E-waste in the circular economy: Molecular and experimental insights into cement incorporation of waste printed circuit board

The escalating generation of electronic waste (e-waste) poses critical environmental and health challenges, with waste printed circuit boards (WPCBs, 4 wt.%–6 wt.% of e-waste) representing a particularly hazardous fraction due to their complex composition of metals, polymers, and brominated flame retardants. This study explores the valorization of WPCBs as a partial cement replacement to both mitigate disposal risks and enhance cementitious performance. Portland cement pastes incorporating 0 wt.%, 5 wt.%, 10 wt.%, and 15 wt.% WPCBs were examined through isothermal calorimetry, Fourier transform infrared (FT-IR) spectroscopy, and reactive molecular dynamics (RMD) simulations using the reactive force field. Calorimetry revealed that 10% WPCBs yielded the highest heat release (≈25 ℃ peak, 10% higher than reference), indicating optimal hydration kinetics, while 15 wt.% WPCBs reduced exothermicity by 8% due to inert filler effects and bromine-induced retardation. FT-IR revealed intensified Si–O stretching (953 cm⁻¹) and free O–H (3640 cm⁻¹) at 10 wt.%, confirming enhanced C–S–H and CH formation. RMD simulations provided molecular-level insights, showing denser C–S–H networks and the lowest total energy (−6.82 × 10⁵ kcal/mol) for 10 wt.% WPCBs, whereas 15 wt.% loading disrupted network formation. The integrated findings suggested that WPCBs can be safely immobilized within cement matrices, with 10 wt.% substitution offering a balance between performance gains and hydration integrity. This work advances the understanding of WPCB–cement interactions and supports the development of sustainable, circular-economy construction materials.