NfST

Nisr

National institute of Standards and Technology

Technology Administration, U.S. Department of Commerce

NIST Special Publication 946

Guide to Rheological Nomenclature:

Measurements in Ceramic Particulate

Systems

Vincent A. Hackley and Chiara F. Ferraris
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'At Boulder, CO 80303. ^Some elements at Boulder, CO.
NIST Special Publication 946

Guide to Rheological Nomenclature:

Measurements in Ceramic Particulate

Systems

Vincent A. Hackley

Ceramics Division

Materials Science and Engineering Laboratory

National Institute of Standards and Technology

Gaithersburg, MD 20899-8520

Chiara F. Ferraris

Building Materials Division

Building and Fire Research Laboratory

National Institute of Standards and Technology

Gaithersburg, MD 20899-8621

January 2001

U.S. DEPARTMENT OF COMMERCE

Norman Y. Mineta, Secretary

TECHNOLOGY ADMINISTRATION

Dr. Cheryl L. Shavers, Under Secretary of Commerce for Technology

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY

Karen H. Brown, Acting Director
National Institute of Standards and Technology Special Publication 945

Natl. Inst. Stand. Technol. Spec. Publ. 946, 31 pages (January 2001)

CODEN: NSPUE2

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 2001

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, DC 20402-9325
Guide to Rheological Nomenclature

Preface

Nomenclature is fundamentally important to the progress of science and technology. Because of

the rapidly growing volume of available technical information, and the speed with which this information must now be processed, it is critical to have a uniform terminology in place for describing experimental methods and instrumentation, to facilitate the exchange of material

property data and for sharing technical ideas and concepts. This is especially true for the ceramics

industry because of its breadth and interdisciplinary nature. The present document addresses the

issue of nomenclature for one important area of ceramic science: rheology and rheometric

measurements.

Ceramic suspensions, gels and pastes are the starting materials for a wide variety of applications,

playing critical roles in the processing of products ranging from whitewares to concrete to paint

and pigments to high-tech multilayer ceramic packages for the advanced electronics industry.

Unfortunately, researchers and engineers working in these diverse fields often speak different

languages, thus resulting in miscommunication and ambiguity. Even within the same field,

variations in terminology are common. The need for widely accepted, uniform and precise

nomenclature was emphasized recently by the Ceramic Processing Characterization Council^

(CPCC), a voluntary organization of participants representing industry, instrument companies,

academia and government. CPCC members identified nomenclature as a high priority issue in the areas of dispersion and rheology. In response to this need, we have initiated a series of guides to help in the interpretation of nomenclature and data relating to particle-liquid ceramic systems.

In compiling the present guide, we drew upon a number of sources, including books, review

articles and published terminologies. To the extent possible, an effort was made to maintain a degree of uniformity with existing standards and conventions. To this end, definitions are generally consistent with nomenclatures published by the American Concrete Institute (ACI), the

British Standards Institute (BSI), the International Union of Pure and Applied Chemistry

(lUPAC) and the Society of Rheology. A complete bibliography of sources is provided.

An international ad hoc committee was formed to review the technical content and language of

the nomenclature and to offer input where needed. The committee members represent a broad

spectrum of experts from industry, academia and government, and include (in alphabetical order)

Lennart Bergstrom (YKI), John Dealy (McGill University), Ed Garboczi (NIST), Bob Hunter

(University of Sydney), Kamal Khayat (University of Sherbrooke), FranQois de Larrard

(Laboratoire Central des Ponts et Chaussees), Makio Naito (JFCC), Celik Ozyildirim (Virginia

Transportation Research Council), Ponserril Somasundaran (Columbia University), and Abbas

Zaman (University of Florida). Their efforts are gratefully acknowledged.

It is our primary hope that this document will serve as a resource to those working in particle

systems applications, particularly in the ceramic sciences. It is our further hope that this document

will serve to promote the establishment of a commonly recognized system of terminology

throughout the ceramics community.

Formerly the Ceramic Processing Characterization Consortium

iii
Guide to Rheological Nomenclature

Table of Contents

PREFACE iii

1. INTRODUCTION 1

2. FUNDAMENTAL RHEOLOGICAL PROPERTIES 1

3. FUNCTIONAL FORMS OF VISCOSITY 2

4. GLOSSARY OF BASIC TERMINOLOGY 4

5. CLASSIFICATION OF EQUILIBRIUM FLOW CURVES 7

6. EXPRESSIONS FOR DESCRIBING STEADY SHEAR NON-NEWTONIAN FLOW 8

7. TIME-DEPENDENT EFFECTS 11

8. OSCILLATORY MEASUREMENTS 13

Material Functions Derived from Oscillatory Tests 1

3

9. MEASUREMENT APPARATUS 15

Capillary Methods 16

Rotational Methods 17

10. CONCRETE AND OTHER COARSE-GRAINED MATERIALS 19

Glossary of Rheological Terms 20

Glossary of Test Methods 2

1

1 1 . UNITS AND SYMBOLS 23

Rheometric Units 23

List of Symbols 24

BIBLIOGRAPHY 25

Primary Sources 25

Other Sources 26

ACKNOWLEDGMENTS 27

AD HOC REVIEW COMMITTEE 27

INDEX 29

iv
Guide to Rheological Nomenclature

GUIDE TO RHEOLOGICAL NOMENCLATURE FOR

LIQUID-BASED PARTICLE SYSTEMS

1. Introduction

Measurements and standards play an integral role in the manufacture and utilization of ceramic

powders, components, coatings and composites. They enhance reliability by providing a basis for quantifying and comparing material properties during each phase of the manufacturing process, from raw materials to the finished product. Equally important is the establishment of a uniform

and widely accepted nomenclature to permit the efficient exchange of scientific and technical

information, and to provide a sound basis on which to standardize measurement methods and data

reporting practices. This document represents the second^ in a series of guides intended to serve

the dual purpose of helping to establish a uniform system of terminology, geared towards the ceramics community, while also providing a convenient resource for the practicing engineer or

scientist.

This document provides definitions of terms and expressions relating to the measurement of

rheological properties in liquid-based ceramic particulate systems (i.e., suspensions, pastes and

gels). The term ceramic is here broadly defined as a non-metallic inorganic material. So, although

the focus is on ceramic applications, the definitions are largely generic in nature, and should be

compatible with many non-ceramic applications. Equations have been used sparingly, and only

where necessary for clarity or where they are integral to the subject at hand.

Besides having a glossary of basic terms, the guide is organized so that the reader can more

readily locate related terms associated with specific subject areas (e.g., concrete applications or

oscillatory measurements). Defined terms are indicated in bold face type. Where alternative or equivalent terms exist, they are shown in brackets adjacent to the preferred term. Terms used in definitions, and which are defined separately in the guide, are indicated in italic at their first appearance in that paragraph or section. The only exception to this rule is the term viscosity,

which is not italicized when it appears by itself, due to its ubiquity throughout the text. Furthermore, an alphabetized index to the defined terms is provided.

Descriptions of instrumentation provided in this guide are generic in nature, and are presented

solely for the purpose of identifying key measurement techniques and their associated

nomenclature.

2. Fundamental Rheological Properties

elastic A conservative property in which part of the mechanical energy used to produce

deformation is stored in the material and recovered on release of stress.

electroviscous The collective effects by which the presence of an electrical double-layer

influences the/Zow behavior of a liquid. The double-layer is usually associated with charged

^ see also Guide to the Nomenclature ofParticle Dispersion Technology for Ceramic Systems, NIST

Special Publication 945, February 2000.

1
Guide to Rheological Nomenclature

particles suspended in the liquid or polyelectrolytes dissolved in solution. There are three

electroviscous effects:

primary The increase of fluid viscosity due to distortion of the double-layer during shear.

