Title: Rheomixer device
Abstract: Device and methods for rotationally mixing and rheological testing of sample liquids, such as cement particle suspensions, employ mixing blades and shear-resistant members having substantially noncoincident orbital paths. Rheology is assessed by measuring the resistance of the liquid to rotation of the device. Both rheological and calorimetric testing can be performed during mixing, which ensures uniformity of rheology and hence the accuracy of results.
Patent Number: 6,997,045 Issued on 02/14/2006 to Wallevik, et al.
| Inventors:
|
Wallevik; Olafur H. (Reykjavik, IS);
Sandberg; Paul (Beverly, MA);
Myers; David F. (Acton, MA)
|
| Assignee:
|
W.R. Grace & Co.-Conn. (Columbia, MD)
|
| Appl. No.:
|
741747 |
| Filed:
|
December 19, 2003 |
| Current U.S. Class: |
73/54.28; 73/54.38; 73/54.39 |
| Current Intern'l Class: |
G01N 11/14 (20060101); G01N 11/10 (20060101) |
| Field of Search: |
73/5401,542.8,543.8,543.9,542.3,542.4
|
References Cited [Referenced By]
U.S. Patent Documents
| 5303578 | Apr., 1994 | Williams et al.
| |
| 5321974 | Jun., 1994 | Hemmings et al.
| |
| 5546791 | Aug., 1996 | Meeten.
| |
| 5610325 | Mar., 1997 | Rajagopal et al.
| |
| 5631409 | May., 1997 | Rajagopal et al.
| |
| 6227039 | May., 2001 | Te'eni.
| |
| 2003/0233867 | Dec., 2003 | Hall.
| |
Other References
American Society for Testing Materials (ASTM) Designation: C 1074-98, "Standard
Practice for Estimating Concrete Strength by the Maturity Method 1,"
Mar. 1999 pp 1-8.
American Society for Testing Materials (ASTM) Designation: C 918-971,
Standard Test Method for Measuring Early-Age Compressive Strength and Projecting
Later-Age Strength 1, Mar. 1997 pp 1-6.
Magna Projects, http://www.magna-projects.com/ttpt.htm, TTPT: "The Tattersall
Two-Point Workability Test for Fresh Cement and Concrete and Other Materials,"
Jan. 8, 2003 pp 1-3.
Engineeringtalk, http://www.engineeringtalk.com/news/mag/mag104.html, "Testing
the flow properties of fresh cement," Jun. 26, 2001 pp 1-2.
Journal of Research of the National Institute of Standards and Technology, "Concrete
Mixing Methods and Concrete Mixers:" State of the Art, vol. 106:2, Mar.-Apr.
2001 pp 391-399.
Wallevik, Rheologieseminar, "Ein Zweitageskurs in Rheology of Fresch Concrete
and Mortar," Congress Hotel Mercure . Bericht vom Seminar, Nov. 8-9, 2001 pp 1-6.
Wallevik, "The MBL Viscometer, Rheology of cement suspensions," The BML
Viscometer, Chapter 2, IBRI-Wallcvik (2000 or earlier) pp 2-2 through 2-19.
Vachon, Martin, ASTM Standards in Building Codes, http://www.astm.org/snews/july_2002/vachon_jul02.html
"ASTM Puts Self-Consolidating Concrete to the Test," Jul. 2002, pp 1-5.
|
Primary Examiner: Williams; Hezron
Assistant Examiner: Bellamy; Tamiko
Attorney, Agent or Firm: Leon; Craig K., Baker; William L.
Claims
It is claimed:
1. A device for mixing and assessing a sample liquid within a container, comprising:
a rotatable shaft member having a generally elongate body;
at least one propeller blade attached to said shaft member and having a blade
face oriented to propel a liquid in a direction along said elongate shaft body
when said shaft is rotated within a liquid; and
at least one elongate shear-resistant member for resisting circular motion when
said shaft member is rotated within the liquid, said at least one shear-resistant
member being spaced at a fixed distance from, and being fixed in a fixed rotational
relationship with respect to, said at least one propeller blade, and said at least
one shear-resistant member being spaced apart from and attached in fixed spatial
relation with respect to said rotatable shaft member.
2. The device of claim 1 further comprising a plurality of blades attached to
said rotatable shaft member, said blades operative to mix a sample liquid in a container.
3. The device of claim 2 wherein said device has two sets of a plurality of blades
attached to said shaft member, each blade set having blade faces oriented to push
liquid in a direction from the other blade set, when said shaft member is rotated.
4. The device of claim 1 wherein said device has at least four propeller blades
attached to said rotatable shaft member at equal distances circumferentially spaced
around said shaft member.
5. The device of claim 2 wherein the set of blades attached lowermost on said
shaft member has a cumulative surface area greater than that of the set of blades
attached uppermost on said shaft member.
6. The device of claim 1 wherein said at least one elongate shear-resistant member
has tapered leading and trailing edges.
7. The device of claim 6 wherein said device has at least two shear-resistant members.
8. The device of claim 7 wherein said at least two shear-resistant members have
different lengths.
9. The device of claim 8 wherein said at least two shear-resistant members are
spaced at different distances from said rotatable shaft member.
