Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N9/00—Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity
  • G01N9/10—Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity by observing bodies wholly or partially immersed in fluid materials
  • G01N9/12—Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity by observing bodies wholly or partially immersed in fluid materials by observing the depth of immersion of the bodies, e.g. hydrometers
  • G01N9/16—Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity by observing bodies wholly or partially immersed in fluid materials by observing the depth of immersion of the bodies, e.g. hydrometers the body being pivoted
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B28—WORKING CEMENT, CLAY, OR STONE
  • B28C—PREPARING CLAY; PRODUCING MIXTURES CONTAINING CLAY OR CEMENTITIOUS MATERIAL, e.g. PLASTER
  • B28C5/00—Apparatus or methods for producing mixtures of cement with other substances, e.g. slurries, mortars, porous or fibrous compositions
  • B28C5/42—Apparatus specially adapted for being mounted on vehicles with provision for mixing during transport
  • B28C5/4203—Details; Accessories
  • B28C5/4206—Control apparatus; Drive systems, e.g. coupled to the vehicle drive-system
  • B28C5/422—Controlling or measuring devices
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B28—WORKING CEMENT, CLAY, OR STONE
  • B28C—PREPARING CLAY; PRODUCING MIXTURES CONTAINING CLAY OR CEMENTITIOUS MATERIAL, e.g. PLASTER
  • B28C7/00—Controlling the operation of apparatus for producing mixtures of clay or cement with other substances; Supplying or proportioning the ingredients for mixing clay or cement with other substances; Discharging the mixture
  • B28C7/02—Controlling the operation of the mixing
  • B28C7/022—Controlling the operation of the mixing by measuring the consistency or composition of the mixture, e.g. with supply of a missing component
  • B28C7/024—Controlling the operation of the mixing by measuring the consistency or composition of the mixture, e.g. with supply of a missing component by measuring properties of the mixture, e.g. moisture, electrical resistivity, density
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N9/00—Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity
  • G01N9/26—Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity by measuring pressure differences
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N11/00—Investigating flow properties of materials, e.g. viscosity, plasticity; Analysing materials by determining flow properties
  • G01N11/10—Investigating flow properties of materials, e.g. viscosity, plasticity; Analysing materials by determining flow properties by moving a body within the material
  • G01N11/14—Investigating flow properties of materials, e.g. viscosity, plasticity; Analysing materials by determining flow properties by moving a body within the material by using rotary bodies, e.g. vane
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N11/00—Investigating flow properties of materials, e.g. viscosity, plasticity; Analysing materials by determining flow properties
  • G01N2011/0046—In situ measurement during mixing process
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/38—Concrete; Lime; Mortar; Gypsum; Bricks; Ceramics; Glass
  • G01N33/383—Concrete or cement
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N9/00—Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity
  • G01N9/32—Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity by using flow properties of fluids, e.g. flow through tubes or apertures
  • G01N9/34—Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity by using flow properties of fluids, e.g. flow through tubes or apertures by using elements moving through the fluid, e.g. vane

Definitions

• the improvements generally relate to the field of concrete production, and more particularly refers to measuring density of fresh concrete inside a drum of a mixer truck.
• Density is usually calculated by dividing a known volume of material by its weight. For a given composition, the measured or calculated density of fresh concrete can be compared to the theoretical density without considering the presence of air to calculate the theoretical air content. The measure of density usually requires the use of a container known volume that is filled with the fresh concrete and the weight of the concrete is determined by discounting the weight of the container.
• International patent publication no. WO 2014/138968 describes a technique for estimating density of fresh concrete inside a drum of a mixer truck. In this technique, the density of the fresh concrete is determined from force pressures using a pressure/force measurement probe.
• pressure or force values indicative of the corresponding pressure or force exerted on the probe and the associated probe angle are recorded for a plurality of circumferential positions of the probe along its movement path in the fresh concrete.
