# THERMOPHYSICAL CHARACTERIZATION OF ECO-PLASTER MADE FROM GIANT SNAIL SHELLS

Ayihaou Djossou, Edmond Vodounnou, Bonou Sidoine, Sophie Cazalbou, Vianou Antoine

<figure><img src="image_1.png" /></figure>

## To cite this version:

Ayihaou Djossou, Edmond Vodounnou, Bonou Sidoine, Sophie Cazalbou, Vianou Antoine. THERMOPHYSICAL CHARACTERIZATION OF ECO-PLASTER MADE FROM GIANT SNAIL SHELLS. International Journal of Current Research, 2021, 13 (01), pp.15542-15546. 10.24941/ijcr.40332.01.2021 . hal-04990180

HAL Id: hal-04990180

https://hal.science/hal-04990180v1

Submitted on 13 Mar 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_2.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_3.png" /></figure>

ISSN: 0975-833X

Available online at http://www.journalcra.com

INTERNATIONAL JOURNAL
OF CURRENT RESEARCH

International Journal of Current Research
Vol. 13, Issue, 01, pp.15542-15546, January, 2021

DOI: https://doi.org/10.24941/ijcr.40332.01.2021

RESEARCH ARTICLE

THERMOPHYSICAL CHARACTERIZATION OF ECO-PLASTER MADE FROM
GIANT SNAIL SHELLS

DJOSSOU Ayihaou Armand¹*, VODOUNNOU Edmond¹, BONOU Sidoine², CAZALBOU Sophie³ and VIANOU Antoine¹

¹Laboratory of Materials Thermophysical Characterization and Energy Appropriation (Labo-CTMAE) - Abomey-
Calavi Polytechnic School (EPAC), 01 BP 2009, Cotonou-Benin; ²Laboratory of Inorganic Chemistry and
Environment (LaCIE) - FAST-UAC-Benin; ³CIRIMAT Carnot Institute, Tourlouse University, UPS-INPT-CNRS
UMR 5085-France

ARTICLE INFO

Article History :

Received 03rd October, 2020
Received in revised form
19th November, 2020
Accepted 23rd December, 2020
Published online 30th January, 2021

Key Words :

Eco-plaster, Snail shells, Mixing rate,
Thermal effusivity, Thermal
Conductivity, Hot strip.

ABSTRACT

The main objective of this work is to carry out the thermophysical characterization of an eco-plaster made from giant snails shells *Achatina Achatina*. To achieve this, it was first synthesized eco-plaster from snail shells collected in nature. Thermal effusivity and conductivity measurements in transient mode and according to mixing rate $\frac{\Delta E}{\Delta m_p}$, were then carried out with hot strip method. Finally, a thermal behavior study face to surface heating and cooling of specimens was carried out. The results obtained showed on one hand that thermal effusivity and conductivity respectively decrease from 555.386 J.m⁻². K⁻¹.s⁻⁰.⁵ to 377.736 J.m⁻². K⁻¹.s⁻⁰.⁵ and from 0.159 W.m⁻¹.K⁻¹ to 0.104 W.m⁻¹.K⁻¹, when mixing rate increases from 1.8 to 2.7. In the same range of mixing rate, a comparative study showed on other hand, that density, thermal effusivity and conductivity of synthesized eco-plaster are lower than those of imported plaster. Surface heating tests with a constant heat flow for 180 s have shown that temperature rise is the same for both types of plaster up to 15 s in mixing rate range from 1.8 - 2.7 and; up to 30 s for mixing rate of 3.6. Beyond 15 s and 30 s respectively for rates of 1.8 - 2.7 and 3.6, we note that eco-plaster heats up faster than imported plaster. When heat flow is eliminated, we notice that the two plasters are cooled in same way.

Copyright © 2021, DJOSSOU Ayihaou Armand et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**Citation:** DJOSSOU Ayihaou Armand, VODOUNNOU Edmond, BONOU Sidoine, CAZALBOU Sophie and VIANOU Antoine. "Thermophysical characterization of eco-plaster made from giant snail shells", *International Journal of Current Research*, 13, (01), 15542-15546.

