DEVICE AND METHOD FOR DETERMINING THE VOLUME, CHANGE IN COMPOSITION AND RHEOLOGICAL PROPERTIES OF A SUBSTANCE

Description

[0001] The present invention relates to the manufacture and transport of a hydraulic binder-based composition such as concrete. The invention aims more particularly to determine a volume, a variation in composition and rheological characteristics of the mixed composition inside a rotating container. BACKGROUND OF THE INVENTION

[0002] The evolution of concrete manufacturing techniques and construction methods has led to the use of increasingly fluid concrete, particularly thanks to the advent of polycarboxylate-polyacrylate superplasticizers which make it possible to reduce the water dosage.

[0003] The advantages provided by such concretes are numerous and well-known: reduction of energy costs for manufacturing and implementation, speed of casting operations, better durability of structures due to the use of lower water / cement ratios for a given consistency, less arduousness for operators, etc.

[0004] There are several tests for determining the consistency of concrete. The best known is the Abrams cone slump, which involves removing the concrete from a truncated cone and measuring the variation in height of the test body before / after removal from the mold (slump). The greater the slump, the more fluid the concrete is considered. For very fluid concretes (so-called self-compacting concrete or SCC), measuring the slump may be insufficient: the diameter of the test body is then measured after removal from the mold (spreading). Another test, called the V-funnel, involves evaluating the flow rate of a predetermined quantity of concrete passing through the orifice of a V-shaped funnel, by measuring the flow time. This last test can only be applied to very fluid concretes.

[0005] However, since the results of these tests depend on numerous parameters specific to the tests themselves (dimensions of the test devices, execution process, etc.), their representativeness is limited (they do not measure a physical quantity specific to the material tested, but assess, by means of synthetic information, the combined effect of several physical quantities). These tests (technological tests) aim to assess the flow behavior of concrete, but do not allow the intrinsic physical behavior of concrete to be determined, particularly from the point of view of flow science (rheological behavior).

[0006] The determination of this behavior is carried out with a rheometer, a device which makes it possible to characterize the deformation by flow of a concrete in response to an applied stress (or vice versa, to measure the resistant stress exerted by the fluid against a given deformation by flow).

[0007] Rheological measurement, as well as the performance of technological tests, also requires the confinement of the concrete to be characterized in a container that is immobile relative to the ground (static measurements). They therefore presuppose the extraction of part of the concrete from the manufacturing (mixer) or transport (mixer truck) devices, which interrupts the delivery of the concrete and limits the number of measurements during the manufacturing and distribution cycle of said concrete. Static measurements also have the limitation of characterizing a material initially at rest (in different conditions, therefore, from those inside the mixer where it is in continuous agitation).

[0008] Document US 2017 / 108421 discloses a device for characterizing a substance mixed inside a container such that the substance is in relative rotational motion with respect to the container. The device comprises a force sensor which is covered by a protective cover fixed to a base of the force sensor by a hinge pin. The displacement of the upper part of the protective cover is transmitted to the force sensor via a bolt forming a stop connection. SUBJECT OF THE INVENTION

[0009] The invention therefore aims to propose a device and a method for characterizing a substance making it possible to at least partially exceed the aforementioned limits, and in particular not to be limited to static measurements. By "characterize", we mean determining a quantity and / or a variation in composition and / or one or more characteristics of the substance. SUMMARY OF THE INVENTION

[0010] To this end, the invention provides a device for characterizing a substance mixed inside a container in such a way that the substance is mobile in rotation relative to the container, the device comprising: a force sensor fixed to a wall of the container, the sensor extending inside said container along an axis substantially normal to said wall; a protective cover covering the sensor; means for recording and processing a signal delivered by the sensor, arranged to determine, from the signal, a volume and / or a variation in composition and / or at least one rheological characteristic of the substance; and means for transmitting the signal delivered by the sensor to the recording and processing means.

[0011] The protective cover is fixed exclusively and immovably to a free end of the sensor so that, during the relative movement of the substance with respect to the container, the cover is subjected to a resistance pressure imparted by the substance and the resistance pressure is concentrated on the free end of the sensor.

[0012] The invention makes it possible to characterize the substance from the signal provided by the sensor. The variation in composition can result, for example, from the addition of water, additives or fibers to the concrete.

[0013] In particular, the mixed substance is a concrete.

[0014] In particular, the rheological characteristic is the yield point and / or the viscosity.

[0015] In particular, the means of signal transmission include a wireless or radio connection system.

