# Improvement of Malagasy Traditional Earth Bricks by Using a Derivative of CNSL as a Binding Agent

Volana Mifelana Holiarinala, Fenia Diane Ramiharimanana, Hermann Rafanoela, Stephanoel Randriatsarazaka, Raymond Razafimahatratra, Estelle Metay, Voahangy Vestalys Ramanandraibe, Marc Lemaire

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Volana Mifelana Holiarinala, Fenia Diane Ramiharimanana, Hermann Rafanoela, Stephanoel Randriatsarazaka, Raymond Razafimahatratra, et al.. Improvement of Malagasy Traditional Earth Bricks by Using a Derivative of CNSL as a Binding Agent. ChemEngineering, 2025, 9 (2), pp.22. 10.3390/chemengineering9020022. [hal-05359288](https://hal.science/hal-05359288v1)

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Article

# Improvement of Malagasy Traditional Earth Bricks by Using a Derivative of CNSL as a Binding Agent

Volana Mifelana Holiarinala<fnref n="1" />, Fenia Diane Ramiharimanana<fnref n="1" />, Hermann Rafanoela<fnref n="1" />, Stephanoel Randriatsarazaka<fnref n="2" />, Raymond Razafimahatratra<fnref n="2" />, Estelle Metay<fnref n="3" />, Voahangy Vestalys Ramanandraibe<fnref n="1" /> and Marc Lemaire <fnref n="1" />,<fnref n="3" />,*

<figure><img src="image_3.png" /></figure>

check for
updates

Academic Editor: Iuliana Deleanu

Received: 29 December 2024

Revised: 14 February 2025

Accepted: 17 February 2025

Published: 21 February 2025

**Citation:** Holiarinala, V.M.; Ramiharimanana, F.D.; Rafanoela, H.; Randriatsarazaka, S.; Razafimahatratra, R.; Metay, E.; Ramanandraibe, V.V.; Lemaire, M. Improvement of Malagasy Traditional Earth Bricks by Using a Derivative of CNSL as a Binding Agent.
*ChemEngineering* **2025**, *9*, 22.
https://doi.org/10.3390/chemengineering9020022

**Copyright:** © 2025 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license
(https://creativecommons.org/licenses/by/4.0/).

**Abstract:** Traditional bricks are still the most widely used building material in Madagascar. Bricks are made from clay that is fired for weeks in open-air kilns (600–750 °C) by using rice husks, peat, charcoal, coal, and wood as fuels. This process contributes significantly to environmental pollution by emitting CO₂ and particles. In addition, the intensive use of wood and charcoal is partly responsible for the deforestation that still taking place on the “Red Island”. The development of sustainable building materials is therefore of global interest. This research provided a solution by implementing the oxyacetic acid derivative of cashew nut shell liquid (CNSL) as a binder to reduce energy consumption in the preparation of earthen materials. This product was obtained from cashew nut waste and was used in a proportion of 5 to 15% with the red soil of Madagascar. The materials were formulated at a much lower temperature (60 °C) compared to the traditional process for 24 to 48 hours in a custom-designed mold. The material with 10% oxyacetic binder from CNSL was a compact, hard solid with higher mechanical properties, including a twice higher compressive strength (5.6 MPa compared to 2.2 MPa) and a higher tensile strength (2.2 MPa compared to 1.6 MPa). This material also had better water resistance after 2 months of immersion; traditional clay bricks absorbed 36.65% of the water, and the material with binder only absorbed 12.62%. This research demonstrates that the utilization of local agricultural waste as a binder is a viable strategy for reducing the carbon footprint of traditional building materials while significantly improving their physico-mechanical properties.

**Keywords:** traditional brick; red soil; CNSL; oxyacetic acid; binding agent; waste management and energy saving

## 1. Introduction

Fired clay bricks are the most common building material used in Madagascar today. Depending on the climatic conditions and the location, the bricks are dried and then fired in open-air kilns for a few days to a few weeks. Firing takes place in kilns fired with charcoal, rice husks, peat, or wood, to reach high temperatures (600–750 °C) [1–3]. Whatever the process, brick production in Madagascar suffers from several drawbacks. First, it contributes significantly to the depletion of essential resources through massive fuel consumption [4]. A study conducted in Sabotsy Namehana, one of the main artisanal brick production sites in the Analamanga region, showed that it is necessary to burn 35 kg of rice husks mixed with 156 kg of fine coal to bake 1000 bricks (at about 1.5 tons) [5]. Wood

<footnote n="1">¹ Laboratoire International Associé, Faculty of Sciences, IST Campus, University of Antananarivo-Lyon, Ampasapito, Antananarivo 101, Madagascar</footnote>

<footnote n="2">² Laboratoire National des Travaux Publics et du bâtiment, BP, 1151 Alarobia, Antananarivo 101, Madagascar</footnote>

<footnote n="3">³ Institut de Chimie et Biochimie Moléculaires et Supramoléculaires (ICBMS), University of Claude Bernard Lyon 1/CNRS, 1 rue Victor Grignard, 69100 Villeurbanne, France</footnote>

