| Abstract [eng] |
Due to the significant increase in consumerism, the amount of household and electronic appliance waste is growing, with particularly large amounts of glass waste from such devices. While glass from window or bottle can be sorted and recycled, the reuse of glass from household and electronic appliances remains one of the challenges of sustainable development due to its different chemical composition. Unrecycled glass waste ends up in general landfills, posing an environmental threat worldwide as it is a nonbiodegradable material with a long decomposition period. This study presents the possibilities and challenges of using hard-to-recycle glass waste from electronic appliances and household appliances in the production of a binder with a reduced cement content, as one of the largest sources of greenhouse gas emissions is associated with the production of construction materials. The manufacture of widely used Portland cement alone accounts for approximately 8% of total global CO₂ emissions. The study analyses the properties of three different types of electronic and household appliance glass waste: old television screens (TV), washing machine glass (WM) and luminescent lamp glass (LL). The chemical and mineral compositions, particle size distribution and morphology of these glass types were examined. The chemical composition of the glass types analysed varies significantly: TV glass consists of 53.1% SiO₂, 8.6% BaO, 7.9% K₂O, 7.7% SrO and 6.4% Na₂O; WM glass contains 81.1% SiO₂, 6.5% Na₂O, 3.7% CaO, 3.7% CO₂, and 2.9% Al₂O₃; while LL glass is composed of 67.9% SiO₂, 14.2% Na₂O, 5.5% CaO, 4.0% CO₂, 2.5% MgO, and 2.1% Al₂O₃. Scanning electron microscopy (SEM) analysis has determined that certain types of glass particles can partially crystallise, forming needle-like crystals. When part of the cement (10%, 20% and 30%) is replaced with these glass waste, the cement hydration rate changes: WM accelerates cement setting time, while TV glass slows it down. Numerous glass particle agglomerates form in the microstructure of the samples, increasing the porosity of the cement matrix and reducing the strength. However, over time, the surfaces of the glass particles dissolve, forming new cement hydrates that gradually fill the voids. Due to this process, the density and compressive strength of the cement samples increase significantly after 90 days compared to the curing periods of 7 and 28 days. For example, the compressive strength of samples with WM glass increased from approximately 62 MPa (after 7 days) to about 96 MPa (after 90 days). After 7 days, this strength is similar to that of control samples without glass additives, but after 90 days, it is about 10% higher when 20% of the cement is replaced. The compressive strength of the samples containing other types of glass was approximately 10% lower than that of the control samples, even after 90 days, which was influenced by differences in microstructure formation. The study also examines the effect of different types of glass on flowability, with results indicating that TV glass reduces flowability the most and these compositions also exhibited the lowest strength. The results show that increasing the amount of glass waste, regardless of its type, decreases flowability due to the irregular shape of the particles, which increases friction between the particles and traps air in the cement mixture. In addition, a larger amount of fine particles requires more water to wet their surfaces. X-ray diffraction (XRD) and thermal analysis (TG and DTG) were performed after 7, 28, and 90 days of curing of the sample. XRD analysis confirmed that as the curing time increases, the intensity of the main peaks of portlandite and cement minerals decreases due to ongoing pozzolanic reactions, with the greatest reduction observed in WM glass samples, which exhibited the most significant positive effects on all properties. DTG analysis confirmed the pozzolanic reaction and differences between the types of glass used. The amount of portlandite decreased the most in the WM samples, and these samples also had the highest mass losses in the 110-350 °C range, where mass loss occurs due to the decomposition of cement hydration products, including CSH and CASH. It was determined that different types of glass waste cannot be used as identical additives because of their distinct chemical and mineral compositions and their varying effects on the cement hydration, structure, and physical-mechanical properties of the binder. The best positive effect was observed in samples with WM glass, which is not only amorphous and also initiates an active pozzolanic reaction, promoting greater formation of the CSH and CASH phases and improving the mechanical properties. |
