Physic Mechanical Behaviours of Raw Earth Bricks: Case of Laterite Stabilized with Gum Arabic and Reinforced with Sugarcane Bagasse in Chad ()
1. Introduction
Chad is a landlocked country in Central Africa and therefore has no access to the sea. This situation means that the supply of building materials is generally done through border transit, thus increasing the cost of these materials. Although a few factories producing building materials exist, prices remain exorbitant and the poverty experienced in Chad does not encourage an improvement in the situation [1] [2]. In this state of affairs, the population resorts to alternative materials that are easy to access both in terms of cost and availability. Hence, the use of earth materials is used in the construction of individual houses. One of these most used materials is laterite. Laterite is abundant in this region of Chad which is the subject of our study. It is a material that designates a gram of earthy mass of generally red colour characteristic of ferruginous soils [3] [4]. It results from an accumulation and sedimentation of rocks transported or existing on site and which are concretions or altered quartz grains. Its use in the world in general does not date from today. However, its mechanical performances are put to the test and this is reflected by the observation of structural and mechanical disorders on bricks made from this material [5]. These problems are being addressed through the process of stabilization with gum Arabic and reinforcing the sugarcane bagasse. Gum Arabic, it should be remembered, is a material derived from the sap of plants in the acacia family. More than a food emulsifier, it has particular properties, in particular its hydrophilic and hydrophobic dual character gives it a state of physicochemical equilibrium [6] [7]. Gum Arabic is used as an admixture to laterite for the treatment of adobe house coverings. It was studied as an alternative binder to cement in the process of making laterite earth bricks in order to evaluate its effects in relation to durability properties [8]. It plays an important role in reducing dry density [9]. The addition of sugarcane bagasse to the laterite plus gum Arabic mixture provides reinforcement in the production of this composite material [10]. Sugarcane bagasse is a fibrous residue from the extraction of sugarcane juice. Given its fibrous potential, it presents a wide morphological heterogeneity consisting of fiber bundles and structural constituents, which are precisely involved in the mechanical behaviour of the composite [11]. In addition, bagasse, a direct waste from the sugar factory, has a humidity of 48%, an apparent specific weight estimated at between 200 kg/m3 [12].
2. Materials and Methods
2.1. Presentation of the Study Area
The study area (Figure 1) is in the southwest of Chad in the Mayo-Kebbi West region. It has an average annual rainfall that seems stable around 700 to 800 mm with an average annual temperature of 38˚C. Pala (latitude 9˚21'0'' and longitude 14˚58'0'') is the capital of the region with a population of more than 50,000 inhabitants. This region borders Cameroon.
2.2. Materials
2.2.1. Laterite
It is taken from the quarry located behind the old Coton Tchad factory. Two types of textures are observed: gravelly laterites and rocky laterites (Figure 2).
Figure 1. Map of the study area.
Figure 2. Rocky laterite (a); gravelly laterite (b).
Gravelly laterites are composed of pisoliths, i.e., small isolated hard fragments, coated or scattered in a fine soil. Meanwhile, rocky laterites are coherent and hard materials, similar to soft rocks, which can explode with a hammer or by exerting any force (explosive), and reduced to rubble and crushed stones, all run or calibrated [13]. For our study, the gravel type was used due to its immediate availability and ease of application.
2.2.2. Gum Arabic
Gum Arabic (Figure 3) is a natural heteropoly molecular polymer exuded by the Senegalese acacia plant. This plant is widespread in the Sahelian areas and the Mayo Kebbi West region (Pala). The gum is made up of approximately 39% to 42% galactose, 24% to 27% arabinose, 12% to 16% rhamnose, 14% to 16% glucuronic acid (which gives it its anionic character), 1.5% to 2.6% protein, 2.22% to 0.39% nitrogen and 12.5% to 16% water, for an average molecular mass of 200 to 300 kilo Daltons and a specific mass of 13.5 KN/m3 [14]. Table 1 shows the chemical composition of gum Arabic.
Figure 3. Gum Arabic.
Table 1. Chemical composition of the gum Arabic used.
Sample |
Rhamnose |
Arabinose |
Galactose |
Glucose |
Ac glucuronic acid |
Unit |
mg/l |
mg/l |
mg/l |
mg/l |
mg/l |
GA |
26.14 |
24.31 |
10.82 |
20.94 |
0.85 |
2.2.3. Sugarcane Bagasse
Sugarcane bagasse is the waste of sugarcane. Sugarcane is a reed 3 to 4 meters high, straight at the end of growth but bends towards maturity. The stem is cylindrical and varies in size between 2 and 6 cm. Although the region does not currently have a sugar manufacturing plant, its production in the locality is very abundant, part of which is intended for the factory of the Chad Sugar Company, in the extreme south of the country (Sarh) and another part for local consumption. The harvest period is often between November and December (dry period). If we consider mature sugarcane without its leaves, it contains 90.44% of sweet juice against 9.56% of woody (Table 2) [15]. Figure 4 shows sugarcane bagasse, and Table 2 shows the percentage of sugarcane constituents.
