The invention relates to a portable viscometer com prising a motor, an axle driven by the motor, and a body mounted on the axle which is arranged for executing a turning motion in a medium of which a viscosity is to be measured, wherein a measuring organ is provided for measuring a torque exerted by the motor on the medium, and a calculating organ is provided that is connected to the measuring organ for deriving the viscosity of the medium from at least the measured torque.

Such a portable viscera meter is known from for in stance the Chinese utility models CN 202083610 and CN 2458618.

CN 202083610 discloses a portable type rotary visco ^¬ meter. This known portable type rotary viscometer comprises a stepping motor, a torque sensor, a cylindrical probe, a func tion selecting key, a CPU (Central Processing Unit) , a temperature sensor and an LCD (Liquid Crystal Display) screen, wherein the stepping motor rotates at a constant speed so as to drive the cylindrical probe to rotate, wherein the cylin drical probe is used for producing torque in the direction re verse to the rotating direction. The torque is transferred to the torque sensor and is then transferred to the CPU after be ing processed by the torque sensor and the CPU is used for processing the data of the torque sensor, wherein a viscosity value is displayed on the LCD. The function selecting key is used for selecting a rotating speed of the stepping motor, and a signal of the temperature sensor is processed by the CPU for display on the LCD.

CN 2458618 relates to an electronic viscometer which is a portable and intelligent measuring instrument for the viscosity of liquids. This electronic viscometer measures the rotary speed of a sensor and the rheological and viscous re sistance torque of the liquid are determined with a microcom puter by using the rotationally shearing movement of a rotary torque sensor. The rheological and viscous resistance torque is changed into data which can be processed by the micropro cessor through a signal processing circuit. Thereafter the in- dexes of the viscosity of the liquids can be worked out through the microprocessor.

The portable viscometer of the prior art is not suitable for measuring the viscosity of granular mixes for constructional works as applied in civil engineering. Those gran ular mixes are different in nature in that they are essentially multiphase viscous mixtures as opposed to single phase viscous fluids that can be measured with the portable viscometer of the prior art.

It is therefore an object of the invention to provide a portable viscometer which is suited to measure the viscosity of a multiphase viscous mix as is applied for constructional works .

It is another object of the invention to help practitioners to determine quickly the workability and functionality of the granular mixes utilized for those constructional works so as to be able to quickly determine the engineering charac teristics of the mixes for the construction such as the optimum compaction time, compression strength and resistance to deformation under stress and thermal loads etc.

Accordingly the invention is not only related to a portable viscometer but also to a method of determining the viscosity of a medium using such viscometer.

JP2001/124685 teaches an apparatus and method of measuring the viscosity of a liquid flowing through a pipe, comprising the steps of inserting a rotary blade into the pipe and providing a baffle plate or a blade cover at the upstream side of the rotary blade, and measuring the viscosity of the liquid by detecting the torque of the rotating blade while ro tating the liquid.

US2016/349163 teaches a rheometer attachment compris ing a shaft having a shaft axis and an outer surface and a plurality of helical vanes each extending radially from the outer surface.

JP S56 97737 teaches a holding body provided with a dial plate, an elastic single bearing supported by the holding body, a small motor rotatably supported by the single bearing, a motor shaft of a motor, and a liquid agitating blade at tached to a liquid stirring blade and a pointer fixed to a frame of the motor and extending on a scale plate in the radial direction of the motor shaft.

CN 103 528 925 teaches a rotary viscometer with a blade type rotor, comprising: a torque sensor, a bracket, a lifting mechanism, a rotating rod, a rotating head, a sample chamber, a paddle type rotor, a test stand, a signal line, a control mechanism, wherein the paddle type rotor is fixed on the rotating head, and the rotating head is connected with the torque sensor through the rotating rod. The sensor is arranged on the bracket of the lifting mechanism. The torque sensor and the lifting mechanism are connected to the control mechanism through the signal line, and are controlled by the control mechanism.

The invention is embodied in a viscometer and in a method for measuring the viscosity of a medium in accordance with one or more of the appended claims.

In a first aspect of the invention the portable vis cometer comprises a motor, an axle driven by the motor, and a body mounted on the axle which is arranged for executing a turning motion in a medium of which a viscosity is to be meas ured, wherein a measuring organ is provided for measuring a torque exerted by the motor on the medium, and a calculating organ is provided that is connected to the measuring organ for deriving the viscosity of the medium from at least the meas ured torque, wherein the body is equipped with at least two blades on opposite sides of the axle which lie in each other' s extended direction, and wherein a thermal sensor is connected to the viscometer to measure an in-situ temperature of the medium whilst measuring said medium's viscosity.