[0016] The invention also relates to a method for characterizing a substance mixed inside a rotating container from such a device. The method comprises the following steps: recording a signal delivered by the sensor during rotations of the container; and determining a volume and / or a variation in composition and / or at least one rheological characteristic of the substance exclusively from the signal.

[0017] In particular, the determination of the volume, the variation in composition and the rheological characteristic of the substance comprises a rectification of the raw signal delivered by the sensor by subtracting from said raw signal a basic signal corresponding to the fluctuations in force to which the sensor is subjected under the effect of its own weight when the container rotates.

[0018] According to a particular embodiment of the invention, the basic signal is determined by recording and analyzing the signal delivered by the sensor when the spinning top is spinning idle.

[0019] According to another embodiment of the invention, the basic signal is determined from the raw signal.

[0020] According to a particular characteristic, the determination of the volume is determined from an angle of presence of the substance.

[0021] In particular, the presence angle is determined from the rectified signal or the raw signal.

[0022] Advantageously, the presence angle is determined from a presence time of the concrete extracted from the rectified signal or the raw signal.

[0023] According to another particular characteristic, the variation in composition is determined by comparing an equivalent value of the rectified signal over a given period with an equivalent value of the rectified signal over a period following the given period.

[0024] According to another particular characteristic, the rheological characteristic of the substance is determined by associating, for a given volume of substance and for at least two values ω i of rotation speed of the container as well as values Seqi of the corresponding equivalent signal, to the couples ( ω i , Seqi) couples ( grad v i , τ i ), Or grad v i is the velocity gradient and τ i shear stress.

[0025] Advantageously, the rheological characteristic is a viscosity of the substance

[0026] Advantageously, the rheological characteristic is a flow threshold of the substance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The invention will be better understood in light of the following description, which is purely illustrative and not limiting, and must be read in conjunction with the appended drawings, among which: [ Fig.1 ] there figure 1 is a side view of a concrete mixer truck equipped with a device according to a particular embodiment of the invention; [ Fig.2 ] there figure 2 is a partial sectional view of the concrete mixer truck shown in figure 1 according to a plane II-II orthogonal to an axis of rotation of the top and passing through a longitudinal axis of the device; [ Fig.3 ] there figure 3 is a detailed sectional view of the device illustrated in figure 2 ; [ Fig.4 ] there figure 4 represents, on the same graph, a raw signal sent by a sensor of the device and a basic signal of said sensor; [ Fig.5 ] there figure 5 represents a rectified signal corresponding to the signals illustrated in figure 4 ; [ Fig.6 ] there figure 6 represents an experimental correlation established between a sensor presence angle and a volume of concrete; [ Fig.7 ] there figure 7 represents a correlation established between a speed gradient grad v i and a shear stress τ i ; [ Fig.8 ] there figure 8 represents, for different concretes, rheological values τ i , µ experimental and corresponding measured values. DETAILED DESCRIPTION OF THE INVENTION

[0028] In reference to the figure 1 , a mixer truck 1, otherwise called a mixer truck, comprises in a manner known per se a rotating mixer 2 forming a container for containing and mixing a concrete B. The mixer 2, arranged along the length of the truck 1, has an axis of rotation X advantageously inclined towards the front of the truck 1 and comprises an outlet orifice 2.1 arranged at the rear of the truck 1.

[0029] During the transport of the concrete to a dumping location, the mixer 2 rotates in a first direction around the rotation axis X in order to mix the concrete B and prevent its segregation in said mixer 2. A helical partition is provided to push the concrete B towards a bottom of the mixer 2 opposite the outlet orifice 2.1 in order to mix it and move it away from said outlet orifice 2.1.

[0030] When pouring concrete B, the mixer 2 rotates around the rotation axis X in the opposite direction to that during its transport, the helical partition then pushing the concrete B towards the outlet orifice 2.1.

[0031] As illustrated in figures 2 And 3, the truck is equipped with a device D according to a particular embodiment of the invention for determining a volume, a variation in composition and rheological characteristics of the concrete B. The device D comprises a force sensor 3 comprising a bar approximately 15 cm long, elastically deformable provided with at least one strain gauge (based on the Wheatstone bridge principle). One end of the bar of the sensor 3 is screwed to a wall 2.2 of the mixer 2 to form a built-in connection and so that the bar extends inside the mixer 2 along an axis Y substantially normal to the wall 2.2, or substantially radial relative to the axis of rotation X of the mixer 2. Advantageously, the sensor 3 is here mounted on an inspection door of the mixer 2, in particular to facilitate maintenance of the sensor 3 which can thus be easily removed from the mixer 2.

