The raw materials used in this study consist of four clay profiles representative of the Missole II zone, three profiles from the interfluves along the Douala-Edéa road, and one profile from drilling in the pit on the lower slope of the valley [20] - [22] . Four clay faces with different mixed textures, such as sandy clay, clayey silt and limo clay, are mainly of sedimentary origin [23] [24] . The average thickness of the exploitable layers is 2.5 m. Two clay samples were taken from the clay layer of each profile, which were representative of mineralogy and chemistry. These data were combined to create an average sample, which was then used for the geotechnical analyses. A sufficient amount of the single mixture (2 - 3 kg of sediment) is collected from a one-metre-long furrow. Sedimentometry is a test that completes the particle size analysis by sieving. This method applies to particles with a diameter of less than 80 micrometres, and the NFP 94-057 standard is recommended for this operation. The mesh size of the sieves used is between 0.1 and 0.002 mm [25] [26] . Clay materials are classified using the Autret method [27] [28] . Bone ash is obtained from waste recovered from bovine bone carcasses, which is then incinerated and crushed according to the particle size recommended by the standard (see Figure 2 ).

The material is obtained from a mixture of three powders: clay, kaolin, and bone ash. The proportions are presented in Table 1 for cylindrical BAC-SP (Bone Ash Clay Specimens) and CPC-SP (Pure Clay Specimens) pieces.

With (C1, C2, C3, C4, C3, C5, C6, C8, C9, and C10) representing the different combinations of five replicates each.

a) Clay

The clay was extracted using a digger and a trowel to facilitate extraction, before being placed in a garbage bag. It should be noted, however, that this clay (see Figure 3 ) is found in solid ground and is devoid of impurities such as dead leaves, pieces of wood, and straw. The contents of the bag were then tipped out to continue the process of sieving. Powder diffractograms of ground bulk samples down to less than 80 µm revealed that the clay materials are kaolinitic and illitic, and allowed the following mineral phases to be detected: kaolinite, quartz, illite, goethite, hematite, and accessory feldspar and anatase [29] - [31] . The particle size required to prepare the powders was obtained using a sieve with mesh sizes ranging from 0.1 to 1 mm.

b) Kaolin

Kaolin, as shown in Figure 4 , is one of the most widely used industrial minerals, with global production exceeding 25 million tonnes [32] . While it is used in the production of paper, which accounts for around 75% of global consumption, kaolin is also widely used in the ceramics, rubber, paint, plastics and pharmaceutical industries [33] [34] . Particle size analysis determines the dimensional distribution of grains in an aggregate with dimensions between 0.063 and 125 mm. The mesh sizes and number of sieves are chosen according to particles and the required level of precision. The current standard (EN 933-2) recommends the following calliper of sieves for particle size analysis: 0.063, 0.125, 0.25, 0.50, 1.00, 2.00, 4.00, 8.00, 16.00, 31.50, 63.00 and 125.00. For laser granulometry, bulk kaolin samples and the 40 µm fraction (10 g) were ultrasonically disaggregated and analysed for size using a Master Sizer IP laser granulometer with a displayed size range of 0.1 to 80 µm. This was combined with the Malvern Digital Data Acquisition System at the HydrASA laboratory of the University of Poitiers, France [35] - [37] .

c) Bovine Bone Ash

Cattle bone waste (10 kilograms) is collected from cattle slaughterhouses in Douala. It is then cleaned with hot water to eliminate impurities such as grease, odours, marrow, and other substances that cause nausea. This makes the bone waste clean and suitable for use. After this phase, the bone ash is dried in the open air. After drying, a firing operation (incineration) is carried out in an open-air oven. Complete cooling is obtained after four hours. It should be noted that the cooling time depends on the quantity of bone ash loaded. The desired powder is obtained using a cereal crushing machine see Figure 5 below [38] - [41] .

There is no risk of contamination when shaping powders. However, we experienced some technical difficulties when developing bovine bone powder. Initially, we opted to use a crushing stone, but subsequently realised that this was difficult, hence the need to use a crusher.

After complete homogenisation, the mixture is introduced into a cylindrical mould coated with a refined oil film, with a diameter of 15 mm and a height of 30 mm. The mixture is then compacted under a maximum axial pressure of 0.05 MPa (see Figure 6 ). This compression occurs between two trays that move slowly at a speed of 0.5 mm/s. This compaction process removes the air in cavitation from the mixture to ensure the cohesion of the constituent elements, the main purpose of which is to produce a sample of constant density. Demoulding takes place at least two hours after compression to avoid premature deformation of the test pieces ( Figure 7 ).

