on the surface of the inspection area are selected. Several pairs of measurement points are divided from the selected measurement points according to their vertical orientation, and the thickness of the concrete slab at the location of each pair of measurement points is obtained. The average thickness of the concrete slab at the location of all pairs of measurement points is taken to obtain the average thickness of the concrete slab in the inspection area. The principle for calculating the average concrete cover thickness of the inspection area is as follows: the distribution of steel bars in the inspection area is determined by scanning with a steel bar scanner, the nearest distance between each steel bar inside the concrete and the upper and lower surfaces of the concrete is calculated, and the average value of these nearest distances is taken to obtain the average concrete cover thickness of the inspection area.

[0009] Furthermore, the principle of fitting the acoustic path correction factor is as follows: Several concrete specimens with varying average concrete slab thickness and average steel reinforcement cover thickness were prepared. The specimens were divided according to the same method as the testing area, resulting in several sample measurement points. For each specimen, ultrasonic testing was first performed in the unreinforced area to obtain the intrinsic sound velocity; then, ultrasonic testing was performed in the area crossing the steel reinforcement to obtain the apparent sound velocity. The intrinsic and apparent sound velocities of each specimen were divided to obtain the acoustic path correction factor. The average steel reinforcement cover thickness and average concrete slab thickness were divided to obtain the thickness ratio of each specimen. A linear fitting formula for the acoustic path correction factor and thickness ratio was constructed, including at least one regression coefficient to be determined. Linear fitting was performed on the acoustic path correction factor and thickness ratio of each specimen, and the regression coefficient was determined based on the least squares method.

[0010] Furthermore, the principle of ultrasonic testing is as follows: For each sample measurement point, a straight line passing through that measurement point and perpendicular to the horizontal plane of the concrete specimen is determined. The intersection points of this line with the upper and lower surfaces of the concrete specimen are then identified. These intersection points are designated as the ultrasonic wave emission and reception points, respectively. Emission and reception probes are installed at these points to obtain the time it takes for the ultrasonic wave to travel from the emission point to the reception point. The time measured at the sample measurement point in the unreinforced area is the original sound time, while the time measured at the sample measurement point in the area crossing the reinforcing steel is the actual sound time. The velocity of sound at each sample measurement point in the unreinforced area is obtained by dividing the thickness of the concrete slab at each measurement point by the original sound time. The average velocity of sound at each sample measurement point in the unreinforced area is then calculated to obtain the velocity of sound in the concrete specimen. Similarly, the apparent velocity of sound at each sample measurement point in the area crossing the reinforcing steel is obtained by dividing the thickness of the concrete slab at each measurement point by the original sound time. The average velocity of sound at each sample measurement point in the area crossing the reinforcing steel is then calculated to obtain the apparent velocity of sound in the concrete specimen.

[0011] Furthermore, the principle underlying the calculation of the true sound velocity at each measurement point is as follows: Substitute the concrete slab thickness and steel reinforcement cover thickness at each measurement point within the detection area into the linear fitting formula of the acoustic path correction factor to obtain the acoustic path correction factor for each measurement point. Ultrasonic measurements were performed at each measurement point in the testing area to obtain the basic acoustic time and the proportion of rebar thickness at each point. The basic sound velocity was obtained by dividing the concrete slab thickness at each measurement point by the basic acoustic time. Based on the basic sound velocity, the proportion of rebar thickness, and the acoustic path correction factor of the testing area, the true sound velocity at each measurement point was obtained. The calculation logic for the true sound velocity is as follows: the true sound velocity includes the sound velocity contribution from the unreinforced portion and the sound velocity contribution from the reinforced portion. The proportion of rebar thickness reflects the sound velocity contribution from the reinforced portion. Therefore, the sound velocity contribution from the unreinforced portion is 1 minus the sound velocity contribution from the reinforced portion. Thus, the formula for calculating the true sound velocity is: in, Indicates the first The true speed of sound at each measurement point This indicates the index of the measurement point within the detection area. Indicates the first The base sound velocity at each measurement point Indicates the first The proportion of rebar thickness at each measurement point Indicates the first Acoustic path correction factor for each measurement point.

[0012] Furthermore, the principle for generating state baselines is as follows: After ultrasonic testing, the locations where the transmitting probes are installed within the testing area are designated as rebound test points. The rebound values ​​at each rebound test point are obtained, which are the rebound values ​​at the corresponding measurement points. Concrete samples that meet the bridge deck concrete strength requirements and have known strength are pre-collected to generate a calibration dataset. A curve relating the rebound value to the true sound velocity is constructed, with the following equation: ;in, Indicates the rebound value. Represents the actual speed of sound. Represents the fitting coefficient; it is derived from the rebound value and true sound velocity of the concrete samples in the calibration dataset. ;Will Substituting the equation of the relation curve, we obtain the state baseline.

[0013] Furthermore, the principle underlying the calculation of the state correction factor for each measurement point is as follows: For each measurement point, the residual and included angle of deviation from the state baseline are calculated using the following formula: in, Indicates the first The residuals of each measurement point deviating from the state baseline Indicates the first The rebound value at each measurement point Indicates the first The angle between each measurement point and the state baseline; The residuals and included angles are standardized separately and converted into probability values ​​for the measured points meeting the strength requirements, specifically as follows: in, This represents the probability that the measured point meets the strength requirements at the residual level. This represents the standard deviation of the residuals from the baseline at all measurement points. The cumulative distribution function represents the standard normal distribution. This represents the probability that the measurement point meets the strength requirements on the included angle plane. This represents the standard deviation of the angles between all measured points and the baseline. The two probabilities mentioned above are linearly weighted and summed to generate a state health factor, and The weight is greater than The weights; Based on the true sound velocity and rebound value at the measurement points, and combined with the average true sound velocity and average rebound value of concrete samples in the calibration dataset, the sound velocity-rebound value coupling term is calculated. The specific formula is as follows: in, Indicates the first The sound velocity-rebound coupling term at each measurement point This represents the average true sound velocity of the concrete samples in the calibration dataset. This represents the average rebound value of the concrete samples in the calibration dataset; Multiplying the state health factor by the sound velocity-rebound coupling term yields the state correction factor for the measurement point.

