The clayey deposit from Bomkoul (Douala, Cameroon): a case study of the geotechnical appraisal and assessment of the characteristics of firing bricks

Abstract This study investigates two clayey facies from the Bomkoul area in the littoral region of Cameroon for their suitability as fired clay building products. The field study consisted of a geological survey and a geotechnical mission (G0). Assessment of the raw clayey materials included their mineralogy, particle size, determination of Atterberg limits, density and shear stress. Firing properties (shrinkage, water absorption and flexural strength) at 900−1100°C were also determined. The two main facies observed in the field are the mottled red/yellow grey clays from surface ‘A’ with a thickness of 2.0–2.5 m and the deep blackish fossiliferous schisteous grey clays ‘B’ with a thickness of 8−10 m. Estimation based on boreholes revealed a minimum of 1,400,000 tons of clayey materials. These reserves will supply a small brick-manufacturing unit for a minimum period of 25 years at an extraction rate of 50,000 tons per year. The main clay minerals of both samples are kaolinite (35% and 49%) and illite (1–11%). Both samples contain quartz (47% and 49%) as non-clay minerals, associated with a small amount of anatase (0.5–2.6%) and trace hematite (<1%). The major oxides are SiO 2 (71–76%) and Al 2 O 3 (14%). The raw clayey material ‘A’ was finer and more plastic than the ‘B’ facies. The technological properties of the fired bricks obtained from the ‘A’ facies showed greater potential than the ‘B’ facies in terms of sonority and flexural strength. A mixture made of 40% ‘A’ and 60% ‘B’ yielded satisfactory brick properties at 1050°C.