Measuring the plasticity of clays: A review

Abstract

Plasticity is the outstanding property of clay–water systems. It is the property a substance has when deformed continuously under a finite force. When the force is removed or reduced, the shape is maintained. Mineralogical composition, particle size distribution, organic substances and additives can affect the plasticity of clays. Several measuring techniques and devices were proposed to determine the optimal water content in a clay body required to allow this body to be plastically deformed by shaping. In this review, methods of evaluating the plasticity of clay–water systems are presented. Despite the advance in the theory of the plasticity and the methods of measurement, a common procedure for all types of materials does not exist. The most important methods are those that simulate the conditions of real processing.Research Highlights► Plasticity is related to deforming a substance continuously under a finite force. ► Composition, particle size, organic matter and additives may affect clay plasticity. ► Several techniques are used to determine the optimal water content of clays. ► Methods for evaluating the plasticity of water-clay systems were reviewed. ► A consolidated method for measuring clay plasticity still does not exist.

Full text

Review Article
Measuring the plasticity of clays: A review
F.A. Andrade
a
, H.A. Al-Qureshi
a,b
, D. Hotza
a,c,
⁎
a
Group of Ceramic and Glass Materials (CERMAT), Department of Mechanical Engineering (EMC), Federal University of Santa Catarina (UFSC), 88040-900 Florianópolis, SC, Brazil
b
Center of Mobility Engineering (CEM), Federal University of Santa Catarina (UFSC), 89219-905 Joinville, SC, Brazil
c
Department of Chemical Engineering (ENQ), Federal University of Santa Catarina (UFSC), 88040-900 Florianópolis, SC, Brazil
abstractarticle info
Article history:
Received 22 March 2010
Received in revised form 23 October 2010
Accepted 28 October 2010
Available online 3 November 2010
Keywords:
Plasticity
Atterberg limits
Pfefferkorn method
Indentation
Rheometer
Stress–strain
Plasticity is the outstanding property of clay–water systems. It is the property a substance has when deformed
continuously under a finite force. When the force is removed or reduced, the shape is maintained.
Mineralogical composition, particle size distribution, organic substances and additives can affect the plasticity
of clays. Several measuring techniques and devices were proposed to determine the optimal water content in
a clay body required to allow this body to be plastically deformed by shaping. In this review, methods of
evaluating the plasticity of clay–water systems are presented. Despite the advance in the theory of the
plasticity and the methods of measurement, a common procedure for all types of materials does not exist. The
most important methods are those that simulate the conditions of real processing.
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
Plastic behavior involves many areas of science and engineering
and has applications in various materials, such as soils, clays, concrete,
plastics and metals. In the beginning, the concept of plasticity was
used to explain and to characterize the rheological behavior of
materials in the solid or liquid state.
Research on plasticity began with the studies of Coulomb in the
18th century (Smith, 2006) on the stability of piles and embankments.
In the last century, the work of Mohr served as a base of some
concepts currently used such as elastic and plastic deformation,
yielding (critical state), shear localization and post-failure behavior
(Ancey, 2007).
Plasticity in the processing of clay-based materials is a fundamental
property since it defines the technical parameters to convert a ceramic
mass into a given shape by application of pressure (Norton, 1938;
1974; Moore, 1963; 1965; Astbury et al., 1966; Singer and Singer,
1979). Plasticity, in this case, and particularly in clay mineral systems,
is defined as “the property of a material which allows it to be
repeatedly deformed without rupture when acted upon by a force
sufficient to cause deformation and which allows it to retain its shape
after the applied force has been removed”(Perkins, 1995). A clay–
water system of high plasticity requires more force to deform it and
deforms to a greater extent without cracking than one of low plasticity
which deforms more easily and ruptures sooner (Brownell, 1977).
The plasticity of clays is related to the morphology of the plate-like
clay mineral particles that slide over the others when water is added,
which acts as a lubricant. As the water content of clay is increased,
plasticity increases up to a maximum, depending on the nature of the
clay. Clay workers are accustomed to speak of “fat”or highly plastic
clay such as ball clay or “lean”, relatively non-plastic clay such as
kaolin, but it is very difficult to express these terms in measurable
quantities. In the industry, plasticity is also referred to as “extrud-
ability”,“ductility”,“workability”or “consistency”(Händle, 2007).
