HK1170568A - Mixer waveform analysis for monitoring and controlling concrete - Google Patents

Description

Mixer waveform analysis for monitoring concrete

Technical Field

The present invention relates to the manufacture of concrete and more particularly to a method of monitoring and obtaining information about the quantity and/or nature of cement material in a mixing tank by analyzing an energy waveform (e.g., hydraulic pressure), and more preferably converting the time domain waveform into a frequency domain spectrum, whereby other information can be obtained and evaluated.

Background

It is known to monitor the "slump" or fluidity of concrete in a mix delivery truck by monitoring the energy required to rotate the mixing tank (e.g. US 4,008,093) and/or the torque applied to the tank by hydraulic pressure (e.g. US 5,713,633) using sensors. The higher the amperage or hydraulic pressure required to turn the tank at a given rate, the harder the concrete mix or the lower the flowability (lower slump).

The automatic control system allows for adjustment of slump in transit by the addition of water or other liquid, enabling the concrete mixer truck to transport concrete over long distances. A hydraulic sensor coupled to the hydraulic transmission and/or a rotational speed sensor connected to the tank may be used for monitoring purposes. Such sensors may be wirelessly connected to a computer processing unit and wireless communication system to allow for improvements during operation. See, e.g., U.S. serial No. 10/599130 (publication No. 2007/01856a 1).

Monitoring of concrete slump involves calibrating the outputs or values obtained by hydraulic and/or electrical sensors on a concrete mixing truck and correlating these with slump values obtained using a standard slump cone test. In the standard slump cone test, a 12-inch truncated cone containing fresh concrete was removed to allow the concrete to fall, and the vertical height drop (ASTM C143-05) of the concrete was measured. Concrete with this known slump property is then added to the rotatable tank mixer so that the hydraulic or electrical values obtained as sensor outputs can be stored in a memory location and subsequently correlated by a computer processing unit. During transport of the concrete to the customer, the concrete hardens over time as a result of hydration, evaporation and other factors, which the sensor detects based on the increase in hydraulic or electrical power required to rotate the mixing tank. The on-board computer processing unit compares the detected energy values obtained by the one or more sensors and compares them to values or value ranges stored in the computer-accessible memory. If the sensors and Computer Processing Unit (CPU) detect that the concrete has begun to harden, the CPU may be triggered to activate a metering or pumping device to inject water or other liquid (e.g., a chemical dispersant) into the concrete to restore the slump to a desired value.

Other methods may be used to manually measure workability (which is defined as the ease and uniformity with which concrete can be mixed, placed, cured, and trimmed). For example, in the flow platform test (EN 12350-5), concrete is filled into a cone placed on a moving platform. The platform consists of a flat plate with one end hinged so that the other end can be raised and lowered a fixed distance. After removal of the cone, the slab was raised and lowered several times and the horizontal flow of the concrete was measured. For highly flowable concrete mixes, such as self-setting concrete, the slump flow test (ASTM C1611-05) is used. In this test, concrete is placed in a standard slump cone, the cone is removed, and horizontal diffusion, rather than vertical drop, is measured.

The present inventors have recognized that a major problem with existing slump monitoring information is that such devices provide only information about slump. Other information regarding the amount and properties of the concrete in the tank, as well as the characteristics of the tank itself, should be understood to provide a more thorough and effective monitoring of the properties of the concrete.

The present inventors have also recognized that a major problem with existing slump monitoring devices is determining when mixing of the components is complete to produce a homogeneous mixture. When the ingredients are initially added to the mixer, the energy of the rotating drum increases as the ingredients mix and then decreases as mixing progresses and the concrete becomes more fluid. In current practice, the number of rotations of the tank is fixed to ensure adequate mixing. If this number is greater than what is actually needed to obtain a complete mix, unnecessary energy and time is wasted. If this number is less than what is actually required to achieve complete mixing, unmixed material may be discharged from the tank prematurely. It is desirable to have a method of monitoring the completion of mixing.

Accordingly, there is a need for novel methods and systems for monitoring and adjusting the rheology of concrete in a mixing tank.

