A paving method for an existing bridge UHPC steel bridge deck pavement

Abstract

This invention relates to the field of bridge construction technology and discloses a method for paving existing UHPC steel bridge decks, including: S1 Mechanical preparation before construction; S2 Sensor module construction, with a three-dimensional laser scanning array installed at the front end of the concrete screed and an incremental photoelectric encoder installed at the traveling mechanism; S3 Control module construction, with an independently controlled segmented scraper unit installed behind the vibrating end, and all the above components connected to the control unit; S4 Pavement layer compensation calculation stage, where the control unit calculates the real-time compensation amount for concrete paving according to a preset program; S5 Pavement layer thickness control execution stage, where the scraper unit is driven to fit the shape of the steel bridge deck in real time. This invention achieves dynamic perception and real-time compensation of uneven surfaces on existing bridge steel decks through the above method, ensuring that the UHPC steel bridge deck pavement layer meets the minimum pavement structure design thickness requirements in some protruding areas, thereby guaranteeing the uniformity of the entire pavement layer thickness and the integrity of the structure.

Description

Technical Field

[0001] This invention relates to the field of bridge construction technology and discloses a method for paving existing UHPC steel bridge decks. Background Technology

[0002] Ultra-high performance concrete (UHPC), as a new type of cement-based composite material with ultra-high strength, high toughness and excellent durability, has gradually become the mainstream material for steel bridge deck paving because it can solve the problems of easy cracking and easy detachment of ordinary pavement layers. It is used to improve the performance and long service life of steel bridge decks.

[0003] In existing construction processes, UHPC steel bridge deck paving is usually carried out using a concrete placement and screed machine that can travel on the bridge deck. The concrete placement and screed machine advances at a constant speed along a pre-set track on the bridge to place the UHPC concrete onto the bridge deck. Then, the machine's vibrating and screeding end flattens the UHPC concrete according to the preset flatness and thickness, so that it forms a continuous paving layer with uniform thickness and qualified density on the steel bridge deck.

[0004] Because newly built bridges generally have good flatness, existing construction techniques using automated concrete placing screeds are well-suited for their pavement projects, resulting in UHPC concrete layers with good flatness and integrity after paving. However, for some existing bridge renovation projects, due to long-term heavy traffic and service fatigue, the steel bridge decks of old bridges often exhibit localized deformation or potholes, resulting in poor flatness. If traditional mechanized concrete placing is relied upon using concrete placing screeds, and the paving is done solely by the machine's vibrating end to achieve a fixed thickness, the resulting UHPC layer thickness will be uneven. This can easily lead to uneven shrinkage within the UHPC during the hardening process, resulting in excessively thin pavement layers at protruding parts of the bridge deck, causing cracking.

[0005] To prevent the aforementioned issues from occurring during paving, manual adjustments are necessary during the initial paving phase, or secondary repairs are required after completion. However, due to the material properties of UHPC concrete, it is highly sensitive to construction disturbances. The time lag between secondary paving and the initial large-area paving not only increases construction time but also makes it difficult for the subsequently paved portion to achieve synchronized initial setting with the first paved concrete. This easily leads to a weak interface between the two at the junction. Ultimately, this results in reduced structural strength of the pavement at the boundary between the repaired and initial paved areas, thus affecting the overall performance and long-term service life of the bridge deck pavement.

[0006] In order to further improve the adaptability of paving construction to the existing bridge conditions and the bridge deck condition, achieve the goal of one-time forming paving of steel bridge deck, and effectively improve the paving quality of UHPC, there is an urgent need in this field for a UHPC steel bridge deck paving method for existing bridges to improve the paving quality. Summary of the Invention

[0007] To address the aforementioned problems, this invention discloses a paving method for existing UHPC steel bridge decks. The method employs a concrete placing screed for paving construction. UHPC concrete is supplied from the placing hopper of the placing screed to the placing bin, and then placed onto the steel bridge deck. Finally, it is vibrated and paved using a vibrating end. The specific construction steps include: Step S1, Preparing machinery before construction: Construction tracks are laid on both sides of the steel bridge deck along the longitudinal direction of the bridge. The concrete screed is then erected across the steel bridge deck on the tracks for debugging of the various components of the machine. Step S2, Sensor module setup: Construct a reference coordinate system for the construction site; install a three-dimensional laser scanning array at the foremost point of the concrete screed machine in the forward direction to scan and acquire three-dimensional point cloud data containing the spatial coordinate values ​​(Xi, Yi, Zi) of each discrete point on the steel bridge deck in the reference coordinate system; install an incremental photoelectric encoder at the traveling mechanism of the concrete screed machine to calculate the displacement information of the concrete screed machine in the longitudinal direction of the bridge in real time. Step S3, Control Module Setup: The concrete screed is equipped with a control unit that receives the three-dimensional point cloud data and displacement information. The control unit presets a pavement layer design elevation model, which includes the design coordinate values ​​(Xs, Ys, Zs) of each discrete point on the pavement layer after the bridge is paved, and the reference coordinate values ​​(Xb, Yb, Zb) of each discrete point on the bottom surface of the pavement layer. A segmented scraper unit with a total width covering the width of the bridge deck is installed behind the vibrating end. The bottom of the scraper unit is parallel to the steel bridge deck. Each scraper unit is independently connected to a servo electric cylinder on the concrete screed. The servo electric cylinder is driven by the control unit and is used to push the scraper unit to move in the vertical direction. Step S4, Pavement Layer Compensation Calculation Stage: The concrete screed is started, and the control unit extracts the actual physical elevation Zi from the spatial coordinates (Xi, Yi, Zi) of each discrete point in the paving area during the forward movement. First, it performs a difference calculation with the reference elevation Zb of the corresponding point, and filters out the points where Zi-Zb>0. Then, it performs a real-time difference calculation on Zi and Zs to obtain the theoretical filling thickness of UHPC concrete required at the corresponding point to achieve the design elevation, H=max{Zs-Zi,Hm}, where Hm is the minimum required thickness of the UHPC concrete pavement layer. Then, a compensation correction coefficient K is introduced to calculate the real-time thickness compensation amount ΔH=H·K for each point. Step S5, Pavement layer thickness control execution stage: The control unit distributes the ΔH value of each point in the area to be paved to the corresponding segmented scraper unit according to the lateral coordinate in real time, and drives the scraper unit to lift upward by a preset displacement so that the distance between the bottom of the scraper unit in this area and the protruding part of the steel bridge deck is equal to ΔH; continue steps S4 and S5 until paving is completed.

