Concrete monitoring system and method

Abstract

This specification discloses a concrete monitoring system and a concrete monitoring method. The concrete monitoring system includes at least one piezoelectric aggregate and a controller that can be embedded in a concrete structure. The controller is configured to perform multiple frequency sweeps of at least one piezoelectric aggregate to obtain multiple phase angles and to determine the state of the concrete structure based on changes in the phase angles among some of the multiple phase angles.

Description

[Technical Field]

[0001] Cross-reference of related applications This application claims priority to Singapore Application No. 10202251418X, filed on 18 October 2022, the contents of which are incorporated herein by reference in their entirety for all purposes.

[0002] This application relates to a concrete monitoring system and a concrete monitoring method. [Background technology]

[0003] Concrete is a mixture of cement (cement paste), water, and fine / coarse aggregate. In the formation or manufacture of ready-mix concrete, cement reacts with water in a process called hydration. During the hydration process, concrete gradually hardens over time. Concrete finishing is a post-forming process to create a smooth and durable surface on the formed concrete structure. Since concrete finishing must begin before the concrete structure is fully hardened, determining the timing of starting concrete finishing plays a crucial role in the final surface finish. Improper finishing can lead to weak, defective, and unattractive slabs. Therefore, contractors pay close attention to the concrete when determining the appropriate time for concrete finishing. However, current methods such as bar drop tests are often inaccurate and can negatively impact the soundness of the concrete structure. [Overview of the project] [Means for solving the problem]

[0004] According to one embodiment, a concrete monitoring system is disclosed herein. The concrete monitoring system comprises at least one piezoelectric aggregate and a controller that can be embedded in a concrete structure. The controller is configured to perform multiple frequency sweeps of at least one piezoelectric aggregate to obtain multiple phase angles and to determine the state of the concrete structure based on changes in the phase angles among some of the multiple phase angles.

[0005] In another embodiment, a concrete monitoring method is disclosed herein. The concrete monitoring method includes performing multiple frequency sweeps of at least one piezoelectric-based aggregate embedded in a concrete structure to obtain a plurality of phase angles, and determining the state of the concrete structure based on changes in the phase angles among some of the plurality of phase angles.

[0006] Various embodiments of this disclosure are described below with reference to the following drawings. [Brief explanation of the drawing]

[0007] [Figure 1] A schematic diagram of a concrete monitoring system according to an embodiment of the present disclosure. [Figure 2] A flowchart of a concrete monitoring method according to one embodiment. [Figure 3] An example of output from multiple impedance measurements of a single piezoelectric aggregate. [Figure 4] Detailed view of Figure 3. [Figure 5] A plot showing the time evolution of the peak phase frequency. [Figure 6] A plot showing the time evolution of the peak phase amplitude. [Figure 7] A perspective view of piezoelectric aggregate according to an embodiment of the present disclosure. [Figure 8] Figure 7 is an exploded view. [Figure 9] Cross-sectional view shown in Figure 8. [Figure 10] A schematic diagram of a piezoelectric structure including a circular piezoelectric cylinder and a concrete cylinder according to an embodiment of the present disclosure. [Figure 11] Lumped constants of the piezoelectric structure of FIG. 10. [Figure 12] A to D are perspective views of the mold 400 for manufacturing the piezoelectric aggregate of FIG. 7. [Figure 13] A to C are images showing a method for producing a smart aggregate using the mold of FIG. 12D. [Figure 14] Schematic diagram of the concrete measurement system according to an embodiment of the present disclosure. [Figure 15] Schematic diagram of the first wireless method of the concrete measurement system according to an embodiment of the present disclosure. [Figure 16] Schematic diagram of the second wireless method of the concrete measurement system according to an embodiment of the present disclosure. [Figure 17] Shows a schematic work flow of the concrete monitoring system according to various embodiments of the present disclosure. [Figure 18] Flow chart showing an algorithm for automatically processing data. [Figure 19] Shows the correlation between the peak phase frequency and the penetration depth. [Figure 20] Shows the correlation between the peak phase amplitude and the penetration depth.

Mode for Carrying Out the Invention

[0008] The following detailed description is made with reference to the accompanying drawings showing the details and embodiments of the present disclosure for illustrative purposes. Features described in the context of an embodiment may be applicable to corresponding same or similar features of these other embodiments even if not explicitly described in these other embodiments. Additions and / or combinations and / or alternatives described for features in the context of one embodiment may be applied to corresponding same or similar features in other embodiments.

[0009] In the context of various embodiments, the articles “a”, “an” and “the” used with respect to a feature or element include reference to one or more of the features or elements.

[0010] In the context of various embodiments, the terms “about” or “approximately” applied to numerical values ​​encompass both the exact value and a reasonable variance generally understood in the relevant technical field, for example, within 10% of the given value.

[0011] As used herein, the term "and / or" includes any combination of one or more of the related enumerated items.

[0012] For brevity, the term "phase angle" may be used to refer to one or more of the following terms, as understood from the context: "peak phase angle," "phase angle curve," "phase angle plot," "phase angle data point," "maximum phase angle," "peak on phase angle plot," "peak on phase angle curve," "measured phase angle," "phase angle database," etc.

[0013] As used herein, the term “aggregate” refers to gravel, sand, crushed stone, and / or various inert materials added to concrete in addition to cement and water. Conventional aggregates may be fine and of a specific size, or they may be coarse and granular. Aggregates are added to a mixture of cement (e.g., usually Portland cement) and water and are known to form part of the final hardened concrete structure, influencing the properties of both the fresh concrete (which has not yet fully hardened) and the fully hardened concrete.

[0014] For brevity, the term "ready-mix concrete" refers to a mixture containing cement and water before the mixture has fully hardened. The term "concrete" more generally refers to a mixture or structure containing cement and water, including but not limited to fully hardened concrete.