Distortion exerts a drag, increasing energy dissipation.

secondary The increase of fluid viscosity due to the interaction or overlap of adjacent

double-layers. Responsible for the formation of gelatin.

tertiary The variation in fluid viscosity that arises from geometrical changes within the

fluid due to double-layer interactions. The viscosity of a polyelectrolyte solution depends on

the conformation of the molecules, which in turn is affected by intramolecular electrostatic

interactions between charged segments located along the polymer backbone or on side chains.

plastic The property of a solid body that is in the elastic state when the stress is below a critical value, termed the yield stress, and in the plastic state when this value is exceeded. During ideal

plastic flow, energy dissipation and stress are independent of the rate of deformation.

viscoelastic A time-dependent property in which a material under stress produces both a viscous

and an elastic response. A viscoelastic material will exhibit viscous flow under constant stress, but a portion of mechanical energy is conserved and recovered after stress is released. Often

associated with polymer solutions, melts and structured suspensions, viscoelastic properties are usually measured as responses to an instantaneously applied or removed constant stress or strain or a dynamic stress or strain.

viscoelectric An effect by which the electric field near a charged interface influences the

structure of the surrounding fluid and thereby modifies the viscosity of the fluid.

viscoplastic A hybrid property in which a material behaves like a solid below some critical stress value, the yield stress, but flows like a viscous liquid when this stress is exceeded. Often

associated with highly aggregated suspensions and polymer gels.

viscous The tendency of a liquid to resist flow as a result of internal friction. During viscous

flow, mechanical energy is dissipated as heat and the stress that develops depends on the rate of

deformation.

3. Functional Forms of Viscosity

Refer to Section 11 for a complete list of symbols used the following definitions. Some viscosity

terms relating to oscillatory measurements are defined both here and more explicitly in Section 8.

apparent viscosity, riapp The value of viscosity evaluated at some nominal average value of the

shear rate. The apparent viscosity applies, for instance, in the capillary method, where a range of

shear rates are employed.

coefficient of fluidity [fluidity], cj) Reciprocal of the coefficient of viscosity.

(j) = l/r)

2
Guide to Rheological Nomenclature

coefficient of viscosity [viscosity], ri The ratio of shear stress to shear rate under simple steady

shear. The abbreviated form "viscosity" is used most often in practice, and is frequently

employed without discriminating between Newtonian and non-Newtonian behavior. When the quotient is independent of shear rate (i.e., follows the Newtonian model), it is considered a

material constant. When the quotient is dependent on shear rate (i.e., non-Newtonian), it should

be referred to as the non-Newtonian viscosity.

Tl = a/Y

complex viscosity, r)* The frequency-dependent viscosity function determined dxmng forced

harmonic oscillation of shear stress; contains both real and imaginary parts.

differential viscosity, Tidiff The derivative of shear stress with respect to shear rate.

Tl,.ff = dd/dy

dynamic viscosity, r|' The ratio of the loss modulus to the angular frequency, determined during

forced harmonic oscillation (dynamic) measurements. The real part of the complex viscosity.

Tl' = G'/C0

infinite shear viscosity, r|<„ The high shear rate limiting value of viscosity. Often associated

with the second Newtonian region in pseudoplastic fluids.

inherent viscosity [logarithmic viscosity], r|inh A natural logarithmic function of the relative

viscosity reduced by the solute concentration.

Inri^

c

intrinsic viscosity [limiting viscosity number], [r\] The zero concentration limiting value of

the reduced specific viscosity. A characteristic function for the single molecule in solution. [r|] is equivalent to the effective hydrodynamic specific volume for the solute.

[Tl] = limTi^,,

c-»0

kinematic viscosity, v The ratio of the viscosity of a fluid to its density.

V=Tls/p

out-of-phase viscosity, r|" The ratio of the storage modulus to the angular frequency,

determined during forced harmonic oscillation (dynamic) measurements. The imaginary part of

the complex viscosity.

rj = G /o)

3
Guide to Rheological Nomenclature

plastic viscosity, ripi For a Bingham model, the excess of the shear stress over the yield stress divided by the shear rate, and equal to the differential viscosity. For non-ideal Bingham

materials, the differential viscosity determined in the high-shear limiting, linear portion of the

flow curve; associated with viscoplastic fluids.

r\ . = lim da/dy

reduced viscosity [viscosity number], r|red The ratio of any viscosity function to the

concentration, c, of the solute or particulate phase. By normalizing viscosity in this way,

concentration effects become more apparent. For instance, the reduced specific viscosity is:

^red=11sp/C

relative viscosity [viscosity ratio], r|r Ratio of the viscosity in a suspension or solution to the

viscosity of the suspending medium or solvent.

T1^=T1/Tls

specific viscosity, rjsp The relative viscosity minus unity.

zero shear viscosity, r|o The low shear rate limiting value of viscosity. Associated with the first Newtonian region in many pseudoplastic fluids.

Tlo = limri

Y-»0

4. Glossary of Basic Terminology

apparent yield stress For non-ideal viscoplastic materials, where the yield stress is indefinite, an apparent yield stress can be defined, for example, by extrapolation from the linear, high-shearrate portion of the flow curve to the stress axis, (see Bingham relation)

compliance The quotient of strain and stress (e.g., shear compliance). The reciprocal of

modulus.

deformation Movement of parts or particles of a material body relative to one another such that the continuity of the body is not destroyed, resulting in a change of shape or volume or both.

dilatant A property often associated with suspensions of irregularly shaped particles, in which

the liquid exhibits an increase in volume while being sheared. The term is also used in common

practice to mean shear-thickening, the increasing resistance to shear with increasing shear rate. It

is possible for either of these two effects to exist in the absence of the other.

dynamic equilibrium A state in which dynamic opposing forces just balance to obtain a quasiequilibrium condition. Dynamic equilibrium is achieved during steady shearflow when

4
Guide to Rheological Nomenclature

breakdown and rebuilding of structure occur at similar rates, and the viscosity is constant at a given shear rate.

dynamic [oscillatory] shear flow Condition under which stress and strain vary harmonically

with time during a rheometric experiment.

Einstein's law of viscosity Describes the relationship between the viscosity of a dilute

dispersion and the volume fraction of the dispersed particles. The relationship is derived with two

major assumptions, that the particles are solid spheres and that their concentration is very low. -^ = 1 + 2.50 + ....

where rjs is the viscosity of the suspending medium and (j) is the volume fraction. The factor 2.5 is known as the Einstein coefficient. To describe more concentrated dispersions, higher terms in the power series have been retained and analyzed with varying success.

equilibrium [steady state] flow Condition under which a constant stress or shear rate is maintained for a sufficient time to allow dynamic equilibrium to be achieved in a fluid containing

time-dependent structure. An equihbriumflow curve can be used to characterize the timeindependent flow properties of a material.

elastic modulus [modulus of elasticity] A modulus of a body that obeys Hooke's law.

flow Continuously increasing deformation of a material body under the action of finite forces. When the force is removed, if the strain does not eventually return to zero, then flow has

occurred.

flow curve A graphical representation of the behavior of flowing materials in which shear stress

is related to shear rate.

Hooke's law Provides that the quotient of stress and strain (i.e., the modulus) is a constant. A

body obeying Hooke's law cannot be viscoelastic nor does flow occur.

laminar flow Flow without turbulence.

modulus The quotient of stress and strain where the type of stress and strain is defined by the

type of deformation employed (e.g., shear modulus in shear deformation).

Navier-Stokes equations The equations of motion for a Newtonian fluid model describing the

balance between external forces (like gravity), the pressure force and the viscous force.

Newtonian Flow model of fluids in which a linear relationship exists between shear stress and

shear rate, where the coefficient of viscosity is the constant of proportionality.

no-slip Condition in which fluid adjacent to a surface moves with the velocity of that surface. The assumption of no-slip is key to most rheometric measurements, especially those involving

rotational devices. Slippage is a significant concern in concentrated suspensions.

