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| Claims [Claim 1] A device for performing in-situ acoustic measurements within a solid medium, comprising: a probe element assembly, arranged to be embedded in and acoustically coupled to a host material, itself comprising separate acoustic transmitting and receiving elements configured at a fixed predetermined offset spacing within a rigid support frame; a means of electronically connecting said probe element with an external control system for the purpose of performing acoustic testing when the probe is embedded in the material; an external control system, connectable to the embedded probe element. [Claim 2] A device for performing in-situ acoustic measurements within a solidifying material, the device including a probe element assembly configured to be embedded in and acoustically coupled to the material, the probe element assembly including acoustic transmitter and acoustic receiver elements configured at a predetermined spacing within a rigid support frame. [Claim 3] A device in accordance with claim 1 or 2, wherein said acoustic transmitting element comprises a waterproof piezo-electric transducer or piezo-electric ceramic element. [Claim 4] A device in accordance with claim 1 or 2, wherein said acoustic transmitting element comprises a type of high-voltage sparking device, such as gas-filled discharge tube. [Claim 5] A device in accordance with any one of the preceding claims, wherein said acoustic receiving element comprises a waterproof piezo-electric transducer or piezo-electric ceramic element. [Claim 6] A device in accordance with any one of the preceding claims, wherein the transmitting and receiving elements are inertly mounted to an open, rigid frame, having the function of maintaining a fixed offset separation between the two elements when the probe is embedded in a test medium. [Claim 7] A device in accordance with any one of the preceding claims, wherein the transmitting and receiving elements are operably mounted to rigid frame, having the function of maintaining a fixed offset separation between the two elements, and serve as a waveguide when the probe is embedded in a test medium. [Claim 8] A device in accordance with any one of the preceding claims, wherein transmitting and receiving elements comprise geometrical design features to optimize coupling of acoustic energy into the test medium. [Claim 9] A device in accordance to claim 8, wherein said geometrical design feature comprises a circular end-plate operably attached to the transducer head. [Claim 10] A device in accordance with any one of the preceding claims, wherein the transmitter and receiver elements have a coupling agent at their respective interface with the test material. [Claim 11] A device in accordance any one of the preceding claims, including means of connecting said embedded probe element with an external control system are provided using electrical wire. [Claim 12] A device in accordance to claim 1, wherein said external control system includes means to provide an electrical pulse, optimized to generate acoustic energy at the embedded transmitting element. [Claim 13] A device in accordance to claim 1, wherein said external control system includes means to detect and digitally acquire voltage fluctuations across the transmitting and receiving element terminals. [Claim 14] A device in accordance to claim 1, 12 and 13, wherein said external control system includes means to trigger a data acquisition system using the transmitter excitation pulse. [Claim 15] A device in accordance to claim 1, wherein said external control system includes means to provide an electrical connection between the embedded receiving element and a data acquisition system. [Claim 16] A method for performing in- situ acoustic measurements within a solidifying medium, the method comprising the following sequential steps: embedding an acoustic probe element assembly into the material when said material is in a fluid or granular phase prior to becoming solid, said probe comprising appropriate transmitting and receiving elements configured at a fixed predetermined offset spacing within a rigid support frame; sending a signal from the transmitter to the receiver through a portion of the material utilizing the received signal to determine a characteristic of the solidifying material; utilizing the received signal to determine a characteristic of the solidifying material. [Claim 17] A method for performing in- situ acoustic measurements within a so- lidifying medium, the method comprising the following sequential steps: embedding an acoustic probe element assembly into the material when said material is in a fluid or granular phase prior to becoming solid, said probe comprising appropriate transmitting and receiving elements configured at a fixed predetermined offset spacing within a rigid support frame; sending a guided wave signal from the transmitter to the receiver through the embedded geometrical