Clay samples were collected from a well located at latitude 9.285126˚ North and longitude 13.455767˚ East. About 2.0 kg of each sample was collected and placed in small polythene bags. 1.0 kg of each sample was dried, pulverized and sieved before analysis. Documentary studies [7] suggested the clay nature of the grayish material.

The ENDECOTTS sieve series, a densimeter, a pycnometer, X-ray diffraction and infrared spectrometry were used to study the particle size as well as the physical and chemical properties of the material.

Mineralogical analyzes were performed using X-ray diffractometry (XRD) and infrared spectroscopy (IR). XRD was performed according to the protocol of the Laboratory of Geology and Sediment Environment (AGES) of the University of Liege in France. The data were recorded using a Brucker D8-Advance type diffractometer, and identification of the crystalline phases with DIFFRAC plus Release software 2000-EVA 6.

From the exploitation of the granulometric curve (Figure 1), we can observe that clay material of Sangaré-Paul has a very spread granulometry with a coefficient of uniformity greater than 200. It is sandy clay with a little silt and traces of gravel.

Granulometric analysis results show that the clay material is actually rich in clay and sand. The coefficient of uniformity being quite important, the grain size curve is much spread. The clay material is therefore good to be used in the manufacture of ceramic products. Indeed the grain size of a material for the manufacture of earth bricks must be spread [8] . It is also noted in the material that the percentage of elements whose diameter is less than 2 μm, clay fraction, is 46?.This value is greater than the 40% required producing fired bricks and/or tiles of very good quality [3] . The projection of the materials in the Winkler and Niesper diagram [9] (Figure 2), shows that it is propitious for the manufacture of tiles, and masonry bricks.

The clay test results that allowed the determination of the Atterberg limits, the

apparent density, the actual density, the volume of methylene blue and pH are given in Table 1.

From Table 1, we can see that Sangaré-Paul clay material can hold up to 30.63% of water without sinking under its own weight. It can deform plastically when it contains 9.21% of water. It is a little plastic clay, and it will not require a lot of water to form a paste of consistency and can support inert bodies (degreasing) while retaining an appreciable process ability and mechanical strength, dry enough to ensure fabrication [10] . Its plasticity index is 21.42%. Compared to the reference clays used in industrial and traditional ceramics, the plasticity index of the Sangaré-Paul clay material is certainly high (≥20%) but is still appreciable because the recommended plasticity index is between 9% and 20%

for the manufacture of clay bricks [10] . The apparent density is 2.12 g/cm³; the real density is 2.45 g/cm³ and the volume of methylene blue giving a positive test of 20 ml. According to the soil classification after the methylene blue test [11] , it can be said that the Sangaré-Paul clay is sandy-clay. The real density and apparent density allow us to know the natural water content of the material and calculate the state parameters of the clay material. Sangaré-Paul clay has a pH level of 8.01. It is therefore considered as a weak basic clay. This would involve the presence in clay material in small amounts of calcite and basic soluble salts such as carbonates. Calcite has the ability to move freely in the solid phase of products during sintering [12] . Laboratory tests show that convincing results are obtained when pH of acid clays is taken between 6 and 8.5 and pH of neutral or slightly basic clays between 7.8 and 10.5 [13] . The clay material of Sangaré-Paul having a pH equal to 8.02, will be adjusted by the addition of calcite so that it rises to between 9 and 10, since it is a weak basic clay.

Examining the total powder diffractogram (Figure 3) obtained for the sample tested, shows the presence of minerals such as kaolinite (Kao), Illite (Ill), Quartz (Qz), Potassium feldspar (Fds).

Figure 4 shows the superposition of the diffractograms obtained on the powder of the raw material (SP1-N) and on the powders of the materials cooked at 950˚C (SP1-950˚C), at 1000˚C (SP1-1000˚C) and at 1100˚C (SP1-1100˚C).