10. The device of claim 1 comprising a plurality of blades and shear-resistant
members, wherein each blade and membrane has a rotational path that does not substantially
coincide with the rotational path of immediately adjacent blades and shear-resistant members.
11. The device of claim 1 wherein said at least one blade is connected in fixed
relation, with respect to said rotatable shaft member, by a connector bar attached
to said shaft member, a collar attached to said shaft member, or a connector bar
attached to said collar which is in turn attached to said shaft member.
12. The device of claim 1 further comprising a container body for containing
sample liquid in which said rotatable shaft member, blades, and shear-resistant
members are rotatable.
13. The device of claim 12 further comprising a heat sensor.
14. The device of claim 13 wherein said container body is thermally insulated.
15. The device of claim 14 wherein said container body is temperature controlled.
16. The device of claim 1 wherein said at least one propeller blade and said
at least one elongate shear-resistant member are located within a container containing
a sample liquid.
17. The device of claim 16 wherein said container contains a particle suspension.
18. The device of claim 17 wherein said particle suspension is cementitious.
19. The device of claim 18 further comprising a torque-resistance-measuring servo-controlled
motor operative for measuring the rheology of said cementitious particle suspension
over a period of time.
20. The device of claim 19 further comprising an additive or admixture operative
to modify a property of said cementitious particle suspension.
21. The device of claim 19 further comprising a temperature sensor operative
to perform calorimetric measurements on said cementitious particle suspension.
22. The device of claim 16 wherein said sample liquid is selected from the group
of particle suspensions, latexes, emulsions, colloidal suspensions, grease and
lubrication compositions, asphaltic or bituminous compositions, adhesives, and caulks.
23. The device of claim 19 wherein said servo-motor is connected with a computer
processing unit operative to provide automated control over said servo-motor.
24. A rheomixer device comprising: mixing blades for mixing a liquid, shear-resistant
members for measuring rheology of a liquid, a mix container for mixing a liquid
using said blades and shear-resistant members, said container having a heat sensor
for calorimetric measurement of the liquid, said mixing blades and shear-resistant
members being attached to a rotatable shaft in fixed rotational and spatial relationship
with respect to each other.
25. The device of claim 24 further comprising a temperature control for maintaining
a constant temperature in the container, a pressure control for maintaining a constant
pressure in the container, or both temperature and pressure controls.
26. A device comprising rotatably mixing and assessing the rheology of a sample
liquid within a container using the device of claim 1.
27. The device of claim 26 further comprising measuring the heat or temperature
of said sample liquid over time.
Description
FIELD OF THE INVENTION
The present invention relates to a rotational mixing and rheology measuring device
suitable for use with viscous fluids, and especially for particle suspensions such
as cement, mortar, and concrete slurries.
BACKGROUND OF THE INVENTION
As mentioned in U.S. Pat. No. 5,546,791 of Meeten, the rheology or thixotropy
of granular fluid slurries, such as cement slurries or drilling mud, can be useful
for determining the behaviour of the resultant material. The current standard rheology
measurement, as specified by the American Petroleum Industry (API), involves testing
of samples in a cup container, and placing a rotor/stator device into the cup.
The rotor/stator device comprises a cylindrical, motor-driven rotor having a vaned
stator coaxially mounted on the rotation axis. Rotation of the rotor applies torque
to the stator. Rate of rotation is compared to the applied torque to determine
rheological characteristics of the cup-contained sample.
Meeten observed that rheometers may be inaccurate due to so-called end effects,
such as "slippage at the wall" of particle-containing liquid in the container cup,
and such as "particle migration" towards the bottom of the cup due to gravity.
End effects arise from the torque generated by flow from the ends of the concentric
cylinders that comprise the rotor/stator arrangement. Such effects can lead to
significant inaccuracies in calculating shear forces applied to the sample fluid,
and, hence, its rheological properties.
The first phenomenon known as "slippage at the wall" occurs when the fluid suspension
is depleted of particles near the walls of the mixing container. This can, in turn,
reduce significantly the measured viscosity and yield stress, consequently leading
to large errors in measured values.
The second phenomenon, known as "particle migration," is primarily caused by
gravity, as mentioned above, and also by centrifugation effects. The effect of
gravity is to reduce the particle content in the sample zone where the yield stress
is measured, and therefore the inaccuracy for rheological measurement is increased
for samples mixed using high shear forces. Furthermore, the build-up of solids
below the rotor/stator device may cause extra torque to be transmitted to the stator,
further increasing error. Meeten further observed that centrifugation was particularly
apparent in the external rotor arrangement specified by API. This centrifugation
effect decreased the number of particles near the inside of the rotor, thus increasing
the inaccuracy of the torque measurement and data obtained.
Meeten further observed that various attempts had been made to reduce one
or more of the effects outlined above. These attempts include the provision of
a pump and baffle arrangement, for example, as described in SPE Paper Production
Engineering, November 1990, pp 415-424. In this publication, the authors Shah and
Sutton provided slots at the upper end of the rotor and a helical flange around
the outside of the rotor. These were intended to provide flow through the rheometer
and to prevent build-up of solids on layers in the region of the rotor/stator.
