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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.
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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
Stressstrain
Plasticity is the outstanding property of claywater systems. It is the property a substance has when deformed
continuously under a nite 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 claywater 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 denes 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 dened as the property of a material which allows it to be
repeatedly deformed without rupture when acted upon by a force
sufcient 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 fator highly plastic
clay such as ball clay or lean, relatively non-plastic clay such as
kaolin, but it is very difcult to express these terms in measurable
quantities. In the industry, plasticity is also referred to as extrud-
ability,ductility,workabilityor consistency(Händle, 2007).
Reed (1995) uses the term consistencyreferring 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 rst 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 ngers 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 ngers and can no longer
maintain a molded shape. The water content which corresponds to
Applied Clay Science 51 (2011) 17
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 inuencing 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 dened 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 (18461916), a Swedish chemist and agricultural
scientist, found that plasticity is a particular characteristic of clay. He
dened the consistency limits, called Atterberg limits (Atterberg,
1911). According to his ndings, there is a dened 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 ow, using a specic apparatus (Fig. 2).
The difference between both values is called the plasticity (or plastic)
index (Fig. 3).
The liquid and plastic limits dene the transitions between liquid
and plastic behavior. Arthur Casagrande (19021981), 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 signicant 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 signicant 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
sufcient 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, ow 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) 17
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
nal 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 dened 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
,nal height) are plotted against the moisture
content (Fig. 5). The steeper the curve, the shorterthe 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) 17
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 denes 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 modied 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 ow 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 sufciently 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 nd signicant 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) 17
dened 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 ow rate, the MooneyRabinowitsch 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 ow 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 ow (Fig. 9). The torque reects
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
dened 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. Stressdeformation curve (adapted from Ribeiro et al., 2005).
5F.A. Andrade et al. / Applied Clay Science 51 (2011) 17
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. Stressstrain 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
inuenced 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 claywater 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 dened 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 coefcient 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 nal height of clay body sample, r
f
is the nal 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 stressdeformation 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) 17
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 dened 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 inuence 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
nancial support.
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7F.A. Andrade et al. / Applied Clay Science 51 (2011) 17
... The plasticity tests are used to determine the water content in which clay minerals show two specific shear forces for pre-established consistencies. The plasticity indices (PI) can be calculated considering that the liquid limit (LL, when the paste starts to flow) and the plastic limit (PL, when the paste is not deformable anymore) are found for consistencies of 1 and 46 N, respectively, where PI = LL -LP [26]. The indentation method, used in this work, is described in Doménech et al. [27] and Modesto and Bernardin [28]. ...
... According to Almeida et al. [3], plastic clays have 80% (by mass) of their particle size distribution below 2 μm. For Andrade et al. [26], bentonites have particle sizes ranging from 2 μm to 0.1 μm, with an average size of ~0.5 μm. ...
... For Andrade et al. [26], plastic clays must have 15% of the size distribution below 0.5 μm. After high-energy milling, 84% of the particle size distribution of kaolin I and 91% of kaolin R was <2 μm. ...
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The production of porcelain tiles is increasing in Brazil besides the production of grés tiles and monoporosa is decreasing since COVID 19. Plastic clays are used in the composition of porcelain tiles to give plasticity to the pastes in the forming step. However, there is a shortage of plastic clays in south Brazil, the largest producer of porcelain tiles. Therefore, the aim of this work was to improve the plasticity of two commercially available kaolins by high-energy milling (HEM). Both kaolins were characterized before and after milling by X-ray diffraction, particle size, plasticity, and cation exchange capacity techniques. After high-energy milling, the processed kaolins were used in the composition of a commercial porcelain tile paste. The performance of the paste before and after use of the processed kaolins was determined regarding its firing shrinkage and sintering temperature. The porcelain tile compositions with the high-energy milled kaolins showed less densification during pressing and greater shrinkage after firing, but the tiles presented dimendional stability, improving the quality of the tiles.
... The suitability of the clay materials for clay-based bricks was evaluated by using the Pfefferkorn method, which is based on the principle of impact deformation [9,27]. This method, described by Amorós et al., was used to determine Pfefferkon's plasticity index (PPI) [28]. ...