<footnote>* Correspondence: marc.lemaire.chimie@univ-lyon1.fr; Tel.: +261-(0)3-4062-5821; +33-(0)6-8964-2844</footnote>
and coal are also used in large quantities in the districts of Toliara and Fianarantsoa to
fire bricks [1,3], causing deforestation and soil erosion [6–8]. Secondly, the combustion of
these fuels produces various types of gas emissions, such as CO, CO2, particle matters,
nitrogen oxides, and sulfur oxides [9–14]. Consequently, the environmental impact in terms
of resource demand, energy consumption, and generation of greenhouse gases makes
traditional brick manufacturing unsustainable. New methods have been developed to
make alternative bricks, such as those based on biomaterials (natural fiber [15], sugar cane
bagasse [16], etc.) and on industrial wastes (fly ash, steel dust, etc.) [17]. Other research
also focuses on the addition of a binder to avoid heating while maintaining the durability
of bricks, like ovalbumin [18], polyethylene [19], etc. However, none of these, fully provide
the desired properties and/or cannot be proposed in a developing country context, such as
in Madagascar.

One theme of the international associated laboratory (LIA) is the valorization of waste
from agro-industry, as in the case of cashew shells [20,21]. Madagascar exports 10,000 tonnes
per year of cashew kernels, generating a large amount of cashew shells [22]. These cashew
shells are usually burned or landfilled. However, these shells contain a viscous oil called
CNSL, which is mainly composed when obtained by the solvent extraction of anacardic acid
(60 to 65%), cardol (15 to 20%), cardanol (10%), and methylcardol (traces) [20,21,23]. For this
unique structural feature, this dark liquid is used as a natural monomer for polymerization
reactions [24]. Therefore, a wide variety of resins can be synthesized from CNSL, which
can be used for composite applications [25–27]. Recently, the use of CNSL acid as a raw
material for the synthesis of oxyacetic acid derivatives for use as paint binders has been
described [28].

In the development of new green advanced functional materials, CNSL and its com-
pounds can be valued and used as raw materials. For the first time, this new study proposes
a derivative of CNSL as a potential binder for earthen materials. The bricks were made
with the red soil of Madagascar and oxyacetic derivatives of CNSL in order to improve
their properties (tensile and compressive strengths and water resistance) and reduce their
environnemental footprint (reduction of energy consumption and gas emission).

The red earth of Madagascar (often called the “Red Island”) is a ferralitic soil char-
acterized by a very advanced decomposition of primary minerals [29]. They have a high
content of iron oxides. The most interesting fact about these ferralitic soils in Madagascar is
that they cover 2/3 of the island, making it abundant and easily accessible [29]. Moreover,
the massive exploitation of clayey deposits, especially in rice fields, is an additional factor
affecting the environment and the fragile hydrogeological system [4].

**2. Materials and Methods**

**2.1. Materials**

Dry cashew nut shells were collected from operators in Antsiranana, the north re-
gion of Madagascar. Organic solvents and reagents were purchased by local and chem-
ical distributors, such as SPCI, Chimidis, and Sigma-Aldrich. Solvents were purified
by distillation before each use. Other reagents were used as received from the chem-
ical company without purification. Molds used for formulation on building materials
were made by a local artisan. These molds were made of galvanized iron and had the
dimensions of a cylinder: 3.6 cm diameter × 2.2 cm height and rectangular parallelepiped
4 cm width × 4 cm height × 16 cm length.

In this study, the red soil was collected in Ampasampito, a district in Antananarivo,
the capital of Madagascar (Supplementary Material S1). The geographical coordinates
of the sampling area were 18°53′38.3″ S and 47°32′46.4″ E. The soil sample was dried in
the sun for about 7 h and then ground and sieved with a square mesh sieve with a 1 mm opening dimension.

Another red soil with a grain size of 40 µm (Aurlac pigment) was also used. This reference used industrially as a pigment was generously offered by the company Aurlac, based in Ambohibao Antananarivo, one of the main paint producers in Madagascar.

A sample of traditional Malagasy brick made with clay from Ambohitrimanjaka, the largest brick manufacturing center in the region of Antananarivo, was used as a reference during the evaluation of the physico-mechanical characteristics (Supplementary Material S1).

## 2.2. Extraction of CNSL

Crushed shells of cashews were macerated at 90 °C in hexane. This extraction protocol was previously developed by Ranarijaona et al. [20,28]. The extraction was carried out three times with the same residues of shells in order to recover a maximum amount of product to recover the CNSL; the mixture was filtered and evaporated.

## 2.3. Synthesis of Oxyacetic Acid of CNSL

The synthesis of oxyacetic acid was carried out according to the procedure previously used [20,28]. CNSL (100 g, approximately 292 mmol) was mixed with KOH (46 g, 818 mmol) and 100 mL of ethanol in a double-membrane reactor equipped with a mechanical stirrer. After the total solubilization of KOH, sodium chloroacetate (51 g, 438 mmol) was added. The reaction mixture was heated at 80 °C for 2 h. After cooling, an acidification of the 2 N HCl solution was performed to obtain a pH equal to 3 and then washed twice with AcOEt to recover the product. The organic phase was dried and evaporated under vacuum. The oxyacetic derivative of CNSL was obtained as a viscous brown paste (71% yield).