In the afore-mentioned U.S. Pat. No. 5,546,791, Meeten sought a different way
to mitigate the detrimental "end effects" discussed above. However, his remedy
remained focused on the use of co-axial rotating cylinders, as employed in the
outer rotor/inner stator arrangement (known as the "Couette geometry") and in the
inner rotor/outer stator arrangement (known as the "Searle geometry"). Meeten's
rheometer, while retaining a cup container and coaxial rotor/stator arrangement,
introduced the use of a pump for providing a pulsatile, non-laminar flow intended
for maintaining the particles in suspension while inducing a rheology effect for
dispersing and maintaining relative dispersion of the particles and for remaining
independent of the measuring system itself.
The present inventors believe that the use of a recirculating pump, as taught
by Meeten, could introduce problems for evaluating relatively stiff and viscous
mixes such as concrete and mortar. This is because such cementitious mixes, which
begin to harden upon hydration, can potentially foul his hoses and pump equipment.
Moreover, it is possible that the effect of high viscous fluids in the
hoses, such as cement slurries, pastes, or mortars, might tend to hinder the use
of pulsing for dispersing the particles.
Accordingly, the present inventors believe that a novel device is needed
for mixing and rheological measurement, one that is particularly capable of assessing
the rheology of high viscosity fluids, and, especially, for particle suspensions
such as cement slurries, pastes, and mortars.
SUMMARY OF THE INVENTION
In surmounting the disadvantages of the prior art, the present invention provides
a device and method for achieving mixing and rheological evaluation of a wide variety
of fluid sample types, including granular materials, particle suspensions (e.g.,
slurries and pastes), highly viscoelastic materials, and gas-solid mixtures.
The mixing and rheological measurement device of the present invention, otherwise
referred to herein as a "rheomixer," is used in association with motor-driven rheology
measurement machines that apply torque to the device and measure resistance of
sample fluid in a container such as a cup. However, the novel and inventive features
of the device minimize inaccuracies caused by "slippage at the wall" and "particle
migration" effects previously described above.
One objective of the present invention is to provide a rotary rheological device
that allows for integrated mixing and rheological evaluation of particle suspensions
such as cementitious slurries, pastes, mortars, and concretes, whereby: (1) segregation
of materials is minimized and fluid sample homogeneity is maintained; (2) three-dimensional
mixing of particles and fluid is achieved; and (3) rheological properties are accurately
evaluated using torque measurements, whereby detrimental effects caused by mixing
(such as non-uniform particle dispersal) is minimized or avoided.
The present invention minimizes errors arising from transferring sample fluids
between separate mixer and rheological testing devices. Errors due to exposure
of sample fluid to ambient temperature and humidity, as well as due to loss or
contamination of liquid sample during transference, are greatly reduced.
An exemplary rheomixer device comprises: a rotatable shaft member having a generally
elongate body; at least one blade attached to the shaft member and having a blade
face angled to propel a liquid in a direction along the elongate shaft body when
the shaft is rotated within the liquid; and at least one elongate shear-resistant
member for resisting circular motion when the shaft member is rotated within the
liquid, the at least one shear-resistant member being spaced at a fixed distance
from, and being fixed in a rotational relationship with respect to, the at least
one propeller blade; the shear-resistant member further being spaced apart from
and attached in fixed spatial relation with respect to the rotatable shaft member.
Preferably, the shear-resistant member is attached to a first end of the rotatable
shaft and defines a circular path that preferably does not overlap or interfere
with the circular path of the propeller blade when the device is rotated. The shear-resistant
member(s) can be mounted in parallel or at an angle with respect to the rotatable
shaft, while the propeller (mixing) blade(s) can be mounted perpendicularly or
at an angle with respect to the shaft.
The invention also relates to methods wherein the above-described rheomixer is
rotated within a sample liquid to mix the liquid, and rheology is assessed by measuring
resistance of the liquid to rheomixer rotation.
In connection with cementitious liquid mixes, the rheomixer is used to mix water
with hydratable cement (e.g., Portland cement, pozzolans such as granulated blast
furnace slag, fly ash, gypsum, mixtures thereof) to provide a substantially uniform
particle suspension that is hydratable and possesses a changing rheology whose
changes can be measured over time. Thus, another exemplary method of the invention
involves mixing dry components with water to provide a particle suspension (e.g.,
including "paste" or "slurry"), and thereafter measuring the rheology of the suspension,
preferably over time, using the same rheomixer device, without having to transfer
the sample liquid between separate mixer and rheology measurement devices.
The ability to mix and measure rheology with the same device is particularly
advantageous for high-throughput mixing and testing of hydratable cementitious
particle suspensions, and this can be done quickly in succession or in parallel
on multiple samples. The quality of liquid samples can be adjusted during mixing
and testing by addition of water, admixtures, solids, and other materials, without
the back-and-forth transfers between separate mixer and rheology measurement devices.
Further exemplary rheomixers comprise a mix container for containing sample
liquid. An optional lid or cover plate having an opening for the rotatable shaft
is used to provide an adiabatic or semi-adiabatic mixing rheology testing environment.
