Characterization and Valuation of a Clay Soil Sampled in Londéla-Kayes in the Republic of Congo

In order to characterize and enhance clay collected in Londéla-kayes in the Republic of Congo, in this work, it was a question of proceeding to the mineralogical, physico-chemical, thermal and geotechnical characterization of this clay. Next, determine the technological properties of fired bricks. For this, various methods were used in particular: X-ray diffraction, infrared spectroscopy, gravimetric thermal analysis and differential thermal analysis, dilatometric analysis, scanning electron microscopy, specific surface and analysis chemical. It appears that, for the mineralogical characterization, kaolinite is the most abundant mineral of this clay. The results of dilatometric analysis have shown that this clay can be fired at low temperatures. The geotechnical characterization showed that it is plastic clay thus exhibiting a high shrinkage. The results of the technological properties of LON1 bricks have shown that this clay cannot be used in the manufacture of fired bricks. The geotechnical properties must be improved by adding additives in order to improve the technological properties of the fired bricks.

construction, in economic housing and in the chemical industry [2]. In the chemical industry, they initiate certain reactions (cracking of mineral oils or polymerization of certain organic molecules) [3]. The structural determination of a clay, directs towards the use of it. In recent years, our laboratory, which favors applied research, has been interested in some applications of clay raw materials, in particular the field of ceramics and, above all, has worked to determine for many clayey sites in Congo Brazzaville the physico-chemical, thermal and mineralogical compositions as well as geotechnical properties [4] [5] [6] [7] [8]. In Londéla-kayes, clay soils are mainly used by rural populations for the manufacture of fired bricks. The fired brick manufacturing units are functional, but the products obtained are not of good quality. This could be due to the lack of mastery of the technology as well as the quality of the clays used. The resulting bricks break and do not withstand heavy rains. In order to support rural populations in this sector, our work consists of characterizing these clays, determining the technological properties of fired bricks in order to better understand their use. By characterizing and determining the technological properties of fired bricks from the clay sample at the study site, using modern techniques and equipment, this research may provide answers to certain questions of fundamental interest.

Location and Site of Clay Sampling
The sample was taken in Kayes Bakou in the village of Londéla-kayes district located in the southwest of the Republic of Congo near the border between the Republic of Congo and the Democratic Republic of Congo. Sampling took place during the dry season. The sample taken from this site was named LON1. The GPS coordinates of the sampling site are presented in Table 1.
The GPS coordinates of the study area allowed us to locate the LON1 sample collection site in Figure 1.

Experimental Study
The sample was dried at room temperature, crushed and then sieved at 2 mm.
The sieve obtained was subjected to a series of physico-chemical and mineralogical analyzes.

X-Ray Diffraction
It was carried out in Abidjan in Ivory Coast at the crystallography laboratory.
This analysis allowed us to know the mineralogical of LON1.

Infrared Spectroscopy
It was carried out in Cameroon at the Faculty of Science of the University of Yaoundé 1 in the Laboratory of Applied Analytical Chemistry. This technique was used for the determination of the functional groups present in LON1. Each link has characteristic vibrations that allow the types of links to be identified.

Gravimetric Thermal Analysis and Differential
Thermal analysis they were carried out in France at the University of Limoge at the Technical Center of ceramic Transfer. These analyzes were made in order to know the behavior of LON1 according to the temperature range going from 0˚C to 1200˚C.

Dilatometric Analysis
It was carried out in France at the University of Limoge at the Technical Center of Ceramic Transfer. It consists of monitoring the sintering ability of LON1 during a thermal cycle over the temperature range from 0˚C to 1400˚C.

Scanning Electron Microscopy
It was performed in China at Fudan University Shanghai in the Physics Applied to Materials Laboratory. This technique allows us to observe the surface mor-phology of LON1, then to determine the quality and quantity of the chemical elements present in this soil.

Chemical Analysis
The chemical analysis of the major elements was carried out at the Petrographic and Geological Research Center (PGRC) of Nancy in France by the method described by Carignan et al. [9].

Linear Shrinkage during Cooking
The determination of the shrinkage percentages during banking was made by studying the variation in the average length of the strokes recorded on the briquettes between drying and firing. It was determined by the following formula:

Water Absorption
Water absorption was determined by immersing a baked brick specimen in water for 24 hours. It was determined by the following relation: With: m h : The wet mass of the test specimen after immersion. m s : The dry mass of the test tube.