[0008] Furthermore, in step S2, the three-dimensional laser scanning array is composed of multiple high-frequency laser ranging sensors arranged equidistantly in the horizontal direction. The spacing between each high-frequency laser ranging sensor is 500mm to 800mm, the installation height is 800mm to 1200mm from the bridge surface, the overlap of the sensor scanning lines is not less than 15%, and the total scanning coverage width is not less than the full width of the bridge surface.

[0009] Furthermore, in step S4, the minimum required thickness Hm of the UHPC pavement layer is 35mm to 50mm, and is not less than the design height of the steel bridge deck shear studs plus 10mm.

[0010] Furthermore, in step S4, the compensation correction coefficient K is corrected based on the slump spread of the pre-mixed UHPC concrete before filling, the ambient temperature during construction, and the paving thickness, and takes a value of 1.02 to 1.08. The logic for taking the value of K is: the greater the spread, the higher the ambient temperature, and the thicker the paving thickness, the larger the value of K.

[0011] Furthermore, in step S5, the preset upward displacement of the scraper unit is determined by the following method: The control unit distributes the ΔH value of each point in the paving area to the corresponding segmented scraper unit according to the horizontal coordinate. The initial reference position of each scraper unit is set to the height corresponding to Zs. When Zi-Zb≤0, the scraper unit does not make any adjustment. When Zi-Zb>0, the control unit calculates the upward displacement ΔZ=ΔH+Zi-Zs required for the scraper unit at that point, and sends ΔZ as a displacement command to the servo cylinder of the corresponding scraper unit. The servo cylinder drives the scraper unit to move vertically a corresponding distance according to ΔZ.

[0012] Furthermore, during the sensor module setup in step S2, a pressure sensor is installed at the bottom of the scraper unit, and several flow supplement valves are installed at the outlet of the concrete hopper. The positions of the flow supplement valves correspond one-to-one with each scraper unit in the bridge width direction and are connected to the inside of the concrete hopper. Both the pressure sensor and the flow supplement valves are connected to the control unit. Before the paving process, the reference pressure value of the scraper unit bottom completely adhering to the UHPC concrete is measured. During the paving process in step S5, when the pressure sensor detects that the pressure data at the bottom of a certain scraper unit is lower than the reference pressure value, or when the pressure data at the bottom of a certain scraper unit is lower than that of other scraper units, the control unit immediately outputs an instruction to increase the concrete flow to the flow supplement valve at the corresponding position of the scraper unit with the reduced pressure data, supplementing the amount of UHPC concrete at that position until the pressure data recovers.

[0013] Furthermore, the distance between the three-dimensional laser scanning array and the scraper unit in the longitudinal direction of the bridge is set to be greater than 500mm to achieve advance scanning of the steel bridge deck; the incremental photoelectric sensor is located at the same level as the scraper unit in the longitudinal direction of the bridge; during construction, the control unit calculates ΔH in advance based on the data scanned in advance, and generates control commands for the scraper unit in advance in combination with displacement information.

[0014] Furthermore, each servo electric cylinder has a built-in absolute displacement sensor. The control unit applies the following triple constraints to the displacement command of the scraper unit, and the absolute displacement sensor monitors and controls these constraints: Lateral constraint: Vertical displacement difference between adjacent scraper units ≤ 1mm; Longitudinal constraint: The maximum allowable height difference of the scraper unit within a unit travel distance of the fabric screed is 0.3mm / 100mm; Global limit: The single adjustment amount of the scraper is limited to 0.1mm to 5mm. Any excess amount is smoothly adjusted according to the slope corresponding to the adjustment amount in the horizontal and vertical constraints.