• a valid data set is extracted from the recorded data so as to calculate a linear relationship which is best fitted to the valid data set.
• This best-fit linear relationship curve is proportional to the concrete density in accordance with a coefficient which is a trigonometric factor of the fluid and the geometrical and mechanical features of the pressure sensor. Henceforth, the proportionality coefficient can be calibrated against measurements of slope for known density.
• the drum of the mixer truck can rotate about a rotation axis which is at least partially horizontally-oriented relative to the vertical.
• the probe is mounted inside the drum so as to extend in a radial orientation of the drum. Accordingly, upon rotation of the drum, the probe is moved circumferentially as the drum rotates.
• a normal pressure is imparted on the probe including normal contributions of buoyancy due to a volume of the probe and of resistance due to the movement of the probe in the fresh concrete.
• a density of the fresh concrete can be determined based on a first pressure value indicative of a normal pressure exerted on the probe at a first circumferential position of the drum and on a second pressure value indicative of a normal pressure exerted on the probe at a second circumferential position different from the first circumferential position. More importantly, it was found that the density value can be determined based on the volume of the probe and on a difference between the first pressure value and the second pressure value. In some embodiments, the difference is compensated by a trigonometric factor corresponding to a difference between the sinus of the first circumferential position and the sinus of the second circumferential position. In further embodiments, the first and second circumferential positions are preferably chosen so as to be circumferentially away from the bottom of the drum to avoid potential discrepancies in the measured pressure values when the probe is in the vicinity of the bottom of the drum.
• a method for determining density of fresh concrete inside a drum of a mixer truck using a probe the drum having a rotation axis being at least partially horizontally-oriented, the probe being mounted inside the drum, extending in a radial orientation of the drum and being moved circumferentially as the drum rotates, and onto which a normal pressure is imparted by buoyancy due to a volume of the probe when the probe is submerged in the fresh concrete and by resistance due to the movement of the probe in the fresh concrete by the rotation of the drum, the method comprising: receiving a first pressure value indicative of a normal pressure exerted on the probe by the fresh concrete at a first circumferential position of the drum during rotation of the drum; receiving a second pressure value indicative of a normal pressure exerted on the probe by the fresh concrete at a second circumferential position during rotation of the drum, the first circumferential position being different from the second circumferential position; and determining a density value of the fresh concrete based on the volume of
• the difference can be compensated by a trigonometric factor corresponding to a difference between the sinus of the first circumferential position and the sinus of the second circumferential position.
• the first and second circumferential positions are preferably chosen so as to be circumferentially away from the bottom of the drum.
• a system for determining density of fresh concrete inside a drum of a mixer truck the drum having a rotation axis being at least partially horizontally-oriented
• the system comprising: a probe mounted inside the drum, extending in a radial orientation of the drum and being moved circumferentially as the drum rotates, and onto which a normal pressure is imparted by buoyancy due to a volume of the probe when the probe is submerged in the fresh concrete and by resistance due to the movement of the probe in the fresh concrete by the rotation of the drum; a computing device communicatively coupled with the probe, the computing device being configured for performing the steps of: receiving a first pressure value indicative of a normal pressure exerted on the probe by the fresh concrete at a first circumferential position of the drum during rotation of the drum; receiving a second pressure value indicative of a normal pressure exerted on the probe by the fresh concrete at a second circumferential position during rotation of the drum, the first circumferential position being different from the second circumfer
• the difference is compensated by a trigonometric factor corresponding to a difference between the sinus of the first circumferential position and the sinus of the second circumferential position, In further embodiments, none of the first and second circumferential positions correspond to the bottom of the drum.
