Valorization of Waste Printed Circuit Boards in Alkali-Activated Slag Concrete: Engineering Performance, Environmental Safety, and Life Cycle Assessment

Manufacturing-derived non-metallic waste printed circuit boards (WPCB) represent an underutilized secondary resource whose sustainable valorization is constrained by limited recycling opportunities and the presence of residual hazardous constituents. In this study, WPCB was simultaneously utilized as a partial precursor and coarse aggregate replacement in alkali-activated slag concrete through the incorporation of waste board powder (WBP) and waste board rejects (WBR), respectively. Ground granulated blast furnace slag (GGBS) was partially replaced with 20% WBP, while natural coarse aggregates were replaced with 0% to 10% WBR. The developed composites were comprehensively evaluated for engineering performance, durability, microstructural evolution, heavy metal stabilization, cradle-to-gate life cycle assessment, and practical validation through concrete paver blocks. The optimum mix, G80P20R4 (containing 20% WBP and 4% WBR), achieved a mean compressive strength of 20 MPa after 28 days of ambient curing, successfully meeting the requirements for concrete paver blocks. X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS) analyses confirmed the formation of C-(N)-A-S-H gel as the principal binding phase, whereas scanning electron microscopy (SEM) revealed the microstructural modifications associated with WPCB incorporation, explaining the observed engineering performance and durability. Heavy metal characterization and toxicity characteristic leaching procedure (TCLP) analysis demonstrated that the alkali-activated concrete matrix meets regulatory thresholds, achieving effective immobilization of the investigated heavy metals under laboratory testing conditions. Moreover, relative to a conventional Portland cement concrete of the same grade, the optimum mix reduced cradle-to-gate greenhouse gas emissions by 42.6%, decreased net production cost by 21.3%, and achieved the highest eco-efficiency index. Finally, the successful fabrication of paver blocks demonstrated the practical feasibility of simultaneously valorizing both WBP and WBR within a single alkali-activated slag concrete system, providing an environmentally safe, economically viable, and low-carbon solution for sustainable construction in the paving industry.