Synthesis and characterization of alkali-activated binders with slag and waste printed circuit board

Abstract

The global production of printed circuit board (PCB) is expected to rise substantially in the next decade due to the advancement in technology. The production of PCB results in generation of hazardous waste of various kinds, and one such waste is the very fine particles of the board material that is generated due to drilling and other preparatory operations. The disposal of such waste in the environment can result in serious consequences which needs attention. Therefore, recycling of waste printed circuit board (WPCB) can mitigate its harmful effects on the environment and also reduce the remediation costs. In this study, the WPCB is used as a substitute to ground granulated blast furnace slag (GGBFS) in development of alkali-activated binder. Alkali-activated binder was synthesized with GGBFS, WPCB, sodium hydroxide sol. (NaOH), and sodium silicate sol. (Na₂SiO₃). GGBFS was replaced with WPCB at replacement rates of 0%, 10%, 20%, and 30% by volume. Additionally, the effect of varying concentration of NaOH and Na₂SiO₃ on the physical and mechanical performance of the binder was studied. The developed binders were evaluated for workability, strength, water absorption, and efflorescence properties. Further, to ascertain its safety on the environment, the toxicity characteristic leaching procedure (TCLP) test was also performed. The results indicate that WPCB characteristics are compatible with GGBFS in terms of its particle size distribution. Moreover, the replacement of GGBFS with up to 20% WPCB provides desirable properties for the alkali-activated binder. However, higher replacements are not recommended, since it had detrimental effect on the mechanical performance of the binder. The study revealed that desirable performance can be achieved for binders with 8 M NaOH and with Na₂SiO₃ to NaOH ratio of 2, and up to 20% GGBFS replaced with WPCB. The results of TCLP test disclose that the contaminant in the leachate from alkali-activated binders with WPCB are within regulatory limits, and do not pose any threat to the environment. Finally, the outcome of this study provides an innovative approach towards formulation of eco-friendly binder for various construction applications such as foundations, buildings, bridges, pavements, etc.