Field of the invention
The present invention relates to a method for controlling
at least one workability parameter, for example the slump,
slump flow, threshold stress, viscosity or the flow rate of a
concrete in the container of a mixer with a non vertical
rotational axis.
Summary of the invention
A concrete is a mixture of aggregates pressed by a binder
and water. The binder may be a hydraulic binder for example
cement. Thus, cement concrete is mentioned. The binder may be
a hydrocarbon binder, for example, bitumen. Thus, bituminous
concrete is mentioned.
When it is produced, the concrete has a more or less fluid
consistency, then it hardens until becoming solid. The
concrete must hence be put in place before substantial
hardening. The workability of concrete corresponds to the
easiness with which the concrete can be handled. The
workability of a concrete may be characterized by the
measurement of rheological parameters such as threshold
stress, concrete viscosity or by the measurement of parameters
resulting from standard tests achieved on the site of usage of
the concrete, such as slump, slump flow or flow rate. By way
of example, the slump may be measured according to the test
described in the European standard NF EN 12350-2 of December
1999.
The measurement of rheological parameters usually requires
specific measurement apparatuses. It may be difficult to
achieve these measurements on the site of usage of the
concrete. On the contrary, the slump, the slump flow and the
flow rate may be easily measured on the site of usage of the
concrete.
However, there is a need for being able to measure the
workability parameter when the concrete is in a mixer with a
non vertical rotational axis and it is hence not possible to
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directly access the concrete in order to prevent an overly
significant drift of the workability parameter. It is the
case, for example, when the concrete is in the container
of a mixer truck during the transport of the concrete from
the concrete manufacturing site to the concrete usage
site.
There exist indirect methods for measuring the slump
of a concrete in a mixer. By way of example, patent US 5
713 663 describes an indirect method for measuring the
slump of a concrete in the turning container of a mixer
truck based on the drive torque applied to the container.
The slump may then be adjusted by adding water or adjuvant
to the concrete. In the case where the container is driven
in rotation by a hydraulic motor, the motor torque may be
determined based on the measurement of the pressure of the
hydraulic fluid supplied to the motor. The slump is then
determined by an empirical formula based on the measured
hydraulic pressure.
The method comprises a prior step of determining, for
each formulation of concrete liable to be manufactured,
the empirical formula representing the variation of the
slump of the concrete according to the hydraulic pressure.
An ordinary concrete corresponds to a concrete for
which the slump usually ranges between 10 mm and 220 mm
measured according to the European standard NF EN 12350-2
of December 1999. The test consists in filling a reference
frustum of a cone with the concrete to be tested, freeing
the concrete from the frustum of a cone, then determining
the height from which the concrete has slumped.
The fluid concrete is a concrete for which the
slumping is too high to be measured correctly by the test
of the European standard NF EN 12350-2 of December 1999.
In this case, it can be measured the slump flow which
corresponds to the previous test with the difference that
it is the diameter of the concrete disc obtained after
removal of the mold which is measured according to
European standard NF EN 12350-8 of November 2010. It can
also be measured the flow rate according to European
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standard NF EN 12350-9 of November 2010 by letting the
concrete flow into a funnel and by measuring the flow duration
of the concrete between two marks of the funnel.
The measuring method described in patent US 5 713 633 is
not suitable for fluid concretes. In fact, for fluid
concretes, the slump/slump flow of the concrete hardly varies
according to the hydraulic pressure. Hence, it is not possible
to obtain a precise measurement of the slump/slump flow of the
concrete by measuring the hydraulic pressure according to the
method of patent US 5 713 633.
Another drawback of such a measuring method is that it is
necessary to determine the empirical formula representing the
variation of the slump of the concrete according to the
hydraulic pressure for each formulation of concrete liable to
be manufactured. Thereby, the method cannot be implemented
when the formulation of concrete is modified. It is thus
necessary to determine a new empirical formula for the new
formulation.
Another drawback of such a measuring method is that it
does not allow measuring workability parameters of the
concrete other than the slump, for example the threshold
stress or the viscosity of the concrete. However, it may be
advantageous to measure such rheological parameters in the
case of fluid concretes which are liable to be pumped.
Hence, there is a need for a method for controlling at
least one workability parameter, in particular the slump, the
slump flow, the threshold stress, the flow rate and/or the
viscosity of a concrete in the container of a mixer with a non
vertical rotational axis which allows determining with
precision this workability parameter even in the case where
the fluidity of the concrete is high.
Summary
An object of the present invention is to compensate for
all or part of the aforementioned drawbacks.
Another object of the present invention is to propose a
method for controlling a workability parameter, in particular
the slump, the slump flow, the threshold stress, the flow rate
and/or viscosity, of a concrete in the container of a mixer
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with a non vertical rotational axis which does not depend
on the fluidity of the concrete.
Another object of the present invention is that the
method may be implemented for new formulations of concrete
without requiring additional adaptation operations.
Thus, the present invention provides a method for
controlling at least one workability parameter of a
concrete contained in the container of a mixer with a non
vertical rotational axis, comprising the following steps:
making the container turn at at least two different
rotational speeds;
determining, for each of said at least two rotational
speeds ω , a rotary drive torque C of the container, a
value of shear stress τ of the concrete and a value of
speed gradient γ of the concrete according to the
following relationships:
τ = T(ω).C
γ = G(ω).ω
where T and G are predetermined functions;
determining a relationship of variation of the shear
stress τ according to the speed gradient γ by
extrapolation and/or approximation based on the determined
values; and
providing an indication of the workability parameter
of the concrete based on the relationship of variation.
According to an embodiment example of the invention,
the method comprises the following steps:
making the container turn at a first rotational speed
and determining a first rotary drive torque of the
container at the first rotational speed;
making the container turn at a second rotational
speed and determining a second rotary drive torque of the
container at the second rotational speed;
determining a first shear stress equal to the product
of the first torque and to the value of the function T at
the first rotational speed;
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determining a first speed gradient equal to the product of
the first rotational speed and to the value of the function G
at the first rotational speed;
determining a second shear stress equal to the product of
the second torque and to the value of the function T at the
second rotational speed;
determining a second speed gradient equal to the product
of the second rotational speed and to the value of the
function G at the second rotational speed; and
determining the relationship of variation of the shear
stress according to the speed gradient by extrapolation and/or
approximation based on the first and second shear stresses and
the first and second speed gradients.
