 Agricultural wastes as a resource of raw materials for developing low-dielectric glass-

ceramics
 Satwinder Singh Danewalia, Gaurav Sharma, Samita Thakur K. Singh
 Scientific Reports volume6, Article number: 24617 (2016) doi:10.1038/srep24617
Agricultural wastes could be used as resource materials in many engineering
applications. In general, silica is a major constituent of the agricultural waste ash. It
varies from 98–36 wt% in ash of rice husk, sugarcane leaves and corn husk etc 1. In
addition to silica, other metal oxides like CaO, MgO and K 2O are also present along
with some trace elements 2. Rice husk after burning in air, produces highly reactive
silica particles (usually nanosized) 3. During this process, about 20% of biomass
remains as ash, which contains different minerals 4. These minerals can be
amorphous or crystalline depending upon the conditions in which rice husk is burnt.
On the other hand, sugarcane leaves ash (SCLA) have silica along with alkali and
alkaline earth metal oxides as the major constituents5. Silica, derived from the
waste, can be utilized as raw materials to form different high performance
materials, such as glasses, refractories, capacitors, glass sealants, bioceramics,
fibres and optical cavities, etc 6,7,8. In addition to this, silica can also be converted to
silicon after heating in the presence of activated charcoal. The formed silicon, after
refinement, can be used in solar energy production and electronic chips 9.

Formation of glasses and glass-ceramics from the agriculture waste have many
benefits. It is environment friendly, economical and renewable source of high
content silica. Moreover, it could be better and effective way to manage huge
agricultural waste for producing different engineering materials. Additionally,
during melt-quench process, the organic contents present in the waste materials
convert in various gasses. These by-product gasses can be collected for further
applications. Moreover, these gasses act as in-situ foaming agents and enhance the
inherent porosity in the glasses and glass-ceramics. Inherent porosity in the glasses
and glass-ceramics decreases the thermal conductivity, dielectric permittivity and
density. On the other hand, it enhances the sensing and absorption of sound
waves10. So, these glasses and glass-ceramics can readily find applications in the
microelectronic devices, such as band-pass filters, dielectric resonant antennas and
oscillators etc. For these applications, the material should have dielectric
permittivity ~10 or above at room temperature with good thermal and mechanical
stability. It also must have temperature and frequency independent behaviour in the
microwave frequency region 11. Silica and silicate based glasses could meet these
requirements. High silica glasses are required for thermophotovoltaic system due to
their good resistance to heat and thermal shock12. The disadvantage of the glasses
and glass-ceramics derived from the agricultural wastes is the inability to vary the
amount of different oxides, which prevents to tailor the properties according to the
need and applications. This problem can be addressed by using different
agricultural waste materials, which have different SiO 2 content along with other
elemental oxides as reported by Cornejo et al.1. So, the raw materials obtained from
different agricultural waste ashes will provide necessary components for glass
formation i.e. network former (SiO 2) as well as network modifiers (K 2O, CaO, MgO
etc.) along with some trace elements. The trace elements may play important role to
decide various properties of these glasses and glass-ceramics, since the role of trace
elements is not known yet 1.