Oxyacetic acid of CNSL (7): proton NMR (300 MHz, MeOD, TMS): (parts per million (ppm) 6.7–7.4 (m, 3H); 6.5–6.3 (m, 3H); 5.8–4.8 (m, 15H); 4.6–4.8 (s, 6H, 2.7) (m, 6H); 13–2.4 (m, 36H); and 0.9 (m, 9H)).

Oxyacetic acid of CNSL (7): carbon NMR (300 MHz, MeOD, TMS): (parts per million (ppm) 170 (6C); 155 (4C); 140 (3C); 137, 122, and 110 (10C); 130–126 (12C), the positive peak at 114 (6C); 65–60 (4C); 36–25 (27C); and 12.6 (3C) (Mp = 114 °C).

## 2.4. Physico-Chemical Analysis of Red Soil

Analyses of red soil and mechanical properties of materials were performed in collaboration with the "Laboratoire National des Travaux Publics et du Batiment" in Alarobia.

The elemental chemical composition of red earth was determined by X-ray fluorescence spectrometry with the AZX 400 Rigaku by Rigaku Company located at Akishima, Japan, and expressed the contents of the major elements constituting the lateritic soil used: Si, Fe, Al, Ti, Ca, Mg, Zr, and Mn.

## 2.5. Formulation of Building Materials

Earthen building materials are usually composed of clay, with water as a lubricant. In our case, the building materials were composed of red soil as filler in water. The oxyacetic acid synthesized from CNSL was used as a binding agent. The formulation trials were conducted with two red soils with sizes of <0.04 mm and <1 mm.

First, the percentage was optimized using the mass of the oxyacetic acid of CNSL and the granulometry of red soil. The manufacturing of the fabrication samples was carried out in cylindrical metal molds, with the dimensions being 3.6 cm diameter × 2.2 cm height. Following these preliminary tests, a protocol for the formulation of materials was developed and then transposed into rectangular, parallelepiped molds measuring 4 cm height × 4 cm width × 16 cm length (briquette). The dimensions of the molds were
chosen according to the standard NF EN 196-1 [30] for the evaluation of mechanical characteristics (Figure 1).

<figure><img src="image_4.png" /><figcaption>Figure 1. Moulds used for the formulation of materials.</figcaption></figure>

The oxyacetic acid of CNSL contains a hydrocarbon chain (hydrophobic tail) attached to a polar group (hydrophilic head). This amphiphilic property makes it insoluble in water and allows it to be used as a surfactant [20]. A suspension of the CNSL oxyacetic acid mixture in water at 1 g/mL of concentration was prepared and mixed with red earth for 25 min with a mechanical agitator (speed: 750 rpm). Water was added gradually under agitation until a mud was obtained, which was introduced into a metal mold using hand molding (Supplementary Material S3). The materials were exposed to the open air for three hours to dry and then heated in an oven at 60 °C for 24 to 48 h. After cooling, the materials were removed from the molds.

The various formulation tests carried out with the amounts of raw materials used corresponded to the same overall volume and mass: mass of red earth + mass of binder = 70 g for the cylinder molds and 440 g for the rectangular parallelepiped molds.

## 2.6. Physico-Mechanical Characterization of Building Materials

### 2.6.1. Material Characterization

Bulk density, stability of materials in water, and water absorption of the prepared materials were measured. It was the ratio of mass to volume of the material. The mass was determined by weighing the dry samples. Their volume was calculated from the internal volume of the rectangular prism (V = L × l × h) using the formula ρ = m (material)/V (parallelepiped molds).

The durability of bricks included the capacity of water resistance. In the absence of a reference test on this water resistance, we measured the time resistance of materials in water. The whole brick was kept in water at room temperature, and the water absorption and the stability of the structure were checked regularly.

The principle of the water absorption test resolved the measurement of the amount of liquid that a brick can absorb when exposed to harsh conditions, such as tropical rain. The bricks were fully submersed in water for about twenty-four hours or more in a container. The samples were weighed, and the difference between the initial and saturated masses offered an indicator of the water absorption tendency of the specimen. Water absorption was calculated using the formula:

$$ \text{Water absorption (\%)} = \frac{W2 - W1}{W1} \times 100 $$

with W2 being the saturated weight in grams and W1 being the dry weight in grams.

### 2.6.2. Mechanical Characterization of Building Materials

After heating, the material was maintained at room temperature for 28 days, and then the manufactured materials in the form of briquettes (4 cm × 4 cm × 16 cm) were
subjected to mechanical characterization tests. We determined the mechanical behavior of materials under applied stresses, like tensile stress, by using bending and compressive strength according to the NF EN 196-1 standard.

## Tensile Strength by Bending

Tensile strength is defined as the ability of a material to withstand a load before it breaks. In our case, the tensile strength by bending was evaluated by using the 3-point bending test. This test consists of stretching a material by applying a destructive force directed vertically on its side face.