section comprised in the probe frame; utilizing the received signal to determine a characteristic of the solidifying material. [Claim 18] A method for performing in- situ acoustic measurements within a solidifying medium, the method comprising the following sequential steps: embedding a disposable probe element assembly into the material at the time of placement or manufacture, when said material is in a fluid or granular phase; providing means of connecting the embedded probe to an external control system by exposing the ends of the connecting wires to the outer surface of the test material; connecting a re-usable control system to the embedded element via said connecting wires; generating an electrical pulse at the control system, which is transmitted through the electrical connection and converted into acoustic energy by the embedded transmitting element; using said pulse to trigger a data acquisition system contained in the control unit; measuring and recording the acoustic response of the embedded receiving element using said data acquisition system. [Claim 19] A method of claim 16, 17 or 18, wherein the solid medium comprises a cement-based material, such as concrete, mortar or fibre-reinforced shotcrete. [Claim 20] A method of claim 16 or 18, further comprising analysis of the compression wave travel-time and associated velocity between the embedded transmitting and receiving elements. [Claim 21] A method of claim 16 or 18, the method comprising analysis of the shear wave travel-time and associated velocity between the embedded transmitting and receiving elements. [Claim 22] A method of any one of claims 16 to 21, wherein measured pulse velocities are used to determine the bulk modulus, shear modulus and Poisson's ratio of the test material. [Claim 23] A method of any one of claims 16 to 21, wherein measured pulse velocities are used to infer early-age strength of the test material. [Claim 24] A method of any one of claims 16 to 21, the method comprising analysis of the acoustic energy attenuation between the embedded transmitting and receiving elements. [Claim 25] A method of any one of claims 16 to 21, wherein the acoustic testing comprises analysis of the frequency content of the received acoustic signal |
Title of Invention: EMBEDDED MATERIAL TESTING DEVICE
AND METHOD
Technical Field
[1]
[2] The present invention relates to the determination of the early-age physical properties of cement-based construction materials such as shotcrete, concrete and mortar through in-situ nondestructive testing.
[3]
Background Art
[4]
[5] The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.
[6] The field of invention relates to the determination of material properties of cementations materials, examples of which include but are not limited to mortar, concrete, fibre-reinforced shotcrete, grout and lime-treated soils. The determination of such properties are of particular importance at early stages of a construction project, when information regarding early-age strength and stiffness of the material is relevant to the scheduling of operations in a safe and efficient manner. The development of fundamental material properties in these materials is governed by the rate of cement hydration, which may be diversely affected by variations in material quality, admixture dosage, mix proportions, placement procedures, ambient temperature and relative humidity.
[7] In certain construction operations it is advantageous to monitor the progress of
hydration at early-age, as the scheduling of subsequent operations is contingent on the material attaining threshold values of engineering parameters such as stiffness and strength.
[8] This is of particular importance in tunnelling operations, where lining may be applied as a support mechanism to the excavated surfaces. The lining typically comprises a ce- mentitious material (such as sprayed concrete commonly known as shotcrete). In these instances, safe re-entry time for personnel and equipment is determined in accordance with estimates of the attained stiffness and strength of the lining material, as governed by the rate of cement hydration.
[9] Similarly, the monitoring of early-age strength development is critical to the safe and efficient advancement of other infrastructure and building operations, such as for the removal of formwork in reinforced concrete structures, and the application of structural loads in foundation elements.
[10] There have been various proposals for determining the characteristics of materials, including early-age strength. These include laboratory testing of representative samples, indirect methods such as use of penetrometers, Windsor probe and rebound hammer testing, as well as 'maturity' or calorimetry testing.
[11] Testing methods comprising the background art can be broadly classified into:
1. in-situ methods, applied to the structure in question, and alternatively
2. the use of representative samples that are removed for off site or laboratory testing.