Figure 4. Sugarcane bagasse.
Table 2. Percentage constituents of sugarcane.
Components |
Percentage (%) |
Water |
71.04 |
Crystallizable sugar |
18.02 |
Woody |
9.56 |
Albumin and other nitrogenous substances |
0.55 |
Fatty and colouring resinous materials |
0.35 |
Mineral salts |
0.48 |
2.3. Methods
2.3.1. Standards
Table 3 presents a set of standards that allowed us to conduct our tests.
Table 3. Testing standards.
Tests |
Standards |
Granulometry |
NF EN ISO 14688-1 [16], p. 14688 |
Atterberg Limits |
NF P94-051 [17] |
Moisture content of laterite |
NF EN ISO 18134-3 [18], p. 13 |
Formulation |
XP P13-901: 2022 [18], p. 1 |
Apparent density |
NF EN ISO 11272 [19], p. 11 |
Compressive strength |
NMX-C-432-ONNCCE-2002 [20] |
Flexural strength |
BS EN 12372:2022 [21] |
Linear shrinkage on drying |
XP P13-901: 2022 [18], p. 13 |
Abrasion resistance |
XP P13-901: 2022 [18] |
Water-proof by immersion |
XP P13-901: 2022 [18] |
2.3.2. Standards
They were made according to XP P13-901: 2022. The mixture of components (laterite plus powdered gum Arabic) was done dry after being placed in an oven at 105˚C for 24 hours. Gum Arabic (7%) in powder form with dimensions varying between 0.2 and 0.6 mm after grinding, was added to the laterite for an initial dry mix (Figure 5). This percentage of gum Arabic is defined by the authors of the literature as being the threshold for optimum compressive strength. This dry mix allows for a uniform distribution of the fine particles of the lateritic matrix before the mixture sets when water and bagasse are added. The length in millimeters of the bagasse is 2.50 to 10.20 for a diameter of 0.55 to 3.50 mm. It is important to ensure a homogeneous distribution of the constituents before molding the bricks in order to avoid the agglomeration of the fibers between them.
Then, once the two components have been homogenized, water is added reasonably according to the water content, then gradually sugarcane bagasse until a nearly homogeneous paste is obtained and finally the moulding in 16*4*4 cm3 (Figure 6). Table 4 shows the proportions of the materials during the operation.
Figure 5. Mixture of Laterite and gum Arabic (a); addition of sugarcane bagasse (b); mixture with addition of water (c).
Table 4. Formulation.
Formulation |
Laterite |
Sugarcane bagasse |
Gum Arabic |
Water |
Number of test tubes |
E |
100% |
0% |
7% |
12% |
15 |
E1 |
100% |
5% |
7% |
15% |
15 |
E2 |
100% |
10% |
7% |
15% |
15 |
E3 |
100% |
15% |
7% |
20% |
15 |
E4 |
100% |
20% |
7% |
25% |
15 |
E5 |
100% |
25% |
7% |
30% |
15 |
E6 |
100% |
30% |
7% |
30% |
15 |
Figure 6. Sample of test tubes 16*4*4 cm3.
2.3.3. Methodological Framework of the Characterization Procedure
As indicated above in Table 3, we started with the granulometric test in order to determine the different grain diameters of the laterite material (NF EN ISO 14688-1). The Atterberg limits were obtained according to the NF P94-051 standard. These conventional physical constants mark the thresholds between the passage of soil from the liquid state to the plastic state (Wl) and the passage from the plastic state to the solid state (plasticity limit Wp). The natural water content makes it possible to know the mass of free water eliminated by drying in an oven at a temperature of 105˚C. Since bricks are subjected to stresses in construction, it is therefore important to understand their physic mechanical behaviour by determining their compressive strength (NMX-C-432-ONNCCE-2002) and flexural strength (BS EN 12372: 2022) using the apparatus shown in Figure 7, their linear shrinkage on drying according to the principle described in XP P13-901: 2022, their abrasion resistance (XP P13-901: 2022) and their resistance to water by immersion (XP P13-901: 2022), the devices of which are shown diagrammatically in Figure 8 and Figure 9 respectively.
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Figure 7. Experimental device for compression testing.
Figure 8. Abrasion test device.
Figure 9. Immersion test device [18].
3. Results and Discussions
3.1. Geotechnical Characterizations of Laterite
The results obtained from some geotechnical tests are listed in Table 5.
Table 5. Geotechnical results.
Characterizations |
Results |
Laterite granulometry |
21% clay; 17% silt; 62% sand |
Atterberg Limits |
Wl (%) = 39; Wp (%) = 22.08; Ip (%) = 16.92 |
Moisture content of laterite |
1.36% ± 0.03% |
The values of the Atterberg limits are reported in Figure 10. The plasticity diagram (Figure 10) allows us to position these values in its coordinates. It suggests that the material is well suited for earth construction needs [18].