The test was performed on a Perrier brand cement bending tensile device with a maximum capacity of 6000 KN, manufactured by Maurice Perrier et Cie, located at 20 Street Marie Debos 92120 Montrouge (France) (Figure S4). The sample was placed between the two supports of the test machine, and then the tensile force was applied until the sample was cut into two pieces. The tensile strength by bending was determined by the formula:

$$ \sigma_T = \frac{1.5 \times F \times L}{b^3} $$

with σT being the tensile strength by bending (MPa); F being the force applied to the middle of the test piece (N); L being the distance between supports (mm); and b being the square side of the prism (mm).

## Compressive Strength

The compressive strength is considered the ability of a material to resist compression applied vertically; this stress causes the crushing of the sample. The measurement of compressive strength was conducted using a cement press « CONTROLS, Model 65-L10G2/C » with a flat surface, manufactured by Controls located at France (Figure S5). The test pieces were carried on the press plate to be subjected to a force until their deformation. The value of the compressive strength was read directly from the machine's display.

Two series of measurements of mechanical characterization were carried out for each type of test. Furthermore, the results were compared with the properties of the controls: the traditional baked clay briquette and red soil briquette without oxyacetic acid. The compressive strength was determined by the formula:

$$ \sigma C = \frac{P}{A} $$

with σC being the compressive strength (MPa), P being the maximum load (or load until failure) to the material (N); and A being a cross-section of the area of the material resisting the load (mm²).

## 2.7. Method of Analysis

During this study and for the synthesis, thin layer chromatography (TLC) was used as the main technology to determine the conversion and the purity of the products. The extraction of CNSL and the synthesis of oxyacetic acid were monitored on TLC using 60 F254 silica gel plates on a MERCK aluminum substrate and using HPLC consisting of a Shimadzu LC-10 AS spectrometer, an SPD-6A Shimadzu UV detector, and a C-R 6A Shimadzu recorder. The TLC was made with an eluent system with ethyl acetate 100% and revealed with vanillin sulfuric acid. NMR and mass spectroscopy analysis were carried out at ICBMS Lyon1 University. The NMR was performed with an NMR spectrometer ¹H and a ¹³C BRUKER 300 MHz in the MeOD.
The differential thermal analysis of materials was carried out using a Mettler Toledo differential scanning calorimeter (DSC) in the ICBMS Laboratory. Prior to the analysis, the materials were ground into powders. For each sample, 8 mg was weighed and hermetically sealed in aluminum DSC pans. The samples were heated to a temperature program of 25 °C to 340 °C with a heating rate of 10 °C/min.

### 3. Results

#### 3.1. CNSL and Oxyacetic Acid of CNSL

The yield of CNSL extracted from cashew shells was 38.2%, compared to the mass of the shells. This yield was very close to those reported by Ranarijaona et al. [20]. TLC analysis showed that the chemical composition of CNSL consisted of anacardic acid, cardanol, cardol, and methylcardol (traces), similar to what was described previously [20]. The batch collected 6 years ago was extracted in similar conditions and showed similar results. This confirms the high stability of cashew shells [20,28].

In this case, the synthesis was carried out in the presence of sodium chloroacetate and a solution of KOH in ethanol and then treated with hydrochloric acid (HCl) (Figure 2). Oxyacetic acid was obtained with a yield of 71%.

<figure><img src="image_5.png" /><figcaption>**Figure 2.** Synthesis of oxyacetic acid of CNSL.</figcaption></figure>

#### 3.2. Chemical Characteristics of Red Soil

The chemical composition of the red soil collected for our study, the other red soil (size < 40 µm, Aurlac pigment), and the traditional baked brick powder are shown in Table 1. The traditional clay bricks were made in the rice fields located in Ambohitrimanjaka and supplied by a hardware store located in Ampasampito. A brick sample was crushed and analyzed with the red earth to compare its chemical composition (Table 1).

<table><caption>**Table 1.** Chemical compositions (%) of red earth and traditional baked brick powder.</caption><thead><tr><th>Chemical Elements</th><th>SiO<sub>2</sub></th><th>Fe<sub>2</sub>O<sub>3</sub></th><th>Al<sub>2</sub>O<sub>3</sub></th><th>TiO<sub>2</sub></th><th>CaO</th><th>MgO</th><th>ZrO</th><th>MnO</th><th>SiO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub></th></tr></thead><tbody><tr><td>Red soil (%)</td><td>40.2</td><td>10.6</td><td>11.3</td><td>0.92</td><td>0.43</td><td>1.3</td><td>0.09</td><td>0.4</td><td>3.5</td></tr><tr><td>Aurlac pigment 40 µm (%)</td><td>36.2</td><td>20.1</td><td>10.6</td><td>1.7</td><td>1.3</td><td>1.4</td><td>0.13</td><td>0.02</td><td>3.4</td></tr><tr><td>Traditional baked brick powder (%)</td><td>36.3</td><td>11.7</td><td>8.3</td><td>0.9</td><td>0.00</td><td>1</td><td>0.08</td><td>0.01</td><td>4.4</td></tr></tbody></table>

The three starting materials were lateritic soils with a ratio of SiO₂/Al₂O₃ > 3. Silica was by far the main component. Alumina and iron oxide were the two other main products, while the other elements (TiO₂, CaO, MgO, ZrO, and MnO) were present in small amounts. Their chemical compositions did not differ significantly. Not surprisingly, the 40 µm red soil supplied by Aurlac contained twice as much iron oxide as the other two; indeed, this material is used as a pigment in the paint factory.