[12] Examples of indirect, in-situ methods, such as probe penetration or rebound velocity measurements are detailed in the following industry standard procedures; ASTM C803/C803M-03 (Standard Test Method for Penetration Resistance of Hardened Concrete), C403/C403M-08 (Standard Test Method for Time of Setting of Concrete Mixtures by Penetration Resistance), ASTM C805/C805M-08 (Standard Test Method for Rebound Number of Hardened Concrete), and ASTM C900-06 (Standard Test Method for Pullout Strength of Hardened Concrete).
[13] Alternatively, the calorimetry or maturity method, based on implanted temperature logging, provides an alternative indirect approach to estimating the rate of hydration and development of physical properties, as outlined in ASTM C1074-04 (Standard Practice for Estimating Concrete Strength by the Maturity Method).
[14] Alternative methods for determining material properties In-situ are provided by
surface-coupled pulse velocity measurements, as specified in ASTM C597-09
(Standard Test Method for Pulse Velocity Through Concrete). This approach, also known as P-wave or ultrasonic pulse velocity (UPV) method can be directly related to fundamental physical properties, and has been successfully used in the past to infer early-age strength of cement-based materials.
[15] Laboratory test methods may include uniaxial compression tests or other forms of destructive testing, used to determine engineering parameters such as stiffness and strength. Some examples of industry practice are detailed in: ASTM C215-08
(Standard Test Method for Fundamental Transverse, Longitudinal, and Torsional Frequencies of Concrete Specimens), ASTM C1550-10 (Standard Test Method for Flexural Toughness of Fiber Reinforced Concrete (Using Centrally Loaded Round Panel)), and ASTM C39/C39M-09a (Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens)
[16] Disclosure of Invention
Technical Problem
[17]
[18] The indirect methods outlined above rely on measurement of related properties and the use of empirically obtained, mix-specific, calibrations in order to obtain estimates of the relevant engineering parameters. For this reason, they are of limited accuracy, require the assumption of consistent mix proportions, and are subject to potentially unforeseen variations between calibration and on-site conditions.
[19] The surface-coupled UPV method is well adapted to laboratory use, and in its current state has limited applicability for the assessment of in-situ material. Some of the limitations of this method are the requirement of smooth, finished testing surfaces, the use of coupling agents and a high degree of operator dependence, due to inconsistencies in surface coupling. The method is therefore not viable on rough surfaces and unfinished concrete or shotcrete, and requires contact to the external surface, therefore precluding its application through formwork or in buried structures such as foundations. Surface- measured properties may also be affected by localized inhomogeneities caused, for example, by surface drying, bleeding or segregation, and not accurately represent the bulk properties of the material.
[20] Although certain laboratory methods provide the most direct evidence of the relevant engineering properties of the sample material, they rely on the assumption of the available sample being a true representation of the in-situ material, and require the additional time and resources associated with sample preparation, transport and laboratory testing. The removal of samples for laboratory testing off-site would normally reduce efficiencies in the feedback of information for time-critical decisions to be made at the construction site.
[21] In regards to early-age properties, multiple factors related to material handling, such as placement procedures, compaction, ambient temperature and humidity, may cause discrepancies between a test sample and the relevant in-situ material, particularly when the test sample must be removed from site for the purposes of testing.
[22] It is against this background that the present invention has been developed.
[23]
Technical Solution
[24]
[25] According to a first aspect of the invention, there is provided a device for performing in-situ acoustic measurements within a solidifying material, the device including a probe element assembly configured to be embedded in and acoustically coupled to the material, the probe element assembly including acoustic transmitter and acoustic receiver elements configured at a predetermined spacing within a rigid support frame.
[26] The device has been devised particularly, although not solely, for measuring
variations in the physical properties of cement-based materials at early stages in the hydration process.
[27] The device may further comprise connection means electronically connecting said embedded probe element with an external control system for the purpose of performing non-destructive acoustic testing. The external control system may be connectable by means of electrical wiring to the embedded probe element.
[28] The external control system may include a battery power supply, pulse generator and data acquisition system.
