International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 6, Issue 1, January 2016)
Thermo-Physical Characterization of Clay Bricks Mixed with
Agricultural Waste: Case Millet’s Pod
Abdallah DADI Mahamat1, Mahamoud Youssouf Khayal2, Macodou Thiam3, Azibert Oumar Abdelakh4,
Gilbert Menguy5, Salif GAYE6
1,4
Institut National Superieur des Sciences et Techniques d’Abeche (INSTA), Tchad.
Faculte des Sciences Exactes et Appliquees, Universite de Ndjamena (FSEA), Tchad
5
Laboratoire d’Etudes thermiques et Solaires, Universite Claude Bernard Lyon1, France.
3,6
Laboratoire de Materiaux et d’Energetique, Institut Universitaire de Thies (IUT), Université de Thies (UT) Senegal.
2
This work, which aims is to determine the thermal
conductivity and the thermal diffusivity of materials
studied, fit into this framework.
Abstract - In the present work, we studied the thermophysical properties of a local building materials based on
clay which is mixed with agricultural waste such as the pod
of millet.
The purpose is to identify the formulation of samples
presenting the best thermal properties in order to improve
the thermal comfort in the building and reduce energy
consumption.
For that, the mixture of clay and pod millet samples
dimension 270 x 270 x 36 mm3 with millet’s pod massing
percentages varying from 1 to 5% have made and
characterized. The «method of box» is used to determine
the thermal conductivity and thermal diffusivity of these
samples. The same method was used to determine the
thermal conductivity of clay and aggregate millet’s pod.
The obtained results show that these materials present a
good thermal performance with a good energy saving.
Keywords—Clay, agricultural
thermal properties, energy saving.
waste,
millet’s
II. PRESENTATION OF THE MATERIALS STUDIED
Clay: In this study, we use the clay of Chad and
precisely that of Abéché levied at a depth of about 2m to
Kamina Seydou’s career. Since decades, this site is
operate and allows the manufacture of bricks for building
construction.
Millet’s pod: Millet grows in areas where rainfall is
between 150 and 800 millimetres, it is a cereal
characterized by the smallness of its grains. Generally, it
is the most cultivated cereal in the Sahelian zone of
Africa mainly in Chad.
The pod of millet (Figure 1) is use as an adjuvant in
the construction material [6].
pod,
I. INTRODUCTION
For a decent housing, the users must have a good
protection against effects of the climate by creating a
relatively comfortable environment while assuring a
good management and optimization of the energy
consumption.
Nowadays, the building consumes more than 70% of
the energy. The production of this energy generates an
important quantity of greenhouse gases. The building
designers are facing a challenge, that of having energyefficient buildings. Therefore, a significant number of
researchers examines the problem of rational use of the
energy in order to satisfy the need for thermal comfort [1,
2,3].
The thermal insulation of the building envelope is an
important energy performance criterion. It reduces the
heat load of the building and so have better thermal
comfort without the need for artificial cooling [4, 5, 6, 7].
The use of clay mixed with agricultural waste such as
millet’s pod is part of a scientific approach to sustainable
development. It presents the advantage of using natural
materials retraining, available and renewable [2, 5, 8].
Figure 1: Photo of millet’s pod in the state
III. SAMPLE FORMULATION
Clay and millet pod aggregate were used for the
preparation of samples. The mixing is done manually to
dryness and water was gradually added to the mixture for
a normal consistency before making the moulding. The
unmoulding is a delicate process, which is facilitated by
the shrinkage phenomenon of clay. It is done after 48
hours in the shade and then drying occurs naturally in the
sun until stabilization of the mass of the dry sample.
38
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 6, Issue 1, January 2016)
Table 1
Formulations of samples
References
of samples
% millet’s
pod
% of
clay
Thickness
(m)
Density
(kg.m-3)
EGM 0%
EGM 1%
EGM 3%
EGM 5%
EGM 100%
0
1
3
5
100
100
99
97
95
0
0.036
0.036
0.036
0.036
0.04
1987
1835
1698
1678
91
The sample thus has a hot face of the side of the box
and a cold face of the side of the isothermal capacity [9,
10].
4.1 Determining the thermal conductivity
The principle of thermal conductivity measurement
consists in providing a known one directional heat flow
through the test sample, by placing it between hot and
cold environments, then performing the steps after
achieving steady state (figure 4).
Figure 2: phenomenon of withdrawals on clay brick samples mixed
with millet’s pod
Figure 4: Diagram of a box
We thus produced samples of dimensions 270x270x36
mm3 with percentages by mass of pod millet of 0 %, 1 %,
3% and 5%.
