Ultrasonic Characteristics of Thermal-Damaged Engineered Cementitious Composites

To study the damage mechanism and ultrasonic properties of thermal-damaged engineered cementitious composites (ECC), ultrasonic monitoring and compression tests were performed on ECC specimens exposed to high temperatures (20, 105, 250, 400, 600 and 800 ℃) . Results indicate that the changes in waveform amplitude, main frequency amplitude, energy, and compressive strength of thermal-damaged ECC are the same; the energy ratio in the 40 ~ 50 kHz band is the largest, which is about 15% of the total energy in the 0 ~ 300 kHz band. The wave velocities of ECC specimens heated from 20 to 250 ℃ show no significant changes, and decrease when heated above 400 ℃ . The reason can be relate to free water vaporizes, hydration products decompose, and aggregate physical properties change at high temperature, which leads to the increasing of pore vapor pressure and damaging to the aggregate interfaces, thus the internal cracks in the ECC are generated and expanded. Scanning electron microscopy test results indicate that PVA fiber softens, melts, and vaporizes with increasing temperature. Voids and pores are generated in the ECC matrix and connect with cracks forming into networks, which are beneficial to the releasing of the pore vapor pressure and reducing the thermal damage of ECC. Results also show that the ultrasonic characteristics can effectively reflect the thermal damage evolution process in the ECC. © 2022 Northeastern University. All rights reserved.