In-Situ monitoring of HPC using ultrasonic guided waves

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 of non-destructive test methods for early age concrete properties determination is crucial. In this study, apart from standardized methods like ultrasonic pulse velocity, vicat penetration and pull-out methods to study the setting of concrete, suitability of Ultrasonic Guided Waves (UGW) methods for young concrete characterization is also explored. In ultrasonic method, guided wave is transmitted and received through a waveguide that is embedded in early age concrete. As the cementitious material sets and hardens, the strength of the received waves changes, indicating the transition from semi-fluid to solid state. This thesis purposes to use Ultrasonic Pulse Transmission (UPT) and Ultrasonic Pulse Echo (UPE) systems for monitoring setting and hardening phase change in High Performance Concrete (HPC). In UPT, a wave is transmitted on one end of an embedded waveguide using a sensor arrangement and then it is received on the opposite end of the propagating bar with another sensor. In UPE, a wave is transmitted on one end of an embedded waveguide and received on the same end of the propagating bar. This approach monitors the attenuation of the fundamental guided (longitudinal) wave mode, resulting from the leakage of energy from the cylindrical steel rod to the surrounding cementitious material. The evolution of the material’s properties is related to the energy leakage or attenuation of the guided waves. Experiments were performed on OPC with 0% fly ash and OPC with 20% fly ash for three w/cm ratios i.e. 0.50, 0.30 & 0.27 respectively. For UGW, slab specimens of size 300mm x 300mm x 100mm with embedded mild steel rod of 25mm diameter and 500mm length were used to monitor young concrete’s strength, setting & hardening process. Ultrasonic Pulse Velocity was also carried out side by side on a standard cube of size 150mm x 150mm x 150mm of the same concrete mixtures to study the microstructure development of concrete.