[0014] Furthermore, the principle for correcting the reference strength at each measurement point is as follows: The average strength of the concrete samples in the calibration dataset is used as the reference strength of the measurement points. The concrete strength of each measurement point is obtained by multiplying the state correction factor of each measurement point by the reference strength.

[0015] This invention also provides a non-destructive testing method for the strength of bridge deck concrete based on ultrasonic rebound. The testing method is performed by the aforementioned non-destructive testing system for the strength of bridge deck concrete based on ultrasonic rebound, and the specific steps include: Step 1: Select the inspection area on the bridge deck to be inspected, and divide the inspection area into a uniform measurement grid to form measurement points. Obtain the concrete slab thickness at each measurement point, and calculate the average concrete slab thickness and the average steel reinforcement cover thickness of the inspection area. Step 2: Prepare several sets of specimens with different average concrete slab thicknesses or different average steel reinforcement cover thicknesses, and perform ultrasonic testing on the reinforced and unreinforced areas of each specimen. Fit an acoustic path correction factor based on the ultrasonic testing results. Step 3: Perform ultrasonic testing at each measurement point to obtain the basic sound velocity of the ultrasonic wave at each measurement point, and calculate the ratio of the steel reinforcement thickness to the concrete slab thickness at each measurement point, which is recorded as the steel reinforcement thickness ratio. Calculate the true sound velocity at each measurement point based on the basic sound velocity, the steel reinforcement thickness ratio, and the acoustic path correction factor. Step 4: Obtain the rebound value of each measurement point, normalize the rebound value of each measurement point and match it with the true sound speed of that measurement point, and generate a state baseline based on the linear regression relationship between the rebound value of the bridge surface to be tested and the true sound speed. Step 5: Calculate the residuals and included angles of each measurement point from the state baseline, then calculate the state correction factor for each measurement point, and correct the reference strength of each measurement point based on the state correction factor to generate the concrete strength of each measurement point.

[0016] Compared with the prior art, the beneficial effects of the present invention are: This invention divides the detection area into several measurement points evenly, avoiding local deviations caused by single-point or sparse point measurements, and more comprehensively reflects the overall condition of the bridge deck concrete. By preparing specimens with different thicknesses and protective layer thicknesses, the sound velocity in areas with and without reinforcement is measured respectively, and a fitting relationship between the acoustic path correction factor and the thickness ratio is established. This achieves structured and quantitative correction of reinforcement interference, and can adapt to bridge deck conditions with different concrete slab thicknesses, protective layer thicknesses, and strength grades, thus improving the universality of this invention in complex practical engineering.

[0017] This invention also quantifies the influence of factors such as steel reinforcement and protective layer thickness on sound velocity by preparing a series of specimens to fit acoustic path correction factors, thereby improving the accuracy of sound velocity measurement and realizing the conversion from apparent sound velocity to actual sound velocity, thus eliminating sound velocity deviation caused by non-material factors. It normalizes the correspondence between the true sound velocity and rebound value at each measurement point and establishes a unique linear regression relationship based on the data of the current bridge deck under test, eliminating systematic deviations caused by differences in materials, mix proportions, and environment. Furthermore, it establishes a numerical relationship between the true sound velocity and rebound value through a state baseline, introduces two geometric and statistical quantities—residue and included angle—and transforms the residual and included angle into probability values ​​that meet strength requirements, strengthening the synergistic effect of the true sound velocity and rebound value on strength and improving the accuracy of strength testing. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the method flow of an embodiment of the present invention; Figure 2 This is a schematic diagram of the fitting curve of the acoustic path correction factor as a function of thickness ratio in an embodiment of the present invention; Figure 3 This is a schematic diagram of the fitting curve of the state baseline in an embodiment of the present invention; Figure 4 This is a schematic diagram of the system modules in an embodiment of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0020] It should be noted that, unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0021] Example: Please see Figures 1 to 3 The present invention provides a technical solution: A non-destructive testing system for bridge deck concrete strength based on ultrasonic rebound specifically includes: The measurement point division module is used to select the inspection area on the bridge deck to be inspected, uniformly divide the inspection area into measurement grids to form measurement points, obtain the concrete slab thickness of each measurement point, and calculate the average concrete slab thickness and average steel reinforcement cover thickness of the inspection area. In this embodiment, a square inspection area of ​​300mm×300mm is marked on the bridge surface to be inspected. The inspection area avoids cracks, joints and damaged areas. The inspection area is evenly divided into 4 rows and 4 columns, totaling 16 measurement grids. Each measurement grid is 75mm×75mm in size. The nodes of the measurement grid are used as measurement points. Measurement points located on the surface of the inspection area are selected. Several pairs of measurement points are divided from the selected measurement points according to their vertical orientation. The thickness of the concrete slab at the location of each pair of measurement points is obtained. The average thickness of the concrete slab at the location of all pairs of measurement points is taken to obtain the average thickness of the concrete slab in the inspection area. The principle for calculating the average concrete cover thickness of the inspection area is as follows: the distribution of steel bars in the inspection area is determined by scanning with a steel bar scanner, the nearest distance between each steel bar inside the concrete and the upper and lower surfaces of the concrete is calculated, and the average value of these nearest distances is taken to obtain the average concrete cover thickness of the inspection area.

[0022] When selecting the inspection area on the bridge deck, cracks, construction joints, repaired areas, water accumulation areas, and damaged parts were avoided to ensure that the measurement data could reflect the true performance of the concrete material. The size of the inspection area was set at 300mm × 300mm to balance measurement representativeness and operational feasibility. After dividing the inspection area into 16 measurement grids, all corner points of these 16 grids were designated as measurement points. From these measurement points, measurement points located on the surface of the inspection area were selected. From these measurement points, several pairs of measurement points were constructed according to the principle of vertical alignment, which could penetrate the inspection area. Each pair of measurement points consisted of two measurement points located on the upper and lower surfaces of the inspection area, respectively. A digital ultrasonic thickness gauge was used to measure at each pair of measurement points, and the thickness of the concrete slab at each measurement point was recorded. The average thickness of the concrete slab in the inspection area was obtained by averaging the thicknesses of all measurement point pairs.