[29] Preferably, the ultrasonic/acoustic transmitting element comprises an acoustic source, such as a piezoelectric transducer, piezo-ceramic element or a high-frequency sparker mechanism, connectable by electrical means to an external control system.
[30] Preferably, the ultrasonic/acoustic receiving element may comprise an acoustic
sensor, such as a piezoelectric transducer or hydrophone element, connectable by electrical means to an external control system.
[31] Preferably, the probe element may comprise transmitting and receiving elements that are mounted to a rigid support frame, having the function of maintaining a fixed offset separation between the two elements when the probe is embedded in a test medium. Said frame may be configured to withstand but not interfere with normal shotcrete/ concrete application and placement procedures, and maintain constant offset separation i.e. maintain the predetermined spacing in the frame.
[32] Preferably, transmitting and receiving elements may comprise geometrical features to optimize coupling of acoustic energy into the test medium. Such features may comprise, for example, a shaped end-plate (such as a circular end plate) operably attached to the transducer head.
[33] Preferably, transmitting and receiving elements may comprise a coupling agent, such as, for example paraffin, epoxy or urethane, at the interface between the probe and the test medium, to aid the repeatable acoustic transmission of energy into the medium.
[34] Preferably, means of connecting the sensors in the embedded probe element to an external control system may be provided using electrical wire.
[35] Preferably, the external control system may include means to provide an electrical pulse optimized to generate acoustic energy at the embedded transmitting element.
[36] Preferably, the external control system may include means to detect and digitally acquire voltage fluctuations across the transmitting and receiving element terminals. Said data acquisition system may preferably be triggered using the transmitter excitation pulse, and may be used to record the data arising from the response of the embedded receiver element. [37] According to a second aspect of the invention, there is provided a method for performing in-situ acoustic measurements within a solidifying medium, the method including:
[38] a) embedding an acoustic probe element assembly into the material when said
material is in a fluid or granular phase prior to becoming solid, said probe including a transmitter and a receiver;
[39] b) emitting an acoustic signal at the transmitter to the receiver through a portion of the material;
[40] c) utilizing the received signal to determine a characteristic of the solidifying
material.
[41] The method may include connecting the embedded probe to an external control
system, for example, by exposing the ends of probe connecting wires to an outer surface of the test material.
[42] An external control system may be used to generate an electrical pulse, which is transmitted through the connection and converted into acoustic energy by the embedded transmitting element. Concurrently, the generated pulse may be detected by a data acquisition unit in the control system, and serves as a trigger to initiate the digital recording sequence. The acoustic response of the embedded receiver element may subsequently be recorded by the data acquisition system.
[43] The method may include four alternative approaches for the analysis of acoustic data, as outlined below:
[44] A first method for data processing, according to one or more embodiments of the present invention, may comprise analysis of compression and/or shear wave travel- times between the embedded transmitting and receiving element locations, allowing the user to calculate associated pulse velocities of the test material in function of the predetermined source-receiver offset separation. Said pulse velocities may be used to determine bulk modulus, shear modulus and Poisson's ratio of the test material, and may be further used to infer early-age strength of the test material.
[45] A second method for data processing, according to one or more embodiments of the present invention, may comprise the analysis of energy attenuation associated with the acoustic pulse transmitted through the test material between the embedded transmitting and receiving element locations.
[46] A third method for data processing, according to one or more embodiments of the present invention, may comprise the analysis of energy attenuation associated with a waveguide propagating within the rigid frame holding the embedded transmitting and receiving elements.
[47] A fourth method for data processing, according to one or more embodiments of the present invention, may comprise the analysis of the frequency content of the acoustic signal transmitted through the test material between the embedded transmitting and receiving element locations.
Advantageous Effects
The embedded device and method, in accordance with the present invention presents several inventive solutions resulting in clear practical advantages for the purpose of determining early-age material properties in construction materials.