Disclosure of Invention

The present invention provides methods and systems for monitoring the rheology and other characteristics of cement materials being mixed in a rotatable mixing tank. While prior art methods analyze a single hydraulic pressure (either measured instantaneously or averaged from measurements over time) to calculate slump or compactness, the present invention involves considering and analyzing changes in the measured energy (e.g., hydraulic pressure) in addition to the average energy to obtain other information about the cement material, such as the degree of mixing, rotational tank speed, or amount of material. In other exemplary embodiments, the time domain information is converted to frequency domain information, for example, by using a Fast Fourier Transform (FFT), a Discrete Fourier Transform (DFT), or a variation thereof. By comparing the waveform (time domain) or transformed waveform data (e.g., FFT) obtained from a given cement mixture and with stored values, the amount and characteristics of the material can be obtained and the rheology and other properties can be adjusted, for example, by adding liquids or other components.

Accordingly, an exemplary method of the present invention of mixing cementitious material includes: providing a rotatable mixing tank having an inner tank wall and at least one mixing blade mounted on the inner tank wall, the mixing tank containing components for making a hydratable cementitious material; at a constant speed S of 1-25 rpm^C1Rotating the mixing tank; providing a sequence of values over time corresponding to the energy required to rotate the mixing tank, at a constant speed S of at least 10 times^C1Monitoring the sequence of values; comparing the provided sequence of values with a sequence of values previously stored in a data memory storage location; and adjusting the rheology or other properties of the cementitious material contained in the mixing tank by introducing a liquid or other cementitious material component into the mixing tank.

In a preferred method, the hydraulic pressure is monitored over time, and the sequence of values obtained corresponding to the hydraulic pressure is stored in a computer accessible data memory storage location so that it can be displayed on a monitor or printed on paper, and the expression also so that it can be compared to a pre-stored sequence of values taken from a control cement sample.

In a preferred method and system, a sequence of values mapped from energy (e.g., hydraulic) in the time domain can be converted to the frequency domain using a Fast Fourier Transform (FFT) algorithm so that the data can be analyzed from the frequency components. Thus, the rheology of the cement material can be monitored based on pre-stored FFT data. For example, if the data indicates that the cementitious material is hardening, this can be quickly determined by measuring the change in peak amplitude and phase difference in the frequency domain, so that the rheology or other properties of the cementitious material can be quickly adjusted by introducing a liquid (e.g., water, a chemical mixture, or both) into the mixing tank.

Thus, a preferred method of the invention comprises: rotating a mixing tank containing the cement mixture at a constant speed of 1-25 rpm; providing a sequence of time domain values corresponding to the amount of energy required to rotate the mixing tank, converting the sequence of time domain values into frequency domain values, and comparing the frequency domain values with stored frequency domain values; and introducing the liquid into the mixing tank based on the compared values.

The value or power output from the sensor corresponding to the amount of electrical energy or more preferably the amount of hydraulic pressure required to turn the tank may be stored in a computer accessible storage location and may be displayed graphically in the form of a periodic waveform. The sequence of energy values over time should be based on a sampling frequency of at least 10 times the mixing tank per revolution, or even higher if greater accuracy is required. Preferably, the mixing tank will have at least one or more internal mixing blades so that the curve of the periodic waveform can have two or more peaks per period in the time domain. Thus, in a preferred embodiment of the invention, the waveform values may be converted to the frequency domain, for example, by using a Fast Fourier Transform (FFT) and/or a Discrete Fourier Transform (DFT) conversion. Analyzing one or both of the time domain or the frequency domain allows analyzing one or more physical cement material mixing parameters selected from the group consisting of: (a) load weight, (b) load volume, (c) concrete density, (d) concrete air content, (e) concrete slump, (f) concrete slump flow, (g) concrete flow plateau value, (h) concrete rheology (e.g., yield stress, viscosity, thixotropy), (i) segregation of concrete components, (j) concrete cure, (k) inclination of mixing tank, (l) size and configuration of internal tank structure; and (m) the build-up of concrete in the tank. Additionally, analysis of the time domain or frequency domain data can be used to determine the progress of the mixing.

For example, a liquid (e.g., water, a chemical mixture, or both) may be introduced into the mixing tank based on analysis of the frequency domain data. The use of a transformation algorithm, such as FFT or Discrete Fourier Transform (DFT), is an efficient method of decomposing or otherwise converting the hydraulic energy value sequence into components of different frequencies for analysis in the frequency domain, so that one or more concrete physical parameters as described above can be monitored, analyzed and, if necessary, adjusted by introducing liquid or other cement components into the mixing tank.