Reed (1995) uses the term “consistency”referring to states of
ceramic raw materials, namely dry powder,granules, plastic body, paste
and slip, which are dependent on the liquid content. Fig. 1 presents the
apparent shear resistance as a function of the water content for a typical
clayish material. When water is added to dry clay, the first effect is an
increase in cohesion, which tends to reach a maximum when waterhas
nearly displaced all air from the pores between the particles. The
minimum amount of water necessary to make clay plastic is commonly
called the “plastic limit”(PL). Addition of water into the pores induces
the formation of a fairly high yield-strength body that, however, may
crack or rupture readily on deformation.
A plastic clay body can withstand the addition of considerable
amounts of water, passing through a stage in which it remains dry to
the fingers and is easily molded. As the water content increases, the
clay becomes a paste, in which the yield strength steadily diminishes.
The clay becomes wet and sticky to the fingers and can no longer
maintain a molded shape. The water content which corresponds to
Applied Clay Science 51 (2011) 1–7
⁎Corresponding author. Federal University of Santa Catarina (UFSC), 88040-970,
Florianópolis, SC, Brazil. Tel.: +55 48 3721 9448; Fax: +55 48 3721 9687.
E-mail address: hotza@enq.ufsc.br (D. Hotza).
0169-1317/$ –see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.clay.2010.10.028
Contents lists available at ScienceDirect
Applied Clay Science
journal homepage: www.elsevier.com/locate/clay

this state is called “liquid limit”(LL). With still higher water contents,
the system becomes a dispersion (slurry or slip). The difference in the
water amounts at these two limiting points, related to the dry mass of
the clay, is expressed as the “plasticity index”(PI), according to Fig. 1.
In traditional clay containing ceramic materials, the measurement
and control of the plasticity are needed to characterize the system and
to optimize the conditions of the processing (Ribeiro et al., 2005).
Factors influencing plasticity may be related to the clay itself or to
the molding process (Henry, 1943; Carman, 1949; Marshall, 1955).
Clay-related factors are moisture content, mineralogical composition,
particle size distribution, type of exchangeable cations, presence of
salts and organic material (Talwalkar and Parmelee, 1927; Wilson,
1936; Whitaker, 1939; Lawrence, 1958; West and Lawrence, 1959;
Dumbleton and West, 1966; Barna, 1967; Onoda, 1996; Schmitz et al,
2004; Bergaya et al., 2006). Process-related factors are application of
pressure, temperature and characteristics of water and additives used
(Jefferson and Rogers, 1998; Malkawi et al., 1999; Ribeiro et al., 2004;
Uz et al., 2009; Zentar et al., 2009). A deeper discussion on the role of
clay composition and processing parameters on plasticity is beyond
the scope of this review.
In this review, techniques commonly used for assessing the
plasticity of clays are presented and discussed.
2. Measuring methods
There are several methods for measurement and characterization
of the plasticity of a clay body. The experimental determination, in
some cases, is operator dependent, which in turn may produce
different results when different methods are compared. Among these
methods, Atterberg, Pfefferkorn, stress/strain curves, indentation and
rheological measurements are the most used techniques (Table 1).
Atterberg and Pfefferkorn tests are widely used owing to the low
cost of the equipment employed (Moore, 1965; Van der Velden, 1979;
Bekker, 1981). The measurement is based on the moisture content at
which the material has some arbitrarily defined consistency. In these
tests, high moisture contents are associated with high plasticity and
vice versa.
Rheometry (McCabe, 1960; Alfani and Guerrini, 2005), indentation
methods (Doménech et al., 1994; Vaillant; 2008; Modesto and
Bernardini, 2008) and techniques which evaluate the relationship
between an applied force and the resulting deformation (Baran et al.,
2001; Ribeiro et al., 2005) are also used for measuring the plasticity of
clays. These methods are often more cost intensive due to the
equipment used. Nevertheless, they can supply important parameters
such as modulus of elasticity, yield strength, maximum deformation
and rupture strength.
