The dependence of the value of ceramics resistance to frost on the composition of raw material mixture/Keramikos atsparumo salciui priklausomybe nuo formavimo misinio sudeties.
Maciulaitis, Romualdas ; Malaiskiene, Jurgita
1. Introduction
An increase in the operational resistance of products to frost is a
very recurring problem, especially in Lithuania, because the buildings
built a few years lose their original appearance (rip off, crumble etc.)
and start collapsing. Resistance of a porous body to frost is a physical
feature indicating the ability to maintain the change limits of some
physical parameters set before the porous body was alternately frozen
and thawed after being soaked.
The resistance of material to frost is expressed in the number of
freezing and thawing cycles where the product coped without any
collapse. The criteria of evaluating resistance to frost are as follows:
a decrease in compressive strength, mass change, visible breaks and
other abrasions (Maciulaitis 1996; [TEXT NOT REPRODUCIBLE IN ASCII]
1997).
We need to regulate the operational resistance of ceramic products
to frost just from the initial moment of the technological process that
includes the selection and dosage of raw material. Therefore, we need to
know how the amount of each component included in the formation mix
influences the final properties of ceramics and especially operational
resistance to frost.
Some scientists (Petrikaitis 1999; Maciulaitis et al. 1995;
Daunoraviciute and Petrikaitis 1997; Kizinievic et al. 2005) were
investigating how the components of the formation mix (the supplements
of peat, coal, sawdust, the dust of wood and dolomite) might influence
the final properties of ceramics, including resistance to frost. They
concluded that a supplement of 1.42% of coal (to 1.5 mm) to the
formation mix increased the indicator of the reserve of pore volume to
22% and the operational resistance of products to frost--to 42 cycles.
However, compressive strength decreases about 33%. The quantity of 4% of
dry peat and 1.5% of coal in the formation mix increase the indicator of
the reserve of pore volume to 37% and the operational resistance of
products to frost to 60 cycles. However, compressive strength also
decreases. More than 5% of sawdust in the formation mix increases the
values of the reserve of pore volume to 30%, however, it extremely
decreases the strength of the products. When decreasing the amount of
sawdust to 4% and adding 1 % of coal, the values of the reserve of pore
volume and mechanical strength increase, however, operational resistance
to frost includes only 48 cycles. The supplements of (3-4%) of the dust
of wood and (1-1.5%) of coal conclude less reserve pores than the same
amount of sawdust and peat, and thus the mechanical strength of products
does not increase. Moreover, the preparation of the formation mix with
the dust of wood is more complex; therefore, the scientists suggest not
using the abovementioned supplement.
A minor dispersal supplement of dolomite raises the operational
resistance of products to frost; however, larger dolomite worsens most
of the final properties of ceramics. Chalk increases the mechanical
strength of ceramic bricks, however, operational resistance to frost
reaches 49 frost-defrost cycles. The work by Maciulaitis et al. (2004)
determined the kind of structural indicators that in most cases
influenced an increase or a decrease in resistance to frost. The
scientists (Kizinievic and Petrikaitis 2005; Kizinievic et al. 2006)
also were exploring the influence of clay properties, reducing, firing,
waste addition, mixing efficiency, the degree of pressure in formation
head, the depth of rare characteristics of the vacuum chamber and the
duration of keeping at the highest firing temperature considering
resistance to frost. Other scientists (Correia et al. 2004a) discovered
that poppy-seeds in ceramics formed more closed pores and the density of
such samples made about 2500 kg/m as the mix was burned at a temperature
of 1570[degrees]C. The valuable results of the performed analyses are
described in the work by (Bhattacharjee et al. 2007) showing how the
porosity of aluminous (alumo-silicates) articles depends on the amount
of albumin and starch in the formation mix. Adding albumin to the
formation mix allows forming more closed and less open pores, and starch
increases in the number ofjoined pores.
