Attack of discarded soda-lime glass with sodium aluminate for the manufacturing of sustainable geopolymer components

Discarded soda-lime glass (SLG) may contain small amounts of ceramic, metallic, and polymeric contaminants, therefore recycling of this material is far from ideal. The quality of newly made glass products made by remelting of cullet, as a result, declines. Consolidation at low temperatures to form materials similar to geopolymers could enable the complete re-use of contaminated cullet. SLG powders, either as received or after pre-washing in an acid solution, were added to a sodium aluminate solution and mechanically stirred at a low speed for three hours at room temperature. The formation of microporous semi-crystalline monoliths involved suspensions casting into plastic molds, followed by an overnight cure at 75 °C. The monoliths prepared from both untreated SLG particles and pre-washed SLG particles contained crystalline phases of zeolite LTA and hydrosodalite. The mechanical characteristics showed good agreement with the properties of cementitious materials, with compressive strength ranging from 22 to 29 MPa and flexural strength ranging from 13.2 to 19.9 MPa. Furthermore, the technique effectively produced Venetian terrazzo-like samples by adding coarse glass particles as fillers with particle sizes of up to 3 mm, which could lead to significant material and energy savings in their fabrication. The suggested method could be expanded to include other challenging-to-reuse glass formulations, providing attractive and versatile recycled materials.