[0015] Furthermore, before paving construction, after the installation of the concrete screed is completed, the initial reference position of the segmented scraper unit is calibrated using the absolute displacement sensor, specifically as follows: The starting point of the paving construction is leveled, and then the scraper unit is gradually raised from its position against the steel bridge deck at the starting point. The control unit reads the real-time position data of each scraper unit through an absolute displacement sensor until the data of the absolute displacement sensor is consistent with the design thickness data of the pavement layer. At this time, the control unit records and stores the current position of each scraper unit and defines the position of the scraper unit at this time as the zero point of vertical displacement. When the paving thickness control in step S5 is executed later, each scraper unit will use the zero point as a reference for displacement adjustment.

[0016] Furthermore, the bottom scraper of the scraper unit that contacts the UHPC concrete is made of high manganese alloy steel that has undergone surface hardening treatment, and its surface roughness Ra is less than 0.8μm. The segmented scraper units are connected to the wear-resistant fluororubber sealing strip through an elastic connection structure set on the side.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention solves the problem of uneven pavement thickness caused by the unevenness and deformation of the steel bridge deck in old bridge reinforcement projects by using a high-precision three-dimensional laser scanning array and dynamic compensation calculation of the control unit, and by precisely controlling the UHPC steel bridge deck pavement layer through a segmented scraper unit. Under the drive of the scraper unit based on the output command of the control unit, the UHPC concrete material can accurately fit the protruding parts of the bridge deck, ensuring that the UHPC pavement layer meets the minimum pavement structure design thickness requirements during the paving process, eliminating the weak points caused by local thinness, and avoiding the risk of stress concentration and shrinkage cracking caused by uneven local thickness of the pavement layer. At the same time, the construction method of this invention also avoids the problem of weak connection interface between the old and new UHPC concrete that may be caused by secondary repair of areas with insufficient thickness, thus ensuring the uniformity of the thickness of the entire UHPC pavement layer and the integrity of the structure, and improving the paving construction quality.

[0018] 2. The entire construction process of this invention has a high degree of automation control. Through the coordinated work of laser scanning, compensation calculation and execution control, the paving construction process does not require secondary manual intervention, and can realize one-time continuous construction of UHPC pavement on existing bridge steel decks, which greatly improves construction efficiency and accuracy. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall structure of the material placing and leveling machine in a conventional bridge UHPC steel bridge deck paving method according to the present invention; Figure 2 This is a partial structural diagram of the material placing and leveling machine in a conventional bridge UHPC steel bridge deck paving method according to the present invention. Figure 3This is a schematic diagram of the steps in the paving method for UHPC steel bridge deck of a conventional bridge according to the present invention. In the attached diagram: 1. Track; 2. Concrete hopper; 3. Concrete bin; 4. Vibrating end; 5. Traveling mechanism; 6. 3D laser scanning array; 7. Scraper unit; 8. Servo electric cylinder; 9. Flow supplement valve. Detailed Implementation

[0020] The technical solution of the present invention will now be described with reference to the accompanying drawings. However, the described embodiments are only some embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] It should be noted that in the description of this invention, the terms "front," "rear," "longitudinal," and "transverse," etc., indicating directional or positional relationships, are based on the directional or positional relationships shown in the accompanying drawings when the screed is operating normally. For example, "front" and "rear" refer to the direction of paving construction along the bridge, "longitudinal" refers to the length direction of the bridge, and "transverse" refers to the width direction of the bridge, and so on. This is merely for ease of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention.