Some scientists (Gregorova and Pabst 2007; Dondi et al. 2003;
Correia et al. 2004b) derived empirical equations with a possibility of
forecasting the values of shrinking ceramics and water absorption in
accordance with the composition of the formation mix (clay, feldspar and
quartz). It is found that when increasing the amount of feldspar in the
formation mix up to 65% we would obtain water absorption of ceramic
crushed bricks close to zero and when increasing the amount of quartz in
the formation mix up to 65% we would highly decrease the firing
shrinkage of the samples (from 11.35% to 3.32%). However, these
scientists did not define how the components of the formation mix would
influence the operational resistance of ceramics to frost. The
scientists (Raimondo et al. 2009) also researched the durability of clay
roofing tiles having influence on phase composition. It was established
that quartz, plagioclase and pyroxene made the most positive influence
on the resistance of clay roofing tiles to frost.
The aim of this work is to find out the components of the formation
mix having the most positive and negative influence on the operational
resistance of ceramics to frost. Besides, the equation forecasting the
operational resistance of ceramics to frost in accordance with the
amounts of the components of the formation mix was determined.
2. Characteristics of Materials. Research Methods
The samples were formed based on plastic shaping from raw materials
as follows: clay from the Girininkai deposit, sand from the Daugeliai
deposit, crushed bricks (milled waste of ceramic bricks) from Rokai
factory, peat from the Rekyvai deposit, anthracite from Archangelsk
region and milled glass. The X-ray pattern (Maciulaitis and Zurauskiene
2007) of the main raw material--clay from the Girininkai deposit is
presented in Fig. 1 and chemical and granulometric (Maciulaitis et al.
2008; Maciulaitis and Malaiskiene 2009; Mandeikyte and Siauciunas 1997)
compositions are accordingly shown in Tables 1 and 2.
According to the analysis of the X-ray pattern of clay from
Girininkai (Maciulaitis and Zurauskiene 2007) (Fig. 1), the minerals of
clay are as follows: hydromica H (0.990, 0.498, 0.448, 0.256, 0.199) nm,
kaolinite K (0.710, 0.335, 0.199) nm, chlorite X (1.410, 0.710, 0.355)
nm, quartz Q (0.425, 0.335, 0.245, 0.228, 0.224, 0.213) nm, dolomite Do
(0.288, 0.240, 0.219) nm, calcite Ca (0.304, 0.249, 0.209, 0.191, 0.188)
nm and some feldspar Ls (0.324 nm). Based on the fired process of the
initial clay minerals from Girininkai, the phases are formed as follows:
hematite F ([Fe.sub.2][O.sub.3]), gelenite G (2CaO [Al.sub.2][O.sub.3]
Si[O.sub.2]), anortite A (CaO x [Al.sub.2][O.sub.3] x 2Si[O.sub.2]),
diopside D (CaO-MgO-2Si[O.sub.2]), cristobalite Kr (Si[O.sub.2]) and
glass phase.
According to the chemical composition, clay mixture from Girininkai
is half-acid with a great amount of iron oxide.
In addition, it includes a great amount of CaO + MgO (more than
10%), which contracts a sintering interval, and therefore, conditions
for firing ceramic articles become worse and the obtained products are
less firm and not resistant to frost.
[FIGURE 1 OMITTED]
Particularly damaging are insertions larger than 1 mm of
CaC[O.sub.3], because firing semi-manufactures produce CaO able to slake
in a humid environment which destroys the products. [K.sub.2]O and
[Na.sub.2]O make the melting temperature of clay lower, accelerate
sintering clay and extend the sintering interval. However, the quantity
of these oxides is sufficiently low (about 2%). L.O.I. is composed of
organic impurities, water from clay minerals and C[O.sub.2], which is
split from carbonates. According to the quantity of clayey particles,
this clay is very dispersive (Malaiskiene 2008).
The compositions of the formation mixtures selected to form ceramic
samples are presented in Table 3.
Selecting the composition of formation mixes, it was taken into
account that an additive of milled glass was effective when came up to
20% in a formation mix. Also, this addition must be dispersive enough,
because during the firing process, larger particles of milled glass may
diffuse into the surface of a product (Paulaitis and Vysniauskas 1995).
The dosage of components was performed according to mass. First, a
dry formation mix was stirred manually, later it was irrigated to
moisture appropriate to form. Such a mass is left for three days in an
environment of (95 [+ or -] 5%) of humidity in order to distribute
moisture in the formation mix evenly. In three days time, the ceramic
samples were formed and obtained dimensions of 70x70x70 mm.