5
Guide to Rheological Nomenclature

non-equilibrium flow Condition under which shear is varied at a rate that does not permit

dynamic equilibrium to be achieved. A thixotropic loop is the result of non-equilibrium flow

conditions during shear cycling.

non-Newtonian Any laminarflow that is not characterized by a linear relationship between

shear stress and shear rate.

normal stress, On The component of stress that acts in a direction normal to the plane of shear.

Peclet number, Pe A dimensionless group used to compare the effect of appHed shear with the

effect of thermal (Brownian) motion; Pe=P'y I Dj, where r is the particle radius and is the

translational diffusion coefficient. For Pe « 1, particle behavior is dominated by diffusional

relaxation, whereas for Pe»l, hydrodynamic effects dominate.

Poiseuille flow Laminarflow in a pipe of circular cross section under a constant pressure

gradient, (see also Capillary Methods)

Reynolds number. Re A dimensionless group that expresses the ratio of the inertial forces to the viscous forces; Re=Dvp/r\, where D is a characteristic dimension (e.g., particle size or pipe

diameter), v is a typical fluid speed, and ri/p is the kinematic viscosity of the fluid. The transition

from laminar to turbulent flow is characterized by high Re values.

rheology The science of the deformation and flow of matter.

rheometric Refers to the measurement of rheological properties.

shear The relative movement of parallel adjacent layers.

shear compliance, / The ratio of shear strain to its corresponding shear stress. The reciprocal

of shear modulus.

shear modulus [modulus of rigidity], G The ratio of shear stress to its corresponding shear

strain. The reciprocal of shear compliance.

shear rate [rate of shear strain], f The rate of change of shear strain with time (dy/dt). For

liquids, the shear rate, rather than strain, is generally used in describing yZow.

shear stress, a The component of stress that causes successive parallel layers of a material body

to move, in their own planes (i.e., the plane of shear), relative to each other.

shear strain, y The relative in-plane displacement, Ax,

of two parallel layers in a material body divided by their separation distance, y. Alternatively, the shear strain can be defined as tan 0, where 9 is the angle of deformation

as shown in Figure 1

.

shear-thickening An increase in viscosity with

increasing shear rate during steady shearflow. The term

dilatant is commonly used in practice to indicate shearthickening, although this usage is strictly incorrect.

6
Guide to Rheological Nomenclature

shear-thinning [pseudoplastic] A decrease in viscosity with increasing shear rate during

steady shearflow.

simple shear In simple shear there is no change in the dimension normal to the plane of shear,

and the relative displacement of successive parallel layers of a material body are proportional to their distance from a reference layer. The type offlow used in most rheometric measurements on

fluids can be approximated by simple shear.

steady shear flow Condition under which a fluid is sheared continuously in one direction during

the duration of a rheometric experiment.

stress Force per unit area.

structure In rheology, structure is a term that refers to the formation of stable physical bonds

between particles (or chemical bonds between macromolecules) in a fluid. These bonds result in aggregate, floe, or network structure, which impacts the rheological behavior of the fluid and

provides elastic and plastic properties. The term may be extended to include structural effects caused by electroviscous interactions, physical bonds between polymers (e.g., associative

thickeners), shear-induced alignment of anisotropic particles, and radial distribution correlations

in concentrated suspensions. Often, the term "structure" is invoked when little is known about the cause of observed changes in rheological properties.

Weissenberg effect The tendency of some viscoelastic fluids ioflow in a direction normal to the

direction of shear. The effect is manifested by behavior such as the climbing of a fluid up a

rotating rod.

Weissenberg number, Wi A measure of the degree of nonlinearity or the degree to which

normal stress differences are exhibited in a flow. For steady, simple shear, the Weissenberg

number is the product of the shear rate and a characteristic time of the fluid. In oscillatory shear

it is the product of the shear rate amplitude and the characteristic time of the fluid. In converging

flows it is proportional to the Deborah number.

yield response For non-ideal viscoplastic materials, the yield stress can be indefinite and

yielding may occur continuously over a narrow range of stress values. In this case, the behavior

may be more properly termed a yield response.

yield stress, Oy A critical shear stress value below which an ideal plastic or viscoplastic material

behaves like a solid (i.e., will not flow). Once the yield stress is exceeded, a plastic material

yields (deforms plastically) while a viscoplastic material flows like a liquid.

5. Classification of Equilibrium Flow Curves

Steady-shear flow curves for suspensions and solutions measured under equilibrium conditions

may exhibit a variety of behaviors over a limited range of shear rates. Additionally, some

materials may exhibit more than one distinct behavior over different shear rate regions of the same flow curve. Several types of behavior can be classified according to their characteristic

shape. The following classification system covers the six most frequently encountered /Zow types

as illustrated in the accompanying graph (Figure 2).

7
Guide to Rheological Nomenclature

1 . Newtonian Differential viscosity and coefficient of viscosity are constant with shear rate.

2. shear-thickening Differential viscosity and coefficient of viscosity increase continuously with

shear rate.

3. shear-thinning

[pseudoplastic] Differential

viscosity and coefficient of

viscosity decrease

continuously with shear rate. No yield value.

4. shear thinning

[pseudoplastic] with yield

response Differential

viscosity and coefficient of

viscosity decrease

continuously with shear rate once the apparent yield stress,

Oapp, has been exceeded.

5. Bingham plastic (ideal)

Obeys the Bingham relation

ideally. Above the Bingham

yield stress (Ob in Figure 2)

the differential viscosity is constant and is called the

plastic viscosity, while the

coefficient of viscosity

decreases continuously to some limiting value at infinite shear rate.

6. Bingham plastic (non-ideal) Above the apparent yield stress the coefficient of viscosity

decreases continuously, while the differential viscosity approaches a constant value with

increasing shear rate. Extrapolation of the flow curve from the linear, high shear rate region

(plastic region) to the stress axis gives the apparent Bingham yield stress (Ob* in Figure 2). The

differential viscosity in the linear region is termed the plastic viscosity.

6. Expressions for Describing Steady Shear NonNewtonian Flow

The expressions shown in this section are used to characterize the non-Newtonian behavior of

fluids under equilibrium, steady shear flow conditions. Many phenomenological and empirical

models have been reported in the literature. Only those having a direct and significant implication

for suspensions, gels and pastes have been included here. A brief description of each relationship

is given, sometimes with examples of the types of materials to which it is typically applied. In defining the number of parameters associated with a particular model, the term "parameter" in

shear rate

Figure 2 Identification of flow curves based on their

characteristic shape.

8
Guide to Rheological Nomenclature

this case refers to adjustable (arbitrary) constants, and therefore excludes measured quantities.

Some of these equations have alternative representations other than the one shown. More detailed

descriptions and alternative expressions can be found in the sources listed in the bibliography.

Bingham

Y = 0 for a < Gg

The Bingham relation is a two parameter model used for describing viscoplastic fluids exhibiting a yield response. The ideal Bingham material is an elastic solid at low shear stress values and a Newtonian fluid above a critical value called the Bingham yield stress, Ob. The plastic viscosity

region exhibits a linear relationship between shear stress and shear rate, with a constant

differential viscosity equal to the plastic viscosity, r|pi.

CarreaU'Yasuda

Tlo-11=

A model that describes pseudoplastic flow with asymptotic viscosities at zero (r|o) and infinite

(t)oo) shear rates, and with no yield stress. The parameter X is a constant with units of time, where

1/X is the critical shear rate at which viscosity begins to decrease. The power-law slope is (n-l)

and the parameter a represents the width of the transition region between r|o and the power-law

region. If r|o and r|oo are not known independently from experiment, these quantities may be

treated as additional adjustable parameters.

Casson

•1/2 ^1/2 , ^1/2 -1/2 ^ =^y +11pl Y

Y = 0 for a < Qy

A two parameter model for describing flow behavior in viscoplastic fluids exhibiting a yield

response. The parameter Oy is the yield stress and r)pi is the differential high shear (plastic)

viscosity. This equation is of the same form as the Bingham relation, such that the exponent is Va for a Casson plastic and 1 for a Bingham plastic.

