Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/38—Concrete; ceramics; glass; bricks
  • G01N33/383—Concrete, cement
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
  • G01N29/04—Analysing solids
  • G01N29/11—Analysing solids by measuring attenuation of acoustic waves
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2291/00—Indexing codes associated with group G01N29/00
  • G01N2291/01—Indexing codes associated with the measuring variable
  • G01N2291/014—Resonance or resonant frequency
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2291/00—Indexing codes associated with group G01N29/00
  • G01N2291/02—Indexing codes associated with the analysed material
  • G01N2291/023—Solids
  • G01N2291/0231—Composite or layered materials
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2291/00—Indexing codes associated with group G01N29/00
  • G01N2291/02—Indexing codes associated with the analysed material
  • G01N2291/025—Change of phase or condition
  • G01N2291/0251—Solidification, icing, curing composites, polymerisation

Definitions

• the invention refers to the field of physical charac- terization of concretes and other composite materials. It is based on the subject-matter as set forth in the preamble of the independent claims.
• the invention resides in a method and apparatus for coupling acoustic waves into a composite material and detecting a transmitted acoustic signal, whereby an oscil- logra of the acoustic signal is measured and is analyzed in order to determine structural and/or mechanical parameters of the composite material.
• This acoustic analysis method allows to perform on-site and real-time measurements of the status and evolution of physical properties of composites, such as mortar, gypsum and Roller Compacted Concrete RCC, that were previously unobtainable .
• an acoustic energy E and optionally other acoustic variables, such as a frequency, airvpli- tude, intensity or signal attenuation of the acoustic wave are determined and correlated to elasticity, density, strength, internal tension, imperfections, discontinuities, phase changes (gaseous, liquid, solid), setting time and/or acoustic impedance of the composite ma- terial .
• a series of oscillograms is measured and analyzed in order to monitor dynamic changes in the composite material, in particular during a hardening process .
• additional measurements of temperature, dimensional changes and/or loss of weight of the composite material are made to complement the measurements of acoustic oscillograms.
• Fig. 1 shows an apparatus according to invention for measuring and analyzing acoustic oscillograms
• Fig. 2 shows experimental curves of acoustic energy versus time characterizing the setting process of Roller Compacted Concrete RCC.
• identical parts are designated by identical reference numerals.
• a composite material is any material made of several components.
• the composite contains in general a base material, a ligand and some kind of admixture or addition which improves the performance of the first two.
• Examples of composite materials are: concrete, mortar, gypsum, epoxy materials, stuccos, and any mixture where a ligand as hydrau- lie cement, fibers, admixtures, additions or other components, which modify the physical or reological properties of the composite, are present.
• the composite being a heterogeneous material makes use of the properties of its fundamental components in order to achieve special characteristics.
• Concrete, gypsum and mortar are composite materials employed in the construction industry. These materials are difficult to charac- terize, and it is also difficult to reliably model their behaviour, especially in the transition period from the fresh to the complete hardened state. Therefore the characterization or modeling of composite materials has so far been restricted to materials with less complex matrices .
• the present invention resides in a method for characterizing composite materials 2 and in particular for measuring physical properties of concrete 2, whereby a wave- form or oscillogram of an acoustic wave having traversed the composite material 2 is detected and the form of or characteristic numbers derived from the oscillogram are correlated to structural and/or mechanical parameters of the composite material 2.
• This detailed acoustic analysis is advantageous over usual propagation velocity measurements, in that more information about internal characteristics of the composite 2 are obtainable, such as the volumetric proportions of solid, liquid and/or gaseous phases, the hard- ening process, the evolution of the material strength during hardening, etc.
• the method can also be applied when the acoustic wavelength is comparable to the size of components, inclusions or inhomogeneities in the composite 2, as it can happen in the case of fresh concrete. Disadvantages of hitherto applied methods are avoided, such as need for special environmental meaasurement conditions, waiting for complete hardening of the composite 2, or using extrapolated data from laboratory tests made under ideal conditions.