The principle of thermal conductivity measurement
consists in providing a known one directional heat flow
through the test sample, by placing it between hot and
cold environments, then performing the steps after
achieving steady state. To minimize the heat exchange
between the box and the external environment is applied
a voltage suited heating so that the temperature of the
box (TB) is as close as possible to the temperature of the
testing room (Ta) while remaining slightly higher (T B - Ta
<1 ° C)
In permanent regime, the system receives power (q1)
provided by heat dissipation in the resistor by Joule
effect, this energy is dissipate in part through the walls of
the box (q1) and through the sample (q2). Thus obtained:
IV. EXPERIMENTAL DEVICE AND MEASUREMENT METHOD
Within the framework of this study, the experimental
measures are performed through the «boxes method»
device; it is the EI702 device (Figure 2) which was
designed in the laboratory of Solar and Thermal Studies
of University Claude Bernard Lyon I [1, 3, 6, 7]. The
EI702 cell, which yields results with an accuracy of
about 5 %, allows the measurement of two thermophysical parameters (thermal conductivity and thermal
diffusivity) of composite solid materials, powder, pastes
and fluids.
̇
̇
̇
(1)
These ratings are determined from the following
relationships:
̇
(2)
̇
(3)
(4)
̇
In steady state, the value of thermal conductivity is
determined from the following relationship [1, 3, 9]:
[
Figure 3: Principle of the cell pattern EI702 [10]
]
(5)
The manufacturer gives the loss coefficient C of the
unit: C = 0.16 W / ° C but should be reassess
periodically.
The parallelepiped samples placed between two plates
and the isothermal capacity (A) such that the lateral flow
are negligible.
39
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 6, Issue 1, January 2016)
The resistance of the heating plate is measure directly
on its connection terminals and the voltage (V) is set to
the measuring console [9].
4.2 Determining the thermal diffusivity
Thermal diffusivity (a) expresses the ability of a
material to transmit a heat flux. It is the speed, in which
the heat propagates by conduction into the material [1, 2,
3].
For the estimation of thermal diffusivity, the box 2 of
EI7002 device is equipped with two lamps, which emit
about 1000 W for a few seconds on the underside of the
sample (figure 5).
As part of the conductivity test for powder materials,
granular, or liquid-tight part closed by two copper plates
allows to contain the sample prior to its introduction into
one of the boxes.
To estimate the thermal diffusivity we applied a
thermal flow by sending a flash on the underside of the
sample. The temperature variation on the upper side is
take as a function of time in order to draw a thermogram
(Figure 6) whose operation determines the thermal
diffusivity. Depending on the nature of the material, the
duration of the flash can be automatically set on the
measurement console.
Figure 6: Thermogram the face not irradiated
To calculate the diffusivity, we applied method of De
Giovanni [1, 3, 10] by using these three formulas and
their average value is retained [1, 2, 9].
(6)
[
]
[
]
[
]
(7)
(8)
The diffusivity of the studied sample is the average of
the preceding three formulas:
(9)
V. EXPLOITATION OF EXPERIMENTAL RESULTS
Conductivity, thermal resistance, and thermal
diffusivity are the most important thermo-physical
properties to be take into account for the choice of a
thermal insulation material [2].
Figure 5: The box 2 for EI702 cell
From the thermogram we identify times corresponding
to 1/3, 1/2, 2/3, 5/6 of the maximum value of the
temperature rises.
40
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 6, Issue 1, January 2016)
From the thermal conductivity and the thermal
diffusivity, we obtain the specific heat (Cp) and the
thermal effusivity (E) from the following formulas:
From the figure 7, we notice the decreases density of
the mixture when adding millet’s pod because of the low
density of this adjuvant.
(12)
(13)
√
V.1 Thermal conductivity
The thermal conductivity is use to quantify the
insulation of each material by calculating the thermal
resistance:
(14)
The equation 14 saw that more lower the thermal
conductivity is, more the material will be insulating.
From our experience, we obtain the results shown in
tables and figures below.
Table 2:
values of thermal conductivities of the samples studied and the
thermal resistances for a wall thickness of 30cm
References of
samples
Density
(kg.m-3)
Thermal
conductivity
(W.m-1.K-1)
Thermal
Resistance
(m2. K.W-1)
EGM 0%
1988
0.51
0.58
EGM 1%
1835
0.44
0.68
EGM 3%
1698
0.40
0.74
EGM 5%
1678
0.37
0.81
EGM 100%
91
0.05
6
Figure 8: Evolution of the thermal conductivity function of the
density of the sample
On the figure 8, we see that the thermal conductivity
of the material increases with the density. The increasing
of the material porosity make it more isolating.
