the effect of the sisal fiber content of agave and/or …

JP Journal of Heat and Mass Transfer © 2021 Pushpa Publishing House, Prayagraj, India http://www.pphmj.com http://dx.doi.org/10.17654/0973576321001 Volume 24, Number 2, 2021, Pages 207-226 P-ISSN: 0973-5763

Received: July 31, 2021; Revised: September 13, 2021; Accepted: October 31, 2021 Keywords and phrases: compressed earth blocks, earth building construction, lime, fiber, thermal properties, mechanical properties, sisal agave fiber.

How to cite this article: Y. Jamil, S. Nasla, K. Bougtaib, K. Gueraoui and M. Cherraj, The effect of the sisal fiber content of agave and/or lime on the mechanical and thermal characterizations of soil-based compressed earth blocks from the province of Rehamna in Morocco, JP Journal of Heat and Mass Transfer 24(2) (2021), 207-226.

DOI: 10.17654/0973576321001 This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Published Online: December 8, 2021

THE EFFECT OF THE SISAL FIBER CONTENT OF AGAVE AND/OR LIME ON THE MECHANICAL AND THERMAL CHARACTERIZATIONS OF SOIL-BASED

COMPRESSED EARTH BLOCKS FROM THE PROVINCE OF REHAMNA IN MOROCCO

Y. Jamil, S. Nasla, K. Bougtaib, K. Gueraoui and M. Cherraj

Team of Modelling and Simulating in Mechanics and Energetics Energy Research Centre Faculty of Sciences Mohamed V. University B. P. 1014, Rabat, Morocco

Abstract

Earth building is a construction method well-known all around the world as it was the first building material used by human. In fact, building in earth means building with a material available in large quantities and almost everywhere, ecological, recyclable and which offers pleasant insulation. The objective of this study is to analyze the

Y. Jamil, S. Nasla, K. Bougtaib, K. Gueraoui and M. Cherraj 208

effect of the content of sisal agave fiber and/or lime on the thermal and mechanical characteristics of compressed earth blocks (CEBs). In this context, we have used three contents of sisal agave fibers (1%, 2% and 3%) and three contents of lime (6%, 10% and 14%) by weight of the dry mixture. The results of this study indicate that the combination of sisal agave fiber and lime can improve the thermal and mechanical properties of compressed earth blocks (CEBs).

1. Introduction

Morocco is a country located at the north-western end of Africa, it opens both on the Atlantic and on the Mediterranean between the 37th and 21st parallels. It extends from the Strait of Gibraltar to practically, on the southern borders of the great African Sahara. The Moroccan climate is both Mediterranean and Atlantic. It has a hot and dry season (May to September) and a cold season (October to April) [1]. The use of conventional materials such as concrete, due to their thermal property, makes these variations more noticeable in the habitat. In addition, the use of cementitious materials has a negative impact on the environment [2, 3] as well as on the building in term of thermal comfort. Moreover, in an international context marked by an energy imbalance and climate change, the design of ecological building systems with low energy consumption is increasingly required. Thus, nowadays, earthen constructions constitute a promising alternative compared to constructions with conventional materials with regard to economic and environmental issues. This type of construction then complies with the objectives of sustainable development, particularly because of the thermo-physical properties of the components and the recyclability of the materials at the end of the building’s life cycle [4, 23]. In fact, during the last ten years, the use of earthen bricks as sustainable building material has an important interest. Among the architectural works inscribed on the UNESCO World Heritage List, about 15% are built in earth [5].

CEBs are modern evolution of molded earth blocks, more commonly referred to as adobe blocks [6]. The CEBs are small masonry elements of parallelepiped shape obtained by the static or dynamic compression of the wet earth placed in a mold then unmolded just after. The use of this type of

The Effect of the Sisal Fiber Content of Agave and/or Lime … 209

material fits suitably in an approach aiming at a high environmental quality, since the process calls upon a material abundant locally and requiring less energy for its transformation [7]. Nevertheless, compressed earth can only be used in construction if its cohesion is sufficient [8]. This essential property is mainly due to the presence of clay which acts as a natural binder. Consequently, the use of clays in industrial applications for CEBs is dependent on detailed knowledge of their physicochemical and technological properties. In particular, the plasticity of clays, their behavior during drying operation, the mechanical resistance of the products after drying are also of great importance [9, 24].