The present invention also provides a mixing system comprising: a mixing tank having an inner tank wall and at least one mixing blade mounted on the inner tank wall, the mixing tank containing components for making a hydratable cementitious material; can be used for a constant speed S of 1-25 rpm^C1A hydraulic transmission that rotates the mixing tank; a sensor operable to provide a sequence of values over time corresponding to the energy required to rotate the mixing tank; a computer processing unit monitoring a value provided by a hydraulic sensor corresponding to a hydraulic quantity required by the hydraulic transmission; a data storage location for storing a first set of data corresponding to a first sequence of values over time corresponding to the energy required to rotate a mixing tank containing a first hydratable cementitious material at a constant speed S of at least 10 times^C1Monitoring said first sequence of values; the computer processing unit is further operable to receive a second sequence of values over time corresponding to the energy required to rotate a mixing tank containing a second hydratable cementitious material at a constant speed S of at least 10 times^C1Monitoring said second sequence of values; the computer processing unit is further operable to compare the second sequence of values to the first sequence of values and adjust the rheology or other property of the second hydratable cementitious material by introducing a liquid or other cementitious material component into the mixing tank based on the comparison. In a preferred mixing system, the computer processing unit is operable (a) to convert said first and second series of values corresponding to the energy required to rotate the mixing tank containing the cementitious material into the frequency domain; (b) comparing the first and second sequences of values after conversion to the frequency domain, and (c) adjusting the rheology of the cement material contained in the mixing tank by adding liquid based on the comparison. Using either or both time domain or frequency domain data, analysis may be made or, for example, by indexing liquids or other componentsInto a cementitious material to improve one or more properties of the cementitious material (e.g., slump flow, load weight, air content, etc.).

The method and system of the present invention may be used, for example, in a static mixing tank at a mixing plant, or in a transport truck having a mixing tank. The analytical method can also be used in mixers other than tank mixers, such as single-shaft mixers, twin-shaft mixers and disk mixers. Other advantages and features of the present invention may be described below.

Drawings

Other advantages and features of the present invention will be more readily appreciated when the following preferred embodiments are described in detail in conjunction with the accompanying drawings, in which

FIG. 1 is a graphical illustration of the hydraulic pressure (i.e., energy as shown in the waveform) required to spin an empty mixing tank;

FIG. 2 is a graphical illustration of the hydraulic pressure required to rotate a mixing tank containing concrete;

FIG. 3 is a graphical illustration of a frequency domain spectrum of the empty mixing tank of FIG. 1 calculated by Fast Fourier Transform (FFT) analysis;

FIG. 4 is a graphical illustration of a frequency domain spectrum of the concrete filled mixing tank of FIG. 2 calculated by Fast Fourier Transform (FFT) analysis;

FIG. 5 is a graphical illustration of hydraulic pressure (wave) over time during mixing of concrete batches;

FIG. 6 is a graphical illustration of the amplitude over frequency calculated for the partially mixed concrete of FIG. 5 using FFT analysis;

FIG. 7 is a graphical illustration of the calculated amplitude with frequency for the fully mixed concrete batch of FIG. 5 using FFT analysis; and

FIG. 8 is a graphical illustration of the relationship between actual rotating canister velocity measured using an encoder and canister velocity calculated using FFT analysis of the hydraulic pressure waveform.

Detailed Description

As used herein, the term "cement" means a material that includes portland cement or another portland cement substitute that functions as a binder to hold together fine aggregate (e.g., sand), coarse aggregate (e.g., crushed stone or gravel), or mixtures thereof.

Such cementitious materials may further comprise fly ash, granulated blast furnace slag, limestone or natural pozzolans which may be combined with or used to replace or replace a portion of portland cement without seriously compromising hydration performance. Incidentally, "mortar" means cement or cement mixture with fine aggregate such as sand; whereas "concrete" more precisely means a mortar also containing coarse aggregates such as crushed stones or gravel. The term "cementitious material" may be used interchangeably with the term "concrete" as concrete is most commonly provided by i.e. mixing trucks having rotatable mixing tanks, but as used herein, the term "concrete" does not necessarily exclude the fact that the invention may be used to transport materials containing only cement or cement substitutes (e.g. pozzolans) or mortar.