The device and method permit the direct measurement of physical properties relevant to engineering parameters. Testing may be carried out by means of sensors that are embedded within the structure, reducing the requirement for production of representative samples, and potential measurement inconsistencies. The method is effective in-situ test for fresh material, and at very early age. Results are immediately available to facilitate the progress of efficient and safe on-site operations. By virtue of the direct coupling of the embedded sensors to the test material, the approach does not require surface preparation and consequently permits a greater degree of operator independence, in contrast to conventional ultrasonic pulse velocity testing.
The device comprises a single embeddable probe, itself containing the acoustic source and receiver elements pre-mounted to a rigid support frame, and configured at a predetermined and consistent offset separation. By virtue of said pre-determined configuration, the system presents unique advantages for practical applications; on-site installation procedures are fast, repeatable and do not require special expertise. The fixed configuration also produces higher reliability in results and is a beneficial factor for the adoption of standard practices within the industry.
Description of Drawings
The invention will be better understood by reference to the following description of at least one embodiment thereof with reference to the accompanying drawings, in which:
Figure 1 is a schematic view of the material testing device according to the embodiment;
Figure 2 is a schematic view of the probe element;
Figure 3 is a detailed view of the transducer, mounting and coupling plate;
Figure 4 is a schematic diagram of the components of the external control system; Figure 5 is a sample data plot from the receiving sensor. Description of the Preferred Embodiments
[62]
[63] Throughout the specification and claims, unless the context requires otherwise, the word 'comprise' or variations such as 'comprises' or 'comprising', will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.
[64] The embodiment shown in the drawings is directed to an acoustic testing device 10 which has been designed particularly, although not necessarily solely, for determining early-age stiffness and strength in cement-based materials. In the arrangement shown in the drawings, the test material is identified by reference numeral 11. The test material 11 has an outer surface 12.
[65] The acoustic test device 10 according the embodiment comprises a disposable probe component 13 comprising a frame and sensor array, to be embedded in the material at the time of construction and an external control system 14 which includes the appropriate power supply, data acquisition and signal processing elements.
[66] The embedded component 13 comprises a rigid frame 21 incorporating two solid bars 22 and terminal elements 23 designed to house and protect the ultrasonic/acoustic transducer elements 24. In the arrangement shown in the drawings, the ultrasonic transducer 24 is mounted within the terminal element 23 using an acoustically inert barrier. The ultrasonic transducer 24 comprises circular end-plate 26 to aid in the coupling of acoustic energy into the test material.
[67] The embedded element is designed to be placed during construction, within the
volume of the test material, which is typically either poured or sprayed into place. Data acquisition, power supplies and other controlling electronics comprise a reusable control unit 14 which remain external to the test material, and are connectable via electrical cables 25. The electrical cables are permanently fixed to the embedded unit, and specified installation procedures ensure the free ends are allowed to protrude from the surface of the test material at the time of installation.
[68] The external control system comprises the elements necessary to drive the ultrasonic/ acoustic transducer element, and to receive, record and analyze data from the receiving element. The signal generation, data acquisition and analysis steps can be performed in a conventional manner well known to persons skilled in the art of non-destructive testing. A typical experimental setup, depicted schematically in Figure 3, would comprise a pulse generator circuit 31, a battery power supply 32, appropriate amplification 33 and data acquisition 34 circuits, and the capability of performing real-time data processing and analysis using a portable field computer 35.
[69] An example of the form of data obtainable with this device is presented in Figure 4.
This trace shows an acoustic signal 41 corresponding to the output of a receiver element, which is plotted in the domains of acoustic pressure 42 vs. time in microseconds 43. Evident on this trace are an initial perturbation 44 corresponding to an electrical trigger signal corresponding to the moment of transmission, followed by a second perturbation 45 corresponding to the arrival of the compressive wave at the receiving element. The difference between transmission and arrival times obtainable from this trace 46 defines the travel time of the pulse. Pulse velocity is subsequently calculated in terms of the travel time and known separation distance between the source and receiver on the embedded sensor element 10.
[70]