Tunisian smectitic clays as raw materials for the production of lightweight aggregates

Smectitic clays from 12 deposits located in the Meridional Atlas domain (Tunisia) are explored for manufacturing of expanded aggregates. Two types of firing processes (slow and quick firing) were carried out, and properties of the bloated products were examined. Used raw materials are mainly composed of smectite, kaolinite and illite phases with quartz, calcite, dolomite and feldspars as impurities. They contain high amounts of fluxes ([Fe.sub.2][O.sub.3], CaO, MgO, [Na.sub.2]O and [K.sub.2]O) with CaO and [Fe.sub.2][O.sub.3] dominating others. Quick firing or "flash heat" must be preceded by two hours drying at 350°C in order to avoid any aggregate explosion which seems to be related to the fineness of a raw material. The clay fineness appears to be the cause of ball explosion. Clay aggregates were heated at the maximum bloating temperature (1170°C) during 5 min. and then characterized through a determination of the apparent density, the mechanical resistance corresponding to the rupture under point compression, and water absorption measured after 72 hours of immersion in distilled water. Obtained results are encouraging and may open new perspectives for the utilization of some investigated smectitic clays in civil construction works. KEYWORDS: smectite, light weight aggregate, firing processes, apparent density, Meridional Atlas domain, Tunisia