Cementitious materials considered "hydratable" are those that harden through chemical interaction with water.

The cementitious material may further contain chemical mixtures such as water reducing agents or large scale water reducing agents, viscosity modifiers, corrosion inhibitors, shrinkage reducing mixtures, set accelerators, set retarders, foaming agents, defoamers, pigments, colorants, fibers for plastic shrinkage control or structural reinforcement, and the like.

Concrete delivery mixing trucks with slump control monitoring equipment such as hydraulic and/or electrical sensors to measure the energy of the rotating mixing tank, speed sensors to measure rotational speed, temperature sensors to monitor air temperature and mixture temperature, and dispensing equipment, as well as computer processing units to monitor signals from the sensors and drive the dispensing equipment are now well known in the industry. Such slump control systems that may be used in conjunction with wireless communication systems are described, for example, in US 5,713,663; US 6,484,079; US serial No. 09/845,660 (publication No. 2002/0015354a 1); US serial No. 10/599,130 (publication No. 2007/01856a 1); serial No. 11/764,832 (publication No. 2008/0316856); and serial No. 11/834,002 (publication No. 2009/0037026). Other exemplary monitoring systems for monitoring various physical properties of concrete mixtures using wireless communication in combination with sensors are taught in US 6,611,755 to Coffee. These teachings are incorporated herein by reference.

In view of the above teachings, the present inventors believe that many exemplary embodiments of the present invention can be implemented using conventional automated concrete mix monitoring equipment. For example, using automatic slump-monitoring devices available under the VERIFI @fromGrace Construction Products, Cambridge, Massachusetts and RS Solutions LLC, West Chester, Ohio, one could proceed with the following steps based on slightly modifying such commercial slump-monitoring devices: introducing cementitious material into a rotatable mixing tank having at least one and preferably two or more mixing blades mounted on an inner tank wall; at a constant speed S of 1-25 revolutions per minute (rpm)^C1Rotating the canister; providing energy (e.g. hydraulic pressure ("P")) corresponding to the time required to rotate the tank^H")) at a constant speed S of at least 10 times per revolution of the tank^C1Monitoring the sequence of values; preferably storing the values in a first computer accessible data memory storage location; comparing the constant speed S over time^C1Lower P^HAnd a constant speed S pre-stored in another data memory storage location^C1Lower P^HThe sequence of measurements of (a); and adjusting the rheology or other property of the cementitious material by introducing a liquid into the mixing tank based on the comparison.

In other exemplary methods and systems of the invention, a sequence of values that can be plotted as a function of energy (e.g., hydraulic pressure) in the time domain is converted to the frequency domain using an algorithm such as a Fast Fourier Transform (FFT), a Discrete Fourier Transform (DFT), or a variant thereof, such that the data can be analyzed as a function of frequency components, and the properties of the cement material can be monitored and/or adjusted based on pre-stored FFT data.

The inventors believe that even based on rotated data, an FFT or Discrete Fourier Transform (DFT) or variations thereof may be used to convert signals from the time domain into frequency domain spectra. For example, US 6,876,168B 1 to Jones teaches that the velocity of a rotating device such as a DC motor can be analyzed in the frequency domain by converting the signals produced by sensors measuring the DC motor dynamics using an FFT or DFT. In the present case, however, the rotation speed sensor can be used on the mixing tank itself, so that it is not necessary to use an FFT or DFT to approach the rotation speed, since this can be determined directly. Instead, by examining hydraulic waveform data in the frequency domain, the present inventors believe that complex concrete mix set and mixer characteristics, even dynamic effects with respect to hydration and other factors, can be monitored, analyzed, and adjusted.

The slump-monitoring system can be calibrated by measuring the slump of a sample concrete mixture using standard slump cone methods (e.g., measuring the vertical fall height of the concrete mixture after the cone is removed and the sample is allowed to fall) and correlating the slump value to the energy required to rotate the same concrete sample mixture in the tank at a given rate for a given mix volume. This correlation may also be used for the purpose of the invention, in particular when analyzing the hydraulic pressure values in the frequency domain.

