Thermal Inertia and Thermal Properties of the Composite Material Clay-plastic

Improving insulation building materials with low energy consumption becomes an obligation so as to reduce the heat energy of houses. For this purpose, a series of experimental studies were performed on composite clay-plastic. The first step in this study is the chemical characterization of clay using the fluorescence X method. The second step is thermal characterization of clay alone and the composites clay-plastic using the asymmetrical hot plate and Flash methods. The third step in the work is the verification of thermal conductivity using different theoretical models. The fourth step in this study is the study of thermal Inertia of walls done from the composite clay-plastic. Finally a study of delay of temperature, heat flow and damping factor for a wall done from those composites were conducted. The obtained results indicate that this composite presents interesting characteristics in term of insulation and thermal Inertia.


INTRODUCTION
Improving insulation materials becomes among the most important scientific research worry in building in order to reduce the consumption of building envelope.However, controlling the thermal Inertia of wall has become a necessity so as to reduce the heat loss of houses and assure the best energy efficiency.For this purpose authors try in this study to improve the thermal characteristic of clay by combing it with waste of plastic as polymer insulation.The thermal characterization of this composite was done using the asymmetrical hot plate and flash methods so as to determine thermal effusively, thermal conductivity, heat capacity and thermal diffusivity.Also, thermal conductivity was confronted to different theoretical models to confirm its values.Besides, a study of thermal Inertia was done to control the heat flow penetrating inside houses by determining the depth of heat flow diffusion, the damping factor and the delay of temperature.A literature study was done on insulation building materials such as the work of Asdrubali et al. (2012) which treats the acoustical properties of sustainable materials both natural and from recycled materials.The work of Khabbazi et al. (2005) which describes the thermal and the mechanical properties of a new material based on granular cork and cement mortar by varying the percentages of cork using the box method.Also a lot of research have been done on clay bounded with additives such as the research of Mounir et al. (2014) which studies the thermal characterization of a mixture of clay bounded by cork and evaluates the energy saving from this composites, the work of Sutcu et al. (2014) in which they studied the thermal behavior of hollow clay bricks made up of paper waste and the optimization of their thermal performance where the thermal conductivity of the microporous brick materials with additives produced in this study reduced the thermal conductivity from 0.68 W/m K to 0.39 W/m K compared with that of the sample without additives.Moreover, a literature study was done concerning the thermal Inertia such as the thesis of Chahwane (2011) in which he evaluates the thermal Inertia so as to assure the best building energetic performance.According to all those studies, authors try in this study to improve the thermal properties of the material clay by combining it with the waste of plastic in order to use it in building envelope.The thermal characterization of clay-plastic was done using the recent asymmetrical Hot Plate method which permits to determine thermal effusivity and heat capacity (Bouchair, 2008;Jannot et al., 2010;Lin et al., 2014;Yves, 2011) and Flash method which permits to define the thermal diffusivity (Degiovanni et al., 1996(Degiovanni et al., , 1979;;Parker et al., 1961).Furthermore, after determining the thermal properties of the composite clay-plastic authors studied the thermal Inertia of this composite in order to control the penetration of heat flow diffusion inside houses and by doing so can we reduce the consumption of energy in building.Plastic waste was taken from the rejected bottle of water composed from polyethylene teraphtalate which presents a good dimensional property, a low hygroscopicity and good mechanical properties (Laetitia Vouyovitch Van Schoors, 2009).
Clay is a mineral coming from the decomposition of rock.It's a heterogeneous material on different scales.In the macroscopic scale, they are associated to another mineral (quartz, feldspath…) and in the microscopic scale they present a structure with leaves.The mineral clay is formed specially from a mixing of hydrated phyllosilicate.The majority mineral gives the names of this phyllosilicate.It is combined with a different mineral like: Carbonate; silica; oxide and hydroxide of aluminum and Ferriferous mineral (Mounir et al., 2014).

DESCRIPTION OF USED MATERIALS X ray of clay:
The clay sample extracted from Bensmim was characterized through fluorescence X.The chemical composition is represented in Table 1.

Chemical composition of clay:
The chemical composition was done by using the fluorescence X method as presented in Table 1.

Plastic:
The plastic used with clay as presented in Fig. 1 was taken from the waste of bottle done from polyethylene teraphtalate.The density of used plastic is 1380 kg/m 3 ; the thermal conductivity is 0.22 W/m.K.In Fig. 2 a granulometry analysis of waste plastic was done to determine the size of plastic used.