[0015] The term "condition" as used in relation to concrete structures generally refers to one or more properties of a concrete structure that can be determined by evaluation, measurement, calculation, estimation, or other means, and can be described by a combination of one or more qualitative and / or quantitatively determined properties of the concrete structure. Quantitatively determined properties include, but are not limited to, mechanical properties such as water content, porosity, brittleness, elasticity, strength, and fracture toughness; electrical properties such as resistance, conductivity, impedance, admittance, and dielectric properties; thermal properties such as coefficient of expansion and heat transfer coefficient; and acoustic properties such as acoustic impedance and stiffness coefficient.

[0016] For the purpose of aiding understanding and not limiting the scope, various embodiments of the concrete monitoring system 100 and concrete monitoring method 200 are described below with reference to the accompanying drawings. The concrete monitoring system 100 and concrete monitoring method 200 can also be described as a system and method capable of monitoring and measuring the condition of recently formed concrete structures or ready-mix concrete structures. For the sake of brevity, various examples of the concrete monitoring system and method are described below, but it will be understood that the system 100 and method 200 can be used in multiple application scenarios relating to concrete structure monitoring and are not limited to the specific examples disclosed herein.

[0017] Figure 1 is a schematic diagram of a concrete monitoring system 100 for monitoring a concrete structure 80 according to various embodiments of the present disclosure. As shown in Figure 1, the concrete monitoring system 100 may include one or more sensor devices (hereinafter referred to as “smart aggregates”) 110. Piezoelectric aggregates 110 may also be called electromechanical impedance measurement-based smart aggregates (EIM-SMA). Various numbers of smart aggregates 110 may be distributed and embedded in different parts of the concrete structure 90. In some embodiments where the concrete structure 80 is relatively small, one smart aggregate 110 may be sufficient to monitor the entire concrete structure 80. In the illustrated example, three smart aggregates 110 are embedded in the concrete structure 80 at approximately the same depth from the surface of the concrete structure 80 and spaced apart from each other. In other examples, multiple smart aggregates 100 may be embedded at different depths from the same surface of the concrete structure 80. In some examples, each of the multiple smart aggregates 110 may be used to determine the state of a local volume or local zone of the concrete structure 80.

[0018] Collectively, multiple smart aggregates 110 can be used to determine the state of a relatively large amount of concrete. In some examples, data collected by the controller 120 from the distribution of smart aggregates 110 can be used to indicate different parts of the concrete structure in each state. The use of smart aggregates 110 allows for the selection of one or more target zones / volumes for monitoring. For example, smart aggregates may be embedded near the surface of the concrete structure 80 to monitor the state close to the surface. Alternatively, smart aggregates 110 may be embedded deeper in the concrete structure 80 to monitor the state of the concrete structure 80 deeper below the surface.

[0019] In some embodiments, the concrete monitoring system 100 may further include a controller 120. During operation, the controller 120 signals to one or more of the smart aggregates 110. In some examples, as shown in Figure 1, the controller 120 may signals to one or more of the smart aggregates 110 via one or more wired connections. In other embodiments, the controller may signals to the smart aggregates 110 via a wireless connection.

[0020] The controller 120 may be configured to implement a concrete monitoring method. The controller 120 is configured to implement a method for determining the state of the concrete structure 80 by executing instructions stored in computer-readable memory. In some embodiments, the controller 120 may transmit signals to or receive signals from each smart aggregate 110 and process and / or calculate outputs corresponding to the state of the concrete structure 80 based on the signals. In some embodiments, the concrete monitoring system 100 includes one or more transmitters 130 configured to enable signal communication between one or more smart aggregates 110 and the controller 120. In some embodiments, the controller 120 may be coupled to a display 121. The controller 120 may be configured to communicate the state of the concrete structure 80 to a user or worker, for example, via the display 121, in order to display outputs corresponding to the state of the concrete structure 80 to the user or worker.

[0021] In some embodiments, the controller 120 may include an impedance analysis unit for processing signals from each smart aggregate 110. The impedance analysis unit measures the impedance of the smart aggregate over a range of frequencies. In some embodiments, the controller 120 may include a driver for driving each smart aggregate 110. For example, the driver may be a piezoelectric driver or piezoelectric drive circuit for driving piezoelectric aggregates.

[0022] When used, the smart aggregate 110 may be placed or embedded in the ready-mix concrete, for example, when a new cement mixture is poured in. Each of the smart aggregates 110 may be embedded in the concrete structure 80 during the concrete structure formation / manufacturing process. In other words, the smart aggregates 110 are placed or embedded inside the concrete structure 80 while the concrete structure 80 is still relatively fluid / wet and has not yet hardened. After the smart aggregates 110 are embedded in the ready-mix concrete structure 80, monitoring of the condition of the concrete structure 80 may begin.

[0023] In one embodiment, the concrete monitoring method includes continuously or intermittently acquiring signals from the smart aggregate 110 over a period of time as the ready-mix concrete structure (in which the smart aggregate 110 is placed) matures or changes from an initial state to a fully hardened state (maturity). In some applications, the controller 120 is configured to determine a recommended time or period for the user to perform finishing work on the concrete structure 80. In some embodiments, the state of the concrete structure 80 may relate to the hydration state for the purpose of concrete finishing. Since concrete finishing must be started before the concrete structure is fully hardened, determining the hydration state of the concrete structure may affect the final surface finish. Therefore, the method may be repeatedly performed throughout the concrete hardening process or the maturation process of the concrete structure 80 to determine the state of the concrete structure.