[0032] A wired connection 4 connects the sensor 3 to a signal recording and processing system 5. The system 5 comprises an electronic unit comprising a processor and a memory containing a program having instructions arranged to analyze a raw Sb signal delivered by the sensor 3 via the wired connection 4. The information resulting from the recording and processing of the signal Sb are transmitted here in real time to an on-board display unit (not shown here) preferably via a wireless link.

[0033] A protective cover 6 covers the sensor 3. The cover 6 comprises a tubular wall having an open end adjacent to the wall 2.2 and an end closed by a transverse partition fixed exclusively and immobile, that is to say to ensure a connection of the embedding type, to a free end of said sensor 3 by screwing so as to transfer the resultant of the forces F exerted on the tubular wall of the cover 6, onto the free end of the bar of the sensor 3.

[0034] A seal 7 extends around the open end of the cover 6 to ensure a seal between the cover 6 and the wall 2.2 of the mixer 2, thereby ensuring that the concrete B is inaccessible to the sensor 3. The seal 7 must not prevent the movements of the cover 6. The seal 7 is constituted, for example, by an in-situ polymerizing edge, by a flat seal or by a non-contact seal so as to make the resistance of the seal to the movements of the cover 6 negligible.

[0035] In operation, the sensor 3 equipped with the cover 6 rotates with the mixer 2 in the direction of rotation indicated by the arrow 8 or in the opposite direction, depending on whether the mixer 2 mixes or evacuates the concrete B. In both cases, the concrete B remains in the lower part of the mixer 2 due to the action of gravity.

[0036] The sensor 3 is thus immersed in the concrete B with each rotation of the mixer 2 and moves relative to the concrete B. The concrete B then exerts, over the entire length of the cover 6, a resistance pressure represented schematically with arrows 9 opposite the rotational movement of the sensor 3. The sensor 3 thus makes it possible to directly measure the force exerted by the concrete B on the cover 6 and send the signal Sb corresponding gross.

[0037] The signal recording and processing system 5 then uses the signal Sb raw to determine the volume, rheological characteristics and possible variation in the composition of concrete B contained in mixer 2.

[0038] To do this, the signal recording and processing system 5 first performs signal rectification. Sb raw signal sent by sensor 3 by subtracting from said signal Sb raw a signal bsinusoidal wave called basic wave corresponding to the force fluctuations to which the sensor 3 is subjected under the effect of its own weight during the rotation of the top 2.

[0039] The signal Sr straightened, the signal Sb raw and signal b basic are linked by the following relation: Sr t = Sb t − b t

[0040] An example of a signal Sb raw and signal b basic is illustrated in the figure 4 . The signal Sr corresponding rectified is illustrated in the figure 5 .

[0041] The signal Sb crude is characterized by a substantially periodic evolution of period T according to the relationship: Sr t ≃ Sr t + T

[0042] The signal b basic can be described according to the equation: b t = A sin ωt + φ in which A represents the amplitude of the signal, ω the pulse and ϕ the phase at the origin.

[0043] The values A, ω And ϕ can in particular be determined, in a manner known per se, by recording and analyzing the signal delivered by the sensor 3 when the mixer 2 is rotating empty, in other words without concrete, around its axis of rotation X. This can be carried out during a calibration phase carried out either in the factory or in operation when the mixer 2 is empty.

[0044] An alternative solution is to determine the values A, ω And ϕ from the signal Sb raw. The signal recording and processing system 5 allows in particular access, over a predetermined time span, to a frequency f signal average Sb raw. The frequency f mean can, for example, be calculated by an analysis of the discontinuities of a numerical derivative or a Fourier transform of the signal Sb raw. The frequency f average of the raw Sb signal coinciding with that of the signalb basic, the pulsation ω can therefore be determined from the equation: ω = 2 πf = 2 π T

[0045] Furthermore, the signal recording and processing system 5 also provides access to the phase ϕ and the amplitude A, in particular by identifying a point M si of the signal Sb raw coordinates t Msi , Sb Msi corresponding to a minimum of the signal Sb gross according to the relationships: φ = π 3 2 − 2 t Msi T et A = Sb Msi

[0046] Determining the amplitude A, of the pulse ω and the phase ϕ of the basic signal b is carried out over at least two complete rotations of the top 2, and preferably over at least five complete rotations in order to have a quasi-instantaneous determination of the signal Sr straightened.

[0047] The signal Srrectified is characterized, over a given period T, by the presence of two sudden variations corresponding to an entry Pe from sensor 3 in concrete B and to an outlet Ps from sensor 3 of concrete B.

[0048] From the signal Sr straightened, the signal recording and processing system 5 determines an angle α p of presence of concrete B corresponding substantially to the angular amplitude during which the sensor 3 is immersed in said concrete B.