DESCRIPTION OF EXPERIMENTAL AND THEORETICAL APPROACH TO DETERMINE THE THERMAL PROPERTIES
Samples preparation and their densities measurement: Authors prepared samples as presented in Fig. 3 for clay-plastic on different percentage.The percentage of water used for this kind of Illite clay which is a non swelling clay is 0.25 (mass water per granular of clay).Moreover samples of clay-plastic were prepared with different percentage of plastic 3% and 5% using a cement mixer to achieve a good distribution.The dimensions of samples are 10×10×2 (cm) so as to specify the different percentage of additives, we fulfilled in the mold a volume of additives until we get full mold then we consider that this mass corresponds to 100% of percentage then we calculated the associated percentage After drying the samples in air ambient, we weight them and we put them in a steam room with ventilation in 60°C temperature and each 3 days, we weight them until we remark that the mass became constant in order to be sure that all the moisture existing in them are deleted.Then we proceeded to define the apparent density and according to the mixture law, we define the volume fraction of plastic in each sample according to relation (1).This relation permits to study two volume fraction of plastic: 0.418 for 3% of plastic and 0.498 for 5% plastic: With: ρ ad, ρ c and ρ c+ad are successively the densities of additives, clay and that of the composites.

Asymmetrical hot plate methods description:
Transient hot plate method: The hot plate method in transient regime permits to define the thermal effusivity and heat capacity, contrarian to the traditional method, this one permit the thermal characterization using only one sample (Jannot et al., 2010;Mounir et al., 2014;Yves, 2011).The system modeled using the hypothesis of 1D heat transfer, using the minimization of sum quadratic error: Between the theoretical and experimental curves calculated using the algorithm Levenberg-Maquardt (Marquardt, 1963).Combining those equations, the system leads to: (3) Hot Plate method in steady state regime: The Hot Plate method in steady state regime (Jannot et al., 2010;Yves, 2011;Yves et al., n.d.) permits to characterize thermal conductivity (λ) of samples.Figure 2b illustrates the experimental device of this method, once the system reaches the steady state regime, we can write: ø is the total flow emitted by the heating element.λ The thermal conductivity of the sample that we look for, e the thickness of the sample; λ 2 = 0.04 W/m.K and e 10 mm: are successively thermal conductivity and thickness of the insulating foam.

Flash method:
Experimental approach of the flash method: This method permits to determine the diffusivity of solid (Degiovanni et al., 1996(Degiovanni et al., , 1979) ) its principle is described in the Fig. 4. We send a strong luminary flow on the sample's parallel faces in a short period.A thermocouple in touch with the bottom face permits to register the rise of temperature in the moment when the face receives the flash.A modeling of heat transfer in the sample has been done to estimate the thermal diffusivity with the experimental thermogram.

According to Laplace:
The method of quadruples permits to write: According to the Laplace transformation: We combine this relation we have: (8) Theoretical model to check the value of thermal conductivity: Authors compare the experimental results with theoretical models which calculate the equivalent thermal conductivity of materials of two components: a continuous phase (Clay) and a dispersed phase (plastic or plastic).Different theoretical model were used to confirm the thermal conductivity for instance: Series model (Wienner et al., 1912;Poulaert, 1987), parallel model (Wienner et al., 1912;Poulaert, 1987), model (Maxwell, 1954;Poulaert, 1987;

DESCRIPTION OF THEORETICAL APPROACH TO MEASURE THE THERMAL INERTIA
According to the thesis of Chahwane (2011) and the ISO 13786 an analysis was conducted to see the variation of thickness of binders according to time of diffusion of heat flow using the relation (3).The relation between the thickness and the time of diffusion of the heat flow inside a homogenous component inside building is defined as the product of heat capacity and thermal resistance of the same component.Dept of heat flow diffusion: Matrix transfer of homogenous layer: where, Thermal admittance Y mn advance: Damping factor: The thermal transmittance U is calculated according to the ISO 6946.
Delay of damping factor:

Density:
The identification of the apparent density was measured by knowing the mass and the dimensions of samples and the results were presented on Table 2.The results of apparent density obtained from the composite clay-plastic permits a gain of 13% for 3% plastic, 16% for 5% plastic because adding plastic on clay creates porosity inside material thing which makes it lighter.The composite clay-plastic permits a gain on lightness of 13% for 3% plastic and 16% for 5%.