Cross

T1-r|^ 1

9
Guide to Rheological Nomenclature

Similar in form to the Carreau-Yasuda relation, this model describes pseudoplastic flow with

asymptotic viscosities at zero (r|o) and infinite (r|„c) shear rates, and no yield stress. The

parameter A is a constant with units of time, and m is a dimensionless constant with a typical

range from % to 1 . If r|o and r|„„ are not known independently from experiment, these quantities

may be treated as additional adjustable parameters.

Ellis

1 +

,a-l

A two parameter model, written in terms of shear stress, used to represent a pseudoplastic

material exhibiting a power-law relationship between shear stress and shear rate, with a low

shear rate asymptotic viscosity. The parameter oi can be roughly identified as the shear stress value at which r| has fallen to half its final asymptotic value.

Herschel-Bulkley

A three parameter model used to describe viscoplastic materials exhibiting a yield response with a power-law relationship between shear stress and shear rate above the yield stress, Oy. A plot of

log (o - Oy) versus log y gives a slope n that differs from unity. The Herschel-Bulkley relation

reduces to the equation for a Bingham plastic when n=l.

Krieger-Dougherty

A model for describing the effect of particle self-crowding on suspension viscosity, where $ is the particle volume fraction, is a parameter representing the maximum packing fraction and

[ri] is the intrinsic viscosity. For ideal spherical particles [ri]=2.5 (i.e., the Einstein coefficient).

Non-spherical or highly charged particles will exhibit values for [r|] exceeding 2.5. The value of

[ri] is also affected by the particle size distribution. The parameter 3>m is a function of particle

shape, particle size distribution and shear rate. Both [r|] and $m may be treated as adjustable

model parameters.

The aggregate volume fraction (representing the effective volume occupied by particle

aggregates, including entrapped fluid) can be determined using this equation if <I>m is fixed at a reasonable value (e.g., 0.64 for random close packing or 0.74 for hexagonal close packing) and

10
Guide to Rheological Nomenclature

[r|] is set to 2.5. In this case, O is the adjustable parameter and is equivalent to the aggregate

volume fraction.

Meter

ll0-11c

1 + {g/oJa-l

Expressed in terms of shear stress, this relation is used to represent a pseudoplastic material

exhibiting a power-law relationship between shear stress and shear rate, with both high {r\„) and

low (t]o) shear rate asymptotic viscosity limits. The parameter 02 can be roughly identified as the shear stress value at which r| has fallen to half its final asymptotic value. The Meter and CarreauYasuda models give equivalent representations in terms of shear stress and shear rate, respectively. If r|o and r\o. are not known independently from experiment, these quantities may be

treated as additional adjustable parameters.

Powell-Eyring

(

X sinh"'(TY)

xy

Derived from the theory of rate processes, this relation is relevant primarily to molecular fluids,

but can be used in some cases to describe the viscous behavior of polymer solutions and

viscoelastic suspensions over a wide range of shear rates. Here, is the infinite shear viscosity,

r|o is the zero shear viscosity and the fitting parameter t represents a characteristic time of the

measured system. If rio and rioo are not known independently from experiment, these quantities

may be treated as additional adjustable parameters.

power-law [Ostwald-de Waele]

A two parameter model for describing pseudoplastic or shear-thickening behavior in materials

that show a negligible yield response and a varying differential viscosity. A log-log plot of a

versus y gives a slope n (the power-law exponent), where n<l indicates pseudoplastic behavior

and n>l indicates shear-thickening behavior.

7. Time-Dependent Effects

Time-dependence includes those effects associated with transient flow conditions as well as those

effects associated with irreversible changes that result from shear history.

11
Guide to Rheological Nomenclature

creep The response of a material to the instantaneous application of a constant stress.

creep function In an applied stress test, where an instantaneous and constant stress is applied to a material while the shear rate (or shear strain) is measured over time, the shear rate (or strain) vs. time function is termed the creep function. The function J{t)=y{t)/o is referred to as the creep

compliance.

Deborah number, De The ratio of a characteristic relaxation time of a material to the duration

of the observation. In equilibrium flow, the effective duration of the experiment is infinity, and

De=0. In oscillatory shear, it is the product of the frequency and the relaxation time of the fluid. In converging flows, the Deborah number is proportional to the Weissenberg number.

flow hysteresis A condition resulting from differences in the rate of energy dissipation due to shear history. In a typical rheometric test, shear stress or shear rate is ramped at a fixed speed up

to a maximum value, then ramped back down at the same speed to the beginning. In hysteresis, one flow curve lies above the other, forming a continuous loop whose internal area depends on

the shear and thermal history of the material, and on how rapidly the stress or shear rate was

ramped. If the down-curve lies below the up-curve, then it is referred to as a thixotropic loop,

whereas if the down-curve lies above the up-curve, then it is called a negative thixotropic loop.

negative thixotropy [anti-thixotropy] A reversible time-dependent increase in viscosity at a

particular shear rate. Shearing causes a gradual buildup of structure over time.

relaxation time, x A time characterizing the response of a viscoelastic material to the

instantaneous application of a constant strain.

retardation time, x A time characterizing the response of a viscoelastic material to the

instantaneous application of a constant stress.

rheomalaxis An irreversible decrease of viscosity during shearing. Attributed to permanent

changes in the material structure.

rheopexy An effect by which a material recovers some of its pre-sheared viscosity at a faster rate when it is gently sheared compared to when it is allowed to stand. Not to be confused with

negative thixotropy.

stress growth When an instantaneous and constant strain (or shear rate) is applied to a material

while stress is measured over time, an increasing stress vs. time or modulus vs. time function is termed stress growth.

stress relaxation When an instantaneous and constant strain (or shear rate) is applied to a

material while stress is measured over time, a decreasing stress vs. time or modulus vs. time

function is termed stress relaxation.

thixotropy A reversible time-dependent decrease in viscosity at a particular shear rate. . Shearing causes a gradual breakdown in structure over time.

12
Guide to Rheological Nomenclature

8. Oscillatory Measurements

Forced harmonic oscillation is a dynamic rheometric test in which both stress and strain vary

harmonically with time, and both viscous and elastic parameters are derived from the material response. Such tests are almost always carried out in the linear viscoelastic regime, which is characterized by a linear response of dynamic viscosity and elasticity with increasing strain

amplitude.

Material Functions Derived from Oscillatory Tests

In a typical sinusoidal oscillation experiment, the applied stress and resulting strain wave forms

can be described as follows:

a = Qq cos cot

Y = Yo cos (cot - 5)

where Oo is the stress amplitude

Yo is the strain amplitude

(x>=2nfis the angular frequency

t is time

6 is the phase lag [loss angle]

The phase lag and amplitude ratio (oc/Yo) will generally vary with frequency, but are considered

material properties under linear viscoelastic conditions. For an ideal solid, 6=0°, and the response

is purely elastic, whereas for a Newtonian fluid yielding a purely viscous response, 5=90°.

The material functions can be described in terms of complex variables having both real and

imaginary parts. Thus, using the relationship:

13
Guide to Rheological Nomenclature

cos X + j sinx = e-'" where j - V-T

Then the stress and strain can be expressed as follows:

a = 9^(aoej"')

where (kq^^^) is termed the complex strain amplitude. The shear storage modulus [or

storage modulus, for short], which represents the in-phase (elastic) component of oscillatory

flow, is defined as:

G' = storage modulus = cos 5

*

The out-of-phase (viscous) component is termed the shear loss modulus [or loss modulus, for

short]:

G" = loss modulus = —^sinS

Yo

The complex shear modulus, G*, is then defined as follows:

complex stress amplitude o f^n • • c- G* = = —^coso + —^jsm 0

complex strain amplitude Yq Yo

so that:

G* = G' + jG'

Tan 5 = G'/G'

G"

Figure 4 Vectorial representation

of moduli.

The function G'/G' measures the relative importance of viscous to elastic contributions for a

material at a given frequency.