First, the formed semi-manufactures were dried in a laboratory
under natural conditions, and at a later stage in the electrical stove.
Consequently, the dried samples were fired in the electrical stove under
an appropriate regime (Fig. 2).
[FIGURE 2 OMITTED]
Five samples were selected from each batch in order to determine
resistance to frost that was determined following LST 1272-92 standard
(LST 1272-92 1993) and applying the one-sided freezing and thawing
method.
The samples had been soaked for three days before the experimental
fragment was formed.
Then, the fired samples were frozen for 8 hours from minus
15[degrees]C to minus 20[degrees]C. Next, the samples underwent the
thawing procedure for 8 hours at a temperature of (20-25[degrees]C) (LST
1272-92 1993). The destruction of ceramics was rated according to its
cycle of disintegration starting using any criteria of the collapse of a
cold surface: stratification, crumbling, cracking and cleaving. The
physical-mechanical and structural parameters of formed, dried and
burned ceramic samples were determined following LST EN 771-1+A1 and
other known methodologies (Kicaite et al. 2010; Malaiskiene 2008;
Mandeikyte and Siauciunas 1997).
3. Research Results
The average values of some physical-mechanical and structural
properties are presented in Table 4 showing that maximum density,
compressive strength, the reserve of pore volume and minimum water
absorption have samples providing a maximum amount of milled glass
(formation mixes 3, 5, 6). The sample indicating a maximum amount of
peat (formation mix 2) has minimum density, compressive strength, the
reserve of pore volume and maximum water absorption. With reference to
the obtained results, it can be predicted that the samples of formation
mixes 3, 5 and 6 will have the highest value of resistance to frost,
whereas the samples of formation mix 2-will have the lowest one.
[FIGURE 3 OMITTED]
The average experimentally determined values of operational
resistance to frost are presented in Fig. 3. The view of the samples
followed the one-sided freezing and thawing procedure is shown in Fig.
4.
Fig. 3 shows that the maximum values of operational resistance to
frost are derived from the samples of batches 3, 4, 5 and 6 in which
milled glass was used as an additive. In other cases, the values of
operational resistance to frost are significantly lower.
Fig. 4 indicates that following one-sided freezing and thawing
ceramic samples start flaking off.
[FIGURE 4 OMITTED]
The X-ray pattern of the most characteristic third formation mix
(Table 1) is presented in Fig. 5.
[FIGURE 5 OMITTED]
Phases as: quartz Q (0.153, 0.167, 0.182, 0.198, 0.213, 0.224,
0.227, 0.245, 0.334, 0.424) nm, hematite F (0.169, 0.184, 0.222, 0.252,
0.269, 0.367) nm, diopside D (0.202, 0.252, 0.294, 0.298, 0.319) nm and
anortite A (0.177, 0.256, 0.322, 0.346, 0.380, 0.405) nm were
identified.
4. Statistical Data Analysis
Statistical data analysis was performed in order to determine how
the value of the operational resistance of ceramic products to frost
depended on the content of the components of the formation mix. Grouping
data and preparation for research were performed applying
"Microsoft Excel" and "Statistica" programs.
Statistical analyses were made according to available literature
(Cekanavicius and Murauskas 2002; MaHHTa 2001; Ostle et al. 1996; Huang
and Hsueh 2007). In order to determine mathematical interdependence, the
function having multivariate correlation and determination coefficients
closest to one was selected. Regression analysis also finds useful to
know the average standard deviation measure from the regression graph.
The average standard deviation measure is defined as the square root of
the fixed square sum of the deviation of errors (Kleinbaum et al. 1998;
Graybill et al. 1994). It was verified in case the distribution of
experimental results was normal using KolmogorovSmirnov criterion
(MaHHTa 2001). If the value of the introduced criterion is lower than
that presented in the statistical table (selected according to the
number of samples and the level of importance (in our case it makes
0.05), it is considered a normal distribution of data. For example, as
we analyze the values of 40 samples at a significance level of 0.05, the
value presented in Kolmogorov-Smirnov statistical table makes 0.210
(MaHHTa 2001). The adequacy of the derived equations was checked using
Fisher criterion. If the above mentioned indicator of an equation is
higher than that presented in the reference table, the equation is
considered adequate and appropriate to describe experimental data. For
example, when studying 40 samples at a significance level of 0.05, the
value presented in the table of Fisher criterion is equal to 2.44
(MaHHTa 2001). The significance of the variables of the equation was
determined applying the Stjudent criterion. If the value of the
indicator is higher than that presented in the reference table (when
studying 40 samples at a significance level of 0.05, the value presented
in the statistical table of the Stjudent criterion is equal to 1.96), it
is considered a significant indicator (Gatti 2005).