Thermal effusively by the asymmetrical transient hot plate method:
The analysis of thermal effusivity as presented in Table 3 for the composite clay-plastic permits a gain in term of thermal effusivity of 5% for the percentage 5% plastic and 3% for the percentage 3% plastic.So we deduce that the composite clayplastic doesn't present a significant reduce of thermal effusivity so the local built by this composites will exchange energy quickly with its surroundings instead of clay-plastic which presents an important reduce of thermal effusivity for the percentage 5%.
Thermal conductivity and heat capacity by the method hot plate in steady state regime: The analysis of thermal conductivity as presented in Table 4 for the composite clay-plastic permits a decrease of thermal conductivity of 34% for the percentage 5% plastic and 29% for the percentage 3% plastic.so we deduce that the composite clay-plastic present a significant reduce of thermal conductivity so the local built by this composite will be more insulating.

Theoretical model of thermal conductivity:
Thermal conductivity of the composite clay-plastic as presented in Fig. 4 was analysed showing that the value of thermal conductivity is between the lower limit series model and the upper model parallel model.The Maxwell model is clearly far to represent our middle because the granular plastic doesn't resemble to spheres.Concerning the Hamilton model, the low values of sphericity parameter, ξ ∈ 0,1 represent those of equivalent thermal conductivity near to those of parallel model.But for its maximum value ξ = 1, the equivalent conductivity of Hamilton return to the Maxwell model.The model the most representative is the geometric and the beck's model which they consider that the granular of plastic are well distributed in the matrix clay.
Thermal diffusivity by the flash method: The analysis of thermal diffusivity as presented in Table 5 for the composite clay-plastic permits a decrease of thermal diffusivity of 41% for the percentage 5 and 17% for the percentage 3% plastic.Concerning the composite clay-plastic it presents a gain of 35% for the percentage of 5% plastic and 33% for the percentage 3% plastic.so we deduce that the composite clayplastic present a significant reduce of thermal diffusivity so the local built by this composite will be retards the transfer of heat flow more than a local built by clay-plastic.

Depth of heat flow diffusion:
Figure 5 presents the depth of heat flow diffusion on 24 h.We remark that this depth decreases when the volume fraction of plastic increases, so the waste plastic play the role of retarding the exterior heat flow to penetrate inside houses, because it creates porosity inside material and this is proved by the measure of density of the composites.This result can be used in order to decrease the heat loss of homes by controlling the penetration of exterior heat flow until night when the exterior ambiance become more colder.
Maximum Delay between the exterior and the interior temperature: Figure 6 presents the maximum delay between the exterior and interior temperature according to different wall's thickness (20, 25 and 30 cm), we observe that the composite clay-5% plastic presents the maximum delay of temperatures, so when we increase the volume fraction of waste plastic; we create an important delay between the exterior and the interior temperature.Also, we deduce that this characteristic of delaying temperature is a very important result for cold area such as Atlas of Morocco which presents a very high peak of temperature in the midday and very cold one at night.So an important delay of temperature permits to store temperature at day and injected it at night in houses.
Figure 7 presents the maximum delay of exterior and interior heat flow density according to different wall's thickness 20, 25 and 30 cm), we observe that for the thickness 20 and 25 cm the composite clay-5% plastic which presents the maximum delay of heat flow density.According to this, we conclude that the increase of volume fraction of plastic retards the penetration of the exterior heat flow inside the interior ambiance.

CONCLUSION
In this study a comparison of thermal properties was done for unfired blocks: clay, clay-3% plastic and clay-5% plastic using the asymmetrical hot plate and flash methods.The results obtained confirm that the composite clay-5% plastic presents the best thermal characteristics in term of thermal conductivity by a gain of 34%, thermal effusivity by a gain of 5% and thermal diffusivity by a gain of 35%.Also, an analysis of thermal transmittance was conducted to demonstrate that the composite clay-5% plastic had presents a gain of 28% for 30cm wall's thickness comparing with clay alone.Moreover, a study of thermal Inertia were conducted by determining the depth of heat flow diffusion, delay of maximum temperature, heat flow density and damping factor, the results proves that when the volume fraction of plastic increases the depth of heat flow diffusion decreases from (11.77 to 9.54 cm), the delay of the maximum temperature and heat flow density increases.Furthermore, analyses of damping factor were conducted proving that when the volume fraction of plastic increases, the exterior heat flow will be more damped.The use of the unfired blocks clay-plastic permits the best control of the exterior heat flow without expanding the energy of calcinations and by doing so, can we assure the best energy efficiency of dry climate area such as Bensmim region.

Fig. 5 :
Fig. 5: Depth of heat flow diffusion according to time

Fig. 8 :
Fig. 8: Thermal transmittance of the different materials studied

Table 1 :
Chemical composition of clay

Table 2
sample -E mean value )/E mean value Gain = 100 *

Table 4 :
Results of thermal conductivity and heat capacity