#### 3.3. Materials with the Oxyacetic Acid of CNSL as a Binding Agent

##### 3.3.1. Study of the Formulation Conditions of Materials (The Binder Proportion and the Granulometry of Red Soil)

The formulation was achieved in water with a mass percentage of oxyacetic acid ranging from 0 to 15% using the red soil that had a size of 1 mm and 10% with the one that was 0.04 mm (Table 2).
<table><caption>**Table 2.** Optimization of the formulation of materials in cylindrical molds that were 3.6 cm in diameter × 2.2 cm in height.</caption><thead><tr><th>Assay</th><th>Size of Red Soil (mm)</th><th>Binder Proportion (g; %)</th><th>Water Amount (mL)</th><th>Aspect</th><th>Bulk Density (g/cm³)</th><th>Time Resistance in Water (h)</th></tr></thead><tbody><tr><td>A1</td><td rowspan="4">&lt;1</td><td>0; 0</td><td>23</td><td>Solid compact</td><td>2.07</td><td>1</td></tr><tr><td>A2</td><td>3.5; 5</td><td>23</td><td>Solid compact and hard</td><td>2.08</td><td>&gt;24</td></tr><tr><td>A3</td><td>7; 10</td><td>20</td><td>Solid compact and hard</td><td>2.13</td><td>&gt;24</td></tr><tr><td>A4</td><td>10.5; 15</td><td>16</td><td>Solid with crack</td><td>1.95</td><td>7</td></tr><tr><td>A5</td><td>&lt;0.04</td><td>7; 10</td><td>15</td><td>Soft solid</td><td>1.9</td><td>8</td></tr></tbody></table>

The bulk densities of the materials varied between 1.9 to 2.13 g/cm³. Despite the compactness of material A1 without binder, it was not stable and broke after 1 h of immersion in water. The formulation of materials with red earth required the presence of a binder to form at a low temperature a solid compact and stable in water compact and stable in water. Other formulations with 5–10% binder (tests A2 and A3) produced compact and hard solids (Table 2). These materials showed a better stability in water (more than 24 h). At 15% binder, the product obtained was a solid with a crack (A4) which deteriorated rapidly in water (7 h after immersion) (Table 2). Assay A5 with red earth being <0.04 mm formulated with 10% of the oxyacetic acid from CNSL resulted in a soft and unstable material in water (Table 2). Formulation of materials with red earth (<1 mm) in water resulted in materials with better cohesion, stability in water, and higher bulk density, with the percentages of CNSL oxyacetic acid being 5 and 10% by mass, compared to the filler.

### 3.3.2. Formulation of Briquettes

For the following, the formulation was made with red earth at 1 mm of granulometry in water in molds with dimensions of 4 cm width × 4 cm height × 16 cm length, according to standard NF EN 196-1. After the release, the materials were placed on the countertop away from the sun.

Compact solids were obtained, except for sample A4 (15% of binder), which showed a crack during cooking (Figure 3D, Table 3). It should be noted that the 10% and 15% binder materials had two slightly different phases; that is to say, the red color of the briquette was slightly darker for the upper phase and probably contained more colored binder (dark brown) (Figure 3C).

<figure><img src="image_6.png" /><figcaption>**Figure 3.** Materials formulated with red soil and oxyacetic acid of CNSL as the binder: (A) 0% binder, (B) 5% binder, (C) 10% binder, and (D) 15% binder.</figcaption></figure>

The bulk densities of the materials varied slightly for the four prepared materials. This variation was consistent with the difference between their constituents. An increase was observed for the material formulated with 10% binder (Table 3). This can be explained by the difference in density between the inorganic material (>2 g/cm³) and the CNSL oxyacetic acid (0.9 g/cm³) and the filling of the space between the laterite particles. In the case of 10% binder, it can be assumed that the majority of the cavities of red earth particles and
the areas between particles were filled (Figure 4B). Below 10%, there were empty cavities, which reduced the density (Figure 4A), and above 10%, homogeneous binder phases of low density were formed, which also led to a decrease in density (Figure 4C).