By correlating the rheological property of viscous binders tested in a lab and comparing it with the viscosity of the granular mixes measured by the viscometer of the inven tion, practitioners are enabled to determine quickly the work ability and the functionality of the granular mixes utilized in various engineering field activities.

Best results are achieved when the body is equipped with four blades, wherein each blade is at an angle of 90° with at least one other blade mounted on the axle. Suitably each of the blades has the same length as seen in a longitudinal direction of the axle.

By using a body with blades instead of a smooth cy lindrical head as known from the prior art, both the rheologi cal and mechanical behaviour of viscous granular mixes can be reliably determined. Because the blades have the same length, an uniform shear zone can be created inside the granular mix and hence a more accurate measurements of viscosity of the mix versus an instantaneously measured temperature and time can be obtained.

Preferably the granular mix is bounded by a viscous binder selected from the group comprising bitumen, emulsions, thermoplastic and thermosetting polymer modified bitumen, cementitious paste.

By varying the rotation speed of the blades of the viscometer, both dynamic viscosity and apparent viscosity of the multiphase viscous material of the medium can be obtained.

The method for measuring a viscosity of a medium comprising a multitude of particles, includes the provision of a body of the portable viscometer in the medium and rotating the body in the medium with a first rotational speed w, and establishing a maximum radius Rc in which still shearing oc ^¬ curs in the medium, wherein beyond the maximum radius R _c no appreciable shearing in the medium occurs, and establishing the viscosity /] _m of the medium using the formula in which T is the torque that the motor applies to the medium via the blades of the viscometer, L _m is the effective length of the blades, Rm is the blade radius and Rc is the above-meant radius of the effective shearing region, and w is the rotation speed of the blades of the viscometer.

It is preferred that establishment of the maximum ra ^¬ dius R _c wherein still shearing occurs in the medium, is done by relating it to a nominal maximum size of the particles in the medium, using the relation i?c=R _m +15i¾+0.035 (m) wherein Rm is the radial length of the blades, and D _n denotes a nominal maximum size of the particles in the medium. The invention will hereinafter be further elucidated with reference to the drawing of an exemplary embodiment of an apparatus according to the invention that is not limiting as to the appended claims.

In the drawing:

-figure 1A and IB shows a viscometer according to the invention provided in a mix of which the viscosity must be measured, wherein the device is shown in a cross-sectional side view and a cross-sectional top view respectively; and

-figure 2A and 2B shows a cross-sectional top view of the mix with a viscometer in operation, and showing respectively a shear stress and velocity profile distribution within the mix.

Whenever in the figures the same reference numerals are applied, these numerals refer to the same parts.

Turning now first to figure 1A and IB, it shows a portable viscometer 1 in operation, wherein the viscometer 1 comprises a motor 2, an axle 3 driven by the motor 2, and a body 4 mounted on the axle 3 which during operation executes a turning motion in a medium 5 of which a viscosity is to be measured. A measuring organ 6 is provided for measuring a torque exerted by the motor 2 that acts on the medium, and a calculating organ 7 is provided that is connected to the meas uring organ 6 for deriving the viscosity of the medium 5 from the measured torque.

Further a speedometer 10 is shown to measure the rotational speed w of the axle 3 on which the body 4 is mounted, as well as a thermal sensor 11 to measure the temperature of the medium 5. Both the speedometer 10 and the thermal sensor 11 are also connected to the calculating organ 7. A visual display unit 12 can for instance be connected to the calculating organ 7 to show the viscosity of the medium 5 that is cal culated and based on the measurements of rotational speed and torque as exerted by the body 4 of the viscometer 1 on the medium 5.

According to the invention the body 4 is equipped with at least two blades 8', 8' ' on opposite sides of the axle 3 which lie in each other's extended direction. This is best shown in figure IB. Preferably the body 4 is equipped with four blades 8', 8 ^r ' , 9', 9' ' , wherein each blade is at an an gle of 90° with at least one other blade mounted on the axle 3, as is also shown in figure IB.

Figure 1A shows that each of the blades 8', 8'', 9',

9' ' has the same length Lm as seen in a longitudinal direction of the axle 3 The minimum insertion depth of the viscometer 1 into the medium is shown in Figure 1A as the parameter H. With this parameter H the measured viscosity and temperature repre sentative of the real status of the medium can be guaranteed. The recommended insertion depth H is 30 cm.

The portable viscometer 1 of the invention can effec tively be used in a method for measuring the viscosity of the medium 5 by providing the body 4 of the portable viscometer 1 in the medium 5 and rotating the body 4 in the medium 5 with a rotational speed w and establishing a maximum radius Rc (see figure 1A) in which still shearing occurs in the medium 5.