... This method calculates the amount of water needed to achieve a 30% contraction of the initial height (H 0 ) of a test specimen under the action of a standard mass. The PPI value was obtained from Pfefferkorn straight lines of moisture content% vs. height ratio of the specimen [9,29]. Then, the plasticity and consistency of the rods were evaluated using a pocket soil penetrometer ST207 (kg/cm 2 ) based on penetration. ...
... Then, the plasticity and consistency of the rods were evaluated using a pocket soil penetrometer ST207 (kg/cm 2 ) based on penetration. The standards for the penetrometer were BS 1377 (1990) [9]. Extrusion measurements with a penetrometer are classified as soft (1.2-1.8 kg/cm 2 ) and stiff (3-4.5 kg/cm 2 ), with the preferred range for consistency being 1.8-3 kg/cm 2 [30]. ...
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This study examined the chemical, mineralogical, physical, thermal, and technological character-istics of the Dostluk (DM), Halach (HM), and Sakar (HM) clay deposits located in the Amu-Darya basin of Turkmenistan. The potential suitability of these deposits was evaluated for the local ceramic brick industry. The chemical and mineralogical features were identified by X-ray fluorescence (XRF), ion chromatography (IC), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) techniques. The physical properties were characterized by granulometric analysis by sieving, par-ticle size distribution, scanning electron microscopy/optic analysis, specific surface area, Pfeffer-kon’s plasticity index, reabsorption, shrinkage, water absorption, mechanical (compression and bending), and freeze–thaw durability tests. The thermal methods were performed using dilatometry and thermogravimetric/differential thermal analyzer (TG/DTA). The test samples for the different clay deposits were extruded, dried, and fired at three different temperatures of 850 °C, 950 °C, and 1050 °C. While the Dostluk and Sakar clays have high plasticity, Halach clay has been found to have low plasticity. The mechanical and freeze–thaw durability tests demonstrated that the out-comes of the clays of different origins were sufficient, achieving compressive strengths of over 10 MPa and mass loss less than 3%, which are acceptable by industry standards. Semi-industrial processed hollow bricks demonstrated promising characteristics. While the Dostluk and Sakar clay-based brick specimens were visibly free of cracks, the Halach specimens showed some cracks. The physical and mechanical improvements of these clays were performed with three mixtures, which are M1 (80 mass% DM + 20 mass% brick waste), M2 (85 mass% SM + 15 mass% brick waste), and M3 (70 mass% HM + 25 mass% SM and 5 mass% brick waste) for the brick industry.
... 'Stickiness' refers to the capacity of soil to adhere to other objects and plasticity is the degree which reworked soil can be deformed without rupturing (e.g. Andrade, Al-Qureshi and Hotza, 2011). For progressive infilling, one needs a non-sticky, non-plastic, loose soil. ...
... MX80 contains montmorillonite (75%-90%), quartz (15%), and feldspar (10%) [15], and FEBEX contains more than 90% montmorillonite [19]. Table 2 shows the clay properties considering the Atterberg limits [13,21]; most bentonites are classified as CH with very high levels of plasticity based on the unified soil classification system (USCS). Higher Atterberg limits imply that they have many expansive characteristics [22]. ...
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In a geological repository system, buffer is indispensable to ensure the safe disposal of high-level radioactive waste (HLW). Because heat generated from spent nuclear fuel in a canister is released to the surrounding buffers, thermal properties of such materials are fundamental in determining the overall disposal safety. Specifically, given that thermal expansion causes thermal stress to canisters and intact rock masses in the near-field location, it is imperative to evaluate the thermal expansion characteristics of the buffer, particularly when bentonite is used. This study investigates the linear thermal expansion properties of Kyeongju bentonite buffer, a type of Ca-bentonite produced in South Korea. The linear thermal expansion coefficient of dried bentonite was measured considering the heating rate, dry density, and temperature variation using dilatometer equipment. The linear thermal expansion coefficient values of the KJ bentonite buffers were found to be 4.0–6.2 × 10⁻⁶/°C. Based on test results, a numerical analysis was conducted, and the thermal strain values were similar between the test and numerical analysis. The overall linear thermal expansion coefficient of the KJ bentonite, considering radially confined or unconfined conditions and dried or saturated states, was predicted to be between 3.2 × 10⁻⁶/°C and 1.0 × 10⁻⁵/°C.
