A Novel Geopolymer-Based Composite Material from Recycled Waste Glass

The construction industry is transforming rapidly, embracing recycled materials, moving toward a climate-resilient future, and advancing a circular economy. There are significant benefits in reusing materials that would otherwise be disposed of in landfills. Repurposing waste will conserve natural resources, reduce the contamination of ground and water by hazardous materials, reduce the impact on natural habitats, and reduce the energy consumption in construction. Many waste materials are recycled by the construction industry: construction demolition, plastics, steel, fabrics, tire chips, and glass. The focus of this paper is to develop a new lightweight composite material using recycled waste glass (RWG) aggregates with the potential to be used in a wide range of construction applications. The new material is a combination of coarse RWG aggregates ranging from 75 μm to 9.5 mm, and a binding material developed using RWG powder. Amorphous silicate-rich general soda lime (bottle) glass powder was used as the precursor in this study, activated with sodium hydroxide (NaOH) and cured at elevated temperatures. A novel concept of predissolving waste aluminum foils in the alkaline activator (NaOH) is exploited to nourish the GP precursor with aluminum. The optimum material combination for both the aggregate mix and the binder was investigated considering six control parameters: (1) particle size distribution of aggregates, (2) Sodium to aluminum predissolving ratio, (3) liquid to solid ratio, (4) molarity of NaOH, (5) curing temperature, and (5) curing period. The optimization was carried out considering the unconfined compressive strength (UCS) of the cured specimens and the highest UCS was achieved with a SiO2/Al2O3 ratio of 7.91∶1 and Na2O/Al2O3 ratio of 3.36∶1 cured at 85°C over 24 h. Microstructural characterization performed on the optimized binder using scanning electron microscopy (SEM) and X-ray diffraction (XRD) showed the formation of alkaline aluminosilicate (N─ A─ S─ H) in the binder, as a result of the geopolymerization process.