2.1. The Atterberg method
Albert Atterberg (1846–1916), a Swedish chemist and agricultural
scientist, found that plasticity is a particular characteristic of clay. He
defined the consistency limits, called Atterberg limits (Atterberg,
1911). According to his findings, there is a defined amount of water at
which the clay is easily moldable. With lower moisture content, the
body cracks when molded. The Atterberg plastic limit is the lowest
water content (expressed in mass percent of the clay dried at 120 °C)
at which the body can be rolled into threads without breaking
(Bergaya et al., 2006). The Atterberg liquid limit is the water content
at which the body begins to flow, using a specific apparatus (Fig. 2).
The difference between both values is called the plasticity (or plastic)
index (Fig. 3).
The liquid and plastic limits define the transitions between liquid
and plastic behavior. Arthur Casagrande (1902–1981), an Austrian-
born American civil engineer, standardized the method to determine
such limits in soil consisting of clayish and non-clayish materials.
These limits can give significant information about the behavior of
clay (Jefferson and Rogers, 1998). Casagrande (1958) studied dif-
ferent types of soil and evaluated plasticity by the Atterberg limits.
Although it is the most used method to evaluate plasticity, the
large number of variables involved hinders a detailed correlation of
the parameters with the behavior of the clay. To solve this, Gutiérrez
(2006) proposed a rigorous probabilistic approach according to a
regression analysis as a technique to express the linear behavior of the
Atterberg limits for a given soil.
Two methods for determining the liquid limit are standardized
(ASTM D4318, 2005): multipoint or one-point test. The correlation on
which the calculations of the one-point method are based may not be
valid for certain soils, such as organic soils or soils from a marine
environment. It is recommended to use the multipoint method in cases
where higher precision is required. Due to the fact that the one-point
method requires the operator to judge when the test specimen is
approximately at its liquid limit, it is particularly not recommended for
use by inexperienced operators. The method proposed by Atterberg
has some advantages such as low cost and sensitivity. In spite of this,
the method's lack of precision is a significant drawback, mainly in one-
point method, which limits its use in controlling materials (Doménech
et al., 1994).
Special care must be taken during the execution of the tests. The
specimens must be thoroughly mixed and be permitted to cure for a
sufficient period before testing. Erroneous results may be caused by
Fig. 1. States of consistency and plasticity limits of clays (adapted from Reed, 1995),
PL=plastic limit, LL = liquid limit, PI = plasticity index.
Table 1
Methods for evaluating the plasticity of clays.
Method Atterberg Pfefferkorn Penetrometer Capillary rheometer Brabender rheometer Tension versus
deformation
Measuring principle Molding Impact deformation Penetration Pressure Torque Pressure
Parameters measured
or calculated
PI (LL and PL) Water content
(mass percent)
Force Viscosity, pressure
extrusion, flow curve
Torque, shear stress, viscosity,
extrusion head pressure
Tension, deformation
Speed Low Low Average Average Average Average
Reproducibility Low Average Average/high High High High
Cost Low Low Average High High Average
Standard ASTM D4318 (2005) BS 1377 (1990)
2F.A. Andrade et al. / Applied Clay Science 51 (2011) 1–7

the loss of colloidal material when removing particles coarser than
0.42 mm (sieve #40) or by testing air-dried or oven-dried soils.
Inaccurate determination of the water content would greatly affect
the determined liquid and plastic limits if small, non-representative
quantities of material are available for the water content determina-
tions. Another source of errors can be the incorrect measure of the
final thread diameter, or stopping the rolling process too soon.
2.2. The Pfefferkorn method
The Pfefferkorn method determines the amount of water required
to achieve a 30% contraction in relation to the initial height of a test
body under the action of a standard mass (Pfefferkorn, 1924). The
results are normally expressed as graphs showing height reduction as
a function of moisture content.