[0024] Figure 2 shows a process flowchart of a concrete monitoring method 200 according to various embodiments of the present disclosure. Method 200 may include, in step 210, performing multiple frequency sweeps of one or more smart aggregates 110, such as piezoelectric aggregates. In some embodiments, the smart aggregates 110 may be calibrated first before performing the frequency sweeps. In some embodiments, performing each of the frequency sweeps may include driving each of the piezoelectric aggregates 110 over a certain frequency range and obtaining the respective electrical signals from each of the piezoelectric aggregates 110 over the same frequency range. The electrical signals from each of the piezoelectric aggregates 110 may correspond to impedance measurements of each piezoelectric aggregate 110 over a frequency range. In some embodiments, performing each of the frequency sweeps may include measuring the impedance of each piezoelectric aggregate 110 over a range of frequencies. In some embodiments, each of the measured impedances may include the respective magnitude of the impedance and the respective phase angle of the impedance. In some embodiments, multiple phase angles are obtained by performing multiple frequency sweeps of the piezoelectric aggregates 110. To avoid misunderstanding, for example, the phase angle of each impedance may be a continuous measurement, a discrete measurement, a discrete measurement, multiple segments of a continuous measurement, multiple segments of a discrete measurement, multiple discrete measurements, etc.

[0025] Therefore, each frequency sweep can result in a measurement or a signal obtained from each piezoelectric aggregate. In some embodiments, multiple frequency sweeps may be performed over a certain duration. A single frequency sweep of a single aggregate performed at a certain point in time may produce a unique signal. Therefore, multiple frequency sweeps of a single aggregate performed over a certain duration may produce multiple unique signals. Furthermore, a single frequency sweep of multiple aggregates performed beyond a certain point in time may also produce multiple unique signals.

[0026] In some embodiments, multiple frequency sweeps may be performed repeatedly based on the measurement cycle rate. For example, the measurement cycle rate may be described as performing one frequency sweep for each piezoelectric aggregate every 30 minutes or every 10 minutes. In some embodiments, there may be multiple embedded piezoelectric aggregates. The frequency sweeps may be performed with time staggers so that only a single frequency sweep is performed at each point in time. This ensures no interference between the piezoelectric aggregates between each frequency sweep.

[0027] Alternatively, multiple frequency sweeps may be performed sequentially based on a measurement schedule. For example, a predetermined schedule may be provided initially to perform frequency sweeps according to schedules such as 10 minutes, 30 minutes, 80 minutes, and 150 minutes after embedding the piezoelectric aggregate.

[0028] In some examples, referring to Figure 3, each impedance measurement may include a plot of the phase angle over a frequency range, for example, 30 kHz to 100 kHz. In other examples, the frequency range may be 50 kHz to 80 kHz. The frequency range may be determined based on the system configuration, aggregate composition, or concrete grade mix. Figure 3 shows multiple impedance measurements from each of multiple frequency sweeps. It can be seen that the plot of the phase angle may show the peak phase angle or peak phase amplitude in each impedance measurement. The peak phase angle or peak phase amplitude may correspond to the peak phase frequency. Referring to Figure 4 as an example, the peak phase amplitude (p n ) is the peak phase frequency (f n This corresponds to the phase angle in typical impedance measurements, which is limited to the range of -90 to +90 degrees. Since only a single peak can exist, it is more convenient to pinpoint the location of the peak phase angle in a frequency sweep. Thus, a shift or change in the peak phase angle can be easily observed. This is beneficial because it allows for the pinpointing of the location of the peak phase angle for determining the condition of a concrete structure, compared to observing the magnitude of the peak impedance (impedance magnitude), which may show several localized peaks.

[0029] In some embodiments, impedance measurements may be received and output as one or more discrete values, such as peak phase amplitude, peak phase frequency, or a combination of both. In other embodiments, impedance measurements may be received and output as a table corresponding to one or both of the peak phase amplitude and / or peak phase frequency.

[0030] In some embodiments, method 200 may further include in step 220 determining the state of the concrete structure based on changes in phase angles among selected phase angles. The phase angles are obtained from a previously performed frequency sweep. In other words, the state of the concrete structure may be determined based on changes in the phase angles of the piezoelectric aggregate by performing multiple frequency sweeps. In some embodiments, determining the state of the concrete structure is based on changes in phase angles between selected phase angles obtained from the same piezoelectric aggregate. In some embodiments, method 200 includes determining the state of the concrete structure during the maturation process of the concrete structure. In some embodiments, each piezoelectric aggregate is monitored individually and observed for changes in its respective phase angle. In other words, signals from each piezoelectric aggregate are collected and analyzed independently. Thus, in such scenarios, the state of the concrete structure determined from one piezoelectric aggregate may correspond to a “local” state of the concrete structure or to a local area of ​​the concrete structure. In embodiments where multiple piezoelectric aggregates are present, each “local” state of the concrete structure may be used to comprehensively determine the “collective” state of the concrete structure.

[0031] In some embodiments, method 200 may further include, at stage 230, determining a target state of the concrete structure based on a change in phase angle among selected ones of the phase angles. In some embodiments, a predetermined threshold or condition of the change in phase angle may be set to determine the target state of the concrete structure. In some embodiments, the target state of the concrete structure may be a state suitable for a post-forming process such as concrete finishing. Thus, the target state may include a state where the preparation for finishing the concrete structure is completed, and in the state where the preparation for finishing is completed, the concrete structure is suitable for concrete surface finishing.