Mechanical Resistance
The determination of the mechanical resistance to bending and compression of  because the naked eye observation of LON1 shows a red coloration. As an associated mineral, characteristic reflections detected at 3.59 Å; 3.34 Å; 2.14 Å; 1.81 Å; 1.26 Å; 1.20 Å; 1.15 Å and 1.03 Å correspond to the peaks of quartz. Quartz is the most common mineral found in clay soils. Figure 3 illustrates the infrared spectrum of LON1. Analysis of this spectrum allowed us to identify the absorption bands located around 3694.11 cm −1 , 3621.33 cm −1 and 911.63 cm −1 . These bands are attributable to the hydroxyl group OH characterizing the presence of dioctahedral minerals, in particular Kaolinite [15]. This is in agreement with the results of XRD which revealed the presence of kaolinite. On the other hand, the absorption bands located around 1026.24 cm −1 , 100.24 cm −1 , correspond to the elongation vibrations of Si-O also characterizing the presence of Kaolinite [15]. The band observed around 795.89 cm −1 may correspond to the different modes of vibration of the Si-O-Fe bond characteristic of illite [15]. The absorption bands located around 778.70 cm −1 , 692.54 cm −1 , 776.96 cm −1 , 691.78 cm −1 may correspond to quartz [16]. All peaks between 600 and 400 cm −1 correspond to angular deformations of Si-O-M bonds (M = Al, Mg, Fe, Li) [14]. Figure 4 gives the ATG/ATD curves for LON1 clay.

Differential and Thermogravimetric Analysis
Analysis of these results shows that the ATG curve shows an overall weight loss at 1200˚C of 7.7% which mainly breaks down into 3 steps: Ambient at 150˚C characteristic of an endothermic phenomenon with a maximum at 70˚C: It would result from the departure of residual humidity (loss of mass of 1.5%), therefore from the desorption of the physically adsorbed water. The results of the ATG/ATD of the clay soil of LOUTETE show us a mass loss of 1.16% with a maximum at 130˚C [8]. In view of the results of LON1, the increase in mass loss may be due to the presence of illite which is a 2:1 clay species reported by the XRD  Between 350˚C and 825˚C: there is an endothermic phenomenon with characteristic peaks at 511˚C and 572˚C which can be explained respectively by the dehydroxylation of 1:1 clays and therefore of kaolinite as indicated by the XRD with a loss of mass of 5.0% deduced by the ATG curve [17] and by the transformation of quartz (passage from the α phase to β).
Above 825˚C, the ATG curve shows a low loss in mass (0.1%). The ATD curve for its part reveals an exothermic peak around 954˚C, characteristic of the structural reorganization of metakaolinite [14]. surface tensions and curvatures between the grains [18]. The dilatometric curve shows that this clay cannot be fired at low temperature around 930˚C.

Chemical Analysis
The results obtained are shown in Table 2. The Al 2 O 3 /SiO 2 ratio of LON1 is 0.30 provides information on the material's permeability to moisture. The greater this ratio, the greater the permeability does not change [19]. This value obtained shows that LON1 is very permeable clay. This permeability can be justified by the presence of illite identified in XRD. The iron oxides present, in large quantities (6.93%) can cause staining of ceramic products [14]. XRD did not reveal the presence of a characteristic iron peak, which suggests that the iron in LON1 is found in the structure of clay species. The large quantity of iron oxides shows that this clay can be used as energetic fluxes which in addition make the materials conductive of heat, resulting in a decrease in the firing temperature [19]. The percentage sum of oxides, sodium and potassium in LON1 is 2.42; accepted value for the use of ceramic clays as a flux [14].
The percentage of titanium oxides in LON1 (1.16%) is high, the peak of anatase not observed in the X-ray spectrum may be masked by the peak of kaolinite. The observation of Figure 6 shows that the clay particles are in the form of platelets in sheets which is in agreement with the results of the XRD which revealed the presence of two types of phyllosilicates. We distinguish the classical flattened accordion shape of kaolinite as observed by Kanon for poorly crystallized kaolinite [20]. The observation of white color aggregate confirms the presence of quartz identified in IR spectrum and in DRX of LON1.     Figure 8 illustrates the particle size curve of LON1.