The results show that the sample millet’s pod presents
a low density and high thermal conductivity (table 2).
2050
2000
Density (kg.m-3)
1950
1900
1850
1800
Figure 9: evolution of the thermal conductivity with the millet’s
pod percentages.
1750
1700
1650
0
1
2
3
4
5
6
% millet's pod
Figure7: density of the samples according to the millet pod
percentage
41
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 6, Issue 1, January 2016)
V.2 The thermal diffusivity
Table 3
Results of thermal diffusivity values
References
of samples
% of millet’s
pod
density
(kg.m-3)
EGM 0%
0
1987
Thermal
diffusivity
(m2.s-1)
6.1 x 10-7
EGM 1%
1
1835
5.9 x 10-7
EGM 3%
3
1699
5.2 x 10-7
EGM 5%
5
1678
3.7 x 10-7
Figure 10: Thermal resistance pod percentage depending mil
The increasing of the millet’s pod decreases the value
of its thermal conductivity and increases the thermal
resistance (figures 9 and 10).
Figure 12: thermal diffusivity according to percentage pod mil
Figure 13: the thermal diffusivity as a function of the density
Figure 11: Density based thermal resistance
The increasing of the proportion of the millet’s pod
decreases the thermal diffusivity (figures 12).
The thermal diffusivity is proportional to the density
(figures 13).
The thermal resistance of the material decreases with
its density.
42
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 6, Issue 1, January 2016)
[3]
Abdallah Dadi, Oumar Idriss, Malloum Soultan, Yassine
Elhamdouni «Effect of cow’s dung on thermophysical
characteristics of building materials based on clay Research»
Journal of Applied Sciences, Engineering and Technology 10(4):
464-470, 2015 ISSN: 2040-7459; e-ISSN: 2040-7467 © Maxwell
Scientific Organization, 2015
[4] P. Meukam, Y. Jannot, A. Noumowe, T.C. Koffane, «Thermo
physical characterstics of economical building materials.
Construction and Building Materials» Vol 18 pp. 437-443, 2004.
[5] Y.Elhamdouni, A. Khabbazi, C.Benayad, A.Dadi, O.Idriss «Effect
of fiber alfa on thermophysical characteristics of a material based
on clay» Energy Procedia 74 (2015) 718 – 727
[6] H. Bal, Y. Jannot, N. Quenette, A. Chenu and S. Gaye. «Water
content dependence of the porosity, density and thermal capacity
of laterite based bricks with millet waste additive» Construction
and Building Materials.
31 (2012) 144-150.
[7] Nassima Sotehi «Caractéristiques Thermiques des Parois des
Bâtiments et Amélioration de L'isolation» Doctorat en Sciences en
Physique.
[8] Lahcen.B ‘’caractérisation «thermophysique des matériaux et
modélisation des transferts couples de chaleur à travers un
bâtiment» Thèse Energétique et Matériaux 2008 Université Ibni
Zoer
[9] D.Sow «Integration of Agricultural Waste in Local Building
Materials for their Exploitation: Application with Rice Straw»
Research Journal of Applied Sciences, Engineering and
Technology 7(15): 3030-3035, 2014 ISSN: 2040-7459; e-ISSN:
2040-7467 © Maxwell Scientific Organization, 2014
[10] Bulletin Technique cellule de mesure EI-700
VI. CONCLUSION
This study identified the thermal parameters of a local
construction material available and cheaper.
The results show that this material, based on clay and
millet’s pod, has interesting thermal characteristics and
generates an energy saving because of its good thermal
insulation capacity.
Therefore, use of this new material in building will
help to reduce energy consumption and the emission of
greenhouse gases.
Knowledge:
We thanks:
- The Senegalese national project PNEEB/typha which
pay for the Energetic and Materials Laboratory
(LME) of IUT the EI700 apparatus.
- The CONFOFOR (Chad) that financed this study.
REFERENCES
[1]
[2]
Salif Gaye « Caractérisation des propriétés mécaniques,
acoustiques, et thermiques de matériaux locaux de construction au
Sénégal ». Thèse d’état, UCAD de Dakar, Sénégal. 2001.
Salif Gaye, Gilbert Menguy « Energie et environnement » Presses
Universitaires de Dakar 2008.
43