## 4 Results and Discussion
### Physicochemical Properties
#### 4.3.2 Plastic Properties  
Plasticity is a very important parameter for manufacturing clayey products [15]. The Atterberg limits are presented on Table 3 and are plotted on the Holtz and Kovacs diagram (Figure 13). The limits of plasticity ranged between 49.5 (Y1C3) and 53 (Y1C2) for Yanyoki, 22.5 (J1C1) and 27.7 (J1C3) for Japoma and 36.5 (N1C3) to 47.3 (N1C1) for Ndogpassi. The plasticity index varied from 19.3 (Y1C2) to 21.9 (Y1C1), 11.1 (J1C3) to 23.4 (J1C2) and 10.2 (N1C3) to 63.9 (N1C2), respectively, for Yanyoki, Japoma and Ndogpassi sites. Globally, the plasticity of the studied samples was mostly influenced by the clay fraction. Hence, the N1C2 sample had a high clay amount and high plasticity index value (63.9), but the N1C3 sample had the lowest plastic index (10.2) with less clay proportion. The Holtz and Kovacs diagram [40] was used to classify the clay soils on a scale of four plasticity domains (Figure 13): non-plastic clay soils, low plasticity, medium plasticity and high plasticity. It was also used to account for the mineralogical nature that was predominant in the clay materials. On the diagram, the samples fall within the zone of high plastic clays (Y1C1, Y1C2, Y1C3, N1C2, N1C1 and N1C4) and medium plastic clay (J1C1, J1C2, J1C3 and N1C3). The liquidity limits of these materials are high and while those of an average plasticity are around 40.31%. This suggests the hygroscopic nature of the materials. Plasticity is favorable for extrusion and manual processing due to the proportion of clays and silts. It is consistent with the classification from the Winkler diagram and confirms the clay and silt content of the studied samples (Figure 12). Based on the Holtz and Kovacs diagram [40], the observations are in agreement with the results of the granulometric tests. According  
Figure 12: Suitability of the studied clayey materials according to the Winkler ternary diagram [38].  
to Bukalo [55], the plasticity of the samples from the eastern part of the Douala sub-basin corresponds to that of the coastal basins of Cameroon.  
Numerous studies have shown that particle size distribution and clay content have an influence on the plasticity of clay raw materials and therefore influence rheological properties [40; 62]. The Atterberg limits of the samples are reported in the Bain diagram [41] presented in Figure 14. The use of this diagram makes it possible to predict the suitability of clay materials for ceramic production. Therefore, the Bain diagram [41] shows that these clay samples can be used to manufacture bricks (N1C3, J1C3 and J1C1) or pottery for the rest of the studied samples (Y1C1, Y1C2, Y1C3, J1C2, N1C2, N1C1 and N2C3). Generally, the samples of the study area may be more improved if they are mixed with coarse particles such as sand. The plasticity index (PI) values of the studied samples are higher than 10%, which implies that these samples are appropriate for building ceramic products due to the appropriate extrusion process [41].  
Figure 14: Potential molding of the analyzed clayey materials according to Bain diagram [41].  
Figure 13: Binary diagram of [PERSON] and Kovacs [40]: correlation between plasticity and mineralogy of clayey materials of the studied area.