Additionally, a complex viscosity, X]*, can be defined using the complex strain rate, j = }(}yY ^ such that:

^ _ complex stress amplitude _ Oq js _ q */

complex strain rate amplitude JYoCO /

14
Guide to Rheological Nomenclature

or alternatively

ri* = n' + jri'

^'=°/«

where r|' is termed the dynamic viscosity, and is equivalent to the ratio of the stress in phase with

the rate of strain (oq sin 6) to the amplitude of the rate of strain (coyo)- The term T)" is referred to as the out-of-phase viscosity, and is equivalent to the ratio of the stress 90° out of phase with the

rate of strain (oo cos 6) to the ampUtude of the rate of strain (coyo) in the forced oscillation.

Finally, an absolute shear modulus is defined as the ratio of the amplitude of the stress to the

amplitude of the strain in forced oscillation {simple shear), or:

|G*| = -^ = (G''+C)'/'

Yo

Alternatively, forced oscillation experiments can be equivalently described in terms of

compliance, as opposed to the derivation above based on the modulus. Similar arguments lead to the following analogous terms:

complex shear compliance, /* The ratio of the complex strain (y*) to complex stress (o*) in forced oscillation (simple shear).

shear storage compliance, /' The ratio of the amplitude of the strain in phase with the stress (yo cos 6) to the ampUtude of the stress (oq) in forced oscillation (simple shear).

shear loss compliance, J" The ratio of the amplitude of the strain 90° out of phase with the

stress (Yo sin 6) to the amplitude of the stress (oq) in forced oscillation (simple shear).

absolute shear compliance, |7*| The ratio of the amplitude of the strain (yo) to the amplitude of

the stress (oq) in forced oscillation (simple shear).

9. Measurement Apparatus

There are two common methods used for rheometric measurements on fluid systems: capillary

(or tube) and rotational. In this section, a brief summary is given for each general method along

with descriptions of common measurement devices and geometries. Measurement devices can be

grouped into one of two general classifications. A viscometer is a device used principally for the measurement of viscosity, while a rheometer is a device used for the measurement of rheological

properties over a varied and extended range of conditions. Only brief descriptions of these

instruments and devices are provided here. For more detailed descriptions, refer to the primary

sources listed in the bibliography.

15
Guide to Rheological Nomenclature

Capillary Methods

In capillary methods the test fluid is made to flow through a narrow tube as a result of hydrostatic or applied pressure. Capillary measurements are considered the most precise way of determining

the viscosity of Newtonian and some non-Newtonian fluids, and are generally simpler in design

and less expensive relative to rotational instruments. Poiseuille's Law, which relates the rate of

flow through a capillary to the viscosity of the liquid, is the basis for the capillary method.

Glass Capillary Viscometer

Widely used for measuring the viscosity of Newtonian

fluids, including dilute solutions and suspensions, the

glass capillary viscometer is the simplest and least expensive viscometric system available commercially.

Typically, in this technique, the time required for a given

volume of fluid to flow through a defined length, L, of

glass capillary under its own hydrostatic head is measured. The flow time, r, is related to the viscosity

using a simple relationship derived from Poiseuille's law,

of the form:

— = At + —

P t

where A and B are instrument constants. The second

term on the right hand side is related to a kinetic energy

correction, and can be ignored for long flow times. In

this case, a simple linear equation results. The viscometer can be easily calibrated using a standard fluid with

known viscosity at the measurement temperature.

Capillaries with different diameters can be used for

different viscosity ranges, while maintaining reasonable

flow times.

Figure 5 Ostwald type

capillary viscometer. A and B

are timing marks, C is a filling

mark.

Extrusion Capillary Viscometer

These instruments are widely used for measuring viscous fluids, such as asphalt cements, polymer

melts, and stable concentrated suspensions. Extrusion viscometers have the advantage of high

precision and simple design, and are less subject to temperature effects that can occur during

shearing of highly viscous fluids in rotational devices.

Extrusion viscometers use a cylindrical piston to force the test fluid from a reservoir through the

capillary tube at a constant velocity. By measuring the pressure drop across the capillary as a function of flow rate for multiple capillaries of the same diameter, d, but differing length, L, it is possible to determine the viscosity as a function of shear rate (see for example Figure 6).

16
Guide to Rheological Nomenclature

Rotational Methods

In rotational methods the test fluid is continuously sheared between two surfaces, one or both of

which are rotating. These devices have the advantage of being able to shear the sample for an

unlimited period of time, permitting transient behavior to be monitored or an equilibrium state to be achieved, under controlled rheometric conditions. Rotational methods can also incorporate

oscillatory and normal stress tests for characterizing the viscoelastic properties of samples. In general, rotational methods are better suited for the measurement of concentrated suspensions,

gels and pastes, but are generally less precise as compared to capillary methods.

Rotational measurements fall into one of two categories: stress-controlled or rate-controlled. In stress-controlled measurements, a constant torque is applied to the measuring tool in order to generate rotation, and the resulting rotation speed is then determined. If a well-defined tool geometry is used, the rotation speed can be converted into a corresponding shear rate. In rate- controlled measurements, a constant rotation speed is maintained and the resulting torque generated by the

sample is determined using a suitable stress-sensing

device, such as a torsion spring or strain gauge. Some

commercial instruments have the capability of operating

in either stress-controlled or rate-controlled modes.

torsion

spring

Simple Rotational Viscometer [Brookfield

type]

The least expensive commercial variant of the controlledrate rotational viscometer is commonly referred to as a "Brookfield type" viscometer^ This device measures fluid

viscosity at fixed rotation speeds by driving a measurement tool ("spindle"), immersed in the test fluid,

through a calibrated torsion spring (see Figure 7). Viscous

drag of the fluid against the spindle causes the spring to deflect, and this deflection is correlated with torque. The

calculated shear rate depends on the rotation speed, the

tool geometry and the size and shape of the sample

Figure 7 Schematic diagram

of a Brool<field-type

viscometer.

^ Certain trade names and company products are mentioned in the text or identified in illustrations in order

to specify adequately the experimental procedure and equipment used. In no case does such identification imply recommendation or endorsement by Nadonal Institute of Standards and Technology, nor does it imply that the products are necessarily the best available for the purpose.

17
Guide to Rheological Nomenclature

container. Conversion factors are needed to calculate viscosity from the measured torque, and are

typically pre-calibrated for specific tool and container geometries. For Newtonian fluids the torque is proportional to the product of viscosity and rotational speed, but this proportionality is lost in the case of a non-Newtonian fluid. Because these instruments are robust and fairly simple

to use, they have found wide application in industry, but they offer limited capabiHties and

precision for research-oriented applications.

Rotational Rheometer

High-precision, continuously-variable-^/jear instruments in which the test fluid is sheared

between rotating cylinders, cones, or plates, under controlled-stress or controlled-rate conditions,

are termed rotational rheometers. Instruments producing oscillatory strains are available, and a few commercial systems permit measurement of the normal stress. The basic rotational system

consists of four parts: (i) a measurement tool with a well-defmed geometry, (ii) a device to apply

a constant torque or rotation speed to the tool over a wide range of shear stress or shear rate values, (iii) a device to determine the stress or shear rate response, and (iv) some means of

temperature control for the test fluid and tool. Depending on the design specifications, rheometers

may also include built-in corrections or compensations for inertia, drift, and temperature

fluctuations during measurement.

Most rheometers are based on the relative rotation about a common axis of one of three tool geometries: concentric cylinder, cone and plate, or parallel plates (See Figure 8).

3

W/MMMMM^^MA WMM/My/MMMM

(a) (b) (c)

Figure 8 Schematic diagram of basic tool geometries for the rotational

rheometer: (a) concentric cylinder, (b) cone and plate, (c) parallel plate.

