Monitoring setting and hardening of concrete using acoustic emission and guided waves techniques

Abstract

At early ages of concrete structures, strength monitoring is important to determine the structure’s readiness for service. Concrete setting and hardening process are the most critical phases during construction works, influencing to properties of concrete structure, so the application of efficiency non-destructive test methods for early age concrete properties determination is crucial. In this study, apart from standardized methods like Ultrasonic Pulse Velocity, integrated approaches consisting of Ultrasonic Guided Waves and Acoustic Emission Techniques for young concrete characterization are explored. In ultrasonic method, guided wave is transmitted and received through a waveguide that is embedded in early age concrete. Whereas in Acoustic Emission arising out of the solidifying of the concrete are recorded using sensors mounted at different locations. Both the techniques are different in their nature of application, i.e., Ultrasonic Guided Wave is active in nature and Acoustic Emission Technique is passive in nature. Ultrasonic Guided Wave depends on the transmitted signal whereas the Acoustic Emission Techniques depends on the stress changes occurring inside the system. Experiments were performed on concrete mixtures with varying water cement ratios i.e. 0.3 and 0.5. For ultrasonic guided waves, cube specimens of size (150mmx150mmx150mm) with embedded mild steel rod of 25 mm diameter and 300 mm length were used to monitor early setting and hardening (i.e. 48 hrs of hydration). And for AET, plain steel bars of diameter 12 mm were placed vertically in the same cube used for UGW. The AET system was paused while UGW reading was taken to in order to prevent the recording of noise. Also, Ultrasonic pulse velocity tests were also performed on the cubes of size 150mmx150mmx150 mm. The focus of the study is be track every aspect of the setting and hardening process of concrete immediately after pouring of fresh concrete.