Impact of Freeze-Thaw Cycling on the Longevity of UPV Sensors in Concrete and the Analysis of Irreversible Effects

This research investigates the effects of freeze-thaw cycles on a specially designed concrete cube embedded with sensors. Over a six-year period, the cube (of volume 8 ft³) underwent over one hundred freeze-thaw cycles, which were monitored utilizing a combination of four Ultrasonic Pulse Velocity (UPV) pairs and fifteen temperature thermistors. The primary objective was to evaluate sensor longevity under repetitive freeze-thaw conditions, while a secondary goal involved a detailed analysis of irreversible effects on the concrete's UPV response. The concrete cube sample was produced six years ago under a Small Modular Reactor (SMR) R&D project. Initial freeze-thaw cycling was performed in the first two years, under natural environmental conditions, by periodically moving the cube outside and inside the laboratory (two cycles of freeze-thaw per week) during the period from November to April. The cube then sat idle for two years, and freeze-thaw cycles recommenced thereafter in an industrial freezer. The analysis methodology involved UPV waveform envelope amplitude, duration, and transit time calculations, with a thorough approach to normalizing data due to instrumentation changes. Challenges in the analysis process, including waveform anomalies and signal errors, are being addressed. The findings not only highlight the scientific rigor applied to the investigation but also emphasize the need for a comprehensive analysis of the embedded UPV sensors’ response in concrete under diverse freeze-thaw conditions.