According to an embodiment example of the invention, the
method comprises the following steps:
making the container turn at a third rotational speed and
determining a third rotary drive torque of the container at
the third rotational speed;
determining a third shear stress equal to the product of
the third torque and to the value of the function T at the
third rotational speed;
determining a third speed gradient equal to the product of
the third rotational speed and to the value of the function G
at the third rotational speed; and
determining the relationship of variation of the shear
stress according to the speed gradient by extrapolation and/or
approximation in addition based on the third shear stress and
the third speed gradient.
According to an embodiment example of the invention, the
workability parameter of the concrete is selected from among
the slump, the slump flow, the threshold stress, the viscosity
and the flow rate.
According to an embodiment example of the invention, the
method comprises the determination of the threshold stress of
the concrete based on the relationship of variation and the
determination of the slump and/or slump flow based on the
threshold stress.
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According to an embodiment example of the invention,
the method comprises the adjusting in the container of the
workability parameter of the concrete by introducing a
compound into the container.
According to an embodiment example of the invention,
the compound comprises water, an adjuvant or a mixture
thereof.
According to an embodiment example of the invention,
providing the indication of the workability parameter of
the concrete includes the display on a display screen of
the workability parameter, the printing of the workability
parameter onto a support and/or the storage of a datum
representing the workability parameter to a memory.
According to an embodiment example of the invention,
the container is driven in rotation by a hydraulic motor
comprising an inlet for receiving a hydraulic fluid and an
outlet for pushing back the hydraulic fluid, the torque
being determined based on a first difference of pressures
equal to the difference between the hydraulic pressure
measured at the inlet of the hydraulic motor and the
hydraulic pressure measured at the outlet of the hydraulic
motor.
According to an embodiment example of the invention,
the first difference of pressures is decreased by a second
difference of pressures equal to the difference between
the hydraulic pressure at the inlet of the hydraulic motor
and the hydraulic pressure at the outlet of the hydraulic
pressure in the absence of concrete in the container at
the measurement rotational speed.
According to an embodiment example of the invention,
the hydraulic pressure measured at the inlet or at the
outlet of the hydraulic motor is equal to the average of a
number of sampled pressure values, said number being
inversely proportional to the rotational speed of the
container.
According to an embodiment example of the invention,
during the sampling of the pressure values used for
obtaining the hydraulic pressure measured at the inlet or
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at the outlet of the hydraulic motor, the variations of the
rotational speed of the container are lower than a threshold.
According to an embodiment example of the invention, the
functions G and T are obtained by determining:
for each concrete of a plurality of different concretes, a
variation curve of the drive torque of the container
containing said concrete according to the rotational speed of
the container;
for each concrete of a plurality of different concretes, a
variation curve of the shear stress of the concrete according
to the speed gradient of the concrete by means of a rheometer;
and
for each pair of concretes of the plurality of different
concretes, a first point of intersection between the variation
curves of the drive torque of the container according to the
rotational speed of the container for the concretes of the
pair and a second point of intersection between the variation
curves of the shear stress according to the speed gradient for
the concretes of the pair.
According to an embodiment example of the invention, for
the first point of intersection and the second point of
intersection of each pair of concretes of the plurality of
different concretes, it is determined the value GiCC of the
function G and the value TiCC of the function T according to
the following relationships:
i
CC i
i ω
G γ =
i
iCC Ci
T = τ
where γ iis the speed gradient at the second point of
intersection, τi is the shear stress of the concrete at the
second point of intersection, Ci is the drive torque at the
first point of intersection and ω i is the rotational speed at
the first point of intersection.
According to an embodiment example of the invention, for
the first point of intersection and the second point of
intersection of each pair of concretes of the plurality of
different concretes, it is determined the value GiAlt of the
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function G and the value TiAlt of the function T according
to the following relationships:
V . i . i
Alt Ci
Gi η ω
=
Pow . V
Gi
Alt 1
Ti =
where V is the volume of concrete in the container,
ŋi is the apparent viscosity of the concrete equal to the
ratio of the shear stress of the concrete at the second
point of intersection and the speed gradient at the second
point of intersection, Ci is the drive torque at the first
point of intersection and ω i is the rotational speed at
the first point of intersection.
The present invention also provides a memory device
on which is stored a computer programme for implementing
the aforementioned method.
The present invention also provides a device for
controlling at least one workability parameter of a
concrete, comprising:
a mixer with a non vertical rotational axis
comprising a container containing the concrete;
a system for driving in rotation the container
adapted for making the container turn at at least two
different rotational speeds;
a first sensor for measuring a datum representing the
rotary drive torque of the container;
a second sensor for measuring a datum representing
the rotational speed of the container; and
a processing module connected to the drive system and
to the first and second sensors and configured to
determine, for each of said at least two rotational
speeds ω , a rotary drive torque C of the container, a
value of shear stress τ of the concrete and a speed
gradient value γ of the concrete according to the
following relationships:
τ = T(ω).C
γ = G(ω ).ω
where T and G are predetermined functions;
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determine, a relationship of variation of the shear stress
τ according to the speed gradient γ by extrapolation and/or
approximation based on the predetermined values; and
provide an indication of the workability parameter of the
concrete based on the relationship of variation.