... Among the raw materials, PV was the one with the highest proportion of particles smaller than 2 μm, known as the clay fraction. It also showed the highest index of plasticity, which confirms the dependence between PI and the clay fraction, previously reported by [28]. Materials with PI between 1 and 7% are considered weakly plastic, from 7 to 15% are moderately plastic and above 15%, highly plastic [29]. ...
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Four clay samples from different deposits in the state of Sergipe, Brazil, were fractionated by dispersion and centrifugation for comparative tests with a standard commercial clay used for cosmetic and pharmaceutical purposes. For this, they were characterized by X-ray diffraction, X-ray fluorescence spectroscopy, measurements of cation exchange capacity, oil absorption and viscosity, in addition to particle sizes and plasticity indexes. The objective was to determine the physical and chemical properties of raw clays and the consequent granulometric fractions to evaluate their potential use in products with high added value. After fractionation, the samples showed significant amounts of smectite and kaolinite, which combined with the size, particle distribution, chemical composition, and high adsorption capacity, especially in the PDL and PV samples, make them potentially interesting for applications in pharmaceutical and cosmetic products, they can also be used in spas and esthetic centers for therapeutic purposes based on their softness and cation exchange capacity.
... Les limites d'Atterberg sont les teneurs en eau présentant les limites de passage de l'argile d'un état plastique à un état liquide. La limite de plasticité (ωP) est la teneur en eau correspondante au passage de l'état solide à l'état plastique, et la limite de liquidité (ωL) correspond au passage de l'état plastique à l'état liquide [65] [67] [68]. ...
Thesis
Devant le besoin de renforcer les actions de réduction des consommations énergétiques pour respecter la réglementation thermique RT2012 qui implique d’avoir des bâtiments économes en énergie, l’amélioration de l’isolation thermique des matériaux de construction s’impose. Le projet BRITER financé par la région Nouvelle-Aquitaine et le Tremplin Carnot MECD, s’inscrit dans ce contexte et vise à développer des briques de terre cuite incorporant des déchets de bois d’ameublement pour en faire des produits de terre cuite poreux utilisables dans la maçonnerie porteuse et dont les propriétés d’isolation thermique sont optimisées. Pour réaliser ces matériaux, les déchets d’éléments d’ameublements (DEA) ont été sélectionnés et préparés pour être incorporés en tant qu’agent porogène dans un mélange argileux (MA). L’effet de la granulométrie et du taux d’incorporation des DEA sur les propriétés thermiques et mécaniques des produits MA/DEA cuits a été évalué. L’ajout des DEA dans le MA a permis d’augmenter le taux de porosité et par conséquent d’améliorer l’isolation thermique du produit. Les résultats ont démontré que l’ajout de 10 %m de DEA a conduit à une diminution de la conductivité thermique de 45 % par rapport au produit brut. L’incorporation des DEA dans le MA a conduit à une diminution des propriétés mécaniques. Cette diminution est directement proportionnelle au taux d’incorporation et à la granulométrie des DEA. Plus le taux d’incorporation et/ou la granulométrie sont élevés, plus la résistance mécanique est réduite. Toutefois, les valeurs des résistances mécaniques restent dans les normes des matériaux de construction en brique de terre cuite. Ce travail s’est également intéressé au bilan énergétique et l’impact environnemental liés au processus de cuisson des produits MA/DEA. Une dernière étude a porté sur le développement de matériaux poreux en terre cuite, incorporant des agents porogènes lamellaires, mis en forme par pressage, ce qui a permis d’orienter 80 % des pores créés perpendiculairement à la direction de pressage et de réduire ainsi la conductivité thermique jusqu’à 54 % par rapport au produit brut.
