Use of scrap glass as raw material for porcelain stoneware tiles

The possibility of recycling scrap glass (soda lime, lead and barium based glasses) by incorporation into a porcelain stoneware tile mix has been examined. Starting from a standard porcelain stoneware body mix, several modified mixes were prepared by replacing different amounts of the fluxing component, a sodium feldspathic sand, with three types of scrap glass: a soda lime glass from urban wastes, a lead based glass from the neck part of cathode ray tubes (CRTs), and a barium based glass from CRT panels. The replacement of feldspar sand with a soda lime scrap glass, in the range 5–10 wt-%, allows porcelain stoneware materials to be obtained with good characteristics. A slight decrease in the water absorption of the fired material is observed after sintering at the same temperature as the reference mix. Furthermore, flexural strength remains high and the microstructural homogeneity enhances reliability. The presence of 2 and 5 wt-%, of lead and barium based scrap glass respectively, both characterised by lower liquid viscosity at higher temperature, makes possible a significant decrease in the sintering temperature of the modified porcelain stoneware products while maintaining good mechanical properties.