During heating, clay minerals transform into new, unhydrated minerals. This transformation is a qualitative function of the energy provided. Thus, as the temperature increases, the atoms in the initial crystal lattices change position, allowing other configurations to form. The new phases and state of equilibrium are acquired more quickly the higher the temperature [42] - [44] . At around 800˚C, the initial crystalline phase of the minerals disappears to make way, in varying proportions, for an amorphous phase and new minerals. This is accompanied by shrinkage. Solid reaction, which is associated with changes in porosity and particle dimensions (see Figure 8 and Figure 9 ), shows the cooking curves of the BAC-SP and CPC-SP. The samples undergo transformations at a temperature of 650˚C and stabilise at 1000˚, 1100˚, and 1300˚C, after which cooling begins. The oven is opened after complete cooling to avoid destroying the samples [45] - [47] .

A square sensor on the back of the device sends and receives low-intensity electromagnetic signals through the material being tested. The display shows the relative humidity of the material (% RH) at a maximum depth of 20 mm. The result is more affected by surface moisture than by deep moisture. The MO280 hygrometer is a self-calibrating device, and no other form of calibration is required. These results were achieved using a device called a non-invasive hygrometer. The maximum thickness of the sample to be tested is 3/4 (20 mm). Stack them if they are thin to ensure accurate readings.

This test determines the tensile strength of the specimen (see Figure 10 ). A force is applied to the cross-section until the specimen cracks in order to determine the stress at fracture.

${\sigma }_{rup}=\frac{F_{\max }}{S}$ (2.1)

where ${\sigma }_{rup}$ denotes the stress at fracture, $F_{\max }$ is the maximum applied compression force and S is the initial cross-section. The monitoring of the deformation within the specimen is done using an extensometer equipped with a sensor to determine the Young’s modulus,

$\sigma =E\epsilon$ (2.2)

$\epsilon =\frac{\Delta l}{l_0}$ (2.3)

where $\sigma$ denotes the axial stress in a specimen, $E$ is the Young’s modulus, $$ \epsilon $$is the axial strain in a piece, $$ ∆l$$ is the length variation in mm and $l_0$ the initial length of a piece.

The compaction test shall be carried out at a low and constant load rate under an imposed stress. The test pieces must be rectified; i.e., the faces in contact with the loading instruments must be smooth to optimise the parallelism of the specimen.

Heating clay products is the most important stage. The cooling process must be controlled so that the products release heat at a quasi-constant rate, in order to avoid deformation and maintain directional stresses. The BAC-SP specimens exhibited outstanding classification performance; the C10 combination achieved the best results, followed by combinations C8, C1, and C5. The CPC-SP specimen also demonstrated overall satisfactory performance. The C4 combination stood out by achieving the best results, while the C8, C5, and C1 combinations exhibited slightly lower performance. The Young’s modulus and fracture constraint histograms confirm these rankings (see figure in Appendix).

Plotting the stress-strain curves of the CPC-SP and BAC-SP specimens made it possible to determine and evaluate their respective Young’s modulus values. These curves are illustrated in the appendices. As can be seen at the end of the stress-strain curve plots, the specimens based on bone ash clay samples highlight the difference compared to pure clay (BAC-SP). This is presented in the Appendix. The BAC-SP specimens have a modulus E between 1.30 and 3.50 GPa, with low breaking stress values. Therefore, it appears that the C3 and C6 combinations present average values of Young’s modulus. However, the respective Young’s modulus values of the CPC-SP specimens are [1.05; 3.56] GPa, with low breaking stress values. The graphs in Appendix illustrate the results of the different Young’s moduli of the BAC-SP and CPC-SP specimens. It should be noted that the compaction process achieved perfect cohesion of the constituent elements. The way the grains are stacked plays a major role in the quality and mechanical strength of the raw specimen. The conditions used to prepare the specimens are similar to those used for industrial tiles (water content: ω = 20%; density: ρ = 2 g/cm³). All specimens were developed under the same experimental conditions using powders from three varieties. The kneaded product is introduced manually into the moulding cylinder; the quantity of dough introduced determines the density after compaction, ρ = 2 g/cm³. The volume of dough to be introduced is defined by m = ρV; with V = π × D² × h/4 for a (cylindrical specimen. The dimensions (diameter: D = 15 mm; height: h = 30 mm) are such that uniform compaction is achieved throughout the thickness of the specimen.

A compaction force of 8.5 kN is applied to produce a homogeneous, compact product. This compaction (see Figure 10 ) also eliminates air bubbles and prevents the formation of pockets in the material, which can lead to sudden rupture and distort the experimental results.