In the concentric cylinder (also called Couette or Coaxial) geometry, either the inner, outer, or both cylinders may rotate, depending on instrument design. The test fluid is maintained in the

annulus between the cylinder surfaces. This tool geometry comes in several configurations, of

which the three most commonly encountered are illustrated in Figure 9. The double-gap

configuration is useful for low viscosity fluids, as it increases the total area, and therefore the

viscous drag, on the rotating inner cylinder, and generally increases the accuracy of the

measurement. The cone and hollow cavity configurations are specifically designed to reduce or account for end effects. In addition, to prevent slippage (see no-slip), the inner cylinder surface is sometimes serrated or otherwise roughened. The concentric cylinder geometry is typically used

for the analysis of fluid suspensions.

18
Guide to Rheological Nomenclature

3

V//>///>///////////?M//}'M U//^//////////y//M/////yM V//>/////////y'/////////MM

(a) (b) (c)

Figure 9 Schematic diagram sliowing tliree alternative

cylindrical tool designs in cut-away view: (a) double gap,

(b) cone and plate at the bottom, (c) hollow cavity at the

bottom to trap air.

The cone and plate geometry consists of an inverted cone in near contact witli a lower plate. The

cone is usually designed with an angle of less than 4°. Either the upper or lower surface may

rotate depending on instrument design. The parallel plate geometry can be considered a

simplified version of the cone and plate, having an angle of 0°. The test fluid is constrained in the narrow gap between the two surfaces. Cone and plate and parallel plate measurement tools are most often used for highly viscous pastes, gels, and concentrated suspensions.

10. Concrete and Other Coarse-Grained Materials

Ceramic materials are typically fabricated from particles in the subsieve or fine size range (i.e., less than roughly 37 jam), though coarse agglomerates may play a role during some phase of

processing. On the other hand, concrete is classified as a ceramic material, but containing a considerably broader range of particle sizes, from less than one micrometer up to about 20 mm

(i.e., well into the sieve range). This wide size range results from the heterogeneous concrete composition, which includes cement (5 )im to 60 |um), mineral fillers (< 1 |Lim to 100 |Lim), fine

aggregates (0.1 mm to 5 mm) and coarse aggregates (4 mm to 30 mm or higher in some special

concretes) or stones.

As a result of the broad range of particle sizes and the presence of sieve-size particles, methods to measure the flow properties of concrete differ significantly from those methods specified for applications involving suspensions of fine particles. Test methods applied to concrete tend to be

largely empirical in nature or they are scaled up versions of the techniques described in the

previous section for fine particle systems. In the former case are the most commonly used tests in the industry; they generally represent an attempt to "imitate" a mode of placement or flow of the concrete during production. In the latter case are less common methods that attempt to measure

fundamental rheological properties of concrete. In addition, rheological test methods for concrete tend to fall into one of four general categories:

confined flow The material flows under its own weight or under an applied pressure through a narrow orifice. The orifice is defined as an opening roughly three to five times larger than the

19
Guide to Rheological Nomenclature

maximum particle size. Because coarse aggregates are often on the order of 30 mm in size, the

orifice must typically be 90 mm to 150 mm in diameter. Confined flow methods include /Zow

cone, filling ability devices, flow test through an opening and the Orimet apparatus.

free flow The material either flows under its own weight, without any confinement, or an object

penetrates the material by gravitational settling. Free flow methods include slump, modified

slump, penetrating rod and turning tube viscometer.

vibration The material flows under the influence of applied vibration. The vibration is applied

by using a vibrating table (e.g., Ve-Be time), dropping the base supporting the material {DIN

slump cone test), an external vibrator (e.g., LCL apparatus) or an internal vibrator (e.g., settling

method).

rotational rheometers The material is sheared between two parallel surfaces, one or both of

which are rotating. These tests are analogous to rheometers described in the previous section,

except in this case the gap between surfaces must be scaled up to reflect the much larger

dimensions of the concrete particles. Rotational rheometers include BTRHEOM, CEMAGREF,

two-point or Tattersall, IBB, and BML.

Separate glossaries of rheological terms and test methods are provided below. For more detailed

summaries of the numerous rheological tests used throughout the concrete industry, including

empirical tests that are widely implemented, see Ferraris (1999) in the list of primary sources.

Glossary of Rheological Terms

Much of the rheological work on concrete and other cementitious materials has, historically, been

directed toward the practical exploitation of the material and, as a result, numerous terms are in common use that are unique to the concrete, mortar and cement industries. The most frequently

encountered rheological terms are defined here.

consistency The relative mobility or ability of freshly mixed concrete or mortar to flow; the

usual measurements are slump for concrete, flow for mortar or grout, and penetration resistance

for neat cement paste, (see also normal consistency, plastic consistency, and wettest stable

consistency)

consistency factor A measure of grout fluidity, roughly analogous to viscosity, that describes

the ease with which grout may be pumped into pores or fissures; usually a laboratory

measurement in which consistency is reported in degrees of rotation of a torque viscometer in a specimen of grout.

consolidation The process of inducing a closer arrangement of the solid particles in freshly

mixed concrete or mortar, during and after placement until setting, by the reduction of voids.

Consolidation is accomplished by vibration, centrifugation, rodding, tamping or some

combination of these actions. This term is also applicable to similar manipulation of other

cementitious mixtures, soils, aggregates or the like.

flnishing Leveling, smoothing, consolidating and otherwise treating the surfaces of fresh or

recently placed concrete or mortar to produce the desired appearance and service.

20
Guide to Rheological Nomenclature

impending slough Consistency of a shotcrete mixture containing the maximum amount of water

such that the product will not flow or sag after placement.

mobility The ability of fresh mixed concrete or mortar to flow.

normal consistency (1) The degree of wetness exhibited by a freshly mixed concrete, mortar, or

neat cement grout when the workability of the mixture is considered acceptable for the purpose at hand. (2) The physical condition of neat cement paste as determined with the Vicat apparatus in accordance with a standard test method (e.g., ASTM C 187).

plastic consistency Condition of freshly mixed cement paste, mortar or concrete such that deformation will be sustained continuously in any direction without rupture.

slump A measure of consistency of freshly mixed concrete, mortar or stucco equal to the

subsidence measured to the nearest 5 mm (1/4 in) of the molded specimen after removal of the

slump cone.

wettest stable consistency The condition of maximum water content at which cement grout and

mortar will adhere to a vertical surface without sloughing.

workability [placeability] That property of freshly mixed concrete or mortar that determines

the ease and homogeneity with which it can be mixed, placed, consolidated and finished.

Glossary of Test Methods

BML Commercial rotational rheometer derived from the two-point test. The principle of

operation is identical to the two-point test, but the shape of the vane has been modified. The vane

is as shown in Figure 10(c).

BTRHEOM Commercial parallel plate concrete rheometer. Measurements can be performed

with and without applied vibration.

CEMAGREF Coaxial rotational rheometer originally developed for testing fluid lava. It has

been occasionally employed to test concrete. Only one prototype currently exists.

DIN slump cone test A vibration method. A variation of the slump cone test in which the cone

is placed on a metal sheet. After filling the cone with concrete, it is lifted and the metal support

sheet is raised on one side and dropped from a pre-established height (usually about 100 mm) a

specified number of times. The spread of the concrete is measured. This standard test is described

in DIN 1045.

filing ability Confinedflow method measuring the ability of concrete to flow into a predefined

form. Several different molds are used: U-shaped and L-shaped are the most common. In both

cases the concrete is forced by gravity to flow into and fill the mold. The volume occupied by the concrete at the end of the test is a measure of the ability of the concrete to flow, or its filling

ability.

flow cone [V-funnel cone] Confinedflow method consisting in filling a funnel with concrete or cement paste and determining the time for the material to flow out through the orifice. This time

21
Guide to Rheological Nomenclature

is a measure of the material's ability to flow. There are several types of funnel, some with round

and others with parallelepiped orifice and upper opening.

flow test Used in accordance with ASTM CI 362. This test measures the flow of concrete or mortar into a perforated tube. This method is appHcable for concrete with coarse aggregates less than 37.5 mm in diameter. The instrument consists of a hollow perforated tube that is inserted in the concrete sample, after which the material is allowed to flow into the hollow tube. The height

of the concrete in the hollow tube is considered a measure of the consistency of the concrete.

