Damage Detection in Ultra High Performance Concrete using Embedded Smart Aggregates

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The distinct feature of UHPC is the tensile strain hardening phenomena and high compressive strength. We can either use this potential as an additional safety margin in structures or design structures with no passive reinforcement.
The advancements in active structural health monitoring devices have opened further possibilities to validate the performance of this material. One such device is the Smart Aggregate (SA). Smart Aggregates are piezoceramic transducers capable of sending and receiving ultrasonic waves. From basic wave theory, we know that elastic waves capture the properties of the medium through which it propagates. We can use this phenomenon to study the damage inside UHPC. This is accomplished by studying the changes in velocity and peak amplitude of an elastic wave as it propagates through the loaded specimen.
This thesis has two main objectives. First, a modified tension test is developed to determine the uniaxial-tensile behavior of UHPC specimen. Second, embedded smart aggregates are used to send and receive elastic waves inside the UHPC specimen subject to modified tension test and the wave parameters such as velocity and peak amplitude are studied. The propagation of elastic waves in UHPC specimen with steel fibres is understood from this experiment. A relationship is established between velocity of the elastic waves versus average strain and peak amplitude of the elastic waves versus average strain. The results obtained could serve as basic knowledge required to conduct elastic wave tomography.
In short, this thesis explores the possibilities of using SA to detect damage in UHPC and whether it can be used as an additional safety measure in active structural health monitoring. Although the huge potential of Ultra-High-Performance Concrete is apparent, considerable effort is required before we can realize safe habitable structures using it.