[0023] The concrete cover thickness represents the minimum distance from the outer surface of a concrete structural member to the outermost layer of reinforcing bars inside the concrete. A rebar scanner is used to scan the inspection area, keeping the scanner in close contact with the concrete surface and moving at a constant speed along the grid lines to cover the entire measurement grid area, thereby obtaining the planar distribution and depth of the reinforcing bars within the inspection area. For each scanned rebar, the nearest vertical distance between it and the upper and lower surfaces of the concrete in the inspection area is calculated, generating the upper and lower concrete cover thicknesses for each rebar. The average of the upper and lower concrete cover thicknesses of all rebars in the inspection area is then obtained to obtain the average concrete cover thickness of the inspection area.

[0024] The path correction module is used to prepare several sets of specimens with different average concrete slab thicknesses or different average steel reinforcement cover thicknesses. Ultrasonic tests are performed on the reinforced and unreinforced areas of each specimen, and an acoustic path correction factor is fitted based on the ultrasonic test results. In this embodiment, the principle of fitting the acoustic path correction factor is as follows: Several concrete specimens with varying average concrete slab thickness and average steel reinforcement cover thickness were prepared. The specimens were divided according to the same method as the testing area, resulting in several sample measurement points. For each specimen, ultrasonic testing was first performed in the unreinforced area to obtain the intrinsic sound velocity; then, ultrasonic testing was performed in the area crossing the steel reinforcement to obtain the apparent sound velocity. The intrinsic and apparent sound velocities of each specimen were divided to obtain the acoustic path correction factor. The average steel reinforcement cover thickness and average concrete slab thickness were divided to obtain the thickness ratio of each specimen. A linear fitting formula for the acoustic path correction factor and thickness ratio was constructed, including at least one regression coefficient to be determined. Linear fitting was performed on the acoustic path correction factor and thickness ratio of each specimen, and the regression coefficient was determined based on the least squares method.

[0025] The path correction module aims to establish a quantitative correction model for the influence of concrete slab thickness and rebar cover thickness on ultrasonic wave propagation velocity. This is achieved by preparing a series of concrete specimens with different geometric and reinforcement characteristics, measuring the difference in ultrasonic wave propagation velocity in unreinforced concrete and in areas crossing rebar, thereby constructing an acoustic path correction factor that eliminates the interference of rebar on sound velocity. The concrete slab thickness of the prepared specimens covers common thicknesses in actual bridge decks, ranging from 150mm to 300mm, and the rebar cover thickness ranges from 20mm to 70mm. Each concrete specimen is divided into 16 measurement grids using the same grid division method as the test area. The corner points of these measurement grids are used as sample measurement points. Several sample measurement point pairs are selected from these points. Sample measurement point pairs without rebar obstruction along the ultrasonic wave propagation path are selected, and the ultrasonic wave propagation time is measured. The sound velocity in the concrete slab is calculated based on the concrete slab thickness of each sample measurement point pair. The specific calculation formula is as follows: in, Indicates the first The sound velocity of the sample measurement points This indicates the index of the sample measurement point located in the unreinforced area. Indicates the first The thickness of the concrete slab at each sample measurement point Indicates the first The original acoustic time of each sample measurement point; The average sound velocity of the concrete specimen is obtained by averaging the sound velocities at various measurement points within the unreinforced area. ; Select a pair of sample measurement points along the ultrasonic wave propagation path that pass through the reinforcing steel, measure the ultrasonic wave propagation time, and then calculate the apparent sound velocity. The specific calculation formula is as follows: in, Indicates the first Apparent sound velocity at each sample measurement point Indicates the index of the sample measurement point located in the area spanning the reinforcing bars. Indicates the first The actual acoustic time of each sample measurement point; The apparent sound velocity of the concrete specimen is obtained by averaging the apparent sound velocity at each measurement point located within the area spanning the reinforcing bars. ; The intrinsic sound velocity represents the speed at which ultrasound propagates in a pure concrete region without reinforcement. It reflects the acoustic characteristics of the concrete material itself, such as its intrinsic properties related to strength, including density, elastic modulus, and internal uniformity. As a reference sound velocity, it is used to correct for sound velocity deviations caused by reinforcement. The apparent sound velocity represents the speed at which ultrasound propagates across a region with reinforcement. It reflects the acoustic behavior of the concrete-reinforcement composite system. The sound velocity in reinforcement is usually higher than that in concrete, and ultrasound propagates faster in reinforcement. Therefore, the apparent sound velocity is higher than the intrinsic sound velocity.

[0026] Following the method described above, the sound velocity of each concrete specimen was obtained. and apparent speed of sound ,in, Indicates the first The sound velocity of the concrete specimen itself. Indicates the index of the concrete specimen, and ,in, Indicates the number of concrete test specimens. Indicates the first The apparent sound velocity of each concrete specimen was measured; the acoustic path correction factor for each specimen was obtained by quotienting the bulk sound velocity and apparent sound velocity of each specimen. ,in, Indicates the first Acoustic path correction factor for a concrete specimen; The acoustic path correction factor reflects the intensity of the acceleration effect of reinforcing steel on ultrasonic waves. Since the longitudinal wave velocity of reinforcing steel is much higher than that of concrete, when reinforcing steel is included in the ultrasonic wave propagation path, the propagation time is shortened and the apparent velocity is increased. The acoustic path correction factor is essentially the ratio of the intrinsic velocity of concrete to the equivalent velocity of the area containing reinforcing steel. The larger the proportion of reinforcing steel, the greater the influence of reinforcing steel and the smaller the acoustic path correction factor. When the influence of reinforcing steel is zero, the acoustic path correction factor is 1.