This maximum radius Rc in which still shearing occurs in the medium 5 must be understood within the scope of the invention such that beyond the maximum radius Rc no appreciable shearing occurs in the medium 5. The viscosity of the medium can then be determined using the formula in which T is the applied torque as measured with the measuring organ 6, L _m is the effective length of the stirrer (blade) , R _m is the stirrer blade radius and R _c is the just mentioned ra dius of the effective shearing region, and w is the rotation speed of the stirrer blades 8', 8'', 9' , 9' ' as measured with the speedometer 10. To avoid misunderstanding it is remarked that within the scope of this application a speedometer is meant to measure a rotational speed of a rotating body, with out need to apply any further functionality such as displaying this speed, although this is also not excluded from the application .

It is possible to establish the maximum radius Rc wherein still shearing occurs in the medium 5 by estimating it visually. It is however preferred to establish the maximum ra dius R _c by relating it to a nominal maximum size of the parti- cles in the medium 5, using the relation -Rc=R _m +15D _n +0.035 (m) wherein Rm is the radial length of the blades, and Dn denotes a nominal maximum size of the particles in the medium 5.

The device and method of the invention are particu larly suitable for application on a medium 5 in the form of a granular mix bounded by a viscous binder selected from the group comprising bitumen, emulsions, thermoplastic and thermo ^¬ setting polymer modified bitumen, cementitious paste. These types of media are typically applied in civil engineering con structions .

The invention uses the principle that the torque re quired to turn the viscometer blades 8', 8'', 9', 9'' in the medium 5 is depending on the viscosity of the medium 5. The viscometer 1 measures the torque required to rotate the blades 8', 8'', 9', 9'' in a multiphase medium consisting of granular particles bounded by viscous binders at a known applied rota tional speed a, wherein the speed is measured with a speedometer 10 which measures the rotational speed of the axle 3, see Fig. 1A. The shear rate between the blades 8', 8'', 9', 9'' and the particles of the medium 5 is assumed constant at any given speed w and, thus, the viscosity can be calculated from factors like stress and rate as discussed hereinafter. In par ticular, the shear stress r in Fig. 2(a) can be expressed as wherein T is the applied torque as measured with the measuring organ 6, and Lm is the effective length of the blades 8' , 8' ' , 9', 9''. It is further assumed that the shear force is perpen dicular to its moment arm (r) .

The viscosity rm of the multiphase medium 5 is assumed to fol low Newton' s fluid law and can be defined by

dii

= (2

^T )

wherein u is the velocity of the multiphase mix of the medium 5 and the negative sign in equation (2} indicates that the ve locity decreases as r increases, r being the distance as meas- ured from a point in the medium 5 to the centre of the axis 3, see Fig. 2(b) . The velocity profile as shown in fig. 2B is as sumed to be linear. The boundary conditions are given as ύ = jR _m when T = R _m

ύ = 0 when T = R _c wherein Rm is the radius of the blades 8', Q' ' , 9', 9’’ (see figure IB) , and Rc is the radius of the effective shearing in terfered area as shown in figure 1A.

There are several ways in which the maximum radius Rc wherein still shearing occurs in the medium 5 can be deter mined, one of which is by visual observation. Other options are to determine the maximum radius Rc by laboratory test or numerical simulation. Another simplified way of determination of Rc is to relate it to the nominal maximum size Dn of parti cles in the medium 5. The preferred relation to be used is then i?c=Rm+15Dn+0.035 (m) , wherein Rm is the radial length of the blades, and D _n denotes the nominal maximum size of the particles in the medium.

From the equations ( 1 )— ( 2 ) the viscosity of medium 5 is given as

and the viscosity of the multiphase medium 5 is given as wherein w is the rotation speed of the blades 8 8 9' 9' ' of the viscometer 1. Example

For tf=0.3 m, Lm=0.15 m, Rm=0.1 m, # _c =0.12 m, T=0.4 Nm, w=20 rpm, the viscosity of the multiphase medium 5 is

Although the invention has been discussed in the foregoing with reference to an exemplary embodiment of the viscometer and method of the invention, the invention is not restricted to this particular embodiment which can be varied in many ways without departing from the invention. The dis cussed exemplary embodiment shall therefore not be used to construe the appended claims strictly in accordance therewith. On the contrary the embodiment is merely intended to explain the wording of the appended claims without intent to limit the claims to this exemplary embodiment. The scope of protection of the invention shall therefore be construed in accordance with the appended claims only, wherein a possible ambiguity in the wording of the claims shall be resolved using this exem plary embodiment.