Brief description of the drawings
These objects, features and advantages, as well as others
will be exposed in detail in the following description of
particular embodiment examples made in a non limiting manner
in relation to the accompanying figures among which:
figure 1 represents, in a partial and schematic manner, an
embodiment example of a device for controlling at least one
workability parameter of a concrete in the container of a
mixer with a non vertical rotational axis according to an
embodiment of the invention;
figure 2 represents, in the form of a block diagram, an
embodiment example according to the invention of a method for
controlling a workability parameter of a concrete;
figure 3 represents an example of the variation of the
torque driving in rotation the container of a mixer with a non
vertical rotational axis according to the rotational speed of
the container for two concretes of different formulations;
figure 4 represents an example of variation of the shear stress
τ according to the speed gradient γ for these two concretes,
measured by a rheometer;
figure 5 represents variation curves of the shear stress τ
according to the speed gradient γ of concretes of different
formulations, measured by a rheometer;
figure 6 represents an example of variation curve of the
correction function G;
figure 7 represents an example of variation curve of the
correction function T;
figure 8 represents, in the form of a block diagram, a more
detailed embodiment example according to the invention of a method
for controlling a workability parameter of a concrete;
figure 9 represents an example of variation of the hydraulic
pressure measured at the inlet of the hydraulic motor or of the
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pressure differential between the inlet and the outlet of the
hydraulic motor driving the container of the mixer in rotation;
figure 10 represents, in the form of a block diagram, an
embodiment example of a method for adjusting the slump of a
concrete according to the invention.
For the sake of clarity, same elements have been
designated by the same references in the different figures.
Furthermore, only the elements necessary for the comprehension
of the invention are represented on the figures and are
described.
Detailed description
In the rest of the description, the expressions
viscosity, apparent viscosity and dynamic viscosity are
employed interchangeably for designating the ratio of the shear
stress and the speed gradient of the concrete.
Figure 1 represents an embodiment example of a device 10
for controlling at least one workability parameter of a
concrete according to an embodiment example of the invention.
A concrete is a mixture of aggregates pressed by a binder
and water.
The hydraulic binder is a material which takes and
hardens by hydration. Preferably, the hydraulic binder is a
cement, in particular a Portland cement, for example a cement
of type CEM I, CEM II, CEM III, CEM IV or CEM V according to
the European standard NF EN 197-1 of February 2001.
The concrete may be a mixture of a hydraulic binder,
aggregates, water, possibly adjuvants, and possibly mineral
additions. It consists, for example, of a high performance
concrete, of a very high performance concrete, of a selfplacing
concrete, of a self-leveling concrete, self-compacting
concrete, of a fiber-reinforced concrete, of a ready-to-use
concrete or of a colored concrete. The term concrete includes
mortars. In this case, the concrete comprises a mixture of
hydraulic binder, sand, water and possibly additives and
possibly mineral additives.
The mineral additives are usually, for example,
pozzolanic materials (for example such as defined in the
European standard NF EN 197-1 of February 2001 paragraph
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5.2.3), silica fume (for example such as defined in the European
standard NF EN 197-1 of February 2001 paragraph 5.2.7 or such as
defined in the “Concrete” standard prEN 13263 :1998 or NF P 18-502),
slags (for example such as defined in the European standard NF EN
197-1 paragraph 5.2.2 or such as defined in the “Concrete” standard
NF P 18-506), burnt shale (for example such as defined in the
European standard NF EN 197-1 of February 2001 paragraph 5.2.5),
materials containing calcium carbonate, for example limestone (for
example such as defined in the European standard NF EN 197-1 of
February 2001 paragraph 5.2.6 or such as defined in the “Concrete”
standard NF P 18-508), siliceous additions (for example such as
defined in the “Concrete” standard NF P 18-509), metakaolins and
mixtures thereof.
The binder may be a hydrocarbon binder, that is to say, a
substance composed of a mixture of hydrocarbons, highly viscous even
solid at room temperature. The hydrocarbon binder may, for example,
be natural bitumen or raw bitumen a derivative of petrol.
The concrete may be a mixture of a hydrocarbon binder and
aggregates, such as for example bituminous concrete, gravel
stabilized with bitumen, asphalt, or bituminous emulsion–based
surface coatings. A concrete with hydrocarbon binder according to
the invention may further comprise usual additives, such as for
example adhesion agents or fibers (for example, glass, cellulose or
asbestos). A concrete with a hydrocarbon binder may further,
comprise recycled materials, such as for example roofing shingles,
glass or cement concrete.
The aggregates comprise gravel, coarse aggregates and/or sand.
The sand corresponds to a granulate having a granulometry which is
strictly lower than 4 mm. The coarse aggregates correspond to
aggregates having a granulometry ranging from 4 to 20 mm. The gravel
corresponds to aggregates having a granulometry which is strictly
higher than 20 mm.
The embodiment examples of the invention are described
hereinafter for a concrete comprising a hydraulic binder.
The device 10 comprises a mixer 11 comprising a container 12 in
which is disposed a concrete 14. By way of example, the mixer 11
corresponds to a mixer truck used for transporting concrete from a
concrete manufacturing site to a concrete usage site. By way of
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alternative, the mixer 11 may be a stationary mixer with a non
vertical rotational axis used for the manufacture of concrete.
Preferably, the axis of the mixer is slanted with respect to
the horizontal direction of an angle lower than or equal to
45°.
The mixer 11 comprises a hydraulic motor 16 which drives
in rotation the container 12 around a non vertical axis Δ by
means of a reducer 18. In the case of a container 12 of a mixer
truck, the axis Δ may be slightly slanted with respect to the
horizontal direction. By way of example, the volume V of the
concrete 14 in the container 12 may vary from 0.5 m3 to 8 m3, in
certain cases, up to 15 m3.
The rotational speed of the container 12 around the axis
Δ may be expressed in radians per second and is thus marked ω
in the rest of the description or is expressed in revolutions
per minute and is thus marked N in the rest of the description.
By way of example, in the case of a mixer truck, the speed of
revolution N may vary from 1 RPM to 20 RPM. By way of example,
for transporting concrete, the speed of revolution of the
container 12 usually varies from 1 RPM to 6 RPM. For an
operation of concrete mixing during the manufacture of the
concrete or before the usage of the concrete on the site of
usage of the concrete, the rotational speed of the container 12
is usually higher than 6 RPM, and may reach 15 RPM.
The actuation of the hydraulic motor 16 may be achieved
by the putting in circulation of a hydraulic fluid by a
hydraulic pump 20 connected to the hydraulic motor 16 by a duct
22 for supplying the hydraulic fluid from the hydraulic pump 20
to the hydraulic motor 16 and by a duct 24 for returning the
hydraulic fluid from the hydraulic motor 16 to the hydraulic
pump 20. The hydraulic pump 20 may be driven in rotation by a
motor 22, for example the motor of the mixer truck.