[0022] In a specific construction scenario of this invention, it is necessary to reinforce and renovate an existing bridge that has been in service for many years in a certain location. The bridge's steel deck has obvious unevenness, and the largest bulge measured to be about 18mm higher than the bridge deck's reference level. Based on the existing working surface, the paving construction stage is initiated, requiring the construction of a UHPC paving layer with a thickness of approximately 50mm. For example... Figure 1 As shown, this invention provides a method for paving existing UHPC steel bridge decks in this construction scenario. For ease of description, the concrete placing screed used in this invention uses a placing hopper 2 as the feeding unit for the paving material (UHPC concrete). After receiving the externally delivered UHPC concrete material, it feeds it to the placing bin 3 at the bottom of the placing screed. The placing bin 3 then places the UHPC concrete onto the steel bridge deck. The vibrating end 4 behind the placing bin 3 compacts and initially levels the UHPC concrete. In addition to the above structure, this invention also sets a three-dimensional laser scanning array 6 on the placing screed to perceive the flatness of the bridge deck in real time. Combined with a segmented scraper unit 7, the thickness and shape of the paving layer are dynamically adjusted. The specific construction process includes the following steps: Step S1, Preparing machinery before construction: On both sides of the steel bridge deck to be paved, the construction track 1 is laid along the longitudinal direction of the bridge; the concrete screed is erected across the steel bridge deck on the track 1, and the various parts of the machine are debugged to confirm that the concrete hopper 2, concrete bin 3 and vibrating end 4 are operating normally. Step S2, Sensor module setup: Establish a reference coordinate system for the construction site; install a three-dimensional laser scanning array 6 at the foremost point of the material laying and leveling machine in the forward direction. The three-dimensional laser scanning array 6 consists of multiple high-frequency laser ranging sensors arranged horizontally at equal intervals. The spacing between each sensor is 500mm to 800mm, and the installation height is 800mm to 1200mm from the bridge deck. The overlap of the sensor scanning lines is not less than 15%, ensuring that the scanning range covers the entire width of the steel bridge deck and that the scanning is continuous without blind spots. An incremental photoelectric encoder is installed at the walking mechanism 5 of the concrete screed to calculate the displacement information of the concrete screed in the longitudinal direction of the bridge in real time. The resolution of the photoelectric encoder is set to 4096 pulses per revolution. In conjunction with parameters such as the diameter of the drive wheel of the walking mechanism 5 of the concrete screed, the displacement information of the positioning paver relative to the construction starting point is calculated in real time through pulse counting logic. Specifically, in this embodiment, the three-dimensional laser scanning array 6 is set to a sampling frequency of no less than 50kHz, and the ranging accuracy error is controlled within ±1mm. It emits laser pulses in real time onto the old steel bridge surface of the area to be paved, and obtains three-dimensional point cloud data of the steel bridge surface by receiving reflected signals. The point cloud data includes the spatial coordinate values ​​(Xi, Yi, Zi) of each discrete point on the steel bridge surface. Xi and Yi are used to locate the position of the screed on the bridge surface, and Zi reflects the actual physical elevation of the bridge surface. The resolution of the photoelectric encoder is set to 4096 pulses per revolution. Combined with parameters such as the diameter of the drive wheel of the screed's walking mechanism 5, the displacement data of the paver relative to the construction starting point is calculated in real time through pulse counting logic.

[0023] Step S3, Control Module Setup: A control unit is pre-installed inside the paving screed, and the three-dimensional point cloud data and displacement information are transmitted to the control unit. The control unit also has a pre-set design elevation model for the top surface of the pavement layer. The design elevation model is a description of the pavement layer surface equation determined by the bridge design documents, covering the design coordinate values ​​(Xs, Ys, Zs) of each discrete point on the pavement layer after the bridge is paved, and the reference coordinate values ​​(Xb, Yb, Zb) of each discrete point on the bottom surface of the pavement layer. Xs, Ys, Xb, and Yb represent the lateral and longitudinal coordinates of each discrete point in the design elevation model, and are used to synchronously position and superimpose with the aforementioned Xi and Yi, so that the points obtained by scanning the area to be paved coincide with the points in the design elevation model, maintaining the consistency of subsequent control operations. Zs represents the design elevation of the pavement layer thickness, and Zb represents the reference elevation of the bridge deck under ideal flat conditions.

[0024] A segmented scraper unit 7 with a total width covering the width of the bridge deck is installed behind the vibrating end 4 of the screed screed. The bottom of the scraper unit 7 is parallel to the steel bridge deck. Each scraper unit 7 is connected to an independent servo cylinder 8. The servo cylinder 8 is driven by the control unit and is used to push the scraper unit 7 to move in the vertical direction, thereby adjusting the local thickness of the UHPC pavement layer laid through the screed bin 3 and the vibrating end 4 at the corresponding part of the steel bridge deck. It should be noted that the reference coordinate system should be consistent with the bridge's design coordinate system. Coordinate transformation parameters are used to accurately match real-time measurement data during construction with the design model. Specifically, before construction, the plane control network and elevation control network data from the bridge design drawings need to be collected. Several reference control points are then established on the bridge deck using surveying equipment such as a total station. The coordinate transformation matrix is ​​obtained through least squares adjustment to ensure that the point cloud data (Xi, Yi, Zi) acquired by the 3D laser scanning array 6 can be accurately transformed to the design coordinate system and effectively compared with the design elevation model (Xs, Ys, Zs) and (Xb, Yb, Zb) of the pavement top surface, providing a unified coordinate reference for subsequent thickness compensation calculations.

[0025] Step S4, Pavement Layer Compensation Calculation Stage: After completing the above steps, the UHPC concrete material is fed into the hopper 2 of the concrete placing screed. The machine is started and moves along the track 1 on the bridge deck. The UHPC concrete is delivered through the hopper 2 to the concrete storage bin 3 for bridge deck paving. At this time, the three-dimensional laser scanning array 6, photoelectric encoder and control unit, and scraper unit 7 in step S2 are started to perform pavement layer compensation calculations, specifically: The control unit uses a bicubic interpolation algorithm to perform high-precision surface reconstruction on the three-dimensional point cloud data, generating a digital map of the steel bridge deck topography covering the entire area to be paved, which serves as the data input basis for subsequent paving thickness compensation calculations.

[0026] The control unit converts the calculated photoelectric encoder displacement data into the current position parameters of the fabric screed on the bridge. Combined with the three-dimensional point cloud data synchronously acquired by the three-dimensional laser scanning array 6, it matches its Y coordinate and positions the real-time position of the fabric screed on the digital map.