• a method for determining density of fresh concrete inside a drum of a mixer truck using a probe the drum having a rotation axis being at least partially horizontally-oriented, the probe being mounted inside the drum, extending in a radial orientation of the drum and being moved circumferentially as the drum rotates, and onto which a normal pressure is imparted by buoyancy due to a volume of the probe when the probe is submerged in the fresh concrete and by resistance due to the movement of the probe in the fresh concrete by the rotation of the drum, the method comprising: receiving a first pressure value indicative of a normal pressure exerted on the probe by the fresh concrete at a first circumferential position of the drum during rotation of the drum; receiving a second pressure value indicative of a normal pressure exerted on the probe by the fresh concrete at a second circumferential position during rotation of the drum, the first circumferential position being different from the second circumferential position; and determining a density value of the fresh concrete based on the volume of
• FIG. 1 is a side elevation view of an example of a system for determining the density of fresh concrete inside a drum of a mixer truck, in accordance with an embodiment
• FIG. 2 is a sectional view taken along line 2-2 of Fig. 1 ;
• FIG. 3 is an example of a graph showing a normal contribution of gravity measured by the probe during a rotation of a drum
• Fig. 4 is an example of a graph showing, for two different rotation speeds of a drum, normal contributions of buoyancy measured by the probe when submerged into water during a rotation of a drum at a corresponding one of the two rotation speeds of the drum, after mathematically discounting the normal contribution of gravity
• Fig. 5 is an example of a graph showing, for two different rotation speeds of a drum, normal contributions of resistance exerted on the probe by the movement of the probe into the fresh concrete during a rotation of a drum at a corresponding one of the two rotation speeds of the drum;
• Fig. 6 is an example of a graph showing, for two different rotation speeds of a drum, normal contributions of buoyancy and resistance measured during a rotation of a drum at a corresponding one of the two rotation speeds of the drum;
• Fig. 7 is an example of a graph showing, for two different rotation speeds of a drum, experimental normal contributions of buoyancy and resistance measured during a rotation of a drum at a corresponding one of the two rotation speeds of the drum, with discrepancies for pressure values measured in the vicinity of the bottom of the drum;
• FIG. 8 is a sectional view of a drum of a mixer truck, showing exemplary circumferential ranges, in accordance with an embodiment
• Fig. 9 is an example of a graph showing, for two different rotation speeds of a drum, experimental normal contributions of buoyancy and resistance measured during a rotation of a drum at a corresponding one of the two rotation speeds of the drum, with discrepancies for pressure values measured in the vicinity of the bottom of the drum and average pressure values for some of the circumferential ranges of Fig. 8; and
• Fig. 10 is an example of a graph showing average pressure values as a function of the rotation speed of the drum, in accordance with an embodiment.
• Fig. 1 shows an example of a system 10 for determining density of fresh concrete 12 inside a drum 14 of a mixer truck 16.
• the drum 14 has a rotation axis 18 which is at least partially horizontally-oriented relative to the vertical 20.
• the system 10 has a probe 22 which is mounted inside the drum 14 and extends in a radial orientation 24 of the drum 14.
• the probe 22 is configured to measure pressure values as the probe 22 is moved circumferentially in the fresh concrete 12 by the rotation of the drum 14 about the rotation axis 18. As the probe 22 is so moved, it reaches a plurality of circumferential positions, which are associated to corresponding ones of the pressure values measured by the probe 22.
• a potential example of the probe 22 is described in international patent publication no. WO 201 1/042880.
• the system has a computing device 26 which is communicatively coupled with the probe 22 so that the computing device 26 can receive the pressure values measured by the probe 22 and the corresponding circumferential positions ⁇ .
• the communication between the computing device 26 and the probe 22 can be provided by a wireless connection, a wired connection, or a combination thereof.
• a density value D of the fresh concrete 12 can be determined by the computing device 26 based on at least two received pressure values and their corresponding circumferential positions ⁇ and on at least one parameter which can depend on a volume of the probe 22, as will be described herebelow.
• the system 10 has a user interface 28 which is communicatively coupled with the computing device 26 and configured to display the density value D of the fresh concrete 12 once determined.
• the density value D can be displayed in real time on the user interface 28 or be stored on a memory of the computing device 26 for display at a later time or on another user interface.
