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 of 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 focus 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 other nondestructive test methods. 1 Dipl.-Ing., Research Associate, Center for Advanced Cement-Based Materials, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208. Email: [email protected], Corresponding Author 2 Ph.D., Research Associate, Center for Advanced Cement-Based Materials, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208. Currently at Istanbul Technical University, Civil Engineering Faculty, Maslak, 80626, Istanbul, Turkey. Email: [email protected] 3 Prof. for Civil Engineering, Director of Center for Advanced Cement-Based Materials, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208. Email: [email protected].