Production of clay ceramics using agricultural wastes: Study of properties,
energy savings and environmental indicators
R. Sani⁎, A. Nzihou
Université de Toulouse, Mines Albi, CNRS, Centre RAPSODEE, Campus Jarlard, Route de
Teillet, F-81013 Albi Cedex 09, France
ARTICLEINFO
Keywords:
Ceramics
Agro-wastes
Thermal conductivity
Mechanical strength
Energy savings
Environmental indicators
ABSTRACT
In this study, agro-wastes were used as additive raw materials for the production of fired clay
ceramics. The
objectives of this study are to evaluate the impact of adding agro-wastes into clay body on the
thermal and
mechanical properties of ceramic materials, to determine the net energy consumption and to
determine gas
emissions during firing process. The clay and agro-wastes were characterized by chemical
elemental analysis,
thermogravimetric and differential thermal analysis (TGA-DTA). The fired clay ceramics
were produced with
clay and optimal proportions of wheat straw (WS) and olive core flour (OCF). The thermal
and mechanical
properties were evaluated by measuring thermal conductivity with hot-disk method and
bending test
respectively. The results showed that for clay incorporated OCF (4, 8 wt%) and WS (3, 7
wt%), thermal
conductivity was decreased by 16 to 30%. However, the mechanical strength of the same
samples has slightly
decreased respectively. TGA-DTA provided an approach to estimate the heat required or
released for both clay
and agro-wastes thermal decomposition. The addition of agro-wastes into the clay body
showed that energy
consumption of fired clay ceramics production decreased to above 36% for clay incorporated
4 wt% OCF (C-4wt
%OCF). The energy saving during the firing process was a tangible outcome. In order to
determine the impact of
the agro-wastes addition, the environmental indicators were discussed for the clay
incorporated WS and OCF
respectively. Total gas yield released were measured by Micro-GC after the combustion of
clay incorporated OCF
and WS in fixed bed reactor respectively. The analysis of gas emissions are related to the
combustion of organic
and inorganic compounds of agro-wastes and clay body, respectively. The CO2 emissions
coming from the
combustion of agro-wastes reached up to 4.38% for C-8wt%OCF. However, the CO2
emissions associated with
decarbonatation of clay body decreased. Adding agro-wastes into the clay body results to
improving thermal
properties without negative impact on the mechanical properties of ceramic materials, also to
a significant
energy saving and decreasing of the inorganic CO2 emissions related to the decarbonatation
of clay body. The
relevance of this work, pointed out in the data presented in regards to the state-of-the art is
that the paper is
focused on fired clay ceramic properties, on energy savings and on the evaluation of
environmental indicators in
the laboratory scale.
1. Introduction
Several scientific research have been carried out on the study of the
physical and chemical properties of ceramic materials in their production
process in order to optimize their final properties (Cultrone et al.,
2004a; Vassilev et al., 2013). Number of studies have investigated the
use of industrial and organic wastes to produce ceramic material such
as bricks (Demir, 2006; Muñoz Velasco et al., 2014; Raut et al., 2011)
including sewage sludge, fly ash and organic residues from agroindustries
paper or wood. (Demir, 2006) mixed Processed Waste Tea
(PWT) with clay body to improve the insulation ability of bricks by
generating porosity. This author noticed also that the compressive
strength of ceramic materials increased significantly by adding PWT
into the clay body. Also, the microstructure of clay and additives,
granulometry and the contents of additives were studied to develop the
optimal formulations (Faria et al., 2012; Madurwar et al., 2013).
The consumption of earth-based materials such as clay and sand in
the production of bricks resulted in resources depletion, environmental
degradation and energy consumption. The biomass as an agricultural
product has been used as an energy source to lower energy consumption
in brick manufacturing process. The application of these agrowastes
for the production of ceramic materials is consistent with the
concept of improving the efficiency of management and the environmental
impact of wastes (Zabalza Bribián et al., 2011). From a
Agri waste as addetives for clay
Abstract
In this study, agro-wastes were used as additive raw materials for the production of fired clay
ceramics. The objectives of this study are to evaluate the impact of adding agro-wastes into
clay body on the thermal and mechanical properties of ceramic materials, to determine the net
energy consumption and to determine gas emissions during firing process. The clay and agro-
wastes were characterized by chemical elemental analysis, thermogravimetric and differential
thermal analysis (TGA-DTA). The fired clay ceramics were produced with clay and optimal
proportions of wheat straw (WS) and olive core flour (OCF). The thermal and mechanical
properties were evaluated by measuring thermal conductivity with hot-disk method and
bending test respectively. The results showed that for clay incorporated OCF (4, 8 wt%) and
WS (3, 7 wt%), thermal conductivity was decreased by 16 to 30%. However, the mechanical
strength of the same samples has slightly decreased respectively. TGA-DTA provided an
approach to estimate the heat required or released for both clay and agro-wastes thermal
decomposition. The addition of agro-wastes into the clay body showed that energy
consumption of fired clay ceramics production decreased to above 36% for clay incorporated
4 wt% OCF (C-4wt%OCF). The energy saving during the firing process was a tangible
outcome. In order to determine the impact of the agro-wastes addition, the environmental
indicators were discussed for the clay incorporated WS and OCF respectively. Total gas yield
released were measured by Micro-GC after the combustion of clay incorporated OCF and
WS in fixed bed reactor respectively. The analysis of gas emissions are related to the
combustion of organic and inorganic compounds of agro-wastes and clay body, respectively.
