Lightweight aggregates based on industrial wastes

The processing of new waste-based lightweight aggregates is described. Main components are sludges generated from potable water filtration/cleaning operations and clay-based by-products from washing process of igneous rocks. The complete characterization of residues is reported, including physical and chemical parameters, and their thermal behaviour. Several mixtures were designed, prepared, and fired at different temperatures, trying to use the materials such as they are available. First we attempted to reproduce typical properties of common lightweight aggregates based on natural resources, such as clays. Then, a further approach was followed, 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. Microstructural evolution was also evaluated (by SEM) while the expansive behaviour of the most promising formulations was studied by hot stage microscopy.