[0027] The average thickness of the concrete cover and the average thickness of the concrete slab were measured for each concrete specimen, and the two were divided to generate the thickness ratio. The calculation formula is as follows: in, Indicates the first The thickness ratio of each concrete specimen Indicates the first Average thickness of concrete cover for reinforcement in each concrete specimen Indicates the first Average concrete slab thickness of each concrete specimen; Based on multiple concrete specimens and The linear fitting formula for the two is constructed as follows: in, Represents the fitting coefficient; The influence of reinforcing bars on the ultrasonic wave propagation path is determined by the relative position and relative contribution of the reinforcing bars in the path. The thickness ratio refers to the proportion of the pure concrete path segment in the ultrasonic wave propagation path to the total path length. This determines the minimum distance that ultrasound waves must travel in pure concrete before entering the reinforcing steel. It is the total distance the sound wave travels; when When the sound is very small, the reinforcing bars are very close to the concrete surface, and their effect on increasing the sound velocity along the entire path is very significant; the apparent sound velocity is much greater than the actual sound velocity, and the acoustic path correction factor is very small at this time. When the value is large, it means that the pure concrete path segment accounts for a large proportion of the ultrasonic transmission path, while the influence of the reinforcing steel is relatively small, resulting in a limited increase in the overall sound velocity. In this case, the acoustic path correction factor is close to 1.

[0028] Sum of squared residuals With the goal of minimizing, the least squares method is used for fitting, and the result is calculated. ; The relationship between the acoustic path correction factor and the thickness ratio is: ,in, Indicates the acoustic path correction factor. Indicates the thickness ratio; Table 1 shows the relationship between the acoustic path correction factor and the thickness ratio. and The overall correlation is positive, indicating that the thicker the concrete cover, the larger the proportion of pure concrete in the propagation path of ultrasonic waves in concrete, and the smaller the influence of the reinforcing steel on the overall sound velocity. The closer it is to 1.

[0029] Table 1. Changes in Acoustic Path Correction Factor The principle of ultrasonic testing is as follows: For each sample measurement point, a straight line passing through that measurement point and perpendicular to the horizontal plane of the concrete specimen is determined. The intersection points of this line with the upper and lower surfaces of the concrete specimen are then identified. These intersection points are designated as the ultrasonic wave emission and reception points, respectively. Emission and reception probes are installed at these points to obtain the time it takes for the ultrasonic wave to travel from the emission point to the reception point. The time measured at the sample measurement point in the unreinforced area is the original sound time, while the time measured at the sample measurement point in the area crossing the reinforcing steel is the actual sound time. The velocity of sound at each sample measurement point in the unreinforced area is obtained by dividing the thickness of the concrete slab at each measurement point by the original sound time. The average velocity of sound at each sample measurement point in the unreinforced area is then calculated to obtain the velocity of sound in the concrete specimen. Similarly, the apparent velocity of sound at each sample measurement point in the area crossing the reinforcing steel is obtained by dividing the thickness of the concrete slab at each measurement point by the original sound time. The average velocity of sound at each sample measurement point in the area crossing the reinforcing steel is then calculated to obtain the apparent velocity of sound in the concrete specimen.

[0030] The sound velocity correction module is used to perform ultrasonic measurements at each measurement point to obtain the basic sound velocity of the ultrasonic wave at each measurement point, and to calculate the ratio of the steel reinforcement thickness to the concrete slab thickness at each measurement point, denoted as the steel reinforcement thickness ratio. Based on the basic sound velocity, steel reinforcement thickness ratio and acoustic path correction factor at each measurement point, the actual sound velocity at each measurement point is calculated. In this embodiment, the principle used to calculate the true sound velocity at each measurement point is as follows: Substitute the concrete slab thickness and steel reinforcement cover thickness at each measurement point within the detection area into the linear fitting formula of the acoustic path correction factor to obtain the acoustic path correction factor for each measurement point. Ultrasonic measurements were performed at each measurement point in the testing area to obtain the basic acoustic time and the proportion of rebar thickness at each point. The basic sound velocity was obtained by dividing the concrete slab thickness at each measurement point by the basic acoustic time. Based on the basic sound velocity, the proportion of rebar thickness, and the acoustic path correction factor of the testing area, the true sound velocity at each measurement point was obtained. The calculation logic for the true sound velocity is as follows: the true sound velocity includes the sound velocity contribution from the unreinforced portion and the sound velocity contribution from the reinforced portion. The proportion of rebar thickness reflects the sound velocity contribution from the reinforced portion. Therefore, the sound velocity contribution from the unreinforced portion is 1 minus the sound velocity contribution from the reinforced portion. Thus, the formula for calculating the true sound velocity is: in, Indicates the first The true speed of sound at each measurement point This indicates the index of the measurement point within the detection area. Indicates the first The base sound velocity at each measurement point Indicates the first The proportion of rebar thickness at each measurement point Indicates the first Acoustic path correction factor for each measurement point.

[0031] The goal of this module is to remove the interference of reinforcing steel bars on the ultrasonic wave propagation path from the measured foundation sound velocity, and to restore the true sound velocity that reflects the acoustic properties of the concrete material itself. The foundation sound velocity is calculated from the data obtained by ultrasonic testing, and the calculation formula is as follows: ,in, Indicates the first The thickness of the concrete slab at each measurement point Indicates the first The acoustic time of a concrete slab foundation; the steel reinforcement thickness ratio is the proportion of the steel reinforcement at the measurement point in the ultrasonic wave transmission path, and its calculation formula is: ,in, Indicates the first The thickness of the reinforcing steel at each measurement point; the propagation path of the ultrasonic wave within the detection area consists of two parts: a part without reinforcing steel and a part with reinforcing steel. The sound velocity in the part without reinforcing steel is the sound velocity of the concrete itself. In the part with reinforcing steel, due to the acceleration effect of the reinforcing steel, its equivalent sound velocity is the ratio of the sound velocity of the concrete itself to the acoustic path correction factor. Therefore, the overall propagation time can be expressed as: Substituting the above equation into... After sorting, we get: Solving for the true speed of sound: ; The true speed of sound is the speed of sound after removing the interference from the reinforcing steel bars. The extent of the reinforcing steel bar interference is determined by the proportion of the steel bar thickness. reflect, The larger the value, the greater the proportion of the ultrasonic wave propagating through the reinforcing steel, the more significant the acceleration effect of the reinforcing steel, and the closer the apparent sound velocity is to the sound velocity of the reinforcing steel. The smaller the value, the less influence the reinforcing steel has, and the closer the apparent sound velocity is to the sound velocity within the concrete itself. The total propagation path of the ultrasonic wave can be considered as two segments in series: the pure concrete segment and the reinforcing steel segment, where the length of the pure concrete segment is... The length of the steel bar segment is By combining the geometric parameters of concrete with its acoustic behavior through an acoustic path correction factor, the conversion from apparent sound velocity to the actual sound velocity of the concrete itself is achieved.