Measurements are carried out using a non-invasive hygrometer (model MO280), which requires the samples to be stable for precise results. Table 2 summarises the different cooking temperature ranges and the recorded humidity levels of all BAC-SP and CPC-SP formulations. Regarding BAC-SP specimens, we recorded values ranging from 1.2% to 4.9%. CPC-SP specimens exhibit values ranging from 0.3% to 4.08%, with the C9 and C10 formulations reaching 4.08%. Increasing the cooking temperature significantly improves the likelihood of achieving defect-free samples with an optimal surface finish [48] - [50] . It is found that specimens made from bone ash are stiffer than those made from pure clay; several technical factors account for this enhancement in stiffness:

Bone ash predominantly consists of calcium phosphate (apatite) along with other mineral oxides [51] . During the firing process, these constituents promote the development of a glassy phase that significantly reinforces the overall microstructure. The resulting mineral phases enhance intergranular cohesion and effectively reduce residual porosity, thereby contributing to increased stiffness of the ceramic material [52] .

At high temperatures, the components of bone ash actively facilitate sintering and improve the bonding between clay particles [53] [54] . In contrast, pure clay tends to remain more porous and exhibits a lower degree of consolidation after firing.

Conversely, the TH (%) BAC-SP > TH (%) CPC-SP rate is higher; it has been observed that specimens made from bone ash exhibit greater stiffness compared with those made from pure clay. This difference is primarily attributed to the composition of bone ash, which is rich in calcium phosphate, particularly in the form of hydroxyapatite. The difference may also be explained by the presence of residual organic matter or more thermally reactive phases in the bone ash. During thermal treatment, these components can lead to a greater release of heat compared with the specimens made from pure clay, which are predominantly mineral and more thermally stable. This compound imparts a denser and more rigid structure to the material, thereby enhancing its overall mechanical properties. Bone ash acts as a ceramic reinforcement agent, promoting the formation of a matrix that is more resistant to deformation [55] . This is simply because the clay itself contains physical water as well as chemical water, which allows ceramists to knead clay easily. Conversely, the addition of bone ash acts as a degreaser, drawing up a large proportion of the physical water and thereby facilitating implementation.

After manufacturing the test pieces, it is essential to measure their mass before and after firing. The results obtained are shown in the table in the Appendix. After cooking at 1000˚C, low linear shrinkage is recorded due to the small dimensional variation. Shrinkage is high for samples with low compaction effort. This applies to specimen CPC-SP43 of combination C9, as well as specimens CPC-SP36 and CPC-SP37 of combination C8. These parts are less fragile and do not show any cracks or deformations after cooking; however, they exhibit a beige colouring and a perfect surface condition [56] - [58] . Defects that cause brittleness in ceramic materials include macroscopic defects such as porosity and surface defects, as well as microscopic defects such as dislocations, vacancies, and interstitial atoms, and their interactions. Porosity reduces mechanical resistance. Since pores concentrate tension, the best materials from a mechanical point of view are those that are completely dense. The opposite occurs for resistance to thermal shock [59] - [61] .

Table 2 summarises the changes to the samples after firing at 1100˚C. We recorded low linear shrinkage for all the samples, except for combinations C1 and C2, which stand out because of their very high kaolin content. Regarding volume shrinkage, it reaches 6.25% for samples with a high clay content; this applies to specimens C3 and C4 [62] - [64] . Samples with a high bone ash content have a better physical appearance than samples with a high kaolin content, which are slightly fragile [65] - [67] . The porosity is low due to the advanced vitreous phase at a higher temperature and the consolidation of materials, which reduces the void volume.

Plotting the stress-deformation curves of the BAC-SP and CPC-SP specimens enables the respective Young’s modulus and breaking stress values of each specimen to be determined with accuracy and precision (see the curves in Appendix). To do this, it is necessary to briefly comment on the behaviour and characteristics of each curve. From the comments on all the curves, one can see that the CPC-SP specimens have a higher average Young’s modulus than the BAC-SP specimens. The BAC-SP specimens have the highest average breaking stress. They experience higher stress than CPC-SP specimens. When subjected to stress, these specimens break with little or no plastic deformation. This is because fragile materials absorb relatively little energy before breaking, even if they are strong. In the case of brittle fracture, no apparent plastic deformation takes place before rupture. Cracks spread quickly. Evidence of these results (average breaking stress and average Young’s modulus of all samples) is presented in Table 3 below. However, BAC-SP specimens are lighter than CPC-SP specimens.