The device 10 comprises a processing module 26,
comprising, for example, a microcontroller, comprising a memory
(MEM) 27. The processing module 26 is connected to a
man/machine interface 28 (MMI) comprising, for example, a
display screen, a touch screen, a keyboard, etc.
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The device 10 comprises a first hydraulic pressure sensor 30
suitable for measuring the pressure of the hydraulic fluid upstream
of the hydraulic motor 16. The device 10 comprises a second
hydraulic pressure sensor 32 suitable for measuring the pressure of
the hydraulic fluid downstream of the hydraulic motor 16. The
sensors 30 and 32 are connected to the processing module 26. One
alternative may be to use a differential pressure sensor connected
to the inlet and to the outlet of the hydraulic motor 16.
The device 10 may further comprise, a speed sensor 34,
connected to the processing module 26, measuring the rotational
speed of the container 12. It may consist of a passive rotational
speed sensor, in particular, of inductive type, or an active
rotational speed sensor, in particular, of magnetoresistive or of
Hall effect type. The device 10 may comprise a sensor 35 suitable
for measuring the output of the hydraulic fluid circulating in the
ducts 22 and/or 24, preferably in duct 22 in the inlet of the
hydraulic motor 16.
The device 10 comprises a system 36 for adding water, adjuvant
or a mixture of adjuvants in the concrete 14. The adjuvant or the
mixture of adjuvants may be added to the water. The system 36 may
comprise a tank 37 containing the water, the adjuvant or the mixture
of adjuvants. The tank 37 is connected to the container 12 by a duct
38 provided with a valve 40. The valve 40 may be controlled by the
processing module 26. By way of example, it may consist of a
compressed air valve, the actuation of the valve 40 being obtained
by making the compressed air circulate under the control of the
processing module 26. By way of alternative, the system 36 may
comprise a pump, not represented, connected to the tank 37.
The adjuvants may correspond to adjuvants added in a usual
manner in the concretes, in particular a water reducing plasticizer,
a superplasticizer, a retarding agent, a setting agent, a thickening
agent or a viscosity modifying agent.
Advantageously, the device 10 allows determining the final
composition of the concrete, just before the on site usage thereof,
with the different additions (in particular, water, the adjuvant or
the mixture of adjuvants) and possibly the edition of this updated
composition upon reception of the concrete by the client on the site
of usage of the concrete.
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Figure 2 represents, in the form of a block diagram, an
embodiment example according to the invention of a method for
controlling at least one workability parameter of a concrete.
The method comprises two steps 50 and 52. The step 50 is to be
achieved once prior to the anticipated usage of the mixer 11.
The step 52 may be implemented at each usage of the mixer 11.
The step 52 may be repeated several times during the usage of
the mixer 11.
The step 50 comprises the determination of the correction
functions G and T and the step 52 comprises the determination
(and possibly the adjustment) of a workability parameter based
on the correction functions G and T.
The workability parameter may correspond to the slump,
the slump flow, to the threshold stress, to the flow rate or to
the viscosity of a concrete.
The threshold stress of a concrete is the stress beyond
which the concrete starts to flow. When the shear stress τ is
expressed according to the speed gradient γ (or shear rate),
the threshold stress τ0 corresponds to the shear stress for a
speed gradient extrapolated to zero. The apparent viscosity ŋ
of a concrete corresponds to the ratio of the shear stress τ
and the speed gradient γ . It is not always constant for a
concrete but, in certain cases, it may be constant.
Usually, the concrete present in the container 12 may be
considered as a Herschel-Bulkley fluid. The expression of the
shear stress τ according to the speed gradient γ is given by
the following function (1):
τ = τ0 + k . γ p (1)
where k and p are positive real numbers. For certain
types of concrete, in particular the standard concretes, the
concrete may be considered as a Bingham fluid. The expression
(1) is thus simplified in the following manner:
τ = τ0 + ηp . γ (2)
Where np is the plastic viscosity of the concrete.
The correction function G is a function which allows
obtaining the speed gradient γ based on the rotational speed
ω of the container 12 according to the following relationship
(3):
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γ = G(ω).ω (3)
The correction function T is a function which allows
determining the shear stress τ based on the rotary drive torque C of
the container 12 according to the following relationships (4):
τ = T(ω).C (4)
The correction functions G and T are functions which are not
constant and may depend, in particular on the rotational speed ω .
Preferably, the correction functions G and T only depend on the
rotational speed ω .
By way of example, the correction functions G and T may be
expressed in the form of polynomials according to the following
relationships (5) and (6):
Σ=
= ω
M
j 0
G Gj j (5)
Σ=
= ω
M
j 0
T Tj j (6)
where GJ and TJ are real numbers and M is an integer higher than or
equal to 1.
The correction functions G and T depend on features of the
mixer 11 but are independent from formulations of concrete
liable to be disposed in the container 12 of the mixer 11.
The method for determining the correction functions G and
T is based on the following principle: two concretes for which
it is measured the same shear stress τi for a given shear
gradient γ i develop, in the mixer 11, the same drive torque Ci
of the container 12 of the mixer 11 for a given rotational
speed ω i of the container 12.
Figure 3 represents the variation curves A and B of the
drive torque C of the container 12 according to the rotational
speed ω of the container 12 for two concrete of different
formulations and the figure 4 represents the variation curves
D and E of the shear stress τ based on the speed gradient γ
for these two concretes. The curves A and B are determined by
using the mixer 11. The curves D and E are determined by using
a rheometer.
Curves A and B intersect at a point Hi. Curves D and E
intersect at a point Li. At point Hi, the two concretes have,
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in the container 12, the same torque Ci at the rotational
speed ω i. At point Li, the two concretes have the same
shear stress Li at speed gradient γ i. Hence, the two
concretes are in the same rheological state at point Li
and at point Hi, i.e. they develop the same stress τi for
the speed gradient γ i.