[0032] The baseline calculation module is used to obtain the rebound value of each measurement point, normalize the rebound value of each measurement point and correspond it one-to-one with the true sound speed of that measurement point, and generate a state baseline based on the linear regression relationship between the rebound value and the true sound speed of the bridge surface to be tested. In this embodiment, the principle for generating the state baseline is as follows: After ultrasonic testing, the locations where the transmitting probes are installed within the testing area are designated as rebound test points. The rebound values ​​at each rebound test point are obtained, which are the rebound values ​​at the corresponding measurement points. Concrete samples that meet the bridge deck concrete strength requirements and have known strength are pre-collected to generate a calibration dataset. A curve relating the rebound value to the true sound velocity is constructed, with the following equation: ;in, Indicates the rebound value. Represents the actual speed of sound. Represents the fitting coefficient; it is derived from the rebound value and true sound velocity of the concrete samples in the calibration dataset. ;Will Substituting the equation of the relation curve, we obtain the state baseline.

[0033] The principle for determining the location of the transmitting probe within the detection area is as follows: For each measurement point within the detection area, a straight line passing through the measurement point and perpendicular to the surface of the detection area is determined. Then, the intersection of this straight line with the upper and lower surfaces of the detection area is determined. The intersection of this straight line with the upper and lower surfaces is set as the transmitting and receiving points of the ultrasonic wave, respectively. The transmitting probe is installed at the transmitting point, and this position is used as the rebound test point.

[0034] Concrete with different bridge decks, material mixes, and environmental conditions may exhibit a general deviation between its rebound value and true sound velocity. A state baseline is constructed by comparing the rebound value and true sound velocity to characterize the relationship between the rebound value and true sound velocity under ideal conditions. This provides a unified reference state for all measurement points, eliminating systematic errors caused by material differences, environmental variations, and other factors. Ultrasonic velocity and rebound value are physical signals, while concrete compressive strength is a mechanical property. There is no universally applicable theoretical conversion formula between the two. The purpose of the calibration dataset is to construct an empirical mathematical model, i.e., the state baseline, using experimental data from standard samples of known strength. Concrete samples of known strength are collected, and ultrasonic and rebound tests are performed on these samples to obtain the true sound velocity and rebound value for each concrete sample. The least squares method is used for fitting, and the fitting coefficient is calculated. ,Will Substituting the relationship curve, we obtain a baseline representing the state of healthy concrete: Used to determine whether each measurement point deviates from a healthy state.

[0035] Table 2 reflects the positive correlation between true sound velocity and rebound value in healthy concrete. True sound velocity mainly reflects the internal density, elastic modulus, and uniformity of the concrete. Higher sound velocity generally means denser concrete, fewer internal defects, and greater strength potential. Rebound value mainly reflects the surface hardness of the concrete; higher rebound value indicates a harder surface layer, which usually also means higher strength. By fitting these data, a state baseline is established, representing an ideal concrete state. If a measurement point deviates significantly from this state baseline, it indicates that the concrete at that point may be abnormal. For example, if the sound velocity is normal but the rebound is low, surface carbonization, looseness, or damage may occur. If the rebound is normal but the sound velocity is low, microcracks or lack of density may exist internally.

[0036] Table 2. Rebound Value Variation Table The integrated output module is used to calculate the residuals and included angles of each measurement point's deviation from the state baseline, and then calculate the state correction factor for each measurement point. Based on the state correction factor, the reference strength of each measurement point is corrected, and the concrete strength of each measurement point is generated.

[0037] In this embodiment, the principle upon which the state correction factor for each measurement point is calculated is as follows: For each measurement point, the residual and included angle of deviation from the state baseline are calculated using the following formula: in, Indicates the first The residuals of each measurement point deviating from the state baseline Indicates the first The rebound value at each measurement point Indicates the first The true speed of sound at each measurement point Indicates the first The angle between each measurement point and the state baseline; By calculating the residuals and included angles of each measurement point's deviation from the baseline, the state of the measurement points is quantitatively evaluated from both geometric and statistical dimensions. The residuals represent the deviation between the measured rebound value and the baseline expected value. The closer the residuals are to 0, the higher the match between the rebound value at that measurement point and the ideal rebound value corresponding to the speed of sound; the closer the intensity is to the intensity that meets the requirements in the calibration dataset; and the more consistent it is with healthy samples. This indicates that the measured rebound value is higher than the baseline expectation, meaning the concrete surface hardness at that measurement point is higher than the healthy value, and the true strength of the concrete is higher. This indicates that the measured rebound value is lower than the baseline expectation, meaning the concrete surface hardness at that measurement point is lower than the healthy value, indicating poor overall concrete quality and failure to meet health standards. The included angle represents the deviation angle between the rebound-sound velocity ratio direction at the measurement point and the baseline direction. The closer the included angle is to 0, the more consistent the rebound-sound velocity ratio at that measurement point is with the healthy baseline. This indicates that the rebound value at that point is either too high or too low relative to the ideal rebound value corresponding to the speed of sound. This indicates that the rebound value at this point is lower than the ideal rebound value corresponding to the speed of sound, or the speed of sound is relatively lower; the residual reflects the absolute deviation and assesses the vertical distance between the current point and the baseline, while the included angle reflects the relative deviation and assesses the directional consistency between the current point and the baseline. Combining the two, we can comprehensively judge whether the measurement point is in a healthy state from the two geometric dimensions of distance and direction.