In other exemplary embodiments of the invention, the sample concrete mixture may be monitored by measuring the slump flow of the concrete mixture sample, and this monitoring is accomplished by measuring the horizontal spread of the concrete sample mixture after the slump cone is removed and the sample is allowed to spread on a surface. Thus, such slump flow values may also be correlated to the average energy (e.g., hydraulic pressure) to rotate the mixing tank at a given rate for a given sample concrete mixture volume. Slump flow testing was performed according to ASTM C1611-05.

In other exemplary embodiments of the invention, the inventors believe that the slump-monitoring system can also be calibrated by using the flow bench test (EN 12350-5), in which concrete is filled into a cone placed on a movable bench, the cone is removed, so that the horizontal spread of the concrete sample can be measured, as described previously in the background. The obtained flow table value may then be correlated to the average hydraulic pressure for a given rate for a given mix volume. This correlation may also be used for the purpose of the invention, in particular when analyzing the hydraulic pressure values in the frequency domain.

Accordingly, other exemplary mixing systems and methods of the invention include providing a sequence of values corresponding to the average hydraulic pressure required to rotate a tank containing a known volume of concrete mixture at a given rate and volume, wherein the values are pre-stored in a computer accessible storage location and correspond to standard slump cone values (vertical drop test; see ASTM C143-05), slump flow values (horizontally expanded, see ASTM C1611-05) and/or flow bench values (see EN 12350-5) obtained from the concrete mixture.

Fig. 1 shows the energy waveform (hydraulic pressure) over time (seconds) required to rotate an empty concrete mixing tank in a typical time domain. These waveforms appear as a sequence of continuous sinusoids. Although hydraulic pressure is primarily referenced herein because most concrete delivery hybrid trucks use hydraulic pressure to turn the tank, it is understood that reference to hydraulic pressure is equally applicable to or includes electrical energy (e.g., current, voltage, or power readings) that is substantially oscillatory-like, having an amplitude that varies over time.

Figure 2 shows a typical hydraulic waveform for rotating a mixing tank filled with concrete mix. The inner surface of the mixing tank includes two mixing blades attached to the inner surface of the tank and arranged in a spiral around the axis of rotation of the tank. The inventors believe that the number of vanes, in this case two, and the characteristics of the empty tank are reflected by pairs of short and high peaks plotted in the curve.

Hydraulic waveforms having a relatively uniform consistency and known slump or slump flow (as measured, for example, by a standard slump cone) and known quantities of a given concrete material may be stored in computer accessible memory in a sequence of values (output from hydraulic sensors) corresponding to hydraulic values required in turning a mixing tank under continuous conditions during rotation. After the mixing tank is emptied and another batch of the same design of concrete components (with the same composition and percentage) is put into the tank, the system can be programmed to recognize when the components (cement, water, aggregate) have been properly mixed and can also determine how much cement material is put into the tank, and this can be done by analyzing the change in hydraulic pressure required to rotate the mixing tank over time. Thus, one may not have to calculate the average energy (which would otherwise require many tank rotations to average), but rather one would presumably require less rotation to determine when uniform compaction has been achieved in a given mixture, simply by ascertaining when the hydraulic waveform fits or is sufficiently close to the control sample, and store it in a computer accessible storage location. In addition, as will be discussed further below, pattern recognition may be used to determine when a waveform corresponds to certain targets. The waveform may also be converted from the time domain to the frequency domain.

FIG. 3 illustrates hydraulic energy from a Fast Fourier Transform (FFT) analysis of an empty can pressure waveform. In other words, the sequence of energy readings is converted from the time domain to the frequency domain, where the hydraulic pressure can be plotted as a function of frequency, and the change in hydraulic pressure as a function of frequency can be monitored over time as mixing progresses, concrete hardens, or material such as water or a chemical mixture is added to the tank. Thus, the amplitude or height of the frequency peak or curve represents the hydraulic pressure (in pounds per square inch, or psi) reflected as a function of frequency. The odd amplitude peaks indicate that most of the hydraulic pressure required to spin the empty tank occurs primarily within a very narrow frequency bandwidth; this is in line with the observation that the hydraulic pressure required to rotate an empty tank is entirely represented by a single sinusoid representing the lowest frequency as implied in figure 1.

In a preferred embodiment of the invention, the hydraulic waveform data (corresponding to the sequence of values of hydraulic pressure required for the rotating tank and the cement material) is converted into the frequency domain, for example by using FFT or DFT, so that the higher tuning behavior of the tank contents can be further analyzed.