First, the diagram showing how each supplement of the formation mix
influences operational resistance to frost was drawn (Fig. 6).
Fig. 6 displays that the operational resistance of ceramics to
frost is most positively influenced by the amount of milled glass in the
formation mix. Also, the operational resistance of ceramics to frost is
positively influenced by the amount of crushed bricks, sand and
anthracite. The amount of peat in the formation mix decreases
operational resistance to frost.
[FIGURE 6 OMITTED]
The regression Eq. (1) evaluating the influence of the components
of the formation mix on the indicator of operational resistance to frost
(y) was formed according to the direct progressive forward stepwise
method ensuring the progressive insertion of independent variables
having the highest coefficients of partial correlation with the
dependent variable in calculating the regression equation (i.e. the
indicators are connected progressively in order the sum of deviations is
the smallest). The values of correlation, determination and average
standard deviation as well as the Stjudent criterion of the derived
empirical equation are presented in Table 5.
y = -82.08+1.23[x.sub.1]+8.48[x.sub.3]+4.48[x.sub.4]. (1)
Table 5 shows a strong linear relationship between operational
resistance to frost and the components of the formation mix because the
correlation coefficient of 0.984 is very close to one. According to the
signs of empirical equation (1) and the values of the Stjudent criterion
of the components of the formation mix presented in Table 5, the
operational resistance of ceramics to frost is most positively
influenced by the amounts of milled glass, crushed bricks and clay
materials in the formation mix (the value of the Stjudent criterion in
statistical Table is 1.96). Other components of the formation mix do not
have such a big influence on operational resistance to frost.
It is possible to explain a positive influence of milled glass on
operational resistance to frost referring to the fact that this
component of the formation mix partially melts at a lower temperature
than clay composition forming an aggressive liquid phase. The driving
force of this firing process is the tension of a melt surface because
negative pressure in closed pore is formed. In such an action, the pores
of ceramic material are filled with melt and particles draw closer to
one another.
When more liquid phase is composed and smaller particles of glass
and clay are present, the diffusion process in a sample goes more
intensively. The particles of material regroup because of this process,
the quantity of open pores with irregular shape decreases and the pores
of a closer, smaller and more regular shape are formed. Therefore, the
reserve of porous volume particularly increases and mostly affects a
rise in the value of operational resistance to frost (Maciulaitis et al.
2004). A positive influence of the crushed bricks on the value of
ceramics resistance to frost could be explained by the fact that the
already fired particles of the crushed bricks have an irregular shape
and stimulate the sintering process providing the product with a
stronger inner carcass thus simultaneously making clay thinner. A
negative influence of the peat additive (Fig. 6) to the value of
operational resistance to frost could be explained by the fact that this
burning out additive composed ceramic systems with open pores and
capillaries allowing water migration. Water expands while freezing and
destroys these products more rapidly.
5. Conclusions
The highest value of resistance to frost was received for samples
that exhibited the highest density, compressive strength, the reserve of
pore volume and the lowest water absorption value. These batches were
designed based on the largest amount of milled glass. The minimum
resistance to frost value was received for samples that exhibited the
lowest density, compressive strength, the reserve of pore volume and the
highest value of water absorption. In these batches, the largest amount
of peat was used while the glass component was absent.
Regression analysis was performed and the influence of the amount
of each component of the formation mix on operational resistance to
frost was evaluated. It was determined that operational resistance to
frost could be highly increased by the presence of the milled glass
component and crushed bricks in the designed mix. Operational resistance
to frost is mostly reduced by an increase in peat amount in the mixture.
doi: 10.3846/13923730.2011.554164
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MaHHTa, A. [TEXT NOT REPRODUCIBLE IN ASCII] [Manita, A. D. Theory
of chance and mathematical statistics]. [TEXT NOT REPRODUCIBLE IN
ASCII].