[0038] The residuals and included angles are standardized separately and converted into probability values ​​for the measured points meeting the strength requirements, specifically as follows: in, Indicates the first The probability that a measurement point meets the strength requirements at the residual level. This represents the standard deviation of the residuals of the baseline deflection at all measurement points. The cumulative distribution function represents the standard normal distribution. Indicates the first The probability that a measurement point meets the strength requirements at the included angle level. This represents the standard deviation of the angles between all measured points and the baseline. The cumulative distribution function representing the standard normal distribution is expressed as follows: Its cumulative distribution function is a random variable The probability is expressed as: ; This represents the probability that a measured point meets the strength requirements, considering only distance error. (Calculation) At that time, the residuals are transformed into z-scores under the standard normal distribution. This represents the standardized error, calculated by dividing the absolute error between the actual measured value and the baseline by the standard deviation of the residuals at all measurement points, and then taking the negative number. It is a standardized negative deviation index. As the upper limit in the cumulative distribution function, only random variables... Only then can the strength requirements be met. It reflects the degree of fit between the measurement point and the ideal state in the rebound-sound velocity relationship. The closer the value is to 1, the closer the measurement point is to the ideal state and the strength meets the requirements. The closer the value is to 0, the greater the deviation from the healthy state and the insufficient strength. Similarly, the closer the value is to 1, the more consistent the ratio of rebound to sound velocity at that point is with that of a healthy sample; the lower the value, the more abnormal the ratio is, and the worse the health status of the measurement point.

[0039] The two probabilities mentioned above are linearly weighted and summed to generate a state health factor, and The weight is greater than The weights; the specific calculation formula is: ,in, Indicates the first The health status factor of each measurement point They are respectively The weight, and .

[0040] The health condition factor reflects the degree to which the concrete strength at the measurement point conforms to the required "health condition" for strength. The two components are: the health factor, the closer the measurement point is to the strength of the concrete in a healthy state, and the closer the value is to 0, the greater the deviation of the measurement point from the healthy state; the residual directly reflects the difference between the measured rebound value and the benchmark expected value, and has a stronger direct correlation with the concrete strength; the included angle reflects whether the ratio between the rebound and the sound velocity is coordinated, and indirectly reflects the concrete strength. Therefore, the weight of the residual is greater than the weight of the included angle.

[0041] Based on the true sound velocity and rebound value at the measurement points, and combined with the average true sound velocity and average rebound value of concrete samples in the calibration dataset, the sound velocity-rebound value coupling term is calculated. The specific formula is as follows: in, Indicates the first The sound velocity-rebound coupling term at each measurement point This represents the average true sound velocity of the concrete samples in the calibration dataset. This represents the average rebound value of the concrete samples in the calibration dataset; The sound velocity-rebound coupling term is a dimensionless intensity co-amplification factor, designed to represent the ratio of the combined signal intensity at the current measurement point to a standard intensity. It is the product of the actual sound velocity at the current measurement point and the rebound value. A high sound velocity usually means that the interior is dense and the elastic modulus is high, while a high rebound value means that the surface hardness is high. When both are high, their product will increase significantly, indicating that the concrete at the measurement point has higher comprehensive strength. This is the product of the average true sound velocity and the average rebound value of healthy concrete samples in the calibration dataset. It represents the comprehensive strength benchmark under healthy conditions. The ratio of the two reflects how many times the comprehensive strength at the current point is greater than the benchmark strength. A higher ratio indicates a higher strength at the current measurement point. Taking the natural logarithm of this ratio and adding 1 ensures... A constant positive value allows for unidirectional amplification or maintenance of the baseline strength through a product, but evaluating strength using a single index has limitations. Sound velocity is sensitive to internal defects, while rebound is sensitive to surface condition. High-strength concrete typically exhibits both high sound velocity and high rebound value simultaneously. Using a product approach can more accurately capture this synergistic effect; the product is only significantly high when both are high, avoiding misjudgment.

[0042] Multiplying the state health factor by the sound velocity-rebound coupling term yields the state correction factor for the measurement point.

[0043] The state correction factor is a prediction multiplier for the concrete strength at the measurement point. When the state correction factor is greater than 1, it indicates that the overall condition of the measurement point is better than the healthy reference sample used for calibration, and the predicted strength should be higher than the reference strength. When the state correction factor is equal to 1, it indicates that the condition of the measurement point is comparable to the reference sample, and the predicted strength is equal to the reference strength. When the state correction factor is less than 1, it indicates that the condition of the point is worse than the reference sample, and the predicted strength should be lower than the reference strength. The state correction factor reflects the proportion by which the concrete strength at the measurement point deviates from the reference strength.

[0044] The principle for correcting the reference strength at each measurement point is as follows: The average strength of the concrete samples in the calibration dataset is used as the reference strength of the measurement points. The concrete strength of each measurement point is obtained by multiplying the state correction factor of each measurement point by the reference strength.

[0045] The reference strength comes from the calibration dataset and is the average strength of healthy concrete samples with known strength. It represents the strength of concrete with a certain sound velocity and rebound value under ideal conditions. If the state correction factor of a certain measurement point is equal to 1, it means that the measurement point is consistent with the state of the reference sample, and the strength of the measurement point is the reference strength. When the state correction factor of the measurement point is greater than or less than 1, the strength of the measurement point is also greater than or less than the reference strength. The reference strength is corrected by the state correction factor to obtain the actual strength of the measurement point.