In other exemplary embodiments of the present invention, the height of the peak, as well as the width of the bottom of the peak, may be evaluated as desired, and also the total area of the peak.

Fig. 4 shows what happens when concrete is loaded into the mixing tank and the resulting hydraulic waveform is converted by Fast Fourier Transform (FFT) into the frequency domain, with the frequency components plotted as a function of frequency. While the waveform of the empty tank shows a peak amplitude at a frequency corresponding to the tank rotational speed, the hydraulic energy waveform of the concrete loaded mixing tank shows a peak amplitude at a higher frequency. The occurrence of such higher frequencies is believed to be caused by mixing blades or paddles mounted on the inner wall surface of the mixing tank. A typical truck mixing tank includes two identical helical or spiral vanes mounted opposite each other inside the tank. The measured waveform provided by the FFT analysis is the sum of the frequency associated with the tank rotation itself and other frequencies associated with the concrete displaced or sheared by the blades. The second peak appearing at a higher frequency (to the right of the first peak) represents a frequency multiplication of the tank rotation. This phenomenon is believed to result from having two evenly spaced mixing vanes mounted on the inner wall of the rotating drum.

Fig. 5 shows the hydraulic pressure waveform when mixing the batch of concrete. Within this time domain plot, it was observed that the waveform gradually changed with time during the mixing operation. In particular, the time domain waveform is varied from a predominantly sinusoidal curve with a single repeating peak to a curve with two peaks per revolution, each peak having a different height. The latter half of the waveform is "M" or "W" shaped. Accordingly, exemplary methods and systems of the present invention involve analysis of waveform performance corresponding to data of "peaks" and "valleys" of an "M" or "W" shaped waveform as illustrated in fig. 5. The appearance of an "M" or "W" shaped waveform is related to a degree of mixing. In addition, the reduction in variation of the non-average hydraulic pressure (e.g., as measured by standard deviation over a certain time interval) and the reduction and eventual stabilization of the average hydraulic pressure are also related to a certain degree of mixing. Thus, these characteristics of the hydraulic waveform can be analyzed and used to evaluate the progress of the mixing and to ensure that the concrete is completely mixed. It is important to confirm the performance of the concrete after it is completely mixed rather than before. In addition, by knowing the degree of mixing, it is possible to infer the final properties of the fully mixed concrete. The present inventors believe that the hydraulic data after complete mixing may be used to correlate with one or more physical properties of the cementitious material contained in the mixing tank, such as (a) load weight, (b) load volume, (c) concrete density, (d) concrete air content, (e) concrete slump, (f) concrete slump flow, (g) concrete flow plateau value, (h) concrete rheology (e.g., yield stress, viscosity, thixotropy), (i) segregation of concrete components, (j) concrete hardening, (k) inclination of the mixing tank, (l) size and configuration of internal tank structure; and (m) the build-up of concrete in the tank. Such physical properties or information about the mixing tank itself may be stored in a data storage location, graphically displayed on a monitor, or printed on paper.

For example, in FIG. 5, the variation between the highest peak and lowest valley (or bottom of wave) is much greater between 900-. Thus, once the variation between peaks is reduced, as suggested by the curve at 1020-.

In an exemplary method and system of the invention, this information may be graphically displayed on a monitor, making it possible for an operator to begin mixing the components at some time prior to pouring (at the shipping location), and the waveform may be compared to the stored waveform, so that the operator can visually ascertain when the concrete mixture has reached homogeneity. Alternatively, the waveform can be analyzed to determine the state of mixing (e.g., partial mixing, complete mixing, or estimated time to complete mixing of the concrete), and this state can be graphically displayed on a monitor so that an operator can visually ascertain when the concrete mixture has reached homogeneity.

The present inventors believe that the waveform pattern in the hydraulic data sequence may be correlated with one or more cement material parameters and verified visually on a monitor or by programming a computer processor to compare stored data with data obtained during the concrete transport and/or pouring process.

For example, a known load weight may be associated with a particular peak height at a given time and stored in a computer accessible storage location, such that for subsequent concrete loads having the same composition, formulation, and rotational speed, the load weight may be automatically detected as a function of peak amplitude. A peak value at the same height as previously recorded would mean that the concrete load has the same weight (at that time recorded by the pressure sensor at the same time and tank speed); while a peak of half the height may mean that the load has somewhat less weight.