• the probe 22 extends in a radial orientation 20 of the drum and reaches a plurality of circumferential positions ⁇ as the drum 14 rotates about the rotation axis 18. More specifically, in this illustrated example, the probe 22 is at a circumferential position ⁇ of 0° when the probe 22 is at the top of the drum 14, the probe 22 is at a circumferential position of 90° when the probe 22 is at the right of the drum 14, the probe 22 is at a circumferential position of 180° when the probe 22 is at the bottom of the drum 14, and the probe 22 is at a circumferential position of 270° when the probe 22 is at the left of the drum 14.
• Such definition of the circumferential positions ⁇ is exemplary only as the circumferential positions ⁇ could have been defined otherwise depending on the embodiment.
• the probe 22 measures a pressure value and transmits the pressure value and the corresponding circumferential position ⁇ to the computing device 26.
• the pressure values that are measured are oriented in a normal orientation with respect to the probe 22.
• Such pressure values can be referred to as "normal pressure values" and can include a normal contribution Pn,g imparted on the probe 22 by gravity due to a weight of the probe 22, a normal contribution Pn,b imparted on the probe 22 by buoyancy due to a volume of the probe 22 when the probe 22 is submerged in the fresh concrete 12 and a normal contribution Pn,r imparted on the probe 22 by resistance due to the movement of the probe 22 in the fresh concrete 12 by the rotation of the drum 14.
• Fig. 2 shows normal contributions Pn,g, Pn,b, Pn,r by way of force vectors acting on the probe 22 when positioned at different circumferential positions.
• Fig. 3 shows an example relationship between the normal contribution Pn,g of the gravity exerted on the probe as a function of the circumferential position ⁇ of the probe 22 in the drum 14.
• the normal contribution Pn,g(9) of the gravity exerted on the probe 22 during a drum rotation varies as:
• K mg is a constant which depends on the weight of the probe, i.e. on the mass m of the probe and on the gravitational acceleration g of earth
• ⁇ is the circumferential position of the probe. Because of the change in orientation and sign convention, the pressure value measured by the probe is negative at the circumferential position 90° and positive in the opposite circumferential position of 270°.
• the constant K mg and the corresponding normal contribution Pn,g(9) of the gravity of a given probe 22 in a given drum 14 can be obtained by measuring the pressure values Pn,g as the drum 14 rotates over the circumferential positions ⁇ when the drum 14 is empty (e.g., filled with air). Such data can be recorded and stored for later use as calibration data for the given probe 22 and the given drum 14.
• the normal contribution Pn,g(9) of gravity can be subtracted from raw pressure measurements of the probe to obtain "weight compensated" (WC) pressure values Pn.wc
• the probe 22 can measure pressure values of 0 with a given precision when the probe 22 in an empty drum.
• the probe 22 can wear with time and its weight and surface can be reduced, it is possible to adjust the weight compensation to account for the wear of the probe 22 over time.
• the probe 22 is configured to compensate its own weight when moved circumferentially as the drum 14 rotates. Accordingly, when the drum 14 is empty, the pressure values measured by such a probe are constant over the plurality of circumferential positions ⁇ . In these embodiments, the relationship between the normal contribution of the gravity exerted on the probe as a function of the circumferential position of the probe would be null or near null for all circumferential positions ⁇ .
• the normal contribution Pn,b of the buoyancy is null.
• the probe 22 can have a high volume and as the density of the fresh concrete can be high, the normal contribution Pn,b of buoyancy on the probe can be significant, especially when the pressure values measured by the probe 22 are weight compensated.
• Fig. 4 shows an example relationship between the normal contribution Pn,b of the buoyancy exerted on the probe 22 as a function of its circumferential position ⁇ when the probe 22 is submerged into water (having a known density of 1 g/cm 3 ) when the weight of the probe 22 has been compensated as described above.
