Determination of early age mortar and concrete strength by ultrasonic wave reflections

The in situ testing of early age concrete strength is crucial for determining the time of form removal from concrete elements, opening highways to traffic, or applying prestress to steel reinforcement. A nondestructive ultrasonic technique, which measures the reflection loss of ultrasonic transverse waves at a concrete-steel interface, is presented in this paper. The aim is to compare wave reflection measurements on mortar and concrete to strength. It is shown that the reflection loss is linearly related to the strength gain of mortar and concrete at early ages. The experiments have revealed a relationship between the homogeneity of the tested materials and the consistency of the reflection measurements. The repetition of simultaneous measurements of wave reflections and compressive strength on mortar results in similar strength-reflection loss relationships. Multiple measurements on the same concrete gave multiple strength-reflection loss relationships. The accuracy of the strength predictions made with the proposed method is discussed and compared to that of other nondestructive test methods.