Table 1 Literature details on hydration monitoring of concrete using PZT patches.
Authors | Experimental details | Conclusions |
|---|---|---|
• Developed a PZT sensor using a square PZT patch of dimensions 20 × 20 × 1 mm coated with three layers of epoxy resin and three layers of hydrophobic coating. • Monitored the signatures at every 10 min for the first 24 h of mixing and after every 24 h for the next 28 days. | • The authors concluded natural frequency and conductance values of the first resonance peak of the PZT sensor with the stiffness increase and state change of the concrete simultaneously. • Correlated the changes in the very initial stage of hydration with the changes in the peak resonance frequency shifts. | |
Bhalla28 | • 10 × 10 × 0.3 mm, surface-bonded on concrete cubes • Applied cyclic loading | • Reported rightward shift (depicting the increase in stiffness) in first peak frequency with an increase in strength of concrete • the second and third peak frequencies (above 500 kHz) were not found to be effective |
Soh and Bhalla29 | • 10 × 10 × 0.3 mm, short term and long term (365 days) hydration monitoring of concrete using surface-bonded piezo patches. • Piezo patches bonded after three days of curing and skipped the monitoring of initial concrete hydration. | • Reported rightward shifting of conductance peaks with the increase in strength/stiffness of concrete and sharper peaks with the decrease in damping • The moisture present in the concrete matrix is the main reason for its damping • The EMI technique recorded much higher (80%) equivalent spring stiffness between the 3rd and 28th day of curing in comparison to UPV with a 7% increase in pulse velocity between the 4th to 7th day of curing |
Shin et al.30 | • 10 × 10 × 0.2 mm surface-bonded PZT patches • Cylindrical concrete specimens after 24 h of casting and acquired admittance signatures for 3, 5, 7, 14, and 28 days of curing in the range of 100–400 kHz. | • Found EMI technique sensitive for strength gain monitoring as it reflected the changes in mechanical impedance during the hydration process Recognized Root Mean Square Deviation (RMSD) shift as a good indicator of strength gain in concrete • Stated that the shift in resonant frequency is not much dependent on the effect of curing conditions |
• Developed a reusable PZT setup for monitoring the early hydration of concrete. • Monitored the concrete cubes for 48 h after casting • Measured the concrete stiffness indirectly using the connecting bolts embedded in the cubes, varied the hydration rates by using a retarder | • Exhibiting a good variation in admittance signatures with the increase in curing time of the concrete • RMSD values showed a good coherence with different hydration rates | |
Tawie and Lee4 | • Compared three statistical metrics, namely, root mean square deviation (RMSD), mean absolute percentage deviation (MAPD), and correlation coefficient deviation (CCD) for measuring the hydration in a quantitative approach in the range of 100–400 kHz • Used 36 cubes for their study and measured 3rd, 7th, 14th, and 28th days strength of concrete in compression | • The stated EMI technique lacks rigorous studies for its practical field application as a commercialized product • Observed a similar pattern of change in resonant frequency shift and compressive strength of concrete with the increase in curing time • Mentioned the importance of the uniformity of PZT patch used and its bonding conditions for proper calibration of the monitoring process |
Wang and Zhu23 | • 8 × 8 × 0.3 mm PZT patches covered with asphalt lacquer as a waterproof coat, embedded in concrete and a few embedded • Correlated RMSD variation and MAPD indexes with cube strength • Tested 42 cubes in a total of a single concrete mix | • Developed an exponential correlation between RMSD variation, MAPD indexes with cube strength • Emphasized using temperature correction while monitoring concrete hydration • 150–350 kHz range was found to be sensitive towards hydration monitoring and damage detection |
Providakis and Liarakos31 | • Used 10 × 10 × 0.2 mm Teflon-based sensor/actuator consisting of a PZT patch confirming to grade PIC151 and AD5933 evaluation board for acquiring impedance signatures. • The range of the excitation was kept between 10–100 kHz and the tests were performed on a single concrete cube | • The configuration was surface bonded to concrete cubes and reported results on a web-based (GUI) platform with an auto peak detection algorithm. • They reported a rightward shift in the signatures with increasing curing time |
Lim et al.32 | • Compared a piezo-based wave propagation method with EMI and other conventional techniques for concrete strength monitoring, through surface-bonded PZT patches | • An increase in resonant frequency was found significant for the first 7 days and later it was near stable • The behavior was analogous with the results of wave propagation technique, ultrasonic pulse velocity test, and Schmidt hammer test |
Zhang et al.33 | • Presented a smart sensing system based on newly developed piezoelectric materials–Lead Magnesium Niobate/Lead Titanate (PMN-PT) transducer for viscosity and density measurement of viscous fluids like early age concrete by analyzing the vibrational properties. | • The proposed smart sensing system was claimed to monitor in situ and real-time early-age concrete. |
Negi et al.34 | • Checked the effect of orientation (0°, 45°, and 90° from the longitudinal axis) of embedded PZT patches in hydration monitoring of real-life size simply supported RC beam • Skipped the first three days monitoring of the beam and used the third day reading as base signatures | • Authors found 45° orientation to be least sensitive amongst the three orientations and 0° orientation was stated the most sensitive • The inclined position experienced lower stiffness in the compressive region resulting in near flat resonant peaks and a random shift in conductance signatures with increasing hydration |
Fan et al.35 | • Used spherical smart aggregate (SSA) which has a spherical piezoceramic shell, for monitoring concrete curing. • Shell inner and outer radius 9.25 mm and 10 mm | • The SSA was sensitive towards the hydration, deformation, and stiffness variation in concrete • The authors suggested further studies in understanding the factors affecting the hardening process and increasing the uncertainties in signatures |
Feng et al.36 | • Developed smart aggregate (SA) using thin PZT patches coated with epoxy and covered with marble protection. • Two different SAs embedded as actuator and sensor used stress wave propagation for monitoring hydration | • Developed hydration monitoring index results in higher amplitudes upon the development of hydration • Proposed a study on monitoring concrete with different water-cement ration and additives, and validation in practical concrete structures |
Zheng et al.37 | • Used active sensing approach using SA for monitoring early age (24 h) hydration in fly-ash based concrete • Validated the results with penetration resistance test on concrete | • Detected the change in hydration from liquid to a hardened state • Developed a hydration completion index using wavelet packet analysis |
• Compared the hydration monitoring capability of compressive (P-wave) and shear (S-wave) using compressive and shear mode SAs respectively • The PZT patches used were 10 × 10 × 1 mm with the final dimension with covering was 25 × 25 × 25 mm • Power spectrum density plots were acquired at different intervals up to 37 h of hydration | • Both P and S waves were influenced during propagation due to the hydration of cement • Observed S-wave be more sensitive in observing the hydration at the initial stage (0–8 h), whereas P-wave was more sensitive in monitoring hardened concrete | |
Kong et al.40 | • Used marble encapsulated PZT patches as actuator and sensor embedded in concrete for monitoring hydration • Swept sine wave used was 50–100 kHz in 3s of 10 V | • Acquired both temporal and frequency response of the receiver PZT • Observed signal responses to be chaotic during transition stage (1 to 7.5 h after mixing). After hardening, the response becomes smooth and the amplitude of the signal gets stable over the change in hydration |