[0049] The angle α p presence can in particular be determined from a presence time T p corresponding substantially to the duration during which the sensor 3 is immersed in the concrete B, according to the formulas: α p = 2 π T p T et T p = t s − t e Or t s And t e are the time values ​​respectively associated with the sudden variations Ps And Pe.

[0050] The angle α p presence can also be determined by transforming the time coordinates t s And t e in angular coordinates according to the relation: α p = α e − α s with α e = ωt e + φ α s = ωt s + φ

[0051] From the angle α p presence, the signal recording and processing system 5 determines the volume of concrete B contained in the mixer 2 by means of a previously established experimental correlation between the angle α p of presence and the volume of concrete B, such as that illustrated in figure 6 .

[0052] Simultaneously, the signal recording and processing system 5 also determines, from the signal S r straightened, a variation in the composition of the concrete.

[0053] To do this, the signal recording and processing system 5 associates a single scalar value over one or more consecutive periods S eq called equivalent signal. The signal S eq equivalent can be in particular an average of the signal S r adjusted over the period(s) considered, an average of the signal S r adjusted in absolute value, but also the value S r (t e ) of the signal S r straightened up right now t e or the value S r (t i ) of the signal S r straightened up right now t i , or even the average of the values S r (t e ) And S r (t i ).

[0054] Then, the signal processing recording system 5 compares a value S eq (t) of the equivalent signal of a given period to a value S eq (t+nT) of the equivalent signal of a period consecutive to the given period by verifying the following condition: S eq t + nT ¯ − S eq t ¯ < m in which m is a sensitivity coefficient strictly greater than 0 which can be determined experimentally to fix the variation considered tolerable, and na positive integer that can be chosen according to the allowed sensitivity.

[0055] Failure to comply with the condition means a sudden variation in the composition of the concrete at a time t. It should be noted that from a previously established experimental correlation between the variation of the signal S eq equivalent and the mass or volume of the added substances, the signal recording and processing system 5 can also determine a quantity of water, admixture or fiber added accidentally or intentionally to the concrete B.

[0056] Simultaneously, the signal recording and processing system 5 also determines, from the signal S r straightened, rheological characteristics of concrete B.

[0057] For this, the signal recording and processing system 5 uniquely associates, for a given volume of concrete and for at least two values ω1, ω2 of rotation speed of the top 2 as well as the values S eq 1, S eq 2 of the signal S eq equivalent corresponding to the couples (ω i , S eqi ) couples (grad v i , τ i ), Or grad v i is a velocity gradient and τ i is a shear stress. The torques (grad v i , τ i ) can be determined by calculation or by means of a previously established experimental correlation between the pairs of quantities, for example by measurement on a rotational rheometer.

[0058] The signal recording and processing system 5 then determines, from at least two pairs (grad v i , τ i ), rheological characteristics of concrete B, such as viscosity µ and a flow threshold τ 0 of concrete B, and more generally of the parameters corresponding to any modeling of the rheological behavior of concrete B based on pairs of values (grad v i , τ i ).

[0059] For example, the dependence relationship between the velocity gradient grad v i and shear stress τ i being linear, the signal recording and processing system 5 determines the viscosity µ and the flow threshold τ 0 of substance B from a linear regression of the couples (grad v i , τ i ), such as the one illustrated in the figure 7 . Viscosity µ is substantially equal to the correlation coefficient of said linear regression represents and the flow threshold τ 0 , to the value of the shear stress τ i when the speed gradient grad v i is zero.

[0060] The relationship of dependence between rotational speed ω i of the top 2 and the value S eqi of the signal S eq equivalent being also linear, an alternative solution consists of collecting couples ( τ 0 , µ) of experimental values ​​of different concretes and to measure, for each of the different concretes, couples (ω i , S eqi ) for two values ω1, ω2 of rotation speed of the top 2. The signal recording and processing system 5 then determines by linear regression the torques (S eq (0),p) Or S eq (0) is the signal value S eq equivalent when the rotation speed ω of top 2 is zero and p the correlation coefficient of said linear regression. An average of the ratios τ 0 / S eq (0) And µ / p of the different concretes then allows us to significantly go back to the values τ 0 And µ from the values S eq (0) And p. An example of this approach is illustrated in the table in figure 8 .

[0061] Other approaches are of course possible, for example using neural networks on the raw Sb signal.

[0062] The invention is of course not limited to what has just been described, but on the contrary encompasses any variant falling within the scope defined by the claims.