The CO2 emissions coming from the combustion of agro-wastes reached up to 4.38% for C-
8wt%OCF. However, the CO2 emissions associated with decarbonatation of clay body
decreased. Adding agro-wastes into the clay body results to improving thermal properties
without negative impact on the mechanical properties of ceramic materials, also to a
significant energy saving and decreasing of the inorganic CO2 emissions related to the
decarbonatation of clay body. The relevance of this work, pointed out in the data presented in
regards to the state-of-the art is that the paper is focused on fired clay ceramic properties, on
energy savings and on the evaluation of environmental indicators in the laboratory scale.

Production of clay ceramics using agricultural wastes: Study of properties,... | Request PDF.
Available from:
https://www.researchgate.net/publication/317299157_Production_of_clay_ceramics_using_a
gricultural_wastes_Study_of_properties_energy_savings_and_environmental_indicators
[accessed Mar 12 2018].

CONCLUSIONS
The effect of 3 mass %, 5 mass % and 8 mass % of wheat straw and sunflower seed husks on the
properties of porous ceramic samples fired at 900o C is elucidated. Both biomasses studied can be
effectively used for pore forming. The apparent density of the fired products decreases with the
addition of biomass due to the increased number of pores created through combustion of the
organic biomass matter, as indicated by the TGA–DTA curves. The increase of the amount of the
pore-forming additive increases the porosity but decreases the thermal conductivity of the samples.
The presence of up to 3 mass % of sunflower seed husks provides compressive strength which is
standard for this type of pottery. An amount of 3 % sunflower husks in the composition of the light
porous ceramic bricks is recommended. The presence of 8 mass % wheat straw decreases the
compressive strength to the limit of the standard (10 MPa). A quantity of 5 % wheat straw is
recommended because the thermal conductivity is reduced by 50 % when compared to that of a
ceramic sample with no additive but the value obtained is greater than the standard one for this
type of material.

Properties and phase composition of the ceramic samples The apparent density of the clay
samples containing no additives is 1.6 g/cm3 . The apparent density of the fired porous samples
decreases with the addition of biomass due to the increased number of pores created by
combustion of the organic biomass compounds. Fig. 4 shows that the apparent density of the porous
clay samples containing 8 mass % wheat straw is 1.23 g/ cm3, while that of the samples containing
sunflower seeds husks is 1.32 g/cm3 . The values of the apparent porosity increases with the
addition of biomass from 32 % for the sample with no pore-forming additive to 53% for the samples
containing 8 mass % WS and 50 % for those cointaining 8 % mass % HSS. This is more than 50 % of
the apparent porosity of the sample without additives. The addition of 8 mass % WS to the basic clay
body decreases the thermal conductivity of the fired clay product from 1,0 W/m·K (for samples
without an additive) to 0.5 W/m·K (a decrease of 50 %). The thermal conductivity of the clay brick
sample decreases to 0,6 W/m·K in presence

Agricultural wastes as a resource of

raw materials for developing
lowdielectric
glass-ceramics
Satwinder Singh Danewalia1, Gaurav Sharma1, Samita Thakur2 & K. Singh1
Agricultural waste ashes are used as resource materials to synthesize new glass and glass-ceramics.
The as-prepared materials are characterized using various techniques for their structural and dielectric
properties to check their suitability in microelectronic applications. Sugarcane leaves ash exhibits
higher content of alkali metal oxides than rice husk ash, which reduces the melting point of the
components due to eutectic reactions. The addition of sugarcane leaves ash in rice husk ash promotes
the glass formation. Additionally, it prevents the cristobalite phase formation. These materials are
inherently porous, which is responsible for low dielectric permittivity i.e. 9 to 40. The presence of less
ordered augite phase enhances the dielectric permittivity as compared to cristobalite and tridymite
phases. The present glass-ceramics exhibit lower losses than similar materials synthesized using
conventional minerals. The dielectric permittivity is independent to a wide range of temperature
and frequency. The glass-ceramics developed with adequately devitrified phases can be used in
microelectronic devices and other dielectric applications.

