| The evaluation of early age concrete is critical for reducing construction times and ensuring quality. In this study, the use of ultrasonic guided waves for monitoring the development of early age cementitious materials is investigated. A torsional wave is transmitted and received through a waveguide that is embedded in early age mortar or concrete. As the cementitious material sets and hardens, the received wave(s) change, indicating the transition from a semifluid to a solid state. This thesis proposes two systems.; The first system is a through-transmission system; 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 rod with another sensor. This approach monitors the attenuation of the fundamental torsional 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 wave.; The second system is a pulse-echo system; a wave is transmitted on one end of a partially embedded waveguide via a sensor arrangement that also receives the reflected signals. This approach monitors both the reflection from the end of the rod and the reflection from the point where the waveguide enters the material. The development of the cementitious material's mechanical properties is related to both the energy leaked into the surrounding material and the energy reflected at the point of entry. The ability of this method to only require access to one side of the specimen makes it attractive for monitoring early age cementitious materials in the field.; Experiments were performed on mixtures with varying water-cement ratios (w/c = 0.40, 0.50, and 0.60), chemical admixtures (accelerant and retardant), mineral admixtures (silica fume and fly ash), and coarse aggregate (pea gravel). The time of setting and compressive strength of the various mixtures was determined in accordance with ASTM standards. Experimental results provide evidence that the setting times and compressive strength of early age cementitious materials can be monitored using ultrasonic guided waves. |