In other exemplary embodiments, the mix container comprises and/or is surrounded
by insulation material to insulate thermally the liquid contents from ambient air
temperature fluctuations. The insulation may comprise a solid material, such as
plastic, foam (e.g., polystyrene), glass, metal, or other material as desired.
Further exemplary mix containers may also have cavities in the container walls
for removing air, so as to create a vacuum; or water or other fluid may be pumped
through the container walls, for example, to maintain the sample fluid at a desired temperature.
Preferred embodiments of the invention also comprise the use of at least
one heat sensor (e.g., thermocouple, heat flow sensor) inside the mix container,
within the container walls or floor, and/or on the outer surface of the container
walls or floor. The heat sensor is operative to facilitate calorimetric measurements
such as heat generated by the sample liquid over time. Preferably, the mix container
comprises or is surrounded by insulation to insulate the liquid contents from ambient
temperature and humidity fluctuations, thus helping the user to obtain uniformity
of data from one mix-test to the next. Thus, the operations of mixing, rheological
measurement, and calorimetric measurement may be accomplished in an integrated fashion.
Further exemplary methods of the invention involve mixing, rheological testing,
and calorimetric testing to obtain data, from hydratable cementitious slurry samples,
upon which set time and later strength characteristics (e.g., compressive strength)
may be extrapolated.
In a further aspect of the invention, the mix container lid and body may be sealed
so that the sample liquid can be pressurized. This enables the behavior of fluids
such as used in subterranean applications (e.g., oil well, geothermal, drilling
mud) to be studied under controllable pressure and temperature conditions.
Thus, a general purpose of the invention is to provide for mixing hydratable
particle suspensions and measuring their rheological properties, including viscosity,
yield value, and thixotropy, as a function of time and preferably within a closed
system. The measurements can be used to characterize or predict the kinetics of
hydration which in turn allow for the prediction of physical and mechanical properties
in the resultant compositions after hydration. The rheomixer of the invention will,
in particular, allow for accurate study of the effects of various additives and
admixtures on the hydratable cementitious mixes.
As a broad concept, the present invention provides a device and method wherein
a rheomixer comprises both mixing blades for mixing a liquid and shear-resistant
members for measuring rheology of a liquid, a mix container having a heat sensor,
and optionally a temperature control for maintaining a constant temperature in
the container, a pressure control for maintaining a constant pressure in the container,
or both temperature and pressure controls.
Further advantages and features of the invention are described hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an illustration of an exemplary rheomixer device of the present invention; and
FIG. 2 is an illustration of another exemplary rheomixer device of the present invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
The exemplary rheomixer of the present invention is designed to work with servo-controlled
electric motors (otherwise referred to as "servo-engines") that are designed to
rotate and to provide an electrical output signal that accurately corresponds to
the amount of torque applied, such that, in combination with the inventive rheomixers
of the present invention, fluid samples can be quickly mixed and their torque resistance
on the rotated rheomixer device can be quickly and accurately measured. Such servo-engines
are able to stop and start with high precision, due to the fact that their electric
motors contain numerous electric coils that provide nearly-instantaneous torque.
A servo-engine believed to be suitable for purposes of the present invention is
available from Samey of Iceland under the tradename Control Technologies™,
and other suitable servo-engines are elsewhere available.
Preferred methods of the invention for mixing involve the ability of servo-engines
to alternate rotational directions, between clockwise and counter-clockwise rotation,
and it is believed that this use of servo-controlled motors to agitate particle
suspensions, such as cementitious compositions, may in itself be unique and novel.
Unlike commercially available mixers for mortars and concretes, the use of a servo-engine
and rheometer may be employed for very low to very high agitation modes, thereby
simulating the various mixing actions that occurs throughout the different commercial
applications of cementitious suspensions.
The term "particle suspensions" as used herein means and refers generally to
particles of matter that are suspended in a carrier fluid. Consequently, "cement"
or "cementitious" particle syspensions include pastes, slurries, mortars, shotcrete,
grouts (such as oil well cementing grouts), and concrete compositions having a
hydratable cement binder. It is helpful to note that the terms "paste", "mortar"
and "concrete" are terms of art. Pastes are mixtures composed of a hydratable cement
binder (usually, but not exclusively, Portland cement, plaster, masonry cement,
or mortar cement and may also include limestone, hydrated lime, fly ash, granulated
blast furnace slag, pozzolans, silica fume, melakaolin, or other materials commonly
included in such cements) and water; mortars are pastes additionally including
fine aggregate (e.g., sand), and concretes are mortars that additionally including
coarse aggregate (e.g., crushed gravel, crushed stone). Cementitious compositions
can therefore be formed by mixing required amounts of certain materials, e.g.,
a hydratable cement, water, and optionally a fine aggregate (e.g., sand), coarse
aggregate (e.g., crushed stone or gravel), or mixture of both fine and coarse aggregates.
However, all of these hydratable cementitious compositions, which begin to hydrate
upon mixing of the water and cementitious binder, are comprehended within the term
"particle suspension."