Figure 10. Plasticity diagram.
3.2. Physical and Mechanical Characterizations
3.2.1. Density
The density after passage in the oven at 100˚C varies from 1525 to 1630 kg/m3 (Figure 11). However, at three days of age, the values are much higher than those after passage in the study. This variation is explained by the capacity for shrinkage during drying as mentioned [22] [23].
3.2.2. Compressive and Flexural Strength
The values of the determined compression (Figure 12) and bending (Figure 13) tests vary according to the percentage of sugarcane bagasse reinforcement. The maximum value for compression is 4.70 MPa for a percentage of 25% of sugarcane bagasse, while that of the bending resistance is 3.33 MPa for an addition of 30% of sugarcane bagasse after passing through the oven at 105˚C. These results are better thanks to the addition of sugarcane bagasse than those obtained by [24]-[26].
Figure 11. Density.
Figure 12. Compressive strength.
Figure 13. Bending resistance.
3.2.3. Linear Withdrawal
Since the raw materials constituting our composite material exhibit plastic behaviour, the shrinkage test is carried out on the test pieces produced [18]. This parameter allows to have an exact idea of the real dimensions of the bricks after drying. By carrying out a daily measurement of the length of the test pieces until the complete drying of the brick, the value of the linear shrinkage RL is determined, expressed as a percentage presented in the form of a graph in Figure 14.
Figure 14. Linear withdrawal.
We observed that the more sugarcane bagasse is added to the composite, the more its linear shrinkage increases. This shrinkage could be explained by the possible presence of pores in the composite material, in addition to the physical and mechanical characteristics of sugarcane bagasse with a low apparent density (200 kg/m3) [12] [27].
3.2.4. Mass Loss by Immersion
We see in Figure 15 that the mass loss by immersion varies from 6% to 16% depending on the percentages of sugarcane bagasse input. This variation is disproportionate depending on whether there is more bagasse; there will be less mass loss and vice versa. This is why at 5% sugarcane bagasse; we obtain 16% mass loss. At 30% sugarcane bagasse, we only have a 6% mass loss. This is explained by the fact that the more fibers there are in the composite, the more the constituents aggregate together in addition to the binding action of gum Arabic as the authors point out [27] [28].
3.2.5. Abrasion Test
This test is all the more important because it allows us to simulate the wear of the material over time. In order to classify our material to the XP 13-901 standard, we use the class defined in Table 6. Figure 16 shows the results.
Figure 15. Mass loss (%).
Figure 16. Abrasion test.
Table 6. Abrasion resistance category.
Abrasion coefficient (g/cm2) |
Abrasion resistance category |
≤0.14 |
Ab1 |
≤0.2 |
Ab2 |
≤0.5 |
Ab3 |
Based on this result, our material is class Ab3 [18].
4. Conclusion
In short, the objective of this article was to study the physics and mechanical behaviours of raw earth bricks using a composite material consisting of laterite stabilized with gum Arabic and reinforced with sugarcane bagasse. Determination of the Atterberg limits gives: Wl (%) = 39; Wp (%) = 22.08 with a plasticity index Ip (%) = 16.62. The plasticity index is between 15 and 40, and the soil is said to be plastic. The values inserted in the spindle of the plasticity indices of the earth indicate the soil studied is recommended for bricks. The maximum compression value is 4.70 MPa for a percentage of 25% of sugarcane bagasse, while that of the flexural strength is 3.33 MPa for a contribution of 30% of sugarcane bagasse after passage in the oven at 105˚C. An increasing variation of these values demonstrates that the addition of sugarcane bagasse in the laterite and gum Arabic mixture increases the mechanical and physical resistances of the bricks. The abrasion test allowed us to classify our bricks as class Ab3 with an abrasion coefficient ≤ 0.5 g/cm2, which confirms that the more sugarcane bagasse the bricks contain, the more they are subject to degradation due to wear and, at the same time, loss in mass. This study made it possible to understand the possibilities of using lateritic earth bricks with plant fibers as reinforcement.
Credit Authority Contribution Statement
TAÏPABE Djoui: Writing-review & editing, Writing-original draft, Methodology, Investigation; DOKO Kouandété Valéry Writing-original draft, Methodology, Investigation., DATCHOSSA Tiambo Abbas: Writing-original draft, Methodology; GIBIGAYE Mohamed: Writing-original draft, Methodology.
Acknowledgements
The authors are grateful to all laboratory technicians of “Laboratoire d’Energétique et de Mécanique Appliquées (LEMA)” of University of Abomey-Calavi (UAC) Benin, and those of the “X-TECHLAB”, Sémé City, Benin for their constant help in the realization of geotechnical and mechanical tests.