Technological behaviour of Cretaceous and Pliocene clays of northern Morocco used in fired brick manufacturing

Northern Morocco has an important local ceramic industry. Twenty-three Craterous and Pliocene clays from Tangier area (Northern Morocco) were studied to test their suitability as raw material for fired brick production. To assess their behaviour, the chemical composition, specific surface area (SSA), cation exchange capacity (CEC), and apparent density of clays were determined. The chemical composition consisted mainly of SiO2 (32 – 60%), Al2O3 (7 – 30%), and CaO (0.5 – 32%). SSA and CEC values of all the samples were low. The apparent density, pore volume, and micropore values were almost similar. Clay bricks were prepared by forming and shaping, and then fired in the range of 800 – 1100°C. Firing shrinkage, loss on mass and water absorption capacity were done in order to characterize clays after firing.
Most of the clay samples have the necessary properties for the manufacturing of brick products. However, some clay samples were above the norm of loss on weight, due mainly to their high amount of carbonates. Furthermore, some kaolinitic samples from Pliocene blue marls and Cretaceous marls are inappropriate for building-related brick fabrication, because of the development of portlandite in brick, when in contact with moisture of the air. However, it will be necessary to mix them with other clays with little or no carbonate to dilute their carbonates content and then enhance their workability.