Cementitious compositions may also include one or more cement additives
or processing aids, or one or more concrete admixtures. A cement additive or processing
aid is a chemical composition that is combined with cement clinker during intergrinding
in the manufacture of cement from clinker. An admixture, on the other hand, is
a material, other than cement, water, or aggregate, which is added generally to
modify one or more properties of the resultant mortar, masonry mortar, concrete,
or shotcrete. Accordingy, rheology devices of the invention may be used for mixing
and measuring the rheology of a cement composition alone (e.g., cement slurry,
paste, mortar, concrete, etc.), or a cement composition which additionally incorporates
one or more additives or admixtures. In particular, the rheomixer devices of the
invention are particularly suited for testing the effect of cement grinding (fineness),
or, as further examples, the effect on the cement slurry or paste rheology of water
reducers, superplasticizers, rheology modifiers, viscosity modifiers, air entrainers,
and other admixtures.
Thus, in exemplary methods of the invention, additives and admixtures may be
incorporated into the sample liquid being mixed and measured, such as by the use
of a pump and capillary (tube fed) dosing system. The additives or admixtures can
thus be mixed and their rheological effects tested without having to transfer the
sample liquid between a separate mixer and separate rheology tester.
The rheology device may also be used for mixing and measuring rheology of other
liquid samples such as latexes (e.g., paints), emulsions (e.g., wax, silicone,
latex), colloidal suspensions, grease and lubrication compositions, asphaltic or
bituminous compositions, adhesives, caulks, and other viscous fluids. A particularly
preferred method involves measuring the rheology of coatings (such as primers,
paints, mastics, adhesives, etc.) containing one or more types of particles (e.g.,
fillers such as sand, talc, clay, pigments, etc.). Paints, for example, are latexes
that may optionally include sand, clay, or other fillers.
As shown in FIG. 1, an exemplary device
10 for mixing and assessing the
rheology of a sample liquid comprises a rotatable shaft member
12 having
a generally elongate body; at least one (and more preferably more than one) propeller
blade
14 attached to the shaft member
12 and having a blade face
oriented to propel a viscous liquid sample (not shown) in a direction along the
elongate shaft body
12 when the shaft
12 is rotated within the liquid
sample; and at least one (and preferably more than one) elongate shear-resistant
member
18 for resisting circular motion when the shaft member
12
is rotated within the liquid sample.
The at least one shear-resistant member
18 is spaced at a fixed distance
from, and fixed in a rotational relationship with respect to, the at least one
propeller blade
14. The at least one shear-resistant member
18 is
also spaced apart from, and attached in fixed spatial relation with respect to,
the rotatable shaft member
12. The shear-resistant member(s)
18 may
be parallel or otherwise angled with respect to the rotatable shaft member
12,
while the propeller blade(s)
14 may be perpendicular or otherwise angled
with respect to the shaft member
12. Preferably, the rotational path of
shear-resistant members should not overlap or coincide with the rotational path
of propeller blades when the shaft is rotated about its axis.
In more preferred embodiments, the rotatable shaft member
12 has an elongate
and preferably cylindrical body with first and second opposing ends, and a connector
or collar member
30 located on the first (upper) end for connecting the
device
10 to a mixing and torque-resistance-measuring servo-controlled motor
or "servo-engine" (not illustrated) which is operative to rotate the shaft member
12 and provide a signal or indication of the resistance of the sample liquid
to rotation.
The rotatable shaft member
12 should preferably be as thin and rigid as
possible. If cylindrical in nature, the shaft
12 may be rotated about its
circumferential axis, or even slightly off-axis in order to minimize agglomeration
of particles or thickening of sample liquid on the shaft
12, although these
effects are probably negligible. It is possible to alter the surface of the rotatable
shaft member
12, such as by using elevated bumps, dimples, grooves, fish
scale textures, or any number of surface disruptions, so as to decrease drag of
liquid on the surface of the shaft, although any increase in accuracy due to the
use of these if also probably negligible.
An optional circular mounting flange
32 is also shown attached to the
collar
member
30 at the upper end of the shaft
12 and surrounding a female
receptacle
34 for coaxial attachment of the rheomixer
10 to a servo-controlled motor.
In preferred embodiments, a plurality of propeller blades
14 are located
at or near the bottom of the rotatable shaft
12 as shown in FIG.
1.
At least two, and more preferably four, blades
14 are preferably spaced
at equal distances circumferentially around the shaft member
12, and have
blade faces that are oriented preferably so as to push fluid in a direction upward
along the elongate body of the shaft
12, when the shaft is rotated (in clock-wise
fashion as suggested by the arrow). This bottom set of blades
14 are intended
as the primary means for mixing the sample liquid.
Preferably, a plurality of propeller blades
16 is also located
further upwards on the rotatable shaft
12 and spaced at equal distances
circumferentially around the shaft
12. These blades
16 are situated
such as to complement the mixing function of the primary blades
14, and
are shown oriented with their faces to push sample fluid in a downward direction,
when the shaft is rotated clock-wise, so as to disrupt the flow pattern of the
liquid at the bottom of the mix container.