Similarly, the present inventors believe that other portions of the waveform or certain patterns of the waveform over time may be used to analyze other parameters (or physical properties) of the cementitious material, such as slump and slump flow. For example, concrete with low slump would be expected to require more energy to turn the tank, and flow over burrs mounted in the tank would be less susceptible, such that the shape of the waveform would be accompanied by a lot of "sharp" energy activity when switching between higher peaks and lower valleys within one revolution of the mixing tank. This is clearly visible when comparing the waveforms within 900-. The waveforms seen in 900-; while a smoother transition between peak amplitude and trough values suggests that the concrete flows more easily over the rotating mixing blades in 1050-.

On the other hand, when the hydraulic energy value sequence is converted into the frequency domain using FFT, other valuable information begins to appear.

Fig. 6 is a graph curve in the frequency domain after the hydraulic energy value is converted into the frequency domain using FFT, in which both a first peak having a frequency of 0.156 Hz and a second peak having a frequency of 0.430 Hz occur. As the mixing progress time passes, fig. 7 shows that the amplitude of the first peak decreases while the amplitude of the second peak increases. The present inventors believe that this amplitude and phase change of different tunings and sub-tunings can be used to monitor the effect of different physical properties of the cement mixture in the rotating tank. In this case, the partially mixed concrete is a hardened granular material that does not flow over the blades inside the mixer. As the mixing progresses and the batch ingredients in the mixer homogenize and change from a granular bulk material to a fluid bulk material, the concrete begins to flow through the blades inside the mixer. The present inventors believe that the behavior of the fluid concrete flowing through the blade is related to the occurrence of peak amplitudes at different frequencies. In addition, the frequencies associated with each peak become tuned or sub-tuned, i.e., multiples of each other. Thus, the appearance and stabilization of this second peak at different frequencies is related to the progress of mixing.

FIG. 8 shows the relationship between actual tank speed measured with an encoder and tank speed calculated based on FFT analysis of the hydraulic pressure waveform. The frequency associated with the first amplitude of the peak determined by the FFT is equal to the tank speed when converted from Hz to rpm. The frequency associated with the second amplitude peak is equal to twice the tank speed. The frequency associated with the second amplitude peak is twice the tank speed as it is believed to be associated with the concrete acting on the blades in the tank. The presence of two vanes in the tank results in a frequency related to twice the tank speed. The use of FFT data avoids the need for an encoder.

The fast fourier transform is an algorithm that allows the calculation of a discrete fourier transform, which converts time domain data into frequency domain data. In practice, there are a number of FFT algorithms available. The FFT may be used to report frequency, amplitude, phase, power spectrum and power spectral density or real and imaginary parts.

The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. It is intended that the invention protected herein not be construed as limited to the particular forms disclosed, since these are to be regarded as illustrative rather than restrictive. Changes and modifications may be made by one skilled in the art without departing from the spirit of the invention.

Claims (17)

1. A method of mixing cementitious material, comprising:

providing a mixing tank having an inner tank wall and at least one mixing blade mounted on the inner tank wall, the mixing tank containing components for making a hydratable cementitious material;

at a constant speed S of 1-25 rpm^C1Rotating the mixing tank;

providing a sequence of values over time corresponding to the energy required to rotate the mixing tank, at a constant speed S of at least 10 times^C1Monitoring the sequence of values;

comparing the provided sequence of values with a sequence of values previously stored in a data memory storage location; and

the rheology or other properties of the cementitious material contained in the mixing tank are adjusted by introducing a liquid or other cementitious material component into the mixing tank.

2. The method of claim 1, wherein the rotatable mixing tank has at least two mixing vanes mounted on an inner tank wall.

3. The method of claim 1, wherein the sequence of values corresponds to hydraulic pressure.

4. The method of claim 1, wherein the sequence of values is stored in a computer-accessible data storage location.

5. The method of claim 1, wherein the components of the hydratable cementitious material are mixed in the mixing tank until a uniform compaction is achieved.