Measuring of plasticity according to Pfefferkorn is based on the
principle of impact deformation (Fig. 4). A defined sample with a
diameter of 33 mm and an initial height of 40 mm, produced either
manually or by extrusion, is deformed by a free falling plate with a
mass of 1.192 kg. The initial height is related to the impact defor-
mation height, the result of which is the ratio of deformation. As a
rule, this measurement is taken with bodies of varying moisture
content. The ratios of deformation or the impact deformation heights
(H
0
, initial height; H
f
,final height) are plotted against the moisture
content (Fig. 5). The steeper the curve, the “shorter”the body, i.e. the
more intensely the body will react to variations of the moisture
content. The deformation heights for bodies to be extruded lie
between ~ 25 mm for soft extrusion and ~37 mm for stiff extrusion
(Händle, 2007).
The Pfefferkorn method is widely accepted in practice and was
originally developed for soft silicate ceramic materials. The method is
less suitable for stiffer bodies, as usually processed in the advanced
ceramics industry, as the low resolution at small deformation heights
reduces reproducibility.
The Pfefferkorn test is laborious and time consuming. It requires
changing the moisture content in order to reach 30% contraction. At
the end of the test, the sample has to be dried. The main problems
regarding plasticity determination using this method are related to
the determination of the moisture, and to the relation between
residual and sedimentary clays (Modesto and Bernardini, 2008).
Fig. 2. Casagrande apparatus for measuring the liquid limit (Timely Engineering Soil
Tests, 2010).
Fig. 3. Atterberg plastic index versus plastic limit of clay materials from Sassuolo, Italy
(Dondi, 1999).
Fig. 4. Pfefferkorn apparatus (Sassuolo Lab, 2010).
Fig. 5. Typical chart of Pfefferkorn for three clays.
3F.A. Andrade et al. / Applied Clay Science 51 (2011) 1–7

2.3. Penetration methods
The penetration (or indentation) method is based on the mea-
surement of the necessary force that a tool produces to make a mark
in the test body. This mark, according to the geometry of the used tool,
will serve to indicate the resistance of the mass to the penetration, and
thus providing information about its plasticity. The measuring
instruments of the penetration method devised for soil mechanics
may be also related to those used for hardness measurement
(Doménech et al., 1994; Händle, 2007).
In the fall cone test, a cone with an angle of 30° and total mass of
80 g is suspended above, but just in contact with, the clay sample. The
cone is permitted to fall freely within 5 s. The water content
corresponding to a cone penetration of 20 mm defines the liquid
limit. The plastic limit is determined by repeating the testing with a
cone of similar geometry, but with a mass of 240 g (Yu and Mitchell,
1998).
Some authors (Doménech et al., 1994; Feng, 2004) proposed the
use of a sample-holding mold of circular cross section, so that the edge
effects could be neglected. Doménech et al. (1994) used a cylindrical
plate of 50 mm diameter and 50 mm height, while Feng (2004) used a
smaller sample holder (20 mm diameter and 50 mm height). The
specimen ring facilitates the sample preparation and increases the
quality of the sample. For lower cone penetrations, when the clay
sample is relatively stiff, the traditional specimen cup apparently
reduces the measuring resolution of the plastic limit. As the fall cone is
recommended in several standards for determining the liquid limit, it
is advantageous to use it also for determining the plastic limit.
Vaillant (2008) investigated the utilization of a modified Vicat
Apparatus (utilized in cement consistency analysis) to evaluate the
plasticity of clays. He adapted an aluminum cone in place of a rod,
reducing the weight to evaluate more accurately the liquid and plastic
limits.
Modesto and Bernardini (2008) presented a method based on an
indentation equipment. When penetration occurs, marks with cracks
or plastic flow mean a lack of plasticity (low water contents, Fig. 6a),
and when there are no cracks, a lack of consistency (high water
contents, Fig. 6b). These extreme points correspond to the Atterberg
plastic and the liquid limit. Adequate plasticity occurs when the marks
do not present either cracks or extreme moisture and the wall formed
is sufficiently smooth.
Measurements of plasticity with the penetrometer are considered
to be more consistent, have better reproducibility, be easier to
determine and less operator dependent (Feng, 2004). Some authors
did not find significant differences between fall cone standard
methods for liquid limit determination (Jefferson and Rogers, 1998;
Vaz and Hopmans, 2001).
However, Benbow and Bridgwater (1993) reported some factors
that can limit the accuracy of the penetration test. If the depth of
penetration is too small, the accuracy is limited. If the sample is
predominantly viscous rather than plastic, the penetration will
depend on the time of penetration. Moreover, forces due to
deceleration of the cone are not taken into account.