Where one or more sets of propeller blades
14 and
16 are used
at different levels within the mix container, it is preferred that the primary
mixing blades
16 located at the bottom of the container have a cumulative
surface area (oriented in the upward pushing direction) that exceeds the cumulative
surface area (oriented in the downward pushing direction) of the other (higher
located) set or sets of blades (
14). Especially for particle suspensions,
in which particles tend to settle towards the bottom of the container, or migrate
towards the walls, it is best that the primary bottom mixing blades
16 have
the best chance of resisting the gravitation of particles downward. The other set
or sets of blades
14 function in a manner that is secondary in that, by
disrupting the flow patterns of the primary mixing blades
14, they ensure
that the flow energy is dispersed throughout the entire volume of sample liquid.
Accordingly, as shown by the exemplary embodiment in FIG. 1, the face
angles of the two blade sets
14/
16 are preferably oppositely oriented.
This will accomplish a "three dimensional" mixing of the fluid sample, whereby
the agglomeration of particles around the shaft and settling of particles due to
gravity are minimized. By mixing the fluid in "three dimensional" fashion, the
exemplary rheomixer
10 constantly chums fluid within the container to maintain
a relatively uniform dispersal of the particles.
Thus, a further exemplary device
10 of the present invention comprises
a plurality of propeller blades
14 attached near or at the bottom of a rotatable
shaft member
12; and a second plurality of propeller blades
16 attached
to the shaft member
12 at a different position higher up on the shaft member
12, wherein the face angle of propeller blades of said first set
14
are oriented in a direction different from the face angle of propeller blades of
the second set
16, and wherein the faces of the blades
14 located
near or at the bottom of the rotatable shaft member are oriented so as to push
fluid sample upwards when the rotatable shaft is rotated.
In some cases, it is preferable to have a small blade or tab located at the bottom
surface of the rotatable shaft
12, to ensure that sample fluid residing
between the bottom of the shaft and the floor of the mix container or cup is mixed
and dispersed within the volume of the sample fluid, and agglomeration is avoided.
Exemplary mixing devices
10 of the present invention, as shown in
FIG. 1, also comprise at least one shear-resistant member
18, and preferably
at least two or more such shear-resistant members
18 spaced evenly around
(or, in other words, equidistant circumferentially) the rotatable shaft member
12.
It is preferred that the shear-resistant members
18 be fixed spatially
with respect to both the propeller blades
14/
16 and shaft member
12. As shown in FIG. 1, the exemplary shear-resistant members
18
have a generally elongate body defined between opposite ends, and are preferably
attached to the shaft member
12 (or the collar
30 member shown in
FIG. 1) by brace members
20. Alternatively, the shear-resistant members
18 may be directly connected to the rotatable shaft
12 by braces
20. Preferably, the brace members
20 are situated higher than the
uppermost propeller blades
16 such that the brace members
20 do not
become immersed or substantially immersed in the fluid sample to be tested, and
do not substantially introduce turbulence into the sample fluid being mixed and
tested. The brace members
20 may assume generally any cross-sectional shape.
As further shown in FIG. 1, exemplary shear-resistant members
18 preferably
have a tapered vertical leading edge
18A and tapered trailing vertical edge
18B operative to reduce or avoid cavitation (or agglomeration or other phenomena
creating nonuniformity of viscosity) behind the shear-resistant member
18
when the device
10 is placed into a sample liquid and rotated. Preferably,
the elongate shear-resistant member or members
18 is/are spaced apart from
the shaft member
12 at a distance that exceeds the distance by which the
propeller blades
14 and
16 extend from the shaft
12. Thus,
it can be said that in such a preferred embodiment, the propeller blades
14
and
16 and shear-resistant members
18 have circular rotation paths
that do not substantially coincide or intersect when the rheometer
10 is rotated.
Moreover, when a plurality of shear-resistant members
18 is employed
(as shown in FIG.
1), it is preferred that they be attached to the rotatable
shaft
12 in such a way that each shear-resistant member
18 does not
travel precisely in the same orbital path as an immediately adjacent shear-resistant
member. The shear-resistant member
18 shown in the right foreground (whose
vertically extending edges are denoted "
18A" and "
18B") is shorter
than the shear-resistant members located immediately adjacent, and is spaced at
slightly greater distance from the rotatable shaft
12. In addition, the
brace connector
20 for this shorter shear-resistant member is also angled
differently from those shown to be connecting the two adjacent shear-resistant
members
18 as well.
The purpose of having the different lengths and different spacings of the shear-resistance
members
18 to minimize their cavitation effects (or agglomeration or particle
migration effects) caused by their passage through the sample fluid medium. Ideally,
at least two of the shear-resistance members should be spaced at different distances
from the shaft
12, with the shorter member being preferably located a greater
distance from the shaft. It is also preferred to position all shear-resistant members,
whether they be long or short, such that their bottom portion travels close to
the bottom of the container. The upper ends of the shear-resistant members are
ideally used to connect them, using a connector
20, to the shaft
12
or (optional) collar member
30. It is also preferable to use different angles
for positioning a connector
20, such that it does not have a rotational
orbit coinciding with an immediately adjacent connector.