<table><caption>**Table 3.** Formulation of materials in prismatic molds that were 4 cm in width × 4 cm in height × 16 cm in length.</caption><thead><tr><th>Assay</th><th>Binder Proportion (g; %)</th><th>Drying Time at 60 °C (h)</th><th>Water Amount (mL)</th><th>Aspect</th><th>Bulk Density (g/cm³)</th></tr></thead><tbody><tr><td>A1<sup>P</sup></td><td>0</td><td>24</td><td>140</td><td>Compact solid</td><td>2.07</td></tr><tr><td>A2<sup>P</sup></td><td>22; 5</td><td>24</td><td>140</td><td>Solid, compact, and hard</td><td>2</td></tr><tr><td>A3<sup>P</sup></td><td>44; 10</td><td>24</td><td>120</td><td>Solid, compact, and hard, two<br>slightly colored phases</td><td>2.14</td></tr><tr><td>A4</td><td>66; 15</td><td>48</td><td>100</td><td>Solid, two phases, crack, air bubbles</td><td>2.03</td></tr></tbody></table>

P: material formulated with prismatic molds 4 cm in width × 4 cm in height × 16 cm in length.

<figure><img src="image_7.png" /><figcaption>**Figure 4.** Representation of the positions of red earth particles in the presence of the oxyacetic acid binder: (A) 5% binder (B) 10% binder and (C) 15% binder.</figcaption></figure>

It seems that the percentage of binder added influenced the firing times of the materials. The materials (5% and 10% binder) were dry at 60 °C after 24 h in the oven, and the 15% binder was only dry after 48 h. It was concluded that the polymerization of the binder in contact with the solid particle was faster than that of the oxyacetic derivative of CNSL in bulk. The proposed drying mechanism of the oxyacetic binder [28] involved the addition of carboxylic acid to the carbon-carbon double bonds of the alkenyl chain. Further bonds were then formed (crosslinking) by oxidation and bridging with oxygen from the air [28] (Figure 5).

<figure><img src="image_8.png" /><figcaption>**Figure 5.** Proposed mechanism for polymerization and the cross-linking of an oxyacetic binder from CNSL.</figcaption></figure>
This mechanism has been proposed for paint preparations, with a very large contact surface with air. For brick like materials, the oxidative mechanism should be of much less importance because of the poor contact with air. In addition, acid-catalyzed polymerization and a Friedel and Craft reaction was also observed with cardanol [31,32]. Also, lateritic soils are acidic, which may promote acid-catalyzed polymerization [29,33,34] by the addition of carboxylic acid on the CC double bond, which appears to be the more important reaction occurring during the material formation.

### 3.4. DSC Analysis

The DSC curves of building materials with different proportions of oxyacetic acid of CNSL (5, 10, and 15%) are shown in Figure 6. The DSC curves of the three materials were quite similar, with endothermic peaks appearing at 281.8 °C for the material A2P (5% binder), 286.9 °C for A3P (10% binder), and 283.6 °C for A4P (15% binder) (Figure 6). This endothermic effect was characterized by the fusion and decomposition of the materials. The melting temperature of the materials increased, compared with that of the oxyacetic acid (114 °C) [28]. This probably indicates a polymerization phenomenon during the formulation of the materials; indeed, many polyesters and polyamides have similar melting points [28]. Once again, the material with 10% binder showed a higher resistance toward temperature, and the material with 5 or 15% appeared to be decomposed at lower temperatures. This may be ascribed to a higher degree of polymerization level and/or greater interaction of the binder with the inorganic matrix.

<figure><img src="image_9.png" /><figcaption>**Figure 6.** DSC curves of building materials with different proportions of oxyacetic acid of CNSL (5, 10, and 15%).</figcaption></figure>

Table 4 shows the amount of heat absorbed by samples during transformation during temperature variation.

<table><caption>**Table 4.** Amount of transformation energy.</caption><thead><tr><th>Entry</th><th>Percentage of Oxyacetic Acid of CNSL (%)</th><th>Amount of Heat from Transformation (mJ/g)</th><th>Amount of Heat of Transformation per g of Product (J/g)</th></tr></thead><tbody><tr><td>A2P</td><td>5</td><td>-926.01</td><td>-102.55</td></tr><tr><td>A3P</td><td>10</td><td>-1009.84</td><td>-122.55</td></tr><tr><td>A4P</td><td>15</td><td>-943.77</td><td>-116.51</td></tr></tbody></table>

P: material formulated with prismatic molds 4 cm in width × 4 cm in height × 16 cm in length.
It was shown that the transformation energy per g of sample with 10% oxyacetic acid of CNSL A3P (–122.55 J/g) was higher, compared to those of the materials A2P (–102.55 J/g) and A4P (–116.51 J/g) (Table 4). Thus, the material A3P was more temperatureresistant, confirming previous results. CNSL was transformed into a more stable material when introduced to 10% oxyacetic acid in laterite and less stable for higher level (15%). In the case of material with 5% binder, the lower energy absorption was mainly due to the lower proportion of organic material.

### 3.5. Materials Characterization

The behaviors of the samples in contact with water were evaluated for 24 h to 2 months of total immersion of the briquettes in water. Traditional bricks of clay (A0) and red earth (A1P) without the addition of binder served as references.

Material A1P (red earth without binder) was not water-resistant and deteriorated after 6 h (Table 5). As the material A4 (15% red earth) had a crack, it broke after 8 h in water. Thus, the more voids there are in the materials, the faster water will infiltrate between the particles. Compared to the A0 traditional material in fired clay, A2P (5% binder) and A3P (10% binder) were stable in water after 24 h of immersion.