IBB Commercially available rotational rheometer. It is derived from the two-point test. The

principle of operation is identical, but the vane shape has been modified, and the vane moves in a

planetary motion and on its axis. The vane is shaped like the letter H and is shown in Figure

10(b).

LCL apparatus A vibration method. The concrete is poured behind a gate in a large

parallelepiped container. The gate is opened and the vibrator is turned on. The time for the concrete to flow and occupy the whole container is measured. A longer time suggests a lower

ability of the concrete to flow.

modified slump test Modification of the slump test described in ASTM C 143. It permits the

measurement of the rate at which the concrete is slumping, which gives an estimate of the concrete plastic viscosity. This test was developed at NIST, but is not currently a standard method

(see Ferraris (1999) in primary sources).

Orimet apparatus Confinedflow method instrument consisting of a tube 600 mm in length that

is closed at the bottom by a removable trap door. The time for the concrete to flow through the

tube once the trap is released is determined. This time is a measure of the ability of concrete to flow.

penetrating rod Freeflow method measuring the distance a rod of fixed mass can penetrate a concrete sample. It is a crude determination of whether the yield stress of the concrete is higher or lower than a predefined value. It is used to monitor concrete at the job site. A specific application

of this test is the Vicat apparatus.

settling method [Fritsch test] A vibration method, this test measures the capability of concrete

to consolidate under vibration. Concrete is placed in a container with an internal vibrator. The

time to obtain full consolidation is measured. The full consolidation is determined when the

surface of the concrete no longer moves.

slump cone test Free flow method in which a truncated metal cone, open at both ends and

sitting on a horizontal surface, is filled with concrete and lifted gradually. The slump of the concrete is measured. This standard test is described in ASTM C143.

turning tube viscometer Free flow method consisting of a tube 60 mm in diameter and 800 mm

long that can be filled with cement paste or mortar. A ball is dropped into the fluid and its velocity is measured between two points 370 mm apart. Using the Stokes equation, the viscosity can be calculated.

two-point test [Tattersall rheometer] First commercially available rotational rheometer for concrete. It is the first attempt to shear concrete at different rates and to measure the induced

22
Guide to Rheological Nomenclature

stress. It consists of a bucket filled with concrete and a vane, shown in Figure 10(a), that rotates

at controlled speeds. The torque generated during rotation is measured.

Ve-Be time [remolding test] Measures the ability of concrete to change shape under vibration.

Concrete is placed in a slump cone. After the cone is lifted away, the time it takes for the concrete

to remold itself into a cylinder while under vibration is measured.

Vicat apparatus Afree flow method, the Vicat apparatus is a penetration device used in the

testing of hydraulic cements and similar materials. The full description of this instrument and the

correct procedure to determine the normal consistency of cement is described in ASTM CI 87.

Figure 10 Various vane geometries used in concrete

rheometers: (a) two-point test or Tattersall, (b) IBB, (c)

BML.

11. Units and Symbols

Rheometric Units

All units should conform to the International System of Units (SI) as described by the National

Institute of Standards and Technology.' The use of CGS and other non-SI units is discouraged.

For convenience, SI units are shown in Table 1 in association with their common non-SI

equivalents (including decimal submultiples and conversion factors where appropriate). Table 2

shows the Sl-derived units with their underlying base units.

' B.N. Taylor, Guide for the Use of the International System of Units (SI), NIST Special Publication 811,

2"** Edition, National Institute of Standards and Technology, U.S. Department of Commerce, Washington,

DC, 1995.

23
Guide to Rheological Nomenclature

Table 1. SI and equivalent rheometric units.

Oiiantitv SI Units Fniiivalent CCS Units

viscosity ra • s 10 P (poise) or 1000 cP (centipoise)

kinematic viscosity o-l m • s 10 St (stoke) or 10 cSt (centistoke)

shear stress Pa 0.1 dyn • cm

strain unitless

shear rate s s modulus Pa 0.1 dyn • cm""^ compliance Pa' 10 cm" • dyn"'

frequency Hz

angular frequency 27lf phase angle rad

Table 2. SI derived units expressed in terms of SI base units.

Symbol Special Name Other SI Units SI Base Units

Pa Pascal N • m"' kg • m"' • s'^ Hz Hertz S-' rad radian m • m' =1

List of Symbols

\J*\ absolute shear compliance

\G*\ absolute shear modulus

0) angular frequency

'Happ apparent viscosity

D characteristic dimension

X characteristic time (retardation, relaxation)

Tl coefficient of viscosity [viscosity]

G* complex shear modulus

J* complex shear compliance

ri* complex viscosity

De Deborah number

Dt Diffusion coefficient, translational

lldiff differential viscosity

dynamic viscosity (real component of the complex viscosity)

fluidity

f frequency

imaginary component of the complex viscosity

rioo infinite shear viscosity

Tlinh inherent viscosity

r

24
Guide to Rheological Nomenclature

L'lJ intrinsic viscositv

V kinematic viscosity

On normal stress Pe Peclet number

5 phase angle

' ircu reduced viscosity

•Ir relative viscosity » T relaxation time, retardation time

Reynolds number

J shear compliance

J" shear loss compliance

G" shear loss modulus

G shear modulus

Y shear rate [rate of shear strain]

G' shear storage modulus

•/r

(J shear stress

|sp specific viscosity

Oq stress amplitude

Y strain Yo strain amplitude

viscosity of suspending medium or solvent

Oy yield stress zero shear viscosity

(for model-specific symbols see Section 6)

Bibliography

This bibliography cites sources used in the compilation of this guide. It is not, nor is it intended to be, an exhaustive list of references available on the vast subject of rheology or rheological

instrumentation. Nevertheless, it may serve as a good starting point for those who are relatively new to this field or searching for relatively fundamental information.

Primary Sources

American Concrete Institute, Cement and Concrete Termmology, ACI 1 16R-90, ACI Manual

of Concrete Practice 2000, Part 1, Farmington Hills, MI, 2000

British Standards Institution, Glossary ofRheological Terms, BS 5168:1975.

A. A. Collyer and D.W. Clegg, Editors. Rheological Measurement, Chapman and Hall, London,

1998.

25
Guide to Rheological Nomenclature

J.M. Dealy, "Official Nomenclature for Material Functions Describing the Response of a

Viscoelastic Fluid to Various Shearing and Extensional Deformations," Journal of

Rheology, 39[1], 253-265 (1995).

C.F. Ferraris, "Measurement of the Rheological Properties of High Performance Concrete: State of the Art Report," Journal ofResearch of the National Institute ofStandards and

Technology, 104[5], 461-478 (1999).

A. Kaye, R.F.T. Stepto, W.J. Work, J. V. Aleman and A. Ya. Malkin, "Definition of Terms

Relating to the Non-Ultimate Mechanical Properties of Polymers," lUPAC

Recommendations 1997, Pure and Applied Chemistry, 70, 701-754 (1998).

Other Sources

H. A. Barnes, "Shear-Thickening ("Dilatancy") in Suspensions of Nonaggregating Solid

Particles Dispersed in Newtonian Liquids," Journal ofRheology, 33[2], 329-366 (1989).

M. Bohdanecky and J. Kovaf, Viscosity ofPolymer Solutions, Elsevier, Amsterdam, 1982.

E.C. Bingham, "An Investigation of the Laws of Plastic Flow," U.S. Bureau of Standards

Bulletin, 13, 309-353 (1916).

F. R. Eirich, Editor. Rheology - Theory and Applications, Vol. 1, Academic Press, NY, 1956;

Vol. 3, 1960; Vol. 4, 1967.

J.W. Goodwin, "Rheology of Ceramic Materials," Ceramic Bulletin, 69[10], 1694-1698 (1990).