[0027] Next, the actual physical elevation Zi of each point in the paving area in front of the current position of the fabric screed is extracted from the digital map. First, a difference calculation is performed between this elevation and the benchmark elevation Zb in the design elevation model. Then, points (Xi, Yi, Zi) greater than Zi - Zb > 0 (indicating that the actual elevation of the bridge deck at this point is higher than the benchmark elevation, and there is a bulge in the bridge deck at this point) are selected. Finally, a real-time difference calculation is performed between Zi and Zs to obtain the theoretical filling thickness H = max{Zs - Zi, Hm} of the UHPC material required to achieve the design elevation at this point; where Hm is the minimum required thickness of the UHPC pavement layer, with a value of... The thickness should be 35mm to 50mm, and should not be less than the design height of the steel bridge deck shear studs + 10mm, to ensure that the shear studs are completely wrapped by the UHPC material, ensuring shear force transfer and corrosion protection, and avoiding shear force transfer failure due to insufficient pavement thickness. In this embodiment, before paving construction, structural safety tests of UHPC concrete were conducted by making pavement layer test blocks of different thicknesses, and the minimum required thickness was selected as 35mm. When the calculated Zs-Zi is less than Hm, the control unit automatically corrects the theoretical filling thickness H at that point to Hm, to ensure that the UHPC layer has sufficient structural strength and durability, and to avoid the pavement layer being too thin due to excessive local bridge deck height.

[0028] Considering the high viscosity and high thixotropic properties of UHPC material, its self-compacting settling effect after paving and surface loss during subsequent finishing processes cannot be ignored. Therefore, the control unit further incorporates a compensation correction coefficient K when calculating H. This compensation correction coefficient K is a dynamic variable, adjusted based on the slump and spread of the pre-mixed UHPC concrete before filling, the ambient temperature during construction, and the paving thickness. Its value ranges from 1.02 to 1.08. The specific logic is as follows: higher spread (higher concrete fluidity), higher temperature (faster concrete shrinkage), and thicker paving (more significant concrete settling under gravity) will lead to a reduction in the effective paving thickness of the UHPC paving material. Therefore, a larger K value ensures sufficient thickness compensation. In this example, under the baseline conditions of 700mm spread, 15-25℃ temperature, and a standard paving thickness of 50mm, K = 1.05 is used. The final determined real-time compensation amount for each point is ΔH = H·K.

[0029] Step S5, Pavement layer thickness control execution stage: As the concrete leveling machine moves forward, the UHPC concrete material is spread onto the steel bridge surface through the concrete bin 3. The material is then vibrated by the vibrating end 4 to eliminate tiny air bubbles inside the UHPC concrete and to help the concrete achieve initial self-leveling. After the control unit performs the compensation calculation in step S3 above, the control unit converts the real-time compensation amount ΔH of each transverse segment into the execution command of the scraper unit 7 in real time, driving the scraper unit 7 corresponding to the point where Zi-Zb>0 to rise by a preset displacement, so that the distance between the bottom of the scraper in this area and the protruding part of the steel bridge surface is equal to ΔH, and the shape of the steel bridge surface is matched in real time.

[0030] The paving process continues to execute steps S3 and S4 as described above until paving is completed.

[0031] Specifically, the conversion process of the above execution instructions is as follows: Based on the real-time position parameters of the fabric screed, the control unit distributes the ΔH value of each point in the paving area to the corresponding segmented scraper unit 7 according to the horizontal coordinate. The initial reference position of each scraper unit 7 is set to the height corresponding to Zs. When Zi-Zb≤0, the scraper unit 7 does not make any adjustment. When there is a protrusion at a certain point (Zi-Zb>0), the control unit calculates the upward displacement ΔZ required for the scraper unit 7 at that point, where ΔZ=ΔH+Zi-Zs. This indicates that when the bridge deck protrudes by a height of Zi, in order to maintain the actual thickness of the UHPC pavement layer at that point as ΔH, the scraper needs to be raised a certain height above the reference position, i.e., ΔZ. The control unit sends the calculated ΔZ as a displacement command to the servo cylinder 8 of the corresponding scraper unit 7, and the servo cylinder 8 drives the scraper unit 7 to move vertically a corresponding distance according to ΔZ.

[0032] In this embodiment, thanks to the use of the three-dimensional laser scanning array 6 and the segmented scraper unit 7, the UHPC material, after being vibrated and compacted on the steel bridge deck, is leveled by the scraper unit 7 through real-time dynamic scanning, calculation, and adjustment. This allows for precise paving according to the design elevation and compensation thickness, achieving accurate compensation for uneven areas on the steel bridge deck. This avoids the problem of excessively thin UHPC pavement layers on protruding parts of the steel bridge deck, thus ensuring the uniformity of the entire pavement layer thickness and the integrity of the structure. The entire process requires no secondary manual intervention, realizing one-time continuous construction of UHPC pavement on existing bridge steel decks. This significantly improves construction efficiency and accuracy, while avoiding weak connection interface problems that may arise from secondary repairs, laying a good foundation for subsequent processes.