In further preferred embodiments, a portion of the propeller blades
14
and shear-resistant members
18 are positioned out-of-phase (and thus not
aligned) with respect to each other, as shown in FIG. 1, to minimize further the
possibility of inaccuracies caused by the propeller blades
14 on the sample
fluid adjacent to circular pathways of the shear-resistant members
18 during
rotation. Accordingly, in preferred devices
10 of the invention, the propeller
blades
14 located bottommost on the shaft
12 comprise at least four
blades
14 that are not radially aligned out with the shear-resistant members
18.
The rheometer device
10 can be fabricated from materials such as metals
(e.g., steel), ceramics, plastics, resins, or other conventionally used materials.
As shown in FIG. 2, another exemplary rheomixer
10 of the invention comprises
the mixing/testing device
10 and mixing container
40 with optional
lid
42. This will provide partially adiabatic testing of rheology and heat
of hydration and other chemical reactions. The lid
42 contains an opening
for the rotatable shaft
12. For the sake of simplicity, two sets of mixing
propeller blades
14 and
16 are shown spaced apart vertically on and
connected to the shaft
12, as is an optional wiping element
15, which
can have a thin tab shape or other shape, for agitating liquid between the bottom
surface of the shaft
12 and the floor of the container
40, to prevent
agglomeration and facilitate uniform dispersion. Two shear-resistant members
18
are also shown having different lengths, preferably the shorter member is located
further away from the shaft
12, and both need not necessarily be disposed
parallel to the shaft but can be angled to conform with the slope of the container
walls, such as plastic coffee cups, to dead spots.
Shear-resistant members
18, incidently, can be connected to
the rotatable shaft using a connector shaped as a bar, as shown, or using any other
shapes (such as a circular disk or flat member.
As further illustrated in FIG. 2, an exemplary rheomixer
10 of the present
invention includes, a mixing container
40 and cover
42, which may
be a plastic coffee cup
40 and plastic lid
42, to provide for adiabatic
or partial-adiabatic testing of the sample liquids. A heat sensor
44 is
located within the mix container
40 for measuring heat output of the liquid
sample, and may otherwise be embedded with the walls or floor of the container
body. Electric wires from the heat sensor can be run through the container wall
(and sealed with tape) or lead out between the container rim and cover. The cover
42 has an opening for passage of the upper shaft
13 which is connected
to a servo-control motor
60. The container
40 and cover
42
may be made of various materials, such as insulative polystyrene foam, plastic,
metal, or other material. The use of plastic, for example, will make it easy to
provide holes for various uses, such as for passing heat sensor
44 wires
into the containers. Holes in the cover may also be used for introducing water,
admixtures, solids, or other materials into the liquid sample. The ability to make
the container
40 and cover
42 using inexpensive materials is advantageous
for mixing and testing of cementitious samples which can be discarded after the
mix hardens without economic hardship.
As mentioned above, the rheomixer
10/
40 shown in FIG. 2 can further
comprise the use of a heat sensor
44 (e.g., thermocouple, heat flow sensor,
infrared detector). The wire leads
46 from the heat sensor
44 (can
be taped against the inner wall of the mixing container
40, and can be accessed
by running them over the top edge of the container
40 and between the cover
42, or, by running them through the wall as illustrated (using tape which
is not illustrated). If the mixing container is a foamed polystyrene cup, the heat
sensor
44 can be physically embedded in the soft inner wall so that it presents
minimal impedance to flow of the sample liquids being mixed and measured. The wire
leads
46 are used for connecting the thermocouple to a computer processing
unit
48 which can also be used for electrically connecting the servo-motor
60 and controlling the mixing and rheological measurements of the sample
being mixed. A data logger
50 and memory
52 for containing information
such as reference temperature profiles are also electronically connected to the
computer processing unit
48.
Thus, the rheomixer device, as illustrated in FIG. 2, can be used as a self-contained
system for evaluating and predicting basic properties of a hydrating cementitious
mixture sample, and is well-suited for automation and high throughput testing.
For example, the rheomixer
10 can be used to mix the sample fluid, even
when starting from an initial mixture of water and dry powder materials, and can
measure rheology over a period of time and as a function of time, eliminating the
need to transfer the mixture from a mixer or blender to a separate rheology measurement
device. At the same time, it protects the mix sample from evaporation and thermal
fluctuations due to the outside environment, and ensures accurate rheology measurements
by periodic mixing in an automated fashion.
Then the heat evolution of the mix sample can be measured as a function of time,
typically 24 hours to several days. The heat evolution can be measured partially
adiabatically and/or isothermally using heat flow sensors
44 that are preferably
installed within the mix container
40, and optionally using a temperature
control device or system (e.g., heating coils, liquid bath) around the mix container
or built into the mix container to maintain a controlled temperature. Although
the sample can be transferred from the mix container
40 into an isothermal
calorimeter (which is kept at a desired, contant temperature), the sample may also
be measured semi-adiabatically using the heat sensor
44 installed within
the mix container
40. As the rheomixer
10 can be made relatively
inexpensively, it can be removed, washed, and reused, or it may be simply left
in the hydrating mix along with the heat sensor and (preferably insulated) mix
container at the end of testing.
