Geotechnical evaluation of clayey materials for quality burnt bricks

Understanding of clayey materials properties continues to elude brick manufacturers, hence unsure of their application for brick making purposes. The raw materials were assessed geochemically, mineralogically, physically and technologically. The geochemical result showed that the fluxing oxides K₂O, N₂O, CaO, MgO and MnO are generally low in content with average abundance ranging from 0.06% to 1.78%. The Fe₂O₃ content varies (4.8–25.5%) thus reflects heterogenous stability in tonality. Most of the studied samples have relatively high Al₂O₃ content which suggest the bauxitic composition from which kaolinite minerals might have resulted from. The XRD analysis revealed the presence of kaolinite and chlorite as the major clay minerals while quartz, feldspar, talc and hornblende were present as non-clay minerals. For DTA, the threshold of new crystallization processes were attained at 1000 °C. The SEM analysis revealed the presence of some stroma in all samples although with sizes >50 nm. These pores were suggested to constitute a capillary system where molten mineral occupy as temperature increases. The Atterberg's limit indicated that the studied materials are inorganic silts with high compressibility and organic clays properties since it plotted below the A-line of plasticity chart. The compressive strength (CS) for brick specimens made from kaolinite-rich material are relatively higher than chlorite-rich specimens. This was attributed to the ineffective pore connection within the kaolinite interstitial particles compared to the chlorite-rich specimen, hence increasing the density. The water absorption (WA) test on twenty brick specimens showed that the pore volume and capillarity for bricks which are chlorite-dominated were comparatively higher, thus absorbing more water molecules. These results revealed that majority of the studied clayey material are not suitable for double storey construction bricks but meet the requirements for single-storey construction when compared with SANS standards.