6. The method of claim 1, wherein in the step of comparing the provided sequence of values with a sequence of values previously stored in a data memory storage location, the sequence of values is related to at least one cement material mixing parameter selected from the group consisting of: (a) load weight, (b) load volume, (c) concrete density, (d) concrete air content, (e) concrete slump, (f) concrete slump flow, (g) concrete flow plateau value, (h) concrete rheology (e.g., yield stress, viscosity, thixotropy), (i) segregation of concrete components, (j) concrete hardening, (k) mixing tank inclination, (l) size and configuration of internal tank structure; and (m) the build-up of concrete in the tank.

7. The method of claim 6, wherein the sequence of values stored at the storage locations of the data store correspond to slump or slump flow.

8. The method of claim 6, wherein said provided sequence of values is graphically displayed in the form of a waveform on a visual display or a chart.

9. The method of claim 6, wherein said provided sequence of values is analyzed in the form of a waveform pattern and said waveform is associated with at least one of said parameters (a) through (m), and said sequence of values analyzed in the waveform pattern is stored in a computer accessible storage location, displayed on a monitor, printed on paper, or a combination thereof.

10. The method of claim 1, wherein the liquid is water, at least one chemical mixture, or a mixture thereof.

11. The method of claim 1, wherein said provided sequence of values is converted into the frequency domain to obtain the second set of data.

12. The method of claim 11, wherein the transforming is accomplished using an algorithm selected from the group consisting of a fast fourier transform and a discrete fourier transform, and variants thereof.

13. The method of claim 1, comprising: rotating a mixing tank containing the cement mixture at a constant speed of 1-25 rpm; providing a sequence of time domain values corresponding to the energy required to rotate the mixing tank; converting the sequence of time domain values into frequency domain values; comparing the converted frequency-domain value with a stored frequency-domain value; and introducing a liquid into the mixing tank based on the comparison.

14. The method of claim 13, wherein in converting the time-domain sequence of values into frequency-domain values, the method further comprises correlating the frequency-domain values with at least one cement material mixing parameter selected from the group consisting of: (a) load weight, (b) load volume, (c) concrete density, (d) concrete air content, (e) concrete slump, (f) concrete slump flow, (g) concrete flow plateau value, (h) concrete rheology (e.g., yield stress, viscosity, thixotropy), (i) segregation of concrete components, (j) concrete hardening, (k) mixing tank inclination, (l) size and configuration of internal tank structure; and (m) the build-up of concrete in the tank.

15. The method of claim 1, further comprising: determining, storing and reporting the progress of mixing based on comparing the provided sequence of values and the pre-stored sequence of values, the comparison involving values corresponding to an "M" or "W" shaped time domain waveform signature, a change in non-average hydraulic pressure, a stabilization of average hydraulic pressure, or a combination thereof, when hydraulic pressure data is graphically depicted as a function of time or frequency of rotating a mixing tank containing hydratable cement material.

16. A mixing system, comprising:

a mixing tank having an inner tank wall and at least one mixing blade mounted on the inner tank wall, the mixing tank containing components for making a hydratable cementitious material;

for a constant speed S of 1-25 rpm^C1A hydraulic transmission that rotates the mixing tank;

a sensor for providing a sequence of values over time corresponding to the energy required to rotate the mixing tank;

a computer processing unit for monitoring a value provided by a hydraulic pressure sensor corresponding to a hydraulic pressure quantity required by the hydraulic transmission;

a data storage location for storing a first set of data corresponding to a first sequence of values over time corresponding to the energy required to rotate a mixing tank containing a first hydratable cementitious material at a constant speed S of at least 10 times^C1Monitoring said first sequence of values;

the computer processing unit is further adapted to receive a second sequence of values over time corresponding to the energy required to rotate a mixing tank containing a second hydratable cementitious material at a constant speed S of at least 10 times^C1Monitoring said second sequence of values;

the computer processing unit is further operable to compare the second sequence of values to the first sequence of values and adjust the rheology or other property of the second hydratable cementitious material by introducing a liquid or other cementitious material component into the mixing tank based on the comparison.

17. The mixing system of claim 16, wherein the computer processing unit is operable to (a) convert the first and second series of values corresponding to the energy required to rotate the mixing tank containing the cementitious material into the frequency domain; (b) comparing the first and second sequences of values after conversion to the frequency domain, and (c) adjusting the rheology of the cement material contained in the mixing tank by adding liquid based on the comparison.