Fracture monitoring of lightweight composite-concrete beams with acoustic emission

Lightweight hybrid concrete beams are advantageous in terms of installation, but their mechanical behaviour is not easy to predict due to their heterogeneity. In the present study composite beams made of Textile Reinforced Cement (TRC) reinforced with Carbon Fibre Reinforced Polymer (CFRP) strips and a concrete layer are subjected to bending (Fig. 1). Their fracture behaviour is complicated as they exhibit multiple failure mechanisms: cracking of the cement matrix, debonding of the CFRP and delamination between successive layers of TRC. Herein, their mechanical performance is evaluated and monitored by Acoustic Emission (AE) and Digital Image Correlation (DIC). AE indices show that beams suffering from one major failure mechanism (matrix cracking) exhibit nearly constant AE characteristics throughout the bending experiment. Beams suffering additionally from delaminations exhibit longer AE waveforms of lower frequency compared to the plain cement cracking (see Fig. 2). These tendencies are obvious from the initial part of the test, enabling predictions about the subsequent failure. More importantly and for the first time in related literature, the use of DIC enables to relate AE not only to the final damage pattern and the ultimate failure mechanism but also to the strain field during loading.