The computer processing unit
48 and data logger
50 may employ software
that employs known relationships between rheological and calorimetric data to convert
output signals from the servo-motor
60 into flow and workability performance
characteristics of cementitious mixture samples before setting/curing of the mixture.
This information is useful for optimizing mixture proportions as well as type and
dosage amounts of chemical admixtures (e.g., water reducers, plasticizers, fluidiers,
set accelerators, set retarders, etc.) to reach a particular performance target.
The software may also employ known relationships to convert heat evolution data
to provide an indication of the degree to which the cementitous binder is hydrated.
Thus, for example, a computer monitor or printer may be connected to the computer
processing unit
48 or data logger
50 to provide visual indication,
in terms of a percentage number, or as a bar graph or other graphic or pictorial
means, of the degree of hydration of the cementitious binder. The degree of hydration
can further be used to compute initial and final setting of the cementitious binder,
as well as to provide an indication, such as in terms of a percentage number or
as a bar graph or other graphic or pictorial means, of strength development in
the sample mixture.
Accordingly, an exemplary method of the invention comprises providing
the aforementioned rheomixer
10 in a mixing container
40, such as
in a foamed polystyrene cup, with water, a hydratable cementitious binder, optionally
with aggregates and/or admixture(s), and mixing these components together to provide
a slurry. The rheology of the mixture is assessed using the rheomixer
10
immediately upon completion of this initial mixing event, and subsequently thereafter
at successive time periods. The rheological property of the sample mix may then
be recorded as a function of time, and thus the degree of hydration may be plotted
or displayed graphically as a function of time (e.g., first 60 minutes, 12 hours,
24 hours etc.). Simultaneously with these measurements, or apart from them, the
heat evolution of the mixed sample can also be measured as a function of time (e.g.,
one hour, 12 hours, 48 hours, 28 days, etc.). The rheological and calorimetric
measurements can be accomplished within the same mix container, without having
to transfer the sample from a separate mixer to a separate rheological measurement
device; or from a mixer or rheological measurement device to a separate calorimetric
measurement device.
Further exemplary methods of the invention comprise obtaining rheological
and calorimetric (e.g., heat evolution) data from a hydratable cementitious composition
over a period of time, using the device illustrated in FIG. 2, comparing the obtained
data with pre-established relationships or correlation's between theological data
and/or calorimetric data and properties of the cured cementitious composition (such
as strength, set time, etc.), and extrapolating one or more later properties of
the cured cementitious composition based on the rheological data and calorimetric
data obtained. In further exemplary methods, the relationship between the data
over time can be plotted as a function of hydration and/or strength over time,
and graphically displayed by the computer processing unit on graph paper or a monitor
screen connected to the computer processing unit.
The combination of a (1) mixer/rheology measurement device and a (2) mixing container
containing a heat sensor has not previously been taught or suggested in the prior
art. The use of a mixer/rheology measurement device is not limited to the one described
and illustrated herein. It is believed that other devices which operate to mix
a hydratable cementitious slurry from its separate components can be used to achieve
this aspect of the invention. Accordingly, a further exemplary device and method
of the invention involves this combination of (1) mixer/rheology measurement device
and a (2) mixing container containing a thermocouple, preferably with the container
providing an adiabatic or partially adiabatic environment (such as the case of
using a plastic coffee cup and cover or lid).
In still further exemplary embodiments of the invention, the mixing container
40 may be used in combination with structures operative to maintain the
sample fluid within the container at a constant temperature. For example, the hollow
wall structure can be evacuated of air in the manner of a vacuum, so that increased
accuracy might be achieved for calorimetric measurements, and the use of a vacuum
may also be employed for the container floor and cover. Alternatively, a fluid
can be pumped through the hollow wall structures at a constant temperature, in
order to maintain the sample fluid at a set temperature within the mix container.
In another exemplary embodiment, the mix container can be situated in a water bath
that can be either cooled or heated and maintained at a desired temperature. Further
exemplary methods comprise measuring the heat of the sample liquid over time, and
optionally the heat that has been added to the mix container over time, to obtain
a (net) calorimetric value corresponding to the heat of reaction.
In still further exemplary embodiments, the sample liquid may be pressurized
so
that the contained liquid sample may be tested under pressure. As mentioned in
the summary, this would be beneficial for testing sample liquids, such as well
drilling cements, which are customarily subjected to high pressure. Thus, exemplary
mix containers
40 and covers
42 of the present invention may be constructed
so as to become, sealed together so that air, oxygen, carbon dioxide, or inert
gases can be pumped into the mix container in order to elevate pressure upon the
sample liquid. One may optionally employ a seal around the rotatable shaft
12
of the rheometer
10 and calibrate the servo-motor device
60 to account
for frictional forces introduced by the seal. One may optionally employ a pressure
control
70 for maintaining a constant pressure in the container.
Accordingly, the present invention provides devices and methods for
mixing, rheological testing, and calorimetric testing, which can be done under
controllable temperature and pressure conditions without having to transfer fluid
between separate mixing, rheological, and calorimetric devices. Such integrated
operations may be automated on a high through put basis using computer processing units.
The invention is not intended to be limited by the foregoing examples and preferred
embodiments which are provided for illustrative purposes only.
*