The latest studies, which appeared on CEBs, have shown that the incorporation of natural fibers reduces the size of shrinkage cracks, improves its durability and tensile strength [10], and that the addition of natural fibers even decreases the thermal conductivity of composite materials [11]. In his study, Namango proved, that within certain limits, there is a considerable increase in compressive and flexural resistance in the dry state with the increase of sisal fibers, manioc powder and cement contents, and that outside these limit values, the presence of sisal fibers has an unfavorable effect on the resistance of the compressed earth block [12]. But Rigassi and without giving any justifications, declares that the vegetable fibers are incompatible with the mode of compaction of the CEBs, because they make the mixture too elastic [13].

In this article, we have developed an experimental study which consists of making earthen bricks with increasing dosages of sisal agave fiber and/or lime. These different combinations were used to make a different set of CEBs to study the effect of agave fiber content and/or lime on their physical and chemical characteristics.

2. Material and Method

2.1. Materials used

2.1.1. Soil

The soil used is extracted from a quarry located in Bounaga, (Rehamna


province in the Marrakech region) with the following GPS coordinates:

.W0.37757N3.089531 ′′′′′′

Table 1 shows the particle size composition of the soil, which is determined using two tests: particle size analysis by sieving according to standard NF P94-056 and by sedimentometry according to standard NF P94-057.

As for the granularity, statistical studies were carried out in order to define the Atterberg limits: (LL liquidity limit, PL plasticity limit, and PI plasticity index) according to the NF P94-051 standard. The results obtained for our soil, show that the plasticity limits are almost within the limits best suited for compressed earth blocks (the standard XP P 13-901) (Figure 1). The standard recommends that the soil must have a minimum of plasticity ensuring cohesion between the grains of the material during compaction ( )%5m2% >μ [25, 26].

Table 1 also shows the results of the methylene blue (VBS) test according to standard NF 994-068.

Table 1. Geotechnic properties of the used soil

Granulometric distribution

Gravel 11.59%

Sand 57.20%

Silt 9.62%

Clay 21.59%

Plastique’s properties

Liquidity limit (LL) 26.9%

Plasticity limit (PL) 13.2%

Plasticity index (PI) 13.7%

Methylene blue test

Methylene blue value ( )100gg 1.32


Figure 1. Diagram of plasticity (XP P 13-901 standard).

The grain size curve of the used soil is shown in Figure 2 with the ideal curve and the limit zone. Analysis of this curve shows that it is composed of 10% gravel, 57.20% sand, 9.62% silt and 21.59% clay. From these results, it can be concluded that the soil studied falls within the particle size range for the formulation of CEBs recommended by the CRATerre standard [14, 27, 28].

Figure 2. Soil grain size curve used with the upper and lower limits of the granular spindle.


2.1.2. Lime

In this study, quicklime produced by the lime plant of Marrakech (Morocco) was used. Lime is especially recommended for soils containing a clay fraction of less than 20% [15].

The chemical composition of quicklime by X-ray fluorescence is presented in Table 2.

Table 2. Chemical composition of the used lime (%)

SiO2 CaO Al2O3 MgO Fe2O3 SO3 K2O Na2O

1.26 83.82 9.74 1.66 3.11 0.18 0.163 0.061

2.1.3. Sisal agave fiber

In this study, sisal agave fibers (Figures 3 and 4) were used. The physical and mechanical characteristics [12] are presented in Table 3.

Figure 3. Sisal plant after cutting.

Figure 4. Fibers cut into pieces.


Table 3. Fibers characterization

Fibers cut into pieces

Fibers cut into pieces 1.3-1.45

Fibers cut into pieces 80-840

Fibers cut into pieces 1.6-2

Fibers cut into pieces 2.5-5

2.2. Composition of mixtures-preparation of samples

In order to improve the mechanical and thermal characteristics of compressed earth blocks, we stabilized the soil by three types of treatment, lime treatment with three different contents: 6%, 10%, 14%, fiber treatment with three different contents: 1%, 2%, 3% and mixed treatment (Lime + Fiber). Table 4 shows the quantity of materials used for each series of blocks.