[0032] Referring to FIGS. 4 and 5, in some embodiments, the change in phase angle corresponds to a shift in peak phase frequency between respective phase angles obtained from a frequency sweep. The peak phase frequency is the frequency at which the phase angle plot / phase angle curve reaches a peak, e.g., f1 or f n corresponding thereto. For example, the change in phase angle (Δf) is from f1 of the peak phase frequency to f n or, in other cases, from f n to f n+1 corresponding to the shift. It will be understood that the shift in peak phase frequency need not be between two consecutive phase angle peaks. In some embodiments, the shift in peak phase frequency is determined between the peak phase frequency (f1) of an initial frequency sweep and the peak phase frequency (f n or f n+1 etc.) of a subsequent frequency sweep. The peak phase angle of the initial frequency can be determined during calibration of the piezoelectric aggregate before embedding it in the concrete structure. Alternatively, the peak phase angle of the initial frequency may be determined based on the first measurement performed after embedding the piezoelectric aggregate. In some embodiments, to determine the target state of the concrete structure, the amount of shift in peak phase frequency between the peak phase angle (f1) of the initial frequency sweep and the peak phase angle (f n+1 ) of a subsequent frequency sweep needs to satisfy a predetermined frequency range of 2 kHz to 10 kHz, e.g., 6 kHz between f1 and f n .

[0033] Referring further to Figures 4 and 6, in some embodiments, the change in phase angle corresponds to the change in peak phase amplitude (Δp) between each of the phase angles obtained from the frequency sweep. The peak phase amplitude is the phase amplitude at which the phase angle plot / phase angle curve reaches its peak, e.g., p1 or p n This corresponds to p n from p n+1 to, or in other cases from p1 to p n This corresponds to a change or decrease in the peak phase amplitude. In some embodiments, the change in peak phase amplitude is between the respective peak phase amplitudes obtained from two consecutive frequency sweeps, i.e., p n and p n+1 This is determined between the following two ranges. In some embodiments, to determine the target state of the concrete structure, the change in peak phase amplitude between two consecutive frequency sweeps is in the range of 3 to 8 degrees, for example, p n from p n+1 It is necessary to satisfy the requirement of a reduction in peak phase amplitude within a predetermined amplitude range, such as 6 degrees, by this time.

[0034] In some embodiments, predetermined conditions must be met for both a predetermined frequency range and a predetermined amplitude range in order to determine the target state of the concrete structure. These predetermined conditions may correspond to concrete bar drop tests with an penetration depth of 2 to 5 centimeters.

[0035] Figures 7 to 9 show examples of piezoelectric aggregate 110 (also known as EIM-SMA or smart aggregate) according to various embodiments of the present disclosure. The piezoelectric aggregate may include a piezoelectric member 112 sandwiched between two concrete members 114 / 116. The two concrete members 114 / 116 together form a concrete pellet. In some embodiments, the pellet may be a cylindrical or plate-shaped member having a thickness (Tp) along the thickness direction 90 that is substantially smaller than the radius along the radial dimension 92. The piezoelectric member 112 may also have a thinner thickness than the concrete members 114 / 116. In some examples, the piezoelectric member 112 may have a thickness (Tp) of 1 to 2 millimeters, and each of the concrete members 114 / 116 may have a thickness (Tc) of about 5 millimeters. In some examples, the thickness ratio between the piezoelectric member 112 and each of the concrete members 114 / 116 is in the range of 1:5 to 2:5.

[0036] In some embodiments, the piezoelectric member 112 may be a piezoelectric sheet whose respective surfaces are coated with a metallic coating such as Hammerite-Direct to Rust. In some embodiments, the piezoelectric member 112 may be a piezoelectric sheet whose respective surfaces are coated with a thin waterproof layer. The piezoelectric member 112 may have a diameter (Dp) smaller than the respective diameter (Dc) of the concrete members 114 / 116. Thus, the piezoelectric member 112 can be positioned in the center between the two concrete members 114 / 116 along the thickness direction 90, and can be positioned in the center between the two concrete members 114 / 116 along the radial direction 92. For example, the two concrete members 114 / 116 may be formed from the same concrete composition to define a center of mass (M) on a plane of symmetry (P), and the plane of symmetry coincides with the interface between the two concrete members 114 / 116. For example, the two concrete members 114 / 116 may be substantially identical so that pellets define a plane of mirror symmetry between the two concrete members 114 / 116. The piezoelectric member 112 may be described as being positioned within the symmetrical plane of the pellet and substantially enclosed by the pellets 114 / 116. The piezoelectric member 112 may be surrounded on approximately all four sides by the pellets 114 / 116. It will be understood that this does not preclude the provision of one or more wires extending from the piezoelectric member (positioned inside the pellets 114 / 116) to the outside of the pellets 114 / 116. The pellets 114 / 116 are fully cured concrete lumps before the piezoelectric aggregate 110 is used, for example, before the piezoelectric aggregate 110 is placed in the ready-mix concrete to monitor the curing or hardening of the ready-mix concrete.

[0037] In some embodiments, each of the concrete members 114 / 116 may be formed from a cement mixture, i.e., sand and water. While not intended to be limiting, exemplary volume ratios of the cement, sand, and water mixture may be 1:0.5:0.4, respectively. In other examples, other combinations of concrete / mortar may also be possible candidates for the concrete members 114 / 116.

[0038] Figures 10 and 11 illustrate the operating principle of the piezoelectric aggregate 110. The operating principle of the piezoelectric aggregate 110 can be derived from the impedance method and electromechanical coupling theory. According to electromechanical coupling theory, the dynamic characteristics of the piezoelectric structure 310, including the piezoelectric element 312 and the coupling structure 314, are governed by the interaction between the piezoelectric element 312 and the structure 314. The impedance of the piezoelectric structure 310 is determined by the characteristics of the piezoelectric element 312, the relative position of the piezoelectric element 312 with respect to the structure 314, the boundary conditions of the structure 314, the stiffness of the structure 314, and so on.

[0039] Figure 10 shows a schematic diagram of a piezoelectric structure 310, including a circular piezoelectric cylinder 312 and a concrete cylinder 314. To better illustrate the dynamic interaction of the piezoelectric structure, Figure 11 shows a lumped-parameter representation of the piezoelectric structure 310. The piezoelectric element 312 has a constant piezoelectric coupling effect and elastic stiffness. Piezoelectric elements 312 of the same model manufactured by a reliable manufacturer may be assumed to have substantially similar or identical properties (i.e., piezoelectric coupling effect and elastic stiffness), provided that slight variations in manufacturing are not taken into account.