According to an embodiment example according to the
invention, the method for determining expressions of the
correction functions G and T according to the rotational
speed ω consists in determining the variation curves of
the drive torque C according to the rotational speed ω
and the variation curves of the shear stress τ according
to the speed gradient γ for several concretes in such a
manner as to obtain several intersecting points Hi and Li.
Figure 5 represents, by way of example, several
variation curves F of the shear stress τ according to the
speed gradient γ for six concretes of different
formulations. These curves intersect at points of
intersection L1 to L7.
According to a first example of method for
determining expressions of correction functions G and T,
for each point of intersection Hi between two variation
curves of the drive torque C according to the rotational
speed ω of a pair of concretes and for the point of
intersection Li between the variation curves of the shear
stress τ according to the speed gradient γ for the same
pair of concretes, it is determined the value GiCC of the
correction function G and the value TiCC of the correction
function T according to the following relationships (7)
and (8):
i
CC i
Gi ω
γ
= 
(7)
Ci
CC i
Ti
τ
= (8)
The determination of the drive torque is made
explicit in further detail hereinafter.
The correction functions G and T may be sought, by
way of example, in the form of the aforementioned
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expressions (5) and (6) by determining parameters Gj and Tj for
which the curves of the correction functions G and T pass by
values GiCC and TiCC or get as close as possible to these vales
according to interpolation or approximation methods. Once they
are determined, the correction functions G and T are stored in
the processing module 26 memory 27.
According to a second example of the method for
determining the correction functions G and T, the correction
functions G and T are determined based on values GiAlt and TiALT
at the points of intersection of index i. The value GiALT of
the correction function G and the value TiALT of the
relationship T at the points of intersection of index i are
obtained by the following relationships (9) and (10):
V . i . i
Alt Ci
Gi η ω
= (9)
Alt . V
Gi
Alt 1
Ti = (10)
where V is the volume of the concrete 14 in the container
12 and ŋi is the apparent viscosity of the concrete at the
junction point Li.
The correction functions G and T may thus be sought, by
way of example, in the form of the aforementioned expressions
(5) and (6) by determining the parameters Gj and Tj for which
the curves of the correction functions G and T pass by values
GiALT and TiALT or come as close as possible to these values
according to the methods of interpolation or approximation.
The second example of the method for determining the
correction functions T and G has the advantage of being less
sensitive to measurement uncertainties than the first example.
Figures 6 and 7 represent two examples of variation curves
CG and CT respectively correction functions G and T.
Figure 8 represents, in the form of a block diagram, a
more detailed embodiment example according to the invention of
step 52 of the method, illustrated on figure 2.
At step 100, the mixer 11 is controlled at a first
operating regime. The processing module 26 determines a first
value ΔP1 from the difference in pressure ΔP of the hydraulic
fluid between the upstream and the downstream of the hydraulic
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18
motor 16 and a first value ω 1 of the rotational speed ω
of the container 12. The difference in pressure ΔP of the
hydraulic fluid between the upstream and downstream of the
hydraulic motor 16 may be measured by the pressure sensors
30 and 32. The rotational speed ω of the container 12 may
be determined directly by the sensor 34 or indirectly
based on the measurement of the flow of hydraulic liquid
crossing the hydraulic motor 16. The method continues in
step 102.
At step 102, the mixer 11 is controlled at a second
operating regime, different from the first operating
regime. This means that the rotational speed of the
container 12 at the first operating regime 12 is different
from the rotational speed of the container 12 at the
second operating regime. The processing module 26 thus
determines a second value ΔP2 from the difference in
pressure ΔP of the hydraulic fluid between the upstream
and the downstream of the hydraulic motor 16 and a second
value ω 2 of the rotational speed ω . The steps 100 and
102 may be repeated several times for other operating
regimes of the mixer 11. Preferably, the mixer 11 may,
further, be controlled at a third operating regime,
different from the first and second operating regimes. The
processing module 26 thus determines a third value ΔP3
from the difference in pressure ΔP of the hydraulic fluid
between the upstream and the downstream of the hydraulic
motor 16 and a third value ω 3 of the rotational speed ω.
The method then continues at step 104.
Steps 100 and 102 may be implemented automatically or
by a voluntary action of the driver of the mixer truck.
They can be implemented during the transport of the
concrete and/or preferably when the mixer truck is at a
standstill.
At step 104, the processing module 26 determines
values C1 and C2 of the torque C driving the container 12
respectively based on values ΔP1 and ΔP2 from the
difference in pressure ΔP as will be described in further
detail herebelow. The method continues at step 105.
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19
At step 105, the processing module 26 determines a first
value τ1 of the shear stress τ and a first value γ 1 of the
speed gradient (or the shear rate) γ of the concrete at the
first operating regime based on values ΔP1 and ω 1 according to
the following relationships (11) and (12):
γ 1 = G(ω1) .ω1 (11)
τ1 = T(ω1) .C1 (12)
Where G(ω 1) is the value of the correction function G at
the rotational speed ω 1 and T(ω 1) is the value of the
correction function T at the rotational speed ω 1.
The processing module 26 further determines, a second
value τ2 of the shear stress τ and a second value γ 2 of the
speed gradient (or shear rate) γ of the concrete at the second
operating regime based on values ΔP2 and ω 2 according to the
following relationships (13) and (14):
γ 2 = G(ω2) .ω2 (13)
τ2 = T(ω2) .C2 (14)
where G(ω 2) is the value of the correction function G at
the rotational speed ω 2 and T(ω 2) is the value of the
correction function T at the rotational speed ω 2.
Preferably, the processing module 26 may further,
determine a third value τ3 of the shear stress τ and a third
value γ 3 of the speed gradient (or shear rate) γ of the
concrete at the third operating regime based on values ΔP3 and
ω 3 according to the following relationships (15) and (16):
γ 3 = G(ω3) .ω3 (15)
τ3 = T(ω3) .C3 (16)
where G(ω 3) is the value of the correction function G at
the rotational speed ω 3 and T(ω 3) is the value of the
correction function T at the rotational speed ω 3.
According to an alternative, the processing module 26 may
further, determine other additional values of the shear stress
τ and the shear gradient γ , in addition to the first, second
and third aforementioned values.