• the normal contribution ⁇ of the buoyancy exerted on the probe 22 varies as:
• Equation (2) assumes that there is no restriction due to the existence of any yield stress.
• the constant K v associated to a given probe can be determined during a calibration step in which the probe 22 is moved inside a drum 14 filled with a fluid having a known density and during which weight compensated pressure values Pn,b(9) are measured by the probe, such as the one shown in Fig. 4.
• the constant K v is associated to the construction of the probe 22, and not to the fluid in which the probe is submerged, the constant K v will remain the same regardless of the type of fluid in which the probe 22 is submerged.
• the resistance exerted on the probe 22 by the fresh concrete 12 acts on the probe 22 in a normal orientation. Accordingly, the normal contribution Pn,r of the resistance exerted on the probe 22 by the fresh concrete 12 is constant for all circumferential positions ⁇ when the probe 22 is moved in the fresh concrete 12 at any given rotation speed (e.g., v1 , v2). For instance, during a rotation of the drum 14, the resistance considerably increases as the probe 22 enters in the fresh concrete 12, is constant during its passage in the fresh concrete 12, and then considerably decreases as the probe 22 exits the fresh concrete 12.
• Fig. 5 shows an example relationship between the normal contribution Pn,r of the resistance exerted on the probe 22 by the fresh concrete 12 as a function of its circumferential position ⁇ when the probe 22 is submerged into the fresh concrete 12 and when without the normal contribution Pn,g of gravity and the normal contribution Pn,b of buoyancy.
• the normal contribution Pn,r of the resistance exerted on the probe 22 by the fresh concrete 12 varies as:
• K R is a constant indicative on the normal resistance exerted on the probe 22 by the fresh concrete 12 when the probe 22 is moved inside the fresh concrete 12 at a given rotation speed v
• ⁇ is the circumferential position at which the probe 22 enters the fresh concrete 12
• 9out is the circumferential position at which the probe 12 exists the fresh concrete 12.
• K R depends on the rotation speed v of the drum 14 and on a workability of the fresh concrete 12. As can be understood, ⁇ and 9out depends on the amount of fresh concrete 12 inside the drum.
• Fig. 6 shows an example relationship between the normal contributions of buoyancy and resistance as a function of the circumferential position ⁇ when the probe is submerged into the fresh concrete 12, without the normal contribution Pn,g of gravity.
• weight compensated pressure values Pn, W c(9) are given by:
• Fig. 7 shows an example of an experimental relationship between the normal contributions Pn, W c(0) of buoyancy and resistance as a function of its circumferential position when the probe is submerged into fresh concrete, without the normal contribution of gravity.
• Example 1 Determining the density of the fresh concrete using weight compensated pressure values
• a first weight compensated pressure value Pn,wc(01 ) is measured when the probe 22 is at a first circumferential position ⁇ 1 and a second weight compensated pressure value Pn, W c(02) is measured when the probe 22 is at a second circumferential position ⁇ 2, as shown in Fig. 6.
• Pn,wc(ei ) - ⁇ , ⁇ ( ⁇ 2) (Pn,b(91 ) + Pn,r(91 )) - (Pn,b(92) + Pn,r(92)),
• D (Pn,wc(91 ) - ⁇ , ⁇ ( ⁇ 2)) / (K v (sin ⁇ 1 - sin ⁇ 2)) (8)
• the first circumferential position ⁇ 1 is 90° and the second circumferential position ⁇ 2 is 270°.
• the trigonometric factor (sin ⁇ 1 - sin ⁇ 2) corresponds to 2 and the density value corresponds to the difference (Pn, W c(91 ) - Pn,wc(02)) which is compensated by a trigonometric factor corresponding to 2Kv.
• the constant K v depends on the volume V of the probe 22, and can be known for a given probe 22, so as to allow the determination of the density value D of the fresh concrete 12.
• the trigonometric factor (sin ⁇ 1 - sin ⁇ 2) may correspond to 1. For instance, it can occur when the first circumferential position ⁇ 1 is 90° and the second circumferential position ⁇ 2 is 180°.