[0040] The concrete cylinder 314 is simplified and represented by a single-degree-of-freedom (SDOF) mechanical oscillator with the following impedance:

number

number

[0041] The admittance (reciprocal of impedance) of the lumped model shown in Figure 11 can be derived as follows.

number

number

number

[0042] When cement and water are mixed, a hydration reaction occurs, resulting in shrinkage and hardening. In other words, the "rigidity" of concrete (k s ) increases. Referring to equation (1), the concrete stiffness (k s The change in the impedance alters the dynamic characteristics of the coupling system composed of the piezoelectric element 312 and the concrete material 314. Based on the above principle, the impedance of fresh concrete can be used for concrete monitoring.

[0043] In some embodiments, the piezoelectric aggregate 110 may be an electromechanical impedance measurement (EIM) based smart aggregate (SMA) for monitoring ready-mix concrete or recently formed concrete. Piezoelectric aggregates may be suitable for mass production. In various embodiments, the smart aggregate is a piezoelectric aggregate or piezoelectric-based aggregate and includes a piezoelectric member made from a piezoelectric material and operates using it.

[0044] In some embodiments, the concrete monitoring method 200 may include obtaining impedance values ​​or results measured from piezoelectric aggregate, which is used directly or indirectly via post-treatment to indicate the state of the concrete structure, such as the hardening state of fresh concrete. Furthermore, the monitoring method 200 is simple and can be automated to reduce any need for human intervention. Thus, the concrete monitoring system 100 and concrete monitoring method 200 can be widely adopted at construction sites or building sites. Moreover, due to the simple and automated nature of the system 100 and method 200, workers at the construction site do not need to have prior knowledge of or understanding of the operating principles of the system 100 and method 200.

[0045] Figures 12A to 12D show a mold 400 for manufacturing several embodiments of piezoelectric aggregate 310. The mold 400 can be used for the rapid manufacturing of the proposed EIM-SMA or piezoelectric aggregate. The mold may be presented in various configurations, and this disclosure is an example. In this embodiment, the mold 400 includes two layers 410 / 420, a bottom layer 410 as shown in Figure 12A and an upper layer 420 as shown in Figure 12B. Each layer 410 / 420 of the mold may be further divided into two components, namely the bottom layer 410 may be formed by two components 412 / 414, and the upper layer 420 may be formed by two components 422 / 424. To facilitate demolding of the piezoelectric aggregate, handles may be provided on all of the components 412 / 414 / 422 / 424.

[0046] A pair of screw holes may be provided on the edges of the assembly and fastening components 412 / 414 / 422 / 424 to form the entire mold during the casting process of the piezoelectric aggregate (EIM-SMA) 110. After each layer 410 / 420 is assembled (independently of the other layers), the bottom layer may form a base with a protruding ring having a diameter in the center (Figure 12A), while the top layer has a circular hole with an inner diameter (Figure 12B). The bottom and top layers 410 / 420 may be further assembled via a sleeve connector (Figure 12C). The mold may be manufactured using a 3D printer to significantly reduce the bare cost.

[0047] Figures 13A to 13C are images illustrating the process of producing piezoelectric aggregate using mold 400. The EIM-SMA casting procedure can be carried out in just a few steps. As shown in Figures 13A to 13C, the method for producing piezoelectric aggregate may include the following: Step 1: Pour concrete into the bottom layer of the mold to fill the bottom layer. Step 2: Place the PZT patch in the center of the bottom layer, with the wire ends extending out of the mold. Step 3: The upper layer is fitted into the lower layer via the sleeve connection, and the upper layer is filled with concrete.

[0048] Figure 14 shows an example application of a concrete monitoring system 100 in which three piezoelectric aggregates 110 are spaced apart by a minimum interval (S). The three piezoelectric aggregates 110 may be arranged in a staggered pattern. The minimum interval (S) minimizes or results in minimal interference between the piezoelectric aggregates 110. In some examples, the minimum interval (S) is approximately 1 meter. This embodiment may be an alternative solution to staggering the frequency sweeps of each piezoelectric aggregate 110 so that the collective state of the concrete structure can be determined collectively at some point in time.

[0049] Referring to Figures 15 and 16, according to various embodiments of the concrete monitoring system, in addition to field mode or wired mode, two wireless methods are proposed to make the measurement process more flexible and efficient. In some embodiments, the smart aggregate 110 is embedded within the slabs 80a and columns 80b of the concrete structure 80. In some embodiments, the smart aggregate 110 may be embedded away from the formwork 82 and reinforcing bars 84 of the concrete structure 80.

[0050] Figure 15 shows a first method (Method I) in which each smart aggregate 110 can be connected to a transmitter 130 installed at the construction site. Alternatively, a multi-channel transmitter may be provided so that a single transmitter can communicate with multiple smart aggregates. Transmitter 130 may include an impedance analysis unit function. In other words, transmitter 130 can perform local impedance measurements. Subsequently, the impedance measurement or impedance spectrum result may be transmitted to receiver 122. Receiver 122 may be located physically away from the construction site via wireless communication. Upon receiving the data or result, a computer 124, including a software program customized for the receiver, may be configured to interpret and present detailed information about the measurement result, but is not limited to visualization of the impedance spectrum. In Method I, transmitter 130 includes an impedance analysis unit function configured to perform a local analysis of the impedance measurement.