Agricultural wastes could be used as resource materials in many engineering applications. In general, silica is
a major constituent of the agricultural waste ash. It varies from 98–36 wt% in ash of rice husk, sugarcane leaves
and corn husk etc1. In addition to silica, other metal oxides like CaO, MgO and K2O are also present along with
some trace elements2. Rice husk after burning in air, produces highly reactive silica particles (usually nanosized) 3.
During this process, about 20% of biomass remains as ash, which contains different minerals4. These minerals can
be amorphous or crystalline depending upon the conditions in which rice husk is burnt. On the other hand, sugarcane
leaves ash (SCLA) have silica along with alkali and alkaline earth metal oxides as the major constituents5.
Silica, derived from the waste, can be utilized as raw materials to form different high performance materials, such
as glasses, refractories, capacitors, glass sealants, bioceramics, fibres and optical cavities, etc6–8. In addition to this,
silica can also be converted to silicon after heating in the presence of activated charcoal. The formed silicon, after
refinement, can be used in solar energy production and electronic chips 9.
Formation of glasses and glass-ceramics from the agriculture waste have many benefits. It is environment
friendly, economical and renewable source of high content silica. Moreover, it could be better and effective way to
manage huge agricultural waste for producing different engineering materials. Additionally, during melt-quench
process, the organic contents present in the waste materials convert in various gasses. These by-product gasses
can be collected for further applications. Moreover, these gasses act as in-situ foaming agents and enhance the
inherent porosity in the glasses and glass-ceramics. Inherent porosity in the glasses and glass-ceramics decreases
the thermal conductivity, dielectric permittivity and density. On the other hand, it enhances the sensing and
absorption of sound waves10. So, these glasses and glass-ceramics can readily find applications in the microelectronic
devices, such as band-pass filters, dielectric resonant antennas and oscillators etc. For these applications,
the material should have dielectric permittivity ~10 or above at room temperature with good thermal
and mechanical stability. It also must have temperature and frequency independent behaviour in the microwave
frequency region11. Silica and silicate based glasses could meet these requirements. High silica glasses are required
for thermophotovoltaic system due to their good resistance to heat and thermal shock12. The disadvantage of
the glasses and glass-ceramics derived from the agricultural wastes is the inability to vary the amount of different
oxides, which prevents to tailor the properties according to the need and applications. This problem can be
addressed by using different agricultural waste materials, which have different SiO 2 content along with other
1School of Physics and Materials Science, Thapar University, Patiala-147004, India. 2Department of Physics, School
of Basic Sciences, Arni University, Kathgarh-176401, India. Correspondence and requests for materials should be
addressed to K.S. (email: kusingh@thapar.edu)
received: 04 December 2015
accepted: 30 March 2016
Published: 18 April 2016

OPEN
www.nature.com/scientificreports/
Scientific Reports | 6:24617 | DOI: 10.1038/srep24617 2
elemental oxides as reported by Cornejo et al.1. So, the raw materials obtained from different agricultural waste
ashes will provide necessary components for glass formation i.e. network former (SiO 2) as well as network modifiers
(K2O, CaO, MgO etc.) along with some trace elements. The trace elements may play important role to decide
various properties of these glasses and glass-ceramics, since the role of trace elements is not known yet1.
The motivation of the present study is to develop low permittivity glasses and glass-ceramics directly from the
ash of agricultural wastes instead of the conventional minerals. The structural and dielectric properties of formed
glasses and glass-ceramics are investigated using different characterization techniques. The study is innovative
and unique in the sense of glass and glass-ceramics derived from the agricultural waste, which leads to new
opportunity to use the agricultural waste as resource for many engineering applications, such as microelectronic
devices and other dielectric applications.
Results and Discussion
Elemental analysis. The ICP analysis of the samples was done to know the amount of the elements present in the
as-quenched samples. R-75 and R-100 contains mainly Si, while alkali and alkaline earth metals have negligible
amount in these samples. Calculated composition of the samples from ICP analysis is given in Table 1. Besides
alkali and alkaline earth content, the samples also contain very small amount of Cu, Zn and Fe. ICP results also
revealed the presence of aluminium in substantial amount in these samples. Random variation of Al in the present
samples comes from the crucible, since the samples are melted in Al 2O3 crucible. Maximum Al2O3 content is
found in R-50 sample. It contains maximum alkali and alkaline earth oxides, which decreases the overall melting
point of this particular sample. So, the diffusion of Al3+ from the crucible is easier than other samples. The mol%
of different minerals are different, as reported earlier, for the different food waste materials1. In the present case,
the amount of different metals and metalloid oxides do not follow any trend as shown in Table 1. It is possible due
to the local environmental effects on different agro-products.