• the density value D is determined mainly based on the constant K v and on the difference (Pn, W c(01 ) - Pn,wc(02)), without considering the trigonometric factor.
• the density value D can thus be determined without necessarily compensating the difference (Pn, W c(01 ) - Pn, W c(02)) with the trigonometric factor.
• Example 2 Determining the density value D of the fresh concrete using raw pressure values (pressure values which are not weight compensated) [0066]
• a first pressure value Pn,raw(91 ) is measured when the probe 22 is at a first circumferential position ⁇ 1 and a second pressure value Pn,raw(92) is measured when the probe 22 is at a second circumferential position ⁇ 2.
• Pn,raw(92) is measured when the probe 22 is at a second circumferential position ⁇ 2.
• Pn.raw ( ⁇ 1 ) - Pn.raw ( ⁇ 2) Pn,g(91 ) + Pn,b(91 ) + ⁇ , ⁇ ( ⁇ 1 ) - Pn,g(92) - Pn,b(92) - ⁇ , ⁇ ( ⁇ 2),
• Pn.raw ( ⁇ 1 ) - Pn.raw ( ⁇ 2) (Pn,g(91 ) - Pn,g(92)) + (Pn,b(91 ) - Pn,b(92)) + ( ⁇ , ⁇ ( ⁇ 1 ) - Pn,r(92)).
• D (Pn.raw ( ⁇ 1 ) - Pn.raw (92))/(K v (sin ⁇ 1 - sin ⁇ 2)) + K mg /K v (10)
• the trigonometric factor (sin ⁇ 1 - sin ⁇ 2) yields 2 and the density value corresponds to the difference (Pn,wc(91 ) - Pn,wc(92)) which is compensated by a trigonometric factor corresponding to 2K V plus a constant value based on the constants Kmg and Kv.
• the constant K v depends on the volume V of the probe 12 whereas the constant K mg depends on the mass m of the probe 22 and on the gravitational acceleration g on earth, which are all constant for a given probe 22, and allows the determination of the density value D of the fresh concrete 12.
• the density value D of the fresh concrete 12 is determined based on the volume V of the probe 22 and on a difference between the first pressure value and the second pressure value being compensated by a trigonometric factor corresponding to a difference between the sinus of the first circumferential position and the sinus of the second circumferential position. That trigonometric factor can be equal to (sin ⁇ 1 - sin ⁇ 2) or to any other suitable trigonometrically equivalent factor.
• the first circumferential position ⁇ 1 is chosen to lie on one side of the drum relative to the vertical 20 and the second circumferential position ⁇ 2 lies on one other side of the drum relative to the vertical 20.
• the first circumferential position ⁇ 1 can lie between 90° and 180° whereas the second circumferential position ⁇ 2 can lie between 180° and 270°.
• the first circumferential position ⁇ 1 is chosen so as to be opposite to the second circumferential position ⁇ 2 with respect to the vertical 20.
• the first circumferential position ⁇ 1 is 90° and the second circumferential position ⁇ 2 is 270°.
• the first circumferential position ⁇ 1 can be 1 12.5° and the second circumferential position ⁇ 2 is 247.5° in another example.
• Fig. 8 shows an example of a section of the drum 14, in accordance with another embodiment.
• the drum 14 is divided into a plurality of virtual circumferential ranges 32. More specifically, in this example, the drum 14 is divided into eight different circumferentially-spaced circumferential ranges which spans in the bottom hemisphere of the drum 14.
• the circumferential position of the first circumferential range spans between 90° and 1 12.5°
• the circumferential position of the second circumferential range spans between 1 12.5° and 135°
• the circumferential position of the third circumferential range spans between 135° and 157.5°
• the circumferential position of the fourth circumferential range spans between 157.5° and 180°
• the circumferential position of the fifth circumferential range spans between 180° and 202.5°
• the circumferential position of the sixth circumferential range spans between 202.5° and 225°
• the circumferential position of the seventh circumferential range spans between 225° and 247.5°
• the circumferential position of the eighth circumferential range spans between 247.5° and 270°.