[0051] Figure 16 shows a second configuration (Configuration II) in which the impedance analysis unit function is integrated on the receiver side. This configuration can beneficially reduce costs and the risk of damage to the analysis unit function (under relatively harsh field conditions). In this embodiment, the transmitter 130 is responsible for collecting and transmitting RAW data, i.e., voltage and / or current signals, and may be configured without the analysis unit function of Configuration 1. The RAW data is transmitted to the receiver via wireless communication and may be received by the receiver 122 for post-processing. Post-processing may include converting the RAW data (voltage and / or current signals) into impedance measurements or impedance spectra. A computer 124 communicating with the analysis unit 126 may then be used to interpret and present detailed information about the measurement results, but is not limited to visualization of the impedance spectrum.

[0052] Figure 17 shows a schematic workflow of a concrete monitoring system according to various embodiments of the present disclosure. The workflow may include embedding piezoelectric aggregates or EIM-SMA units in ready-mix concrete at a construction site. The wiring of each piezoelectric aggregate may be connected to an impedance analysis unit. As an example, a Wayne Kerr Electronics Limited 6500B precision impedance analysis unit may be used to measure the impedance of the piezoelectric aggregates. As another example, a Sciospec ISX3 may be used as the impedance analysis unit for measuring the impedance of the piezoelectric aggregates. The frequency sweep range of the impedance analysis unit can be up to 120 MHz, and the impedance measurement accuracy is ±0.05%. The measurement data may be saved as a CSV file. In addition to the above configuration, the 6500B series impedance analysis unit may provide a GPIB interface, i.e., a parallel port designed to enable communication between the device and other PC-like control terminals. Furthermore, this impedance analysis unit also provides a standard RJ45 LAN connector that enables connection to a high-speed Ethernet network. In other words, it has an extended capability that allows for remote control.

[0053] Subsequently, the impedance analysis unit may be controlled or configured to perform measurements at regular time intervals, for example, every 10 to 30 minutes, and record the results. The measurement results are collected in RAW data format and saved in the same folder. Under free conditions, i.e., before being embedded in a concrete structure, a frequency sweep can be performed on a given piezoelectric aggregate in the frequency range of 20 kHz to 200 kHz. Any clear frequency peak, for example, around 60 kHz, is recorded. It should be noted that after the piezoelectric aggregate is embedded in concrete, the resonant frequency of the piezoelectric aggregate under constrained conditions increases. Therefore, the measurement frequency range is set to 40 kHz to 100 kHz, taking this frequency increase into account.

[0054] Impedance is a complex number and can be expressed in terms of its real and imaginary parts. Alternatively, impedance can be expressed in terms of its magnitude and angle. The magnitude of impedance depends on many factors and can vary over a vast range, not only being decomposed into real and imaginary parts. During the concrete hardening process, the magnitude of the impedance of piezoelectric aggregate can increase monotonically.

[0055] The peak in the impedance (magnitude of impedance) plot corresponding to electromechanical coupling resonance may indicate a local maximum. Generally, it is difficult to detect or distinguish the peak in impedance magnitude with consistent reproducibility.

[0056] In terms of instrument configuration, this method involves obtaining the magnitude and angle of impedance as the parameters to be measured. Under current conditions, the natural limit of the phase angle is -90° to 90°, and the peak in the phase angle plot is likely to correspond to the maximum value. Once the instrument settings are determined, they can be stored (during setup) in the memory of the controller and / or computing device. This allows other operators without prior knowledge of the system configuration parameters to load the settings from memory for rapid measurement.

[0057] In the experiments conducted, coded Matlab programs were provided to automatically identify raw data, analyze impedance changes, and / or interpret the state of the concrete, such as the hydration state or maturity of the concrete. In other examples, a Python script with a Sciospec ISX3 impedance analysis unit providing impedance data could be used in the experiments. The experiments are described below merely as examples to aid understanding and are not limiting. To monitor the state of the concrete, impedance measurements were repeated every 10 to 30 minutes. With the implementation of an advanced impedance analysis unit based on the method proposed herein, the task of determining the strength of a concrete structure can be completed automatically and even remotely by the instrument in a consistent manner at different points in time over a period of time. This is beneficial because it does not require workers to be physically present on-site at all times during the acquisition of measurement data, and it allows for the acquisition and processing of relatively large sets of data.

[0058] A file naming scheme has been proposed for MATLAB programs to enable automatic identification of RAW data files to be post-processed. RAW data files may be named using the same prefix, e.g., agg4. The prefix may be followed by a separator such as a hyphen (-) or underscore (_). Time information is preferably placed after the separator. Some examples of acceptable file names are "agg4-30mins.csv" and "agg5_210mins.csv".

[0059] Before running the Matlab algorithm, the program files were placed in the same folder as the test data files. Figure 18 is a flowchart of an example of an algorithm for automatically processing data. The algorithm first searches for all CSV files in the current directory. If no CSV files are found in the current directory, the algorithm displays an error message to the user. According to the prefixes and separators appearing in the filenames, the algorithm first screens all files to identify the test data files. The data files are then sorted according to the test time information contained in the filenames. The algorithm reads the data in these files in order. If a data file is incorrectly formatted, the algorithm displays an error message to alert the user. Assuming that the data in the files has been successfully read by the algorithm, the data is saved in the Matlab workspace. Next, a peak search algorithm may be used to identify peaks and extract corresponding frequency and amplitude information. Subsequently, the trend of peak changes over time is plotted to reflect the progression of concrete hydration or maturation. The plot is saved as a JPEG drawing in the current directory.

