Monitoring the concrete early-age strength gain at any arbitrary time from a few minutes to a few hours after mixing is crucial for operations such as removal of frameworks, prestress, or cracking control. This paper presents the development and evaluation of a potential active wireless USB sensing tool that consists of a miniaturized electromechanical impedance measuring chip and a reusable piezoelectric transducer appropriately installed in a Teflon-based enclosure to monitor the concrete strength development at early ages and initial hydration states. In this study, the changes of the measured electromechanical impedance signatures as obtained by using the proposed sensing system during the whole early-age concrete hydration process are experimentally investigated. It is found that the proposed electromechanical impedance (EMI) sensing system associated with a properly defined statistical index which evaluates the rate of concrete strength development is very sensitive to the strength gain of concrete structures from their earliest stages.
The present study deals with the application of laser scanning vibrometry in monitoring of concrete dynamic behavior and evaluation of dynamic response changes when structural damage occurs. Concrete specimens that exhibit different types of damage are excited artificially using a vibration shaker actuator, and velocity response is acquired on multiple points by employing a PSV‐500H laser scanning vibrometer. As optical interaction between laser beam and concrete surfaces yields speckle‐related noise to measured velocity response, multi‐peak frequency response functions are employed for the simulation of measured spectra and smoothing of induced noise. Surface mapping of concrete elements dynamic modes is achieved by exploiting ordinary kriging regression. Proposed experimental arrangement and data post‐processing are attained to illustrate efficiently concrete surficial dynamic response and reveal simultaneously velocity map discontinuities that correspond to crack existence.
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