2.4. Capillary rheometer
The plasticity of extrudable materials can also be measured by a
capillary rheometer. Various instruments are available, in the form of
either single-bore capillary or twin-bore capillary rheometers. Using a
pressure piston, the ceramic body is forced through a nozzle of a
Fig. 6. Clay indentation, showing (a) too low water content and (b) an excess of water (Modesto and Bernardini, 2008).
Fig. 7. Capillary rheometer (Alfani and Guerrini, 2005).
4F.A. Andrade et al. / Applied Clay Science 51 (2011) 1–7

defined geometry at different feed rates (Fig. 7). The resistance of the
ceramic body against the deformation in the nozzle causes a pressure
drop within the capillary, which corresponds to a certain shear stress
(σ). This pressure drop is the measured value, taken in the in-feed
zone of the nozzle (Händle, 2007).
This test could be also applied for determining the material's
apparent viscosity. To calculate the real viscosity of the materials as a
function of the flow rate, the Mooney–Rabinowitsch correction is
applied (Alfani and Guerrini, 2005) and a viscosity curve as a function
of the shear rate (γ) is derived
η
˙
γðÞ=σw
˙
γw
:ð1Þ
According to the Bagley correction, the measured pressure ΔP
tot
can be calculated by:
ΔPtot =ΔPent +ΔP
L

die
Lð2Þ
where ΔP
ent
represents the pressure drop in the s tatic zone, and (ΔP/L)
die
is the pressure drop along the die length. Eq. (2) shows that the pressure
decreases along the die as the capillary length increases. The evaluation
of (ΔP/L)
die
is essential to determine the flow of the material inside the
rheometer and to measure the viscosity. Typical capillary rheometer data
are in Fig. 8.
The main advantage in this method is the possibility to evaluate
more accurately the operational conditions on the extrusion process,
as different geometries of the die can be used.
2.5. Torque rheometer
The torque rheometer or Brabender plastograph (McCabe, 1960)
consists of a mixer with eccentric blades, inside which powdered clay
is mixed with rising quantities of water by a proportioning system
that allows keeping a steady liquid flow (Fig. 9). The torque reflects
the change of consistency of dry powdered state to a plastic solid. The
data represent the work required by the motor to move the blades
inside the sample at a constant rotating speed and are recorded as
torque versus time or amount of water (Sanchez et al., 1998).
When water is added, a point (A) is reached at which the
material's consistency starts to increase (Fig. 10) and reaches a
maximum (τ
x
). Adding more liquid, the consistency decreases. At
point E, the solid is no longer plastic. In general, plasticity can be
defined by the maximum relative consistency (τ
x
) or the range of
plastic behavior (He-Hx) (Sanchez et al. 1998).
An advantage of this method is to perform an extrusion test, by
installing a barrel with an extrusion screw and several types of die in
the rheometer, monitoring the force by a pressure transducer. This
Fig. 8. Data obtained with a capillary rheometer (adapted from Alfani and Guerrini,
2005).
Fig. 9. Torque rheometer (C.W. Brabender Instruments, 2010).
Fig. 10. Torque rheometer test (adapted from Sanchez et al., 1998).
Fig. 11. Stress–deformation curve (adapted from Ribeiro et al., 2005).
5F.A. Andrade et al. / Applied Clay Science 51 (2011) 1–7

apparatus works with small quantities of material, which has to be
considered when passing into the industrial scale (Alfani and Guerrini,
2005). The test is very fast (b20 min), compared to traditional plas-
ticity measuring methods.
2.6. Stress–strain curves
As for other types of materials, a compression test can be used to
evaluate the plasticity of clays. The typical test curve gives information
about the modulus of elasticity, yield strength, maximum deformation
and rupture strength. As shown in Fig. 11, the material shows elastic
behavior up to point A, then plastic behavior until reaching point B
where cracks start to appear. Due to the small effective area, the
tension increases quickly until the test body breaks (Ribeiro et al.,
2005).
Some parameters obtained in the compression test are strongly
influenced by the chemical composition and moisture of the clay.
