Monitoring the effects of incorporating plastic waste on carbonation degrees of concrete using piezo-impedance spectroscopy

Purpose – This study aims to evaluate the feasibility of using piezoelectric lead zirconate titanate (PZT) sensors to monitor the effects of adding low-density polyethylene (LDPE) beads, made from waste plastic, on carbonation mineralization of modified concrete during accelerated CO₂ curing. Design/methodology/approach – Two concrete mixtures (P20 and P40) were prepared by replacing 20% and 40% of coarse aggregates with LDPE beads. PZT patches installed in both surface-bonded and embedded configurations were employed to capture electromechanical impedance (EMI) responses experimentally, in the user-defined 250–350 kHz frequency ranges at ten different curing ages of 0, 1, 3, 7, 10, 14, 18, 21, 24 and 28 days from plastic waste admixed-concrete mixes, and were further validated using finite element analysis. Findings – The results indicate that carbonation curing significantly influences the EMI responses with increasing plastic waste content in concrete. Embedded PZT sensors exhibited higher sensitivity than surface-bonded sensors, showing maximum root mean square deviation (RMSD) and mean absolute percentage deviation (MAPD) values of up to 39.23% and 75.90%, respectively, for P40 mixes at 28 days curing duration. In contrast, surface-bonded sensors demonstrated lower deviations, with maximum RMSD and MAPD values of 7.69% and 14.28%. Originality/value – This study demonstrates that the inert solid plastic additions up to 40% significantly increase the sensitivity of health indices, conclusively showing an intensified carbonation effect due to increased porosity and weak interfaces, which are ultimately correlated to strength gains with higher confidence levels.