The ICP results were further used to calculate the number of different structural units. Depending upon the
number of different units, number of bridging and non-bridging oxygens was also calculated. In silicate glasses,
the silicon-oxygen tetrahedron serves as the basic building block of the glass network13. These tetrahedra, linked
at four corners, form a three dimensional network. Disorder in this structure is introduced by variable Si-O-Si
angles, rotation of adjacent tetrahedra, oxygen vacancies (Si-Si) and peroxy defects (Si-O-O-Si)14. The modifier
ions occupy the interstices in the network, which may reduce free volume of the glass structure. Sometimes, the
occupancy of these modifiers is taken place in such a way, that free volume becomes zero or negative 15. For every
alkali (R1+) ion, there will be one non-bridging oxygen (NBO) and for alkaline (R2+) ion, there will be two NBOs.
In the presence of the intermediate oxides like Al2O3, the estimation of NBOs and BOs becomes a little bit complicated
due to its dual role as glass former and/or modifier. Alumina is a conditional glass former in the presence
of silica13. It can form [AlO4] units, which incorporate alkali and alkaline earth metal ions to maintain the charge
neutrality. R1+ and R2+ ions are consumed for the formation of AlO4 tetrahedra and decrease the NBOs. Al2O3
can act as a glass modifier also, depending on its local environment and amount within glass network 16,17. By
considering the contribution of all the components of the present samples, the NBOs and BOs are calculated. The
calculated parameters are tabulated in Table 2. The number of NBOs and BOs can give fair idea about the transport
properties of the material. More number of NBOs facilitates the easy motion of charged ions due to weak
structure of such glasses. It may lead to enhance the conducting properties, which further influences the dielectric
properties of the material.
Research paper
Production of clay ceramics using agricultural wastes: Study of properties,
energy savings and environmental indicators
R. Sani⁎, A. Nzihou
Université de Toulouse, Mines Albi, CNRS, Centre RAPSODEE, Campus Jarlard, Route de Teillet, F-81013 Albi Cedex 09, France
ARTICLEINFO
Keywords:
Ceramics
Agro-wastes
Thermal conductivity
Mechanical strength
Energy savings
Environmental indicators
ABSTRACT
In this study, agro-wastes were used as additive raw materials for the production of fired clay ceramics. The
objectives of this study are to evaluate the impact of adding agro-wastes into clay body on the thermal and
mechanical properties of ceramic materials, to determine the net energy consumption and to determine gas
emissions during firing process. The clay and agro-wastes were characterized by chemical elemental analysis,
thermogravimetric and differential thermal analysis (TGA-DTA). The fired clay ceramics were produced with
clay and optimal proportions of wheat straw (WS) and olive core flour (OCF). The thermal and mechanical
properties were evaluated by measuring thermal conductivity with hot-disk method and bending test
respectively. The results showed that for clay incorporated OCF (4, 8 wt%) and WS (3, 7 wt%), thermal
conductivity was decreased by 16 to 30%. However, the mechanical strength of the same samples has slightly
decreased respectively. TGA-DTA provided an approach to estimate the heat required or released for both clay
and agro-wastes thermal decomposition. The addition of agro-wastes into the clay body showed that energy
consumption of fired clay ceramics production decreased to above 36% for clay incorporated 4 wt% OCF (C-4wt
%OCF). The energy saving during the firing process was a tangible outcome. In order to determine the impact of
the agro-wastes addition, the environmental indicators were discussed for the clay incorporated WS and OCF
respectively. Total gas yield released were measured by Micro-GC after the combustion of clay incorporated OCF
and WS in fixed bed reactor respectively. The analysis of gas emissions are related to the combustion of organic
and inorganic compounds of agro-wastes and clay body, respectively. The CO2 emissions coming from the
combustion of agro-wastes reached up to 4.38% for C-8wt%OCF. However, the CO2 emissions associated with
decarbonatation of clay body decreased. Adding agro-wastes into the clay body results to improving thermal
properties without negative impact on the mechanical properties of ceramic materials, also to a significant
energy saving and decreasing of the inorganic CO2 emissions related to the decarbonatation of clay body. The
relevance of this work, pointed out in the data presented in regards to the state-of-the art is that the paper is
focused on fired clay ceramic properties, on energy savings and on the evaluation of environmental indicators in
the laboratory scale.