The method continues at step 106.
At step 106, the processing module 26 determines the
expression of the shear stress τ according to the speed
gradient γ based on the pairs of values (τ1, γ 1) and (τ2, γ 2)
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20
(and, preferably, in addition, the pair of values (τ3, γ
3). At step 106, the processing module 26 may seek the
expression τ in the form of expressions (1) or (2) by
determining the parameters τ0, k and p (or ŋp) for which
the variation curve of the shear stress τ according to the
speed gradient γ passes by the points (τ1, γ 1) and (τ2,
γ 2) (and, preferably, in addition to the point (τ3, γ 3))
or gets as close as possible to these values according to
methods of interpolation or approximation. The method
continues at step 108.
At step 108, the processing module 26 determines the
workability parameter or the required workability
parameters based on the previous expression. The threshold
stress τ0 may be determined directly based on the
relationship (1) or (2). The slump or slump flow of the
concrete may be determined based on the threshold stress
τ0. By way of example, the slump or slump flow may be
obtained according to the following relationships (17) and
(18):
τ0 = E0 + E1 ⋅ Slumpα (17)
ρ E2 E3 Slumpα
τ0 = + ⋅ (18)
where E0, E1, E2, E3, and α are real numbers
determined beforehand and which are independent from the
mixer 11 and the formulation of the concrete and where ρ
is the density of the concrete. The apparent viscosity ŋ
of the concrete corresponds to the ratio of the shear
stress τ and the speed gradient γ . The processing module
26 may further, control the interface 28 in order to
display the measured workability parameter or workability
parameters. Furthermore, the measured workability
parameter or workability parameters and the measuring
instant may be memorized. The method continues at step
110.
At step 110, the processing module 26 may control the
addition in the concrete of water or adjuvants for
modifying the measured workability parameter or
workability parameters. The step 110 may not be present.
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21
In the embodiment example of the method according to the
invention described in relation to figure 8, at steps 100 and
102, the pressures are determined based on pressure sensors 30
and 32.
Figure 9 represents an example of variation curve I of the
signal provided by the sensor 30 for several rotations of the
container 12. The curve J represents the variation of the
signal provided by the sensor 30 after a low-pass filtering
operation. The curve J may comprise oscillations during a
revolution of the container 12 which may be in particular due
to balancing defects of the container 12, to the nature of the
concrete, etc. The frequency of the oscillations substantially
corresponds to the frequency of rotation of the container 12.
At aforementioned steps 100 and 102, the measured pressure
corresponds to an average pressure. It is advantageous, in
order to determine average pressure, to take into
consideration at least a complete revolution of the container
12. This is why the frame number of successive samples used
for determining the average pressure varies according to the
rotational speed ω of the container 12. The frame number of
samples depends on the number of oscillations Nbosci of the
curve during a revolution of the container 12, on the
rotational speed N of the container 12 and the frequency f of
acquisition of the pressure samples according to the following
relationship (19):
N
Frame Nbosc f = 60 . (19)
The samples are considered as stable when, for each
measured sample from among the Frame number of samples, the
rotational speed N of the container 12 hardly varies with
respect to an average rotational speed for the Frame number of
samples, for example varies by less than 1 revolution per
minute with respect to the average rotational speed for the
Frame number of samples. The average pressure is only measured
when the samples are stable.
The signal provided by the sensor 30 is marked Pe and the
signal output from the hydraulic motor 16 obtained based on
the sensor 32 is marked Ps. The differential pressure ΔP is
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22
equal to the difference between the input Pe and output Ps
pressures. The average value of the differential pressure
is obtained by calculating the average of the values of
the differential pressure ΔP of the set of samples from
the Frame number of samples.
The relationship between the differential pressure ΔP
and the drive torque C is obtained in the following
manner. The mechanical power PM used for the rotation of
the revolving drum is given by the following relationship
(20):
PM = C . ω (20)
When the hydraulic motor 16 operates in a linear
operating range, the mechanical power Phv of the hydraulic
motor 16 is given by the following relationship (21):
Phy = ΔP . Q (21)
where Q is the output of hydraulic fluid, expressed
in m3/s, driving the hydraulic motor 16. The output Q is
given by the following relationship (22):
Q = Cy . nm (22)
Where nm is the rotational speed of the hydraulic
motor 16 expressed in revolutions per second and Cy is the
cubic inch displacement of the hydraulic motor 16. The
cubic inch displacement Cy, expressed in m3/R, corresponds
to the volume of hydraulic fluid which transits in the
hydraulic motor 16 during a revolution of the hydraulic
motor 16.
Considering that the mechanical power PM is equal to
the product of the hydraulic power Phy and an efficiency
factor R and that the rotational speed nm of the hydraulic
motor 16 is equal to the product of the rotational speed
ω of the container 12 and a reduction factor Kr, the
following relationship (23) is obtained:
C = R . ΔP . Cy . Kr
(23)
The drive torque C may be determined by replacing in
the expression (23) the difference in pressure ΔP by the
23
23
input pressure Pe. However, the inventors have emphasized that
the precision of the determination of the drive torque C is
increased by using the difference in pressure ΔP rather than
only the input pressure Pe.
The drive torque C which is sought to be measured must
represent as much as possible the behavior of the concrete and
not other parameters such as for example the friction between
the container 12 and the container 12 supporting system or the
no load operation container 12 mass.
It may be hence advantageous to measure the variation
curve of the input pressure Pe0 and the variation curve of the
outlet pressure Ps0 according to the rotational speed ω of the
container 12 in the absence of the concrete in the container
12 and to subtract the value Pe0 from the rotational speed of
the measurement of the measured pressure Pe and the value Ps0
from the rotational speed of the measurement of the measured
pressure Ps during the determination of ΔP.
By naming ΔP0 the difference of no load operation
pressure, i.e. the difference between Pe0 and Ps0, the following
relationship (24) may thus be used instead of the previous
relationship (23):
C = R . (ΔP - ΔP0) . Cy . Kr (24)
The inventors have, further, emphasized that the precision
of the determination of the drive torque C is increased by
using the corrected differential pressure ΔP - ΔP0 rather than
the differential pressure ΔP alone.