• Fig. 9 shows an example of experimental weight compensated pressure values Pn,wc(0) measured by the probe 22 during one rotation of the drum 14. As it can be seen, the pressure values associated with the circumferential positions of each one of the circumferential ranges 32 can be averaged to yield averaged pressure values Pavg in each of the circumferential ranges 32.
• the first pressure value with which the density value D of the fresh concrete 12 is determined corresponds to an average of the pressure values measured when the probe 22 was moved in one of the circumferential ranges, e.g., the first circumferential range.
• the second pressure value with which the density value D of the fresh concrete 12 is determined corresponds to an average of the pressure values measured when the probe 22 was moved in another one of the circumferential ranges, e.g., the second, third or eighth circumferential range.
• the density value D determined can be precise. For instance, as the level of fresh concrete 12 in the drum 14 progressively lowers, the density D of the fresh concrete 12 can be determined using first and second pressure values measured correspondingly progressively closer to the bottom of the drum 14. As can be understood, due to the presence of the discrepancies 30 in the vicinity of the bottom of the drum 14, the fourth and fifth circumferential ranges can be ignored. [0086] It was found that the difference between the first and second pressure values is generally constant regardless of the rotation speed v of the drum 14. For instance, as shown in Fig.
• the difference between a first pressure value measured when the probe 22 is at a first circumferential position ⁇ 1 and a second pressure value measured when the probe 22 is at a second circumferential position ⁇ 2, during a rotation of the drum 14 at the first rotation speed v1 is similar to the difference between a first pressure value measured when the probe 22 is at a first circumferential position ⁇ 1 and a second pressure value measured when the probe 22 is at a second circumferential position ⁇ 2, during a rotation of the drum 14 at the second rotation speed.
• the density value D of the fresh concrete 12 can be determined either based on pressure values measured as the probe 22 moves at the first rotation speed v1 or on pressure values measured as the probe 22 moves at the second rotation speed v2.
• the density value D of the fresh concrete 12 can be determined based on a first pressure value measured when the probe 22 is a first circumferential position ⁇ 1 during a rotation of the drum 14 at the first rotation speed v1 and on a second pressure value measured when the probe 22 is at a second circumferential position ⁇ 2 during a rotation of the drum 14 at the second rotation speed v2, given that the either one of the constants K1 , K2 and K3 above be known.
• One can thus calibrate the probe 22 based on a known variation of the rotation speeds. That is, the first and second pressure values need not to be measured at a same rotation speed.
• Fig. 10 shows an example of a graph showing the average of the first and second pressure values as measured when the probe is at the first and second circumferential positions ⁇ 1 and ⁇ 2 during rotation at different rotation speeds of the drum as function of the different rotation speeds of the drum.
• rheological properties of the fresh concrete 12 can be determined from the graph of Fig. 10. More specifically, the viscosity ⁇ of the fresh concrete 12 can be determined by calculating a slope of the resulting linear relationship 34. Further, a yield ⁇ of the fresh concrete 12 can be determined by extrapolating the pressure value at a null rotation speed.
• pressure values taken far away from the bottom of the drum can yield more precise rheological property measurements than measurements using pressure values taken in the vicinity of the drum because it may not be disrupted by the level of fresh concrete in the drum.
• the trigonometric factor which is used to compensate the difference between the first pressure value and the second pressure value can correspond to the difference between the sinus of the first circumferential position and the sinus of the second circumferential position in some embodiments whereas the trigonometric factor can alternatively correspond to the difference between the cosine of the first circumferential position and the cosine of the second circumferential position in some other embodiments.
• the sinus/cosine is determined based on how the circumferential positions are defined relative to the circumference of the drum. The scope is indicated by the appended claims.

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