This standard provides procedures for estimating in-place mechanical properties of concrete structures using the acoustical resonance of a specially designed sensor. The sensor directly measures the dynamic modulus of concrete during its hardening process and calculates the strength based on the dynamic modulus and pertinent formulas. This method is distinct from the maturity method specified in T 276, T 325, and ASTM C1074, which correlates the in-place strength of concrete with traditional cylinder testing results based on a temperature profile. The proposed method relies on direct, in-place measurements of concrete's mechanical properties rather than on a pre-established strength–maturity relationship that was developed in a laboratory for a particular mix design. This method does not require mix design-specific calibration and readily allows use for any mix design at any time of interest. Also, unlike current standards for resonant frequency testing specified in ASTM C215 and ASTM E1050, this method allows in-place testing of a localized region within a concrete structure, making it practical to apply resonance-based testing methods onsite. This standard requires the determination of resonant frequencies of a localized region of a concrete structure using a piezoelectric sensing device and an impedance analyzer. This test method covers the application of the test using either inch-pound or SI units. The values stated in either SI units or inch-pound units are to be regarded separately as standard. Within the text, the inch-pound units are shown in brackets. The values stated in each system may not be exact equivalents; therefore, each system must be used independently of the other. Combining values from the two systems may result in nonconformance with the standard.