• An acoustic pulse generator 1 excites an acoustic emitter transducer 3 that sends acoustic waves into the composite 2.
• the waves are picked up by an acoustic receiver transducer 8 and transformed into an electric signal to be detected and analyzed in the measuring means 7.
• the measuring means 7 comprise a high-speed data acquisition board or apparatus 4 for storing oscillograms of the acoustic waves and a microprocessor or computer 5 for analyzing the oscillograms.
• a single transducer 3, 8 can function as emitter 3 and receiver 8.
• the acoustic pulse generator 1 and emitter transducer 3 can be replaced by a sclerometric hammer.
• the high-speed acquisition apparatus 4 can be a digital oscilloscope 4.
• the measuring means 7 are an amplifier 10 for received signals, an acoustic spectrum analyzer 11, as well as a calorimeter 12 for heat of reaction measurements and/or a thermometer, a defor- mimeter 6 and/or a balance 9 for measuring temperature, dimensional and/or weight changes of the composite material 2.
• the deformimeter or dimensional change tester 6 can be a magnetic displacement transducer (LVDT) 6.
• the balance 9 can be a digital balance 9.
• the apparatus ⁇ comprises a coupling system 13, 14, in particular a pneumatic coupler 14 connected to a pneumatic compressor 13, for pressing the acoustic transducer 3, 8 to the composite material 2.
• the microprocessor or computer 5 shall be designed for controlling the acoustic pulse generator 1 and the measuring means 7.
• the computer 5 shall be equipped with an IEEE communication board and an A/D converter and be programmed by specific software. 15 signifies the output.
• the operation of the apparatus according to Fig. 1 is as follows:
• This signal is fed to the digital oscilloscope 4, which stores the oscillogram of the wave train that has crossed the composite material volume in that instant, in its memory.
• the stored signal is sent to the computer 5 practically in real time.
• the computer 5 also registers in a continuous way data coming from the balance or scale 9 that measures weight changes of the probe 2, from a deformimeter 6, which follows the volume changes of the composite material 2, from thermocouples that register the ambient and the ma- terial temperature and optionally from the calorimeter 12.
• the data recording time in particular the time intervals between the acoustic and other complementing measurements, can be controlled by the software .
• characteristic curves of the evaluated composite material 2 are generated, in which it is possible to observe the variation of hydration with time (ultrasonic energy versus time) , and at the same time it is possible to obtain curves of sample tem- perature versus time. It is possible to characterize in detail the hydrate formation for the case of a mortar or a concrete.
• the other parameters can complete the information obtained from the acoustic diagnosis according to invention. In summary, a whole package of information of great value and utility for the constructor is pro- vided on the site of construction and essentially in real time.
• ⁇ (x, t) ⁇ n A n *cos ( ⁇ n t-k n x) + B n *sin( ⁇ n t-k n x)
• ⁇ n represent the eigenfrequencies
• k n the wave numbers of the system.
• the type of composite material 2 and its characteristics define the type of impact or (ultra) sound waves to be used.
• the principle of the method and apparatus remains the same for both types of acoustic excitations, they are referred to as sonic or acoustic waves.
• the acoustic energy is proportional to the square of the oscillation amplitude ⁇ of the particles.
• the energy coming from the source transducer 3 at any moment is always constant, as well as its frequency, wavelength and other acoustic parameters related to the energy, such as acoustic impedance, density or the vibration speed of the particles.
• Table 1 shows preferred types of waves and frequencies.
• the composite materials 2 mentioned in this description typically have a solid, a liquid and a gaseous phase. In all cases the sum of the volumetric proportions of the phases will be one.
• a wave train which crosses a composite material 2 is build up by a finite series of
• the importance of the concept of measuring acoustic oscillograms lies in the fact that the acoustic impedance varies as a function of the structure of the composite 2, and in particular can be higher or lower depending on the aggregates in the composite 2.