<table><caption>**Table 5.** Time resistance in water and water absorption rates of briquettes.</caption><thead><tr><th>Assay</th><th>Binder Proportion (%)</th><th>Time Resistance in Water</th><th>Water Absorption Rate (After 24 h of Immersion)</th><th>Water Absorption Rate (After 2 Months of Immersion)</th></tr></thead><tbody><tr><td>A0 (Traditional clay brick)</td><td>0</td><td>&gt;2 months</td><td>29.32%</td><td>36.65%</td></tr><tr><td>A1P (red soil)</td><td>0</td><td>&lt;6 h</td><td>-</td><td>-</td></tr><tr><td>A2P (red soil)</td><td>5</td><td>&gt;24 h</td><td>13.14%</td><td>-</td></tr><tr><td>A3P (red soil)</td><td>10</td><td>&gt;2 months</td><td>9.27%</td><td>12.62%</td></tr><tr><td>A4 (red soil)</td><td>15</td><td>8 h</td><td>-</td><td>-</td></tr></tbody></table>

The water absorption rate of the materials was evaluated with stable materials A0, A2P, and A3P after total immersion in water for 24 hours. We also measured the water absorption rate of A0 and A3P after 2 months of immersion in water. The materials were dried for 10 minutes and then weighed.

The results in Table 5 show that the material A0, the traditional baked clay, absorbed three times more water than the materials prepared in the presence of CNSL oxyacetic acid, with an absorption rate equal to 29.3% after 24 h of immersion (Table 5). Its absorption rate was also 3 times higher after 2 months of immersion in water (36.7%), which converted to mud on the surface, compared to our A3P material (12.6%), which remained much more stable. Moreover, the results showed that this rate of water absorption decreased when the percentage of hydrophobic oxyacetic acid increased to 10% (9.27%), compared to the briquette with 5% binder (13.14%) after 24 hours of immersion (Table 5). This can be explained by the better filling of inter-particle voids of laterite with 10% binder in the mass, making the material more compact and water resistant.

### 3.6. Mechanical Characteristics of Materials

Tensile strength indicates the maximum tensile force, supported by a material before undergoing permanent breaking. This mechanical characteristic was evaluated with 28-day-old materials. Two samples were evaluated for each type of material.

The results obtained are illustrated in Figure 7, with a tensile strength value of 0.6 to 2.1 MPa. A lower value was observed with the binder material of 15% (0.6 MPa) (Figure 7). This may be explained by the presence of a crack on this briquette.

However, materials with 5 and 10% binder showed higher tensile strength values (1.2 and 2.1 MPa, respectively), compared to the reference material formulated at 60 °C with red earth without binder (0.8 MPa). The 10% binder material was even more resistant
than the traditional clay-baked material at 600–750 °C [1,3] (1.6 MPa). The addition of 10% CNSL binder improved the tensile strength of the red earth materials, making them 28% more resistant than traditional fired clay bricks (Figure 7).

<figure><img src="image_10.png" /><figcaption>Figure 7. Tensile strength by the bending of materials.</figcaption></figure>

Compressive strength measures the ability of a material to withstand weights without crushing, as opposed to tensile strength, which is an elongation resistance (burst). Compressive strength values are shown in Figure 8 below.

<figure><img src="image_11.png" /><figcaption>Figure 8. Compressive strengths of materials.</figcaption></figure>

The results showed that all materials formulated with the oxyacetic acid of CNSL were more resistant to compression than reference materials prepared without binder or traditional bricks (Figure 8). The maximum value of compressive strength was obtained in this case, with the material also containing 10% binder (5.6 MPa) (Figure 8). This high value may be due to the absence of voids between the inorganic particles and a strong bond between the red earth grains and the oxyacetic acid derivatives of CNSL. The material with 10% binder was five times stronger (5.6 MPa) than the red earth material without binder (1.1 MPa) and more than twice as strong as the traditional baked clay brick (2.2 MPa). Indeed, the compressive strength of traditional bricks depends on the quality of clay, the firing temperature, and the fuels used. The average value in other countries is more than 3.5 MPa [35–37].

On the contrary, the material prepared with 15% binder was less resistant than the 10% oxyacetic material, in line with previous results with other physical and mechanical characteristics.
### 3.7. Comparison of the Mechanical Properties of the Material with CNSL Oxyacetic Acid with Those of Recently Improved Bricks

In the field of lateritic building materials, several studies have described methods that help improve the mechanical properties of earth bricks. In Table 6, we have compared the characteristics of the A3P material formulated with 10% CNSL oxyacetic acid with most of the materials obtained in these studies.

