**6. Acknowledgment**

90 Modern Telemetry

where Zi,0 is the impedance function at the baseline (the impedance data of 3rd day), Zi,1 is

each dataset, respectively. The data was normalized to the maximum value. Fig. 14 shows the 1-CC data of 60MPa and 100MPa respectively. The 1-CC data shows the same pattern with a commercial strength development curve (Fig. 1). Also, the wired data and wireless data has similar pattern. Therefore, the 1-CC value can provide more reliable quantitative

(a) 60MPa Wired Data (b) 60MPa Wireless Data

(c) 100MPa Wired Data (d) 100MPa Wireless Data

This study evaluated the application of PZT sensors for monitoring the strength development of high strength concrete. The applicability of the conventional impedance measuring technique, which is normally used to detect damage, was extended to monitor the curing process of concrete. The impedance signals were obtained at six different curing ages. The compressive strengths of the test concrete cylinders were also evaluated by considering the resonant frequency variations and cross-correlation coefficient. Based on the experimental results, the resonant frequencies in the impedance signals shifted gradually to the right side with increasing curing time, which confirms the applicability of impedance measurements to monitor the strength development of concrete. The largest deviation of the resonant frequency shift was observed between days 3 and 5, and the change decreased with time. In addition, the 1-CC values increased due to strength development during the curing process. A wireless impedance system showed similar results to that of the wired

σ σ

*Z Z* are the standard deviations of

the current impedance at each measured day, and 0 1 ,

Fig. 14. 1-CC-based estimate of strength development

**5. Conclusion** 

information on strength development.

This study was supported by National Nuclear R&D Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2010-0025889) and u-City Master and Doctor Support Project funded by Ministry of Land, Transport and Maritime Affairs (MLTMA). This all-out support is greatly appreciated.