P.C. Hiemenz and R. Rajagopalan, Principles of Colloid and Surface Chemistry, 3rd Edition,

Chapter 4, pp. 145-192, Marcel-Dekker, 1997.

R.J. Hunter, "Rheology of Colloidal Dispersions," Chapter 18 in Foundations of Colloid

Science, Vol. 2, Oxford University Press, NY, 1989.

J. Mewis and A.J.B. Spaull, "Rheology of Concentrated Dispersions," Advances in Colloid and

Interface Science, 6, 173-200 (1976).

D. Quemada, "Models for Rheological Behavior of Concentrated Disperse Media under Shear,"

pp. 571-582 in Advances in Rheology, Vol. 2: Fluids, Universidad Nacional Autonoma de

Mexico, Mexico, 1984.

H.N. Stein, "Rheological Behavior of Suspensions," pp. 3-48 in Encyclopedia of Fluid

Mechanics, Vol. 5: Slurry Flow Technology, Gulf Publishing Company, Houston, 1986.

J.R. Van Wazer, J.W. Lyons, K.Y. Kim, and R.E. Colwell, Viscosity and Flow Measurement - A Laboratory Handbook ofRheology, Interscience Publishers, New York, 1963.

R.W. Whorlow, Rheological Techniques, Ellis Horwood Ltd., Chichester, 1980.

26
Guide to Rheological Nomenclature

A. A. Zaman, Techniques in Rheological Measurements: Fundamentals and Applications,

Instructional Module, NSF Engineering Research Center for Particle Science and

Technology, University of Florida, Gainesville, 1998.

Acknowledgments

American Concrete Institute, International Union of Pure and Applied Chemistry (lUPAC), and

The Society of Rheology (Journal of Rheology) have kindly granted permission to use or adapt

their published definitions in developing the current document. Their publications are fully cited

in the Ust of primary sources shown above. Extracts from BS 5168:1975 are reproduced with the

permission of British Standards Institution under license number PD\1999 0296. Complete copies

of the standard can be obtained by post from BSI Customer Services, 389 Chiswick High Road,

London W4 4AL.

Ad Hoc Review Committee

Lennart Bergstrom

YKI (Institute for Surface Chemistry), Stockholm, Sweden

John M. Dealy

Faculty of Engineering, McGill University, Montreal, Canada

Edward J. Garboczi

Leader, Inorganic Materials Group, National Institute of Standards and Technology,

Gaithersburg, MD

Robert J. Hunter

School of Chemistry, University of Sydney, Sydney, Austraha

Kamal Khayat

Department of Civil Engineering, University of Sherbrooke, Sherbrooke, Canada

Francois de Larrard

Methodes et Materiels de Construction et d'Entretien des Routes, Laboratoire Central des Fonts et Chaussees, Bouguenais, France

Makio Naito

Japan Fine Ceramics Center, Nagoya, Japan

Celik Ozyildirim

Virginia Transportation Research Council, Charlottesville, VA

27
Guide to Rheological Nomenclature

Ponserril Somasundaran

Langmuir Center for Colloids & Interfaces, Department of Chemical Engineering, Columbia

University, New York, NY

Abbas A. Zaman

NSF Engineering Research Center for Particle Science & Technology, University of Florida,

Gainesville, FL

28
Guide to Rheological Nomenclature

Index

A

anti-thixotropy. See thixotropy, negative

B

Bingham model, 9

BML, 21

BTRHEOM, 21

C

capillary methods, 16

Carreau-Yasuda, 9

Casson, 9

CEMAGREF, 21

Coaxial. See concentric cylinder

coefficient of fluidity, 2

complex strain amplitude, 14

compliance, 4

absolute shear, 15

complex shear, 15

shear, 6

shear loss, 15

shear storage, 15

concentric cylinder, 18 cone configuration, 18

double-gap configuration, 18

hollow cavity configuration, 18

confined flow methods, 19

consistency, 20

normal, 21

plastic, 21

wettest stable, 21

consistency factor, 20

consolidation, 20

Couette. See concentric cylinder. See

concentric cylinder

creep, 12

creep function, 12

Cross, 9

D

Deborah number, 12

deformation, 4

dilatant, 4

dynamic equilibrium, 4

E

Einstein coefficient, 5 Einstein's Law of Viscosity, 5

elastic, 1 electroviscous, 1 electroviscous effect

primary, 2

secondary, 2

tertiary, 2

Ellis, 10

F

filling ability, 21

finishing, 20

flow, 5 dynamic shear, 5 equilibrium, 5 laminar, 5 non-equilibrium, 6

oscillatory. See flow, dynamic shear

sheady shear, 7

steady state. See flow, equilibrium

flow cone, 21

flow curve, 5 Bingham plastic, ideal, 8

Bingham plastic, non-ideal, 8

Newtonian, 8

pseudoplastic with yield, 8

shear thinning with yield, 8

shear-thickening, 8

shear-thinning, 8 flow hysteresis, 12

flow test, 22

fluidity. See coefficient of fluidity

Forced harmonic oscillation, 13

free flow methods, 20

Fritsch test. See settling method

H

Herschel-Bulkley, 10

29
Hooke's law, 5

I IBB, 22

impending slough, 21

K

Krieger-Dougherty, 10

L

LCL apparatus, 22

limiting viscosity number. See viscosity,

intrinsic loss angle. See phase lag

M

Meter, 11 . mobility, 21

modified slump test, 22

modulus, 5 absolute shear, 15

complex shear, 14

elastic, 5

shear, 6

~

shear loss, 14

shear storage, 14

modulus of elasticity. See modulus, elastic modulus of rigidity. See modulus, shear

N

Navier-Stokes equations, 5 Newtonian, 5

non-Newtonian, 6

no-slip, 5 O

Orimet apparatus, 22

oscillatory test. See forced harmonic

oscillation

Ostwald-de Waele. See power-law

P

Peclet number, 6

penetrating rod, 22

phase lag, 13

placeability. See workability

plastic, 2

Poiseuille flow, 6

Guide to Rheological Nomenclature

Poiseuille's Law, 16

Powell-Eyring, 1

power-law, 11 pseudoplastic. See shear-thinning

R

rate of shear strain. See shear rate rate-controlled, 17

relaxation time, 12

remolding test. See Ve-Be time

retardation time, 12

Reynolds number, 6

rheology, 6

rheomalaxis, 12

rheometer, 15

Tattersall, 22

rheometric, 6

rheopexy, 12

rotational methods, 17

rotational rheometers, 20

S

settling method, 22

shear, 6

simple, 7

shear rate, 6

shear-thickening, 6

shear-thinning, 7

slippage. See no-slip

slump, 21

slump cone test, 22

strain

shear, 6

strain amplitude, 13

stress, 7

normal, 6

shear, 6

yield, 7

stress amplitude, 13

stress growth, 12

stress relaxation, 12

stress-controlled, 17

structure, 7

T

thixotropy, 12

negative, 12

two-point test, 22

30
Guide to Rheological Nomenclature

V

Ve-Be time, 23

V-funnel cone. See flow cone

vibration methods, 20

Vicat apparatus, 23

viscoelastic, 2

viscoelectric, 2

viscometer, 15

Brookfield-type. See simple rotational

extrusion capillary, 16

glass capillary, 16

simple rotational, 17

turning tube, 22

viscoplastic, 2

viscosity

apparent, 2

coefficient of, 3 complex, 3

differential, 3

dynamic, 3

infinite shear, 3

intrinsic, 3

kinematic, 3

non-Newtonian, 3

out-of-phase, 3

plastic, 4

reduced, 4

relative, 4

specific, 4

zero shear, 4

viscosity number. See viscosity, reduced

viscosity ratio. See viscosity, relative

viscous, 2

W

Weissenberg effect, 7

Weissenberg number, 7

worlcability, 21

Y

yield response, 7 yield stress apparent, 4

31

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