[0046] Please see Figure 4 The present invention also provides a non-destructive testing method for the strength of bridge deck concrete based on ultrasonic rebound. The testing method is performed by the aforementioned non-destructive testing system for the strength of bridge deck concrete based on ultrasonic rebound, and the specific steps include: Step 1: Select the inspection area on the bridge deck to be inspected, and divide the inspection area into a uniform measurement grid to form measurement points. Obtain the concrete slab thickness at each measurement point, and calculate the average concrete slab thickness and the average steel reinforcement cover thickness of the inspection area. Step 2: Prepare several sets of specimens with different average concrete slab thicknesses or different average steel reinforcement cover thicknesses, and perform ultrasonic testing on the reinforced and unreinforced areas of each specimen. Fit an acoustic path correction factor based on the ultrasonic testing results. Step 3: Perform ultrasonic testing at each measurement point to obtain the basic sound velocity of the ultrasonic wave at each measurement point, and calculate the ratio of the steel reinforcement thickness to the concrete slab thickness at each measurement point, which is recorded as the steel reinforcement thickness ratio. Calculate the true sound velocity at each measurement point based on the basic sound velocity, the steel reinforcement thickness ratio, and the acoustic path correction factor. Step 4: Obtain the rebound value of each measurement point, normalize the rebound value of each measurement point and match it with the true sound speed of that measurement point, and generate a state baseline based on the linear regression relationship between the rebound value of the bridge surface to be tested and the true sound speed. Step 5: Calculate the residuals and included angles of each measurement point from the state baseline, then calculate the state correction factor for each measurement point, and correct the reference strength of each measurement point based on the state correction factor to generate the concrete strength of each measurement point.

[0047] The above formulas are all dimensionless calculations. The formulas are derived from software simulations based on a large amount of collected data to obtain the most recent real-world results. The preset parameters in the formulas are set by those skilled in the art according to the actual situation.

[0048] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented in software, the above embodiments can be implemented, in whole or in part, as a computer program product. Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented by electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution.

[0049] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment, depending on actual needs.

[0050] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A non-destructive testing system for bridge deck concrete strength based on ultrasonic rebound, characterized in that, Specifically, it includes: The measurement point division module is used to select the inspection area on the bridge deck to be inspected, uniformly divide the inspection area into measurement grids to form measurement points, obtain the concrete slab thickness of each measurement point, and calculate the average concrete slab thickness and average steel reinforcement cover thickness of the inspection area. The path correction module is used to prepare several sets of specimens with different average concrete slab thicknesses or different average steel reinforcement cover thicknesses. Ultrasonic tests are performed on the reinforced and unreinforced areas of each specimen, and an acoustic path correction factor is fitted based on the ultrasonic test results. The sound velocity correction module is used to perform ultrasonic measurements at each measurement point to obtain the basic sound velocity of the ultrasonic wave at each measurement point, and to calculate the ratio of the steel reinforcement thickness to the concrete slab thickness at each measurement point, denoted as the steel reinforcement thickness ratio. Based on the basic sound velocity, steel reinforcement thickness ratio and acoustic path correction factor at each measurement point, the actual sound velocity at each measurement point is calculated. The baseline calculation module is used to obtain the rebound value of each measurement point, normalize the rebound value of each measurement point and correspond it one-to-one with the true sound speed of that measurement point, and generate a state baseline based on the linear regression relationship between the rebound value and the true sound speed of the bridge surface to be tested. The integrated output module is used to calculate the residuals and included angles of each measurement point's deviation from the state baseline, and then calculate the state correction factor for each measurement point. Based on the state correction factor, the reference strength of each measurement point is corrected, and the concrete strength of each measurement point is generated.

2. The non-destructive testing system for bridge deck concrete strength based on ultrasonic rebound according to claim 1, characterized in that: The measurement point division module marks a square detection area of ​​300mm×300mm on the bridge surface to be inspected. The detection area avoids cracks, joints and damaged areas. The detection area is evenly divided into 16 measurement grids in 4 rows and 4 columns. Each measurement grid is 75mm×75mm in size. The nodes of the measurement grid are used as measurement points. Measurement points located on the surface of the detection area are selected. Several measurement point pairs are divided from the selected measurement points according to the vertical relationship. The thickness of the concrete slab at the location of each measurement point pair is obtained. The average thickness of the concrete slab at the location of all measurement point pairs is taken to obtain the average thickness of the concrete slab in the detection area. The principle for calculating the average concrete cover thickness of the inspection area is as follows: the distribution of steel bars in the inspection area is determined by scanning with a steel bar scanner, the nearest distance between each steel bar inside the concrete and the upper and lower surfaces of the concrete is calculated, and the average value of these nearest distances is taken to obtain the average concrete cover thickness of the inspection area.

3. The non-destructive testing system for bridge deck concrete strength based on ultrasonic rebound according to claim 1, characterized in that: The principle behind fitting the acoustic path correction factor in the path correction module is as follows: Several concrete specimens with varying average concrete slab thickness and average steel reinforcement cover thickness were prepared. The specimens were divided according to the same method as the testing area, resulting in several sample measurement points. For each specimen, ultrasonic testing was first performed in the unreinforced area to obtain the intrinsic sound velocity; then, ultrasonic testing was performed in the area crossing the steel reinforcement to obtain the apparent sound velocity. The intrinsic and apparent sound velocities of each specimen were divided to obtain the acoustic path correction factor. The average steel reinforcement cover thickness and average concrete slab thickness were divided to obtain the thickness ratio of each specimen. A linear fitting formula for the acoustic path correction factor and thickness ratio was constructed, including at least one regression coefficient to be determined. Linear fitting was performed on the acoustic path correction factor and thickness ratio of each specimen, and the regression coefficient was determined based on the least squares method.

4. The non-destructive testing system for bridge deck concrete strength based on ultrasonic rebound according to claim 3, characterized in that: The principle of ultrasonic testing is as follows: For each sample measurement point, a straight line passing through that measurement point and perpendicular to the horizontal plane of the concrete specimen is determined. The intersection points of this line with the upper and lower surfaces of the concrete specimen are then identified. These intersection points are designated as the ultrasonic wave emission and reception points, respectively. Emission and reception probes are installed at these points to obtain the time it takes for the ultrasonic wave to travel from the emission point to the reception point. The time measured at the sample measurement point in the unreinforced area is the original sound time, while the time measured at the sample measurement point in the area crossing the reinforcing steel is the actual sound time. The velocity of sound at each sample measurement point in the unreinforced area is obtained by dividing the thickness of the concrete slab at each measurement point by the original sound time. The average velocity of sound at each sample measurement point in the unreinforced area is then calculated to obtain the velocity of sound in the concrete specimen. Similarly, the apparent velocity of sound at each sample measurement point in the area crossing the reinforcing steel is obtained by dividing the thickness of the concrete slab at each measurement point by the original sound time. The average velocity of sound at each sample measurement point in the area crossing the reinforcing steel is then calculated to obtain the apparent velocity of sound in the concrete specimen.