In Table 2 , the same temperature range has been set for the two specimens: (BAC-SP) and (CPC-SP). However, at temperatures of 1000˚C to 1050˚C, the C9 and C10 combinations have an equal humidity percentage of around 4.09%, making them the highest values for the BAC-SP specimens. The lowest percentage, around 1.2%, is found in combination C1. It is also noted that, within the temperature range of 1000˚C to 1050˚C, the C9 and C10 CPC-SP specimen combinations have an equal humidity percentage of around 4.08%. The lowest humidity percentage is around 0.3%; this is the case for combination C1. Overall, the humidity rate percentage of the BAC-SP specimens is higher than that of the CPC-SP specimens, indicating that these materials are suitable for producing ceramics.

Table 4 summarises the colour change of CPC-SP specimens after firing, as well as the low linear shrinkage observed in all samples. No cracks were observed, but slight deformations were noted, which did not affect the test results. The lowest percentage of mass variation is around 0.45% for combination C6 and around 1.75% for specimen C1. Volume variation is around 4.21% for the C5 specimens, C6, and C10, and around 0.32% for the C7, C8, and C9 combinations. In terms of fire losses, the lowest percentage is around 0.25% for combination C5 and the highest is around 2.06% for combination C8.

Table 5 also shows the colour variation of the BAC-SP test pieces after cooking, as well as the average variations in mass and volume of all combinations. The lowest variation in mass is around 0.85% for the C10 combination. The highest average value is around 2.06% for combination C3. The lowest average

M₁: Mass before drying. M₂: Mass after drying. M₃: Mass after cooking. H₁: Height before drying. H₂: Height after drying. V₁: Volume before drying. V₂: Volume after drying. D_v: Volume variation. D_m: Mass variation. Pf: Ignition loss. E_m: Average Young’s modulus. ${\sigma }_{rm}$: Average breaking stress.

volume change is around 0.32%; this applies to combinations C7, C8, and C10. The largest average volume variation is around 6.25%; this occurs for combinations C3 and C4. The average percentage ignition loss (Pf) is recorded; the lowest value is around 0.22% for combination C7, and the largest value is around 0.43% for combination C10.

After observing the results in Table 3 and Table 4 , it is noted that the two test pieces (BAC-SP and CPC-SP) underwent the manufacturing process provided for by the regulations in force for ceramic products, as the compaction effort ensured that the material was homogeneous and resistant during heat treatment.

$D_v=\frac{V_1-V_2}{V_1}\times 100$

$D_m=\frac{M_1-M_2}{M_1}\times 100$

Table 6 is, in some way, the synthesis of Table 5 and Table 3 . Table 3 presents the general results of the Young’s moduli and breaking stresses of the two specimens, BAC-SP and CPC-SP. The Young’s modulus of BAC-SP is between 1.32 GPa and 2.49 GPa. It is seen that certain combinations have common results; this is the case for C1, C6, and C7: the modulus is of the order of 2.05 GPa. The C2 combination has the lowest result, of around 1.32 GPa, and C3 has the highest result of all the CPC-SP combinations (see Table 7 ). The other combinations, namely C5, C9, and C10, have modulimodules ranging from 2.06 GPa to 2.08 GPa. We also see that combinations C4 and C8 are equal, the common Young’s modulus being of the order of 2 GPa. These materials are light and rigid, not very fragile and have no plastic deformation; they have low breaking stress. Just like the previous case, some combinations of the CPC-SP specimen have common results; this is the case for combinations C4 and C4 and, among others, combinations C6 and C7. Combination C2 has the lowest result, of around 1.05 GPa. Combinations C3 and C10 have results of 3.10 GPa and 3.49 GPa, respectively. The others, C9, C8, and C1 respectively, result in 2 GPa, 2.06 GPa, and 2.08 GPa. The C4 and C5 combinations stand out from all other combinations with a value of 4 GPa. CPC-SP specimens are rigid, not light, and fragile. As compared to the BAC-SP specimens, the breaking stresses of the CPC-SP specimens are lower.

Despite the reaction of the raw materials to cooking, heat causes changes in density, porosity, hardness, and dimensions. It also causes dehydration, decomposition, and combinations, which modify the mechanical properties [68] - [70] . This leads us to conclude that the specimens we produced are suitable for the production of ceramic products. In fact, this observation can be verified by examining the results of the mechanical tests; CPC-SP specimens are the most effective product. Missole II clay materials are ideal for manufacturing bricks, tiles, and sandstones [71] - [73] .