• the wave front when crossing such aggregates, will loose, in absolute values, a given quantity of energy E or pressure, which will be absorbed or redistributed in the composite 2. This process will repeat a finite number of times until the wave front reaches the reception transducer 8, which in the case of the apparatus is a piezoelectric crystal 8 or a pressure cell 8.
• Each wave front that belongs to the ultrasonic pulse, which crossed the material 2 excites the piezoelectric crystal 8 of the reception transducer.
• the piezoelectric crystal 8 responds to the pressure stimulation by oscillating, at the same time generating from this mechanical signal an electromagnetic signal. This continuous series of pressures on the piezoelectric crystal 8 appears on the oscilloscope screen 4. From this oscillogram all the acoustic variables of the composite material 2 can be obtained.
• the form of the pressure oscillogram is established by parameters such as: frequency, amplitude, intensity and signal attenuation. It determines the energy value, calculated for a delta of time between two limits of the signal, that are fixed according to the analyzed mate- rial 2.
• the form of the pressure oscillogram and some of its acoustic variables (as e.g.
• the ultrasonic energy is calculated by a numeric integration of the pressure oscillo- gram of the wave train over a time interval.
• the inferior limit is given by the time it takes the front of the wave emitted by the emitting transducer 3 to reach the reception transducer 8.
• the superior time limit corresponds to the time of the first peak, after the one with highest amplitude, when the form of the oscillogram has stabilized. As long as the same composite material 2 is examined, always the same value for the superior limit is used.
• FIG. 2 An experimental example is shown in Fig. 2, where the ultrasonic energy is given as a function of time for two curves 1 and 2, that exemplify the setting behaviour of two variants of Roller Compacted Concrete RCC.
• the experimental parameters are: 32 °C, 75% relative humidity.
• Curve 1 cement weigth 70 kg/m 3 , water 4.8%, gravel (19- 38 mm) 249 kg/m 3 , gravel (4.8-12.5 mm) 543 kg/m 3 , crushed sand 566 kg/m 3 , fine sand 362 kg/m 3 ;
• curve 2 same composition as in curve 1, except that a setting retarder admixture is added with a dosage of 2% of the cement weight.
• F. I. signifies the initial setting and F. F.
• the curves 1 and 2 describe very sensitively the evolution of the liquid and gaseous phases to solid (hydration process and crystal formation) . This type of measurements can also detect the tension state, the presence of internal discontinuities of the material, and the behavior of the aggregate-paste transition zone for the case of concrete.
• the acoustic energy E for a given time interval ⁇ t can be calculated as
• E acoustic energy (in erg)
• a ⁇ potential difference between a base state and an i-th maximum excitation, provoked by the wave front, of a piezoelectric transducer or crystal 8 (in mV)
• ⁇ t is the time difference (in ⁇ s)
• K constant that relates the mechanical amplitude of the displacement of the piezoelectric crystal 8 to the electromagnetic response.
• the constant K also includes characteristics of the matrix like density, and characteristics of the emitter 3, like signal frequency or period.
• the apparatus and method of the present invention are very appropriate for the characterization of the materials 2 used in the field of construction, such as concrete, mortar and gypsum.

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• 1998
  • 1998-09-11 CO CO98052430A patent/CO4810262A1/es unknown
• 1999
  • 1999-09-10 WO PCT/IB1999/001527 patent/WO2000016092A2/en not_active Application Discontinuation
  • 1999-09-10 BR BR9913578-7A patent/BR9913578A/pt not_active Application Discontinuation
  • 1999-09-10 AU AU54396/99A patent/AU5439699A/en not_active Abandoned
  • 1999-09-10 CN CN 99810785 patent/CN1317086A/zh active Pending
  • 1999-09-10 EP EP99940419A patent/EP1112493A2/de not_active Withdrawn

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