Table 4. Composition of the CEBs mixtures (%)

Components Designation

Soil (%) Lime (%) Sisal agave fiber (%)

C0F0T100 100 0 0

C6F0T94 94 6 0

C10F0T90 90 10 0

C14F0T86 86 14 0

C0F1T99 99 0 1

C6F1T93 93 6 1

C10F1T89 89 10 1

C14F1T85 85 14 1

C0F2T98 98 0 2

C6F2T92 92 6 2

C10F2T88 88 10 2

C14F2T84 84 14 2

C0F3T97 97 0 3

C6F3T91 91 6 3

C10F3T87 87 10 3

C14F3T83 83 14 3


Before mixing we must make sure that our mixture is well dry. For this

we must subject the soil to drying in an oven for 24 hours at .C60 Next, the mixture is dry mixed for 2 min in a cement mixer [29, 30].

For the preparation of the test pieces according to the test program, a mold was used. Its walls are made of hardened steel, composed of 5 elements

that forms, after assembly, a volume of .cm1608040 3×× The mold is fitted with a piston to ensure the transmission of the compaction stress from the press to the mixture [30, 31].

Figure 5. The mold used.


Figure 6. Presentation of the prepared blocks.


2.3. Experiment

2.3.1. Experiment dispositive

The devices used to evaluate the thermal and mechanical parameters are respectively given by:

Figure 7. CT-meter devices used for thermal testing.

Figure 8. Experimental material of the compression and bending test.


2.3.2. Physical and thermo-mechanical parameters of CEBs

• Thermo-physical properties:

The thermal properties are quantities which characterize the behavior of materials when they are subjected to a temperature variation.

Thermal conductivity λ is the physical quantity that characterizes the ability of an object to conduct heat. It represents the heat flow through a material one meter thick, for a temperature difference of one Kelvin between the two incoming and outgoing faces.

Thermal effusivity E characterizes the ability of a material to change temperature when it receives a supply of thermal energy. It is given by equation (1).

,CE λρ= (1)

where E is thermal effusivity (in ,).K2.mJs 121 −−− λ is thermal

conductivity (in ,).KWm 11 −− C is (in ).KJm 13 −− specific heat density and

ρ is the density (in ).Kg.m 3−

Thermal diffusivity α is the physical quantity that characterizes the ability of a material to transmit a temperature signal from one point to another of this material. It is given by equation (2):

Cρλ=α (2)

with α is (in ).sm 12 − the thermal diffusivity, λ is (in ).KWm 11 −− the

thermal conductivity, C is (in ).KJm 13 −− the specific heat density and ρ is

the density (in ).Kg.m 3−

Specific heat pC of a material is the energy it takes to increase its

temperature by one degree. It is given by equation (3):

.ρCCp = (3)


Here pC denotes the specific heat (in ,).KKJ.Kg 11 −− C is the specific

heat by volume (in ).KJ.m 13 −− and ρ is the density (in ).Kg.m 3−

• Mechanical properties:

The sizing of a structure requires knowledge of the material and its mechanical characteristics, these are determined using mechanical tests. The most widely used are, tensile, bending and compression tests. Monoaxial compression and 3-point bending tests according to standards NF EN14617-15 and NF EN 12372.

• Compressive strength Rc:

In the current state of knowledge, the compressive strength of CEBs is the most important mechanical parameter, it will determine the architecture and the dimensioning of constructions [16].

Maximum compressive strength is determined by equation (4):

,SFRc = (4)

where cR is (in MPa) the compressive strength, F is (in N) the breaking

force and S is (in )mm2 the force application area.

• Bending strength fR :

For the in-situ quality control of CEBs, a simpler test which is the “three-point bending” test is used. The importance of this in situ test is not to be demonstrated, when we know that often there is only this de facto control [16].

The maximum tensile stress due to bending is determined by equation (5):

,..

100.23

2 Fel

LR f−= (5)


where fR is (in MPa) the three-point bending tensile strength, F is (in N) the

breaking force, L is (in mm) the length of the CEBs, e is (in mm) the thickness of the CEBs and l is (in mm) the width of the CEBs.

3. Results and Discussions

3.1. Thermal parameters

Figures 9, 10 and 11 show the variations in thermal diffusivity, thermal conductivity and thermal effusivity of CEBs as a function of fiber content.