[TEXT NOT REPRODUCIBLE IN ASCII] [Maciulaitis, R. Frost resistance
and durability of fasade ceramic products]. Vilnius: Technika. 307 c.
Romualdas Maciulaitis (1), Jurgita Malaiskiene (2)
Department of Building Materials, Vilnius Gediminas Technical
University, Sauletekio al. 11, LT-10223 Vilnius, Lithuania
E-mails: (1) romualdas.maciulaitis@vgtu.lt; (2)
jurgita.malaiskiene@vgtu.lt (corresponding author)
Received 21 Oct. 2009; accepted 30 Sept. 2010
Romualdas MACIULAITIS. Professor, a Habilitated Doctor of
Technological Sciences at the Department of Building Materials of
Vilnius Gediminas Technical University (VGTU). Research interests:
development of building materials and analysis of their characteristics.
Jurgita MALAISKIENE. A Doctor of Technological Sciences at the
Department of Building Materials of Vilnius Gediminas Technical
University (VGTU). Research interests: development of new conglomerates
from local resources, research of their properties and possibilities of
using them.
Table 1. The average chemical composition of clay
Chemical composition, wt %
Si[O.sub.2] [Al.sub.2] [Fe.sub.2] CaO MgO [K.sub.2]O
[O.sub.3] [O.sub.3]
+ Ti[O.sub.2]
47.66 18.32 6.27 8.11 3.04 2.68
Si[O.sub.2] [Na.sub.2]O S[O.sub.3] L.O.I
47.66 0.16 -- 12.60
Table 2. The average granulometric composition (mm) of clay
Particle size distribution, wt %
more than from 0.5 to from 0.2 to from 0.09 to from 0.06 to
0.5 0.2 0.09 0.06 0.01
0.13 0.07 0.10 0.08 4.58
more than from 0.01 to from 0.005 to less than
0.5 0.005 0.001 0.001
0.13 9.28 24.28 61.48
Table 3. The compositions of formation mixes
Formation The amount of The amount of The amount of
mix clay sand glass
[x.sub.1], % [x.sub.2], % [x.sub.3], %
1 74.5 18.0 0.0
2 80.0 15.0 0.0
3 70.5 12.0 10.0
4 69.5 18.0 5.0
5 59.5 18.0 15.0
6 54.0 30.0 10.0
7 82.5 10.0 0.0
8 82.5 10.0 0.0
Formation The amount of The amount of The amount
mix crushed bricks anthracite of peat
[x.sub.4], % [x.sub.5], % [x.sub.6], %
1 6.0 1.5 0.0
2 0.0 0.0 5.0
3 6.0 1.5 0.0
4 6.0 1.5 0.0
5 6.0 1.5 0.0
6 5.0 1.0 0.0
7 5.0 0.0 2.5
8 5.0 2.5 0.0
Table 4. The average values of physical-mechanical and structural
properties: p--density, [R.sub.gn]--compressive
strength, [R.sub.p]--reserve of pore volume, [W.sub.h]--water
absorption following 72 h
Formation P, [R.sub.gn], [R.sub.p], [W.sub.h],
mix kg/[m.sup.3] MPa % %
1 1752 24.34 43.64 9.31
2 1624 19.35 39.56 12.72
3 2022 39.11 65.75 2.90
4 1920 29.74 49.15 5.75
5 2246 40.99 71.15 2.34
6 2170 28.94 48.62 4.34
7 1626 27.86 48.43 8.80
8 1664 29.20 47.28 8.21
Table 5. The values of correlation R, determination [R.sup.2],
average standard deviation se and the Stjudent criterion of
empirical, Eq (1)
The values of Stjudent criterion
R [R.sup.2] [s.sub.e), The amount The amount The amount
in cycles of clay of glass of crushed
([x.sub.1]) ([x.sub.3]) bricks
([x.sub.4])
0.984 0.968 7.98 4.88 18.7 6.15