The rotational speed ω of the container 12 may be
determined directly based on the rotational speed sensor 34 or
may be determined indirectly based on the output of the oil Q
measured by the sensor 35 according to the following
relationship (25):
Kr .Cy
ω = Q (25)
Figure 10 represents, in the form of a block diagram, an
embodiment example of the step 110 of the method illustrated
on figure 8 in the case where, at step 108, the method
provides a slump value and in the case where the slump is
adjusted by adding water to the concrete. This method of
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24
adjustment may also be employed for controlling the slump
flow, the flow rate, the viscosity, or the threshold
stress.
At step 200, the processing module 26 determines the
last slump value Sk. The last slump value Sk may
correspond, for example, to the average of the latest
slump values, for example the 5 last slump values,
obtained at step 108. The method continues at step 202.
At step 202, the processing module 26 determines the
difference Δs between a comparison slump value Se and the
last slump value Sk. If the difference Δs is higher than a
threshold TH, the method continues at step 204. If the
difference Δs is lower than the threshold TH, the method
returns to step 200. The threshold TH translates the
accepted slump variation. Typically for a standard
concrete, the threshold TH may be of the order of 30 mm.
At step 204, the processing module 26 determines the
quantity of water (Addition) to be added. The Addition
quantity may be determined by the following relationship
(26):
Addition = Txwater . V . ΔS . Ks (26)
where Txwater corresponds to the quantity of water to
be added by cubic meter of concrete and by millimeter of
slump variation, Ks is a safety coefficient and V is the
volume of concrete. The quantity of water Txwater ranges,
for example, between 0.1 L/m3/mm and 3 L/m3/mm and the
safety coefficient Ks ranges for example between 0 and 1.
The method continues at step 206.
At step 206, the processing module 26 determines the
total quantity of water added (Watertot) to the concrete
from the placing of the concrete in the container 12. The
total quantity of added water Watertot corresponds to the
sum of the successive additions already achieved since the
placing of the concrete in the container 12, the water
addition (Addition) calculated at the previous step and
not yet achieved, and of the quantity of water initially
introduced in the concrete before loading into the
container. The total quantity of water (Watertot) is
25
25
compared with a maximum quantity of water (Max) able to enter
into the composition of said concrete. If the quantity of
water Watertot is strictly higher than Max, the method continues
at step 208. If the quantity of water Watertot is lower than or
equal to Max, the method continues at step 212.
At step 208, the processing module 26 sends an alarm, for
example to the driver of the mixer truck, by means of the
interface 28.
At step 212, the processing module 26 determines if the
addition of the quantity of water (Addition) must be achieved
automatically. If the quantity of water (Addition) must be
added automatically, the method continues at step 214. If the
quantity of water (Addition) must not be added automatically,
the method continues at step 216.
At step 216, the processing module 26 waits for a manual
validation to be achieved, for example, by the driver of the
mixer truck, by means of the interface 28. When the manual
validation is achieved, the method continues at step 214. If,
at step 216, the manual validation is not achieved, the method
returns to step 200.
At step 214, the quantity of water (Addition) is added
into the container 12. This may be achieved by controlling the
valve 40 by the processing module 26. The method continues at
step 218.
At step 218, the method waits during a determined period,
for example 5 minutes, for the added water to be appropriately
mixed with the concrete, before returning to step 200.
The method may further, comprise the display on the
display screen 28 of information pertaining to the concrete,
the printing out of these information on a support or the
storage of these information to a memory. These information
may comprise the workability parameter determined at step 200,
the quantity of water and/or adjuvant added to the concrete at
step 214 or the formulation of the modified concrete after
addition of the water and/or the adjuvant.
The control method according to the invention implemented
by the processing module 26 may be achieved by material
process, i.e. by a dedicated electronic circuit. By way of
26
26
alternative, the control method according to the invention
may be at least partially implemented by executing by the
module 26 for processing instructions from a computer
programme for example stored in the memory 27.
The control method according to the invention
advantageously allows determining a workability parameter
when the concrete is in the mixer with a non vertical
rotational axis. It further, allows obtaining a
measurement of the workability parameter which is more
representative of the state of the concrete than the
measurement which would be obtained based on a test
implementing a sampling of a low volume of concrete with
respect to the total volume contained in the mixer with a
non vertical rotational axis.
Particular embodiment examples of the present
invention have been described. Various alternatives and
modifications will become apparent to the one skilled in
the art. Particularly, even though the present invention
has been described in the case where the motor torque is
determined based on measurements of hydraulic pressure, it
is clear that the present invention may be implemented in
the case where the motor torque is measured directly by a
torque sensor, comprising for example strain gauges.
Furthermore, although the present invention has been
described in the case of a mixer with a non vertical
rotational axis of which the container is driven in
rotation by a hydraulic motor, it may be implemented in
the case where the container is driven in rotation by a
thermal motor or by an electric motor by means of a speed
reduction mechanical system. The motor torque may thus be
measured by any suitable means. Particularly, when the
container is driven in rotation by an electric motor, the
motor torque may be determined based on a measurement of
the supply current of the electric motor.
27
27
CLAIMS
1.A method for controlling at least one workability
parameter of a concrete (14) contained in the container (12)
of a mixer (11) with a non vertical rotational axis,
comprising the following steps:
making the container turn at at least two different
rotational speeds;
determining, for each of said at least two rotational
speeds ω , a rotary drive torque C of the container, a value of
shear stress τ of the concrete and a value of speed gradient γ
of the concrete according to the following relationships:
τ = T(ω).C
γ = G(ω).ω
where T and G are predetermined functions;
determining a relationship of variation of the shear
stress τ according to the speed gradient γ by extrapolation
and/or approximation based on the determined values; and
providing an indication of the workability parameter of
the concrete based on the relationship of variation.