5. The non-destructive testing system for bridge deck concrete strength based on ultrasonic rebound according to claim 4, characterized in that: The principle underlying the calculation of the true sound velocity at each measurement point in the sound velocity correction module is as follows: Substitute the concrete slab thickness and steel reinforcement cover thickness at each measurement point within the detection area into the linear fitting formula of the acoustic path correction factor to obtain the acoustic path correction factor for each measurement point. Ultrasonic measurements were performed at each measurement point in the testing area to obtain the basic acoustic time and the proportion of rebar thickness at each point. The basic sound velocity was obtained by dividing the concrete slab thickness at each measurement point by the basic acoustic time. Based on the basic sound velocity, the proportion of rebar thickness, and the acoustic path correction factor of the testing area, the true sound velocity at each measurement point was obtained. The calculation logic for the true sound velocity is as follows: the true sound velocity includes the sound velocity contribution from the unreinforced portion and the sound velocity contribution from the reinforced portion. The proportion of rebar thickness reflects the sound velocity contribution from the reinforced portion. Therefore, the sound velocity contribution from the unreinforced portion is 1 minus the sound velocity contribution from the reinforced portion. Thus, the formula for calculating the true sound velocity is: in, Indicates the first The true speed of sound at each measurement point This indicates the index of the measurement point within the detection area. Indicates the first The base sound velocity at each measurement point Indicates the first The proportion of rebar thickness at each measurement point Indicates the first Acoustic path correction factor for each measurement point.

6. The non-destructive testing system for bridge deck concrete strength based on ultrasonic rebound according to claim 5, characterized in that: The principle behind generating state baselines in the baseline calculation module is as follows: After ultrasonic testing, the locations where the transmitting probes are installed within the testing area are designated as rebound test points. The rebound values ​​at each rebound test point are obtained, which are the rebound values ​​at the corresponding measurement points. Concrete samples that meet the bridge deck concrete strength requirements and have known strength are pre-collected to generate a calibration dataset. A curve relating the rebound value to the true sound velocity is constructed, with the following equation: ;in, Indicates the rebound value. Represents the actual speed of sound. Represents the fitting coefficient; it is derived from the rebound value and true sound velocity of the concrete samples in the calibration dataset. ;Will Substituting the equation of the relation curve, we obtain the state baseline.

7. The non-destructive testing system for bridge deck concrete strength based on ultrasonic rebound according to claim 6, characterized in that: The principle upon which the state correction factor for each measurement point is calculated in the integrated output module is as follows: For each measurement point, the residual and included angle of deviation from the state baseline are calculated using the following formula: in, Indicates the first The residuals of each measurement point deviating from the state baseline Indicates the first The rebound value at each measurement point Indicates the first The angle between each measurement point and the state baseline; The residuals and included angles are standardized separately and converted into probability values ​​for the measured points meeting the strength requirements, specifically as follows: in, This represents the probability that the measured point meets the strength requirements at the residual level. This represents the standard deviation of the residuals from the baseline at all measurement points. The cumulative distribution function represents the standard normal distribution. This represents the probability that the measurement point meets the strength requirements on the included angle plane. This represents the standard deviation of the angles between all measured points and the baseline. The two probabilities mentioned above are linearly weighted and summed to generate a state health factor, and The weight is greater than The weights; Based on the true sound velocity and rebound value at the measurement points, and combined with the average true sound velocity and average rebound value of concrete samples in the calibration dataset, the sound velocity-rebound value coupling term is calculated. The specific formula is as follows: in, Indicates the first The sound velocity-rebound coupling term at each measurement point This represents the average true sound velocity of the concrete samples in the calibration dataset. This represents the average rebound value of the concrete samples in the calibration dataset; Multiplying the state health factor by the sound velocity-rebound coupling term yields the state correction factor for the measurement point.

8. The non-destructive testing system for bridge deck concrete strength based on ultrasonic rebound according to claim 7, characterized in that: The principle for correcting the reference strength at each measurement point is as follows: The average strength of the concrete samples in the calibration dataset is used as the reference strength of the measurement points. The concrete strength of each measurement point is obtained by multiplying the state correction factor of each measurement point by the reference strength.

9. A non-destructive testing method for the strength of bridge deck concrete based on ultrasonic rebound, characterized in that: The detection method is performed by the non-destructive testing system for bridge deck concrete strength based on ultrasonic rebound as described in any one of claims 1-8, and the specific steps include: Step 1: Select the inspection area on the bridge deck to be inspected, and divide the inspection area into a uniform measurement grid to form measurement points. Obtain the concrete slab thickness at each measurement point, and calculate the average concrete slab thickness and the average steel reinforcement cover thickness of the inspection area. Step 2: Prepare several sets of specimens with different average concrete slab thicknesses or different average steel reinforcement cover thicknesses, and perform ultrasonic testing on the reinforced and unreinforced areas of each specimen. Fit an acoustic path correction factor based on the ultrasonic testing results. Step 3: Perform ultrasonic testing at each measurement point to obtain the basic sound velocity of the ultrasonic wave at each measurement point, and calculate the ratio of the steel reinforcement thickness to the concrete slab thickness at each measurement point, which is recorded as the steel reinforcement thickness ratio. Calculate the true sound velocity at each measurement point based on the basic sound velocity, the steel reinforcement thickness ratio, and the acoustic path correction factor. Step 4: Obtain the rebound value of each measurement point, normalize the rebound value of each measurement point and match it with the true sound speed of that measurement point, and generate a state baseline based on the linear regression relationship between the rebound value of the bridge surface to be tested and the true sound speed. Step 5: Calculate the residuals and included angles of each measurement point from the state baseline, then calculate the state correction factor for each measurement point, and correct the reference strength of each measurement point based on the state correction factor to generate the concrete strength of each measurement point.

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