INTRODUCTION

Faced with the energy poverty situation and while building
impact in terms of greenhouse gas emissions is very heavy,
eco-materials choice is crucial. These judiciously produced
materials like plaster and many others, can indeed limit the
building negative environmental impacts. Evrard et al. (2010)
cited by Kabore [2] showed that a plaster board with a density
of 900 kg.m⁻³ has a gray energy of 5.8 MJ.kg⁻¹ and emits 0.22
kgCO₂.kg⁻¹, which is relatively low compared to other building
materials. Plaster uses are multiple. Plaster is used in building
(wall and floor cladding, partition walls, ceilings, decoration,
fire protection, hygrometric regulation, sound insulation) and
also in artistic field for shapes molding during production and
works restoration [3]. It is also used as in buildind sector as
insulating material considering its thermal conductivity less
than 2 W.m⁻¹.K⁻¹ (Langlais et al., 2004). In Benin, there is no
gypsum deposit for plaster production; as a result, plaster
supply for these applications is based exclusively on imports.

However, there is a biomaterial available at lower cost which
can be used as raw material for plaster local production : snail
shells. According to Sodjinou et al. [5], a large quantity of
snails (about 62.5 tons) are delivered every year on Cotonou
market, which corresponds to about 216 shells tons. This
estimated quantity comes, not from a formal purchase
iniculture but, from collection of snails developing in wild.
This collection is favored by two rainy seasons recorded in
Benin. Snail consumption increase in Benin without purchase
iniculture promotion strengthens snails collection and is a
threat to biodiversity. Adherence to valorization vision of
uneaten parts of snails can encourage purchaseiniculture in
Benin. This work is therefore part of energy saving in housing,
environment protection and snail shells valorization in thermal
insulation field.

MATERIALS TESTED

**Basic raw material :** Acclimated giant snail shells *achatina*
*achatina* from Benin are the basic raw material used in this
study (Figure 1).

<footnote>*Corresponding author: DJOSSOU Ayihaou Armand</footnote>

<footnote>Laboratory of Materials Thermophysical Characterization and Energy Appropriation
(Labo-CTMAE) - Abomey-Calavi Polytechnic School (EPAC), 01 BP 2009, Cotonou-
Benin</footnote>
<figure><img src="image_4.png" /><figcaption>Figure 1. Giant snail shells *achatina achatina*</figcaption></figure>

**Eco-plaster synthesis from snail shells:** Procedure is summarized in Figure 2 After collection, snail shells were reduced to powder in an oven at 900 °C. Powder thus obtained was treated with excess sulfuric acid. After total decarbonation, white paste obtained was separated from supernatant and then rinsed with distilled water and neutralized with an aqueous solution of calcium hydroxide. Calcium sulfate paste thus obtained was filtered and rinsed with distilled water. Hydrated calcium sulfate obtained was heated in a muffle furnace at (200 ± 5) °C for two hours in open air, in order to obtain hemi-hydrated calcium sulfate which is plaster (Karim *et al*, 2013).

<figure><img src="image_5.png" /><figcaption>Figure 2. Eco-plaster synthesis from snail shells</figcaption></figure>

**Plaster mixing:** Mixing rate $\frac{m_e}{m_p}$ is water mass ratio to plaster powder mass put into play to manufacture set plaster. In β-hemihydrates case, this ratio varies between 0.5-1.2 and makes β-hemihydrates commonly used as construction material. In α-type hydrates case used in ceramics manufacture or in dental industry, this ratio varies between 0.3 - 0.5 (Coquard, 1992; Eve, 2003). When plaster setting, only a small fraction 18.6% mixing water participates in chemical reaction (Coquard, 1992). Additional water quantity provides a good paste fluidity and determines material porosity after setting. In this work, plasters were wasted at different ratios $\frac{m_e}{m_p} = 1.8; 2.3; 2.7$ and 3.6 (Table 1). Specimens densities were determined. Indeed, preliminary mixing tests showed that is impossible to dissolve plaster powder synthesized with snail shells with a mixing ratio $\frac{m_e}{m_p} < 1$ whereas it was possible for commercial plaster used as reference. Indeed, during dissolution experiments, water quantity corresponding to $\frac{m_e}{m_p} < 1$ were insufficient to dissolve powder; which obliges to supplement water quantity initially taken. These preliminary tests led us to increase water quantities provided for mixing. Plasters are finally elaborated with $\frac{m_e}{m_p}$ mixing ratios greater than 1 and between 1.5 - 4. Plaster set results from rehydration of semi hydrate in water during mixing operation. Mixing protocol used is that described by Coquard (1992). Semi

hydrate powder was poured into water and stirred for about 30 seconds. Then it was left to rest for 30 seconds followed by mixture agitation for 30 seconds. This agitation was followed by another rest of 30 seconds and then a final agitation of 30 seconds until homogenization. Plaster setting was carried out according to Equation (1):

$$ (\text{CaSO}_4\text{,l} \rightarrow (\text{CaSO}_4\text{2H}_2\text{O}) + \text{1/2H}_2\text{O},\text{2H}_2\text{O}) \quad (1) $$

To obtain plaster taken, it was proceeded to mix at different ratios $\frac{m_e}{m_p} = 1.8; 2.3; 2.7$ and 3.6.