1. Introduction
Several scientific research have been carried out on the study of the
physical and chemical properties of ceramic materials in their production
process in order to optimize their final properties (Cultrone et al.,
2004a; Vassilev et al., 2013). Number of studies have investigated the
use of industrial and organic wastes to produce ceramic material such
as bricks (Demir, 2006; Muñoz Velasco et al., 2014; Raut et al., 2011)
including sewage sludge, fly ash and organic residues from agroindustries
paper or wood. (Demir, 2006) mixed Processed Waste Tea
(PWT) with clay body to improve the insulation ability of bricks by
generating porosity. This author noticed also that the compressive
strength of ceramic materials increased significantly by adding PWT
into the clay body. Also, the microstructure of clay and additives,
granulometry and the contents of additives were studied to develop the
optimal formulations (Faria et al., 2012; Madurwar et al., 2013).
The consumption of earth-based materials such as clay and sand in
the production of bricks resulted in resources depletion, environmental
degradation and energy consumption. The biomass as an agricultural
product has been used as an energy source to lower energy consumption
in brick manufacturing process. The application of these agrowastes
for the production of ceramic materials is consistent with the
concept of improving the efficiency of management and the environmental
impact of wastes (Zabalza Bribián et al., 2011). From a
http://dx.doi.org/10.1016/j.clay.2017.05.032
Received 16 January 2017; Received in revised form 23 May 2017; Accepted 24 May 2017
⁎ Corresponding author.
E-mail address: rababe.sani@mines-albi.fr (R. Sani).
Applied Clay Science 146 (2017) 106–114
Available online 01 June 2017
0169-1317/ © 2017 Elsevier B.V. All rights reserved.

Clay characterization
The clay is composed of illite, kaolinite, quartz, feldspars, calcite
and hematite. As shown in Table 3, clay typically contains silicon
dioxide percentages (SiO2) between 50 wt% and 60 wt%. The SiO2
content increases the porosity, but also the risk of cracking during
cooling after firing (from 573 °C). The second common chemical
compound in clay, is Al2O3 and it presents 15.8 wt% (Table 3). During
firing CaCO3 decomposes to produce CO2 and CaO. The CaO released
from CaCO3 decomposition can be combined with SiO2 to increase
mechanical strength. The presence of Fe2O3 with 11.0 wt% can lead to
the “black core” formation.
The presence of Ca and Mg oxides or hydroxides are not clearly
shown in X-Ray Diffraction results (Fig. 3) mainly due to their low
concentrations (< 10 wt%) and because their main diffraction peaks
are masked by other major phase peaks (hematite, feldspars, quartz).
The calcite decomposes at higher temperature (830–870 °C) according
to Boynton (Robert and Boynton, 1980). Ca from carbonates may act as
melting agents, but it is reported to somehow limit the extent of
vitrification at T > 1000 °C. In fact, we observed that vitrification i
more extended at higher T when no carbonates exist.

Characterization of fired clay ceramics

3.3.1. Thermal and mechanical properties
The samples of clay with and without agro-wastes were dried and
fired. Several measures were carried out to evaluate the thermal and
mechanical properties of the fired clay samples with and without agrowastes.
The thermal insulation of fired clay ceramics was influenced by the
pore formation due to the thermal decomposition of agro-wastes into
the clay body. For the samples of clay without agro-wastes, the thermal
conductivity was found to be 0.5 W/m.K (Table 5). A low thermal
conductivity was obtained by the samples of clay incorporated WS and
OCF respectively. Table 5 shows that for C-4wt%OCF and C-8wt%OCF
their values of thermal conductivity (λ) were decreased by 16% and
28% in comparison with the one of fired clay ceramic respectively.
Increasing the amount of WS and OCF contributes to decrease the
thermal conductivity of samples respectively. Adding WS into the clay
body has shown also a decreasing of λ by 20% and 30% for C-3wt%WS
and C-7wt%WS respectively.