Therefore, this method shows a great potential to be used in the
evaluation of the plasticity of clays used in extrusion. The high
precision and reproducibility of the test make it possible to evaluate
and to compare different clay–water systems.
Baran et al. (2001) applied the workability test for metals to
measure the yield stress (σ
0.2
) and the plastic tensile strain limit (ε
⁎θ
).
The product of the two characteristic values (σ
0.2
×ε
⁎θ
) was defined as
the workability. The variation of these three values as a function of the
moisture content of the green bodies is shown in Fig. 12. From the
maximum point of the σ
0.2
×ε
⁎θ
curve, called the workability curve,
the optimum moisture was determined (in this case, 22%).
Flores et al. (2010) modeling of plasticity of clays determined
several parameters such as the coefficient of friction and the effective
compressive stress (μand σin Eq. (3)), from the curves of the
compression test (Fig. 13). The developed mathematical model is a
potential and useful tool for the evaluation of clay-based materials
with optimized properties for a given application.
F=−2πσ−
h
2μrf+h
2μ

+h2
4μ2exp 2μrf
h

"#
ð3Þ
where his the final height of clay body sample, r
f
is the final sample
radius.
This method, where the clays are compressed until the cracks
appear (Fig. 14), seems to be more precise and independent of the
operator ability. It is faster to evaluate diverse types of clay bodies and
supplies parameters to specify the extrusion process (Andrade et al.,
2010).
2.7. Other methods
According to Linseis and Hofmann's method (Händle, 2007), the
materials to be extruded at different moisture contents are forced
through a nozzle of approximately 1 cm
2
cross section by means of a
piston extruder, and the shearing strength required for this process is
determined. The column is subsequently torn apart and the tear
resistance measured. The degree of plasticity is the ratio of tear
resistance to the shear strength. Highly plastic bodies are those which
offer little resistance to deformation, but nevertheless they still have a
high tear resistance.
In the Dietzel method (Händle, 2007), the same equipment is used
as in the Pfefferkorn method. Rather than using a high deformation
speed, the cylinder is compressed slowly, until cracks form. The
Fig. 12. Workability test (adapted from Baran et al., 2001).
Fig. 13. Experimental and theoretical data obtained in stress–deformation tests of clay
with different water contents (Flores et al., 2010).
Fig. 14. Compression test of clays (Flores et al., 2010).
6F.A. Andrade et al. / Applied Clay Science 51 (2011) 1–7

compression in percent of the original height is considered to be a
measure of plasticity.
Based on the Atterberg method, the plasticity number according to
Riecke (Händle, 2007) is considered to be the range between the roll-
out limit and the make-up requirement, which is defined to be the
moisture content at which the mass just stops sticking to a person's
hand.
3. Conclusions
The plasticity concept is employed in many areas of engineering
and science. Therefore, it is a hard task to choose a method that can be
used for any type of raw material or processing condition. The main
criteria that must be taken into account in the choice of the mea-
surement method are the required information, the type of proces-
sing, as well as verifying the influence of one or more parameters on
the plastic behavior of the clay body.
In laboratory scales, for developing new formulations, more than
one method should be used. In the industry, where fast methods and
low cost are required, the automated methods will be preferred for
tests of raw materials or control process parameters.
Acknowledgements
The Brazilian agencies CNPq and Capes are acknowledged for
financial support.
References
Alfani, R., Guerrini, G.L., 2005. Rheological test methods for the characterization of
extrudable cement-based materials —a review. Mater. Struct. 38 (2), 239–247.
Ancey, C., 2007. Plasticity and geophysical flows: a review. J. NonNewtonian Fluid
Mech. 142 (1–3), 4–35.
Andrade, F.A., Al-Qureshi, H.A., Hotza, D., 2010. Modeling of clay paste extrusion
through a rectangular die. Int. Rev. Chem. Eng. 2 (4), 478–483.
Astbury, N.F., Moore, F., Lockett, J.A., 1966. A cyclic torsion test for study of plasticity.
Trans. Br. Ceram. Soc. 65, 435–461.
ASTM Standard D4318, 2005. Standard Test Methods for Liquid Limit Plastic Limit, and
Plasticity Index of Soils, ASTM International.