... Atterberg limits (liquid limit (LL) and plastic limit (PL)) were determined according to ASTM Standard (ASTM Standard D4318 2005) as described by Casagrande (1948) and Andrade et al. (2011). These limits are widely used for the optimization of ceramic bodies . ...
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This study aims to characterize the clayey materials from the site of Mzouda in the Marrakech area, one of the largest producers and suppliers of tajines in Morocco. This traditional production is only based on empirical knowledge of artisans, causing some flaws, such as cracking under the effect of thermal shocks. The physical, chemical and mineralogical characterization of the starting clayey material will improve understanding of the thermal shocks resistance character of Mzouda tajine. The physical properties of raw materials were identified by particle size distribution and consistency limits. Chemical composition was evaluated through XRF, total organic content and calcimetry, while mineralogical characteristics were investigated by the XRD technique. Two common raw clay materials used for Tajine’s manufacturing in Morocco were chosen as references. Results showed that the main oxides in the studied samples were SiO2 and Al2O3, whereas the other oxides were present only in small quantities. Quartz, feldspars and clay minerals were the dominant mineral phases, associated with minor phases of dolomite and hematite. Illite was the dominant phase among the clay minerals, followed by smectite, while kaolinite, chlorite and vermiculite may also be present in small abundance. Compared to the reference clays, the clay mixture adopted by the potters is adequate in terms of mineralogy and chemistry to produce Tajines. In terms of plasticity, the clay mixture used is suitable for moulding owing to its moderate plasticity parameters. However, the clay mixture used by the potters of Mzouda site has a fine texture with a relatively high percentage of clay fractions (28%), hence the need for some modifications, in particular grain size corrections, to make it suitable for Tajine manufacturing.
... Atterberg limits (liquid limit (LL) and plastic limit (PL)) were determined according to ASTM Standard (ASTM Standard D4318 2005) as described by Casagrande (1948) and Andrade et al. (2011). These limits are widely used for the optimization of ceramic bodies . ...
Article
Studies have been widely carried out on drying techniques and equipment. However, the analysis of the behavior of clays subjected to the drying stages becomes a topic that needs research. This study aims to evaluate the behavior of the clay ceramic body during the different zones of the drying cycle and match the characteristics of the raw materials with the final quality of the pieces. In this work, the behavior of three different clays in terms of drying performance was studied. The clays were selected, and their chemical, mineralogical, and particle size characteristics were measured. The mixture design (DoE) developed ten formulations and was processed through vacuum extrusion. The samples were subjected to forced drying cycles of 180 min, varying the temperature from 30 to 90°C and air speed from 1.5 to 4.0 m/s. At the end of the cycle, the retraction was a determining factor for the crack probability indicator, where formulations that obtained ∼10% retraction in the dry zone showed losses >25%. On the other hand, it is possible to state that claystone assists the drying process of the ceramic piece, minimizing losses. The drying sensitivity coefficient (k-factor) presented values that reproduce the number of losses during drying, proving to be a valid tool to relate clay properties, drying conditions, and losses in this process. In this case, drying process losses >25% were observed when the k-factor was from 1.6.
Article
Full-text available
In the forming of ceramic materials the plasticity concept is commonly used. This term is related to a particular mechanical behavior when clay is mixed with water. A plastic ceramic material shows a permanent strain without rupture when a compressive load produces a shear stress that exceeds the material's yield strength. For a plastic ceramic body it observes a measurable elastic behavior before the yield strength and when the applied load is removed. In this work, a mathematical model was developed from applied concepts of the plasticity theory by using the stress/strain diagram under compression.