Figure 9. Thermal diffusivity of CEBs as a function of fiber content.

Figure 10. Thermal effusivity of CEBs as a function of fiber content.


Figure 11. Thermal conductivity of CEBs as a function of fiber content.

In Figure 11, a decrease in thermal conductivity is observed as a function of the % of fiber, this decrease is due to the fact that the presence of the fibers in the matrix increases the porosity and the air pockets at the level of the interstices, which has, as a consequence, the increase of its thermal resistance [21, 22]. Similarly in Figure 10, we observe a decrease in thermal effusivity, the decrease in conductivity directly leads to a decrease in effusivity because conductivity and effusivity are linked. Figure 9 also shows that the diffusivity decreases with the percentage of fiber, which is quite normal because the drop in conductivity makes the material less and less diffusive.

The thermal conductivities vary from 0.33 to 0.94 ,.KW.m 11 −− we can say that the conductivity values are close to those measured by Coulibaly [17]. Also, these conductivities are in the same orders of magnitude as those of compressed bricks stabilized with cement, sawdust and pozzolan, whose

average values vary from 0.55 to 0.95 11.KW.m −− [18].

3.2. Thermal parameters

Figures 12 and 13 show the variations in compressive strength of CEBs as a function of fiber content.


Figure 12. Effect of fiber content on compressive strength.

Figure 13. Effect of lime content on compressive strength.

The effect of varying the fiber content on the compressive strength of CEBs is shown in the figure. Through these results of untreated CEBs (0% lime) we observe an increase in strength with increasing fibers. The test pieces containing the fibers resist compression better than the test pieces of natural soil.

For the other cases 6% and 10% and also 14% lime content, we notice that the addition of fibers led to an increase in strength up to 2% in fibers.

For blocks reinforced with a fiber content greater than 2%, there is a decrease in strength with increasing fiber content. The decrease in compressive strength of CEBs can be attributed to the dominance of the


effect of fibers over that of lime content. This can be explained by the fact that the quantity of hydration products is small compared to the size of the voids created by the fibers. These voids are due to the elastic nature of the fibers during compaction. Once the compaction stress is removed, the material relaxes and the volume occupied by the fibers increases creating additional porosity and consequently negatively affects the strength.

Figure 14. Effect of fiber content on flexural strengths.

Figure 15. Effect of lime content on flexural strengths.

For example, the compressive strength of unreinforced fiber blends increases by 1.42, 1.66 and 1.98 MPa when the blocks are stabilized by 6%, 10% and 14%, respectively.

These percentages are calculated relative to the reference mix (natural soil).


Figures 14 and 15 show the variations in flexural strength of CEBs as a function of fiber and lime content.

The results also show that flexural strength increased with increasing fiber content up to certain fiber content. In our case, the increase in flexural strength for a lime content of 6%, 10% and 14%, respectively. In accordance with the results obtained for compressive strength. From Figure 10, it can be seen that the increase in lime content caused an increase in flexural strength [32, 33].

For example, the flexural strength of blends reinforced with 2% fiber increases by 0.193, 0.25 and 0.31MPa when the blocks are stabilized by 6%, 10% and 14%, respectively. These percentages are calculated relative to the reference mix (natural soil with 2% fibers). These results are in agreement with the work of Millogo [19] and Meukam et al. [20].

4. Conclusions

As part of this study, we have tried to contribute to the study of compressed earth blocks intended for construction. This choice results from the economic and thermal advantages of this material.

The experimental study allowed us to specify a number of points:

* Identification of the soil before use is necessary, it may also lead to recommendations concerning their possible treatment.

* In most examined cases, the addition of fiber has a negative effect on the compressive strength and tensile strength of the compressed earth block.

* Considering the mechanical and thermophysical properties, the blocks stabilized with fibers and lime offer the best advantages. They have the highest compressive strength (approx. 2.3 MPa) and three-point flexural

strength (0.31 MPa), low thermal conductivities (0.33 ).KW.m 11 −− and low densities.

* The thermal insulation of manufactured bricks where the fiber percentage is 3% is the best because of the presence of the fiber which imposes the best insulation.


Acknowledgement

The authors are highly grateful to the referee for his careful reading, valuable suggestions and comments, which helped to improve the presentation of this paper.

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