<table><caption>**Table 6.** Comparison of the mechanical properties of the material A3 with other materials.</caption><thead><tr><th>Material</th><th>Tensile Strength [MPa]</th><th>Compressive Strength [MPa]</th><th>Reference</th></tr></thead><tbody><tr><td>A3<sup>P</sup>: Material with 10% of CNSL oxyacetic acid</td><td>2.1</td><td>5.6</td><td>-</td></tr><tr><td>Traditional fired clay brick</td><td>1.75</td><td>2.2</td><td>-</td></tr><tr><td>Bagasse-stabilized clay brick</td><td>-</td><td>4.84–5.85</td><td>[38]</td></tr><tr><td>Clay brick stabilized with palm fiber</td><td>1.44–2.58</td><td>2.2–4.5</td><td>[39]</td></tr><tr><td>Polyethylene fired clay brick</td><td>0.03–0.07</td><td>2.3–2.7</td><td>[5]</td></tr></tbody></table>

P: material formulated with prismatic molds 4 cm in width × 4 cm in height × 16 cm in length.

Indeed, the use of oxyacetic acid from CNSL as a binder led to a higher tensile strength than that of clay bricks stabilized with palm fiber (1.44–2.58 MPa), and polyethylene-stabilized baked bricks had a very low tensile strength (0.03–0.07 MPa) (Table 6).

The material A3P had a compressive strength similar to that of bagasse-stabilized clay bricks (4.84–5.85 MPa) [38]. Both palm fiber or polyethylene had a compressive strengths that was much lower: 2.2–4.5 MPa [39] and 2.3–2.7 MPa [5], respectively.

Thus, CNSL's oxyacetic acid provides materials with superior mechanical properties, making them more efficient in construction.

## 4. Conclusions

This study highlights the potential of the oxyacetic acid derivative of CNSL as a binder in the manufacture of bricks. The manufacturing process is more environmentally friendly because the temperature required for baking is lower (60 °C) and drying time is shorter (24 h), compared to traditional baked clay bricks (670 °C for several days). The results of this study promote the reduction of CO₂ (greenhouse gas) emissions and can contribute to the decreasing of deforestation; the environmental impact of the manufacturing of these new bricks is therefore limited. In addition, the use of a derivative of CNSL valorizes cashew shells, a waste that would otherwise end up burning or in landfills. It has also been shown that the addition of 10% binder improves the tensile strength and compressive strength of the briquettes by up to 28% and 154%, respectively, compared to traditional baked clay bricks. Similarly, the water absorption rate of the 10% binder for two months of immersion in water is three times less than that of traditional baked bricks. This leads to the conclusion that the material with 10% binder can be used as a building material because of its long-term water stability and high tensile strength, compressive strength, and thermal stability.

These results are a starting point but could be an example of research adapted to the potential and the needs of a developing country such as Madagascar. However, further studies are needed to optimize the formulation of the materials according to various parameters, such as red earth granulometry (smaller or higher than 1 mm sizes) and the proportion of oxyacetic acid to be added (around 10). Consideration should also be given to producing briquettes by pressing rather than molding. Long-term stability still needs to be investigated. The toxicity of the oxyacetic acid derivatives of CNSL were evaluated to be very low in the case of using these molecules as amphiphiles [20], but new studies in this area also need to be carried out. Indeed, many more studies need to be performed before proposing the replacement of century-old technologies, but reducing the ecological
impact and improving the physical properties using new but adapted technologies are in
high demand in developing countries.

**Supplementary Materials:** The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/chemengineering9020022/s1, Figure S1: Raw materials used (red soil and traditional clay brick); Figure S2: Grain size curve of red soil; Figure S3: the hand molding method; Figure S4: Apparatus used for evaluation of tensile strength by bending; Figure S5: Apparatus used for evaluation of compressive strength; Figure S6: Materials formulated with CNSL in rectangular parallelepiped molds, 4 cm width × 4 cm height × 16 cm length. Table S1: Grain size characteristics of red soil used between 0.08–5 mm; Table S2: Grain size characteristics of red soil used less than 0.08 mm.

**Author Contributions:** Conceptualization, M.L.; methodology, V.M.H., F.D.R., H.R., S.R., R.R., and M.L.; software, V.M.H., F.D.R., and H.R.; validation, M.L., R.R., V.V.R., and E.M.; formal analysis, V.M.H. and F.D.R.; investigation, V.M.H., F.D.R., H.R., S.R., R.R., E.M., V.V.R., and M.L.; resources, V.M.H., F.D.R., H.R., S.R., R.R., E.M., V.V.R., and M.L.; data curation, V.M.H., F.D.R., and M.L.; writing—original draft preparation, V.M.H., F.D.R., and M.L.; writing—review and editing, V.M.H., F.D.R., H.R., S.R., R.R., E.M., V.V.R., and M.L.; visualization, V.M.H., F.D.R., H.R., S.R., R.R., E.M., V.V.R., and M.L.; supervision, V.V.R. and M.L.; project administration, R.R., V.V.R., and M.L.; funding acquisition, E.M., V.V.R., and M.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Data Availability Statement:** The original contributions presented in this study are included in the article/Supplementary Materials. Further inquiries can be directed to the corresponding author.

**Acknowledgments:** We acknowledge Aurlac Madagascar for the red soil and the Aurlac pigment used for experiments.

**Conflicts of Interest:** The authors declare no conflicts of interest.

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