Measuring moduli of elasticity of concrete prisms using length-insensitive resonant modes and electromechanical impedance technique

Modulus of elasticity ( E c ) is a crucial parameter for structural design and quality control. A baseline-free electromechanical impedance (EMI) technique employing piezoelectric sensors has recently emerged and proven promising for continuously monitoring E c of concrete specimens. For long members, fundamental resonant modes are widely employed in traditional dynamic testing methods. However, these modes may not work for the piezoelectric sensors-based EMI techniques because their corresponding frequencies may be lower than the working frequency range of piezoelectric sensors (> 3 kHz). Therefore, searching for resonant modes in a technologically viable range, which can be easily identified, accessed, and generalized, is highly desirable. To this end, special length-insensitive modes were employed in the EMI technique for the first time to evaluate E c of concrete prisms by leveraging symmetry properties. Six sensor installation strategies were initially designed to achieve different numbers of symmetry planes, and their abilities to extract target resonant modes below the middle-frequency range (<25 kHz) were compared. Then, the accuracy of using such length-insensitive modes to assess E c of concrete was validated experimentally, and a comparison with the results obtained using the 1 st longitudinal mode showed minimal differences (≤7%). Finally, the advantage of using target modes in concrete prisms was illustrated at the early ages of concrete, as well as under different boundary conditions (with relative differences < 1.2%). • Length-insensitive modes of concrete prisms were employed to measure the modulus of elasticity. • Length-insensitive modes showed higher sensitivity than fundamental modes, improving measurement accuracy. • Some length-insensitive modes were insensitive to the end’s boundary conditions. • The middle-frequency range was utilized by leveraging the concept of symmetry in EMI techniques.