[0033] Furthermore, when constructing the sensing module in step S2, the following steps are also included: a pressure sensor is installed at the bottom of the scraper unit 7, and several flow supplement valves 9 are installed at the discharge port of the material distribution bin 3. The positions of the flow supplement valves 9 correspond one-to-one with each scraper unit 7 in the bridge width direction and are connected to the inside of the material distribution bin 3. The valve ports face the bottom of the scraper unit 7 and are used to additionally transport UHPC concrete to the steel bridge deck corresponding to each scraper unit 7. The pressure sensor and the flow supplement valves 9 are both connected to the control unit.

[0034] Specifically, before the paving process, the reference pressure value of the bottom of scraper unit 7 being fully in contact with the UHPC concrete is measured. When paving is carried out, if the pressure sensor detects a decrease in the pressure data at the bottom of a certain scraper unit 7 (e.g., below 85% of the reference pressure value), or if the pressure data at the bottom of a certain scraper unit 7 is significantly lower than that of other scraper units 7, it indicates that the paving layer thickness at the current position is inconsistent with the thickness control command executed by the corresponding scraper unit 7, and the UHPC concrete at the bottom of the corresponding scraper unit 7 is not dense. At this time, the control unit immediately outputs a command to increase the material flow to the flow supplement valve 9 at the position corresponding to the scraper unit 7 with the decreased pressure data. The valve opening degree is increased by 10%-20%, and the pressure recovery is dynamically monitored at a period of 2 seconds. The amount of UHPC concrete material at this position is supplemented until the pressure data recovers, so that the UHPC concrete densely fills the current paving position and meets the paving thickness requirements.

[0035] Furthermore, in step S2, the three-dimensional laser scanning array 6 is installed at the front end of the fabric screed, and the distance D between it and the segmented scraper unit 7 is specifically set to be greater than 500mm, so as to realize the advance scanning of the terrain of the steel bridge surface in front during the forward movement of the fabric screed; while the incremental photoelectric sensor is located at the same level as the scraper unit 7, so as to ensure that the position of the fabric screed obtained by the control unit is the same as the position of the scraper unit 7, thereby ensuring the synchronization of the control execution commands of the scraper unit 7 based on the digital map. Specifically, the control unit establishes a dynamic database indexed by displacement information, and binds and stores the scanned coordinate points (Xi, Yi, Zi) and their calculated ΔH with the reference reading of the current incremental photoelectric encoder; when the real-time reading of the incremental photoelectric encoder meets the reference reading plus the distance D, the set of ΔH commands is triggered and sent to the servo cylinder.

[0036] Based on the case where the three-dimensional laser scanning array 6 is set up and scanned in advance before the scraper unit 7, the real-time compensation amount ΔH it determines has a certain lead time. The control unit will calculate all ΔH in advance so as to generate control commands for the scraper unit 7 in advance.

[0037] In the actual execution process, to avoid sudden displacement of the scraper unit 7 causing steps or waves on the top surface of the paving layer, each servo cylinder 8 is equipped with an absolute displacement sensor. The control unit applies the following triple constraints to the displacement command of the scraper unit 7, and the absolute displacement sensor monitors and controls the movement, so that all adjustment actions of the scraper unit 7 follow the rules of smooth lateral movement, gradual longitudinal change, and global amplitude limitation: Lateral constraint: The vertical displacement difference between adjacent scraper units 7 is ≤1mm. Specifically, the displacement of the scraper unit 7 corresponding to the maximum protrusion position of the bridge deck is used as the benchmark, and the adjacent scraper units 7 adjust their vertical displacement according to this constraint. Longitudinal constraint: The maximum allowable height difference of scraper unit 7 within a unit travel distance of the fabric screed is 0.3mm / 100mm, that is, for every 100mm that the fabric screed advances, the vertical height change of the scraper does not exceed 0.3mm; In specific execution, the control unit calculates the travel distance L=v×T in a single cycle in real time based on the real-time travel speed v of the screed and the fixed control cycle T of the scraper unit 7, and automatically derives the maximum allowable adjustment amount of scraper unit 7 within this control cycle according to the above 0.3mm / 100mm; Global limit: The single adjustment amount of the scraper is limited to 0.1mm to 5mm. Any excess amount is smoothly adjusted according to the slope corresponding to the adjustment amount in the horizontal and vertical constraints.

[0038] Under the control of the above triple constraints, combined with the advance scanning and calculation process in the above technical solution, the displacement adjustment process of scraper unit 7 presents a continuous and smooth transition state, effectively avoiding the problems of uneven, discontinuous and unsmooth pavement surface caused by excessive adjustment range.

[0039] For example, when there are localized protrusions on the steel bridge deck, the control unit will acquire relevant information in advance and perform pre-calculation based on the height and range of the protrusion, combined with the aforementioned triple constraints, to determine a series of adjustment commands to be made before the scraper unit 7 reaches the area. Once the incremental photoelectric sensor confirms that the scraper unit 7 is gradually approaching the area, the control unit can retrieve the corresponding control command for the current position and send it to the scraper unit 7 for execution. This gradually instructs the scraper unit 7 in the corresponding area and its adjacent scraper units 7 to adjust according to the triple constraints during the movement of the screed machine, causing the bottom height of the scraper unit 7 to change slowly. This ensures that the UHPC material is evenly distributed after being leveled by the scraper unit 7, forming a smooth paving surface. This ensures that the paving layer thickness is met for the protruding areas while avoiding abrupt undulations on the bridge deck. Under this pre-calculation and control mechanism, the present invention can better handle sudden changes in terrain such as localized bulges on the steel bridge deck during paving, avoiding inadequate scraper adjustment due to scanning, calculation, and execution delays. Moreover, this triple constraint control method further improves the flatness and overall quality of the paving layer.