[0060] To implement the algorithm described above, two separate Matlab programs were developed. Matlab program I is responsible for identifying and sorting CSV files in the current directory. Matlab program II is responsible for post-processing the data in the identified CSV files. Detailed descriptions of the functions, inputs, and outputs of the Matlab programs are provided in Tables 1 and 2 below. [Table 1] [Table 2] Calibration and Correlation Analysis

[0061] According to various embodiments of this disclosure, the methods proposed herein include predicting maturity or hardening state based on at least the phase angle of measured impedance. The prediction may be based on one or more reference data developed to facilitate the interpretation of impedance measurement results. For example, in the experiments conducted, the set of reference data was developed based on the conventional bar drop test. Alternatively or additionally, reference data based on other tests relating to concrete maturity may be used. As an exemplary example, the bar drop test was selected for the experiment because the user was accustomed to describing concrete maturity in relation to the results of the bar drop test. This method does not preclude the use of reference data obtained through other methods. This method does not preclude the possibility that a correlated back reference may become unnecessary for the interpretation of impedance measurement results, for example, if this method becomes widely accepted in the industry and / or codified into a standard. In the experiments conducted, the measured impedance correlated with the bar drop depth, which indicates concrete maturity. Table 3 shows the mixing ratios of the constituent materials of the concrete tested and monitored in the experiments. [Table 3]

[0062] To ensure that the established correlation map is valid for multiple piezoelectric aggregates, the aggregates were calibrated to exhibit the same initial impedance characteristics in a free state, i.e., before being embedded in fresh concrete. Multiple piezoelectric aggregates calibrated against a common standard can be used in different scenarios without recalibration. This means that changes in concrete maturity can be monitored over time with more consistent and quantifiable results, in contrast to bar drop tests, which can be influenced to some extent by the inherently random way in which the object is released by human hands and the inherently random way in which the object lands. Results from bar drop tests may include non-trivial or large variability, such as the overall penetration depth decreasing over time, but the actual measurement results showing that the change in penetration depth does not necessarily change monotonically. In possible application scenarios, piezoelectric aggregates can be mass-produced and calibrated against a standard so that they can be immediately used by on-site construction workers, without the need for construction workers to perform separate calibrations for each concrete structure being monitored. This helps to address the variability of bar drop tests conducted on-site.

[0063] As an example, Figures 19 and 20 show correlation maps between a series of impedance results (obtained from the present method and piezoelectric aggregate) and results from a conventional bar-drop test. In the example, the test was performed on G40 concrete. The impedance phase peaks include both peak phase frequency shifts and peak phase amplitude changes. The two graphs in Figures 19 and 20 are plotted to show the correlation between penetration depth (obtained using a conventional bar-drop test) and peak phase amplitude (obtained using the proposed piezoelectric aggregate), respectively. Penetration depth can be observed to decrease over time as the concrete hardens.

[0064] The peak phase frequency or impedance peak frequency may be observed to increase monotonically during this process, indicating an increase in the concrete's "stiffness" that coincides with the hardening of the concrete. The peak phase amplitude decreases monotonically during this concrete hardening process, providing another indicator that reflects the maturity or hardening state of the concrete. Correlation or calibration involves establishing a reference table or fit function suitable for correlating the impedance results (obtained from piezoelectric aggregate) with bar drop test or other reference results.

[0065] Once calibrated, given impedance measurement results (peak phase frequency and peak phase amplitude), the state of the concrete or the hardening state of the concrete can be interpreted by referring to a reference table or using a fit function. Once a correlation map is established, references in the form of reference tables, fit functions, etc., can be made to interpret the impedance measurement results of any standardized piezoelectric aggregate. As used herein, “standardized piezoelectric aggregate” refers to piezoelectric aggregate or EIM-SMA units that have been calibrated (pre-calibrated) against the same or similar standard. Peak phase frequency shift and peak phase amplitude can be extracted. Subsequently, by referring to the correlation map, the state of the concrete or the progress of concrete maturation can be obtained. A larger peak frequency shift indicates a higher degree of concrete hardening, and a larger change in magnitude indicates a higher degree of concrete hardening.

[0066] Several beneficial applications of the proposed system and method can be understood from the above description. For example, for the purpose of monitoring concrete structures, the conventional bar drop test is known to provide relatively inconsistent measurements. Furthermore, the bar drop test can cause irreversible damage to concrete structures, such as the formation of internal cracks or external damage. Another drawback of the bar drop test is that it needs to be repeated by on-site workers. These and other problems can be addressed from a practical standpoint by using the system and method proposed herein instead.

[0067] Bar drop tests can be affected by many external factors. Therefore, conducting several bar drop tests in parallel often results in significant differences. Compared to bar drop test results, impedance curves are relatively smoother and exhibit superior monotonicity. Furthermore, impedance measurements can be performed automatically by equipment without human intervention. This makes it possible to avoid or significantly reduce operator-related external factors, indicating that the proposed system and method are a more reliable solution for monitoring the condition of concrete structures.

[0068] In one embodiment, various embodiments of the present disclosure include a concrete monitoring system. The concrete monitoring system comprises at least one piezoelectric aggregate and a controller, which can be embedded in a concrete structure. The controller is configured to perform multiple frequency sweeps of at least one piezoelectric aggregate to obtain multiple phase angles and to determine the state of the concrete structure based on the change in phase angle between some of the multiple phase angles. In various embodiments, the state of the concrete structure corresponds to the hydration state of the concrete structure. In various embodiments, the state of the concrete structure includes a finish-ready state of the concrete structure, in which the concrete structure is suitable for concrete surface finishing. In various embodiments, the change in phase angle between some of the multiple phase angles includes the change in phase angle between some of the multiple phase angles of the same piezoelectric aggregate. In various embodiments, the change in phase angle includes a shift in peak phase frequency between some of the multiple phase angles. In various embodiments, the shift in peak phase frequency is determined between an initial frequency sweep and a subsequent frequency sweep. As an example, the shift in peak phase frequency is in the range of 2 kHz to 10 kHz.

[0069] In various embodiments, the change in phase angle includes a change in peak phase amplitude between several of a plurality of phase angles. In various embodiments, the change in peak phase amplitude is determined between several of each phase angles of a plurality of phase angles of two consecutive frequency sweeps. In various embodiments, the change in peak phase amplitude corresponds to a decrease in peak phase amplitude within the range of 3 to 8 degrees. In various embodiments, the plurality of frequency sweeps are performed sequentially based on a measurement schedule.