Atterberg, A., 1911. Die Plastizität der Tone. Internationale Mitteilungen für
Bodenkunde 1, 10–43.
Baran, B., Erturk, T., Sarikaya, Y., Alemdaloglu, T., 2001. Workability test method for
metals applied to examine a workability measure (plastic limit) for clays. Appl. Clay
Sci. 20 (1–2), 53–63.
Barna, G.L., 1967. Plasticity of clay minerals. Ceram. Bull. 46, 1091–1093.
Bekker, P.C.F., 1981. Simple clay testing methods. Ziegelindustrie International, vol. 9.
Bau-Verlag, Wiesbaden, Germany, pp. 494–503.
Benbow, J., Bridgwater, J., 1993. Paste Flow and Extrusion. Clarendon Press, Oxford.
Bergaya, F., Theng, B.K.G., Lagaly, G. (Eds.), 2006. Handbook of Clay Science. Elsevier,
Amsterdam, pp. 141–246.
Brabender, C.W., 2010. www.cwbrabender.com, Instruments, Inc. (accessed August 20).
Brownell, W.E., 1977. Structural clay products. Applied Mineralogy, vol. 9. Springer,
Berlin.
BS 1377, 1990. Methods of test for soils for civil engineering purposes. British Standards
Institution.
Carman, P.C., 1949. Clays. Chemical Constitution and Properti es of Engineering
Materials. Edward Arnold, London, pp. 375–410.
Casagrande, A., 1958. Notes on the design of the liquid limit device. Geotechnique 8 (2),
84–91.
Doménech, V., Sánchez, E., Sanz, V., García, J., Ginés, F., 1994. Assessing the Plasticity of
Ceramic Masses by Determining Indentation Force. III World Congress on Ceramic
Tile Quality, AICE/ITC, Castellón, Spain.
Dondi, M., 1999. Clay materials for ceramic tiles from the Sassuolo District Northern
Apennines, Italy. Geology, composition and technological properties. Appl. Clay Sci.
15 (3–4), 337–366.
Dumbleton, M.J., West, G., 1966. Some factors affecting the relation between the clay
minerals in soils and their plasticity. Clay Miner. 6, 179.
Feng, T.W., 2004. Using a small ring and a fall-cone to determine the plastic limit.
J. Geotech. Geoenviron. Eng. 130 (6), 630–635.
Flores, O.J.U., Andrade, F.A., Hotza, D., Al-Qureshi, H.A., 2010. Modeling of plasticity of
clays submitted to compression test. World Acad. Sci. Eng. Technol. 61, 191–196.
Gutiérrez, A., 2006. Determination of Atterberg limits: uncertainty and implications.
J. Geotech. Geoenviron. Eng. 132 (3), 420–424.
Händle, F. (Ed.), 2007. Extrusion in Ceramics. Springer, New York.
Henry, E.C., 1943. Measurement of workability of ceramic bodies for plastic molding
processes. J. Am. Ceram. Soc. 26, 37–39.
Jefferson, I., Rogers, C.D.F., 1998. Liquid limit and the temperature sensitivity of clays.
Eng. Geol. 49 (2), 95–109.
Lawrence, W.G., 1958. Factors involved in plasticity of kaolin–water systems. J. Am.
Ceram. Soc. 41, 147–150.
Malkawi, A.I.H., Alawneh, A.S., Abu-Safaqah, O.T., 1999. Effects of organic matter on
the physical and the physicochemical properties of an illitic soil. Appl. Clay Sci. 14
(5–6), 257–278.
Marshall, C.L., 1955. A new concept of clay plasticity. Ceram. Bull. 34, 54–56.
McCabe, C., 1960. Rheological measurements with the Brabender plastograph. Trans.
Soc. Rheol. IV 335–346.
Modesto, C.O., Bernardini, A.M., 2008. Determination of clay plasticity: indentation
method versus Pfefferkorn method. Appl. Clay Sci. 40 (1–4), 15–19.
Moore, F., 1963. Two instruments for studying the plasticity of clays. J. Sci. Instrum. 40,
228–231.
Moore, F., 1965. Rheology of Ceramic Systems. McLaren and Sons, London, pp. 51–57.