Book
1. History and Classification.- 1.1. Early History.- 1.2. Industrial Revolution.- 1.3. Scientific Revolution.- 1.4. Classification of Structural Clay Products.- References.- 2. Mineralogical Composition of Structural Clay Products.- 2.1. Structure of Disilicate Minerals.- 2.2. Classification of Disilicate Minerals.- 2.3. Essential Minerals.- 2.4. Nonessential Minerals.- 2.5. Typical Compositions.- References.- 3. Raw Materials and Processing.- 3.1. Mining.- 3.1.1. Exploration for Raw Materials.- 3.1.2. Testing and Evaluation of Deposits.- 3.1.3. Mining Procedures.- 3 1 4 Mining Pollution Controls.- 3.2. Raw Material Processing.- 3.3. Particle-Size Distribution.- 3.4. Dust Pollution Controls.- 3.5. Blending and Additives.- References.- 4. Forming of Structural Clay Products.- 4.1. Structure and Properties of Water.- 4.2. Clay-Water Interaction.- 4.3. Plasticity of Clays.- 4.4. Plastic Forming Methods.- 4.4.1. Plasticity in Forming.- 4.4.2. Soft-Mud Process.- 4.4.3. Stiff-Mud Process.- 4.4.4. Plastic Pressing.- 4.4.5. Cutting of Extruded Columns.- 4.4.6. Automatic Hacking of Bricks.- 4.4.7. Dry-Press Forming.- References.- 5. Drying Process.- 5.1. Fundamentals of Drying Clay Bodies.- 5.2. Shrinkage, Stresses, and Strength.- 5.3. Practical Drying Schedules.- 5.4. Types of Dryers and Energy Sources.- 5.4.1. Periodic and Continuous Dryers.- 5.4.2. Energy Sources.- 5.5. Heat Balance in Dryers.- 5.6. Scum Development.- References.- 6. Firing Process.- 6.1. High-Temperature Reactions in Disilicate Minerals.- 6.2. Reactions in Typical Clay Bodies.- 6.3 Influences of Kiln Atmospheres.- 6.3.1. Kiln Atmospheres.- 6.3.2. Oxidation-Reduction.- 6.3.3. Oxidation of Carbon and Pyrite.- 6.3.4. Color Development and Control.- 6.4. Types of Kilns.- 6 5 Kiln Firing.- 6.6. Burner System.- 6.7. Cooling Stresses.- References.- 7. Decoration, Panels, and Packaging.- 7.1. Sanded Surfaces.- 7.2. Texturing of Extruded Bricks.- 7.3. Coating Decorations.- 7.3.1 Engobes and Slurries.- 7.3.2. Glazes.- 7.4. Panelling.- 7.5. Packaging.- References.- 8. Jointing of Vitrified Clay Sewer Pipe.- 8.1. Factory Installed Jointing Units.- 8.2. Requirements for Good Joints.- 8.3. Types of Compression Joints.- 8.3.1. Polyvinyl Chloride Joints.- 8.3.2. Polyester Joints.- 8.3.3. Polyurethane Joints.- 8.3.4. Jointing of Plain-End Pipes.- 8.4. Specifications and Tests for Vitrified Clay Pipe Joints.- References.- 9. Quality Control.- 9.1. Philosophy.- 9.2. Nature of the Quality-Control Program.- 9.3. Procedure.- 9.4. Statistical Approach.- References.- 10. Plant Layout and Design.- 10.1. Predesign Planning.- 10.2. Factors Affecting Plant Design.- 10 3 Planning for Starting the Plant.- References.- 11. Serviceability and Durability.- 11.1. Serviceability of Structural Clay Products.- 11.2. Durability of Bricks and Roofing Tiles.- 11.3. Durability of Sewer Pipes.- 11.4. Moisture Expansion.- 11.5. Bonding of Mortar to Bricks and Tiles.- 11 6 Efflorescence and Staining of Brickwork.- 11.7. Cleaning Brickwork.- References.- 12. Future Trends.- 12.1. Production.- 12.2. Technical Changes.- 12.3. Research of the Future.- 12 4 Summary.- References.
Article
Cone tip resistance is the most widely measured quantity in the cone penetration test. A brief review is made of presently available theories for the analysis of cone resistance. The theories are presented in farms that enable direct comparisons among them. The simplifying assumptions made in the analysis using various theories are emphasized. In the light of experimental evidence and the fundamental principles of mechanics, the limitations and advantages of each theory are: assessed. Comparison with limited experimental data indicates that cavity expansion theories give the closest overall agreement between predicted and measured penetration resistance.