Production of expanded-clay aggregate for lightweight concrete from non-seltbloating clays

A technology of processing non-selfbloating clays into expanded-clay aggregate (fillers) for lightweight concrete in a melting-converter with submerged combustion was developed, tested and implemented in the building industry. The technology involves melting tuf-claystone with sandstone and/or other charging materials in a melting-converter, draining the melt into a water pool with water-jet granulation inside a draining chute, drying granules inside a drying drum, granule grinding, mixing the resultant powder with a foaming agent (coal powder) and binder (clay), and granulation of the mixture with subsequent roasting inside a rotary kiln. This technology allows production of expanded-clay aggregate for lightweight concrete from non-selfbloating clays with predetermined properties: bulk weight within the range 160-850 kg/m(3) and cylinder compressive strength within the range 0.78-14.4 MPa. Concrete with azerit as a filler is at least twice lighter than regular concrete and has thermal conductivity at least in two times less than regular concrete. Specific to the melting process is the use of a gas-air-oxygen mixture (02 up to 75%) with direct combustion inside a melt (submerged combustion). The submerged combustion provides melt bubbling and helps achieve: maximum heat transfer from combustion products to the melt; an increased rate of the chemical reactions; improved mixing and, thus, a highly homogenized melt. The annual plant capacity is about 120,000-150 000 m(3) of "azerit", i.e., expanded-clay aggregate for lightweight concrete. (C) 2003 Elsevier Ltd. All rights reserved.