<table><caption>Table 1. Plaster mixing ratios $\frac{m_e}{m_p}$</caption><tr><td>Water mass m<sub>e</sub> (g)</td><td>67</td><td>83.7</td><td>100.5</td><td>134</td></tr><tr><td>Powder masse m<sub>p</sub> (g)</td><td>37</td><td>37</td><td>37</td><td>37</td></tr><tr><td>Mixing ratio m<sub>e</sub>/m<sub>p</sub></td><td>1.8</td><td>2.3</td><td>2.7</td><td>3.6</td></tr></table>

**Samples manufacture:** For test pieces manufacture, powder mass equal to 37 g was retained after several tests. Indeed, it represents the maximum powder mass that allows after mixing with a water volume of 67 ml, to completely fill, without material loss, the mold of $(5 \times 3.5 \times 3)$ cm$^3$ size used for production of specimens intended for thermal measurements (Figure 3). At the end of setting, samples ground in molds of same volume have different densities. This shows that water quantity used had acted on particles dispersion when plaster setting.

<figure><img src="image_6.png" /><figcaption>Figure 3. Plaster specimens</figcaption></figure>

**Plaster density variation according to mixing rate $\frac{m_e}{m_p}$:** The plot of density curve as a function of ratio $\frac{m_e}{m_p}$ shows a good correlation (Figure 4) for the samples wasted with the ratios $\frac{m_e}{m_p} = 1.8; 2.3$ and 3.7, for both imported and elaborated plaster. With the samples obtained with ratio $\frac{m_e}{m_p} = 3.6$, it is noticed a defect of setting and a very bad cohesion of particles; which causes them to crumble at touch. Therefore, it is retained that ratio $\frac{m_e}{m_p} = 3.6$ is too high to make plasters set with powders used. The comparison of specimens densities for the same mixing rate shows that the plaster made from snail shells is less dense than the commercial plaster. This mass difference for same volume indicates that when plaster is set, its bassanite particles are more dispersed in mixing water than in commercial plaster case. Thus, elaborated plaster samples imprison a greater water quantity than those of commercial plaster. Therefore, after water removal by microwave heating, these samples become more porous and have a lower density. This density difference will certainly lead to differences in thermal properties between the two plaster types. These results agree well with those of Jaffel (2006), which shows that porosity increases with mixing rate; which consequently leads to density reduction of material.
<figure><img src="image_7.png" /><figcaption>Figure 4. Plaster density variation according to mixing rate $\frac{m_e}{m_p}$ (DP = Developed plaster; RP = Reference plaster)</figcaption></figure>

## HOT STRIP METHOD PRINCIPLE

The hot strip was a rectangular-shaped electrical resistance with thin thermocouple wires embedded. Temperatures were measured at resistance center, avoiding thermal losses through the electrical wires at one end of the resistance. The resistors were inserted between two plane surfaces of the test samples of dimensions large for the system to be considered semi infinite medium in all directions during the experiment times (Figure 5). The ratio of length to width of the resistance was chosen so that heat transfer at center was bidirectional during minimum testing time of 180 s (Meukam et al, 2004; Jannot, 2008). The hot strip method had advantages of simplified data processing based on separated heat transfer models at the hot strip center; unidirectional during time interval $t_1$ for thermal effusivity estimation by hot plane model, and bidirectional during time interval $t_2$ for thermal conductivity estimation by hot wire model.

<figure><img src="image_8.png" /><figcaption>Figure 5. 2D model hot strip</figcaption></figure>

**Thermal Effusivity (E):** The temperature recorded during time interval $t_0 - t_1$ for heat transfer at resistance center in unidirectional was used to estimate thermal effusivity of each sample with hot plane model using Equation (2) (Meukam and al, 2004; Jannot, 2008):

**Thermal Effusivity (E):** The temperature recorded during time interval $t_0 - t_1$ for heat transfer at resistance center in unidirectional was used to estimate thermal effusivity of each sample with hot plane model using Equation (2) [10, 11]:

$$T_s(0,0,t) - T_s(0,0,0) = \frac{2}{E} \sqrt{t} + \left[ R_c - \frac{m_s c_s}{(E)^2} \right] \quad (2)$$

The thermal effusivity was estimated from the mean slope of the experimental curve $T_s(0,0,t) - T_s(0,0,0) = f(\sqrt{t})$, which was equivalent to $\frac{2\Phi}{E\sqrt{t}}$ determined by linear regression between two times $t_0 - t_1$, when the heating curve was assumed to be linear (steady state conditions) in the time interval.