Figure 4 shows the disappearance of certain phases with the evolution of the temperature. At the temperature of SP-950˚C on the diffractogram, the characteristic lines of kaolinite disappeared. Pabst, Gregorov and Ticha suggest that from 450˚C up to 750˚C, the clay minerals decompose, losing their water content. This is the case of kaolinite which is converted into metakaolin (2SiO₂, Al₂O₃) by dehydroxylation [14] .

Then the metakaolin obtained is characterized by a lack of order at great distance in the arrangement of the constituent elements of its solid [15] , which is not detectable by XRD. It is transformed into the spinel type phase (Si₃Al₄O₁₂) [16] with, in addition, β (SiO₂) quartz [17] , which is a polymorph of silica at a temperature of 1000˚C and at low pressure.

The increase of the sintering temperature (1100˚C) leads to the disappearance of the spinel phase and the appearance of a high mullite content as shown by the SP1-1100˚C and SP1-1000 diffractograms with the multiplication of the main lines of mullite between 1000˚C and 1100˚C. Mullite is an aluminum silicate that forms at high temperature and low pressure [2] . The mullite crystals (3Al₂O₃, 2SiO₂) appear at 1000˚C resulting from metakaolin and the spinel phase [2] .

Figure 4 also shows the disappearance of illite phase; Huger suggests that illite, just below 1050˚C, becomes mullite [18] . Up to the sintering temperature of 1000˚C; residual peaks of illite which have dehydroxylated from 450˚C, are observed. At 1100˚C (SP1-1100˚C), these peaks disappear; the illite completely transforms into mullite during a mullitization parallel to that of metakaolin. [2] . Obtaining mullite from metakaolin and the spinel phase is due to primary mullitization [19] .

Quartz and feldspars are present on all diffractograms obtained at different sintering temperatures tested. The melting point of quartz (1700˚C) and that of potassium feldspars (1300˚C) is much higher [17] . Quartz is nevertheless subjected to allotropic transformations which occur around 573˚C. The transformation of quartz from the so-called low-temperature form α to the so-called high-temperature form β, which is accompanied by a volume expansion. Around 600˚C, there is a reversible dimensional change characteristic of the quartz transition. Around 850˚C, it is transformed into β-quartz or tridymite according to the pressure gradient [17] . As long as it is not partially dissolved in the viscous flow, the quartz forms a percolating rigid skeleton which opposes the densification of the materials. The densification of ceramics is due to the formation of viscous flux from the dehydroxylation products of illite and kaolinite [2] .

The results of the infrared spectrometry analysis are shown in Figure 5. In the clay material of Sangaré-Paul, band characteristics of the presence of kaolinite (3689 cm⁻¹ and 3649 cm⁻¹) were found [20] . The band at 3619 cm⁻¹ reflects the O-H bond deformation and materializes the presence of kaolinite. The band at 1114 cm⁻¹ and that at 1004 cm⁻¹ correspond to the lengthening vibration of the Si-O bond of kaolinite [21] [22] . The bands observed around 914 and 916 cm⁻¹ correspond to the deformation vibrations of the Al-O bond of the clay minerals [23] . The presence of Quartz is indicated by bands between 600 and 800 cm⁻¹ [3] .

The quality control tests carried out are designed to evaluate certain properties such as color, bulk density, mechanical flexural strength, compressive strength and linear shrinkage, loss of cooking mass and water absorption rate. Table 2 below summarizes all these properties.

To obtain bricks and even tiles of good quality as suggested by the diagram of Wrinkler and Niesper [9] , from Sangaré-Paul clay material, it is essential to cook it at a temperature which gathers the greatest satisfaction from the point of view of technological parameters. These parameters include the loss of mass during cooking, the linear shrinkage during cooking, the rate of water absorption, the mechanical resistance to compression and bending.

From the graph presented in Figure 6, we see that for the three experimental temperatures, the optimum cooking temperature is 1100˚C because it is a good compromise for all technological parameters mentioned. It makes it possible to avoid a water absorption rate greater than 10%, to have maximum mechanical performances, a loss of mass at the conventional cooking and a linear shrinkage at the end of cooking.