Lightweight aggregates made of industrial wastes or sub-products

This study describes the use industrial wastes, namely sludges generated from granitecutting and potable water treatment processes, as raw materials for the fabrication of lightweight aggregates. As inert residues, they are usually dumped in landfills but the pointed solution might assure a significant income for the lightweight aggregates producer, besides the direct environment benefits. Wastes were characterized in terms of chemical (XRF) and mineralogical (XRD) composition, and their thermal behaviour (TG/DTA) was also evaluated. Different compositions were then prepared and tested, trying to use the materials such as they are available. This means that no special pre-treatment steps such as milling were used, and the addition of expansive additives were also avoided. First we attempt to reproduce typical properties of common lightweight aggregates based on natural resources, such as clays. However, another approach was done, involving the production of aggregates with improved mechanical strength. In this attempt, the firing cycle seems to play an important role. The bulk density of this new aggregate is somewhat higher but still low due to the formation of an internal cellular structure made of closed pores and an external shell that is partially vitrified.