Particle Size Analysis
The particle size curve thus obtained allowed us to obtain the distribution of particles shown in Table 3.
In view of the results obtained, we can say that LON1 is a soil very rich in silt.
The results of the particle size analysis allowed us to position LON1 in the Texture triangle (Figure 9).   Observation of this triangle shows that LON1 is found in the area of a soil with a silty texture. By positioning LON1 in the Winkler triangle ( Figure 10).
LON1 is not found in any brick manufacturing area. By also positioning LON1 in the Shepard triangle ( Figure 11).
We find that LON1 is in the low frequency area. Table 4 gives the results of the ATTERBERG limits of LON1.    The results of ATTERBERG Limits of LON1 allowed us, while using the Casagrande diagram (Figure 12), to give the classification of LON1.

ATTERBERG Limits
LON1 is found in the zone corresponding to the section of moderately compressible inorganic silts and organic silt. The moderately compressible inorganic clays section of LON1 can be explained by its high percentage of silt, since its mineralogical composition consists of illite, which has in its structure the presence of alkalis and alkaline earths. The results of ATTERBERG Limits also allowed us, using the fecundability map (Figure 13), to predict molding properties and soil shrinkage based on criteria related to soil plasticity.

Specific Surface
The results are reported in Table 5.   The value of the specific surface area thus obtained is characteristic of a kaolinite [21]. Kaolinite therefore represents the most abundant mineral in LON1.  used in the manufacture of fired bricks, the addition of additives or other clays will be necessary to reduce its shrinkage [22] [23]. Figure 15 shows the absorption rate of the test pieces obtained after firing LON1.

Water Absorption Rate
Analysis of the results obtained shows that the absorption rate of LON1 decreases with increasing temperature. According to Dondi, the rate of fusible material does not provide sufficient flux to improve densification and reduce pores [24]. This result is in agreement with the high silt and clay contents revealed by the particle size analysis. The loamy clayier the soil, the more water it takes to make it plastic. Using less water would reduce the friction between the grains less and also reduce the pores in the bricks less. Blanchard and his collaborators mentioned in their research work on silicate ceramics that the open porosity after firing of terracotta (briquettes, tiles, tiles, etc.) between 950˚C and 1150˚C should be between 10% and 25% [14]. The sample studied has values greater than 25%. This clay cannot be used in the manufacture of fired bricks. The addition of an adjuvant would be important to improve the absorption values of LON1.  European standards are low. The low values can be explained by the particle size composition. In fact, silts, the majority fractions in LON1, have almost no cohesion between the particles. On the other hand, the fractions clays less represented in LON1 than the silts, make up the finest fraction of soils (less than two microns) do not have the same characteristics as silts and sand. Each clay particle is surrounded by a film of water that is absorbed very strongly. This gives the clay its cohesion and most of its mechanical strength. The clay therefore gives the finished products its cohesion and acts as a bond between the coarser elements that make up the skeleton [14]. Figure 17 shows the mechanical resistance to compression.

Mechanical Resistance to Compression
The curve obtained shows that between 850˚C and 1050˚C. There is an in-  resistance to compression. The strong decrease in the mechanical resistance in compression observed from the firing temperature of 1050˚C makes it possible to formulate the hypothesis of the distribution and the nature of the main crystalline phases present in the skeleton of the fired material [14]. In general, the values of mechanical resistance to compression are low in LON1. This can be explained by higher values of absorption rate as a result of porosity.

Conclusion
This work had for general objective, the characterization and the valorization of clay taken in Londéla-kayes. Its specific objectives were to carry out a mineralogical characterization and to study the technological properties in order to provide the necessary answers linked to the breakage of bricks made by rural populations. To carry out this study, we used as characterization methods: XRD, IR, ATD/ATG, SEM/EDS, specific surface area by BET method, chemical analysis and geotechnical analyzes. We evaluated the technological properties by linear shrinkage, absorption rate, mechanical resistance to bending and compression. The results of characterization revealed that this soil exhibits kaolinite and illite as clay minerals. This clay can be fired at a low temperature around 930˚C. Analysis of different ceramic tools has shown that this soil has a low frequency to be used in ceramic. The addition of adjuvants would therefore be necessary to improve these geotechnical properties. The results of technological properties compared to standards have shown that this clay cannot be used in the manufacture of fired bricks. The high shrinkage observed in this clay would therefore be the cause causing the breakage of the fired bricks. We plan to continue this study by adding an adjuvant to the Londela-kayes clay to correct this shrinkage in order to obtain products that meet the requirements of the fired brick manufacturing standards.