**Thermal conductivity (λ):** The bidirectional heat transfer coupled with hot wire method were used to determine the thermal conductivity for entire temperature range recorded using the Equation (3) (Meukam et al. 2004; Jannot, 2008):

$$T_s(0,0,t) - T_s(0,0,0) = \frac{\Phi}{4\pi L_{h1}} \ln(t) + \left[ R_c - \frac{1}{2\pi L_{h1}} \left( \frac{1}{\sqrt{t}} + \frac{0.5}{4\pi L_{h1}} \right) \right] \quad (3)$$

where $L_{hw} = 2l$ is length, r is radius

However, the hot strip behaved as a hot wire after a very long time interval so that the asymptotic behavior could be used to estimate thermal conductivity in a relatively short time as intended. If the slope of the curve, $T_s(0,0,t) - T_s(0,0,0) = f(l_1(t))$, varied for hot strip, the variation was sufficiently slow and considered constant on reduced time intervals. The thermal conductivity λ was estimated from slope $\frac{\Phi}{4 L_{h1}}$ of the experimental curve determined by linear regression between 100 s and 180 s. Figure 6 shows the experimental hot strip device used.

<figure><img src="image_9.png" /><figcaption>Figure 6. Experimental hot strip device (1. stabilized alimentation, 2. recorder temperature, 3. electrical resistance inserted between two material samples)</figcaption></figure>

## RESULTS AND DISCUSSIONS

**Eco-plaster thermal conductivity variation according to density:** Figure 7 shows that eco-plaster thermal conductivity increases with its density. It indicates that plaster thermal conductivity is an affine function of density. From literature, it is noted that lower is density, lower is useful thermal conductivity of set plaster (Daligang, 2002). Thus, porosity is main parameter favoring insulating nature of material, in order to have low thermal conductivities (< 1 W.m⁻¹.K⁻¹ for insulating materials), it would be necessary to formulate rather porous plasters, having low densities (Coquard, 1992; Eve, 2003).

**Eco-plaster thermal conductivity according to mixing rate:** Figure 8 analysis shows that thermal conductivity of eco-plaster developed based on snail shells are lower than those of reference plaster for the same $\frac{m_e}{m_p}$ ratios. It can be deduced that when shell plaster setting, the junction between crystallites is
such that more pores develop there than commercial plaster case.

<figure><img src="image_10.png" /><figcaption>Figure 7. Thermal conductivity variation according to density</figcaption></figure>

**Eco-plaster thermal conductivity according to mixing rate:**
Figure 8 analysis shows that thermal conductivity of eco-plaster developed based on snail shells are lower than those of reference plaster for the same $\frac{m_e}{m_p}$ ratios. It can be deduced that when shell plaster setting, the junction between crystallites is such that more pores develop there than commercial plaster case. This relatively greater porosity would give to developed plaster, the property of better thermal insulating compared to commercial plaster studied.

<figure><img src="image_11.png" /><figcaption>Figure 8. Eco-plaster thermal conductivity according to mixing rate</figcaption></figure>

**Eco-plaster thermal effusivity according to mixing rate:**
Figure 9 analysis shows that thermal effusivities values of shell plaster are lower than those of reference plaster. That mean heat flow is less easily propagated from a surface inward of plasters based on snail shells.

<figure><img src="image_12.png" /><figcaption>Figure 9. Eco-plaster thermal effusivity according to mixing rate</figcaption></figure>

These results are consistent with the recorded thermograms. Indeed, with a lower effusivity, heat flux at surface has difficulty in circulating in material with lower thermal conductivity. So on this surface, temperature measured will be higher. In total, the low values of effusivity and thermal conductivity recorded, made plaster a relatively higher thermal comfort material than commercial plaster.

**Sample heating and cooling thermograms:** Figure 10 (10-a – 10-d) thermograms reflect heating and cooling thermal behavior of plaster according to different mixing rate. Indeed, a constant heat flow was imposed for 180 s (heating phase) and then removed (cooling phase). These thermograms show that heat flow propagates more in commercial plaster samples than in developed plaster samples. It is also noted that this propagation decreases as the $\frac{m_e}{m_p}$ ratio increases (or specimens density decreases). The air presence in set plaster network would contribute to this behavior. Depending on the $\frac{m_e}{m_p}$ ratios, a temperature difference of 3 °C to 5 °C is recorded after 180 s on the surfaces subjected to constant flow.

