Athens Institute for Education and Research ATINER ATINER ' s Conference Paper Series GEL 2015-1758

The potential valorization of two types of wastes, sewage sludge from a wastewater treatment plant and washing aggregate sludge from a gravel pit, has been evaluated as raw materials for the manufacturing of lightweight aggregates. These sludges were chemically, physically and mineralogically characterized. They were mixed, milled, formed into pellets, pre-heated for 2 min and sintered in a rotary kiln at temperatures between 1225oC and 1275 oC for heating times ranging between 2 and 30 min. The effects of heating temperatures and dwell time on basic properties of the produced aggregates have been investigated. The obtained products were lightweight aggregates (LWAs) in accordance with the standard EN 13055-1 (2002). They showed water absorption values between 23.54% and 27.85% and compressive strength values between 0.82 MPa and 1.07 MPa. The possible applications of the obtained LWAs was similar to those of Arexpan E07 ® (a special variety of LWAs produced by the Spanish company ARCIRESA), which are mainly used for the manufacture of structural concretes, mortar and grout. The manufacturing of artificial LWAs from wastes is considered to be a very satisfactory environmental alternative for dealing with them, since a product with many and very important applications is obtained from raw materials with no value (sludges).