Monitoring of the Structural Behaviour of Hybrid Composite-Concrete Beams by Means of Acoustic Emission and Digital Image Correlation

Textile Reinforced Cements (TRC) and Fibre Reinforced Polymers (FRP) allow the development of lightweight components. The lightweight design examined herein for structural applications consists of prefabricated TRC hollow beams with FRP reinforcement, on which a concrete layer is cast. Before however, such designs find their way to application, their load bearing capacity and failure mechanisms should be fully understood. The beams were tested in four-point bending while the basic design was slightly changed in terms of the amount of carbon FRP and
concrete layer thickness. During loading two monitoring non-destructive testing
(NDT) techniques were applied: Acoustic Emission (AE) and Digital Image Correlation (DIC). The characteristics of AE waveforms were analysed and correlated to the active fracture mechanisms including TRC and concrete cracking, as well as debonding between the successive TRC layers and delamination of the carbon strip. DIC is used to measure the real time strain fields on the surface enabling the visualization of the stress concentration points. The two techniques work complimentary in that DIC supplies accurate strain development and damage localization on the surface while AE collecting emissions from all the volume of the beam indicates the load of the failure onset and enlightens the fracture mechanisms. This is one of the first studies where essential combination of the two NDT techniques is applied for monitoring of these innovative hybrid structural elements.