[0040] Based on the above technical solution, furthermore, before paving construction, after the installation of the screed machine is completed, the initial reference position of the segmented scraper unit 7 can be calibrated using the absolute displacement sensor. Specifically, the starting point of the paving construction is leveled, and then the scraper unit 7 is gradually raised from its position against the steel bridge deck at the starting point. The control unit reads the real-time position data of each scraper unit 7 through the absolute displacement sensor until the data of the absolute displacement sensor is consistent with the pavement thickness data. At this time, the control unit records and stores the current position of each scraper unit 7 and defines the position of the scraper unit 7 at this time as the zero point of vertical displacement. When the paving thickness control is executed in step S5, each scraper unit 7 can have a unified zero point reference, avoiding displacement control deviation caused by initial position deviation, which would lead to paving thickness control error and ensure accurate control of pavement thickness.

[0041] Furthermore, in a preferred embodiment of the present invention, the bottom scraper of the scraper unit 7 that contacts the UHPC concrete is made of high manganese alloy steel that has undergone surface hardening treatment, and its surface roughness Ra is less than 0.8μm. This is intended to reduce the frictional resistance between the scraper unit 7 and the UHPC concrete during the process of leveling the concrete and to prevent UHPC concrete residue from remaining on the scraper unit 7. Each segmented scraper unit 7 has a preset width of about 150mm and is connected to a wear-resistant fluororubber sealing strip through an elastic connection structure set on the side. If a spring connection is used, and a wear-resistant fluororubber sealing strip is covered on the outside of the connection part, the UHPC material will not leak from between the scraper units 7 when there is a vertical displacement difference between adjacent scraper units 7, ensuring that the paving layer is continuous and dense.

[0042] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for paving existing UHPC steel bridge decks, comprising a material placing and leveling machine including a material placing hopper, a material placing bin, and a vibrating end for paving construction, characterized in that, The construction steps include the following: Step S1, Preparing machinery before construction: Construction tracks are laid on both sides of the steel bridge deck along the longitudinal direction of the bridge. The concrete screed is then erected across the steel bridge deck on the tracks for debugging of the various components of the machine. Step S2, Sensor module setup: Construct a reference coordinate system for the construction site; install a three-dimensional laser scanning array at the foremost point of the concrete screed machine in the forward direction to scan and acquire three-dimensional point cloud data containing the spatial coordinate values ​​(Xi, Yi, Zi) of each discrete point on the steel bridge deck in the reference coordinate system; install an incremental photoelectric encoder at the traveling mechanism of the concrete screed machine to calculate the displacement information of the concrete screed machine in the longitudinal direction of the bridge in real time. Step S3, Control Module Setup: The concrete screed is equipped with a control unit that receives the three-dimensional point cloud data and displacement information. The control unit presets a pavement layer design elevation model, which includes the design coordinate values ​​(Xs, Ys, Zs) of each discrete point on the pavement layer after the bridge is paved, and the reference coordinate values ​​(Xb, Yb, Zb) of each discrete point on the bottom surface of the pavement layer. A segmented scraper unit with a total width covering the width of the bridge deck is installed behind the vibrating end. The bottom of the scraper unit is parallel to the steel bridge deck. Each scraper unit is independently connected to a servo electric cylinder on the concrete screed. The servo electric cylinder is driven by the control unit and is used to push the scraper unit to move in the vertical direction. Step S4, Pavement Layer Compensation Calculation Stage: The concrete screed is started, and the control unit extracts the actual physical elevation Zi from the spatial coordinates (Xi, Yi, Zi) of each discrete point in the paving area during the forward movement. First, it performs a difference calculation with the reference elevation Zb of the corresponding point, and filters out the points where Zi-Zb>0. Then, it performs a real-time difference calculation on Zi and Zs to obtain the theoretical filling thickness of UHPC concrete required at the corresponding point to achieve the design elevation, H=max{Zs-Zi,Hm}, where Hm is the minimum required thickness of the UHPC concrete pavement layer. Then, a compensation correction coefficient K is introduced to calculate the real-time thickness compensation amount ΔH=H·K for each point. Step S5, Pavement layer thickness control execution stage: The control unit distributes the ΔH value of each point in the area to be paved to the corresponding segmented scraper unit according to the lateral coordinate in real time, and drives the scraper unit to lift upward by a preset displacement so that the distance between the bottom of the scraper unit in this area and the protruding part of the steel bridge deck is equal to ΔH; continue steps S4 and S5 until paving is completed.

