Environmental safety of electronic and construction and demolition waste based geopolymer breakwaters under simulated marine leaching.

This study presents the evaluation of the environmental performance of a geopolymer based breakwater using a novel dual-waste valorisation approach that combines electronic waste (e-waste) derived sodium silicate from cathode ray tube glass (CRT) as a geopolymer activator, and construction and demolition waste (C&DW) aggregates. It will systematically investigate the leaching of major (Ca, Si, Al, Mg, Na) and trace/heavy metals (Cr, As, Zn, Fe, Pb, Ni, Cd, Cu) under simulated marine exposure. Geopolymer blocks incorporating e-waste derived sodium silicate and C&DW aggregates were compared with ordinary Portland cement (OPC) concrete and commercial silicate-based geopolymers. Standard dynamic surface leaching tests were performed in deionized water (DIW) and seawater (SW) for 64 days, with extrapolated predictions for a 50-year service life. Cumulative release of major ions during 64-day immersion ranged from 3.5 to 700 gm-2, while trace/heavy metals remained within 30-150 mgm-2. Extrapolation over 50 years indicated that all trace/heavy metals, including Pb, Cd, Ni, Cu, Mn, As, Cr, Zn, and Fe, would remain below 1 gm-2, while abundant elements such as Al, Mg, Si, Na, and Ca would remain below 1 kgm-2 in seawater. Higher Na (in GEO-RSiA-NA) and Ca (in NC-NA and GEO-RSiA-RA) releases were observed in DIW compared to SW, confirming its more aggressive leaching environment. Overall, trace/heavy metal concentrations remained well below Dutch regulatory thresholds, confirming the environmental safety of geopolymer breakwaters. These findings demonstrate the feasibility of recycled silicate-aggregate geopolymers as a sustainable breakwater material with reduced carbon footprint and controlled environmental impact. Further field validation under real hydrodynamic forces is recommended.