2. The method according to claim 1, comprising the
following steps:
making the container (12) turn at a first rotational speed
and determining a first rotary drive torque of the container
at the first rotational speed;
making the container turn at a second rotational speed and
determining a second rotary drive torque of the container at
the second rotational speed;
determining a first shear stress equal to the product of
the first torque and to the value of the function T at the
first rotational speed;
determining a first speed gradient equal to the product of
the first rotational speed and to the value of the function G
at the first rotational speed;
determining a second shear stress equal to the product of
the second torque and to the value of the function T at the
second rotational speed;
We Claim:
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28
determining a second speed gradient equal to the
product of the second rotational speed and to the value of
the function G at the second rotational speed; and
determining the relationship of variation of the
shear stress according to the speed gradient by
extrapolation and/or approximation based on the first and
second shear stresses and the first and second speed
gradients.
3. The method according to claim 2, comprising the
following steps:
making the container (12) turn at a third rotational
speed and determining a third rotary drive torque of the
container at the third rotational speed;
determining a third shear stress equal to the product
of the third torque and to the value of the function T at
the third rotational speed;
determining a third speed gradient equal to the
product of the third rotational speed and to the value of
the function G at the third rotational speed; and
determining the relationship of variation of the
shear stress according to the speed gradient by
extrapolation and/or approximation in addition based on
the third shear stress and the third speed gradient.
4. The method according to any one of claims 1 to 3,
in which the workability parameter of the concrete is
selected from among the slump, the slump flow, the
threshold stress, the viscosity and the flow rate.
5. The method according to any one of claims 1 to 4,
comprising the determination of the threshold stress of
the concrete based on the relationship of variation and
the determination of the slump and/or slump flow based on
the threshold stress.
6. The method according to any one of claims 1 to 5,
comprising the adjustment in the container of the
workability parameter of the concrete by introducing a
compound into the container (12).
29
29
7. The method according to claim 6, in which the compound
comprises water, an adjuvant or a mixture thereof.
8. The method according to any one of claims 1 to 7, in
which providing the indication of the workability parameter of
the concrete includes the display on a display screen (28) of
the workability parameter, the printing out of the workability
parameter onto a support and/or the storage of a datum
representing the workability parameter to a memory.
9. The method according to any one of claims 1 to 8, in
which the container (12) is driven in rotation by a hydraulic
motor (16) comprising an inlet for receiving a hydraulic fluid
and an outlet for pushing back the hydraulic fluid, the torque
being determined based on a first difference of pressures
equal to the difference between the hydraulic pressure
measured at the inlet of the hydraulic motor and the hydraulic
pressure measured at the outlet of the hydraulic motor.
10. The method according to claim 9, in which the first
difference of pressures is decreased by a second difference of
pressures equal to the difference between the hydraulic
pressure at the inlet of the hydraulic motor (16) and the
hydraulic pressure at the outlet of the hydraulic pressure in
the absence of concrete in the container (12) at the
measurement rotational speed.
11. The method according to claim 9 or 10, in which the
hydraulic pressure measured at the inlet or at the outlet of
the hydraulic motor (16) is equal to the average of a number
of sampled pressure values, said number being inversely
proportional to the rotational speed of the container (12).
12. The method according to claim 11, in which during the
sampling of the pressure values used for obtaining the
hydraulic pressure measured at the inlet or at the outlet of
the hydraulic motor (16), the variations of the rotational
speed of the container (12) are lower than a threshold.
13. The method according to any one of claims 1 to 12, in
which the functions G and T are obtained by determining:
for each concrete of a plurality of different concretes, a
variation curve of the drive torque of the container (12)
30
30
containing said concrete according to the rotational speed
of the container;
for each concrete of a plurality of different
concretes, a variation curve of the shear stress of the
concrete according to the speed gradient of the concrete
by means of a rheometer; and
for each pair of concretes of the plurality of
different concretes, a first point of intersection (Hi)
between the variation curves of the drive torque of the
container according to the rotational speed of the
container for the concretes of the pair and a second point
of intersection (Li) between the variation curves of the
shear stress according to the speed gradient for the
concretes of the pair.
14. The method according to claim 13, in which for
the first point of intersection (Hi) and the second point
of intersection (Li) of each pair of concretes of the
plurality of different concretes, it is determined the
value GiCC of the function G and the value TiCC of the
function T according to the following relationships:
i
CC i
i ω
G γ =
i
iCC Ci
T = τ
where γ i is the speed gradient at the second point of
intersection, τi is the shear stress of the concrete at
the second point of intersection, Ci is the drive torque
at the first point of intersection and ω i is the
rotational speed at the first point of intersection.
15. The method according to claim 13, in which for
the first point of intersection (Hi) and the second point
of intersection (Li) of each pair of concretes of the
plurality of different concretes, it is determined a value
GiAlt of the function G and a value TiAlt of the function T
according to the following relationships:
i i
iAlt V . ηi .ω
G = C
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31
G . V
T = iAl1t
iAlt
where V is the volume of concrete (14) in the container
(12), ŋi is the apparent viscosity of the concrete equal to the
ratio of the shear stress of the concrete at the second point
of intersection (Li) and the speed gradient at the second point
of intersection, Ci is the drive torque at the first point of
intersection (Hi) and ω i is the rotational speed at the first
point of intersection.
16. A memory device on which is stored a computer
programme for implementing the method according to any one of
claims 1 to 15.
17. A device (10) for controlling at least one workability
parameter of a concrete, comprising:
a mixer with a non vertical rotational axis (11)
comprising a container (12) containing the concrete (14);
a system (16, 18) for driving in rotation the container
suited for making the container turn at at least two different
rotational speeds;
a first sensor (30, 32) for measuring a datum representing
the rotary drive torque of the container;
a second sensor (34, 35) for measuring a datum
representing the rotational speed of the container; and
a processing module (26) connected to the drive system and
to the first and second sensors and configured to
determine, for each of said at least two rotational speeds
ω , a rotary drive torque C of the container, a value of shear
stress τ of the concrete and a speed gradient value γ of the
concrete according to the following relationships:
τ = T(ω).C
γ = G(ω).ω
where T and G are predetermined functions;
determine, a relationship of variation of the shear stress
τ according to the speed gradient γ by extrapolation and/or
approximation based on the predetermined values; and
provide an indication of the workability parameter of the
concrete based on the relationship of variation.