[0063] Although here the sensor 3 is fixed to the wall 2.2 of the router 2 by screwing, it could also be fixed by riveting or by any other method of fixing allowing the sensor 3 to be mechanically secured to the router 2 and thus form a rigid assembly.

[0064] Although here the cover 6 is fixed to the free end of the sensor 3 by screwing, it could also be fixed by riveting or by any other method of fixing allowing the cover 6 to be mechanically secured to the sensor 3 and thus form a rigid assembly.

[0065] Although here the connection between the sensor 3 and the signal recording and processing system 5 is wired, it can be wireless or radio.

[0066] It is understood that the sensor 3 can be used with a rotating container other than a router which can contain substances having rheological characteristics other than concrete B, such as fluids for the food industry, for the paint industry, for the oil industry, etc.

[0067] Similarly, the container is not necessarily supplied on a truck and other types of mixers can be used. For example, the mixer can be an industrial mixer, a mixing system including high shear mixers, in-line mixers or agitators.

[0068] The processing of signals from the sensor can be carried out, for example, in a processing unit connected by wire to the sensor and located close to it or in a remote processing unit connected wirelessly to the sensor.

Claims

1. A device (D) for characterising a substance (B) mixed inside a container (2) in such a manner that the substance is in relative rotational movement with respect to the container, the device comprising: - a force sensor (3) fixed to a wall (2.2) of the container (2), the sensor extending inside said container along an axis (Y) substantially normal to said wall, and placed in such a way that it is immersed at least periodically in the substance during rotation; - a protective cover (6) covering the sensor (3); - means (5) for recording and processing a signal (Sb) delivered by the sensor arranged to determine, from the signal, a volume and / or a variation in composition and / or at least one rheological characteristic of the substance; and - means (4) for transmitting the signal delivered by the sensor to the recording and processing means (5), characterised in that the protective cover is fixed exclusively and immovably to a free end of the sensor so that, during the relative movement of the substance with respect to the container, the cover is subjected to a resistance pressure imparted by the substance and so that the resistance pressure is concentrated on the free end of the sensor.

2. The device according to claim 1, wherein the mixed substance is a concrete or mortar (B).

3. The device according to claim 1 or claim 2, wherein the rheological characteristic is the yield point and / or viscosity.

4. The device according to any one of the preceding claims, wherein the signal transmission means (4) comprise a wireless or radio connection system.

5. A method for characterising a substance (B) mixed inside a container (2) in such a way that the substance is in relative rotational movement with respect to the container from a device (D) according to any one of the preceding claims, the method comprising the following steps: - recording a signal (Sb) delivered by the sensor (3) during rotations of the container (2); and - determine a volume and / or a variation in composition and / or at least one rheological characteristic of the substance exclusively from the signal (Sb).

6. The method according to claim 5, wherein determining the volume, the variation in composition and the rheological characteristic of the substance comprises rectifying (Sr) the raw signal (Sb) delivered by the sensor (3) by subtracting from said signal (Sb) a basic signal (b) corresponding to the force fluctuations to which the sensor (3) is subjected under the effect of its own weight when the container (2) rotates.

7. The method according to claim 6, wherein the basic signal (b) is determined by recording and analysing the signal (Sb) delivered by the sensor (3) when the container (2) is running empty.

8. The method according to claim 6, wherein the base signal (b) is determined from the raw signal (Sb).

9. The method according to any one of claims 6 to 8, wherein the determination of the volume is determined from an angle (αp) of presence of the substance (B).

10. The method according to claim 9, wherein the angle (αp) of presence is determined from the rectified signal (Sr) or the raw signal (Sb).

11. The method according to claim 10, wherein the angle (αp) of presence is determined from a presence time (TP) of the concrete (B) extracted from the rectified signal (Sr) or the raw signal (Sb).

12. The method according to claim 6, comprising the step of determining a variation in composition of the substance by comparing an equivalent value (Seq(t)) of the rectified signal (Sr) over a given period (T) with an equivalent value (Seq(t+nT)) of the rectified signal over a period following the given period (T).

13. The method according to claim 12, wherein the rheological characteristic of the substance (B) is determined by associating to the pairs (ωi, Seqi), for a given volume of substance (B) and for at least two values (ωi) of the rotation speed of the container (2) as well as values (Seqi) of the corresponding equivalent signal (Seq), pairs (grad Vi, Ti), where grad Vi is the speed gradient and τi is the shear stress.

14. The method according to claim 13, wherein the rheological characteristic is a viscosity (µ) of the substance (B).

15. The method according to claim 13, wherein the rheological characteristic is a yield point (T0) of the substance (B).