[0070] In various embodiments, multiple frequency sweeps are performed repeatedly based on the measurement cycle rate. For example, the measurement cycle rate is one frequency sweep within 30 minutes. In some examples, each of the multiple frequency sweeps is performed over a range of sweep frequencies, which is 30 kHz to 100 kHz.

[0071] In various embodiments, each of at least one piezoelectric aggregate comprises a piezoelectric member sandwiched between two concrete members. In some examples, the thickness ratio between the piezoelectric member and the concrete members is 2:5 or less. In various embodiments, the piezoelectric member is a piezoelectric sheet, each surface of which is coated with a metallic paint. In various embodiments, each surface of the piezoelectric member is coated with a thin waterproof layer. In various embodiments of the concrete monitoring system, at least one piezoelectric aggregate comprises two piezoelectric aggregates spaced a minimum distance apart, the minimum distance corresponding to the distance at which interference between the two piezoelectric aggregates is minimized. In various embodiments, the controller is further configured to determine the state of the concrete structure during the maturation process of the concrete structure.

[0072] According to another aspect of this disclosure, a concrete monitoring method is disclosed in various embodiments. The method includes performing multiple frequency sweeps of at least one piezoelectric-based aggregate embedded in a concrete structure to obtain multiple phase angles, and determining the state of the concrete structure based on changes in the phase angles among some of the multiple phase angles. In various embodiments, the method further includes determining a target state of the concrete structure based on changes in the phase angles, in which the concrete structure is suitable for concrete surface finishing. In various embodiments, the method further includes determining the state of the concrete structure during the maturation process of the concrete structure.

[0073] All examples described herein, whether of apparatus, methods, materials, or products, are presented for illustrative purposes and to aid understanding, and are not intended to be limiting or exhaustive. Those skilled in the art can modify these examples without departing from the claimed scope of the invention.

Claims

1. A concrete monitoring system, At least one piezoelectric aggregate that can be embedded in a concrete structure, It is a controller, To obtain multiple phase angles, multiple frequency sweeps are performed on the at least one piezoelectric aggregate. The state of the concrete structure is determined based on the change in phase angle among some of the aforementioned multiple phase angles. A controller configured in such a way A concrete monitoring system equipped with the following features.

2. The system according to claim 1, wherein the state of the concrete structure corresponds to the hydration state of the concrete structure.

3. The system according to claim 1 or 2, wherein the state of the concrete structure includes a state in which the concrete structure is ready for finishing, and in the state in which the concrete structure is ready for finishing, the concrete structure is suitable for concrete surface finishing.

4. The system according to any one of claims 1 to 3, wherein the change in the phase angle among some of the plurality of phase angles includes the change in the phase angle among some of the plurality of phase angles of the same piezoelectric aggregate.

5. The system according to any one of claims 1 to 4, wherein the change in phase angle includes a shift in the peak phase frequency between some of the plurality of phase angles.

6. The system according to claim 5, wherein the shift of the peak phase frequency is determined between an initial frequency sweep and a subsequent frequency sweep.

7. The system according to claim 5 or 6, wherein the shift of the peak phase frequency is within the range of 2 kHz to 10 kHz.

8. The system according to any one of claims 1 to 7, wherein the change in phase angle includes a change in peak phase amplitude between some of the plurality of phase angles.

9. The system according to claim 8, wherein the change in the peak phase amplitude is determined between several respective phase angles of the plurality of phase angles of two consecutive frequency sweeps.

10. The system according to claim 8 or 9, wherein the change in the peak phase amplitude corresponds to a decrease in the peak phase amplitude within the range of 3 to 8 degrees.

11. The system according to any one of claims 1 to 10, wherein the plurality of frequency sweeps are performed sequentially based on a measurement schedule.

12. The system according to any one of claims 1 to 11, wherein the plurality of frequency sweeps are repeatedly performed based on the measurement cycle rate.

13. The system according to claim 12, wherein the measurement cycle speed is one frequency sweep within 30 minutes.

14. The system according to any one of claims 1 to 13, wherein each of the plurality of frequency sweeps is performed over a range of sweep frequencies, the range of sweep frequencies being 30 kHz to 100 kHz.

15. Each of the at least one piezoelectric aggregate is A piezoelectric element sandwiched between two concrete members A system comprising any one of claims 1 to 14.

16. The system according to claim 16, wherein the ratio of the thickness of the piezoelectric member and the concrete member is 2:5 or less.

17. The system according to claim 15 or 16, wherein the piezoelectric member is a piezoelectric thin plate whose respective surface is coated with metallic paint.

18. The system according to claim 17, wherein each of the surfaces of the piezoelectric member is coated with a thin waterproof layer.

19. The system according to any one of claims 1 to 18, wherein the at least one piezoelectric aggregate includes two piezoelectric aggregates spaced apart by a minimum distance, the minimum distance corresponding to the distance at which interference between the two piezoelectric aggregates is minimized.

20. The system according to any one of claims 1 to 19, wherein the controller is further configured to determine the state of the concrete structure during the maturation process of the concrete structure.

21. A concrete monitoring method, To obtain multiple phase angles, multiple frequency sweeps are performed on at least one piezoelectric-based aggregate embedded in the concrete structure, The state of the concrete structure is determined based on the change in phase angle among some of the aforementioned plurality of phase angles. A concrete monitoring method, including...

22. The method according to claim 19, further comprising determining a target state of the concrete structure based on the change in the phase angle, wherein in the target state, the concrete structure is suitable for concrete surface finishing.

23. Determining the state of the concrete structure during the maturation process of the concrete structure. The method according to any one of claims 21 to 22, further comprising:

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