Norton, F.H., 1938. An instrument for measuring the workability of clays. J. Am. Ceram.
Soc. 21, 33–36.
Norton, F.H., 1974. Elements of Ceramics, 2nd edn. Addison-Wesley, Reading, MA,
pp. 78–79.
Onoda, G.Y., 1996. Mechanism of plasticity in clay–water systems. Science of
Whitewares. The American Ceramic Society, Columbus, OH, pp. 79–87.
Perkins, W.W., 1995. Ceramic Glossary. The American Ceramic Society, Westerville, OH.
Pfefferkorn, K., 1924. Ein Beitrag zur Bestimmung der Plastizität in Tonen und Kaolinen.
Sprechsaal 57 (25), 297–299.
Reed, J.S., 1995. Principles of Ceramic Processing, 2nd ed. Wiley, New York.
Ribeiro, C.G., Correia, M.G., Ferreira, L.G., Gonçalves, A.M., Ribeiro, M.J., Ferreira, A.A.L.,
2004. Estudo sobre a influência da matéria orgânica na plasticidade e no
comportamento térmico de uma argila. Cerâmica Ind. 9 (3), 1–4.
Ribeiro, M.J., Ferreira, J.M., Labrincha, J.A., 2005. Plastic behaviour of different ceramic
pastes processed by extrusion. Ceram. Int. 31 (4), 515–519.
Sanchez, E., Ines, F.G., Sanz, V., Gozalbo, A., 1998. Study of Clay Plastic Behaviour by a
Torque Rheometer. V World Congress on Ceramic Tile Quality, AICE/ITC, Castellón,
Spain.
Sassuolo Lab., 2010. www.sassuololab.it, (accessed August 20).
Schmitz, R.M., Schroeder, C., Charlier, R., 2004. Chemo–mechanical interactions in
clay: a correlation between clay mineralogy and Atterberg limits. Appl. Clay Sci. 26
(1–4), 351–358.
Singer, F., Singer, S.S., 1979. Industrial Ceramics. Chapman & Hall, London, pp. 299–302.
Smith, I., 2006. Elements of Soil Mechanics, 8th edn. Blackwell, Oxford, pp. 94–95.
Talwalkar, T.W., Parmelee, C.W., 1927. Measurement of plasticity. J. Am. Ceram. Soc. 10,
670–685.
Timely Engineering Soil Tests, 2010. http://www.test-llc.com, (accessed August 20).
Uz, V., Ceylan, A., Yilmaz, B., Ozdag, H., 2009. Plasticity and drying behavior of terra cotta
bodies in the presence of cellulose. Appl. Clay Sci. 42 (3–4), 675–678.
Vaillant, J.M.M., 2008. Cone de penetração adaptado para determinação da plasticidade
das argilas. 52nd Brazilian Ceramics Congress, Florianópolis, Brazil.
Van der Velden, J.H., 1979. Analysis of the Pfefferkorn test. Ziegelindustrie International,
vol. 9. Bau-Verlag, Wiesbaden, Germany, pp. 532–543.
Vaz, C.M.P., Hopmans, J.W., 2001. Simultaneous measurement of soil penetration
resistance and water content with a combined penetrometer–TDR moisture probe.
Soil Sci. Soc. Am. J. 65, 4–12.
West, R.R., Lawrence, W.G., 1959. The plastic behavior of some ceramic clays. Ceram.
Bull. 38, 135–138.
Whitaker, H., 1939. Effect of particle size on plasticity of kaolinite. J. Am. Ceram. Soc. 22,
16–23.
Wilson, E.O., 1936. The plasticity of finely ground minerals with water. J. Am. Ceram.
Soc. 19, 115–120.
Yu, H., Mitchell, J., 1998. Analysis of cone resistance —review of methods. J. Geotech.
Geoenviron. Eng. 124 (2), 140–149.
Zentar, R., Abriak, N.E., Dubois, V., 2009. Effects of salts and organic matter on Atterberg
limits of dredged marine sediments. Appl. Clay Sci. 42 (3–4), 391–397.
7F.A. Andrade et al. / Applied Clay Science 51 (2011) 1–7