Number of studies (Demir, 2008; Khedari et al., 2004; Onésippe
et al., 2010) has discussed the impact of porosity generated by agrowastes
in the clay body to the thermal properties. These authors showed
that the thermal decomposition of additives into the clay body led to
pore formation then to an improving of the thermal insulation of
ceramic materials. (Demir, 2008) demonstrated that organic residues
can be used as a type of pore-forming additive in the clay body without
any damaging effect on the other brick manufacturing parameters.
Also, the pore formation has an effect on the mechanical strength.
Adding 3 wt% of WS into the clay body contributes to the diminution of
the bending stress compared to the fired clay bricks without using agrowastes
(Table 5). The samples using OCF showed a mechanical strength
higher than those using WS. These results may be related to the pores
Fig. 4. TGA-DTA curves of clay body.
Table 4
Quantification of crystalline phases of clay body at 600 °C by RIR method and enthalpies
of reaction calculated from the enthalpies of formation.
Crystalline phases %Weight of crystalline phase Enthalpy H (kJ/g)
Calcite 11 1796 (reaction 10)
Kaolinite 9 1158 (reaction 12)
Illite 13 374 (reaction 13)
Quartz 52 11.7
Potassium feldspar 11 207
Table 5
Thermal and mechanical properties of fired clay bricks using agro-wastes.
Thermal conductivity, λ (W/m·K) Fired-bending stress, σ
(MPa)
C 0.50 11.45
C-4 wt% OCF 0.42 11.23
C-8 wt% OCF 0.36 8.50
C-3 wt% WS 0.40 11.02
C-7 wt% WS 0.35 7.65
R. Sani, A. Nzihou Applied Clay Science 146 (2017) 106–114
110
sizes created into the clay body (Aouba et al., 2016; Wagh et al., 1991;
Yakub et al., 2012).
The porosity increment leads to decrease thermal conductivity also
has an impact on mechanical strength. However, the impact of using
OCF is not considered as negative according to the industrial standards
which recommend at least 8 MPa.
Conclusion
This paper demonstrated that the reuse of agro-wastes as a raw
material in ceramic industry contributed to both profitable thermal
properties and environmental benefits. The results showed that adding
agro-wastes into clay body contributed to improving the thermal
properties without negative impact on the mechanical properties of
ceramic materials. Also, three environmental indicators have been
presented in this work, namely: energy saving, CO2 from organic
fraction emission factor coming from the decomposition of agro-wastes
and CO2 from inorganic fraction emission factor related to the
decarbonatation of clay body.
On one hand, the thermal insulation of fired clay bricks was
influenced by the pore formation due to the thermal decomposition
of agro-wastes into the clay body. Adding WS and OCF into clay body
showed a decreasing of thermal conductivity by 16 to 30% for clay
incorporated OCF (4, 8 wt%) and WS (3, 7 wt%) respectively. On other
hand, adding 3 wt% and 7 wt% of WS into the clay body respectively,
contributes to diminution of the bending stress compared to the fired
clay bricks without agro-wastes. The impact of using OCF was not
considered negative in order to have a compromising between the
thermal insulation and the mechanical strength of ceramic materials.
The TGA-DTA analyses provided an approach to determine the heat
reaction of thermal decomposition of OCF, WS and clay bricks
incorporated agro-wastes (OCF and WS) respectively. The higher
heating values were added by self-combustion within the clay mixture
so less energy is needed to fire the bricks. Then, the energy consumption
of manufacturing bricks decreased to above 36% with incorporating
4 wt% of OCF into the clay body. So, the addition of agro-wastes
into clay body has been demonstrated to be efficient for energy savings
in the clay bricks manufacturing. This study has also established the
difference between the CO2 released from inorganic source such as
CaCO3 (clay) and the one released from organic source (agro-wastes).
The results confirmed that adding the agro-wastes into clay body lead
to decrease the firing rejects by decreasing the inorganic CO2 emission
coming from the dacarbonatation of clay body. The CO2 emission
factors related to the decomposition of agro-wastes (organic) and the
decarbonatation of clay (inorganic) respectively could be used as
environmental indicators in the database in the ceramic manufacturing.
The recycling of agro-wastes as a sustainable construction material
seems to be feasible solution, not only to pollution problem but also an
economical option to produce green buildings.