Embedded PZT-EMI sensor-based equivalent structural parameters for monitoring strength evolution in carbon-cured concrete

A rapid and sustainable technique to increase concrete strength is by carbon dioxide curing, but careful observation of the stiffness development phases and CO₂-uptake is necessary to guarantee its efficacy and long-term performance. This study focuses on assessing the real-time health of concretes under accelerated carbonation curing at 60 psi pressure using affordable smart embeddable piezoelectric sensors. The Electro-mechanical impedance (EMI) technique, which involves electrically exciting the embedded lead zirconate titanate (PZT) sensor and capturing admittance spectra within a user-defined high-frequency range of 100–350 kHz, is employed to evaluate health at 0–28 days treatment durations under laboratory-controlled conditions. The conductance signatures were found to be more sensitive and are primarily classified using statistical indices demonstrating up to 8.7% deviations, which are then further processed through advanced signal processing to estimate PZT-EMI-derived equivalent structural parameters. The dynamic response, in terms of stiffness, mass, and damping, is found to be significant in tracking and characterizing the strength evolution in three stages, having corresponding stiffness rates of 156.49 N.s/m/day, 43.19 N.s/m/day, and −16.93 N.s/m/day, during the complex carbonation-hydration phenomenon within the concrete. The results align with the patterns observed in compressive strength, modulus of elasticity, and ultrasonic pulse velocities, showing improvements up to 14 days of curing, followed by deterioration due to over-carbonation. Besides experimental work, the developed finite element numerical models also accurately predict impedance responses, ultimately validating the technique. The study concludes by correlating the compressive strength gains with novel non-dimensional stiffness and damping indices, recommending its potential for real-time, in-situ monitoring of concrete structures under carbon curing regimes.