2. The paving method for existing bridge UHPC steel bridge deck as described in claim 1, characterized in that, In step S2, the three-dimensional laser scanning array is composed of multiple high-frequency laser ranging sensors arranged horizontally at equal intervals. The spacing between each high-frequency laser ranging sensor is 500mm to 800mm, the installation height is 800mm to 1200mm from the bridge surface, the overlap of the sensor scanning lines is not less than 15%, and the total scanning coverage width is not less than the full width of the bridge surface.

3. The paving method for existing bridge UHPC steel bridge deck as described in claim 1, characterized in that, In step S4, the minimum required thickness Hm of the UHPC pavement layer is 35mm to 50mm, and is not less than the design height of the steel bridge deck shear studs plus 10mm.

4. The paving method for existing bridge UHPC steel bridge deck as described in claim 1, characterized in that, In step S4, the compensation correction coefficient K is corrected based on the slump spread of the pre-mixed UHPC concrete before filling, the ambient temperature during construction, and the paving thickness, and the value ranges from 1.02 to 1.

08. The logic for the value of K is: the greater the spread, the higher the ambient temperature, and the thicker the paving thickness, the larger the value of K.

5. The paving method for existing bridge UHPC steel bridge deck as described in claim 1, characterized in that, In step S5, the preset upward displacement of the scraper unit is determined by the following method: The control unit distributes the ΔH value of each point in the paving area to the corresponding segmented scraper unit according to the horizontal coordinate. The initial reference position of each scraper unit is set to the height corresponding to Zs. When Zi-Zb≤0, the scraper unit does not make any adjustment. When Zi-Zb>0, the control unit calculates the upward displacement ΔZ=ΔH+Zi-Zs required for the scraper unit at that point, and sends ΔZ as a displacement command to the servo cylinder of the corresponding scraper unit. The servo cylinder drives the scraper unit to move vertically a corresponding distance according to ΔZ.

6. The paving method for existing bridge UHPC steel bridge deck as described in claim 1, characterized in that, When building the sensing module in step S2, a pressure sensor is installed at the bottom of the scraper unit, and several flow supplement valves are installed at the outlet of the concrete hopper. The positions of the flow supplement valves correspond one-to-one with each scraper unit in the bridge width direction and are connected to the inside of the concrete hopper. The pressure sensor and the flow supplement valves are both connected to the control unit. Before the paving construction process, the reference pressure value of the bottom of the scraper unit being completely in contact with the UHPC concrete is measured. During the paving construction process in step S5, when the pressure sensor obtains that the pressure data at the bottom of a certain scraper unit is lower than the reference pressure value, or when the pressure data at the bottom of a certain scraper unit is lower than that of other scraper units, the control unit immediately outputs an instruction to increase the concrete flow to the flow supplement valve at the corresponding position of the scraper unit with the reduced pressure data, supplementing the amount of UHPC concrete at that position until the pressure data recovers.

7. A method for paving existing UHPC steel bridge decks according to claim 1, characterized in that, The distance between the three-dimensional laser scanning array and the scraper unit in the longitudinal direction of the bridge is set to be greater than 500mm to achieve advance scanning of the steel bridge deck; the incremental photoelectric sensor is located at the same level as the scraper unit in the longitudinal direction of the bridge; during construction, the control unit calculates ΔH in advance based on the data scanned in advance, and generates control commands for the scraper unit in advance based on the displacement information.

8. A method for paving existing UHPC steel bridge decks according to claim 7, characterized in that, Each servo electric cylinder has a built-in absolute displacement sensor. The control unit applies the following triple constraints to the displacement command of the scraper unit, and the absolute displacement sensor monitors and controls the operation: Lateral constraint: Vertical displacement difference between adjacent scraper units ≤ 1mm; Longitudinal constraint: The maximum allowable height difference of the scraper unit within a unit travel distance of the fabric screed is 0.3mm / 100mm; Global limit: The single adjustment amount of the scraper is limited to 0.1mm to 5mm. Any excess amount is smoothly adjusted according to the slope corresponding to the adjustment amount in the horizontal and vertical constraints.

9. A method for paving existing UHPC steel bridge decks according to claim 8, characterized in that, Before paving construction, after the installation of the concrete screed is completed, the initial reference position of the segmented scraper unit is calibrated using the absolute displacement sensor, specifically: The starting point of the paving construction is leveled, and then the scraper unit is gradually raised from its position against the steel bridge deck at the starting point. The control unit reads the real-time position data of each scraper unit through an absolute displacement sensor until the data of the absolute displacement sensor is consistent with the design thickness data of the pavement layer. At this time, the control unit records and stores the current position of each scraper unit and defines the position of the scraper unit at this time as the zero point of vertical displacement. When the paving thickness control in step S5 is executed later, each scraper unit will use the zero point as a reference for displacement adjustment.

10. A method for paving existing UHPC steel bridge decks according to claim 1, characterized in that, The bottom scraper unit that contacts the UHPC concrete is made of high manganese alloy steel that has undergone surface hardening treatment, with a surface roughness Ra of less than 0.8μm. The segmented scraper units are connected to the wear-resistant fluororubber sealing strips through an elastic connection structure set on the side.

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