Characterization, firing behavior and ceramic application of clays from the Gabes region in South Tunisia

In this study, a part of paper has been conducted on geological survey of Gabes clays and their surroundings; so we can focus on the highest thicknesses of clay sediments, for subsequent investigation or exploration. The greatest part of work focuses on the mineralogical, chemical, physical, and geotechnical tests carried out on Creatceous clays collected from the Zimlet El Beida in Gabes area (South-eastern Tunisia). Firing behavior and ceramic application are also conducted for these clay materials. The mineralogy study shows illitic clays; however, other clay minerals, such as kaolinite, mixed-layer I/Sm and chlorite are also present. The mineralogical phases during the firing process were recorded at 300, 600, 800, 1000 and 1150 °C for 3 h with heating rate of 10 °C/min. The main transformations were observed at 1000 °C with the appearance of new crystalline phases, such as diopsite, cristobalite, mullite and spinel. The chemical analysis indicates that these clays are notably siliceous. The alkali content (K2O + Na2O) is high (~ 4.13%), thus explaining why these clays can be fired at relatively low temperatures. The amount of alumina and iron oxide, with an average of 16.42 and 7.07% respectively, is variable. The tests show that these clays have medium plasticity values (PI = 14-20%). The firing shrinkage and the expansion are limited. A lower firing and drying temperature can be translated into significant energy savings. Technical tests show that the properties fall within the ceramic International Standards (ISO). Ceramic tiles made of these clays have appropriate characteristics without defects and can be classified in group BIII and BIIb according to the European Standard NF EN 159 (1991).