<figure><img src="image_13.png" /><figcaption>Figure 10 a. Plaster samples heating and cooling thermograms $\frac{m_e}{m_p}$ = 1.8</figcaption></figure>

<figure><img src="image_14.png" /><figcaption>Figure 10-b. Plaster samples heating and cooling thermograms $\frac{m_e}{m_p}$ = 2.3</figcaption></figure>

<figure><img src="image_15.png" /><figcaption>Figure 10-c. Plaster samples heating and cooling thermograms $\frac{m_e}{m_p}$ = 2.8</figcaption></figure>
<figure><img src="image_16.png" /><figcaption>Figure 10-d. Plaster samples heating and cooling thermograms $\frac{m_e}{m_p} = 3.6$</figcaption></figure>

## CONCLUSION

The present work shows that it is possible to develop low density plaster from Achatina Achatina snails shells. The elaborated plaster mixing requires a water quantity of water corresponding to $\frac{m_e}{m_p} > 1$ ratios. Thermal measurements show that elaborated plaster has relatively low thermal conductivities and effusivities compared to commercial plaster chosen as reference. These results contribute to snail shells valorisation, which, instead of being considered waste thrown in garbage, can be used as raw material for low density plaster synthesis with interesting thermal characteristics. Synthesized plaster can also better meet the comfort and energy needs in building at low cost.

**Conflicts of Interest:** Authors declare no interest conflicts regarding the publication of this paper.

## NOMENCLATURE

a: Thermal diffusivity, m².s⁻¹

E: Thermal effusivity, J.K⁻¹.m⁻².s⁻⁰.⁵

L: Length, m

m: Mass, kg

R: Electrical Resistance, Ω

S: Surface, m²

T: Temperature, K

t: Time, s

w: Water content, %

x, y, z: Space variables, m

## Greek letters

ρ: Density, kg.m⁻³

λ: Thermal conductivity, W.m⁻¹.K⁻¹

θs: Laplace transform of probe temperature

φ: Heat flux, W

## Indices / Exhibitors

s: Related to prob

## REFERENCES

Coquard, P. (1992) Résistance mécanique des plâtres secs et humides. PhD Thesis, Université de droit, d’économie et des sciences d’Aix-Marseille III.

Dalingang, D. (2002) Plâtre. Techniques de l’Ingénieur, Traité ‘Construction’ (C910) : 24 p.

Ebanda, F. B. (2012) Etude des propriéties mécaniqueset thermiques du plâtre renforcé de fibres végétales tropicales. Autre, Université Blaise Pascal - Clermont-Ferrand II. Français.

Eve, S. (2003) Comportement à la prise et caractérisation mécanique de matériauxcomposites à base de plâtre. PhD Thesis, Université de Caen.

Evrard, A. & De Herde, A. (2010) Le béton et la construction durable. Projet contextualiser, la durabilité.

Jaffel, H. (2006) Caractérisation multi-échelles de matériaux poreux en évolution: cas du plâtre. PhD Thesis, Ecole Polytechnique, 2006.

Jannot, Y. (2008) Théorie et pratique de la métrologie thermique. Séminaire PER AUF, 78p.

Kabore, A. (2019) Modélisation hygrothermique de l'enveloppe du bâtimentavec le matériau de chanvre. Mémoire de maîtrise de l'Ecole de Technologie Supérieure-Université du Québec, Montréal.

Karim, F., Waqif, M., Saâdi, L. (2013) Caractérisation physico-chimique du gypse synthétisé et du phosphogypse. Verres Céramiques & Composites, vol.2 N°2, 19 - 31

Langlais, C. and Klarsfeld, S. (2004) Isolationthermique à température ambiante. Classification des isolants. *Techniques de l'ingénieur*, vol. C3370, pp. 1 - 12.

Meukam, P., Jannot, Y., Noumowe, A., Koffane, T. C. (2004) Thermo physical characteristics of economical building materials. *Construction and Building Materials*, vol 18, pp. 437-443.

Sodjinou, E., Biaou, G. & Codjia, J. C. (2002)Caractérisation du marché des escargots géants africains (achatines) dans les départements de l’Atlantique et du littoral au Sud-Bénin. *Tropicultura*, vol. 20, 2, pp. 83 - 88.

*******